Re: Mossbauer effect and retarded interactions

Eugene Stefanovich wrote:
> Igor Khavkine wrote:
> > Eugene Stefanovich wrote:
> >
> >>In the Mossbauer effect a radioactive nucleus in the crystal
> >>lattice emits a gamma quantum and the recoil is felt instantaneously
> >>by the entire crystal. Do you smell any controversy between this
> >>fact and the retarded propagation of interactions required by
> >>the special theory of relativity?
> >
> >
> > No, no controversy. Your assertion is incorrect. Disturbances in a
> > solid propagate with the speed of sound. For metals, the speed of sound
> > is on the order of km/s.
>
> Most often this is true, but not always. The Mossbauer effect is an
> exception, that's what makes it so delicious.
>
> In the Mossbauer effect, a radioactive nucleus in the crystal lattice
> emits a photon. Normally, such an emmission should be
> accompanied by recoil: the nucleus jerks back causing creation of the
> phonon (sound) wave propagating outside in all directions.
>
> That's not what happens in rare cases when the Mossbauer effect
> works. In these cases, the emitted photon gets coupled to the
> so-called "zero-phonon" vibrational mode of the crystal. This is
> simply the mode in which all atoms in the crystal move together
> in one direction. No lattice vibrations (phonons) are created.
> In these cases the recoil momentum is spread evenly (and
> instantaneously) between all atoms in the crystal lattice.

Again. Nothing is spread instantaneously. The recoil momentum could
be distributed among all the atoms very fast, but never
instantaneously. Sometimes "fast" can be approximated by "instantenous"
in a calculation. But don't forget that this is no more than an
approximation. Reasoning from false suppositions is dangerous and
wasteful. Better make sure your claim is actually correct before making
deductions from it. Do you have a reference?

> Moreover, there is no reduction of the photon's energy due to the
> recoil effect. The photon can be absorbed (in resonance) by
> similar nucleus in another crystal. The possibility of the resonance
> absorption is what makes the Mossbauer effect so valuable in
> experimental studies.

By conservation of energy, there must be and is a reduction in the
energy of the photon. However, since the recoil velocity of the crystal
is very small, the Doppler shift of the photon frequency is also very
small. It is small enough to fit within the natural line width of the
gamma ray emission/absorption frequency. That is why an emitted gamma
ray can be reabsorbed in the Mossbauer effect.

> I suggest to look at another property of the Mossbauer effect.
> Excitation of the zero-phonon mode means that the crystal
> behaves as an absolutely rigid body: the recoil momentum
> is transferred instantaneously to all parts of the crystal.
> This is expressly forbidden by the special relativity.
> This is exactly what RQD would predict.

Approximations must not be confused with facts. Deductions from false
suppositions are worthless.

Igor

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