<p> This dissertation is an account of the first calorimetric detection of individual He*<sub>2</sub> excimers within a bath of superfluid <sup>4</sup>He. When superfluid helium is subject to ionizing radiation, diatomic He molecules are created in both the singlet and triplet states. The singlet He molecules decay within nanoseconds, but due to a forbidden spin-flip the triplet molecules have a relatively long lifetime of 13 seconds in superfluid He. When He*<sub> 2</sub> molecules decay, they emit a ~15 eV photon. Nearly all matter is opaque to these vacuum-UV photons, although they do propagate through liquid helium. The triplet state excimers propagate ballistically through the superfluid until they quench upon a surface; this process deposits a large amount of energy into the surface. The prospect of detecting both excimer states is the motivation for building a detector immersed directly in the superfluid bath.</p><p> The detector used in this work is a single superconducting titanium transition edge sensor (TES). The TES is mounted inside a hermetically sealed chamber at the baseplate of a dilution refrigerator. The chamber contains superfluid helium at 100 mK. Excimers are created during the relaxation of high-energy electrons, which are introduced into the superfluid bath either in situ via a sharp tungsten tip held above the field-emission voltage, or by using an external gamma-ray source to ionize He atoms. These excimers either propagate through the LHe bath and quench on a surface, or decay and emit vacuum-ultraviolet photons that can be collected by the detector.</p><p> This dissertation discusses the design, construction, and calibration of the TES-based excimer detecting instrument. It also presents the first spectra resulting from the direct detection of individual singlet and triplet helium excimers.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:10012481 |
| Date | 17 February 2016 |
| Creators | Carter, Faustin Wirkus |
| Publisher | Yale University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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