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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

Pyrochemical neutron multiplicity counter design

Description: Pyrochemical process materials are difficult to measure using conventional neutron counting methods because of significant self- multiplication and variable ({alpha},n) reaction rates. Multiplicity counters measure the first three moments of the neutron multiplicity distribution and thus make it possible to determine sample mass even when multiplication and ({alpha},n) rate are unknown. A new multiplicity counter suitable for inplant measurement of pyrochemical process materials has been designed using Monte Carlo simulations. The goals were to produce a counter that has high neutron detection efficiency, low die-away time, a flat spatial efficiency profile, and is insensitive to the neutron energy spectrum. Monte Carlo calculations were performed for several prototype models consisting of four rings of 71-cm active length {sup 3}He tubes in a polyethylene body. The cadmium-lined sample well is 25 cm in diameter to accommodate a wide variety of inplant sample containers. The counter can be free-standing or in-line without mechanical modification. The calculations were performed to determine the above design criteria for several configurations of tube spacing, cadmium liners, and sample height. Calculations were also performed for distributed sample sources to understand the integrated effects of variable neutron spectra on the counter. 5 refs., 8 figs., 1 tab.
Date: January 1, 1990
Creator: Langner, D.G.; Ensslin, N. & Krick, M.S.
Partner: UNT Libraries Government Documents Department

Test and evaluation of the dual-range coincidence counter at the Savannah River Plant

Description: This report describes the test and evaluation of a Los Alamos National Laboratory-designed dual-range neutron coincidence counter at the Savannah River Plant Separations Area. A variety of incoming plutonium metal and oxide shipments were assayed with the counter. Assay accuracies were 2% l sigma for pure metal, about 10% l sigma for impure metal, and 3% l sigma for oxide that was analyzed on a batch-by-batch basis.
Date: April 1, 1981
Creator: Ensslin, N.; Gibbs, A.; Denard, C. & Deason, P.
Partner: UNT Libraries Government Documents Department

Experimental comparison of the active well coincidence counter with the random driver

Description: A direct comparison has been made between the IAEA Active Well Coincidence Counter (AWCC) and the LASL Random Driver at CMB-8. The comparison included an experimental evaluation of precision, counting rate, accuracy, penetrability, stability, and the effect of sample inhomogeneity. Samples used in the evaluation included highly enriched U/sub 3/O/sub 8/, U/sub 3/O/sub 8/ mixed with graphite, highly enriched uranium metal discs, and depleted uranium metal. These materials are typical of the samples of interest to the IAEA inspectors. It is concluded that the two instruments had very similar performance characteristics with the Random Driver giving better penetrability and the AWCC giving better stability.
Date: January 1, 1979
Creator: Menlove, H.O.; Ensslin, N. & Sampson, T.E.
Partner: UNT Libraries Government Documents Department

Experimental comparison of the active well coincidence counter with the random driver

Description: A direct comparison has been made between the IAEA Active Well Coincidence Counter (AWCC) and the CMB-8 Random Driver. The comparison included an experimental evaluation of precision, counting rate, accuracy, penetrability, stability, and the effect of sample inhomogeneity. Samples used in the evaluation included highly enriched U/sub 3/O/sub 8/, U/sub 3/O/sub 8/ mixed withe qgraphite, highly enriched uranium metal discs, and depleted uranium metal. These materials are typical of the samples of interest to the IAEA inspectors. It was concluded that the two instruments had very similar performance characteristics with the Random Driver giving better penetrability and the AWCC giving better stability.
Date: June 1, 1979
Creator: Menlove, H.O.; Ensslin, N. & Sampson, T.E.
Partner: UNT Libraries Government Documents Department

