Low Level Gamma Radiation

[Mike Monett]

My Radiascan Radiacode finally arrived from Russia. After the sanctions, I
was surprised to see it made it.

After learning how to operate it, I began to be curious about the low level
background radiation. This is shown in the photo at

https://www.mrmonett.com/RADIACOD.JPG

I wonder what the spectrum curve is saying, particularly the rise and quick
drop near zero. Scouring google, I was unable to find any source that
explained it. What mechanism could produce such weak gamma or x-rays?

Thanks





--
MRM

[bitrex]

What does the X axis represent?

There's a long decay chain from naturally-occurring thallium 232 and
uranium 238 down to stable lead, and a number of steps in the chain
produce a gamma photon

[bitrex]

On 6/5/2022 9:24 PM, bitrex wrote:
> On 6/5/2022 7:07 PM, Mike Monett wrote:
>> My Radiascan Radiacode finally arrived from Russia. After the
>> sanctions, I
>> was surprised to see it made it.
>>
>> After learning how to operate it, I began to be curious about the low
>> level
>> background radiation. This is shown in the photo at
>>
>> https://www.mrmonett.com/RADIACOD.JPG
>>
>> I wonder what the spectrum curve is saying, particularly the rise and
>> quick
>> drop near zero. Scouring google, I was unable to find any source that
>> explained it. What mechanism could produce such weak gamma or x-rays?
>>
>> Thanks
>
> What does the X axis represent?
>
> There's a long decay chain from naturally-occurring thallium 232

Er, Thorium 232, not thallium

[Ricky]

What do you know of the calibration of the unit itself? Does it have the equivalent of frequency response?

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

[Ricky]

When I look at the decay chain, I don't see any gamma emissions. Is this in a more rare decay event?

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

[bitrex]

For thorium the gory details are here:

<https://pubs.usgs.gov/of/2004/1050/thorium.htm>

[bitrex]

On 6/5/2022 9:56 PM, Ricky wrote:
> On Sunday, June 5, 2022 at 7:07:22 PM UTC-4, Mike Monett wrote:
>> My Radiascan Radiacode finally arrived from Russia. After the sanctions, I
>> was surprised to see it made it.
>>
>> After learning how to operate it, I began to be curious about the low level
>> background radiation. This is shown in the photo at
>>
>> https://www.mrmonett.com/RADIACOD.JPG
>>
>> I wonder what the spectrum curve is saying, particularly the rise and quick
>> drop near zero. Scouring google, I was unable to find any source that
>> explained it. What mechanism could produce such weak gamma or x-rays?
>
> What do you know of the calibration of the unit itself? Does it have the equivalent of frequency response?
>

For his device it looks like the plot is a histogram of absorbed energy,
and can be set on the 1 MeV, 2 MeV and 3 MeV scales, see top of page 19:

<https://scan-electronics.com/files/EN/RadiaCode/SFX/RC-101_Device_Manual.pdf>

If the widget is set on the 1 MeV scale and the left extreme of the X
axis is about 100 keV and the right hand extreme is about 1 MeV, and the
amplitude on a log plot it seems somewhat congruent with page 4 here:

<https://arxiv.org/ftp/arxiv/papers/1305/1305.2572.pdf>

Seems to be detecting background radiation if that's how it's set up,
situation normal I think?

[Anthony William Sloman]

How about

https://en.wikipedia.org/wiki/Potassium-40

I seem to remember that it is the most important gamma ray source in regular terrestrial environments.

--
Bill Sloman, Sydney

[whit3rd]

As a general rule, X-rays excite fluorescences in lots of materials; unless you
have only low-atomic-number elements around, some of those
fluuorescences will be in the low X-ray region, and would presumably be
a low-energy high-count source that penetrates the window of your sensor
(whatever the sensor is). For some sources, secondary radiation
is the easiest to detect (a detector can be transparent to high energy photons).

[Mike Monett]

Thanks for your reply. As a beginner, it is easy to get confused. I'm
confused.

To get more information, I decided to get the spectrum of Potassium-40 by
extending the scale of the Radiacode to 3MV, and sitting it on 3 jars of
Windsor Salt Free shown here:

https://windsorsalt.com/product/salt-free/

Wikipedia gives the following information on Potassium-40 decay:

Potassium-40 is a rare example of a nuclide that undergoes both
types of beta decay. In about 89.28% of events, it decays to
calcium-40 (40Ca) with emission of a beta particle (an electron)
with a maximum energy of 1.31 MeV and an antineutrino. In about
10.72% of events, it decays to argon-40 (40Ar) by electron capture
(EC), with the emission of a neutrino and then a 1.460 MeV gamma
ray.[1] The radioactive decay of this particular isotope explains
the large abundance of argon (nearly 1%) in the Earth's atmosphere,
as well as prevalence of 40Ar over other isotopes. Very rarely
(0.001% of events), it decays to 40Ar by emitting a positron (?+)
and a neutrino.[2]

https://en.wikipedia.org/wiki/Potassium-40

The detector in the Radiacode is a 1 cm cube of Thallium Doped Caesium
Iodide (CsI:TI). This is a very popular scintillation detector and has good
performance when coupled to a avalanch diode.

The Potassium-40 spectrum is here:

https://www.mrmonett.com/POTASS40.JPG

You can see a slight hump at 1.31 MeV and a clearer hump at 1.46 MeV. This
is very satisfying, but it's not clear how the hump at 1.31 MeV is
produced. Is the Radiacode sensitive to beta decay?

Also notice the shelf extending back to zero energy. Where does this come
from?

You mentioned above "X-rays excite fluorescences in lots of materials".

But the sources are presumably beta and gamma. Where is the fluorescence
coming from?

Thanks for your help!


--
MRM

[Anthony William Sloman]

The neutrino was pretty much invented to explain why the electron came out with a range of energies - the neutrino carried away the rest of the energy.

> You mentioned above "X-rays excite fluorescences in lots of materials".
>
> But the sources are presumably beta and gamma. Where is the fluorescence coming from?

Fluorescence can also be excited by energetic electrons - "beta rays". Gamma ray is just another name for an X-ray. It took a while for us to understand that they were both energetic photons.

--
Bill Sloman, Sydney

[bitrex]

And in the more modern physics it helps conserve spin and lepton
number/flavor, they're on the lookout for something like muon ->
electron + gamma where the energies are correct but lepton flavor
conservation is violated. Haven't seen it yet AFAIK

>> You mentioned above "X-rays excite fluorescences in lots of materials".
>>
>> But the sources are presumably beta and gamma. Where is the fluorescence coming from?
>
> Fluorescence can also be excited by energetic electrons - "beta rays". Gamma ray is just another name for an X-ray. It took a while for us to understand that they were both energetic photons.
>

I think in particle physics all photons that come from decay tend to be
called "gamma" even if they overlap with the X-ray's domain below about
100 keV.

At the bottom of page 4:

<http://www-odp.tamu.edu/publications/tnotes/tn26/CHAP5.PDF>

"About 90% of the counts come from the low-energy part of the
spectrum, which is degraded by Compton scattering." I think this means
the area around 100 keV in the background radiation is very noisy with
contributions from the scattered photons of lots of stuff.

[Martin Brown]

On 06/06/2022 03:12, Ricky wrote:
> On Sunday, June 5, 2022 at 9:25:18 PM UTC-4, bitrex wrote:
>> On 6/5/2022 9:24 PM, bitrex wrote:
>>> On 6/5/2022 7:07 PM, Mike Monett wrote:
>>>> My Radiascan Radiacode finally arrived from Russia. After the
>>>> sanctions, I
>>>> was surprised to see it made it.
>>>>
>>>> After learning how to operate it, I began to be curious about the low
>>>> level
>>>> background radiation. This is shown in the photo at
>>>>
>>>> https://www.mrmonett.com/RADIACOD.JPG
>>>>
>>>> I wonder what the spectrum curve is saying, particularly the rise and
>>>> quick
>>>> drop near zero. Scouring google, I was unable to find any source that
>>>> explained it. What mechanism could produce such weak gamma or x-rays?
>>>>
>>>> Thanks
>>>
>>> What does the X axis represent?

Energy I presume. There will be a mix of elements contributing to the
background and some will have characteristic lines. Potassium nitrate or
instant coffee may have enough K40 in to allow some calibration.

https://gammaspectacular.com/blue/k-40-gamma-spectrum#

>>>
>>> There's a long decay chain from naturally-occurring thallium 232
>> Er, Thorium 232, not thallium
>
> When I look at the decay chain, I don't see any gamma emissions. Is this in a more rare decay event?

No they are common but they occur in conjunction (shortly after) either
an alpha or beta decay due to the recoil and necessary rearrangement of
the remaining components of the atomic nucleus.

Just after the alpha or beta particle escapes the nucleus is in an
excited state with a hole in it where the emitted particle once sat.
Gamma ray(s) get emitted as it rearranges back to its new ground state.

Only emissions that alter the atomic number and/or mass are normally
shown on decay chain diagrams.

--
Regards,
Martin Brown

[Dimiter_Popoff]

X-axis should be energy, the spectrum looks right for it to be that.
Clearly with such a device you won't see much energy resolution,
probably the 1461 keV line of 40K won't be visible even if it were
within the energy range of the device (probably not, by the size of it
the detector would be too small for that; buy a kilogram of bananas and
measure it to see if that's the case).
Here is what the 40K peak looks like (the marker, a red X, is on top
of it): http://tgi-sci.com/tgi/nmc3spc.htm#nmc3demo

If the banana pack yields higher counts per second and no visible peak
(which is what I expect you will see) it will be due to Compton etc.,
others may be more familiar with the details, I just design the
spectrometers and have learnt only as much as it takes to do the
measurement and the evaluation of the spectra....

======================================================
Dimiter Popoff, TGI http://www.tgi-sci.com
======================================================
http://www.flickr.com/photos/didi_tgi/

[Dave Platt]

In article <d14769a6-4607-49b7...@googlegroups.com>,

>> I wonder what the spectrum curve is saying, particularly the rise and quick
>> drop near zero. Scouring google, I was unable to find any source that
>> explained it. What mechanism could produce such weak gamma or x-rays?
>
>As a general rule, X-rays excite fluorescences in lots of materials; unless you
>have only low-atomic-number elements around, some of those
>fluuorescences will be in the low X-ray region, and would presumably be
>a low-energy high-count source that penetrates the window of your sensor
>(whatever the sensor is).

