Properties of Neutronium
David Adams
neutronium? For example, color, conductivity, density, stability vs. mass,
thermal characteristics, magnetic characteristics, whatever. Would 1 Kg
of it be stable at room temperature? If I had a wire of the stuff weighing
1Kg/m could I make some super magnet out of it. If I had an refrigerator
size piece of it in orbit around some planet, would I have to keep it in
a stasis field to keep wierd things from happening? Will the NRC come
after me if I make some in my garage? Will the NSA come after me for
posting this message?
David "watching out for tides" Adams
--
||||||| David Adams ||||||||||||||||||||||||||||||||||||||||||||||||||||
||||||| ve...@netcom.com ||||||||||||||||||||||||||||||||||||||||||||||||||||
David Adams
Would anyone like to take a crack at describing the physical properties of
neutronium? For example, color, conductivity, density, stability vs. mass,
thermal characteristics, magnetic characteristics, whatever. Would 1 Kg
of it be stable at room temperature? If I had a wire of the stuff weighing
1Kg/m could I make some super magnet out of it. If I had an refrigerator
size piece of it in orbit around some planet, would I have to keep it in
a stasis field to keep wierd things from happening? Will the NRC come
post this message?
Erik Max Francis
> Would anyone like to take a crack at describing the physical properties of
> neutronium? For example, color, conductivity, density, stability vs. mass,
> thermal characteristics, magnetic characteristics, whatever. Would 1 Kg
> of it be stable at room temperature? If I had a wire of the stuff weighing
> 1Kg/m could I make some super magnet out of it.
As I understand it, neutronium is only stable at substellar (~0.1
solar) masses. So little chunks of it would fly apart.
Erik Max Francis, &tSftDotIotE ...!uuwest!alcyone!max m...@alcyone.darkside.com
USMail: 1070 Oakmont Dr. #1 San Jose, CA 95117 ICBM: 37 20 N 121 53 W __
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"Omnia quia sunt, lumina sunt." (All things that are, are lights.) \__/
Thomas T. Cheng
: of it be stable at room temperature? If I had a wire of the stuff weighing
: 1Kg/m could I make some super magnet out of it. If I had an refrigerator
: size piece of it in orbit around some planet, would I have to keep it in
: a stasis field to keep wierd things from happening? Will the NRC come
--
Thomas T. Cheng Friendship is the only cement that
will ever hold the world together.
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GS@ d? -p+ c++++ l--() u e+ m+(*) s-/ n+ h+ f+ g+ w+ t+ r- y?
aqua...@uclink.berkeley.edu *** tomc...@soda.berkeley.edu
cs3...@po.berkeley.edu *** tomc...@ocf.berkeley.edu
ro...@straylight.hip.berkeley.edu
David DeLaney
>Would anyone like to take a crack at describing the physical properties of
>neutronium? For example, color, conductivity, density, stability vs. mass,
>thermal characteristics, magnetic characteristics, whatever. Would 1 Kg
>of it be stable at room temperature? If I had a wire of the stuff weighing
>1Kg/m could I make some super magnet out of it. If I had an refrigerator
>size piece of it in orbit around some planet, would I have to keep it in
>a stasis field to keep wierd things from happening? Will the NRC come
>after me if I make some in my garage? Will the NSA come after me for
>posting this message?
To the last: probably not. To the second-last - if you manage to make some in
your garage, you'll quite probably either lose it through the floor or get
real rich.
As Far As I Know, neutronium is *only* kept stable by the gravitational
forces of a neutron star-type mass, and decays quickly into ordinary
matter if you don't have enough of it in one place for its gravity to
make squishing the electron gas into the protons energetically favorable.
Para-, ferro-, and dia-magnetism are right out, as are conductivity and
superconductivity, because those all rely on electrons, which neutronium has
not got. Density (before it decayed): *very* dense. Tons/cubic inch-type
densities. Now there *may* (or may not) be a form of matter called "strange
matter" which *is* both stable and denser than neutronium, occurring when the
neutrons get squashed together enough to make a "quark fluid" - but nobody
knows if it exists, and experiments haven't shown it yet (let alone whether
it's actually stable or not).
>David "watching out for tides" Adams
Dave "reducing the Earth to a small silvery blob" DeLaney
--
\/ David DeLaney: d...@utkux.utcc.utk.edu; "It's ALIIIIVE!! MUAHAhaha!!" - Happy
Mad Scientists' Easter ... :-); Disclaimer: UTK? Agree with me? Yeah, right...;
Thinking about this disclaimer may cause brain seizure or physics. VRbeableDJK
http://enigma.phys.utk.edu/~dbd for the net.legends FAQ + miniFAQs, or anon-ftp
Keith Warren Rickert
>As Far As I Know, neutronium is *only* kept stable by the gravitational
>forces of a neutron star-type mass, and decays quickly into ordinary
>matter if you don't have enough of it in one place for its gravity to
>make squishing the electron gas into the protons energetically favorable.
>Para-, ferro-, and dia-magnetism are right out, as are conductivity and
>superconductivity, because those all rely on electrons, which neutronium has
>not got.
Neutrons do have a magnetic moment, and spin, even though they
don't have any charge. I dont know the size offhand, but would guess
that its in the par of the same magnetic moment as the proton, which
is if I remember about 10^3 times smaller than that for the electron.
I suspect that for a good sized chunk of neutronium, they
would tend to mostly cancel out, but I'm not really sure about that.
(i.e. thats only based on my very limited knowledge of what
nuclear spin values tend to be).
Keith
--
Keith Rickert |
ke...@imppig.caltech.edu | "death - the undiscovered country from
ric...@cco.caltech.edu | whose bourne no traveler returns"
| -Hamlet, Act III
Michael Moroney
> Would anyone like to take a crack at describing the physical properties of
> neutronium? For example, color, conductivity, density, stability vs. mass,
> thermal characteristics, magnetic characteristics, whatever.
Well, many of the properties of what could be called "neutronium" are
well-known. First of all, it's best described as a _gas_, but this isn't
really accurate. You see, free thermal neutrons (neutrons at normal
temperature) are made in nuclear reactors all the time. I say "not quite a
gas" because while it does have some properties of gases it has many unique
properties. Neutrons don't really interact with the electrons of atoms so they
penetrate matter, so you can't really "bottle" it, it can coexist inside normal
matter to some extent. The neutrons only really interact with a nucleus. Some
nuclei tend to reflect them (beryllium, carbon) so maybe you could build a
"leaky" bottle of the stuff. Other nuclei undergo nuclear reactions with
them and there's no "normal" equivalent to this with other matter.
It's certainly not a solid or liquid, since neutrons don't "stick" to each
other, their reactions with each other are like molecules of an ideal gas.
> Would 1 Kg of it be stable at room temperature?
Neutrons are radioactive with a half-life of about 12 minutes.
> If I had a wire of the stuff weighing
> 1Kg/m could I make some super magnet out of it.
It's not solid, but regardless, since there are no electrons it wouldn't
conduct electricity at all.
> If I had an refrigerator
> size piece of it in orbit around some planet, would I have to keep it in
> a stasis field to keep wierd things from happening?
