Can Hempcrete be an effective blocker of gamma radiation?

My basic question is if Hempcrete walls or blocks could potentially be effective against gamma radiation. Now I want to say no due to gamma rays being destructive against carbon material in general and well hempcrete is largely carbon based.




It will depend on the energy of the gamma photons, if it was something very low energy such as the 30 keV photons from americium-241 then a thick layer of carbon would be usful. But for things like Cs-137, Co-60 and Zr-95 a few inches of carbon or plastic will be close to worthless.


Keep in mind that even with a low density material like water or air it is possible to attenuate even high energy gamma photons like those from Co-60 and Na-24. By using miles of separation from the radiation source you can screen out much of the gamma radiation and also take advantage of the inverse square law.


I have been inside a large scale used nuclear fuel store and I have also stood above a TRIGA reactor and I was able to look down into the ponds, I had about 10 meters of water between me and the fuel. I have seen large amounts of used fuel inside a hot cell. There I had about 3 meters of lead glass between me and the fuel. Both ten meters of water and three meters of glass do give you some funny optical effects. It can distort the shapes of things. I suspect that I would be able to see more clearly without the shielding but I would only be able to spend a very short time in the room before I would have to leave.


There is one use of a plastic sheeting, this is as a radioactivity / nuclear version of an antispall liner.


When you subject high density substances such as lead to high energy gamma rays the surface of the lead emits secondary radiations such as photoelectrons, compton electrons and lower energy photons.


The best thing you can do if you have a wall of lead is to cover it with a sheet of steel. The steel will stop a lot of the secondary radiation from the lead. Then you put up a sheet of aluminium on top of of the steel to block the secondary radiation from the iron. Then if you are very keen you add a layer of plastic to finsih the job off.


Another option would be to use concrete made with either barium added to it or lots of steel shot added to the concrete. This gives good shielding against both gamma and neutrons.


If you think that you will have exceptionally high energy gamma rays, then you need to worry about neutron production as a result of the photonuclear reactions. These only become something to worry about normally above 2 MeV photon energy. For this I would suggest a thick lead shield and then plastic to slow down the neutrons, even if you do not stop the neutrons by slowing them you reduce the amount of harm that they can do. So a thick layer of the carbon based plastic on the human side of the shielding would be helpful under these conditions even if we ignore the secondary radiation from gamma photons at about 1 MeV (like Co-60).


Another use of the plastic sheeting is if you have large amounts of very high energy beta emitters it is better to adsorb the beta particles in a material with a low atomic number as this reduces the amount of X-rays that are generated as the electrons slow down. So for vast amounts of Sr-90 and P-32 / P-33 I would suggest a thick layer of plastic followed by a layer of lead to catch any of the X-rays generated in the shielding. If you wanted to do a perfect job you would use the graduated Z method on the outside of the shielding pot for super high amounts of Sr-90 and other high energy beta emitters.


So while the plastic is close to no use on its own for stopping gamma rays it can be used to optimise the shielding.


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