Prototype fast neutron counter for the assay of impure plutonium

Description: A fast coincident neutron counter using liquid scintillators and gamma-ray/neutron pulse-shape discrimination has been constructed for the analysis of plutonium samples with unknown self-multiplication and (..cap alpha..,n) production. The counter was used to measure plutonium-bearing materials that cover a range of masses and (..cap alpha..,n) reaction rates of importance to the safeguards community. Measured values of the /sup 240/Pu effective mass differed, on average, from their declared values by 0.4% for plutonium oxides and by -2.2% for metal and MgO-loaded samples. Poorer results were obtained for materials with large (..cap alpha..,n) reaction rates and low self-multiplication such as plutonium ash and plutonium fluoride.
Date: January 1, 1987
Creator: Wachter, J.R.; Adams, E.L. & Ensslin, N.
Partner: UNT Libraries Government Documents Department

Calorimetric assay of minor actinides

Description: This paper reviews the principles of calorimetric assay and evaluates its potential application to the minor actinides (U-232-4, Am-241, Am- 243, Cm-245, Np-237). We conclude that calorimetry and high- resolution gamma-ray isotopic analysis can be used for the assay of minor actinides by adapting existing methodologies for Pu/Am-241 mixtures. In some cases, mixtures of special nuclear materials and minor actinides may require the development of new methodologies that involve a combination of destructive and nondestructive assay techniques.
Date: December 31, 1996
Creator: Rudy, C.; Bracken, D.; Cremers, T.; Foster, L.A. & Ensslin, N.
Partner: UNT Libraries Government Documents Department

Application of neutron multiplicity counting to waste assay

Description: This paper describes the use of a new figure of merit code that calculates both bias and precision for coincidence and multiplicity counting, and determines the optimum regions for each in waste assay applications. A tunable multiplicity approach is developed that uses a combination of coincidence and multiplicity counting to minimize the total assay error. An example is shown where multiplicity analysis is used to solve for mass, alpha, and multiplication and tunable multiplicity is shown to work well. The approach provides a method for selecting coincidence, multiplicity, or tunable multiplicity counting to give the best assay with the lowest total error over a broad spectrum of assay conditions.
Date: April 1, 1997
Creator: Pickrell, M.M.; Ensslin, N. & Sharpe, T.J.
Partner: UNT Libraries Government Documents Department

Uranium cross-calibration measurements using an active well coincidence counter

Description: This paper reports on the cross-calibration of an Active Well Coincidence Counter for use in the Materials Protection, Control, and Accountability Graduate Program at the Moscow State Engineering Physics Institute (MEPhI). The cross-calibration procedure and its application to nuclear material types available at MEPhI for instructional purposes is described. Cross-calibration results at Los Alamos and initial applications at MEPhI are summarized. Based on the results so far, the authors conclude that the cross-calibration approach seems useful, with good prospects for potential applications at other Russian and US Dept. of Energy facilities.
Date: December 31, 1998
Creator: Nikolaev, V.; Prochine, I.; Smirnov, V.; Ensslin, N. & Carillo, L.
Partner: UNT Libraries Government Documents Department

Analysis of active neutron multiplicity data for Y-12 skull oxide samples

Description: Previous work on active neutron multiplicity measurements and analyses is summarized. New active multiplicity measurements are described for samples of Y-12 skull oxide using an Active Well Coincidence Counter and MSR4 multiplicity electronics. Neutron multiplication values for the samples were determined from triples/doubles ratios. Neutron multiplication values were also obtained from Monte Carlo calculations using the MCNP code and the results compared with the experimental values. A calibration curve of AmLi source-sample coupling vs neutron multiplication was determined and used for active multiplicity assay of the skull oxides. The results are compared with those obtained from assay with the conventional calibration-curve technique, where the doubles rate is calibrated vs the {sup 235}U mass. The coupling-multiplication relationship determined for the skull oxides is compared with that determined earlier for pure high-enrichment uranium metal and pure uranium oxide. Conclusions are drawn about the application of active multiplicity techniques to uranium assay. Additional active multiplicity measurements and calculations are recommended.
Date: September 1996
Creator: Krick, M. S.; Ensslin, N.; Ceo, R. N. & May, P. K.
Partner: UNT Libraries Government Documents Department

