Neutron Reactions in Superheated Fluids

• Author / Creator

  Coutu, Clayton B.

• The PICO-60 experiment offers world leading sensitivity to the spin-dependent WIMP search, looking for the direct measurement of dark matter nuclear recoils with protons. The primary background in moderately super-heated C3F8 bubble chambers are neutrons, which can produce a signal indistinguishable from a dark matter candidate. To study the detectors response to neutrons, I show the relationship between bubble multiplicity and neutron energy is non-linear; meaning there is insufficient information in multi-bubble events to reconstruct the primary energy. This observation is explained by nuclear reactions at energies above 1.5 MeV, from fast neutrons depositing more energy above threshold into a single bubble event. Studying the acoustic energy emitted from nuclear reactions, I predict that these fast neutrons can be identified in the tail of the acoustic parameter (AP) distribution, which PICO originally uses to identify background alphas associated with the decay of222Rn. In an attempt to reconstruct direction, a technique to assign 3D coordinates to multi-bubble events is described using PICO-60 data and compared with Monte-Carlo simulations. The result is inconclusive, primarily because of a lack of statistics in the neu-tron calibration data. Finally, the commissioning of the PICO-40L detector at SNOLAB is discussed, focusing on my contributions to the thermal and camera installation. The new detector offers increased sensitivity to the dark matter search, and will continue the neutron AP and direction analysis presented.

• Subjects / Keywords

  • WIMP
  • PICO
  • Backgrounds
  • Neutrons
  • Acoustics
  • Physics
  • Bubble
  • Particle

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-1z4m-8f74

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.