13 research outputs found
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A Study of 3He detectors for Active Interrogation
3He proportional counters have long been used as neutron detectors for both passive and active detection of Special Nuclear Material (SNM). The optimal configuration of these detectors as far as gas pressure, amount of moderating material, and size are concerned is highly dependent on what neutron signatures are being used to detect and identify SNM. We present here a parametric study of the neutron capture response of 3He detectors, based on Monte Carlo simulations using the MCNPX radiation transport code. The neutron capture response of the detectors has been modeled as a function of time after an incident neutron pulse
Field desorption ion source development for neutron generators
A new approach to deuterium ion sources for deuterium-tritium neutron
generators is being developed. The source is based upon the field desorption of
deuterium from the surfaces of metal tips. Field desorption studies of
microfabricated field emitter tip arrays have been conducted for the first
time. Maximum fields of 30 V/nm have been applied to the array tip surfaces to
date, although achieving fields of 20 V/nm to possibly 25 V/nm is more typical.
Both the desorption of atomic deuterium ions and the gas phase field ionization
of molecular deuterium has been observed at fields of roughly 20 V/nm and 20-30
V/nm, respectively, at room temperature. The desorption of common surface
adsorbates, such as hydrogen, carbon, water, and carbon monoxide is observed at
fields exceeding ~10 V/nm. In vacuo heating of the arrays to temperatures of
the order of 800 C can be effective in removing many of the surface
contaminants observed
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Monte Carlo Simulations of the Response of Shielded SNM to a Pulsed Neutron Source
Active interrogation (AI) has been used as a technique for the detection and identification of Special Nuclear Material (SNM) for both proposed and field-tested systems. Idaho National Laboratory (INL) has been studying this technique for systems ranging from small systems employing portable electronic neutron generators (ENGs) 1 to larger systems employing linear accelerators as high-energy photon sources for assessment of vehicles and cargo2. In order to assess the feasibility of new systems, INL has undertaken a campaign of Monte Carlo simulations of the response of a variety of masses of SNM in multiple shielding configurations to a pulsed neutron source using the MCNPX3 code, with emphasis on the neutron and photon response of the system as a function of time after the initial neutron pulse. We present here some preliminary results from these calculations. 1. D.L. Chichester and E.H. Seabury, “ Using Electronic Neutron Generators in Active Interrogation to Detect Shielded Nuclear Material,” IEEE Transactions on Nuclear Science 56 (2009) pp 441-447. 2. J.L. Jones et al., “Photonuclear-based, nuclear material detection system for cargo containers,” Nuclear Instruments and Methods in Physics Research B 241 (2005) pp 770-776. 3. D.B. Pelowitz, “MCNPXTM User’s Manual version 2.6.0,” Los Alamos National Laboratory Report LA-CP-07-1473 (2008)
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X-ray Measurements of a Thermo Scientific P385 DD Neutron Generator
Idaho National Laboratory is experimenting with electrical neutron generators, as potential replacements for californium-252 radioisotopic neutron sources in its PINS prompt gamma-ray neutron activation analysis (PGNAA) system for the identification of military chemical warfare agents and explosives. In addition to neutron output, we have recently measured the x-ray output of the Thermo Scientific P385 deuterium-deuterium neutron generator. X-rays are a normal byproduct from a neutron generator and depending on their intensity and energy they can interfere with gamma rays from the object under test, increase gamma-spectrometer dead time, and reduce PGNAA system throughput. The P385 x-ray energy spectrum was measured with a high-purity germanium (HPGe) detector, and a broad peak is evident at about 70 keV. To identify the source of the x-rays within the neutron generator assembly, it was scanned by collimated scintillation detectors along its long axis. At the strongest x-ray emission points, the generator also was rotated 60° between measurements. The scans show the primary source of x-ray emission from the P385 neutron generator is an area 60 mm from the neutron production target, in the vicinity of the ion source. Rotation of the neutron generator did not significantly alter the x-ray count rate, and the x-ray emission appears to be axially symmetric within the neutron generator