The generalized linear Boltzmann equation is a recently developed framework based on non-classical transport theory for modeling the expected value of particle flux in an arbitrary stochastic medium. Provided with a non-classical cross-section for a given statistical description of a medium, any transport problem in that medium may be solved. Previous work has only considered one-dimensional media without finite boundary conditions and discrete binary mixtures of materials. In this work the solution approach for the GLBE in multidimensional media with finite boundaries is outlined. The discrete ordinates method with an implicit discretization of the pathlength variable is used to leverage sweeping methods for the transport operator. In addition, several convenient approximations for non-classical cross-sections are introduced. The solution approach is verified against random realizations of a Gaussian process medium in a square enclosure.
Particle accelerators play a key role in a broad set of defense and security applications, including war-fighter and asset protection, cargo inspection, nonproliferation, materials characterization, and stockpile stewardship. Accelerators can replace the high activity radioactive sources that pose a security threat to developing a radiological dispersal device, and, can be used to produce isotopes for medical, industrial, and research purposes. An overview of current and emerging accelerator technologies relevant to addressing the needs of defense and security is presented.
Basics of ratio-based porosity response of four proposed generator-based neutron tools are studied using Monte Carlo simulation of the radiation transport to examine, at a fundamental level, their potential to replace Americium-Beryllium (Am-Be) sources. Accelerator-based sources considered include a dense plasma focus (DPF) alpha-particle accelerator, Deuterium-Tritium (D-T), Deuterium-Deuterium (DD), and Deuterium–Lithium (D-Li7) neutron generators. The DPF alpha-particle accelerator utilizes the (-Be) reaction generating a neutron spectrum that is nearly identical to that from an Am-Be source. D-T and D-D neutron generators utilize compact linear accelerators and emit, respectively, 14.1 and 2.45 MeV neutrons. The D-Li7 neutron spectrum resembles the Am-Be spectrum at lower energies, and has a neutron peak at 13.3 MeV. In the present work, simple spherical geometry models that do not include tool and borehole are first used to explore the basic physics. A tool-borehole-formation configuration is then utilized to briefly explore key observations from the simpler model. In both models, the responses at various detectors are examined to understand the behavior of the ratios constructed. Sensitivity to formation conditions such as low porosity and presence of thermal absorbers, and operational conditions, such as tool standoff are examined. The state of neutron generator technology is also discussed in terms of neutron yield, target properties, power demands, etc., which would be important considerations in actually utilizing generators in nuclear logging tools.
An associated particle neutron generator is described that employs a negative ion source to produce high neutron flux from a small source size. Negative ions produced in an rf-driven plasma source are extracted through a small aperture to form a beam which bombards a positively biased, high voltage target electrode. Electrons co-extracted with the negative ions are removed by a permanent magnet electron filter. The use of negative ions enables high neutron output (100% atomic ion beam), high quality imaging (small neutron source size), and reliable operation (no high voltage breakdowns). The neutron generator can operate in either pulsed or continuous-wave (cw) mode and has been demonstrated to produce 106 D-D n/s (equivalent to ~108 D-T n/s) from a 1 mm-diameter neutron source size to facilitate high fidelity associated particle imaging.