BEYOND THE FIRST YEAR Today we are going to do two experiments. We will determine the rest-mass energy of an electron using gamma spectroscopy. We will calibrate a NaI(Tl) scintillation detector plus multi-channel analyzer (MCA) system to observe the spectrum from some common radioisotopes. A plot of the Compton edges will be used to determine the rest mass of the electron. This experiment is an excellent test of the idea of relativistic mass-energy. First, we will calibrate the system as above and use the multi-channel scaling (MCS) feature of the MCA to measure the half-life of the 1st excited state of 137mBa and to measure the statistical nature of the decay process. Due to the length of time needed to run this experiment, we will start it at the beginning of class. MULTICHANNEL SCALING AND 137mBa HALF LIFE: The spectrometer memory locations (channel numbers) used to store the gamma data can be use in a different manner called Multichannel scaling (MCS). Using the MCS option will result in the computer storing the total number of gammas counted in the selected time period (called the dwell time), starting with channel 0 and proceeding through all the channels in order. This will allow you to record the gamma intensity as a function of time. This will be used to determine the half-life of 137mBa. 137m

Ba has a half-life of only a few minutes and therefore is very appropriate for use in a class lab. The Ba is obtained from a 137Cs/137Ba “mini-generator” or “cow”. The mini-generator contains a small quantity of 137Cs (