Correct. In fact, when building high-quality isolation chambers for
measuring gamma specta (the gamma equivalent of a Faraday cage, in
effect) it's necessary to use a layered approach. The outer layer is
usually lead, but when gammas from outside hit the lead it will
fluoresce in the X-ray spectrum. So, inside the lead, you have
another layer which effectively absorbs those X-rays... and *it* may
fluoresce at a lower-energy X-ray frequency, so you may need a third
layer of yet another material.

I've used a home-made gamma spectrometer (NaI crystal, a PMT, and my
own electronics) to look at some naturally-occurring radioactive
materials. One interesting source is some monazite sand from a local
beach - it has a significant amount of thorium in the mix and I get an
appreciable count rate if I lower the sensor down onto a big box of
the stuff.

The spectrum does show the expected gamma-ray peaks for thorium, but
they're not as "clean" as for a purer thorium sample and there's a
strong continuum of lower-energy gamma/X-rays just as the OP's photo
showed. My understanding is that this is "degraded" gamma - in other
words, gamma-induced fluorescence occurring within the sample itself.
Reducing or eliminating this requires flattening out the sample (so
that there's a better chance for a thorium-generated gamma to hit the
NaI sensor before it hits an atom of the sand and causes
fluorescence).

One spectrum I looked at was that of a "quantum energy pendant" that
can be bought inexpensively on eBay and elsewhere. It's supposedly a
natural negative-ion source with semi-mystical healing powers. What
it actually seems to be is a pendant made from a natural ore rich in
thorium. It emits "negative ions" in the form of beta-decay
electrons, and reportedly its emission rates are high enough that if
you wear it next to your skin every day you'd exceed certain government
safety limits for ionizing-radiation exposure in that area (possible
cancer risk or a localized radiation burn).

http://www.radagast.org/~dplatt/gamma/quantum-pendant.png

The green trace is the background radiation level in my work
area. The purple trace is from sampling for the same amount
of time, with the pendant in contact with the NaI sensor. The
thorium-228 peak is clear, there's another from lead and radium
decay daughters, and the actinium-228 peak is also visible.

With another sensor and voltage setting, the background signal
from potassium-40 is visible... and bringing a bottle of
Morton "lite salt" or a bag of water-softener potassium
chloride around the sensor really makes it obvious!

[amdx]

  Yep, used to built bore hole equipment that explored what layers were
below.
One piece was a gamma ray detector. This description doesn't mean much
to me anymore,
if it ever did, but but here are some down hole gamma graphs.
> https://www.kgs.ku.edu/Publications/Bulletins/LA/03_gamma.html

                               Mikek


--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[John Miles, KE5FX]

On Sunday, June 5, 2022 at 4:07:22 PM UTC-7, Mike Monett wrote:

> My Radiascan Radiacode finally arrived from Russia. After the sanctions, I
> was surprised to see it made it.

This listing is also very interesting:

https://www.ebay.com/itm/194659036410

Basically 2000+ PMT+CsI(Tl) assemblies for sale at around $20 each.
Wonder how they'd compare to the solid-state CsI(Tl) detector assembly
in the Radiacode unit?

-- john, KE5FX

[Dimiter_Popoff]

This is incredibly cheap indeed. I thought even Hamamatsu can't make
PMT-s that small :). (4 years ago they sold us some of their R12421 at
450 euro each IIRC).
But just the scintillation crystal would probably cost much more,
let alone the PMT at Hamamtsu.... No idea how they manage that.

[Mike Monett]

I tried to order one. Does not ship to Canada. Can you order one and mail it
to me? I can pay you via Paypal. Thanks.



--
MRM

[Jan Panteltje]

On a sunny day (Sat, 25 Jun 2022 18:16:39 -0000 (UTC)) it happened Mike Monett
<spa...@not.com> wrote in <XnsAEC1913D78...@144.76.35.252>:

I just found this on tomshardware.com:
https://www.tomshardware.com/news/raspberry-pi-pico-detects-radiation
nice spectra (github link)
https://github.com/Open-Gamma-Project/Open-Gamma-Detector

[John Miles, KE5FX]

On Saturday, June 25, 2022 at 11:16:45 AM UTC-7, Mike Monett wrote:
> I tried to order one. Does not ship to Canada. Can you order one and mail it
> to me? I can pay you via Paypal. Thanks.

Maybe. I'll have to surf through the Commerce and ITAR lists to see if there's
a reason why the seller doesn't ship to Canada. Shifty folk, Canadians.

(It'll be a few days before I have time to deal with it, for various reasons.)

-- john, KE5FX

[Mike Monett]

"John Miles, KE5FX" <jmi...@gmail.com> wrote:

That's fantastic. Thanks.

A lot of US vendors don't want to ship to Canada. But the majority do ship
with no problem. Spending time to find out why may give mixed results. I
can probably ask the vendor what his reasons are. In the meantime, my main
goal is to get a copy of his model before he runs out or gives up.

I will send my name and address to your gmail address. Again, thanks.

Mike



--
MRM

[Phil Hobbs]

For any serious use, I'd budget for a replacement PMT. They age out
after several years, which is probably why these assemblies were
replaced. They also wear out on account of photocurrent--the usual rule
is that you can get an integrated anode charge of about 1000 C/cm**2 of
photocathode area before the gain drops by ~half.

If you're going to use an ionic scintillator in contact with an end-on
PMT (one where the photocathode is deposited directly on the faceplate)
you'll need to keep the cathode near ground to avoid ions migrating
through the glass and corroding the PC. That means running the anode at
high voltage and coupling the pulses out with a cap or transformer or
something.

Using an air gap between scintillator and tube allows you to keep the
anode near ground, which is much more convenient, but costs you about
half your light. (The collection efficiency goes like the etendue,
which has a factor of n**2 in it.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

[Mike Monett]

Good information. Thanks.

I'm not planning on heavy use. The idea is to compare the scintillator
againt the Radiacode, and try to measure any Radon gas in the basement.
Then it will probably go into storage.



--
MRM

[Chris Jones]

If you have radon, try running a CRT television for a few hours and then
wipe down the screen with a damp piece of tissue that has been folded to
about the size of your geiger tube (or its end window if it has one). I
find the dust on my CRT screen is quite radioactive but it has a short
half-life. I'm guessing it is some polonium isotopes. The dust that
collects on the screen doesn't end up in my lungs, so perhaps CRTs are
healthier to have in the house than flatscreens.

[Clifford Heath]

On 28/6/22 13:31, Chris Jones wrote:
> If you have radon, try running a CRT television for a few hours and then

> ... The dust that

> collects on the screen doesn't end up in my lungs, so perhaps CRTs are
> healthier to have in the house than flatscreens.

Not as healthy as having no TV. That crap bypasses the lungs and goes
straight to the brain

[Jan Panteltje]

On a sunny day (Tue, 28 Jun 2022 13:31:26 +1000) it happened Chris Jones
<lugn...@spam.yahoo.com> wrote in <eCuuK.190184$pqD1....@fx01.ams4>:

>If you have radon, try running a CRT television for a few hours and then
>wipe down the screen with a damp piece of tissue that has been folded to
>about the size of your geiger tube (or its end window if it has one). I
>find the dust on my CRT screen is quite radioactive but it has a short
>half-life. I'm guessing it is some polonium isotopes. The dust that
>collects on the screen doesn't end up in my lungs, so perhaps CRTs are
>healthier to have in the house than flatscreens.

Some CRTs from sets that came in for repair had collected tar from smokers.. nicotine.
Wiping clean with alcohol increased brightness considerably :-)
So yes, functioned as air filter ;-)

[Jan Panteltje]

On a sunny day (Tue, 28 Jun 2022 17:03:04 +1000) it happened Clifford Heath
<no_...@please.net> wrote in
<16fcb6d40dd74681$1$391142$70dd...@news.thecubenet.com>:

There are some informative science related programs on (sat) TV Astra1
and there is (at least on the continent) tetelext / ceefax / videotext
Caesar: give the people bread and TeeFee
or was it games? :-)

Its a shame UK dropped Ceefax. no way to see the program schedule other then
internet, talk about a DANGEROUS medium ? Just read this group!

Radon detectors and test kits are 14 USD upwards on Amazon...

I was looking for a sold state PMT diode .. for that tomshardware link I gave,
delivery November, about 56 Euro 1 piece

I will hang on to my good old PMTs for now, have also many plastic scintillators.
Big PMT will likely last to WW3 (2024??). After that all lights up in the dark anyways

BTW I have a nice scintillation screen too.

[Phil Hobbs]

> Good information. Thanks.
>
> I'm not planning on heavy use. The idea is to compare the scintillator
> againt the Radiacode, and try to measure any Radon gas in the basement.
> Then it will probably go into storage.

It ought to work fine for light-duty use like that, though you'll need
the PMT supply and bias string. If you know the tube P/N, I can
probably tell you what to use.

[Mike Monett]

Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

> Mike Monett wrote:

[...]

>> I'm not planning on heavy use. The idea is to compare the scintillator
>> againt the Radiacode, and try to measure any Radon gas in the basement.
>> Then it will probably go into storage.
>
> It ought to work fine for light-duty use like that, though you'll need
> the PMT supply and bias string. If you know the tube P/N, I can
> probably tell you what to use.
>
> Cheers
>
> Phil Hobbs

I don't think the PMT P/N is available. I also assume the bias string is
buried inside the assembly. I'll probably have to find the operating voltage
by experimenting, a time-honored tradition among hackers.



--
MRM

[Phil Hobbs]

Turns out the p/n is (more or less) in the listing title: it's some
flavour of R7400, whose datasheet is here, courtesy of Jeroen & Co:
<https://ctf3-tbts.web.cern.ch/instr/PMT/R7400U_TPMH1204E07.pdf>.

CsI(Tl) emits in the visible (the peak is around 550 nm), so the tube is
probably an R7400-02 or -20.

It's an 8-stage tube that likes about 75-100V per stage, and is
interestingly fast at 800 ps FWHM. That's fast like an APD, and much
faster than a SiPM/MPPC. I ordered a few of them to try out, probably
without the scintillator.

For scintillation counting, you don't need brilliant linearity, so a
resistor string is probably fine for the dynode bias. I'd start with a
current-limited -1 kV variable supply and some 1M resistors, with a
2.2-nF cap across each of the bottom two or three resistors. That way,
at 800V you'll be dissipating about 80 mW.

[Mike Monett]

Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

[...]

