On 03.11.2012 23:51, Poutnik wrote:
> Pentcho Valev from
pva...@yahoo.com posted Sat, 3 Nov 2012 12:36:09 -0700
> (PDT)
>>
>> Clever Andersen,
>>
>> Pound and Rebka measured the gravitational redshift by measuring the
>> frequency, not the wavelength.
>
> Exactly said, they did not measure either wavelength either frequency.
What was (indirectly) measured was the energy and momentum
of gamma photons. Since the energy is given by the frequency,
and the momentum is given by the wavelength, you could say that
both were measured.
>
> The former can be done AFAIK only by Xray difraction
> on crystals, as la 88.5 pm is comparable to hydrogen atom,
> but I doubt about accuracy.
>
> The latter is very high, 14 keV is equivalent 3.38e18 Hz,
> that is very diffictult to measure, expecially precisely.
>
>
> They determined needed relative move of the acoustic device
> with gamma emittor to compensate gravitational redshift
> by contraacting relastivistic doppler shift.
>
> At given phase of ocilation the effects nullified each other
> and the same kind of atoms could absorb that radiation.
The Mossbauer effect was used.
This effect is basically that when an atom in a crystal
lattice emits/absorbs a photon, you get close to 'recoil free'
emission/absorption because the whole crystal is recoiled,
and not only a single atom. The effect is that the energy/momentum
of the photon is very precisely defined because (almost) nothing
is lost in the recoil.
In the Pound and Rebka experiment:
The source is a Co57 crystal. This is a radioactive Cobol
isotope, and decays to Fe57 (an iron isotope) with
an electron in exited state. When this electron falls
to ground state, a 14.4 keV gamma photon with a very precise
energy/momentum is emitted.
The absorber is a Fe57 crystal. The gamma photons will
pass through this absorber, to a detector/counter.
The absorber will absorb gamma photons only if the energy
is exactly right (equal to the one emitted). So when the
energy is exactly right, the counter will count a minimum.
The oscillation you are talking about was that (a bit simplified)
the source was moving rapidly (oscillating) up and down,
and absorption (minimum count) was observed when the phase of
the oscillation was so that the Doppler effect was just right
to compensate for the gravitational shift.
In other words, the speed the source must have to maximize
absorption was measured.
>> Can you PROVE that the method used in measuring the quasar 3C273's
>> redshift was wavelength-sensitive but frequency-insensitive?
>
> Can you show us wave measurement ( wave of the same kind )
> that is wavelength-sensitive but frequency-insensitive ?
Sure.
A diffraction grating spectroscope measure wavelength only.
That's the kind of instrument that is used to measure
the spectra of astronomical objects from IR to UV.
--
Paul
http://www.gethome.no/paulba/