Experiments measuring rare events, such as neutrinoless double beta decay, and those searching for very weakly interacting particles, such as low energy solar neutrino experiments or direct dark matter searches, require ever lower backgrounds. Placing the detectors deep underground greatly reduces cosmic ray backgrounds, while large active and passive shielding minimizes the background from radioactivity in the rock of the underground caverns. What remains, however, is the radioactivity inside or on the surface of the detector components. The underground physics community strives to identify and develop materials with radioactive contamination at permissible levels, and to remove radioactive contaminants from materials, but each such material represents a separate dedicated research and development effort. A direct method to establish the radioactive contamination in materials is to measure the emitted gamma radiation directly through gamma ray spectroscopy.
This team has access to two high purity germanium detectors in the Kimballton Underground Facility and access to the lowest background germanium detector in the world, NRL-1 at the Laboratori Nazionali del Gran Sasso in Italy. Part of this proposal is to use these three detectors to perform material assay on items needed for experiments. Several techniques have been developed to directly measure isotopic abundances and infer the activity. One of these methods is Inductively-Coupled Plasma Mass Spectrometry (ICP-MS), which can measure isotopic concentrations at the part per trillion level. It is planned to make a comparison of ICP-MS and direct gamma-ray spectroscopy at levels near those required for planned experiments.
Radioactive radon in the air can create radioactive surface contamination on detector components. Although it is possible to create gases with a very low radon concentration, human contact with a detector during construction, assembly, and operation requires an air atmosphere. Underground laboratories will need to have radon removed from the laboratory air. The final part of this proposal is to develop the technology needed to create a radon scrubber for removing the radon from air, and for establishing the limitations to this technology.
Knowledge and expertise in low levels of radiation detection and radon mitigation has direct coupling to occupational health, national security, radiation medicine, etc. This program will also expand the knowledge base for underground physics in the U.S. that will transfer to DUSEL, and develop a new generation of physicists searching for the rarest events and weak interactions.