The state-of-the-art of thermal neutron multiplicity counting

Description: Neutron multiplicity counting is a maturing technology. It has been implemented at many facilities to address the increasing need to rapidly measure impure plutonium bearing materials. At Hanford Site and Rocky Flats Environmental Technology Site, multiplicity counting has also been used with excellent results by the International Atomic Energy Agency to verify excess plutonium inventories now under their safeguards. Neutron multiplicity counting as currently implemented, however, will not address all forms of impure plutonium. Materials containing large concentrations of matrix elements like fluorine and beryllium cannot be assayed successfully without extremely long count times. Assays of compact plutonium metals and oxides having a large uranium concentration relative to their plutonium content tend to bias low because of a breakdown in the theoretical model now used to translate the measured multiplicity distributions to plutonium mass. In this paper, the authors will discuss the most recent efforts to extend the range of materials that can be measured successfully with thermal neutron multiplicity counting and a use of multiplicity counting to detect sample changes during long-term storage.
Date: November 1, 1997
Creator: Langner, D.G.; Krick, M.S.; Stewart, J.E. & Ensslin, N.
Partner: UNT Libraries Government Documents Department

Expected precision for neutron multiplicity assay using higher order moments

Description: This paper reports on the development of a new Figure of Merit code that can calculate the expected precision in neutron multiplicity assay using higher order moments. The code is used to provide a first look at the quadruple coincidence count rate and its expected precision. The results are good enough to warrant further study of potential applications of quadruple (quad) coincidences for large multiplying plutonium items. Also, the new code makes it possible to estimate the multiplicity assay precision if only randomly-triggered moments are used. This approach is described briefly, along with the current status of the investigation.
Date: November 1, 1997
Creator: Ensslin, N.; Gavron, A. & Harker, W.C.
Partner: UNT Libraries Government Documents Department

Expected precision of neutron multiplicity measurements of waste drums

Description: DOE facilities are beginning to apply passive neutron multiplicity counting techniques to the assay of plutonium scrap and residues. There is also considerable interest in applying this new measurement technique to 208-liter waste drums. The additional information available from multiplicity counting could flag the presence of shielding materials or improve assay accuracy by correcting for matrix effects such as ({alpha},n) induced fission or detector efficiency variations. The potential for multiplicity analysis of waste drums, and the importance of better detector design, can be estimated by calculating the expected assay precision using a Figure of Merit code for assay variance. This paper reports results obtained as a function of waste drum content and detector characteristics. We find that multiplicity analysis of waste drums is feasible if a high-efficiency neutron counter is used. However, results are significantly poorer if the multiplicity analysis must be used to solve for detection efficiency.
Date: August 1, 1995
Creator: Ensslin, N.; Krick, M.S. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Some target assay uncertainties for passive neutron coincidence counting

Description: This paper provides some target assay uncertainties for passive neutron coincidence counting of plutonium metal, oxide, mixed oxide, and scrap and waste. The target values are based in part on past user experience and in part on the estimated results from new coincidence counting techniques that are under development. The paper summarizes assay error sources and the new coincidence techniques, and recommends the technique that is likely to yield the lowest assay uncertainty for a given material type. These target assay uncertainties are intended to be useful for NDA instrument selection and assay variance propagation studies for both new and existing facilities. 14 refs., 3 tabs.
Date: January 1, 1990
Creator: Ensslin, N.; Langner, D.G.; Menlove, H.O.; Miller, M.C. & Russo, P.A.
Partner: UNT Libraries Government Documents Department

Active neutron multiplicity counting of bulk uranium

Description: This paper describes a new nondestructive assay technique being developed to assay bulk uranium containing kilogram quantities of {sup 235}U. The new technique uses neutron multiplicity analysis of data collected with a coincidence counter outfitted with AmLi neutron sources. We have calculated the expected neutron multiplicity count rate and assay precision for this technique and will report on its expected performance as a function of detector design characteristics, {sup 235 }U sample mass, AmLi source strength, and source-to-sample coupling. 11 refs., 2 figs., 2 tabs.
Date: January 1, 1991
Creator: Ensslin, N.; Krick, M.S.; Langner, D.G. & Miller, M.C.
Partner: UNT Libraries Government Documents Department

