Paul Hausladen

A ‘Pretty Good’ Measurement for Distinguishing Quantum States

Abstract We address the problem of extracting information from a single quantum system whose state is known to be in one of several possible states. In the generic case, it is notoriously difficult to find the optimal measurement, that is the measurement that provides the most possible information about the systems state. We consider a simple general prescription for a measurement that is typically not optimal but appears to be quite good. It seems to be particularly good when the states to be distinguished are equally likely and almost orthogonal.

Fusion of radioactive Sn-132 with Ni-64

Evaporation residue and fission cross sections of radioactive 132Sn on 64Ni were measured near the Coulomb barrier. A large subbarrier fusion enhancement was observed. Coupled-channel calculations, including inelastic excitation of the projectile and target, and neutron transfer are in good agreement with the measured fusion excitation function. When the change in nuclear size and shift in barrier height are accounted for, there is no extra fusion enhancement in 132Sn+64Ni with respect to stable Sn+64Ni. A systematic comparison of evaporation residue cross sections for the fusion of even 112-124Sn and 132Sn with 64Ni is presented.

Pulsed D-D Neutron Generator Measurements of HEU Oxide Fuel Pins

Pulsed neutron interrogation measurements have been performed on highly enriched uranium (HEU) oxide fuel pins and depleted uranium (DU) metal using a D‐D neutron generator (2×106 neutrons‐s−1) and moderated 3He tubes at the Idaho National Laboratory Power Burst Facility. These measurements demonstrate the ability to distinguish HEU from DU by coincidence counting using a pulsed source. The amount of HEU measured was 8 kg in a sealed 55‐gallon drum compared to 31 kg of DU. Neutron events were counted during and after the pulse with the Nuclear Materials Identification System (NMIS) and used to calculate the neutron coincidence time distributions. Passive measurements were also performed for comparison with the pulsed measurements. This paper presents the neutron coincidence time distribution and Feynman variance results from the measurements.

A Comparison of GEANT4 and DETECT2000 for the simulation of light transport in scintillation detectors

Monte Carlo simulation techniques are powerful tools for investigating the performance of imaging detectors. DETECT2000, a Monte-Carlo package for light transport simulation, has been commonly used to model the optical properties of scintillation detectors and is able to realistically estimate the response of photodetectors. However, DETECT2000 generally runs slowly when complex detector geometries are specified and the lack of visualization tools makes it difficult to accurately define complex geometries. GEANT4 is a simulation toolkit that can also realistically model optical photon transport for scintillation detectors. This paper describes a case study in which GEANT4 was found to be significantly faster both in computing time and, aided by visualization tools, in the user time required to develop the geometry of a scintillation detector. In addition, because the detector geometry can be easily parameterized using GEANT4, it was possible to perform automated searches of large amounts of the solution space for an optimal design. In this work, we compared the results from simulations of a custom-designed scintillation detector obtained using both packages. Both yielded similar flood images and were able to resolve the same number of pixel elements from a segmented light guide with slight differences in the peak-to-valley ratios. A simulation-speed comparison on a common computer using a simplified geometry showed that GEANT4 is about 40% faster than DETECT2000. In this paper we compare simulation results for the initial design with experimental data and describe subsequent simulations that were used to arrive at the optimal design.

Detection of Special Nuclear Material by means of promptly emitted radiation following photonuclear stimulation

Techniques have been developed to exploit abundant prompt emissions from photonuclear reactions for the identification of special nuclear material (SNM). These enhancements are designed to reduce inspections times and delivered dose in systems which have, historically, relied solely on delayed emissions. Experimental evidence is presented for prompt neutron time-of-flight measurements, neutron/photon correlations in multiple detectors, and novel detector development, specifically LaBr3 scintillators with new gating and buffering circuits to identify prompt gamma signatures. Significant and specific signatures indicative of the presence of SNM can be distinguished for the prompt neutron time-of-flight experiment and the neutron/photon correlations in multiple detectors.

Electromagnetic Moments of Radioactive 136Te and the Emergence of Collectivity 2p ⊕ 2n outside of Double-Magic 132Sn

Radioactive ^{136}Te has two valence protons and two valence neutrons outside of the ^{132}Sn double shell closure, providing a simple laboratory for exploring the emergence of collectivity and nucleon-nucleon interactions. Coulomb excitation of ^{136}Te on a titanium target was utilized to determine an extensive set of electromagnetic moments for the three lowest-lying states, including B(E2;0_{1}^{+}→2_{1}^{+}), Q(2_{1}^{+}), and g(2_{1}^{+}). The results indicate that the first-excited state, 2_{1}^{+}, composed of the simple 2p⊕2n system, is prolate deformed, and its wave function is dominated by excited valence neutron configurations, but not to the extent previously suggested. It is demonstrated that extreme sensitivity of g(2_{1}^{+}) to the proton and neutron contributions to the wave function provides unique insight into the nature of emerging collectivity, and g(2_{1}^{+}) was used to differentiate among several state-of-the-art theoretical calculations. Our results are best described by the most recent shell model calculations.

Enhancing pixelated fast-neutron block detector performance using a slotted light guide

The first fast-neutron scintillation block detector has been developed for use in neutron imaging applications. The low-cost, large field of view (FOV) block detector consists of a 10 × 10 array of plastic scintillator crystals, each with a size of approximately 1 × 1 × 5 cm3. To achieve both low cost and fast response time, the detector uses a 2 × 2 array of photomultiplier tubes (2-in. Photonis XP20D0) optically coupled to the array of scintillation crystals through a custom-made light guide. The light guide is segmented in such a way that all scintillator crystals can be resolved, including the edge crystals, to fully utilize the entire FOV of the detector. The thickness and depth of the light-guide segments were also optimized to maintain nearly uniform linearity between the true pixel locations and the reconstructed positions. Flood images from simulation and experiment show that each of the 100 pixels is resolved with an average peak-to-valley ratio for 14 MeV neutrons of 9:1. A mean deviation of 3.3 mm is obtained between the resolved image peaks and the respective true positions demonstrating good linearity. A coincidence measurement performed using a deuterium-tritium neutron generator, in which the neutrons were measured with the block detector and the corresponding alpha particles were measured with another scintillation detector revealed a total time resolution of 1.3 ns full width at half maximum.

Sub-barrier Fusion Enhancement in Neutron-Rich Radioactive 132Sn on 64Ni

Evaporation residue cross sections have been measured using neutron-rich radioactive 132Sn beams incident on a 64Ni target in the vicinity of the Coulomb barrier. This is the first experiment using accelerated 132Sn beams to study nuclear reaction mechanisms. The average beam intensity was 2x 104 particles per second and the smallest cross section measured was less than 5 mb. A large sub-barrier fusion enhancement was observed compared to evaporation residue cross sections for 64Ni on stable even Sn isotopes. The enhancement cannot be accounted for by a simple barrier shift due to the change in nuclear sizes. Coupled-channel calculations including inelastic excitation underpredict the measured cross sections below the barrier. The presence of several neutron transfer channels with large positive Q values suggests that multinucleon transfer may play an important role in enhancing the fusion of 132Sn and 64Ni.

Characterizing the Timing Performance of a Fast 4H-SiC Detector With an

An SPX4 4H-silicon carbide detector consisting of 4 × 4 pixels was developed and studied experimentally. Its pixel size is 400 × 400 μm2. A timing resolution of 117 ± 11 ps full width at half-maximum (FWHM) has been measured for the detection of alphas. With such good timing performance and high granularity, the SiC pixel detector holds great promise as an associated alpha-particle detector for fast neutron imaging.

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Evaporation residue cross sections have been measured with neutron-rich radioactive