Q.1. In order to calibrate the strength of an Fe-55 source, several measurements of the radiation field are made with the same detector located at different distances. Both the source strength and the absorption coefficient of these photons by air are unknown, so three measurements suffice to overdetermine them, thereby providing a handle on the uncertainty.

Trial Time (sec) Counts R(cm) r(cm)
A 10 264,605 11.77 12.17
B 10 48,072 23.79 24.19
C 10 21,496 31.92 32.32

R = distance to aperture whose diameter = 0.375 inch
r = distance of air traversed from source to detector
efficiency of detector = 0.806 (transmission through light-tight paper)
background = 100 counts in 10 sec

a) What are I(0) and D? A graphical analysis is sensible.

b) How accurately are the three rates determined?

c) How accurately are I(0) and D determined from these data?

2. Identify the three primary absorption mechanisms for high energy photons passing through matter. Discuss the nature of the secondary and tertiary radiation produced. Indicate the approximate range of photon energies where each is the dominant mechanism.

3. Compare and contrast the passage of alpha and beta charged particle radiations through matter: how does the typical particle transfer its energy to the target material, what does the spectrum of particle energies look like initially and at progressively greater depths, etc.