The neutrons would all like to go on their merry way, just like the atoms in
a "refrigerator size piece" of helium would. See above about the "leaky
bottle".
> Will the NRC come
> after me if I make some in my garage?
Well generally the easiest way to make the stuff is fission uranium or
plutonium, which the NRC *really* frowns upon without the proper equipment
or license. But your biggest worry is bathing yourself in the stuff which
would kill you in more than a tiny dose.
I hear many of you screaming "what about neutron star stuff?" Well that is
held together with gravity and if you were to bring a sample of the stuff
back to earth it wouldn't be held together by gravity anymore (unless you
brought back a huge piece of the star) so the neutrons would fly apart as
before. But what a neutron star would "look like" etc. close-up is an
interesting question that I don't have an answer for. We do know they are
incredibly powerful magnets though.
-Mike
Erik Max Francis
> Para-, ferro-, and dia-magnetism are right out, as are conductivity and
> superconductivity, because those all rely on electrons, which neutronium has
> not got.
Though, as I understand, superfluidity _is_ possible in neutron star
cores, which is an analogous process to superconductivity.
Paul Moyland
>d...@martha.utcc.utk.edu (David DeLaney) writes:
>
>> Para-, ferro-, and dia-magnetism are right out, as are conductivity and
>> superconductivity, because those all rely on electrons, which neutronium has
>> not got.
>
>Though, as I understand, superfluidity _is_ possible in neutron star
>cores, which is an analogous process to superconductivity.
>
>
>Erik Max Francis
Since when does superconductivity depend on electrons? All you need is
something that forms bosons ( pairs of electrons for conventional
superconductors ) or is a boson ( like 4He ). The cores of the neutron
stars are calculated to have a density such that you get a superfluid,
which is the same thing as a superconductor ( flow without dissipation ).
paul moyland
Tom Stark
"Dragon's Egg" by Robert L. Forward. Bob Forward may not be the worlds best
writer but he is in the forefront of scientists thinking about gravitation and
unusual forms of matter. He has published many technical articles in various
places.
Tom Stark st...@lf.hp.com
Hewlett-Packard
Little Falls Site
Christopher Neufeld
Paul Moyland <moy...@uful07.phys.ufl.edu> wrote:
>In article <D2B9Jc...@alcyone.darkside.com> m...@alcyone.darkside.com (Erik Max Francis) writes:
>>d...@martha.utcc.utk.edu (David DeLaney) writes:
>>
>>> Para-, ferro-, and dia-magnetism are right out, as are conductivity and
>>> superconductivity, because those all rely on electrons, which neutronium has
>>> not got.
>>
>>Though, as I understand, superfluidity _is_ possible in neutron star
>>cores, which is an analogous process to superconductivity.
>>
>something that forms bosons ( pairs of electrons for conventional
>superconductors ) or is a boson ( like 4He ).
>
carry a net charge. Without that you have no superconductivity, though
you can still have condensation into a superfluid state.
However, as I seem so fond of pointing out, the substance deep inside
a neutron star contains a truly vast number of electrons, far more
electrons per unit volume than you find in any conventional metal. The
Fermi energy of electrons in the star is 1.19 MeV above the Fermi energy
of neutrons, so the Fermi surface of electrons in a neutron star is
actually relativistic! A heavy neutron star is about 11% protons by mass,
and each of those protons has to have an electron in the vicinity, or at
least in the neutron star, to prevent "bad things" happening.
I'm not qualified to guess as to whether there's a good pairing
mechanism for electrons inside a neutron star, yielding a true
superconductivity at ridiculously high temperatures.
>The cores of the neutron
>stars are calculated to have a density such that you get a superfluid,
>which is the same thing as a superconductor ( flow without dissipation ).
>
No, a superconductor requires flow of electric current, not just
macroscopic flow of particle species.
--
Christopher Neufeld....Just a graduate student neu...@physics.utoronto.ca
"Don't edit reality for | "The nerd projection operator recovers most of his
the sake of simplicity" | amplitude." Insult, probably self-referential.
| -rw-rw-rw- : the file permission of the beast
David DeLaney
>m...@alcyone.darkside.com (Erik Max Francis) writes:
>>d...@martha.utcc.utk.edu (David DeLaney) writes:
>>> Para-, ferro-, and dia-magnetism are right out, as are conductivity and
>>> superconductivity, because those all rely on electrons, which neutronium has
>>> not got.
>>Though, as I understand, superfluidity _is_ possible in neutron star
>>cores, which is an analogous process to superconductivity.
>
>something that forms bosons ( pairs of electrons for conventional
>superconductors ) or is a boson ( like 4He ). The cores of the neutron
>stars are calculated to have a density such that you get a superfluid,
>which is the same thing as a superconductor ( flow without dissipation ).
Paul, superconductivity relies on *charged* particles, which neutrons aren't.
They can form fermion pairs and simulate bosons, probably, but they're not
going to transport charge anywhere. Superfluidity means flow of *particles*
or *material* without resistance, which is entirely different.
Plus, I've received a couple emails reminding me that there's still electron
gas inside neutron stars - but remember that under neutron-star-forming
conditions, the combination of e- + p+ will "decay" into a neutron plus a
neutrino rather than the other way around, because of the tremendous
gravitational potential well; I'd think the electrons would be too busy
reacting to do much conduction, and note that you can also tell that the
electron gas goes away almost entirely because the star *collapses* - if it
were still there, it would still be holding the star's material up, but it
doesn't, so it isn't. Degenerate matter ("squashed" matter) has significant
amounts of electron gas - neutron stars don't, in comparison.
And finally, I find it interesting that so many people who wouldn't respond to
the original query wrote (here and in email) to correct my information... :-)
Dave "wall of science" DeLaney
--
David DeLaney: d...@utkux.utcc.utk.edu; WARNING: DO NOT PUT BEANS IN YOUR EARS!
Disclaimer: UTK agree with me? Yeah, right...; Thinking about this disclaimer__
may cause offense, brain seizure, confusion, or particle physics. VRbeableDJK\/
Paul Moyland
> No, a superconductor requires flow of electric current, not just
>macroscopic flow of particle species.
>--
> Christopher Neufeld....Just a graduate student neu...@physics.utoronto.ca
Perhaps in general people associate an electrical current with a
superconductor. In practice, people who work on these systems
make small distinction, if any, between a "superconductor" or
a "superfluid".
Ask somebody in condensed matter physics if there is a true p-wave
superconductor. Superfluid 3He is.
The basic physics in "superfluids" and "superconductors" is the
same.
paul moyland
john baez
>In article <2nqj5d...@no-names.nerdc.ufl.edu>,
>Paul Moyland <moy...@uful07.phys.ufl.edu> wrote:
>>In article <D2B9Jc...@alcyone.darkside.com> m...@alcyone.darkside.com (Erik Max Francis) writes:
>>>d...@martha.utcc.utk.edu (David DeLaney) writes:
>>>> Para-, ferro-, and dia-magnetism are right out, as are conductivity and
>>>> superconductivity, because those all rely on electrons, which
>>>>neutronium has not got.
>>>Though, as I understand, superfluidity _is_ possible in neutron star
>>>cores, which is an analogous process to superconductivity.
