Neutron Spectroscopy Development in Tensioned Metastable Fluid Detectors

<div> <div> <div> <p>This dissertation describes work conducted in pursuit of interests in adapting Tension Metastable Fluid Detectors (TMFDs) for dosimetry-related applications with the specific intent of engineering a neutron ambient dose spectrometer. TMFDs possess several charac- teristics desirable for neutron spectrometry, including high efficiencies, complete blindness to gamma and beta radiation, and tailorable-threshold response functions. Prior spectro- scopic work with TMFDs, aptly named Single Atom Spectroscopy (SAS), was constrained to a specific subset of detection fluids who’s composition includes hydrogen and only one other higher Z element (e.g. hydrocarbons), where only one element is assumed capable of initiating a cavitation detection event (CDE). The present work alleviates these restrictions, enabling spectroscopy in detection fluids with multiple constituent elements. </p> <p>Simulating the detector’s response predicates knowledge of the energy necessary for ra- diation induced nucleation, which has been theoretically derived with nucleation theory for superheated fluids, but remains unbeknownst for tensioned metastable states. This limi- tation was overcome using MCNPX-PoliMI to model the spatial recoil nuclei spectra from isotope sources and coupled with SRIM to generate the ion energy deposition probabil- ity density within a critical length scale of each interaction event. Thereafter, the energy deposition threshold necessary to generate a detection event, and corresponding response matrix, was derived empirically by solving for the solution curve that minimizes the residual difference between the measured and simulated count rates. </p> <p>The accuracy of the derived response matrix was evaluated through comparisons with a 6LiI Bonner Sphere Spectrometer in which, for 252Cf and 239PuBe/241AmBe isotope source neutron spectra, the two systems offered results within ±10% of each other for ambient equivalent fluences on the order of 100 μRem/hr fields. Notably, when under ultra-low (10 μRem/hr) fields the Bonner spectrometer and other traditional detectors proved impractical. In contrast, the TMFD system was capable of resolving underlying spectral features and corresponding ambient dose rates within ±5% of MCNP predictions. </p> </div> </div> </div>