Confirmatory measurements of UF/sub 6/ using the neutron self-interrogation method

Description: A passive neutron counting method has been developed for measurement of the /sup 235/U mass in Model 5A cylinders of UF/sub 6/. The unique neutronic properties of UF/sub 6/ containing highly enriched uranium (HEU) permit /sup 235/U assay using only passive neutron counting. The sample effectively assays itself by self-interrogation. Shipped from enrichment plants and received at fuel fabrication and conversion facilities, 5A UF/sub 6/ cylinders hold up to approx.17 kg of /sup 235/U each. Field measurements at the Portsmouth Gaseous Diffusion Plant (GDP) showed an average assay accuracy of 6.8% (1sigma) for 44 cylinders with enrichments from 6 to 98% and with a range of fill heights. Further measurements on 38 cylinders containing 97%-enriched material yielded an accuracy of 2.8% (1sigma). Typical counting times for these measurements were less than 5 min. An in-plant instrument for receipts confirmation measurements of 5A UF/sub 6/ cylinders has been developed for the Savannah River Plant. The Receipts Assay Monitor (RAM) is currently being tested and calibrated. It is designed to confirm declared fissile mass in all incoming 5A cylinders containing HEU in the form of UF/sub 6/. One of the computer-controlled features is a removable cadmium liner for the sample cavity. The liner allows a sample fill-height correction, which significantly improves assay accuracy.
Date: January 1, 1985
Creator: Stewart, J.E.; Ensslin, N.; Menlove, H.O.; Cowder, L.R. & Polk, P.J.
Partner: UNT Libraries Government Documents Department

Uncertainty analysis for determination of plutonium mass by neutron multiplicity counting

Description: This paper describes an uncertainty analysis carried out in association with the use of neutron multiplicity counting to collect data, and assign a total plutonium mass. During 1997, the Los Alamos Safeguards Science and Technology Group carried out careful calorimetry and neutron multiplicity certification measurements on two {sup 239}Pu metal foils used as reference standards at the Idaho National Environmental Engineering Laboratory (INEEL). The foils were measured using a five ring neutron multiplicity counter designed for neutron measurement control activities. This multiplicity counter is well characterized, and the detector parameters were reaffirmed before the measurements were made using several well-known Los Alamos standards. Then, the {sup 240}Pu effective mass of the foils was determined directly from the multiplicity analysis without a conventional calibration curve based on representative standards. Finally, the {sup 240}Pu effective mass fraction and the total plutonium mass was calculated using gamma ray isotopics. Errors from statistical data collection, background subtraction, cosmic ray interaction, dead time corrections, calibration constants, sample geometry, and sample position were carefully estimated and propagated. The authors describe these error sources, the final calculated relative error in the foil assay, and the comparison with very accurate calorimetry measurements.
Date: December 31, 1998
Creator: Carrillo, L.A.; Ensslin, N.; Krick, M.S.; Langner, D.G. & Rudy, C.R.
Partner: UNT Libraries Government Documents Department

