Instead of using brass to absorb gamma rays in Investigation 4 that you will do
ID: 1272428 • Letter: I
Question
Instead of using brass to absorb gamma rays in Investigation 4 that you will do in lab this week, we will use aluminum (density = 2.7 g/cm3) for this problem. The linear attenuation coefficient for gamma rays of 0.662 MeV is 0.178 cm-1. You have several samples of three thicknesses of aluminum foils: 1/32", 1/16", and 1/8" (where the symbol " stands for inches and 1 inch = 2.54 cm).
a) What reduction in intensity, I(x)/I0, occurs if you use one sample of the thinnest foil to absorb the gamma rays?
1
b) What reduction in intensity, I(x)/I0, occurs if you use one sample of the thickest foil to absorb the gamma rays?
2
c) What reduction in intensity, I(x)/I0, occurs if you use two samples each of all three foil thickness to absorb the gamma rays?
3
Explanation / Answer
a) I(x)/I0 = e^(-lambda x)
1/32 in = 0.0794 cm
so I(x)/I0 = e^(-0.178*0.0794)= 0.986
b) now foil 4 times thicker so
Ix /I0 = e^(-0.178*4*0.0794)=0.945
c) 2/32 + 2/16 + 2/8= 7/16 = 14/32
so 14 times thicker than thinnest so
Ix/I0 = e^(-0.178*14*0.0794)=0.82