11 research outputs found
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Estimated and observed performance of a neutron SNM portal monitor for vehicles
In July 1987, we completed our development of a neutron-detection- based vehicle SNM portal monitor with a conference paper presented at the annual meeting. The paper described the neutron vehicle portal (NVP), described source-response measurements made with it at Los Alamos, and gave our estimate of the monitor`s potential performance. Later, in December 1988, we had a chance to do a performance test with the monitor in a plant environment. This paper discusses how our original performance estimate should vary in different circumstances, and it uses the information to make a comparison between the monitor`s estimated and actual performance during the 1988 performance testing
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Neutron-chamber detectors and applications
Detector applications in Nuclear Safeguards and Waste Management have included measuring neutrons from fission and (alpha,n) reactions with well-moderated neutron proportional counters, often embedded in a slab of polyethylene. Other less-moderated geometries are useful for detecting both bare and moderated fission-source neutrons with good efficiency. The neutron chamber is an undermoderated detector design comprising a large, hollow, polyethylene-walled chamber containing one or more proportional counters. Neutron-chamber detectors are relatively inexpensive; can have large apertures, usually through a thin chamber wall; and offer very good detection efficiency per dollar. Neutron-chamber detectors have also been used for monitoring vehicles and for assaying large crates of transuranic waste. Our Monte Carlo calculations for a new application (monitoring low-density waste for concealed plutonium) illustrate the advantages of the hollow-chamber design for detecting moderated fission sources. 9 refs., 6 figs., 2 tabs
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Application of Wald's sequential probability ratio test to nuclear materials control
We have replaced traditional analysis methods for nuclear material control monitoring with hypothesis testing, specifically with Wald's sequential-probability-ratio test. Our evaluation of Walds'd method, applied in both vehicle and pedestrian SNM monitors, is by Monte Carlo calculation to determine the alarm probability and average monitoring times of the monitors. The vehicle monitor with Wald's test has a much shorter monitoring delay than with traditional methods, without serious compensating changes in operating characteristics. The pedestrian monitor with Wald's method also has advantages over traditional single-interval test, in that the Wald method duplicates the advantages of a moving-average technique. We verified the Monte Carlo calculations for the pedestrian monitor by means of a special program for the monitor's microprocessor controller. The observations of false-alarm probability and average monitoring time for over 500,000 tests verified the Monte Carlo results