DOE Science Highlight
Abstracted from a PNNL Science Highlight provided to the DOE Office of Science:
PNNL scientists in the National Security Directorate have a long history developing advanced radiation detection instrumentation for application to unique or specialized measurements. Applied research examples include field-deployed arrays of high-purity germanium detectors for isotope-specific screening of cargo containers and low-energy threshold gas proportional counters for measuring argon-37 signatures of clandestine nuclear weapons testing. Now, in the last three years, these PNNL researchers have employed their expertise in ultra-low-background radiation detection to deploy an experiment searching for signals from cosmological dark matter particles. Dark matter is known to have played a major role in the evolution of the universe; its existence is readily apparent by its gravitational imprint on the distributions of stars and galaxies. However, no experimental effort to date has decisively measured these sub-atomic dark matter particles in the laboratory.
Three years ago, PNNL recognized a state-of-the-art radiation detector developed by the University of Chicago and CANBERRA Industries was a candidate instrument for measuring signals from dark matter, if such a detector was installed in a low-background shield at an underground location. As part of the CoGeNT Collaboration, PNNL staff worked toward making an initial search for signals from dark matter at the Soudan Underground Laboratory using the University of Chicago/CANBERRA-developed detector. An initial report, published in Physical Review Letters, has garnered numerous references in the first year of being available online.
In addition to leading the underground deployment of the low-background shield to house the low-energy threshold germanium detector, PNNL staff have contributed to furthering the detector development and the scientific results. Early in the effort PNNL staff identified a class of signal pulse through analysis of digitized waveform data. University of Chicago and PNNL researchers recognized the source of these events as due to low electric field surface regions of the crystal. This led to the use of a waveform digitizing data acquisition system that is now used to remove these degraded pulses. Removing these unwanted signals directly improves the experiment's sensitivity to potential dark matter signals. PNNL and the University of Chicago are currently working on three fronts to (1) analyze the first full year of recorded data for signatures of dark matter, (2) develop a lower noise detector cryostat to improve the low-energy threshold performance of the detector, which will result in improved dark matter sensitivity, and (3) design a next-generation four-detector shield design to expand the experimental sensitivity to cosmological dark matter signals.