Measurement and modeling of cosmic ray exposure for SuperCDMS dark matter detectors.

Dark matter is an unknown type of matter that composes roughly 27% of the observable universe and, as cosmological structure models suggest, the earth should be passing through a “dark halo” of this unknown matter present in the Milky Way galaxy. As we pass through this halo, the Super Cryogenic Dark Matter Search (SuperCDMS) experiment aims to directly detect dark -matter particles. Though many dark matter particle candidates exist, SuperCDMS focuses on the detection of particles called WIMPS (weakly interacting massive particles) as predicted by super-symmetric theories beyond the standard model. Due to the high-sensitivity of the germanium detectors employed, shielding from cosmic rays is paramount, thus the measurements will be performed 6561 feet below ground at SNOLAB. While the experiment will be performed underground, fabrication of the germanium detectors will occur above ground. During this fabrication period, the germanium detectors are exposed to cosmic ray secondaries (i.e., neutrons, protons, and muons). These high-energy secondary particles can interact with the germanium nuclei in the detector crystals through a spallation process that breaks apart the nuclei resulting in unstable products. Of particular concern is the production of tritum that has a ling, 12 year half-life. The eventual beta decay of tritium will create a background contribution that diminishes the sensitivity to WIMP detection. A goal of this work is to model and predict cosmogenic exposure at the fabrication sites to account for this tritium production. Expected integrated cosmic ray fluxes were derived for three cosmic ray particles: secondary muons, protons, and neutrons, at ten different fabrication and experimental sites involved in the SuperCDMS experiment. In addition to the cosmic ray fluxes, location and time depend cosmic ray attenuation parameters were developed to account for three main variables: elevation, position with respect to the earth’s magnetic field, as well as time of exposure with respect to the sun’s 11 year solar cycle. In addition, for each of the ten fabrication sites a CRY simulation was developed and run to predict the constituent cosmic ray flux for each particle. A portable cosmic-ray muon detector will be shipped to each site to gather cosmic-ray exposure to confirm these predictions. This detector was assembled and cosmic ray fluxes were measured above ground at PNNL as well as in PNNL’s shallow underground laboratory

Design and Fabrication of Liquid Scintillator Counter

Pacific Northwest National Laboratory (PNNL) is currently developing an ultra-low background liquid scintillator counter (ULB LSC) in the shallow underground laboratory. At a depth of 35-meters water-equivalent, the underground laboratory has a multi-layered shielding to keep out cosmic-ray induced background. The ULB LSC, which is located in a clean room facility, is a multi-layered design made up of various materials, including plastic scintillator veto panels, borated polyethylene, lead and copper. These layers help lower the contributions of the terrestrial background and intrinsic background, resulting from the impurities present in the materials, to the overall background count rate observed by the detectors. After the completion of the instrument, the first liquid scintillation sample will be tested using a pulley-like design. The design consists of a sample holder which holds the vial in place as it is lowered down into a light guide. The second component of the design is a piece which helps lower the sample holder in the correct orientation into the light guide in order to maximize light output and collection efficiency. The system is designed using Solidworks, a computer aided design (CAD) program, and 3D printed using Acrylonitrile Butadiene Styrene (ABS) plastic. The design for the sample holder is based off of another more complex design originally made of copper. This simplified sample handling design will accelerate the project toward initial data collection, an important milestone toward validating the UBL LSC system concept

Final Report for Monitoring of Reactor Antineutrinos with Compact Germanium Detectors

This 2008 NCMR project has pursued measurement of the antineutrino-nucleus coherent scattering interaction using a low-energy threshold germanium gamma-ray spectrometer of roughly one-half kilogram total mass. These efforts support development of a compact system for monitoring the antineutrino emission from nuclear reactor cores. Such a monitoring system is relevant to nuclear safeguards and nuclear non-proliferation in general by adding a strong method for assuring quantitative material balance of special nuclear material in the nuclear fuel cycle used in electricity generation

Antineutrino Detectors Remain Impractical for Nuclear Explosion Monitoring

Fission explosions produce large numbers of antineutrinos. It is occasionally asked whether this distinctive, unshieldable emission could help reveal clandestine nuclear weapon explosions. The practical challenge encountered is that detectors large enough for this application are cost prohibitive, likely on the multi-billion-dollar scale. In this paper, we review several hypothetical use cases for antineutrino detectors as supplements to the seismic, infrasound, hydroacoustic, and airborne radionuclide sensors of the Comprehensive Nuclear-Test-Ban Treaty Organization's International Monitoring System. In each case, if an anti-neutrino detector could be constructed that would compete with existing capabilities, we conclude that the cost would considerably outstrip the value it might add to the existing monitoring network, compared to the significantly lower costs for the same or superior capability.Comment: 16 pages, 3 figure

Snowmass 2021 Underground Facilities & Infrastructure Frontier Report

The decade since Snowmass 2013 has seen extraordinary progress of high energy physics research performed--or planned for--at underground facilities. Drs. T. Kajita and A.B. McDonald were awarded the 2015 Nobel Prize in Physics for the discovery of neutrino oscillation, which show that neutrinos have mass. The U.S. has embarked on the development of the world-class LBNF/DUNE science program to investigate neutrino properties. The Generation 2 dark matter program is advancing to full data collection in the coming 5 years, a Dark Matter New Initiatives program has begun, and the U.S. dark matter community is looking toward a Generation 3 program of large-scale dark matter direct detection searches. The Sanford Underground Research Facility has become a focal point for U.S. underground facilities and infrastructure investment. The status since the 2013 Snowmass process as well as the outcome from the 2014 P5 program of recommendations is reviewed. These are then evaluated based on the activities and discussions of the Snowmass 2021 process resulting in conclusions looking forward to the coming decade of high energy physics research performed in underground facilities.Comment: Snowmass 2021 Underground Facilities & Infrastructure Frontier Repor

Operation of a high purity germanium crystal in liquid argon as a Compton suppressed radiation spectrometer

A high purity germanium crystal was operated in liquid argon as a Compton suppressed radiation spectrometer. Spectroscopic quality resolution of less than 1% of the full-width half maximum of full energy deposition peaks was demonstrated. The construction of the small apparatus used to obtain these results is reported. The design concept is to use the liquid argon bath to both cool the germanium crystal to operating temperatures and act as a scintillating veto. The scintillation light from the liquid argon can veto cosmic-rays, external primordial radiation, and gamma radiation that does not fully deposit within the germanium crystal. This technique was investigated for its potential impact on ultra-low background gamma-ray spectroscopy. This work is based on a concept initially developed for future germanium-based neutrinoless double-beta decay experiments.Comment: Paper presented at the SORMA XI Conference, Ann Arbor, MI, May 200