#### Date of Award

6-2019

#### Degree Name

Doctor of Philosophy

#### Department

Physics

#### First Advisor

Dr. Michael A. Famiano

#### Second Advisor

Dr. Lisa M. Paulius

#### Third Advisor

Dr. Thomas W. Gorczyca

#### Fourth Advisor

Dr. Michael W. Rabin

#### Keywords

Transition Edge Sensor (TES), neutrino mass, exchange effects, electron capture, microcalorimeter, holmium

#### Abstract

The direct neutrino mass is a fundamental physics quantity with far-reaching implications for the physics community. Current experimental limits put the direct neutrino mass at less than 2 eV. The neutrino mass can be explored through an end-point measurement of tritium beta decay, which is currently underway in the KArlsruhe TRItium Neutrino experiment (KATRIN). KATRIN has a lower limit of 0.2 eV, at which point there will be either a mass measurement or another upper bound. In either case, an alternative experiment with different systematics is needed to verify the results and/or push the upper bound lower. The end point of a calorimetric electron capture spectrum is sensitive to the neutrino mass, and low temperature microcalorimeters have reached the technological maturity necessary to make such a measurement. An open question is whether the theoretical spectral shape used to interpret such a measurement is well enough understood for a sensitive mass determination. This dissertation seeks to explore the feasibility of a neutrino mass measurement using low temperature microcalorimeters by determining the sensitivity of theoretical calculations and comparing predictions of experimental observables from these calculations to experimental spectra of ^{163}Ho, ^{193}Pt, and ^{55}Fe to avoid material-specific biases.

In this dissertation, the theoretical shape of a calorimetric electron capture spectrum is re-categorized as a set of decisions. The effects of decisions in these categories are quantitatively explored, with a focus on experimental observables and predictions of spectral reach needed to differentiate between different calculations. While calorimetric data from ^{163}Ho and ^{55}Fe exists in the literature, new ^{193}Pt data was taken for the purposes of comparison to calculations. The unique ^{193}Pt-in-Pt absorber matrix is characterized with gamma spectroscopy and modeling for the irradiation creation process. Acquisition and analysis of the calorimetric electron capture data from this absorber is discussed. Calculations are compared to ^{163}Ho, ^{193}Pt, and ^{55}Fe spectra.

#### Access Setting

Dissertation-Open Access

#### Recommended Citation

Koehler, Katrina E., "Sensitivity of the Theoretical Electron Capture Shape and Comparisons to Experiment" (2019). *Dissertations*. 3467.

https://scholarworks.wmich.edu/dissertations/3467