> Turns out the p/n is (more or less) in the listing title: it's some
> flavour of R7400, whose datasheet is here, courtesy of Jeroen & Co:
> <https://ctf3-tbts.web.cern.ch/instr/PMT/R7400U_TPMH1204E07.pdf>.
>
> CsI(Tl) emits in the visible (the peak is around 550 nm), so the tube is
> probably an R7400-02 or -20.
>
> It's an 8-stage tube that likes about 75-100V per stage, and is
> interestingly fast at 800 ps FWHM. That's fast like an APD, and much
> faster than a SiPM/MPPC. I ordered a few of them to try out, probably
> without the scintillator.
>
> For scintillation counting, you don't need brilliant linearity, so a
> resistor string is probably fine for the dynode bias. I'd start with a
> current-limited -1 kV variable supply and some 1M resistors, with a
> 2.2-nF cap across each of the bottom two or three resistors. That way,
> at 800V you'll be dissipating about 80 mW.
>
> Cheers
>
> Phil Hobbs

Very valuable information. Thanks.



--
MRM

[John Miles, KE5FX]

On Sunday, June 26, 2022 at 5:23:43 PM UTC-7, Mike Monett wrote:
> I will send my name and address to your gmail address. Again, thanks.

Go ahead and send your address to me at john (at) miles.io if you'd
still like one, and I'll throw one in a padded envelope next time I go to
the post office. My GMail account is almost unusable due to people
confusing their email address with mine and signing me up for
all kinds of junk mail. Right now there are 217,959 unread messages
and I don't see yours anywhere. :(

I powered one up just now and took a video:

http://www.ke5fx.com/r7400u.htm

Hopefully I'm looking at a lot of dark counts or other PMT artifacts,
because jeez, that sure seems like a lot of pulses.

-- john, KE5FX

[Mike Monett]

"John Miles, KE5FX" <jmi...@gmail.com> wrote:

Hi John,

Very nice page !

That is a very nice offer. Thanks.

Various sources say the PMT voltage is critical and must be adjusted
individually for each PMT. One way to do this is to find a known
radioactive source and generate a spectrum, then adjust the PMT voltage so
the source lines up with the known energies in KeV or Mev.

Getting samples of thorium has turned out to be impossible, except for
traces in welding rods. However, radium is readily available in the form of
watch hands painted with radium. These are for sale extremely cheap on
Ebay.

The watch hands no longer glow in the dark since the phosphor will have
worn out. However, the radium will still be active since it has a half-life
of 1600 years. Below is the radioactive series of radium-226. You can see
the first step is radon, which releases alpha particles and gamma
radiation:

https://www.ld-
didactic.de/software/524221en/Content/Appendix/Ra226Series.htm

Radon gas is extremely dangerous. There is a small amount in every
basement. You breath it into your lungs, where it emits alpha particles,
which are the nucleus of helium-4. This causes lung cancer and you die.

We need to be able to monitor the amount of radon in our basements and be
certain it doesn't increase, such as during the winter when most
ventilation is shut off.

So it pays to learn a bit about gamma spectrometers to be able to protect
yourself and your family.

Regular radon detectors are very expensive, but gamma spectrometers can be
quite modest in cost. You can get the Radiacode, which is a very nice unit,
or build the Hamamatsu R7400U PMT version as a backup and verification.



--
MRM

[Anthony William Sloman]

On Saturday, July 16, 2022 at 8:25:08 PM UTC+10, Mike Monett wrote:
> "John Miles, KE5FX" <jmi...@gmail.com> wrote:
> > On Sunday, June 26, 2022 at 5:23:43 PM UTC-7, Mike Monett wrote:
> >> I will send my name and address to your gmail address. Again, thanks.
> >
> > Go ahead and send your address to me at john (at) miles.io if you'd
> > still like one, and I'll throw one in a padded envelope next time I go to
> > the post office. My GMail account is almost unusable due to people
> > confusing their email address with mine and signing me up for
> > all kinds of junk mail. Right now there are 217,959 unread messages
> > and I don't see yours anywhere. :(
> >
> > I powered one up just now and took a video:
> >
> > http://www.ke5fx.com/r7400u.htm
> >
> > Hopefully I'm looking at a lot of dark counts or other PMT artifacts,
> > because jeez, that sure seems like a lot of pulses.
>

> Very nice page !
>
> That is a very nice offer. Thanks.
>
> Various sources say the PMT voltage is critical and must be adjusted
> individually for each PMT. One way to do this is to find a known
> radioactive source and generate a spectrum, then adjust the PMT voltage so
> the source lines up with the known energies in KeV or Mev.

The photomultiplier voltage just adjusts the gain of the photomultiplier tube - photons hitting the photocathode produce electrons in the cathode space, and the voltage drop across the dynode chain just adjusts the number of electrons that each electron hitting the first dynode ends up delivering to the anode.

Getting the energy of individual particles coming out of the radiation source takes rather more than fiddling with the gain of the electron multiplication stages inside the photomultiplier tube. Because you've got a lot of stages of multiplication - anything from 10 to 14 - you can vary that gain a lot.

> Getting samples of thorium has turned out to be impossible, except for
> traces in welding rods. However, radium is readily available in the form of
> watch hands painted with radium. These are for sale extremely cheap on
> Ebay.
>
> The watch hands no longer glow in the dark since the phosphor will have
> worn out. However, the radium will still be active since it has a half-life
> of 1600 years. Below is the radioactive series of radium-226. You can see
> the first step is radon, which releases alpha particles and gamma
> radiation:
>
> https://www.ld-
> didactic.de/software/524221en/Content/Appendix/Ra226Series.htm
>
> Radon gas is extremely dangerous. There is a small amount in every
> basement.

If your house is built above granite rocks, or any other kind of rock that contains uranium, you can get radon gas leaking into the basement. If it is, put in an extractor fan to move it out before it can drift up to diffuse through the floor into the rest of the house.

> You breath it into your lungs, where it emits alpha particles, which are the nucleus of helium-4. This causes lung cancer and you die.

Helium four won't do any damage at all, but energetic alpha particles can cause mutations in any cell that they hit, and some mutations can make cell cancerous

> We need to be able to monitor the amount of radon in our basements and be
> certain it doesn't increase, such as during the winter when most
> ventilation is shut off.

If there's uranium - or the like - in the rocks under your basement it makes sense to monitor for radon. If there is, it makes sense to ventilate that space, even in winter.

> So it pays to learn a bit about gamma spectrometers to be able to protect yourself and your family.

Learning about geology is cheaper.

> Regular radon detectors are very expensive, but gamma spectrometers can be
> quite modest in cost. You can get the Radiacode, which is a very nice unit,
> or build the Hamamatsu R7400U PMT version as a backup and verification.

Radon itself decays by emitting a 4.6 Mev alpha particle. This isn't any kind of gamma ray, but it is energetic enough that if it hits an adjacent atom it may generate a gamma ray (an energetic photon) which is likely to have a longer range.

The Radiacode 101 monitor uses a scintillation detector - the chunk of thallium doped cesium iodide - which produces a flash of light when hit by a gamma ray photon (or anything else that can get at it).

> crystal CsI (Tl) of cesium iodide doped with thallium in a sealed container;
> silicon photomultiplier;

Also called an avalanche photodiode.

> optical interface between scintillator and photomultiplier;

A window, so the photons emerging from the transparent can get at the sensitive face of the photodiode

> precision temperature-compensated power supply for photomultiplier;

Avalanche photodiodes are tricky to bias.

> high-speed analog-digital circuit for processing pulses from a photomultiplier.

The pulses do tend to be narrow. You need fast op amps and comparators, but they are widely available and not that expensive.

https://ctf3-tbts.web.cern.ch/instr/pmt/r7400u_tpmh1204e07.pdf

The minature Hamamatsu R7400U photomultiplier tubes are pretty compact (but not as compacts as an avalanche photodode) and need a higher voltage supply, but they aren't quite as tricky to bias as an avalanche photodiode.

--
Bill Sloman, Sydney

[Dave Platt]

In article <XnsAED63FC6A8...@88.198.57.247>,

Mike Monett <spa...@not.com> wrote:
>Getting samples of thorium has turned out to be impossible, except for
>traces in welding rods. However, radium is readily available in the form of
>watch hands painted with radium. These are for sale extremely cheap on
>Ebay.

Also on eBay, you can find "quantum energy" or "scalar energy" or
"negative ion" pendants made out of a black volcanic rock. They're
often touted as a way of protecting oneself from the (supposed)
harmful effects of electromagnetic radiation.

They do generate "negative ions", in the form of beta-decay
electrons... these are not your gentle after-the-rainstorm negative
ions by any means!

By one report the radiation level is high enough that wearing one next
to the skin for a year can exceed safe exposure levels and might even
cause a mild radiation burn. I understand that Singapore has banned
the import of such products for this reason.

The rock from which they are made appears to be rich in thorium and
its decay products (perhaps something like monazite?).

I measured one on my home-made gamma spectrometry system and got
a very recognizable thorium-decay signature (the isotope markers
are from a best-efforts calibration).

https://www.radagast.org/~dplatt/gamma/quantum-pendant.png

Another useful calibration source (for higher-energy gammas from
potassium-40) is a sack of potassium chloride water-softener recharge
crystals from your local big-box home/hardware store (or, on a smaller
scale, a box of Morton "Lite Salt" which is about half potassium
chloride).

And, one can still find orange Fiestaware and green uranium glass at
the occasional estate or garage sale or antique store.

[a a]

-Low Level Gamma Radiation is all fake

[John Miles, KE5FX]

On Saturday, July 16, 2022 at 7:16:38 AM UTC-7, Dave Platt wrote:
> I measured one on my home-made gamma spectrometry system and got
> a very recognizable thorium-decay signature (the isotope markers
> are from a best-efforts calibration).
>
> https://www.radagast.org/~dplatt/gamma/quantum-pendant.pn

Resolution of that setup looks really good -- is it written up anywhere?

-- john, KE5FX

[Mike Monett]

Thanks for the information. I will try to find the black volcanic rock
products. I recall an article describing these that got them kicked off
Amazon (I think).

Your gamma spectrometry system sounds very interesting. Can you supply more
information, such as what kind of scintillator crystal do you use, how big
is it, and do you use a PMT or diode for the detector, what software do you
use to generate the spectrum, how do you drive it, and any other details
that might be interesting.

I use pure potassium chloride (KCl) in the form of Windsor Salt Free
seasoning, but my Radiacode is not sensitive enough to detect the decay
products. I left it sitting on three containers for several days but had no
luck. I need a more sensitive detector, which is why yours is so
interesting.

On a related topic, I have been trying to find out why the background gamma
spectrum has a sharp rise at low energies, and where does it come from? Do
you have any ideas?

Thanks,

Mike



--
MRM

[Sjouke Burry]

why did somebody snip off the last letter of .PNG????

