How much gamma ray photons does this lab technician absorb ?

Question

I'm confused about something here, the 2.9 mJ of energy that the body absorbed here, is more than the total energy it was subjected to (0.5 MeV), so is the 0.5 not the total energy ? Is it the energy/ 1 gamma photon ? And is that whats always given to us ? 
So if they gave me the activity of a source in Ci, are they giving me the activity of 1 gamma photon ?

Anonymous · Accepted Answer

The 0.5MeV is the energy of a single photon of gamma ray radiation.
There are two ways of representing energy, one is by using the units of   electron volts and the other is in Joules. We convert MeV to Joules by multiplying by 1.6 x 10^-19
0.5 MeV = 0.5 x 10^6 x 1.6 x 10^-19 (J)
0.5 Mev = 8 x 10^-13 J

Each gamma ray photon has an energy of 8 x 10^-13 J. However, the technician absorbed a lot more than that. He/She absorbed 2.9 mJ. Therefore, the number of photons absorbed is:-
No. of gamma ray photons absorbed = 2.9 x 10^-3 / 8 x 10^-13
= 3.6 x 10^9
Ans B.

? · Answer

To understand the energy, calculate the energy needed to prepare a cup of tea. Now divide that by the energy of a photon of 0.5 Mev. You will see the number needed.

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How much gamma ray photons does this lab technician absorb ?

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