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The Gamma Array Simulation Toolkit (GAST) is a multi-physics software stack comprised of Geant4, MATLAB, and experimentally measured photomultiplier tube (PMT) impulse response waveforms that is used to model and inform the end-to-end performance of radiation detector systems. In order to validate the ability of GAST to predict the impulse response of a modeled detector configuration operated in current mode, experimental measurements using the Nevada National Security Site Transformational Diagnostics and Imaging 2 MeV endpoint energy electron linear accelerator (linac) with a tungsten target were performed. Seven different detector configurations consisting of unique combinations of scintillator material, size, reflectivity conditions, presence or absence of light guide, and PMT were evaluated. The resultant impulse response of each detector configuration was recorded and compared to a GAST simulation that emulated the respective linac experiment conditions. The comparison of the experimental and simulated detector impulse responses indicated that GAST can reliably predict detector impulse responses.

A proof-of-concept investigation of a rapid detection system for shielded high-Z material using a petawatt laser-based muon source is presented. Unlike cosmic-ray muons, a laser-induced muon beam has unique characteristics that can be exploited for use in a rapid detection system. These characteristics include: (1) a near-point source of muons, (2) well-characterized muon energies, (3) directionality of the beam, and (4) well-defined timing of the muons. A detector system is being developed that combines multiple muon detection technologies to characterize an active muon source. This detection system and the associated data acquisition and analysis techniques are designed to search for deflections of the muon beam as it passes through high-Z materials. Additionally, the ability of the system to differentiate muons from the expected secondary particles, such as high-energy gammas and electrons, is being explored. The detector system's ability to differentiate muons from other particles, muon angular distribution, and measured muon flux will be discussed.

This work will describe the proof-of-concept research applying muon tomography technologies based on drift tube systems to create images using near-horizontal trajectory muons. To date, the majority of imaging studies using cosmic-ray muons have used near-vertical trajectory muons. This work compares imaging results using near-vertical trajectory muons with results using near-horizontal trajectory muons. The muon flux is much lower for the near-horizontal trajectory muons, requiring longer imaging times, but the average muon energy is higher, so the horizontal results are expected to better differentiate high-Z materials. The muon tracking system is easily configurable and can be oriented to capture near-vertical trajectory or near-horizontal trajectory cosmic-ray muons. The software can track each muon passing through the system, and generate 3D images of the scene. The experimental design and preliminary results will be presented, including the comparisons of detection efficiency, image resolution, and integration times.

Soft cosmic ray tomography has been shown to successfully discriminate materials with various density levels due to their ability to deeply penetrate matter, allowing sensitivity to atomic number, radiation length and density. Because the multiple muon scattering signal from high Z-materials is very strong, the technology is well suited to the detection of the illicit transportation of special and radiololgical nuclear materials. In addition, a recent detection technique based on measuring the lower energy particles that do not traverse the material (range radiography), allows to discriminate low and medium Z-materials. We have demonstrated it first using Monte Carlo simulations. More recently, using a Mini-Muon Tracker developed at Los Alamos National Laboratory, we performed various experiments to try out the radiation length technology. This paper presents the results from real experiments and evaluates the likelihood that soft cosmic ray tomography may be applied to detect high-explosives.

We discuss an innovative low-dose approach for detecting shielded strategic nuclear materials (SNM) based on measuring the energy-loss of energetic protons penetrating an object.