[Mike Monett]

Mike Monett <spa...@not.com> wrote:

> dpl...@coop.radagast.org (Dave Platt) wrote:

>> Also on eBay, you can find "quantum energy" or "scalar energy" or
>> "negative ion" pendants made out of a black volcanic rock. They're
>> often touted as a way of protecting oneself from the (supposed)
>> harmful effects of electromagnetic radiation.

>> The rock from which they are made appears to be rich in thorium and
>> its decay products (perhaps something like monazite?).

>> I measured one on my home-made gamma spectrometry system and got
>> a very recognizable thorium-decay signature (the isotope markers
>> are from a best-efforts calibration).
>>
>> https://www.radagast.org/~dplatt/gamma/quantum-pendant.png

> Thanks for the information. I will try to find the black volcanic rock
> products. I recall an article describing these that got them kicked off
> Amazon (I think).

> Thanks,

> Mike

Ebay was a bust. Quantum Energy turned out to be a fishing reel. Scalar
energy was some patterns on a piece of paper.

However, Amazon turned up lots of volcanic rock emi protectors. I got one
titled

"Volcanic Stone Pendant,Energy Necklace Fashionable Health Care for Women
for Daily Wear Quantum Science Scalar Energy Necklace Round Pendant for Men
Woman Tourmaline Volcanic Stone Jewelry",

$15.86 FREE delivery August 22 - September 16

https://www.amazon.ca/gp/product/B09V9Y7359/

This one sounds like it will do the job. Thanks.

Mike


--
MRM

[a a]

Gamma Radiation is never Low Level
beware of cancer

[jla...@highlandsniptechnology.com]

On Sat, 16 Jul 2022 18:48:41 -0000 (UTC), Mike Monett <spa...@not.com>
wrote:

The classic radiation test source was a thoriated Coleman lantern
mantle.

[Dave Platt]

In article <7cc8f810-1325-4542...@googlegroups.com>,

John Miles, KE5FX <jmi...@gmail.com> wrote:

I don't think I've written up anything in detail - it's been a few
years since I played with it much.

I have a couple of probes, both built with surplus commercial PMTs,
one with a NaI(Tl) crystal and another with a BGO crystal.

The signal processing uses a charge-sensitive amplifier with some
pulse shaping built in (I like the CSA architecture because it's not
particularly sensitive to the cable length and capacitance). The
original design was done by Richard Hester; I did some tweaks for my
version and did a custom board layout. The files are in the
https://www.radagast.org/~dplatt/gamma/ directory.

The biggest disadvantage to this circuit is that if I forget, and
connect or disconnect the probe cable with the power on (or without
letting it discharge to zero) the spike usually blows out the
front-end JFET, and I have to cuss and pull it out of the
air-wire socket and replace it :-)

The high-voltage supply is based on a flyback with diode voltage
multiplier, based on a circuit I found some years ago intended for
use with GM tubes.

The output of the CSA goes into a moderately-priced USB sound card
line input.

I wrote the pulse detection and filtering code myself. The first
version was strictly command-line (record audio to a .WAV file, then
post-process to detect and bin the pulses and generate data files which
could be fed to gnuplot). I then wrote a Linux GUI based on the FLTK
toolkit which can read/process/display in real time.

The trickiest part was handling high pulse rates, where one pulse
starts while the CSA is still recovering from the previous one.
At some point I may sit down and try writing some DSP code to
de-convolve the CSA's pulse shaping and turn the signal back
into narrow impulses.

[Dave Platt]

In article <XnsAED696ABEA...@88.198.57.247>,

As I understand it, you're seeing is largely Compton radiation and
X-ray fluorescence. When naturally occurring gammas (from K40 decay,
transuranincs, and cosmic rays) smack into atmosphere or into solid
matter, the energy of the gamma is scattered... it's dissipated a bit
at a time as the gamma photon interacts with electrons or the nucleus
of the impacted materials.

If a gamma scatters off of an electron, some of the energy is
transferred to the electron. If the electron is bumped up to a
higher-energy orbital and then decays back to its ground state, the
decay can cause the emission of an X-ray photon - fluorescence. This
necessarily has a lower energy than the gamma, and its energy will
depend on just what element was involved in the scattering. The
original scattered gamma will have less energy than it did before, of
course.

So, the rise you see in the spectrum is probably the sum of a whole
bunch of Compton scattering events which involved gammas that were
originally of higher energy.

From what I've read, skyglow (gammas and X-rays originating from
cosmic-ray impacts on the atmosphere) is a big part of this.
NORM is another big part.

A few years ago I collected a box of monazite sand from a local
beach. It definitely shows a thorium signature, but the peaks are
nowhere near as sharp as the ones in the "quantum pendant" data.
I believe this is because the thorium is diffused throughout a
much larger amount of base material (I have to use a couple of
pounds of it to get a good reading) and most of the decay gammas
end up Compton-scattering at least once as they work their way
through the sand to the sensor crystal. As a result, the
sharp peaks from the original decay events are weakened, and
blurred by the Compton scattering effect.

[Mike Monett]

dpl...@coop.radagast.org (Dave Platt) wrote:

> In article <7cc8f810-1325-4542...@googlegroups.com>,
> John Miles, KE5FX <jmi...@gmail.com> wrote:
>>On Saturday, July 16, 2022 at 7:16:38 AM UTC-7, Dave Platt wrote:
>>> I measured one on my home-made gamma spectrometry system and got
>>> a very recognizable thorium-decay signature (the isotope markers
>>> are from a best-efforts calibration).
>>>
>>> https://www.radagast.org/~dplatt/gamma/quantum-pendant.pn
>>
>>Resolution of that setup looks really good -- is it written up anywhere?
>
> I don't think I've written up anything in detail - it's been a few
> years since I played with it much.
>
> I have a couple of probes, both built with surplus commercial PMTs,
> one with a NaI(Tl) crystal and another with a BGO crystal.

How big are the crystals?



--
MRM

[whit3rd]

On Saturday, July 16, 2022 at 5:38:44 PM UTC-7, Dave Platt wrote:

> The trickiest part was handling high pulse rates, where one pulse
> starts while the CSA is still recovering from the previous one.
> At some point I may sit down and try writing some DSP code to
> de-convolve the CSA's pulse shaping and turn the signal back
> into narrow impulses.

The analog-days solution was a delay line amplifier; the long recovery tail
is exponential, so a difference amplification of V(t) - (1+epsilon)V(t-s)
flattens the recovery when (1+epsilon) equals the diminution of the signal
during 's' seconds. The infinite-impulse response or FIR filter is relatively easy
work to do that.

Some good info here:
<https://www.ortec-online.com/-/media/ametekortec/manuals/4/460-mnl.pdf>

[Mike Monett]

Thanks to Phil and John, I will soon have a PMT gamma detector to compare
with the Radiacode. Hopefully, it will be more sensitive so I can be more
certain of measuring Radon in the basement as well as other radiation
sources.

Assembling the electronics turned out to be much easier than some DIY pages
describe on the web. There is a company in Israel that supplies complete
Gamma Spectroscopy electronics. The company is RH-Electronics at

http://rhelectronics.net

I got the PIC18 MCA Module for $95.00 plus shipping at $17.95:

https://www.rhelectronics.store/diy-pic18-mca-kit-for-gamma-spectroscopy

Generating the high voltage for the PMT turned out to be easy. Amazon sells
CCFL inverter boards very cheap. I got one for $13.46 at

https://www.amazon.ca/gp/product/B07YM68GVM/

The last item is a fast high voltage diode to supply the PMT. This turned
out to be the hardest problem until I found Dean Technology in Dallas,
Texas, 75370

They sell a 5KV 100ns diode for a couple of bucks:

https://www.deantechnology.com/products/hl500

The total price is CDN $95.00 + $17.95 + $13.46 + $2.50 = $128.91, not
including the PMT that the seller refuses to sell to Canada.

The US price is about $120 USD including the PMT, so nobody has any excuse
for not being able to detect radon in their basement.





--
MRM

[Mike Monett]

A very lucid explanation. Thanks.

I was able to find out what NORM is without having to ask you: "Naturally
ocurring radioactive materials." I'm so proud of myself:)

How big are your scintillator crystals?



--
MRM

[a a]

Gamma Radiation is never Low Level

since
what matters is
long-term exposure to cancerogenic Gamma Radiation
so
Long-term Low Level exposure
turns into
High Level Gamma Radiation

[whit3rd]

On Sunday, July 17, 2022 at 1:00:00 PM UTC-7, a a wrote:

> Gamma Radiation is never Low Level

False, of course.

> since
> what matters is
> long-term exposure to cancerogenic Gamma Radiation

Not at all; for human health, what matters is the generation of ion pairs
and gamma radiation includes energies that go right through a human
body without much likelihood of interaction.

> Long-term Low Level exposure
> turns into
> High Level Gamma Radiation

That's just nonsense; word salad, plus some capitalizations.

[a a]

you are exactly stupid dog

--
Gamma Radiation Sterilization: What You Need to Know
https://int-enviroguard.com/blog/what-is-the-gamma...

Gamma Radiation Sterilization ExplainedAdvantages of Gamma Radiation SterilizationDisadvantages of Gamma Radiation Sterilization

Image
As the name implies, this is a sterilization process, and it's commonly used to kill bacteria and microorganisms that may be living on the surface of products, packaging, or goods. Powered by Cobalt-60, the low-dose process is administered when high-energy photons are emitted from a radiation source, which works to io…

---
Gamma Radiation - an overview | ScienceDirect Topics
https://www.sciencedirect.com/.../gamma-radiation

Gamma rays are a form of electromagnetic radiation, whereby gamma radiation kills microorganisms by destroying cellular nucleic acid [1]. The use of gamma irradiation is relatively widespread and was first described in the British Pharmacopeia in 1963 and in the


---

What are gamma rays and how dangerous are they?
Gamma rays are ionizing radiation and are thus biologically hazardous. Due to their high penetration power, they can damage bone marrow and internal organs. Unlike alpha and beta rays, they pass easily through the body and thus pose a formidable radiation protection challenge.