>>Since when does superconductivity depend on electrons? All you need is
>>something that forms bosons ( pairs of electrons for conventional
>>superconductors ) or is a boson ( like 4He ).
> No, superconductivity also requires that the bosonic quasi-particles
>carry a net charge. Without that you have no superconductivity, though
>you can still have condensation into a superfluid state.
I'm no expert on this but I recently asked about superfluidity and
superconductivity on sci.physics.research, and it appears that neutron
star cores are both superfluid and superconductive. As Neufeld noted,
there are plenty of protons and electrons in neutron star cores to serve
as charge carriers.
Even better, the angular momentum of the neutron star is carried by
quantized vortices, as usual for a superfluid, each of which has angular
momentum given by a multiple of Planck's constant, while the magnetic
fields are confined to quantized flux tubes, as usual for a type II
superconductor. These vortices should be imagined as long thin tubes
threading the core, packed in a roughly hexagonal array. For the Crab
Nebula pulsar, the spacing between the superfluid vortices can be
calculated as about ~ 10^{-2} cm, while for a magnetic field of 10^{12}
Gauss the spacing between the superconducting vortices is ~ 10^{-9} cm.
(Thanks to folks who sent me email on this.)
Peter Austin
ric...@cco.caltech.edu writes:
> Neutrons do have a magnetic moment, and spin, even though they
> don't have any charge. I dont know the size offhand, but would guess
> that its in the par of the same magnetic moment as the proton, which
> is if I remember about 10^3 times smaller than that for the electron.
> I suspect that for a good sized chunk of neutronium, they
> would tend to mostly cancel out, but I'm not really sure about that.
> (i.e. thats only based on my very limited knowledge of what
> nuclear spin values tend to be).
Where does the magnetic field of Pulsars come from then ?
I have read that pulsars (spinning neutron stars) have ferocious magnetic
fields (tens of millions of Tesla ?). The magnetic field confines
charged particle emmision to narrow beam, which rotate with the star
causing a lighthouse effect.
Does this imply that there must be some alignment of the individual
neutron magnetic moments, or is the field generated by the degenerate
matter on the neutron star surface.
Peter Austin
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Christopher Neufeld
Paul Moyland <moy...@uful07.phys.ufl.edu> wrote:
>
>> No, a superconductor requires flow of electric current, not just
>>macroscopic flow of particle species.
>
>superconductor. In practice, people who work on these systems
>make small distinction, if any, between a "superconductor" or
>a "superfluid".
>
less particular about the distinction, but experimentalists working on
superconductors (such as myself) treat them very differently, probably
primarily because the probes of the two materials are usually very
different. Studies such as ultrasonic attenuation, magnetic torque
anisotropy, ACAR, and so on are difficult or impossible to apply to a
non-conductive superfluid material, or any superfluid not intimately
embedded in a solid matrix such that perturbations in the matrix directly
affect the number density of bosonic quasiparticles in the system.
>The basic physics in "superfluids" and "superconductors" is the
>same.
>
I agree on this point. I do take issue with your suggestion that the
terms are equivalent and interchangeable. I have heard theorists talk
about the superconducting states as a charged superfluid, but I've never
heard them refer to superfluid helium as an uncharged superconductor.
Similarly, an experimentalist does not talk about his superfluid
solenoid, or complain about superconductor leaks into the vacuum space
below 2.174 K.
--
Christopher Neufeld....Just a graduate student neu...@physics.utoronto.ca
Benjamin J. Tilly
ba...@guitar.ucr.edu (john baez) writes:
> I'm no expert on this but I recently asked about superfluidity and
> superconductivity on sci.physics.research, and it appears that neutron
> star cores are both superfluid and superconductive. As Neufeld noted,
> there are plenty of protons and electrons in neutron star cores to serve
> as charge carriers.
>
> Even better, the angular momentum of the neutron star is carried by
> quantized vortices, as usual for a superfluid, each of which has angular
> momentum given by a multiple of Planck's constant, while the magnetic
> fields are confined to quantized flux tubes, as usual for a type II
> superconductor. These vortices should be imagined as long thin tubes
> threading the core, packed in a roughly hexagonal array. For the Crab
> Nebula pulsar, the spacing between the superfluid vortices can be
> calculated as about ~ 10^{-2} cm, while for a magnetic field of 10^{12}
> Gauss the spacing between the superconducting vortices is ~ 10^{-9} cm.
> (Thanks to folks who sent me email on this.)
>
So can a magnet hover above a neutron star? (You have all seen the
demonstration of a magnet above a superconductor.)
What if two neutron stars try to collide? (Both of them should have
magnetic fields.)
Ben Tilly
r...@ngc.com
In article <nlndjaE9...@world.std.com>, <mor...@world.std.com> writes:
> Neutrons don't really interact with the electrons of atoms so they
> penetrate matter, so you can't really "bottle" it, it can coexist inside
> normal matter to some extent. The neutrons only really interact with a
> nucleus. Some nuclei tend to reflect them (beryllium, carbon) so maybe you
> could build a "leaky" bottle of the stuff. Other nuclei undergo nuclear
> reactions with them and there's no "normal" equivalent to this with other
> matter.
Question: what you are saying is that neutrons can't be contained very well by
normal matter. OK, I bring a hand-ful :) of netronium to earth in some sort of
statis field, then release the field. Because I have less than 0.1 solar
masses, my sample flies apart. Now, where do they go? Normal matter can't
contain them, so do they fall down to the earth's center? What about nuclear
reactors? At some point, collisions with nuclei are going to slow down the
neutrons, and not all will fuse with normal matter. How many neutrons are
bouncing around at the center of our planet?
Or is a neutron unstable? What is the half-life before a neutron change into
something else? What would it change into (I had the imporession that a neutron
is at a lower energy state than an electron/proton pair)?
Rob.
Jeremy Whitlock
>
>Or is a neutron unstable? What is the half-life before a neutron change into
>something else? What would it change into (I had the imporession that a neutron
>is at a lower energy state than an electron/proton pair)?
The half-life is about 11 minutes, beta-decaying into a proton (Q=800 keV).
We in the nuclear reactor business like to use them before that happens...
--
Jeremy Whitlock e-mail: whit...@mcmaster.ca
Department of Engineering Physics phone: (905)-525-9140 ext.27140
McMaster University, 1280 Main West
Hamilton, Ontario, Canada, L8S 4L7 "My thoughts are mine, not Mac's"
Carl J Lydick
=In article <CnuLJ...@ngc.com> r...@ngc.com writes:
=>
=>Or is a neutron unstable? What is the half-life before a neutron change into
=>something else? What would it change into (I had the imporession that a neutron
=>is at a lower energy state than an electron/proton pair)?
=
=The half-life is about 11 minutes, beta-decaying into a proton (Q=800 keV).
That's for a free neutron. Neutrons in atomic nuclei are far more stable. I
don't know that the half-life of a neutron in a neutron star would be.
However, I suspect it's considerably longer than 11 minutes.
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: CA...@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL
Disclaimer: Hey, I understand VAXen and VMS. That's what I get paid for. My
understanding of astronomy is purely at the amateur level (or below). So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it. If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.
