You have a mechanism by which you can use a magnetic spectrograph to chose the energy of the beta rays from a 137Cs source. Your spectrograph only allows beta rays of 0.8 MeV to exit. You are going to use this monoenergetic source of 0.8 MeV beta rays in Investigation 3 of this week's lab. You have a collection of thin brass foils just like you are going to use in lab with exactly the same thickness that you will use in lab. However, for purposes of this problem, we will assume that the density of the brass foils is 8.4 g/cm3 (in the lab we will assume the foils are made of pure copper and that the density of copper is 8.92 g/cm3). You can use Figure 5 in the lab manual for the range in g/cm2 of the beta rays in brass versus the beta ray energy. 1 inch = 2.54 cm.

a) What thickness of the brass foils in g/cm2 does it take to stop the 0.8 MeV beta rays?

g/cm2

b) What thickness of the brass foils in cm does it take to stop the 0.8 MeV beta rays?

cm

c) If you use 0.001 inch thick foils, how many foils will it take to just barely stop the beta rays? (You may use tenths and hundreths of a brass foil. The answer does not have to be an integer.)