modified
1/E’ –1/E = (1/mc2) (1-cos q)
where mc2 is the rest mass energy of the electron (511 keV) and q is the scattering angle of the photon. In this experiment you will measure E’(q) for two values of E.
Experimental approach:
PROPORTIONAL COUNTER
241Am source: This source emits a 59.54 keV gamma ray, much lower energy, so the dependence of E’ on angle will be less. However, the beam is very well collimated and well suited to a Compton scattering measurement. (This is a very strong source. Do not spend time in front of the source. You will be instructed in its use by your instructor.) You will measure the energy spectrum using a proportional counter, which gives a pulse proportional to the energy of the photon absorbed. The spectrum is actually rather complicated, so just use the 59.54 keV peak and ignore the rest. Place the source about ten inches from the detector and measure a spectrum. Then change the geometry so that the beam from the source scatters off a block of Al at an angle into the detector. Take a spectrum for long enough to get good statistics (a couple of minutes at each angle at least). Measure E’ as a function of angle. Plot out a direct spectrum and spectra taken at different angles. Indicate on the direct spectrum which peak is the 59.54 keV photon, and use this to calibrate the energy scale of the spectra. Then take spectra at other angles (say 0,45,90,135 degrees) . Plot out all spectra in your book, and indicate on each plot where E’ is. Make a graph of E’ versus angle and plot the calculated values of E’ from the above equation on the same graph. Does the equation work? Put all plots in your data book and explain them.