Hope Hancock

2022-09-01

What other shielding material than lead is effective against gamma rays?

Brendan Bradley

Beginner2022-09-02Added 11 answers

There are three processes by which gamma rays interact with matter: the photoelectric effect, Compton scattering, and pair production.

The photoelectric effect is an interaction between the gamma ray and an electron. It's forbidden by conservation of energy and momentum unless there is some other body present as well, such as an atomic nucleus. For this reason, the probability of the photoelectric effect is proportional not just to the density of electrons but also approximately to Z^n, where Z is the atomic number and n is about 4 to 5.

Compton scattering can occur without the presence of anything besides an electron, so it only depends on electron density.

Pair production goes like Z^2 at typical gamma-ray energies.

For these reasons, the best shielding against gamma rays is achieved with a substance that has a high density of electrons (which correlates with a high mass density) and also a high Z. Lead has these properties. It's also cheap. There are elements with a higher Z, such as bismuth, polonium, and uranium, but they aren't cheap, and their atomic numbers are only slightly higher.

The photoelectric effect is an interaction between the gamma ray and an electron. It's forbidden by conservation of energy and momentum unless there is some other body present as well, such as an atomic nucleus. For this reason, the probability of the photoelectric effect is proportional not just to the density of electrons but also approximately to Z^n, where Z is the atomic number and n is about 4 to 5.

Compton scattering can occur without the presence of anything besides an electron, so it only depends on electron density.

Pair production goes like Z^2 at typical gamma-ray energies.

For these reasons, the best shielding against gamma rays is achieved with a substance that has a high density of electrons (which correlates with a high mass density) and also a high Z. Lead has these properties. It's also cheap. There are elements with a higher Z, such as bismuth, polonium, and uranium, but they aren't cheap, and their atomic numbers are only slightly higher.

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