Results from the first Waste and Residue NDA Measurements School

Description: The first Waste and Residue Nondestructive Assay (NDA) Measurements School was given at Los Alamos on June 3--7, 1996. This school is a new part of the DOE Office of Safeguards and Security, Safeguards Training Program, with additional instructor support from the National Transuranic Waste Program, Idaho National Engineering Laboratory, Oak Ridge National Laboratory, Portsmouth Gaseous Diffusion Plant, Westinghouse savannah River Company, Pajarito Scientific Corporation, and Canberra Industries. The school was attended by 22 safeguards and waste measurement personnel from DOE facilities, and included lectures on waste characterization requirements, the WIPP Performance Demonstration Program, waste and residue NDA techniques, and a workshop discussion on waste assay issues. Hands-on training modules with 55-gallon-drum waste assay systems were held using a Segmented Gamma-ray Scanner, a Tomographic Gamma-ray Scanner, two Add-a-Source Waste-Drum Assay Systems, a Californium Shuffler, and a Differential Die-away system that included Combined Thermal-Epithermal Neutron Interrogation (CTEN). This paper will describe the new school and report on the measurement results obtained during the school with the above-mentioned waste-drum assay systems.
Date: September 1, 1996
Creator: Ensslin, N.; Abhold, M.; Coop, K.; Prettyman, T.; Rinard, P.; Sheppard, G. et al.
Partner: UNT Libraries Government Documents Department

Inventory verification measurements using neutron multiplicity counting

Description: This paper describes a series of neutron multiplicity measurements of large plutonium samples at the Los Alamos Plutonium Facility. The measurements were corrected for bias caused by neutron energy spectrum shifts and nonuniform multiplication, and are compared with calorimetry/isotopics. The results show that multiplicity counting can increase measurement throughput and yield good verification results for some inventory categories. The authors provide recommendations on the future application of the technique to inventory verification.
Date: December 31, 1998
Creator: Ensslin, N.; Foster, L.A.; Harker, W.C.; Krick, M.S. & Langner, D.G.
Partner: UNT Libraries Government Documents Department

A state-of-the-art passive gamma-ray assay system

Description: We report details of the development of a high-accuracy, high-precision system for the non-destructive assay of /sup 235/U in solution. The system can measure samples with concentrations ranging from 0.0001 to 500 g /sup 235/U/l using 200-ml samples at low concentrations, 30-ml samples at high concentrations, and 1000-s measurement times. The accuracy and precision goals of 0.1% were essentially attained for concentrations above 100 g/l. This at-line system, designed for a production plant environment, represents a significant improvement in the state of the art.
Date: January 1, 1987
Creator: Sampson, T.E.; Parker, J.L.; Cowder, L.R.; Kern, E.A.; Garcia, D.L. & Ensslin, N.
Partner: UNT Libraries Government Documents Department

Neutron multiplicity counter development

Description: We have designed and built two multiplicity counters to test the usefulness of multiplicity counting for the safeguards assay of plutonium-bearing materials. The first prototype counter has been characterized and a variety of plutonium-bearing materials have been measured with it. Assays accurate to {approximately}0.7% have been obtained for both pure and impure plutonium oxide samples in reasonable measurement times. Assays accurate to {approximately}5% have been obtained for metal samples. A second multiplicity counter has been designed using experience gained from the first as well as Monte Carlo simulations. The second counter was designed to be more suitable for in-plant measurement of pyrochemical process materials. This paper presents the results of characterization studies of the two instruments. 10 refs., 9 figs., 2 tabs.
Date: January 1, 1991
Creator: Langner, D.G.; Krick, M.S.; Ensslin, N.; Bosler, G.E. & Dytlewski, N.
Partner: UNT Libraries Government Documents Department

Conceptual design for a receiving station for the nondestructive assay of PuO/sub 2/ at the fuels and materials examination facility

Description: We propose a conceptual design for a receiving station for input accountability measurements on PuO/sub 2/ received at the Fuels and Materials Examination Facility at the Hanford Engineering Development Laboratory. Nondestructive assay techniques are proposed, including neutron coincidence counting, calorimetry, and isotopic determination by gamma-ray spectroscopy, in a versatile data acquisition system to perform input accountability measurements with precisions better than 1% at throughputs of up to 2 M.T./yr of PuO/sub 2/.
Date: November 1, 1981
Creator: Sampson, T.E.; Speir, L.G.; Ensslin, N.; Hsue, S.T.; Johnson, S.S.; Bourret, S. et al.
Partner: UNT Libraries Government Documents Department