I was invited to give a talk and poster at the 22nd International Conference on Nuclear Engineering (ICONE) in Prague. The poster that accompanied this talk and paper was selected as a Winner in the student competition. I have submitted a revised version of this paper for publication in a new ASME journal, Nuclear Engineering and Radiation Science.
Characterization and Optimization of a Tensioned Metastable Fluid Nuclear Particle Sensor Using Laser Based Profilimetry
Jul 11, 2014
Citation
Hagen, A., Grimes, T. F., Archambault, B. C., Harris, T. N., & Taleyarkhan, R. P. (2014). Characterization and Optimization of a Tensioned Metastable Fluid Nuclear Particle Sensor Using Laser Based Profilimetry. In Proceedings of the International Conference on Nuclear Engineering. Prague, Czech Republic: American Society of Mechanical Engineers.
Abstract
Tensioned metastable fluid detectors (TMFDs) are under development at Purdue University along with S/A Labs., LLC with support from the United States federal, state and industry sponsors. These novel sensors offer unique features to enable replacement of state of the art sensors for monitoring fissile material actinide content, detecting neutron emission rates and spectra, and measuring fission power levels. They possess: \( 90%+ \) intrinsic efficiency, no gamma sensitivity, permit audible and visible detection of nuclear particles, and lower cost; it is these factors and their simplicity of operation that make TMFDs enticing for the fields of neutron, fission product or alpha detection for nuclear power, homeland security, nonproliferation, and health physics applications. TMFDs operate on the principle that under tensile metastable pressure states, a fluid can be made to cavitate to locally form audible-visible bubbles for neutrons with individual energies in only the picoJoule range which is over ten orders of magnitude less energy than required for bulk boiling. Elastic neutron collisions or ionization by alphas or alpha recoils deposit sufficient energy to generate cavitation nuclei at modest tensile pressures (of about \(-2\,\mathrm{bar}\)). These cavitation events initiated at the femtometer scale, become aubile and visible to the naked eye, making for a physically intuitive detection event. In TMFDs the fluid is tensioned either centrifugally or acoustically. Optimizing a TMFD involves on-demand tailoring of the radiation sensitive region. The sensitive region comprises the volume below a threshold tensile pressure at which cavitated supercritical state fluid molecule nuclei are formed in the presence of ionizing radiation beyond a critical dimension beyond which they may grow to macroscopic levels. To characterize and maximize the sensitive volume (and hence, detection efficiency), a method has been developed to conduct non-intrusive profilimetry of the high frequency oscillating pressure fields - spatially and temporally within the fluid space. Called Laser Induced Cavitation (LIC), the method involves the use of a modest (\( 32\,\mathrm{uJ} \)) pulse energy UV to IR laser photons incident onto the fluid space in a TMFD. The energy absorbed within the fluid via focused joule heating from the laser photon beam, acts as a simulant for localized energy deposition onto atoms of fluids in metastable states via elastic collisions between neutrons (or alphas, etc.). The resultant event can be located in space and time, and thus provide for profiling of the oscillating compressive-tensile pressure field isobars in the TMFD sensitive volume. A parameterization of cavitation thresholds has been made with a ThermoScienceTM \( 337.1\,\mathrm{nm}\) UV nanosecond laser. Initial tests have shown that hand-held continuous beam UV-IR lasers may also be used. An apparatus for actuating the laser beam waist into correct positioning for profiling has been created. The method then provides pointwise data for the presence of below threshold negative pressure levels. Profiling of a Directional Acoustic TMFD (D-ATMFD) has been accomplished using this method – thereby, permitting the qualification and optimization of a one-of-a-kind neutron sensor which not only detects, but also provides for directionality and imaging of a radiation source. A simulation of the negative pressures within this chamber has been developed separately and the results from that simulation are successfully compared to the isobars generated through the LIC method. LIC will have widespread use in future design and optimization of TMFD sensors. With sensitive volume increases that can be derived via optimization of key design features, TMFD efficiency appears possible to tailor and increase and become an even more enticing solution for the fields of special nuclear material actinide monitoring, fast-to-thermal neutron detection, and fission power level monitoring. The full paper will present details pertaining to this novel method for optimization of TMFD sensors for transformational application in the field of nuclear engineering.