David DeLaney
><mor...@world.std.com> writes:
>Question: what you are saying is that neutrons can't be contained very well by
>normal matter. OK, I bring a hand-ful :) of netronium to earth in some sort of
>statis field, then release the field. Because I have less than 0.1 solar
>masses, my sample flies apart. Now, where do they go? Normal matter can't
>contain them, so do they fall down to the earth's center? What about nuclear
>reactors? At some point, collisions with nuclei are going to slow down the
>neutrons, and not all will fuse with normal matter. How many neutrons are
>bouncing around at the center of our planet?
They do literally "fly apart"; they also dribble down through the rock very
much like sand through water (considering the relative densities involved).
Neutrons, when not under terrible horrible gravitational pressure, enough to
change the energy levels involved (okay, okay, there's Fermi spheres involved
too; I'm never gonna be able to explain them in a short note), are unstable,
and decay to proton plus electron plus antineutrino (whoosh! there it went)
with a half life of eleven-plus minutes. *Also*, "slow" (thermal) neutrons
will tend to possibly get absorbed by various nuclei before they decay.
The pressure inside an actual neutron star "forces" the electrons back into
the protons; once you take that off, there's no bar to ordinary decay,
so they will. Thus there's no neutronium core at the core of the Earth...
>Or is a neutron unstable? What is the half-life before a neutron change into
>something else? What would it change into (I had the imporession that a neutron
>is at a lower energy state than an electron/proton pair)?
Only in special circumstances: when the outer layers of the Fermi surface
for the electrons and protons are far above the outer layers of the Fermi
surface of the neutrons (hmm, now that I think about it, this says there
*must* indeed be some protons & electrons still running around ... fooey).
In ordinary conditions, a neutron by itself is at a higher energy state
than a proton + electron, which is why it decays (neutrons in nuclei may
or may not follow this, due to binding energy).
Dave "okay, thermodynamics was years ago. Foo." DeLaney
Goran Olsson, Plasma Physics, KTH
>Only in special circumstances: when the outer layers of the Fermi surface
>for the electrons and protons are far above the outer layers of the Fermi
>surface of the neutrons (hmm, now that I think about it, this says there
>*must* indeed be some protons & electrons still running around ... fooey).
>In ordinary conditions, a neutron by itself is at a higher energy state
>than a proton + electron, which is why it decays (neutrons in nuclei may
>or may not follow this, due to binding energy).
>Dave "okay, thermodynamics was years ago. Foo." DeLaney
Under this thread I come to think of this: Why aren't there any isotopes
of element zero? Or to rephrase: Are nuclei consisting of two, three...
neutrons at all possible? If they are, I understand they must be unstable
to beta decay and possibly fission, with short half lives. Have there been
any attempts to create any? If they are impossible, then why is it so?
========================================================================
Goran Olsson, Plasma Physics, KTH, Stockholm, Sweden
Space Physics, Electronic Engineering
ols...@plasma.kth.se
========================================================================
Peter Ceresole
> r...@ngc.com writes:
> They do literally "fly apart"; they also dribble down through the rock very
> much like sand through water (considering the relative densities involved).
A fellow in nuclear research at Birmingham University (now out of my
reach) told me that they were working with very cold neutron 'gas'
which they could contain, and pour, and experiment with.
I didn't ask him of what they made the container, or how lossy it was.
What material would you use to contain very slow neutrons?
Peter Ceresole pe...@cara.demon.co.uk
Carl J Lydick
=In article <1994Apr7.0...@martha.utcc.utk.edu>, d...@martha.utcc.utk.edu (David DeLaney) writes:
=
=>Only in special circumstances: when the outer layers of the Fermi surface
=>for the electrons and protons are far above the outer layers of the Fermi
=>surface of the neutrons (hmm, now that I think about it, this says there
=>*must* indeed be some protons & electrons still running around ... fooey).
=>In ordinary conditions, a neutron by itself is at a higher energy state
=>than a proton + electron, which is why it decays (neutrons in nuclei may
=>or may not follow this, due to binding energy).
=
=>Dave "okay, thermodynamics was years ago. Foo." DeLaney
=
=Under this thread I come to think of this: Why aren't there any isotopes
=of element zero? Or to rephrase: Are nuclei consisting of two, three...
=neutrons at all possible?
No. The term "nucleus" implies that it's at the center of something. Now,
just how the hell is an uncharged agglomeration of neutrons supposed to keep
itself surrounded by electrons? So you can't have "nuclei" with an atomic
number of zero.
Goran Olsson, Plasma Physics, KTH
>In article <2o0d2t$n...@news.kth.se>, ols...@plasma.kth.se (Goran Olsson, Plasma Physics, KTH) writes:
>=Under this thread I come to think of this: Why aren't there any isotopes
>=of element zero? Or to rephrase: Are nuclei consisting of two, three...
>=neutrons at all possible?
>No. The term "nucleus" implies that it's at the center of something. Now,
>just how the hell is an uncharged agglomeration of neutrons supposed to keep
>itself surrounded by electrons? So you can't have "nuclei" with an atomic
>number of zero.
>--------------------------------------------------------------------------------
>Carl J Lydick | INTERnet: CA...@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL
I was using "nucleus" in the generalized sense that is often used. For
example, neutron star matter is sometimes referred to as "nuclear matter",
alpha particles are described as "helium nuclei" and so on. Seems to work
fine and causes no confusion although electron shells are absent.
Calling a single neutron "the nucleus of element 0" or "the atom of element 0"
is a natural extension, and is often seen in periodic tables of atoms
and nuclear tables. The rule that element n has n protons and n electrons
applies also for n=0.
Goran
Jeremy Whitlock
>In article <1994Apr6.1...@muss.cis.mcmaster.ca>, whit...@mcmail.cis.mcmaster.ca (Jeremy Whitlock) writes:
>=The half-life is about 11 minutes, beta-decaying into a proton (Q=800 keV).
>
>That's for a free neutron. Neutrons in atomic nuclei are far more stable. I
>don't know that the half-life of a neutron in a neutron star would be.
>However, I suspect it's considerably longer than 11 minutes.
I thought the question was about a bucket of neutrons being spilled.
Carl J Lydick
=In article <2nvd9v$m...@gap.cco.caltech.edu> ca...@SOL1.GPS.CALTECH.EDU writes:
=>In article <1994Apr6.1...@muss.cis.mcmaster.ca>, whit...@mcmail.cis.mcmaster.ca (Jeremy Whitlock) writes:
=>=The half-life is about 11 minutes, beta-decaying into a proton (Q=800 keV).
=>
=>That's for a free neutron. Neutrons in atomic nuclei are far more stable. I
=>don't know that the half-life of a neutron in a neutron star would be.
=>However, I suspect it's considerably longer than 11 minutes.
=
=I thought the question was about a bucket of neutrons being spilled.
Well, this thread started out with the title "properties of neutronium."
