The Student Room Group

Radioactivity!

Hello, I have this question on radioactivity which Im finding hard to do:

Potassium-42 decays with a half life of 12 hours. When potassium-42 decays it emits B- particles and gamma rays. One freshly prepared source has an activity of 3.0 x10^7 Bq.

(a) To determine the dose received by a scientist working with the source the number of gamma ray photons incident on each cm² of the body has to be known.

One in every five of the decaying nuclei produces a gamma ray photon. A scientist is initially working 1.50m from the fresh shorce with no shielding. Show that at this time approximately 21 gamma ray photons per second are incident on each cm² of the scientist's body.


Thanks a lot
From john
Reply 1
The number of photons through the area will be the fraction of the total that goes through the area in question ie a fraction of 1cm^2 / 4 pi x 150 ^ 2.
Reply 2
Oh right thanks a lot