HPGe Imagers (BS Internship)

My introduction to Lawrence Livermore National Laboratories began in 2011 when I worked with Dr. Morgan Burks in the Physical and Life Sciences Division under a DOE grant funded project to develop radiation detection systems for use in homeland and national security applications. The main project I worked on my first summer (2011) at LLNL was developing an imager program in Matlab to display contour maps of radiation source profiles from a 2-D planar, segmented strip, HPGe detector onto panoramic images of a room. We also determined strip efficiencies and energy resolution.

My second summer at LLNL (2012), I worked on capacitive multiplexing of the same HPGe imager I had worked on the summer before. My capacitive multiplexing project earned me an award for my poster presentation at the AAPT conference in Portland, Oregon in July of 2013. More information about this project is provided below.

Capacitive Multiplexing

Gamma-ray imagers based on high purity germanium (HPGe) use multiple segmented strips of germanium to determine the position of gamma emitters. To reduce electronic complexity, we investigated a simple readout method involving nonuniform capacitive multiplexing. Goals of this investigation included maximizing the number of multiplexed channels, maintaining high resolution, optimizing external capacitance values, and determining the intrinsic capacitance and ground capacitance. Measurements were taken on an eight strip, orthogonal, 2-D, dual-planar, high-purity germanium detector. A maximum of six strips were capacitively multiplexed together at energies of 122keV and 662keV. Multiplexed strips were successfully reconstructed back into individual channel spectra with FWHM of approximately 3keV on average. We also developed and verified equations describing the multiplexed photopeak energies and verified them by experiment for up to six multiplexed configurations.