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Multi-energy neutron detector for counting thermal neutrons, high-energy neutrons, and gamma photons separately

Description: This scintillation detector is composed of two scintillators optically coupled and mounted on a single photomultiplier tube. The first scintillator is a {sup 6}Li-loaded glass that has high efficiency for thermal neutrons, and the second is a liquid scintillator (BC 501) that has fairly high efficiency for higher energy neutrons. The {sup 6}Li glass scintillator emits light with a characteristic time constant of {approximately}60 ns, whereas light emitted in the liquid scintillator by proton recoil from energetic neutrons has a time constant of {approximately}30 ns and the time constant for scintillations occurring from gamma-scattered Compton electrons in the liquid scintillator is {approximately}3.7 ns. These differences in light decay time constants make this detector conducive to electronic separation of pulses generated by the three different radiations. Thermal neutrons, high-energy neutrons, a gamma radiation can be counted separately by operating this detector with a pulse-shape discriminator recently developed. Experimental data demonstrates the proof of principle of this dual scintillator detector for many applications. 4 figs.
Date: January 1, 1989
Creator: Chiles, M.M.; Bauer, M.L. & McElhaney, S.A.
Partner: UNT Libraries Government Documents Department

Upper limits on neutron bursts emitted from Ti pressurized D sub 2 gas cells

Description: In a search for bursts of neutrons from Ti in pressurized D{sub 2} gas cells, no statistically significant deviations from the background were observed for events where five or more neutrons are detected over a ten day experiment, including 103 hours of counting with cells on, and 28 hours counting of various backgrounds. Up to four cells were used including some 60 grams of 662-Ti fillings in a pressurized cylinder with 40-60 atmosphere of D{sub 2} gas. Other Ti samples were used too. The samples were cooled to liquid nitrogen temperature and placed in front of the neutron detector while warming up to room temperature. Seven cooling cycles were used, for each sample. The neutron detector system included 12 liquid scintillator neutron detectors, arranged in a close packed geometry, with six detectors in the upper hemisphere and six in the lower hemisphere. A central detector placed 2 cm from the cells was used, in each hemisphere, as a scatterer for a time of flight coincidence measurement, yielding the total coincidence efficiency of {epsilon}=2{plus minus}1%. The system was also used in singles mode to allow for counting with large efficiency. A neutron event is characterized by measuring its pulse heights, pulse shapes, and in some cases its time of flight. Special attention was given to reducing the background by using massive shielding, cosmic ray veto counters and geometrical arrangement that allowed to distinguish between a background event and expected data events. The so obtained background rate is 100 cph in the singles mode'' and in the upper hemisphere 0.4 cph in the coincidence mode.'' We are currently continuing our data analysis in search for random emission and a detailed study of background effects that may reveal the origin of conflicting results reported on neutron emission from cold fusion.'' 3 refs., 5 ...
Date: October 27, 1989
Creator: Rugari, S. L.; France, R. H., III; Gai, M.; Lund, B. J.; Smolen, S. D.; Zhao, Z. et al.
Partner: UNT Libraries Government Documents Department

The neutrino program at LAMPF

Description: There are two neutrino experiments that this paper discusses: the first experiment is designed to verify the interference between charged and neutral current amplitudes in {nu}{sub e}- e scattering. The experiment is situated at 90{degree} to the beam stop, and detected recoil electrons from neutrino electron scattering. The experiment is sensitive to recoil electrons from {nu}{sub {mu}}, {nu}{sub e}, {bar {nu}}{sub {mu}} but the cross section for {nu}{sub e} - e scattering is the dominant contribution. The magnitude of this cross section depends on the size of the interference term between charged and neutral current scattering, and the value for this term is {minus}1.07 {plus minus} 0.017 {plus minus} 0.11 to be compared to {minus}1.08 from standard electroweak theory with sin{sup 2}{theta}{sub W} = 0.23. The observation of this interference is unique to this experiment. The second experiment, which is presently finishing data analysis after concluding data taking in 1989, is a search for neutrino oscillations of the type {bar {nu}}{sub mu} {yields} {bar {nu}}{sub e}. The experiment was designed to search for the reaction {bar {nu}}{sub e} + p {yields} e{sup +} + n, which has a large relative cross section compared to that on complex nuclei due to the absence of Pauli Suppression of the reaction on free nucleons producing electrons in the energy range 30--50 MeV in contrast to the dominant background from {nu}{sub e} + {sup 12}C {yields} e{sup +} + {sup 12}N, in which the electron energies are limited to 30 MeV from the Q value of the reaction. 5 refs., 13 figs.
Date: January 1, 1989
Creator: White, D.H.
Partner: UNT Libraries Government Documents Department

