Can photovoltaic cells capture gamma photons?

[logannc]

I am by no means well versed in nuclear power, but from my limited exposure I have gathered that a very large portion of nuclear energy (and antimatter) is expressed in high energy gamma radiation. All forms of electromagnetic radiation are expressed as photons, correct?

Taking the concept of photovoltaic cells, which capture photons in the visible spectrum, can that not be applied to high energy gamma photons to capture some of that energy?

I would imagine that significant damage would occur to the cells from the ionizing radiation. But from what i gather from the source of all accurate* knowledge (wikipedia), even non-photoelectric effect interactions would produce smaller (less energetic photons) that through enough iterations would be low enough in energy to be absorbed through the cells.

Granted I know nothing of the engineering of such photovoltaic cells, but the concept itself seems to lend itself rather well.

Would this be feasible in anyway whatsoever?

 

[Drakkith]

One of the problems is that while visible light will easily be asborbed in a thin layer on a solar cell, gamma radiation will easily penetrate large layers of shielding.

 

[logannc]

I am aware. However I would think that if it were possible to absorb a significant amount given a thick enough cell then the energy absorbed might be worth the costs of making such a thick photoelectric cell.

Again, I don't know if it is feasible, I was more or less just asking whether it is a possibility.

 

[Drakkith]

Maybe, but I don't think a photovoltaic cell would even work for gamma radiation. Not sure though.

 

[logannc]

perhaps not at first because they are too high energy, but after multiple matter reactions it might have split enough to become several photons of a low enough energy so that they can be absorbed by the photoelectric effect when hitting a cell.

Really, it would initially seem that the hardest part would be making something that could capture photons of that wavelength and something thick enough to capture them once they have lost enough energy and then convert it usefully.

EDIT:
after the latter two matter interactions it can be absorbed through the photoelectric effect theoretically.
from wikipedia:

Photoelectric effect: This describes the case in which a gamma photon interacts with and transfers its energy to an atomic electron, ejecting that electron from the atom. The kinetic energy of the resulting photoelectron is equal to the energy of the incident gamma photon minus the binding energy of the electron. The photoelectric effect is the dominant energy transfer mechanism for X-ray and gamma ray photons with energies below 50 keV (thousand electron volts), but it is much less important at higher energies.

Compton scattering: This is an interaction in which an incident gamma photon loses enough energy to an atomic electron to cause its ejection, with the remainder of the original photon's energy being emitted as a new, lower energy gamma photon with an emission direction different from that of the incident gamma photon. The probability of Compton scatter decreases with increasing photon energy. Compton scattering is thought to be the principal absorption mechanism for gamma rays in the intermediate energy range 100 keV to 10 MeV. Compton scattering is relatively independent of the atomic number of the absorbing material, which is why very dense metals like lead are only modestly better shields, on a per weight basis, than are less dense materials.

Pair production: This becomes possible with gamma energies exceeding 1.02 MeV, and becomes important as an absorption mechanism at energies over about 5 MeV (see illustration at right, for lead). By interaction with the electric field of a nucleus, the energy of the incident photon is converted into the mass of an electron-positron pair. Any gamma energy in excess of the equivalent rest mass of the two particles (1.02 MeV) appears as the kinetic energy of the pair and the recoil nucleus. At the end of the positron's range, it combines with a free electron. The entire mass of these two particles is then converted into two gamma photons of at least 0.51 MeV energy each (or higher according to the kinetic energy of the annihilated particles).

 

[Hepth]

But its also a question of how much the sun emits of what frequency, and it falls of pretty fast :
http://www.vicphysics.org/documents/events/stav2005/spectrum.JPG

So it's not worth going after those high energy photons as there are so few of them, at least from the sun.

Now if you make a photovoltaic material that is dense enough to stop high energy radiation with only a few feet thick of material, and to capture its energy at least to some decent efficiency, then I'd say use them to build reactor shells. Though I'm not sure its even worth going after.

 

[logannc]

Now if you make a photovoltaic material that is dense enough to stop high energy radiation with only a few feet thick of material, and to capture its energy at least to some decent efficiency, then I'd say use them to build reactor shells. Though I'm not sure its even worth going after.

It was the reactor shell idea that I was going for. If there were appreciable amounts of gamma radiation hitting us from the sun, I'm pretty sure we'd be dead.

I recall seeing a number as to how much energy is emitted as gamma radiation that we just can't use. I recall it being rather high as well. If we can even capture a decent fraction of that extra energy it would increase the overall efficiency of the reactor while getting rid of some of the potentially harmful radiation.

I don't know if its worth going after either. I had hoped someone on here could give insight into that. I think that it would be worthwhile though, because unless the cells degrade relatively fast or they are simply insanely expensive, I believe the extra electricity generated could cover the costs over time

 

[QuantumPion]

It was the reactor shell idea that I was going for. If there were appreciable amounts of gamma radiation hitting us from the sun, I'm pretty sure we'd be dead.

I recall seeing a number as to how much energy is emitted as gamma radiation that we just can't use. I recall it being rather high as well. If we can even capture a decent fraction of that extra energy it would increase the overall efficiency of the reactor while getting rid of some of the potentially harmful radiation.

I don't know if its worth going after either. I had hoped someone on here could give insight into that. I think that it would be worthwhile though, because unless the cells degrade relatively fast or they are simply insanely expensive, I believe the extra electricity generated could cover the costs over time

You may be confusing gammas with neutrinos. Energy lost by neutrinos accounts for about 5% of the reactor's fission energy and cannot be recovered. Energy released by gammas however IS recovered, in the form of heat.

 

[ZapperZ]

I am aware. However I would think that if it were possible to absorb a significant amount given a thick enough cell then the energy absorbed might be worth the costs of making such a thick photoelectric cell.

No. At some point, if the penetration depth is too deep, it will be longer than the electron escape depth. This means that even if you create electrons that have enough energy to escape, it is created too deep into the material that it loses energy first before it can migrate to the surface.

This is why we have no photodetector for gamma photos, and why such photovoltaic cell doesn't quite work.

Zz.

 

[Dogs2120]

Gamma vs photovoltaic

I am by no means well versed in nuclear power, but from my limited exposure I have gathered that a very large portion of nuclear energy (and antimatter) is expressed in high energy gamma radiation. All forms of electromagnetic radiation are expressed as photons, correct?

Taking the concept of photovoltaic cells, which capture photons in the visible spectrum, can that not be applied to high energy gamma photons to capture some of that energy?

I would imagine that significant damage would occur to the cells from the ionizing radiation. But from what i gather from the source of all accurate* knowledge (wikipedia), even non-photoelectric effect interactions would produce smaller (less energetic photons) that through enough iterations would be low enough in energy to be absorbed through the cells.

Granted I know nothing of the engineering of such photovoltaic cells, but the concept itself seems to lend itself rather well.

Would this be feasible in anyway whatsoever?

Hey Logannc,
I had the same thoughts back in 2005. I looked around and found no info. I did speak to a few ppl in PV research at two of our Uni's and at our Nuclear Science facility. I got silence!

I even took a PV down to our radiation store to see any current was generated. I don't think I had put a load on the cell correctly. However nil output!

I started searching the net again and found your post, along with other pubs.

http://www.publish.csiro.au/?act=view_file&file_id=PH610443.pdf

http://nvlpubs.nist.gov/nistpubs/jres/64A/jresv64An4p297_A1b.pdf

My guess is would a lower energy emitter along with a higher Z value semiconductor work?

 

[Drakkith]

The last post in this thread was over 2 years ago.