X-ray fluorescence photons question

[GTrax]

TL;DR Summary

If electrons in elements are energized by an incoming gamma photon, what happens to excess energy? Can a very energetic photon affect more than one atom?

Tentatively, I ask in this forum for a qualitative pointer to what end effects one might expect when a gamma energy photon energizes an atom of a substance, and causes fluorescence. It relates to a practical endeavour about using a PIN diode as an X-ray detector, where the device considered happens to generate currents from X-ray photons having energies in a useful range from about 1.5keV to about 200keV.

This leads to a some questions. I use, as example, (say) molybdenum, for which I have data in a fragment from a table of X-ray emission energies.

1. Will an incoming (gamma) photon of energy a bit more than the total required to excite all the shell electrons always get to cause fluorescence at all the wavelengths corresponding? Is there some probability that only one or two might glow?

2. For an incoming photon of (say) enough energy to excite all the electrons twice over, what happens to the excess energy? Can it ever go on to excite electrons in another atom?

3. Is there any forced order in the probabilities of electrons shells accepting energy? For example, do the L-shell electrons get raised by their quanta first, such that a photon with insufficient energy to affect the K-shell candidates, will still get glows from L-shell probable action? Is it take-up in order of energy, lowest first?

4. Is there some probability that a 20keV photon might excite a single Kβ1 ray from molybdenum at 17.48keV, without any others happening?

5.. Are there probabilities that an incoming photon, of enough energy to do something, might fail to do anything at all?

6.. Once a photon has caused some electron excitations, is it then "used up"? Does the excess then simply raise the temperature of the atom?

Please forgive the very basic nature of these questions. I do understand they may be inappropriate in this forum, but they do also fall outside the range of most other electronics design groups.

 

[hutchphd]

You use Molybdenum for what exactly? Are you building an Xray source for your experiment?
A PIN diode is a PIN diode and xrays create an ionization trail which will cause current in a hard-biased photodiode. The rest of your question is nonsensical to me.

 

[GTrax]

You use Molybdenum for what exactly? Are you building an Xray source for your experiment?
A PIN diode is a PIN diode and xrays create an ionization trail which will cause current in a hard-biased photodiode. The rest of your question is nonsensical to me.

The few elements and their shell energies are only there for illustrative example, and a particular fluorescence for molybdenum is mentioned, but of course, there can be excitation of any elements where the incoming photon has energy higher than that required to raise the L-shell and/or K-shell electrons state by their quanta.

The X-rays emanate from the material that the incoming gamma strikes. It happens that a PIN diode can usefully detect the X-rays. For me, knowing what excitations might happen is important. The amplitude and duration of the photoelectric absorption current pulses from the 100mm^2 PIN diode area, detected against thermal and other background noise is what one is dealing with, and that I know how to do.

I am reasonably sure someone already knows what happens in the excitation of element atoms.

 

[hutchphd]

Do you have an reference for this technique (of using the secondary
emission)?
ALSO: I have used BPW34 PIN diodes for lots of designs and they are very sensitive to ambient electric fields (and light obviously). FYI

 

[GTrax]

It is late here (UK) right now, so references and links will have to wait. I will get back to it.
There are a number of (expensive!) hand-held tools which are used in industry (and by scrap metal merchants) to produce plots of X-Ray fluorescence peaks, along with substance identification signatures.
The more affordable project kits developed from modified Geiger counter projects. Many started out with using photomultiplier tubes with scintillation materials at the photocathode. I have one of these, apparently Russian surplus new old stock.

There are low-cost open source projects that use this technique, and there are much more affordable kits and gadgets. Finding small, safe, isotopes for the gamma source is not easy. Currently, I find the 59.5keV gamma pulse coming from Am241 in certain types of household smoke detectors works OK.

The technique is to use a very low noise, very high gain transconductance amplifier, and a low noise bias current, for a large area PIN diode, like the one for which I have posted a datasheet. One needs to capture a useful analogue of the current pulses that happen, measure their amplitude, and if possible, their duration. The collection of these makes a count vs energy spectrum plot characteristic of the elements present, and their relative proportions.

Sampling by modern ADC (analog-to-digital converter) then allows counts of pulses separated by amplitude threshold windows. The counts are stored as "buckets" of counts proportionally related to electron-volt energies that provoked the pulse in the first place.

The example photo-diode I mention can be had for about $65 as part of the "Pocket-Geiger" kit.
I will get back to you on this, though I am sure you can make search engines work just as well as I can.

Meantime, I was hoping to elicit some qualitative description of the quantum effect at the heart of all this.

 

[GTrax]

I will have one last try before abandoning the attempt to get a (sort of) qualitative understanding of the possible outcomes of an atom being exited into higher energy states by an incoming, sufficiently energetic photon, being more than enough to exceed all the outgoing characteristic X-ray energies.

Does the single incoming photon have ability to simultaneously excite more than one electron state ?
Could it raise the energy state of electrons in both K and L shells, such that, (say like in the example of molybdenum shown in the first posting), all four X-Rays would emanate at once?

I would guess that whether they do, or whether instead, they might deliver the X-ray responses one at a time, as the shells drop back to their normal state, it is likely the separate X-ray photons would each be in their own random direction.

The other questions seem obvious, but I do accept this may be stuff that nobody yet really knows.