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Evaluation of NaI(TL) and plastic scintillators for use in remote, unattended, and portal monitoring

Description: The authors have evaluated and compared some of the relevant operating characteristics of NaI and plastic scintillators for use in various safeguards monitoring applications. These include a sensitivity analysis of the two scintillators to various radiation fields and scintillator response as affected by environmental temperature. A comparison of experiment and modeling via the Monte Carlo N-Particle (MCNP) code has been performed to validate the calculational techniques. This then enables complex detector situations to be simulated with increased confidence.
Date: December 31, 1998
Creator: Staples, P.; Audia, J.; Bai, Y.; Briggs, M.; Halbig, J.K. & Ianakiev, K.D.
Partner: UNT Libraries Government Documents Department

High-energy characterization of two large-volume multi-element CdZnTe detectors

Description: We present results of experiments to characterize two large-volume, multi-element CdZnTe detectors for gamma-ray spectroscopy at high energy. The first detector consisted of four 1.5 cm x 1.5 cm x 0.75 cm coplanar grid detectors. The measurements for the four-element design were performed with various configurations. The second detector consisted of eight 1 cm x 1 cm x 0.5 cm coplanar grid detectors arranged in a 2 x 2 x 2 array. The high-energy gamma-ray sources included {sup 60}Co(1332), {sup 228}Th(2614), {sup 244}Cm/{sup 13}C(6129), and Fe(n,{gamma})(7645). The front-end electronics consisted of eight spectroscopy-grade preamplifiers/shapers/pulse stretchers, built on circuit boards close to the arrays. For the four-element measurements the shapers/pulse stretchers were replaced with commercial amplifiers. An eight-channel data acquisition system with list mode output was used to record gamma-ray events for each detector element in each array. The list mode data were analyzed to produce coincidence and singles spectra and efficiencies for the various sources. The Compton continuum and the escape peaks are suppressed in the coincidence spectra relative to the singles spectra. We compare these spectra and efficiencies at high energy to results at lower energies and to Monte Carlo predictions.
Date: January 1, 2001
Creator: Moss, C. E. (Calvin E.); Browne, M. C. (Michael C.); Ianakiev, K. D. & Prettyman, T. H. (Thomas H.)
Partner: UNT Libraries Government Documents Department

CdZnTe gamma ray spectrometer for orbital planetary missions

Description: Knowledge of surface elemental composition is needed to understand the formation and evolution of planetary bodies. Gamma rays and neutrons produced by the interaction of galactic cosmic rays with surface materials can be detected from orbit and analyzed to determine composition. Using gamma ray spectroscopy, major rock forming elements such as Fe, Ti, Al, Si, Mg, and Ca can be detected. The accuracy of elemental abundance is limited by the resolution of the spectrometer. For space missions, scintillators such as BGO and NaI(Tl) have been used for gamma ray spectroscopy. New planetary science missions are being planned to explore Mars, Mercury, the asteroid belt, and the outer planets. Significant improvements in the pulse height resolution relative to scintillation detectors can be made using CdZnTe, a new room temperature detector technology. For an orbiting instrument, a CdZnTe detector at least 16 cm{sup 3} in size is needed. A 4 x 4 array of 1-cm{sup 3} coplanar grid detectors can be manufactured that meets requirements for resolution and counting efficiency. The array will shielded from gamma rays produced in the spacecraft by a BGO detector. By improving pulse height resolution by a factor of three at low energy, the CdZnTe detector will be able to make accurate measurements of elements that are currently difficult to measure using scintillation technology. The BGO shield will provide adequate suppression of gamma rays originating in the spacecraft, enabling the gamma ray spectrometer to be mounted on the deck of a spacecraft. To test this concept, we are constructing a flight qualified, prototype CdZnTe detector array. The prototype consists of a 2 x 2 array of coplanar grid detectors. We will present the results of mechanical and electronic testing and radiation damage tests, and the performance of the array for gamma ray spectroscopy.
Date: January 1, 2001
Creator: Feldman, W. C. (William C.); Storms, S. A. (Steven A.); Fuller, K. R. (Kenneth R.); Moss, C. E. (Calvin E.); Browne, M. C. (Michael C.); Lawrence, David J. (David Jeffery), et al.
Partner: UNT Libraries Government Documents Department

An approach to multiplicity counting for a versatile new sensor for plutonium assay with a very short die-away time, and independent measurements of neutrons and gamma rays

Description: A unique detector design incorporating a {sup 6}Li-based capture medium, ZnS scintillator, and wavelength shifting optical fibers is the basis of a new neutron coincidence counter for measurements of plutonium in highly-impure residues. The sensor elements have a high efficiency for detecting neutrons and exhibit excellent gamma-ray discrimination based on pulse-shape analysis. The short die-away time of the counter that is based on these detector elements allows coincidence-gate settings shorter than 10 microseconds. This qualifies the technology for measurements of materials with high yields of uncorrelated neutrons from {sup 241}Am(alpha,n) reactions. The characteristics of the new neutron counter will be illustrated with test data from measurements of plutonium, {sup 252}Cf, and gamma-ray sources. The integrated electronics design of the new detector also permits the simultaneous but independent measurement of both neutrons and gamma rays. Recent test results that illustrate some unique applications of the sensor's versatility will also be presented.
Date: January 1, 2002
Creator: Belian, A. B. (Anthony B.); Browne, M. C. (Michael C.); Clay, W. A. (William A.); Geist, W. H. (William H.); Nguyen, H.; Ianakiev, K. D. et al.
Partner: UNT Libraries Government Documents Department

A versatile new sensor for Pu assay and independent measurements of neutrons and gamma rays

Description: A new well counter has been developed at Los Alamos National Laboratory that integrates the neutron capture medium (6LiF) and scintillator (ZnS) into a thin screen, which is coupled to wavelength shifting fiber-optic ribbon. A foursided prototype well counter has been built. It has a short neutron die-away time (t = 5.8 {micro}s), which increases its sensitivity to measurements of 240Pu by neutron coincidence counting. The neutron detection efficiency for this counter is 20%.
Date: January 1, 2002
Creator: Belian, A. P. (Anthony P.); Browne, M. C. (Michael C.); Clay, W. A. (William A.); Geist, W. H. (William H.); Nguyen, H.; Ianakiev, K. D. et al.
Partner: UNT Libraries Government Documents Department