---

Gamma Radiation: A brief background Gamma particles consist of energy photons and were discovered by Paul Villard in 1900 when he was researching gamma radiation that comes from radium. These particles are a form of ionizing radiation and can be dangerous to humans, animals and plant life. The decay of the atomic nucleus downgrades from high levels of energy to lower energy. This process is call gamma decay which is what gives birth to radiation gamma. The nucleus releases particles decreasing its energy. Gamma radiation Radiation gamma How Gamma Radiation is Produced Typically, the gamma particles that are released during gamma decay are radioactive so there is enough power in them to do harm. It has the ability to damage physical structure and cause genetic mutations. Because of the ability to break natural bonds in the human body, it can potentially do a high level of harm and cause many severe health problems. Some of the health concerns can be acute and the damage cannot be repaired through the body’s natural repair process. This is commonly the case with high exposure that is long term and will accumulate to cause serious health problems. What can Stop Radiation Gamma? Gamma radiations can travel very fast at the speed of light and chances of penetration are very high. It can penetrate even through metal and do damage. Even though these rays are dangerous with high exposure, they are still used in the medical field for cancer treatment and for imaging equipment such as x-rays. Your exposure amount can only be measured using a Geiger counter and to determine what can stop gamma radiation. This is the reason why during the x-ray process, you will use a lead apron. Normally, you would need 3 meters of concrete to prevent gamma radiation from penetrating. Gamma radiations Gamma radiation in USA Side Effects of Gamma Radiation Some of the possible problems with heavy exposure to gamma radiations include radiation sickness. This is also known as radiation poisoning. Some of the gamma radiation signs can be nausea, vomiting, bleeding, mouth sores, nausea, diarrhea and loss of hair. Radiation sickness was very common after the bombs in Hiroshima as well as Nagasaki. This is also common after nuclear power plant disaster such as the one in Chernobyl. Radiation sickness can happen with fast exposure to high levels of radiation. Even if you are given gamma radiation for the treatment of an illness, you may still experience side effects from it even though it was meant to help you. Sometimes, you may see a change in your skin that can be mild to severe redness but sometimes it can be dark like a burn. Just like the symptoms of radiation sickness, you may have those with this treatment. This type of exposure can also damage the number of blood cells you have, causing a decrease. These effects are usually not long lasting but there are possibilities of having long term effects. Other effects include weak bones, difficulty with swallowing and dry mouth. It may also cause infertility problems in men or women. Chernobyl Tours ☢ Please support us with LIKE :) PLEASE ☢ Share On FacebookPinterestTwitterGoogle+ Previous Article What is Beta Radiation? Next Article Hiroshima and Nagasaki Related Posts A Definition of Alpha Decay VladyslavMarch 2, 2016 Effects of radiation on the body The Effects of Radiation on the Human Body VladyslavFebruary 23, 2016 One Response May 21, 2018 Hanan Khan Reply Great. Enjoyed reading it. I was looking for what types of medicines are Gamma rays used in. Maybe you could include that in another article. Thanks. Learned a thing or two. Leave a Reply Your email address will not be published. Comment Name* Email*

Read more at: https://chernobylguide.com/what_is_gamma_radiation/

[Mike Monett]

Ignore him. I PLONKED him long ago as soon as he appeared.




--
MRM

[a a]

Gamma Radiation

Gamma radiation (7.5Gy) resulted in a significant decrease in body weight, tissue weight, testis: body weight ratio (the gonadosomatic index (GSI)) and tubular diameter up to 15 days of irradiation.

https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/gamma-radiation

[Anthony William Sloman]

On Monday, July 18, 2022 at 8:10:23 PM UTC+10, a a wrote:
> On Monday, 18 July 2022 at 04:12:12 UTC+2, Mike Monett wrote:
> > whit3rd <whi...@gmail.com> wrote:
> >
> > > On Sunday, July 17, 2022 at 1:00:00 PM UTC-7, a a wrote:
> > >
> > >> Gamma Radiation is never Low Level
> > >
> > > False, of course.
> > >> since
> > >> what matters is
> > >> long-term exposure to cancerogenic Gamma Radiation
> > >
> > > Not at all; for human health, what matters is the generation of ion pairs
> > > and gamma radiation includes energies that go right through a human
> > > body without much likelihood of interaction.
> > >
> > >> Long-term Low Level exposure
> > >> turns into
> > >> High Level Gamma Radiation
> > >
> > > That's just nonsense; word salad, plus some capitalizations.
> > Ignore him. I PLONKED him long ago as soon as he appeared.
> >

> Gamma Radiation
>
> Gamma radiation (7.5Gy) resulted in a significant decrease in body weight, tissue weight, testis: body weight ratio (the gonadosomatic index (GSI)) and tubular diameter up to 15 days of irradiation.
>
> https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/gamma-radiation

A a really doesn't know what he is talking about.

https://en.wikipedia.org/wiki/Rad_(unit)

The Gy - or Gray - is defined in terms of the energy absorbed - in Joules per kilogram - by the object being irradiated. Gamma rays - higher energy X-rays - go straight through human flesh, so the amount of energy deposited is a bit uncertain.

What is certain is that it is the energy deposited that matters. and a a doesn't seem to know enough to understand this.

--
Bill Sloman, Sydney

[a a]

@BillSydneyLowScience
stop fooling us


IEEE NSW Section’s Committee Members (2021)

Section Section Chair Colin Elston
Section Vice Chair Sudipta Chakraborty
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The IEEE New South Wales (NSW) Section provides local activities and services to IEEE members who live, work and visit us in New South Wales, Australia. The NSW Section is member of the IEEE Australia Council and is located within the Asia-Pacific region of the IEEE, known as Region 10. The NSW Section has in excess of 3,000 members (Feb-19) that work together to advance technology for the benefit of humanity. This is done through a variety of local student branches, technical chapters and groups. IEEE NSW is the oldest Section in Australia.

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About
IEEE is the trusted voice for engineering, computing, and technology information around the globe

So IEEE is not science body, organization at all

[John Walliker]

A simple way of checking whether it is even worth worrying about radon is to look it up!

https://www.ukradon.org/radonmaps/

https://www.epa.gov/sites/default/files/2015-07/documents/zonemapcolor.pdf

https://www.arpansa.gov.au/understanding-radiation/radiation-sources/more-radiation-sources/radon-map

There are similar maps for lots of other countries.

John

[Anthony William Sloman]

On Monday, July 18, 2022 at 9:40:19 PM UTC+10, a a wrote:
> On Monday, 18 July 2022 at 12:29:57 UTC+2, bill....@ieee.org wrote:
> > On Monday, July 18, 2022 at 8:10:23 PM UTC+10, a a wrote:
> > > On Monday, 18 July 2022 at 04:12:12 UTC+2, Mike Monett wrote:
> > > > whit3rd <whi...@gmail.com> wrote:
> > > > > On Sunday, July 17, 2022 at 1:00:00 PM UTC-7, a a wrote:

<snip>

> So IEEE is not science body, organization at all.

If a a knew what he was talking about, he'd know that the main function of the IEEE is to publish a large collection of high-impact peer-reviewed scientific journals that deal with the science that underlies electronics. That is what science is about, even if a a doesn't have a clue about it.

That's why I joined the organisation back around 1980. It's not all that obvious the current activities of the NSW Branch, but that's where the serious effort goes , and where the serious money gets spent.

I've got just one short comment in that literature

Sloman, A.W. "Comment on 'Computer aided simulation study of photomultiplier tubes'", IEEE Transactions on Electron Devices, ED-38 679-680 (1991).

Because I mostly worked in the UK I published more the UK Institute of Physics journals, but there aren't as many of them, and Americans do tend to ignore them.

--
Bill Sloman, Sydney

[a a]

ok, ok, stop your delusiones and day dreaming

IEEE lives on Facebook

IEEE is the world's largest technical professional organization dedicated to advancing technological innovation and excellence for the benefit of humanity.
IEEE has offices in China, India, Japan, Singapore, and in the United
States (California, New Jersey, New York, Washington, D.C.)
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just visit and find me a single thread or comment, having anything to do with science or research

[Dimiter_Popoff]

Oh God. Is this "a a" a new troll or a renamed version of the old ones.
Perhaps new, some of the old ones at least knew to not be too loud
on topics other than politics. Perhaps posting utterly illiterate
claims is a technique to engage us, who knows. Like I do at the moment,
what am I thinking....

[a a]

On Monday, 18 July 2022 at 15:34:22 UTC+2, Dimiter Popoff wrote:
> On 7/18/2022 15:58, a a wrote:
> > On Monday, 18 July 2022 at 14:36:34 UTC+2, bill....@ieee.org wrote:
> >> On Monday, July 18, 2022 at 9:40:19 PM UTC+10, a a wrote:
> >>> On Monday, 18 July 2022 at 12:29:57 UTC+2, bill....@ieee.org wrote:
> >>>> On Monday, July 18, 2022 at 8:10:23 PM UTC+10, a a wrote:
> >>>>> On Monday, 18 July 2022 at 04:12:12 UTC+2, Mike Monett wrote:
> >>>>>> whit3rd <whi...@gmail.com> wrote:
> >>>>>>> On Sunday, July 17, 2022 at 1:00:00 PM UTC-7, a a wrote:
> >> <snip>
> >>
> >>> So IEEE is not science body, organization at all.
> >>
> >> If a a knew what he was talking about, he'd know that the main function of the IEEE is to publish a large collection of high-impact peer-reviewed scientific journals that deal with the science that underlies electronics. That is what science is about, even if a a doesn't have a clue about it.
> >>
> >> That's why I joined the organisation back around 1980. It's not all that obvious the current activities of the NSW Branch, but that's where the serious effort goes , and where the serious money gets spent.
> >>
> >> I've got just one short comment in that literature
> >>
> >> Sloman, A.W. "Comment on 'Computer aided simulation study of photomultiplier tubes'", IEEE Transactions on Electron Devices, ED-38 679-680 (1991).
> >>
> >> Because I mostly worked in the UK I published more the UK Institute of Physics journals, but there aren't as many of them, and Americans do tend to ignore them.
> >>
> >> --
> >> Bill Sloman, Sydney

--ok, ok, stop your delusiones and day dreaming
> >
-- IEEE lives on Facebook
> >
--IEEE is the world's largest technical professional organization dedicated to advancing technological innovation and excellence for the benefit of humanity.
--IEEE has offices in China, India, Japan, Singapore, and in the United

> > States (California, New Jersey, New York, Washington, D.C.)
> > 3,409,150 people like this
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-- https://www.facebook.com/IEEE.org/
> >
--just visit and find me a single thread or comment, having anything to do with science or research

@Dimiter Popoff’s profile photo
@Dimiter Popoff
we all love your fake

[Anthony William Sloman]

On Monday, July 18, 2022 at 10:58:40 PM UTC+10, a a wrote:
> On Monday, 18 July 2022 at 14:36:34 UTC+2, bill....@ieee.org wrote:
> > On Monday, July 18, 2022 at 9:40:19 PM UTC+10, a a wrote:
> > > On Monday, 18 July 2022 at 12:29:57 UTC+2, bill....@ieee.org wrote:
> > > > On Monday, July 18, 2022 at 8:10:23 PM UTC+10, a a wrote:
> > > > > On Monday, 18 July 2022 at 04:12:12 UTC+2, Mike Monett wrote:
> > > > > > whit3rd <whi...@gmail.com> wrote:
> > > > > > > On Sunday, July 17, 2022 at 1:00:00 PM UTC-7, a a wrote:

<snip>

> just visit and find me a single thread or comment, having anything to do with science or research

The tricky bit would be finding something that you would comprehend as having anything to do with science or research.

