Procedure

We will be using a NaI detector on a goniometer arm so that more precise angles can be made with correlation to the direction of incoming photon's incidence with the aluminum target. For this experiment we use as a target an aluminum sphere around one inch in diameter. Aluminum is a good target as it maintains a large number of valence electrons with small ionization energies so that we can treat these electrons as being free. The goniometer arm is able to be rotated from zero degrees (directly in line with the direction of the incoming photons) to 90 degrees (perpendicular to the direction of the incoming photons with target as our axis). Scattered photons from the target will then incidence with our detector with about 30% efficiency. This incidence will be measured and amplified by a photomultiplier tube (PMT) which will then be amplified further before reaching our multi-channel analyzer (MCA). The size of the electrical pulse arriving at the MCA will be proportional to the energy of the photon incident with the detector so after some calibration we will be able to measure the energy of incoming scattered photons. To calibrate the MCA we used a source with known gamma emission, namely , directly in line with our detector then set the two channel calibration on the MCA program to be in line with the two known gamma emissions in the sodium-22 spectrum. After everything is aligned we specify a time interval to take data over then collect data for multiple angles to check that the energy of the photons arriving at the detector are in line with what is believed from Compton's equation. Here we used once more a sodium-22 source and looked for scattered 511 MeV photons. Angles close to zero degrees are left out of the data collection as these angles receive a large number of photons directly from the source.

Data

Data was taken at multiple angles all over intervals of two hours then regions of interest (ROI) were issued to the area about where the peak occurred. Our MCA program was then able to give an approximation of the center of our peak along with the uncertainty in that peak which I have taken as the full width half max (FWHM) of each given peak.