Detectors for the Superconducting Super Collider, design concepts, and simulation

Description: The physics of compensation calorimetry is reviewed in the light of the need of the Superconducting Super Collider (SSC) detectors. The four major detector types: liquid argon, scintillator, room temperature liquids, and silicon, are analyzed with respect to some of their strengths and weaknesses. Finally, general comments are presented which reflect the reliability of simulation code systems. 29 refs., 20 figs., 6 tabs.
Date: January 1, 1989
Creator: Gabriel, T.A.
Partner: UNT Libraries Government Documents Department

Multi-energy neutron detector for counting thermal neutrons, high-energy neutrons, and gamma photons separately

Description: The need for an improved, compact, wide-energy neutron detector for neutron monitoring and surveillance in nuclear facilities and weapons storage, where a possibility of fission excursion exists, led to development of a single detector that is sensitive to thermal neutrons, high-energy neutrons, and gamma radiation. Previously, separate detectors have been required to count these three different radiations separately. This development is a great advantage when experimental space is limited. 4 figs.
Date: January 1, 1989
Creator: Chiles, M.M. & McElhaney, S.A.
Partner: UNT Libraries Government Documents Department

Development of neutron multiplicity counters for safeguards assay

Description: This paper reports on the development of a new generation of neutron multiplicity counters for assaying impure plutonium. The new counters will be able to obtain three measured parameters from the neutron multiplicity distribution and will be able to determine sample mass, multiplication, and (..cap alpha..,n) reaction rate, making it possible to obtain a more matrix-independent assay of moist or impure materials. This paper describes the existing prototype multiplicity counters and evaluates their performance using assay variance as a figure of merit. The best performance to date is obtained with a high-efficiency, low die-away-time thermal neutron counter with shift-register electronics. 10 refs., 2 figs., 4 tabs.
Date: January 1, 1989
Creator: Ensslin, N.
Partner: UNT Libraries Government Documents Department

Studies of nuclei using radioactive beams. [Space Astronomy Lab. , Univ. of Florida, Gainesville, Florida]

Description: The 12 month period from May 1988 to July 1989 represents the first full year of our 18 month pilot program in nuclear structure research. In this period, research was initiated to develop a capability for radioactive secondary beams at Argonne National Laboratory using the Atlas and the new Fragment Mass Analyzer (FMA), which is currently under construction. Two major new detector facilities are currently in the final stages of design and testing. The Large-Area, Scintillator Telescope (LAST) detector is fully operational and will be shipped to Argonne National Laboratory in August for fit-tests and in-beam calibrations. The first segments of a new sixteen-segment neutron multiplicity detector have been built and tested. The remaining segments are currently being constructed. Research was continued in the areas of (1) Coulomb excitation studies of rare earth and actinide nuclei; (2) In-beam, gamma-ray spectroscopy of nuclei in the mass 100 region, and (3) Advanced detector design. Several journal articles and abstracts were published or submitted for publication in the reporting period, and others are currently in preparation. Three graduate students participated in the program, one from the University of Florida and two from the Royal Institute of Technology, Stockholm, Sweden.
Date: July 1, 1989
Creator: Piercey, R.B.
Partner: UNT Libraries Government Documents Department

Use of liquid scintillation in the appraisal of non-radioactive waste shipments from nuclear facilities

Description: On the Savannah River Site (SRS), non-radioactive or clean waste, is normally assayed to appraise the extent of surface contamination by using a survey meter. Because of the nature of the operations conducted at SRS, the majority of the waste generated is treated as contaminated waste until proven otherwise. Before such waste can be shipped off-site, more rigorous assay must demonstrate compliance with government standards. In particular, it is necessary to appraise the samples with regard to the Department of Transportation (DOT) guideline for a total activity of 2 nanoCuries per gram of waste material. Furthermore, the assay methods must be sufficient to comply with Environmental Protection Agency (EPA) regulations to prevent overcrowding of waste storage locations. Thus, the present work developed efficient liquid scintillation methods for meeting these requirements. The method of phase separation, sample processing, and liquid scintillation analysis proved effective for the analysis of mixed phase, hydrocarbon based waste samples. The described method was readily applicable to a variety of circumstances and was straightforward enough to be used by staff analysts after a minimum of training. The results were obtained in far shorter time (usually less than 2 hours for a single sample) than would be required for other typical methods of analysis. All samples analyzed by the methods presented were found to have activities below the 2 nCi/g DOT guideline for shipment of non-nuclear waste. 5 refs., 3 figs., 1 tab.
Date: January 1, 1989
Creator: McDowell, W.L.
Partner: UNT Libraries Government Documents Department