The comment that I published in the IEEE Transactions on Electron Devices and listed above - which you have snipped - had a quite a lot to do with research - it cited a bunch of references on photomultiplier non-linearity which are relevant to anybody doing serious research that exploits photomultipliers. So you've already had what you asked for, but failed to recognise it, which is exactly how you have always performed ever since you started posting your inanities here.

--
Bill sloman, Sydney

[a a]

On Monday, 18 July 2022 at 15:41:36 UTC+2, bill....@ieee.org wrote:
> On Monday, July 18, 2022 at 10:58:40 PM UTC+10, a a wrote:
> > On Monday, 18 July 2022 at 14:36:34 UTC+2, bill....@ieee.org wrote:
> > > On Monday, July 18, 2022 at 9:40:19 PM UTC+10, a a wrote:
> > > > On Monday, 18 July 2022 at 12:29:57 UTC+2, bill....@ieee.org wrote:
> > > > > On Monday, July 18, 2022 at 8:10:23 PM UTC+10, a a wrote:
> > > > > > On Monday, 18 July 2022 at 04:12:12 UTC+2, Mike Monett wrote:
> > > > > > > whit3rd <whi...@gmail.com> wrote:
> > > > > > > > On Sunday, July 17, 2022 at 1:00:00 PM UTC-7, a a wrote:
>
> <snip>
> > just visit and find me a single thread or comment, having anything to do with science or research

you are stupid dog

and your comments exactly represent media standards by IEEE.org
since you use official email by IEEE.org

listen me once again
visit IEEE.org on Facebook
and find a single thread, comment having anything to do with science or research

https://www.facebook.com/IEEE.org/

I am really not interested in your delusiones and day dreaming

[Dimiter_Popoff]

Oh dear. if you are to be a troll at least learn how to post.
Finding me/my photos is about the easiest thing to find on the net,
at least learn how to do it. Better, instead of trolling invest
your time into learning how to do something useful.

======================================================
Dimiter Popoff, TGI http://www.tgi-sci.com
======================================================
http://www.flickr.com/photos/didi_tgi/

[Dave Platt]

In article <7cce474a-9b26-43bc...@googlegroups.com>,

whit3rd <whi...@gmail.com> wrote:
>On Saturday, July 16, 2022 at 5:38:44 PM UTC-7, Dave Platt wrote:
>
>> The trickiest part was handling high pulse rates, where one pulse
>> starts while the CSA is still recovering from the previous one.
>> At some point I may sit down and try writing some DSP code to
>> de-convolve the CSA's pulse shaping and turn the signal back
>> into narrow impulses.
>
>The analog-days solution was a delay line amplifier; the long recovery tail
>is exponential, so a difference amplification of V(t) - (1+epsilon)V(t-s)
>flattens the recovery when (1+epsilon) equals the diminution of the signal
>during 's' seconds. The infinite-impulse response or FIR filter is relatively easy
>work to do that.

Yes, that would be pretty easy to code.

Part of the complexity is that the signal chain in my setup is
AC-coupled, so the strong positive-going pulse and its
exponential-decay recovery are followed by a "sag" down into negative
voltages, which then recovers exponentially to zero. If a second
pulse hits before this recovery-to-DC is complete, the second
pulse's peak will be offset downwards and a naive measure of its
height will underestimate its energy.

https://www.radagast.org/~dplatt/gamma/pulses.png is a screen-shot from
my software's GUI when running in the "look at the signal" mode.

What I did in my pulse-detection software was to use a state-machine
approach, modeling the pulse in phases - waiting to trigger (blue),
rising (green), falling back to the DC baseline (yellow), falling down
below DC (orange), and then exponential recovery back upwards to
baseline (red). For the latter I have a model for how long it
_should_ take to recover back to DC (white), and I hold off further
triggers until the estimated recovery time is complete. If the
software sees a sudden rise in the signal during any of the
post-peak phases, it's interpreted as a second pulse "too soon"
and is discarded.

Another approach I've been musing about, would be to use correlation -
correlate the incoming pulse train with a known-good sample of the
system's impulse response. I could capture one good clean pulse (or a
few, and then average them) to create a reference... this would
accurately model the impulse response of the crystal/PMT/amplifier as
actually built. Then, simply run a multiply-and-add correlation to
the samples as they come in during a measuring run. This ought to
give me a nice, clean, fairly narrow (and close-to-symmetrical)
detection pulse for each incoming pulse from the amplifer. This would
give my state-machine pulse detector and input with the pulses
more cleanly separated.

The data rate is low enough and the pulses are short enough that it's
probably cheaper to do it through brute-force multiply-and-add, rather
than coding it as an FFT/multiply/iFFT.

>Some good info here:
><https://www.ortec-online.com/-/media/ametekortec/manuals/4/460-mnl.pdf>

Thanks!

[Dave Platt]

In article <XnsAED78EB5BE...@88.198.57.247>,

Mike Monett <spa...@not.com> wrote:

>A very lucid explanation. Thanks.

Quite welcome!

>I was able to find out what NORM is without having to ask you: "Naturally
>ocurring radioactive materials." I'm so proud of myself:)

:-)

The next step in the obsession is to find NORM sources for yourself.
Government and business buildings with granite facades are one
source.

>How big are your scintillator crystals?

Ugh... it's been years since I built the probes so I don't recall the
exact size. I think they're both about 1" in diameter and an inch or
two long.

I also experimented with using one or more small LYSO crystals, as are
used in PET scanners. They do work, but the lutetium is itself
slightly radioactive and there's a constant flux of pulses from gammas
generated within the crystal itself. Commercial PET scanners deal
with this by ignoring (filtering out) pulses of the specific height
corresponding to this gamma energy. That approach doesn't seem to
work as well (for me at least) for doing gamma spectroscopy of low-
level sources since the lutetium gammas still generate a broad
Comptom continuum which tends to obscure the features I'm looking for.

[Mike Monett]

dpl...@coop.radagast.org (Dave Platt) wrote:

> In article <XnsAED78EB5BE...@88.198.57.247>,
> Mike Monett <spa...@not.com> wrote:
>
>>A very lucid explanation. Thanks.
>
> Quite welcome!
>
>>I was able to find out what NORM is without having to ask you: "Naturally
>>ocurring radioactive materials." I'm so proud of myself:)
>
>:-)
>
> The next step in the obsession is to find NORM sources for yourself.
> Government and business buildings with granite facades are one
> source.
>
>>How big are your scintillator crystals?
>
> Ugh... it's been years since I built the probes so I don't recall the
> exact size. I think they're both about 1" in diameter and an inch or
> two long.

Wow! That's big. That's why your detectors are so sensitive.

I found some sources for crystals. The smaller ones are not too expensive:

1. https://www.gammaspectacular.com/blue/nai-tl-crystals

2. Saint-Gobain has a lot of papers as well as crystals:

https://www.crystals.saint-gobain.com/radiation-detection-
scintillators/crystal-scintillators/lanthanum-bromide-labr3

3. Hiler has more info on crystals. Quotes on request:

https://www.hilger-crystals.co.uk/guide-to-inorganic-scintillator-crystals/

4. More info:

https://www.mirion.com/learning-center/lab-experiments/gamma-ray-detection-
with-scintillators-lab-experiment

5. Berkeley has a wide variety of detectors:

https://www.berkeleynucleonics.com/scintillation-crystals-and-detectors

Wow! You could get really deep into this topic. And spend 11,780 bazillion
dollars.

Thanks,

Mike



--
MRM

[John Miles, KE5FX]

On Monday, June 27, 2022 at 4:42:33 AM UTC-7, Phil Hobbs wrote:
> If you're going to use an ionic scintillator in contact with an end-on
> PMT (one where the photocathode is deposited directly on the faceplate)
> you'll need to keep the cathode near ground to avoid ions migrating
> through the glass and corroding the PC. That means running the anode at
> high voltage and coupling the pulses out with a cap or transformer or
> something.

Phil, can you elaborate on this point? If the crystal and PMT are well-
insulated from their surroundings, which they are, what mechanism
would cause noticeable amounts of ion migration?

It's definitely more convenient to run these with negative HV than it would be
with positive HV, where you not only have to worry about DC blocking but
also ripple. The latter seems to be a big deal, going by the Theremino
docs and other sources.

-- john, KE5FX

[Anthony William Sloman]

A high voltage across a photomultiplier faceplate will do it.

At Cambridge Instruments, the photomultipliers we bought were selected to deliver the gain we needed with less than 1kV across the tube - which is to say across the glass faceplate.

A quartz - silicon-dioxide - face-plate might have been expected to be immune, but they needed an expensive graded seal to couple them onto the glass body of the photopmultiplier tube

Quite how 1kV got to be selected as the cut-off point was never revealed to me, but it was embedded in our purchasing specification.

The tubes themselves were mounted hard up against a glass window in the (grounded metal) specimen chamber, so that they could detect the flashes of light coming of the scintillator in the Everhart-Thornley secondary electron detection system.

Regular glass seems to contain enough metal ions for ionic migration to be a problem under kilo-volt potential differences.

--
Bill Sloman, Sydney

[John Miles, KE5FX]

On Tuesday, July 19, 2022 at 7:01:46 PM UTC-7, bill....@ieee.org wrote:
> A quartz - silicon-dioxide - face-plate might have been expected to be
> immune, but they needed an expensive graded seal to couple them

> onto the glass body of the photomultiplier tube

I see, so the issue is the potential difference between the photocathode
and the exterior metalwork. They seem to have thought of that, as the
tube's metal frame is tied to the cathode pin.

-- john, KE5FX

[Anthony William Sloman]

Some of it is. The anode isn't and none of the dynodes are, and every last one of them it is tied to a metal pin coming out of the base.

--
Bill Sloman, Sydney

[John Miles, KE5FX]

On Tuesday, July 19, 2022 at 11:02:22 PM UTC-7, bill....@ieee.org wrote:
> Some of it is. The anode isn't and none of the dynodes are, and every
> last one of them it is tied to a metal pin coming out of the base.