J. D. (Chip) Sample
ca...@SOL1.GPS.CALTECH.EDU (Carl J Lydick) writes:
> In article <2o0d2t$n...@news.kth.se>, ols...@plasma.kth.se (Goran Olsson, Plasma Physics, KTH) writes:
> =In article <1994Apr7.0...@martha.utcc.utk.edu>, d...@martha.utcc.utk.edu (David DeLaney) writes:
> =
> =>Only in special circumstances: when the outer layers of the Fermi surface
> =>for the electrons and protons are far above the outer layers of the Fermi
> =>surface of the neutrons (hmm, now that I think about it, this says there
> =>*must* indeed be some protons & electrons still running around ... fooey).
> =>In ordinary conditions, a neutron by itself is at a higher energy state
> =>than a proton + electron, which is why it decays (neutrons in nuclei may
> =>or may not follow this, due to binding energy).
> =
> =>Dave "okay, thermodynamics was years ago. Foo." DeLaney
> =
> =Under this thread I come to think of this: Why aren't there any isotopes
> =of element zero? Or to rephrase: Are nuclei consisting of two, three...
> =neutrons at all possible?
>
> No. The term "nucleus" implies that it's at the center of something. Now,
> just how the hell is an uncharged agglomeration of neutrons supposed to keep
> itself surrounded by electrons? So you can't have "nuclei" with an atomic
> number of zero.
Granted, but that doesn't answer the question, except
semantically. The question is: Can two or more neutrons
bind together, even if they only have an 11 minute
lifetime?
Further, I would describe an alpha particle as a helium
nucleus, even though it is not "at the center of anything".
J. D. (Chip) Sample
Sam...@Shire.AC.ArkNet.edu
Physics
Lyon College (was Arkansas College)
john baez
>Under this thread I come to think of this: Why aren't there any isotopes
>of element zero? Or to rephrase: Are nuclei consisting of two, three...
>neutrons at all possible? If they are, I understand they must be unstable
>to beta decay and possibly fission, with short half lives. Have there been
>any attempts to create any? If they are impossible, then why is it so?
They are not stable. The neutron has a lifetime of about 15 minutes.
The dineutron is not stable either. The reason the neutron isn't stable
is basically because it's heavier than the proton + electron +
antineutrino, so that because it can turn into them, it does. The
reason the dineutron is not stable is subtler... one needs to understand
binding energies better than I do to see why it's heavier than the
deuteron to the point of wanting to decay into it. Perhaps the Pauli
exclusion principle plays a role (the neutrons must have anti-aligned
spins if they are otherwise in the same state), but I think I've heard
that if the coupling constants of nature were somewhat different, the
dineutron would be stable and the universe would be very different.
To get stable agglomerations of neutrons you need to get lots of 'em ---
a neutron star! But even this isn't "pure" neutrons.
Okay: what would be the necessary adjustment in coupling constants to
make the dineutron stable, and what would be the consequences for US
citizens?
SCOTT I CHASE
>=
>=Under this thread I come to think of this: Why aren't there any isotopes
>=of element zero? Or to rephrase: Are nuclei consisting of two, three...
>=neutrons at all possible?
>
>No. The term "nucleus" implies that it's at the center of something. Now,
>just how the hell is an uncharged agglomeration of neutrons supposed to keep
>itself surrounded by electrons? So you can't have "nuclei" with an atomic
>number of zero.
OK, so they won't form atoms. But the nuclei themselves might still exist,
i.e., you could have hadronic bound states of only neutrons, but you don't.
The poster is asking why.
The answer, to first order, is simple - neutrons are fermions, and clusters
of neutrons must obey the Pauli exclusion principle. So, for example,
let's compare deuterium (one proton and one neutron), with a di-neutron.
Why is the latter unstable while the former is bound by 2.2 MeV?
The answer is that the strong interaction is spin-dependent. The deuteron
is a triplet, that is, it has spin one, so that the proton and neutron spins
are aligned. There is no corresponding bound state for singlet deuterium.
But a triplet di-neutron cannot exist, because it would require putting two
neutrons in an overall S state with parallel spins, in violation of the
exclusion principle.
-Scott
--------------------
Scott I. Chase "It is not a simple life to be a single cell,
SIC...@CSA2.LBL.GOV although I have no right to say so, having
been a single cell so long ago myself that I
have no memory at all of that stage of my
life." - Lewis Thomas
Lawrence R. Mead
: Rob.
Free neutrons have a half life of about 15 min. The decay scheme is:
N -> P + e + nubar, P = proton, e = electron, nubar = electron anti-
neutrino.
--
Lawrence R. Mead (lrm...@whale.st.usm.edu) | ESCHEW OBFUSCATION !
Associate Professor of Physics
Jim Carr
>of element zero? Or to rephrase: Are nuclei consisting of two, three...
>neutrons at all possible? If they are, I understand they must be unstable
>to beta decay and possibly fission, with short half lives. Have there been
>any attempts to create any? If they are impossible, then why is it so?
There is. At least, nuclear physicists include "n1" on the chart of
the nuclides and in the Nuclear Wallet Cards.
However, as you point out, there are no known stable systems of a few
neutrons. I am glad you raised this point, since it is an important
aspect of the physics issue raised in the original thread, but I never
got around to posting a comment to it.
As you know, the neutron is stable if it lives in a nucleus that,
because of the properties of the nucleon-nucleon interaction and
some interesting aspects of many-body physics, is more tightly
bound than the nucleus with one more proton and one less neutron.
Contrarywise, the proton will decay to a neutron if it lives in a
nucleus that is less bound than one with one more neutron and one
less proton. There are plenty of examples of each of these cases
in nature.
The really interesting question concerns the di-neutron or other
few-neutron systems. These have been looked for many times because
of the importance of such systems to an understanding of the nucleon-
nucleon interaction -- since the properties of the di-neutron tell us
about the n-n scattering length. It turns out that you can get a good
guess on this one from the deuteron, whose ground state is S=1, T=0
(isoscalar) and has no excited states. If the di-neutron was bound
by the strong force, then there would have to be a T=1 bound state of
the deuteron and the deuteron does not have any excited states. Notice
that I am referring to the strong force here, where unbound states
decay in 10^{-20} seconds or less -- anything that lives long enough
to beta decay is 'bound' as far as I am concerned.
It remains an open question whether a larger system, such as 4 neutrons,
is bound. I do not know, for example, whether the big _ab initio_
type calculations of Wiringa and friends have looked at this case in
addition to He-4 and O-16. What *is* interesting is that the di-neutron
is very close to being bound, and ends up being stable if in the
presence of a little extra nuclear mean field. The case of current
interest is the nucleus Li-11, which looks like a very loosely bound
cluster of Li-9 and n-2. (A nucleus with 3 protons and 8 neutrons
is as close as get to neutronium right now.)
--
J. A. Carr <j...@scri.fsu.edu> | "The New Frontier of which I
Florida State University B-186 | speak is not a set of promises
Supercomputer Computations Research Institute | -- it is a set of challenges."
