Question

21, (a) What is the γ-ray flux (γ's per unit area) a distance of 1.0 m from a 7.5-mCi source of 6°Co? (b) How many ions per minute are produced in a cubic centimeter of air at that distance?

Answer 1

Activity of the Co-60 sample is A = 7.5 mCi = 7.5 x 10-3 x 3.7 x 1010 decay per second =2.775 x 108 decay per second

this implies that the number of gamma rays produced in 1 second = 2.775 x 108

distance from the source, r = 1.0 m

gamma ray flux = totat number of photons/area of the surface

2.775 x 10⁸ /4 x 3.14 x1 x 1 = 0.221 x 10⁸

gamma ray flux = 0.221 x 10⁸

assuming each photon produce one ionization ,then total number of ionization per second = 0.221 x 10⁸

total number of ionization per minute = 0.221 x 10⁸/60 = 3.68 x 10⁵