Right, I'm talking about the metal frame that would be the other electrode
in any ion-migration scenario involving the photocathode. You can see it
in the photo at http://www.ke5fx.com/tube.png where the seller sacrificed
one of the units for disassembly.

That metal frame is at the same potential as the photocathode, so
nothing is going to migrate across the faceplate.

-- john, KE5FX

[Phil Hobbs]

It's just ion migration through the glass envelope. I don't know if
folks have found a good solution to it, but BITD this was a serious
limitation.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

[Mike Monett]

Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

> John Miles, KE5FX wrote:
>> On Monday, June 27, 2022 at 4:42:33 AM UTC-7, Phil Hobbs wrote:
>>> If you're going to use an ionic scintillator in contact with an end-on
>>> PMT (one where the photocathode is deposited directly on the
>>> faceplate) you'll need to keep the cathode near ground to avoid ions
>>> migrating through the glass and corroding the PC. That means running
>>> the anode at high voltage and coupling the pulses out with a cap or
>>> transformer or something.
>>
>> Phil, can you elaborate on this point? If the crystal and PMT are
>> well- insulated from their surroundings, which they are, what mechanism
>> would cause noticeable amounts of ion migration?
>>
>> It's definitely more convenient to run these with negative HV than it
>> would be with positive HV, where you not only have to worry about DC
>> blocking but also ripple. The latter seems to be a big deal, going by
>> the Theremino docs and other sources.
>>
>> -- john, KE5FX
>>
>
> It's just ion migration through the glass envelope. I don't know if
> folks have found a good solution to it, but BITD this was a serious
> limitation.
>
> Cheers
>
> Phil Hobbs

RH Electronics doesn't seem worried:

https://www.rhelectronics.store/diy-pic18-mca-kit-for-gamma-spectroscopy

Here they show the output of the PMT and the pulse stretcher:

https://static.wixstatic.com/media/e43988
_a63520f4ed07436a843ddc1be0fda46a~mv2.jpg

Here they show the pulses from random gamma rays:

https://video.wixstatic.com/video/e43988_
8006efb319884c72b9d7f7418abdfa97/720p/mp4/file.mp4

I guess it may take years for ion migration to show up. It probably depends
on the type of glass, the thickness, the type of ion, any separating
material, and the applied voltage. 800 Volts is not much.

It should be easy to add a simple inverter and ground the cathode.

Hamamatsu shows several types of cathodes:

What is a photocathode?

A thin photosensitive film formed on the inner side (vacuum) of the light
input window. It converts light entering through the light input window
into photoelectrons.

- I didn't know that. Near infrared is 0.75 to 1.3 microns, so the file
doesn't have to be very thick.

Types of photocathode

Bialkali photocathode for visible light region

Multialkali photocathode with sensitivity extending to near infrared
region

Alkali-halide photocathode for UV light detection

GaAs, InGaAs (group III-V compound semiconductors) with sensitivity from
UV to near infrared region

https://www.hamamatsu.com/us/en/product/optical-sensors/pmt/about_pmts.html




--
MRM

[Mike Monett]

Mike Monett <spa...@not.com> wrote:

[...]

> It should be easy to add a simple inverter and ground the cathode.

Oops - it is already grounded.
--
MRM

[Mike Monett]

And the positive anode should eliminate any ion migration through the glass.

--
MRM

[John Walliker]

On Wednesday, 20 July 2022 at 15:11:13 UTC+1, Mike Monett wrote:
> Mike Monett <spa...@not.com> wrote:
>
> > Mike Monett <spa...@not.com> wrote:
> >
> > [...]
> >
> >> It should be easy to add a simple inverter and ground the cathode.
> >
> > Oops - it is already grounded.
> And the positive anode should eliminate any ion migration through the glass.
>
>

Well, there are both positive and negative ions in the crystal, so reversing the
polarity would just change the nature of what migrates.

John

[jla...@highlandsniptechnology.com]

Migration after 10 dynodes of gain is better than migration at the
photocathode where every electron literally counts.

[Phil Hobbs]

Yup. Grounded-cathode is the usual method with scintillators. You
couple the pulses out with a capacitor, so it's not that big a deal.

[Phil Hobbs]

Mike Monett wrote:
> Mike Monett <spa...@not.com> wrote:
>
>> Mike Monett <spa...@not.com> wrote:
>>
>> [...]
>>
>>> It should be easy to add a simple inverter and ground the cathode.
>>
>> Oops - it is already grounded.
>
> And the positive anode should eliminate any ion migration through the glass.
>

The anode isn't vulnerable to corrosion because it's not deposited on
the glass, and it's a nice beefy piece of metal, compared with the very
thin transparent photocathode.

[John Miles, KE5FX]

On Wednesday, July 20, 2022 at 12:51:46 PM UTC-7, Phil Hobbs wrote:
> Yup. Grounded-cathode is the usual method with scintillators. You
> couple the pulses out with a capacitor, so it's not that big a deal.

I seriously do not understand this. With a grounded cathode, the
signal you're extracting at the anode end is exposed to ripple from
the PMT supply, without benefit of a multi-megohm divider chain.
There's also the need to use a DC restorer of some sort to figure out
where the baseline is. Both of these problems go away with a
grounded anode. Seems like a no-brainer.

-- john, KE5FX

[whit3rd]

On Wednesday, July 20, 2022 at 5:55:04 PM UTC-7, John Miles, KE5FX wrote:
> On Wednesday, July 20, 2022 at 12:51:46 PM UTC-7, Phil Hobbs wrote:
> > Yup. Grounded-cathode is the usual method with scintillators. You
> > couple the pulses out with a capacitor, so it's not that big a deal.
> I seriously do not understand this. With a grounded cathode, the
> signal you're extracting at the anode end is exposed to ripple from

> the PMT supply...

Photomultipliers are current sources; the current gain is 'exposed to
ripple from the PMT supply', so that isn't a design feature from which to expect
any difference at all. If the pulses are short, filtering against the ripple (longer duration
than the pulses) might not be difficult. You'll be rejecting dark current either way.

I'd think transformer-coupling would be a natural way to capture pulses while rejecting lower
frequency ripple and DC. In my experience with PMTs we used good regulated DC power.

[Martin Brown]

On 21/07/2022 07:36, whit3rd wrote:
> On Wednesday, July 20, 2022 at 5:55:04 PM UTC-7, John Miles, KE5FX wrote:
>> On Wednesday, July 20, 2022 at 12:51:46 PM UTC-7, Phil Hobbs wrote:
>>> Yup. Grounded-cathode is the usual method with scintillators. You
>>> couple the pulses out with a capacitor, so it's not that big a deal.
>> I seriously do not understand this. With a grounded cathode, the
>> signal you're extracting at the anode end is exposed to ripple from
>> the PMT supply...
>
> Photomultipliers are current sources; the current gain is 'exposed to
> ripple from the PMT supply', so that isn't a design feature from which to expect
> any difference at all. If the pulses are short, filtering against the ripple (longer duration
> than the pulses) might not be difficult. You'll be rejecting dark current either way.

PMTs were mostly used in pulse counting mode for astronomy. Height of
the pulse doesn't matter provided that there is one (or not).

Image Photon Counting System, IPCS from Imperial College being the first
new generation microchannel plate based imaging device in the 1980's.

https://www.ing.iac.es/PR/wht_info/ipcs.html

For the time it was incredibly sensitive (when compared to film or
CCDs). CCDs improved very rapidly in the following decades.

>
> I'd think transformer-coupling would be a natural way to capture pulses while rejecting lower
> frequency ripple and DC. In my experience with PMTs we used good regulated DC power.

My own experience was mostly of ion counting mass spec systems rather
than photon counting. Deconstructed PMT in a hard vacuum and ion beams
rather than light. We had to do some elaborate ion optics to provide a
photon stop to prevent light from the plasma reaching the detector.

Hard vacuum requires stainless steel and no paint so an effective photon
stop is harder to make than it sounds.

ISTR that in pulse counting mode it needed dead time correction once the
count rate got high and that there was a cute way to run it in analogue
mode by dropping the supply voltage and monitoring the current.

In both cases the supply voltages were as stable as we could reasonably
make them (more so for the analogue mode). Cross calibrating the
analogue to pulse counting modes as a function of mass was quite bad for
the detector but essential if the results were to be meaningful.

https://en.wikipedia.org/wiki/Electron_multiplier

--
Regards,
Martin Brown

[Phil Hobbs]

Right, as far as that goes.

The photocathode is the high-Z end of the photomultiplier, and so most
naturally goes furthest from ground. In free-space applications, we run
the anode near ground and the photocathode at -1 to -2 kV, because the
PC end doesn't draw any cuarrent to speak of.

That makes it easy to get the (largish) anode current out into normal
low-voltage circuitry. (*)

The large scintillator crystal is out there where you can touch it, so
for safety reasons it's good if it's kept near ground.

It's important for sensitivity reasons that the scintillator crystal be
connected to the PMT faceplate through a continuous path with refractive
index at least as large as the glass of the PMT envelope.

The reason is that a major fraction of the light from the scintillator
is incident on its exit facet from angles beyond the critical angle for
CsI -> air.

I suspect that this is where the difficulty lies: If you have diffuse
light in a medium of refractive index n, and want to couple the light
efficiently into air, it turns out that your maximum efficiency is
1/n**2, even with an arbitrarily good AR coating, That's usually a problem.

Sooooo, to avoid losing signal, you want to avoid coupling light from
your scintillator into air.

The most straightforward way to avoid that is to optically-couple the
scintillator to the PMT faceplate, either by direct contact or using
some sort of index oil or gel. OK so far?
It's also good if your detector survives use, though. Putting the
scintillator at ground and the photocathode at -1 kV Photocathode
corrosion due to halide ions drifting through the glass faceplate has
been a real issue for a long time, and the saPower supply ripple is an
easily-soluble problem, especially since a scintillation event is very
bright in PMT terms--you aren't trying to do photon counting.

I've used cascades of PNP cap multipliers to do some pretty fun things
with PMTs, including getting (to me) impressive linearity for analogue
RF modulated detection.

Usually it's important for safety reasons that the metal housing for the
big ugly scintillator crystal is near ground.

Overall, for slowish counting applications, floating the PMT anode is a win.

Cheers

Phil Hobbs

(*) That approach is also a good match to the (IME badly overrated)
Cockroft_Walton scheme, where you run each dynode off a tap of a C-W
multiplier. The C-W approach naturally gives you vaguely equally-spaced
taps, and the high-Z end of the C_W matches the high-Z end of the PMT.
It's superficially neat, but has serious problems with linearity and
noise (especially at lower gain), not to mention the super ugly supply
ripple effects.

