Calibration of $^{22}$Na Using the Sum-Peak Counting Method

A calibrated positron emitter, $^{22}$Na, is needed for nuclear cross section measurements. The calibration of this source was performed using a self-calibrating sum-peak counting method which has the potential to replace calibrated sources for various other applications. The sum-peak method was used with three different detector setups: a single high purity germanium detector, a 4"x5" NaI well detector and the same NaI well detector paired with a 3"x3" NaI detector, obtaining a 4$\pi$-counting geometry. The $^{22}$Na decays via positron emission mostly to an excited state of $^{22}$Ne which promptly de-excites and emits a 1275 keV gamma ray. The 511 keV gamma ray produced from the positron annihilation sums with the 1275 keV gamma generating a 1786 keV peak in the observed spectra. The total counts in the three peaks as well as the total counts observed in the spectrum are used to calculate a value for the activity of the source. In order to get a better understanding of the source and the detector geometries, a simulation of the setups was generated using EGSnrc: software that uses Monte Carlo simulations to model radiation transport. Using this program, and subsequent Monte Carlo calculations, a model of the spectra produced from each setup was created and used to fit theory to data and get a more accurate number for the activity of the source. Results obtained from this experiment are being compared to independent measurements from HPGe gamma ray spectrometry and 4$\pi$ NaI integral counting using calibrated detectors.