Tallahassee, FL 32306-4052 | John F. Kennedy (15 July 60)
Karl Hahn
> Mime-Version: 1.0
> Date: Wed, 6 Apr 1994 17:08:27 GMT
> Lines: 24
>
>
> In article <nlndjaE9...@world.std.com>, <mor...@world.std.com> writes:
> > Neutrons don't really interact with the electrons of atoms so they
> > penetrate matter, so you can't really "bottle" it, it can coexist inside
> > normal matter to some extent. The neutrons only really interact with a
> > nucleus. Some nuclei tend to reflect them (beryllium, carbon) so maybe you
> > could build a "leaky" bottle of the stuff. Other nuclei undergo nuclear
> > reactions with them and there's no "normal" equivalent to this with other
> > matter.
>
> Question: what you are saying is that neutrons can't be contained very well by
> normal matter. OK, I bring a hand-ful :) of netronium to earth in some sort of
> statis field, then release the field. Because I have less than 0.1 solar
> masses, my sample flies apart. Now, where do they go? Normal matter can't
> contain them, so do they fall down to the earth's center? What about nuclear
> reactors? At some point, collisions with nuclei are going to slow down the
> neutrons, and not all will fuse with normal matter. How many neutrons are
> bouncing around at the center of our planet?
At room temperature, the neutrons will diffuse at about 600 meters per second.
They won't get very far though. Every nucleus has what is called a neutron
absorbtion cross section, which varies according to the type of nucleus.
The cross section is in the form of an area, and depicts how big a target
a nucleus is to the neutron. The cross section together with the density
of nuclei determines mean free path, which is the average distance a neutron
travels though a material before being absorbed. A quick calculation of
mean free path before absorbtion through water yields about 45 cm.
water is about 0.056 moles per cm^3 or about or about 3.4e22 molecules
per cubic meter (which means 7.8e22 hydrogen nuclei per cm^3). The cross
section of a hydrogen nucleus is 3.3e-25 cm^2. Take the reciprocal
of the product of these two numbers to get the mean free path in cm.
If lambda is the mean free path, then the probability of being absorbed
before traveling distance x is exp( -x/lambda ).
After just 10 meters, no appreciable number fraction of neutrons remain.
In air (nitrogen, cross section = 1.9e-22 cm^2), the mean free path is
much longer -- about 1e4 cm. So even in air, all but an tiny minority
are absorbed before even a kilometer.
>
> Or is a neutron unstable? What is the half-life before a neutron change into
> something else? What would it change into (I had the imporession that a neutron
> is at a lower energy state than an electron/proton pair)?
Free neutrons are unstable and decay into p + e- + antineutrino with a
halflife of about 13 minutes and energy of 0.78 Mev. A free neutron is,
contrary to your impression, 0.78 Mev higher energy than a electron/proton
pair. If it were lower, hydrogen atoms would necessarily decay into neutrons
by electron capture (a mechanism that is known for some unstable nuclides).
Cross sections and halflife obtained from Lange's Handbook of Chemistry,
10th edition, pages 127 and 128.
--
| (V) | "Tiger gotta hunt. Bird gotta fly.
| (^ (`> | Man gotta sit and wonder why, why, why.
| ((\\__/ ) | Tiger gotta sleep. Bird gotta land.
| (\\< ) der Nethahn | Man gotta tell himself he understand."
| \< ) |
| ( / | Kurt Vonnegut Jr.
| | |
| ^ |
Michael Moroney
> Under this thread I come to think of this: Why aren't there any isotopes
> of element zero? Or to rephrase: Are nuclei consisting of two, three...
> neutrons at all possible? If they are, I understand they must be unstable
> to beta decay and possibly fission, with short half lives. Have there been
> any attempts to create any? If they are impossible, then why is it so?
Read a good explanation once. A system of two bound nucleons is at a lower
energy state if the spin of the two particles is aligned than if they are
anti-aligned. If you look at the deuteron, it is a bound state of a proton
and a neutron. It is stable (barely). A deuteron with the spins anti-aligned
is a higher energy state, and is in fact a higher energy state than a proton
and a neutron, so such an excited deutron doesn't exist (it breaks apart as
soon as it's formed)
But when you have two of the _same_ particle, the state with the two spins
aligned is forbidden by the Pauli Exclusion Principle. The only allowed
state is the two particles with the spins anti-aligned, which is the higher
energy state. Again this is higher than the energy of the two particles
so such a thing as n2 breaks apart as soon as it forms (in an absurdly short
period of time) So there is no dineutron. For the same reason there is no
He-2 (two protons and no neutrons).
I don't know if higher states such as n3 are theoretically possible.
-Mike
Jon J Thaler
> Neutrons don't really interact with the electrons of atoms so they
> penetrate matter, so you can't really "bottle" it, it can coexist inside
> normal matter to some extent. The neutrons only really interact with a
> nucleus. Some nuclei tend to reflect them (beryllium, carbon) so maybe
> you could build a "leaky" bottle of the stuff. Other nuclei undergo
> nuclear reactions with them and there's no "normal" equivalent to this
> with other matter.
I recall that it *is* possible to "bottle" very slowly moving neutrons.
I don't remember the mechanism responsible, but I think it works well
enough to allow accurate measurement of the neutron lifetime (about
900 seconds).
Lawrence R. Mead
: In article <2o0d2t$n...@news.kth.se>
: >
: >Under this thread I come to think of this: Why aren't there any isotopes
: >of element zero? Or to rephrase: Are nuclei consisting of two, three...
: >neutrons at all possible? If they are, I understand they must be unstable
: >to beta decay and possibly fission, with short half lives. Have there been
: >any attempts to create any? If they are impossible, then why is it so?
: There is. At least, nuclear physicists include "n1" on the chart of
: the nuclides and in the Nuclear Wallet Cards.
: However, as you point out, there are no known stable systems of a few
: neutrons. I am glad you raised this point, since it is an important
: aspect of the physics issue raised in the original thread, but I never
: got around to posting a comment to it.
[some good discussion omitted]
: It remains an open question whether a larger system, such as 4 neutrons,
: is bound. I do not know, for example, whether the big _ab initio_
: type calculations of Wiringa and friends have looked at this case in
: addition to He-4 and O-16. What *is* interesting is that the di-neutron
: is very close to being bound, and ends up being stable if in the
: presence of a little extra nuclear mean field. The case of current
: interest is the nucleus Li-11, which looks like a very loosely bound
: cluster of Li-9 and n-2. (A nucleus with 3 protons and 8 neutrons
: is as close as get to neutronium right now.)
Jim, i suspect that even Wiringa's , or most many-body calculations are
as yet not capable of answering the few-neutron binding question. Even
complicated potentials such as the Reid or Paris potentials are only
approximate and ignore some relativistic corrections and effects of three
body forces. Correct me if I am wrong, but I still don't think that anyone
has gotten both the nuclear matter binding energy (per nucleon) *and*
the nucleon density right, even with "sophisticated" potentials. Thus,
I suspect (though I've been out of the field a few years) that nuclear
many-body theory still is not at the stage where it can answer the
delicate question of few neutron binding.
: --
: J. A. Carr <j...@scri.fsu.edu> | "The New Frontier of which I
: Florida State University B-186 | speak is not a set of promises
: Supercomputer Computations Research Institute | -- it is a set of challenges."
: Tallahassee, FL 32306-4052 | John F. Kennedy (15 July 60)
--
Stanley J. Sramek
[most of previous post deleted]
>Or is a neutron unstable? What is the half-life before a neutron change into
>something else? What would it change into (I had the impression that a neutron
>is at a lower energy state than an electron/proton pair)?
