The restart of the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory and consequent refurbishment of the Fuel Motion Monitoring System (FMMS), or Hodoscope, offers the opportunity to upgrade the detector system used for neutron imaging. Silicon photomultipliers (SiPMs) are a viable option for updating the Hodoscope to yield improved fuel monitoring capability. The Hodoscope uses ZnS(Ag) proton recoil scintillators (PRS) that provide good gamma-ray suppression and discrimination. Previous work showed that the Hamamatsu S13360-6075CS SiPM offers the best neutron detection and gamma-ray discrimination capability with the ZnS PRS. This work optimizes a SiPM-based detector and develops a PRS prototype for testing. Specifically, possible overvoltages for use are determined by confirming steady operation over extended measurement times. In addition, various SiPM-circuit implementations are tested to optimize the detector according to desired properties, and ultimately a PRS prototype is developed with modifiable components for versatile testing. Measurements of the neutron detection efficiency and gamma-ray rejection efficiency of SiPM-based PRS detectors and a reference PMT-based detector are also carried out. Neutron detection efficiency ranges between 1–2%, and detected gamma-ray rejection efficiency is on the order of 10−7. Use of a low-pass filter only or a low-pass filter and 50-ω shunt resistor is recommended for the SiPM-based detector, and both configurations demonstrate improved performance over the PMT-based detector.

This document serves as both an FY2103 End-of-Year and End-of-Project report on efforts that resulted in the design of a prototype fast neutron multiplicity counter leveraged upon the findings of previous project efforts. The prototype design includes 32 liquid scintillator detectors with cubic volumes 7.62 cm in dimension configured into 4 stacked rings of 8 detectors. Detector signal collection for the system is handled with a pair of Struck Innovative Systeme 16-channel digitizers controlled by in-house developed software with built-in multiplicity analysis algorithms. Initial testing and familiarization of the currently obtained prototype components is underway, however full prototype construction is required for further optimization. Monte Carlo models of the prototype system were performed to estimate die-away and efficiency values. Analysis of these models resulted in the development of a software package capable of determining the effects of nearest-neighbor rejection methods for elimination of detector cross talk. A parameter study was performed using previously developed analytical methods for the estimation of assay mass variance for use as a figure-of-merit for system performance. A software package was developed to automate these calculations and ensure accuracy. The results of the parameter study show that the prototype fast neutron multiplicity counter design is very nearly optimized under the restraints of the parameter space.

Digital pulse shape analysis (dPSA) has been used with a Cuttler-Shalev type (3)He ionization chamber to measure the fast-neutron spectra of a deuterium-deuterium electronic neutron generator, a bare (252)Cf spontaneous fission neutron source, and of the transmitted fast neutron spectra of a (252)Cf source attenuated by water, graphite, liquid nitrogen, and magnesium. Rise-time dPSA has been employed using the common approach for analyzing n +(3)He→(1)H+(3)H ionization events and improved to account for wall-effect and pile-up events, increasing the fidelity of these measurements. Simulations have been performed of the different experimental arrangements and compared with the measurements, demonstrating general agreement between the dPSA-processed fast-neutron spectra and predictions. The fast-neutron resonance features of the attenuation cross sections of the attenuating materials are clearly visible within the resolution limits of the electronics used for the measurements, and the potential applications of high-resolution fast-neutron spectrometry for nuclear nonproliferation and safeguards measurements are discussed.

Single neutron and gamma charge pulses were captured using a fast ADC. These data were used to populate simulated 5-µs active interrogation flash events. Analysis of these simulations revealed that long pulse tail accumulation during the flash leads to an unpredictable charge background for several microseconds after the flash. The existence of this changing background will make retrieving prompt neutron information immediately after the flash problematic. The tail accumulation is accentuated for every pulse in the flash, making the time just after the last pulse in the flash the worst possible time to measure prompt neutron data. Obtaining prompt neutron data during the flash—particularly near the beginning of the flash, where background tail accumulation is minimal—is feasible if shielding is used to control the count rates, but requires fast gamma-neutron pulse shape discrimination. A means of accentuating the pulse shape difference between neutron and gamma data is given, along with a means of compensating for the long pulse components in the dominant gamma pulses.

Active interrogation with pulsed bremsstrahlung beams can saturate detectors and produce high count rates of overlapping pulses in the prompt region (< 1 mu s) after the interrogating pulse. We describe a method to eliminate saturation by modifying the photomultiplier voltage divider and by gating intermediate pairs of dynodes and the anode. To process the high count rate of overlapping pulses, we convert the output current pulses to charge-pulse steps that can be digitally processed more easily and rapidly in real time. We discuss the application to LaBr3, liquid, and plastic scintillators and present some preliminary data.

Idaho National Laboratory, along with Idaho State University’s Idaho Accelerator Center and Los Alamos National Laboratory, is developing an electron accelerator-based, photonuclear inspection technology, called the Pulsed Photonuclear Assessment (PPA) system, for the detection of nuclear material concealed within air-, rail-, and, primarily, maritime-cargo transportation containers. This report summarizes the advances and progress of the system’s development in 2005. The contents of this report include an overview of the prototype inspection system, selected Receiver-Operator-Characteristic curves for system detection performance characterization, a description of the approach used to integrate the three major detection components of the PPA inspection system, highlights of the gray-scale density mapping technique being used for significant shield material detection, and higher electron beam energy detection results to support an evaluation for an optimal interrogating beam energy. This project is supported by the Department of Homeland Security Office of Research and Development and, more recently, the Domestic Nuclear Detection Office.

The Client Behavior System was used to evaluate the therapeutic process with 27 sexually abused girls enrolled in psychoeducationally based individual counseling. Based on ratings collected for the session in which the topic of sexual abuse was formally introduced, it was found that girls were more likely to provide abuse-related answers in response to questions pertaining to child sexual abuse, regardless of whether they were treated by a male or female counselor. These findings provide reason to reconsider previous recommendations that sexually abused girls are best treated by female counselors.