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Say a 1 MeV gamma ray is shielded by 1 cm (halving thickness) of lead. Now, what does "havling the intensity" mean ? Like will the new gamma ray exit with energy of 0.5 MeV ? and by that we can say that the material absorbed 0.5 MeV ? or it will be halved in another way ?

Sorry if the question seem too amateur, I am just not good at particle physics.

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have a look at and the next paragraph. – anna v Aug 22 '13 at 18:35

When we say a gamma ray has an energy of 1 MeV we normally mean that the energy of each photon is 1 MeV, where the energy of each photon is related to the frequency or wavelength by $E = h\nu$ or $E = hc/\lambda$. The intensity of the radiation is the number of the 1 MeV photons per unit area per second.

So if half the gamma radiation is absorbed, the energy of each photon is still 1 MeV, but there are only half as many photons left unabsorbed.

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