A free neutron decays quickly into a proton/electron/neutrino (the
neutrino is needed to conserve spin angular momentum). I don't remember
the half life anymore (I was in MIT class of '69) but I believe that it
is several minutes. That is, neither long nor short.
Energetically, all you have to do is look up the rest masses of neutron,
proton, and electron. The mass of the neutron is greater than the sum of
the proton and electron masses, so the neutron decay is energetically
allowed.
**************************************************************************
* Stanley J. Sramek I flame thee not, and flamed not would I be. *
* Physics Ph.D. You too I ask to hold this rule of gold: *
* Doggerel Poet "To others do as you would they to thee." *
* Houston, Texas, U.S.A. Thy kindness may return ten thousand fold! *
**************************************************************************
* My posted statements do not reflect the views of my employer. *
**************************************************************************
Stanley J. Sramek
>Jeremy Whitlock writes:
>>r...@ngc.com writes:
>>>Or is a neutron unstable? What is the half-life before a neutron change into
>That's for a free neutron. Neutrons in atomic nuclei are far more stable. I
>don't know that the half-life of a neutron in a neutron star would be.
>However, I suspect it's considerably longer than 11 minutes.
My comments now:
I am not a nuclear or particle physicist, but I suspect that neutrons in
most nuclei are -absolutely- stable. Otherwise, all nuclei would be
observably subject to beta decay. I suspect that neutrons in neutron stars
are -absolutely- stable also. Otherwise, every neutron star would be
spraying a shower of electrons and protons into the space around it.
Lech Borkowski
> I disagree, at least in the experimental side of things. Theorists are
>less particular about the distinction, but experimentalists working on
>superconductors (such as myself) treat them very differently, probably
>primarily because the probes of the two materials are usually very
>different. Studies such as ultrasonic attenuation, magnetic torque
>anisotropy, ACAR, and so on are difficult or impossible to apply to a
>non-conductive superfluid material, or any superfluid not intimately
>embedded in a solid matrix such that perturbations in the matrix directly
>affect the number density of bosonic quasiparticles in the system.
Think about superfluid 3He and an ordinary superconductor.
In both cases Cooper pairs are made of fermions.
This fact has more important consequences than the fact
electrons carry charge and 3He atoms do not.
My opinion, of course.
>>The basic physics in "superfluids" and "superconductors" is the
>>same.
> I agree on this point. I do take issue with your suggestion that the
>terms are equivalent and interchangeable. I have heard theorists talk
>about the superconducting states as a charged superfluid, but I've never
>heard them refer to superfluid helium as an uncharged superconductor.
nitpicking...
How about an order parameter?
>Similarly, an experimentalist does not talk about his superfluid
>solenoid, or complain about superconductor leaks into the vacuum space
>below 2.174 K.
more nitpicking... :-)
> Christopher Neufeld
Lech Borkowski
Mark P.
>> In article <2o0d2t$n...@news.kth.se>, ols...@plasma.kth.se (Goran Olsson, Plasma Physics, KTH) writes:
>> =
>> =Under this thread I come to think of this: Why aren't there any isotopes
>> =of element zero? Or to rephrase: Are nuclei consisting of two, three...
>> =neutrons at all possible?
>The question is: Can two or more neutrons
>bind together, even if they only have an 11 minute
>lifetime?
I strongly suspect not. Neutrons are fermions, and obey the Pauli exclusion
principle: no two can occupy the same quantum state. So neutron/neutron
pairs tend to be further separated then neutron/proton pairs, and thus
have a higher potential energy wrt the attractive strong nuclear force.
With higher potential energy _and_ higher rest mass, the neutrons are doomed
to decay to protons.
-------------------------------------------------------------------------
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Carl J Lydick
=Carl J Lydick writes:
=>Jeremy Whitlock writes:
=>>r...@ngc.com writes:
=>>>Or is a neutron unstable? What is the half-life before a neutron change into
=>>>something else? What would it change into (I had the impression that a neutron
=>>>is at a lower energy state than an electron/proton pair)?
=>>The half-life is about 11 minutes, beta-decaying into a proton (Q=800 keV).
=>That's for a free neutron. Neutrons in atomic nuclei are far more stable. I
=>don't know that the half-life of a neutron in a neutron star would be.
=>However, I suspect it's considerably longer than 11 minutes.
=
=My comments now:
=
=I am not a nuclear or particle physicist, but I suspect that neutrons in
=most nuclei are -absolutely- stable. Otherwise, all nuclei would be
=observably subject to beta decay. I suspect that neutrons in neutron stars
=are -absolutely- stable also. Otherwise, every neutron star would be
=spraying a shower of electrons and protons into the space around it.
That doesn't follow. Suppose a neutron in a neutron star decays. Unless
either the proton or the electron is ejected from the star at escape velocity
or higher, it falls back into the neutron star where the gravity once again
causes the proton and electron to combine into a neutron. Of course, the
particles, as they were accelereated, emitted radiation, so the total energy of
the star would decrease. And, yes, it's been too long since I dealt with QM
for me to know whether the above argument is valid or not.
SCOTT I CHASE
>
>I am not a nuclear or particle physicist, but I suspect that neutrons in
>most nuclei are -absolutely- stable. Otherwise, all nuclei would be
>observably subject to beta decay. I suspect that neutrons in neutron stars
Actually, most nuclei are not absolutely stable. There are more than 6000
hypothetical isotopes (of which most have never yet been seen in the laboratory)
the vast majority of which, though bound, are not absolutely stable. Even
of the many hundreds (perhaps 1200 or so?) which we do know and have studied,
most are unstable. Many of these decay by beta decay. with timescales from
tiny fractions of a second up to many years.
-Scott
--------------------
Scott I. Chase Mutationem motas proportionalem
SIC...@CSA2.LBL.GOV esse vi motrici impressae.
Jim Carr
>
>most nuclei are -absolutely- stable. Otherwise, all nuclei would be
>observably subject to beta decay.
You may not be a specialist in the field, but there is no substitute
for common sense and some knowledge of basic facts in physics.
The neutron in some (there are many more nuclei known away from the
valley of stability than there are stable ones) nuclei are absolutely
stable, just as the protons in some nuclei are unstable.
Great Cthulhu
>Actually, most nuclei are not absolutely stable. There are more than 6000
>hypothetical isotopes (of which most have never yet been seen in the laboratory)
>the vast majority of which, though bound, are not absolutely stable. Even
>of the many hundreds (perhaps 1200 or so?) which we do know and have studied,
>most are unstable. Many of these decay by beta decay. with timescales from
>tiny fractions of a second up to many years.
Well, that depends on how you look at it, now, doesn't it? Sure, if you pick
a random nucleus from your chart of known nuclei, chances are it won't be
stable. On the other hand, if you pick a random nucleus out of the universe,
chances are it WILL be stable. I'd like to think that at least a majority of
the nuclei making up this console won't radioactively decay leaving me with no
net connection. B^)
--
-Doug Gibson d...@wiffin.chem.ucla.edu
"I didn't like the way he was bleeding, so I made him stop."
