Measurement of 146Sm Half-Life and Ionization Produced by 254 eVnr Nuclear Recoils in Germanium
Kavner, Alexander
2024
Abstract
Cryogenic-quantum radiation detectors have long been heralded for their unique capabilities, though have been utilized in only a few use cases given their high complexity and operational cost. Historically, cryogenic calorimeters and bolometers have been used for study of the cosmic microwave background, dark matter searches, and neutrino experiments. In such experiments, magnetic microcalorimeters and/or transition edge sensors measure the micro-heat imparted by electromagnetic radiation and fundamental particle interactions. Recently, groups have developed detectors and techniques for nuclear sciences and applications such as high-resolution X-ray and gamma-ray spectroscopy. This dissertation discusses the development of absolute decay counting for long-lived isotopes based upon decay energy spectroscopy whereby radioactive samples are embedded within a cryogenic detector enabling measurement of the entire decay energy. These techniques were developed for the measurement of the 146Sm half-life, an important value for nuclear astrophysics and cosmo-chemistry with tension between prior measurements. A 146Sm source was produced at the TRIUMF Laboratory and then processed and purified at Lawrence Livermore National Laboratory, yielding a pure sample. The source was embedded within a 4π thermal absorber coupled to a magnetic microcalorimeter achieving nearly 100% counting efficiency. Experimental uncertainties were studied and modeled, including the thermal coupling of the source to the absorber, pulse pile-up, trigger, and event selection efficiencies. The absolute activity of the pure 146Sm source was measured to better than 1% uncertainty. The precise sample mass was determined by mass spectrometry measurements performed by radio-chemists at Lawrence Livermore National Laboratory. From these measurements, the half-life was found to be 86 million years, a value between the two previous measurements. A second decay counting experiment was performed which verified this half-life value. A second experimental campaign was preformed to measure the ionization produced by 254 keVnr nuclear recoils within high purity germanium. This work was conducted to better characterize the material response of germanium for use as a dark matter or neutrino detector. The ionization produced by low-energy nuclear recoils is the primary signature of dark matter. Despite the urgency of dark matter detection and the recent measurements of coherent elastic neutrino-nucleus scattering, detector response is still not well characterized across a variety of materials in the keVnr and sub-keVnr regime. We have re-performed a measurement of the ionization produced by monoenergetic 254 eVnr nuclear recoils in Ge with improved digital electronics and event tagging scheme. Our results indicate an ionization yield of 66 ± 5 eVee corresponding to a quenching factor of 25 ± 2%, greater than the 14% predicted by Lindhard Model. This quenching enhancement would greatly improve the sensitivity of high-purity Ge detectors for both dark matter detection and measurement of neutrinos via coherent scattering.Deep Blue DOI
Subjects
Nuclear Physics Absolute Decay Counting
Types
Thesis
Metadata
Show full item recordCollections
Remediation of Harmful Language
The University of Michigan Library aims to describe library materials in a way that respects the people and communities who create, use, and are represented in our collections. Report harmful or offensive language in catalog records, finding aids, or elsewhere in our collections anonymously through our metadata feedback form. More information at Remediation of Harmful Language.
Accessibility
If you are unable to use this file in its current format, please select the Contact Us link and we can modify it to make it more accessible to you.