Physics & Astronomy ETDs

Publication Date

Summer 7-16-2018

Abstract

This thesis details the design and operation of a high-sensitivity radon detector for use in background radiation characterization and mitigation for the MAJORANA DEMONSTRATOR Neutrinoless Double Beta Decay Experiment and Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay (LEGEND) Collaboration. Understanding and mitigating background radiation is especially important in searches for very rare nuclear processes, which utilize sensitive detectors. One such rare process is the yet-to-be-observed neutrinoless double beta decay. Observation of this process would imply that the neutrino is its own antiparticle, called a Majorana particle, violate lepton number, and provide experimental constraints on the masses and mixing angles between neutrino mass and flavor eigenstates.

While most sensitive rare search experiments are placed deep underground to shield from cosmic radiation, radon provides a significant and pervasive source of background radiation. This background radiation could potentially make an experiment futile as any small signal of interest could be hidden in a large amount of background events. Radon is a decay product of both uranium and thorium, which are found in rock, soil, and many common materials. Radon is the only daughter in the uranium and thorium decay chains that is gaseous, so it is able to escape materials either through pores and fissures or diffusion through the material.

Our radon detector utilizes a large electropolished stainless steel vessel to collect gas and a high electric field to collect charged radon daughters on a silicon PIN photodiode. Alpha particles from radon daughter decays, primarily that of 214Po, are measured with the photodiode and a radon concentration in the gas is determined from the measured activity. The collection efficiency, and thus calibration factor from photodiode activity to radon activity, is determined by using air and an ore-like mineral as sources and a Durridge RAD7 radon detector as a calibration standard. The detector also includes an in-line emanation chamber to test the radon emanation from materials of interest. Utilization of this detector in the construction and operation of any ultra-low background search provides valuable quantization of ambient radon backgrounds to a sensitivity of the order mBq/m2.

Degree Name

Physics

Level of Degree

Masters

Department Name

Physics & Astronomy

First Committee Member (Chair)

Dinesh Loomba

Second Committee Member

Douglas Fields

Third Committee Member

Michael Gold

Project Sponsors

Los Alamos National Laboratory

Language

English

Keywords

radon, low background, radiation detection, neutrinoless double beta decay, material assay

Document Type

Thesis

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