-from Mutant League Football
GS d-(+) p-@ c++ !l u++ e+++ m+(-) s+/+ n- h---(*) f+ !g w+ t+ r++ y+
SCOTT I CHASE
>
>Well, that depends on how you look at it, now, doesn't it? Sure, if you pick
>a random nucleus from your chart of known nuclei, chances are it won't be
>stable. On the other hand, if you pick a random nucleus out of the universe,
>chances are it WILL be stable. I'd like to think that at least a majority of
>the nuclei making up this console won't radioactively decay leaving me with no
>net connection. B^)
Most nuclei in the Universe are hydrogen nuclei, i.e., lone protons. We
actually do not know whether protons are absolutely stable. Many extensions
of the Standard Model of particle physics suggest that they should be
unstable with very long lifetimes (10^30 or more years). But we have
never been able to do more experimentally than set a lower limit to this
lifetime. People are still looking.
Incidentally, if the lifetime of the Universe from Big Bang to heat death
(or the Big Crunch) is on the order of 100 billion years, then if protons
are unstable with a half-life of 10^30 years, it follows that the entire
lifetime of the Universe is only 10^-19 of one half-life. So the
ultimate stability of nuclei is not going to affect your connection to the
Net, even if it should survive until The End.
-Scott
-------------------- i hate you, you hate me
Scott I. Chase let's all go and kill barney
SIC...@CSA2.LBL.GOV and a shot rang out and barney hit the floor,
no more purple dinosaur.
Jim Carr
lrm...@whale.st.usm.edu (Lawrence R. Mead) writes:
>
>Jim, i suspect that even Wiringa's , or most many-body calculations are
>as yet not capable of answering the few-neutron binding question. Even
>complicated potentials such as the Reid or Paris potentials are only
>approximate and ignore some relativistic corrections and effects of three
>body forces.
They use the Urbana V-something-or-other potential which includes a
3-body force. This is tuned to get the mass-3 systems correct and
the saturation & binding for nuclear matter, although I think there
is dispute about its compressibility and how much d-state they get
in the deuteron. They do pretty well on He-4 and mass 6, and I think
the latest work had O-16 bound against alpha decay in a self-consistent
calculation but there was some truncation involved.
Close enough to ask what they might say about n-4, for example. I
do not think they can do Li-11 with its deformation, but not sure
on that. Tricky business.
--
James A. Carr <j...@scri.fsu.edu> | "It's never confusing though,
http://www.scri.fsu.edu | because ultimately it all fits
Supercomputer Computations Res. Inst. | -- its just cockeyed and fits
Florida State, Tallahassee FL 32306 | and is fire." - Norman Maclean
Jim Carr
>
I really like the concept of anonymous postings here. Sort of like
the double-blind refereeing system available at the Physical Review.
>I strongly suspect not. Neutrons are fermions, and obey the Pauli exclusion
>principle: no two can occupy the same quantum state. So neutron/neutron
>pairs tend to be further separated then neutron/proton pairs, and thus
>have a higher potential energy wrt the attractive strong nuclear force.
This is not quite accurate. The n-n system and the n-p system do have
the same separation when they are in the *same quantum state*. That is,
one expects that the S=0, T=1 states of H-2 and n-2 are the same, although
the coulomb effects in He-2 (p-p) do force the protons further apart.
The difference is that the Pauli principle forbids an S=1, T=1 state
for a lowest (hence spherically symmetric, L=0) level of that type,
and n-n must be T=1. The nucleon-nucleon force is just attractive
enough in the S=1, T=0 channel to bind p-n into the deuteron. Note
that it is convenient here to use isospin even though the symmetry
is broken; it is really shorthand for the two different n-p states
one can build: symmetric (T=1) under exchange of the n and p and
anti-symmetric (T=0) under exchange.
To answer John Baez's question succinctly, I will just say that the
phenomenology says that the triplet scattering length is positive,
hence bound states are possible in that S=1 arrangement. Thus the
triplet-even (S=1,T=0,L=0) is attractive. The singlet scattering
length is large and negative. This means the singlet-even (S=0,T=1,
L=0) is attractive but not enough to bind -- as the attraction
increases, the scattering length goes to negative infinity and then
becomes positive. (See Preston and Bhaduri, pg 38, Fig. 2-5 for a
graph of this.) Reverse the situation and the deuteron is bound
with S=0 and the n-2 would also be bound. It would not take a
large change. John, if you want to mess with numbers, this is a
normal grad-nuclear homework problem if done with a square well.
It is the spin-dependent parts of the NN interaction that are
responsible for the small extra attraction that binds the deuteron,
as someone else pointed out. Without the deuteron, solar fusion
reactions would be in big trouble.
Lawrence R. Mead
: In article <2o3ph1$d...@server.st.usm.edu>
Thanks for the info. Of course nuclear many-body theory had to develop
further than i knew it. Can you give me a reference to the Urbana ...
potential?
Josh J Fielek
|> In article <1994Apr8.1...@texhrc.uucp>
|> gpc...@sjstat.NoSubdomain.NoDomain (Stanley J. Sramek) writes:
|> >
|> >I am not a nuclear or particle physicist, but I suspect that neutrons in
|> >most nuclei are -absolutely- stable. Otherwise, all nuclei would be
|> >observably subject to beta decay.
|>
|> You may not be a specialist in the field, but there is no substitute
|> for common sense and some knowledge of basic facts in physics.
|>
|> The neutron in some (there are many more nuclei known away from the
|> valley of stability than there are stable ones) nuclei are absolutely
|> stable, just as the protons in some nuclei are unstable.
Um. shouldn't that be "observably stable", or "observably unstable". For all we
know, the "stable" nuclei could have something like a 10.4 billion year half
life.
--
_______________________________________________________________________________
Joshua J. Fielek DoD#385 AMA#517381 WERA#969
Inter-National Research Institute 1986 VF1000R 1984 XL250R
j...@speedy.inri.com 1982 CM450E 1975 RD350
"Whip it. Whip it Good." - Devo 1988 EX500 198X Aero 80
Michael Moroney
> |> The neutron in some (there are many more nuclei known away from the
> |> valley of stability than there are stable ones) nuclei are absolutely
> |> stable, just as the protons in some nuclei are unstable.
>
> Um. shouldn't that be "observably stable", or "observably unstable". For all we
> know, the "stable" nuclei could have something like a 10.4 billion year half
> life.
It would have to be longer than that. Thorium has been known to be radioactive
for a long time and it has a half-life of something like 14 billion years.
A few nuclei are known to have a half-life of something like 10^15 years
(including one or two isotopes of platinum)
Also, some nuclei either must be absolutely stable or can only be radioactive
by some mode never seen before. For them to decay by a known mode they'd
have to absorb energy or violate the conservation of energy. Consider
iron-56. It has the largest mass defect per nucleon of any nucleus. For it to
decay to *any* other nucleus it would have to violate the conservation of
mass-energy, or decay by an unknown mode such as a proton -> e+ + neutrino +
energy.
-Mike
Casimiro de A. Barreto (kofuji)
Workshop: Introduction to UNICHEM
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