[Phil Hobbs]

You can use black chrome, though, no?

>
> ISTR that in pulse counting mode it needed dead time correction once the
> count rate got high and that there was a cute way to run it in analogue
> mode by dropping the supply voltage and monitoring the current.
>
> In both cases the supply voltages were as stable as we could reasonably
> make them (more so for the analogue mode). Cross calibrating the
> analogue to pulse counting modes as a function of mass was quite bad for
> the detector but essential if the results were to be meaningful.
>
> https://en.wikipedia.org/wiki/Electron_multiplier
>

Yup. The microchannel plate is basically a massively-parallel version
of the Channeltron electron multiplier.

I was looking at Photonis's MCP page the other day, and they were all
smug about nobody using curved or chevron-shaped channels anymore, just
their original version.

The reason for the curved channels, of course, was to force ions to hit
the walls instead of being accelerated directly at the photocathode,
damaging it and causing very very bright ion events.

[Phil Hobbs]

[fixed a few editing scars]

|doesn't work well, it turns out.

Photocathode corrosion due to halide ions drifting through the glass
faceplate has been a real issue for a long time, and

| I don't know whether improved faceplate materials have helped that much.

Power supply ripple is an easily-soluble problem, especially since a
scintillation event is very bright in PMT terms--you aren't trying to do
photon counting.

I've used cascades of PNP cap multipliers to do some pretty fun things
with PMTs, including getting (to me) impressive linearity for analogue
RF modulated detection.

Usually it's important for safety reasons that the metal housing for the
big ugly scintillator crystal is near ground.

Overall, for slowish counting applications, floating the PMT anode is a win.

Cheers

Phil Hobbs

(*) That approach is also a good match to the (IME badly overrated)
Cockroft_Walton scheme, where you run each dynode off a tap of a C-W
multiplier. The C-W approach naturally gives you vaguely equally-spaced
taps, and the high-Z end of the C_W matches the high-Z end of the PMT.
It's superficially neat, but has serious problems with linearity and
noise (especially at lower gain), not to mention the super ugly supply
ripple effects.

[Phil Hobbs]

Phil Hobbs wrote:
> John Miles, KE5FX wrote:

<snip long explanation>

I should add, of course, that having a huge E field inside the glass is
bound to reduce the photocathode quantum yield despite the shielding
effect of the PC itself.

Cheers

Phil Hobbs

[jla...@highlandsniptechnology.com]

There is the idea of an active capacitor for an RC lowpass filter,
nanely a modest-sized cap whose low end is intelligently driven by an
amp, so it looks like a much bigger cap on the top end.

[Phil Hobbs]

Yup. Back in the long ago (1984ish), I built a power supply filter that
got rid of 10 Vpp of 120 Hz ripple on a 2 kV supply for some piezo
stacks. It worked by lifting the cold end, sensing the hot end via a
100 nF, 3 kV film cap, and wiggling the cold end to keep it still. (It
had some TVS protection too, obviously.)

With an LF356 op amp, I got 100 dB of ripple rejection, which came in
pretty handy. I could probably have done considerably better with that
feedforward trick of Woodward's, where you use another op amp to measure
the error voltage of the main one, and add in its output.

Another approach like that is the Kanner Kap, which wasn't first
invented by Kanner, but he now owns it on account of the cute name.
That's the trick where you use an RC lowpass, and drive the cold end of
the cap with some super beefy amplifier to make the top stay still.

Cheers

Phil Hobbs

[Martin Brown]

On 21/07/2022 15:25, jla...@highlandsniptechnology.com wrote:

> We had the opposite problem: detecting the light from a plasma but
> blocking the ions that would darken our window. I wanted to do a thing
> with angled slats to bounce the light forward but that the ions would
> impact, but the semi company stuck with a plate with tiny holes, to
> let a little light and a few ions through.

Simplest solution to stop ions going in straight lines (but not
neutrals) is a local magnetic field and some drift length.

> Bad idea, but then they stole our detector circuit so I hope their
> windows all darken.

There is usually plenty of light (and heat) from a 8000K plasma (at
least one at 1 bar like ours). There is a pinhole sampling cone into it.

Protecting the instrument from coolant failure and the hard vacuum from
plasma flame out was a major part of the safety critical side of things.
It was worse in the early days when the vacuum pumps were diffusion. Any
sort of cock up and you had hot silicone oil all over the place.

--
Regards,
Martin Brown

[Phil Hobbs]

Yeah, I used to own a Denton 502 bell-jar evaporator that had an oil
diffusion pump. Getting that sucker cleaned up after a roughing-pump
incident was a huge pain.

[John Miles, KE5FX]

On Thursday, July 21, 2022 at 7:31:07 AM UTC-7, Phil Hobbs wrote:
> I should add, of course, that having a huge E field inside the glass is
> bound to reduce the photocathode quantum yield despite the shielding
> effect of the PC itself.

Yep, I think it's clear enough that allowing the faceplate to act as an
HV dielectric is a Bad Idea. But it also seems easier to avoid doing
that by tying the exterior frame to the cathode as the manufacturer has
done here, than to swap the polarity and deal with the HV at the
other end where the signal is extracted.

As far as the need to insulate the crystal is concerned, you'll need to
do that anyway to avoid exposing the user to thallium, I'd imagine. :-P

The question of whether it makes a difference in terms of ripple
is worth thinking through a little further. I see whit3rd's point, but
the effect of stray C seems worth considering before concluding that
the polarity doesn't make a difference.

-- john, KE5FX

[Mike Monett]

Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

> Mike Monett wrote:
>> Mike Monett <spa...@not.com> wrote:
>>
>>> Mike Monett <spa...@not.com> wrote:
>>>
>>> [...]
>>>
>>>> It should be easy to add a simple inverter and ground the cathode.
>>>
>>> Oops - it is already grounded.
>>
>> And the positive anode should eliminate any ion migration through the
>> glass.
>>
>
> The anode isn't vulnerable to corrosion because it's not deposited on
> the glass, and it's a nice beefy piece of metal, compared with the very
> thin transparent photocathode.
>
> Cheers
>
> Phil Hobbs

The anode pin goes through the glass. Metal ions are positively charged, so
they are repelled by the positive anode. This eliminates any metal ion
migration through the glass.




--
MRM

[Mike Monett]

The capacitor will have high voltage on it. This could destroy any electroncs
that inadvertently got connected badly.

You don't need to couple to the anode. Just take the signal off the cathode
like the old cathode followers of yesteryear.

--
MRM

[Phil Hobbs]

There's no signal at the cathode to speak of--almost all the anode
current comes in via the dynodes.

[whit3rd]

On Thursday, July 21, 2022 at 3:50:40 PM UTC-7, Mike Monett wrote:
> "John Miles, KE5FX" <jmi...@gmail.com> wrote:
>
> > On Wednesday, July 20, 2022 at 12:51:46 PM UTC-7, Phil Hobbs wrote:
> >> Yup. Grounded-cathode is the usual method with scintillators. You
> >> couple the pulses out with a capacitor, so it's not that big a deal.
> >
> > I seriously do not understand this. With a grounded cathode, the

> > signal you're extracting at the anode end is exposed to ripple...

> The capacitor will have high voltage on it. This could destroy any electroncs
> that inadvertently got connected badly.
>
> You don't need to couple to the anode. Just take the signal off the cathode
> like the old cathode followers of yesteryear.

A PMT cathode is typically a multialkali evaporated coating on the end of the tube, has
significant stray capacitance, and the signal there is weak (un-multiplied, no benefit
from the PMT gain).

[Mike Monett]

Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

[...]

> Yup. Back in the long ago (1984ish), I built a power supply filter that
> got rid of 10 Vpp of 120 Hz ripple on a 2 kV supply for some piezo
> stacks. It worked by lifting the cold end, sensing the hot end via a
> 100 nF, 3 kV film cap, and wiggling the cold end to keep it still. (It
> had some TVS protection too, obviously.)
>
> With an LF356 op amp, I got 100 dB of ripple rejection, which came in
> pretty handy. I could probably have done considerably better with that
> feedforward trick of Woodward's, where you use another op amp to measure
> the error voltage of the main one, and add in its output.
>
> Another approach like that is the Kanner Kap, which wasn't first
> invented by Kanner, but he now owns it on account of the cute name.
> That's the trick where you use an RC lowpass, and drive the cold end of
> the cap with some super beefy amplifier to make the top stay still.
>
> Cheers
>
> Phil Hobbs

The CCFL inverter I got from Amazon runs at 40KHz.

A simple half-wave rectifier running at 40 KHz with a 1nF cap and 9e6 Ohm
load will produce about 2V sawtooth ripple.

This is about 2/800 = 0.0025 * 100 = 0.25% ripple.

That should be good enough.





--
MRM

[Phil Hobbs]

Totally. You can probably use one of the HV caps that came with it to
couple the anode pulses to the outside world.

[Mike Monett]

That is a problem. The RH Electronics MCA expects positive pulses. These
won't come from the anode.

https://static.wixstatic.com/media/e43988_a63520f4ed07436a843ddc1be0fda46a~
mv2.jpg

https://video.wixstatic.com/video/e43988_8006efb319884c72b9d7f7418abdfa97/7
20p/mp4/file.mp4

I shall write them and ask where they get those positive pulses.



--
MRM

[Mike Monett]

Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

> Mike Monett wrote:
>> "John Miles, KE5FX" <jmi...@gmail.com> wrote:
>>
>>> On Wednesday, July 20, 2022 at 12:51:46 PM UTC-7, Phil Hobbs wrote:
>>>> Yup. Grounded-cathode is the usual method with scintillators. You
>>>> couple the pulses out with a capacitor, so it's not that big a deal.
>>>
>>> I seriously do not understand this. With a grounded cathode, the
>>> signal you're extracting at the anode end is exposed to ripple from
>>> the PMT supply, without benefit of a multi-megohm divider chain.
>>> There's also the need to use a DC restorer of some sort to figure out
>>> where the baseline is. Both of these problems go away with a
>>> grounded anode. Seems like a no-brainer.
>>>
>>> -- john, KE5FX
>>
>> The capacitor will have high voltage on it. This could destroy any
>> electroncs that inadvertently got connected badly.
>>
>> You don't need to couple to the anode. Just take the signal off the
>> cathode like the old cathode followers of yesteryear.
>>
>
> There's no signal at the cathode to speak of--almost all the anode
> current comes in via the dynodes.
>
> Cheers
>
> Phil Hobbs

Right. I got derailed by the positive pulses from the RH Electronics MCA.

Got to find out how they do that.



--
MRM