January 1, 2019.
Based on current observations of distant galaxies and galaxy clusters, it is estimated that 85% of the matter in the universe is actually dark matter. Dark matter is thought to exist due to observed gravitational effects in other galaxies and is possibly composed of undiscovered subatomic particles. Several experiments are being conducted for the direct detection of dark matter. These ultra-low background experiments operated deep underground, including the Super Cryogenic Dark Matter Search (SuperCDMS), are becoming increasingly sensitive to trace levels of radioactivity in the detector construction materials. Cosmic ray secondaries (produced by cosmic ray collisions with particles in the atmosphere) are the main source of concern for background radiation on the germanium crystal detectors used by the SuperCDMS experiment. In some cases, such experiments are limited by the cosmogenically produced radioactive nuclides created in detector construction materials due to exposure to cosmic ray secondary particles while on the surface of the Earth. A comprehensive model of the cosmic ray secondary exposure for detector components on the Earth’s surface - or in shallow underground facilities - is presented. Phenomenon included in the model include elevation above sea level, geomagnetic latitude, phase of the solar cycle, and shielding overburden. This model is applied to the cosmic ray secondary exposure of the SuperCDMS detectors with a focus on estimation of the tritium levels in the detector crystals.
Pacific Northwest National Laboratory (PNNL)
The 2019 STEM Teacher and Researcher Program and this project have been made possible through support from Chevron (www.chevron.com), the National Science Foundation through the Robert Noyce Program under Grant #1836335 and 1340110, the California State University Office of the Chancellor, and California Polytechnic State University in partnership with Pacific Northwest National Laboratory. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the funders.