NUCLEATION AND DETECTION IN TENSION METASTABLE FLUIDS (2015)

Neutron detection and spectroscopic techniques using state-of-the-art systems is covered. A novel approach using conventional (e.g., LiI, He-3, BF3) detectors coupled with Monte-Carlo code simulations to develop spectroscopy information was developed (in lieu of present-day tedious methods involving data acquisition using a multi-sized set of Bonner spheres). Focus of this thesis work was on developing neutron spectroscopy and multiplicity technology using the underlying science of tensioned metastable fluid detectors (TMFDs) in which neutron radiation interactions with atoms of TMFD fluids cause onset of cavitation bubbles. There are many applications and areas of science that would benefit from an increased knowledge about the relationship between the conditions and states of a metastable liquid and the appearance of cavitation bubbles due to ionizing radiation. One specific area that benefits significantly is the application of such knowledge to TMFDs, which already boast demonstrated and impressive advantages over traditional detection systems with sensitivity over 8 orders of magnitude in neutron energy, 90% intrinsic neutron detection efficiency (in optimal geometry), complete insensitivity to gamma radiation when operating in a neutron detection mode, ∼100% sensitivity to dissolved alpha emitters and fission decays, directional information and potentially orders of magnitude reduced cost. Despite the significant advantages as a versatile particle detector, the response matrix for TMFD detectors (pertaining to unfolding for deriving spectroscopic information of external neutron sources) had remained unknown. This is fundamentally because of the incomplete knowledge of nucleation theory for fluids in states of tension metastability. In this thesis, various aspects of the prevailing nucleation theory are evaluated and updated including aspects pertaining to ion transport; the wall velocity assumptions; the density of the vapor; the effect of motion on the critical radius; the effect of non-condensible gas; the surface tension; the initial conditions; the Bjerknes force; and the dynamics of cavity formation. A number of empirical, and semi-mechanistic methods were attempted in parallel with 3-D monte-carlo particle-by-particle interaction and theoretical models of energy transfers with TMFD fluid atoms so that the two could support each other. A versatile, relatively easy to use and accurate technique named here as “Single Atom Spectroscopy” was developed to allow the response matrix for any class of a TMFD fluid that included hydrogen and only one other higher Z element (e.g., C). Response matrices developed using the spectrum of Cf-252 and Pu-Be isotope sources were then successfully tested for their predictive capability for 2.5 MeV and 14 MeV monoenergetic neutron sources. This method shows much promise in rapidly allowing the development of a fielded system with sound theoretical underpinnings. Neural networking was also pursued as an option for empirical modeling database based predictions, but the required database used to train the network for deriving meaningful results was found to be impractically large. The photon detection characteristics of the system were analyzed in order to show that the system is sufficiently gamma blind for field use (and to justify the use of IR radiation for the sensing of cavitation in the bulb). Calculations supported by experimental data show that any practical nuclear power reactor fission generated gamma flux (even from freshly discharged spent nuclear fuel), is orders of magnitude too small to cause cavitation. Finally, the same tools that were developed to allow spectroscopy in the CTMFD system were leveraged to allow multiplicity information to be discerned as well. The technical specifications for a TMFD-based multiplicity determining system using a range of different schemes are discussed.