Gamma Spectrometry Forum

Hi Everyone

I have come across various situations in which a single photon gets absorbed by something and that thing then emits a large number of lower energy photons. Each of these lower energy photons might then get absorbed by something leading to the emission of a large number of even lower energy photons. I think that this can be described as a "photon cascade".

Do any of you know what is the lowest frequency of photons that can be produced by such a photon cascade? Or is there no lower limit?

Thank you very much.

Kind regards

Tim

Great question, I had to look up the answer to this one.

According to the Bohr model the formula is:

\[ E_n = - \frac{13.6eV}{n^2} \]

Meaning there is theoretically no lower limit for the energy of a photon.

This raises the question, why do we see energy peaks from scintillation crystals and not a continuous spectrum, and the answer must be that the crystal chooses the most efficient way to expel the energy and return to it's ground state.

Steven

Hi Steven

Thank you very much indeed for your very kind reply.

So, does this mean that there is no lower energy limit (other than obviously zero) that photons can cascade down to in the manner I described in my original post?

Thank you very much.

Kind regards

Tim

Tim,

Theory is one thing, reality is another, who knows what really goes on inside a solid ?

In order for the cascading effect you mentioned to take place, there would have to be an unlimited number of atoms with electrons at just the right levels to be absorbed and re-emitted. My guess FWIW, is that most solids that absorb a gamma will either re-emit it as a scattered gamma, a visible photon, or in the case of opaque materials it will just bounce around and eventually heat the material slightly, which then settles back to ground potential by the emission of infra red waves.

Hi Steven

Thank you very much indeed for your very informative reply.

Kind regards

Tim