Polyethylene-reflected plutonium metal sphere : subcritical neutron and gamma measurements.

Mattingly, John

doi:10.2172/974870

Cited by 35 publications

(32 citation statements)

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“…The dead time of the nPod detector 3 He tubes could also account for the over-prediction that was observed in the plutonium sphere results. If the dead time was increased, then it would result in the distribution shifting in the correct direction.…”

Section: Dead Timementioning

confidence: 99%

“…Figure 3 shows an image of the MCNPXPoliMi model geometry. The detector output file produced by MCNPX-PoliMi lists detailed information about each event that occurred in each of the 15 3 He detectors within the nPod. With this information it is possible to calculate the response of the nPod.…”

Section: Simulationmentioning

confidence: 99%

“…With this information it is possible to calculate the response of the nPod. A FORTRAN post-processing code was developed to perform this calculation, which requires taking into account the dead time of the individual 3 He detectors, an effect that cannot be simulated in MCNPX-PoliMi. The post-processor sorts all of the capture events on 3 He that correlate to events detected by the nPod.…”

Section: Simulationmentioning

confidence: 99%

“…The source was measured with a portable neutron multiplicity counter (the nPod) designed and constructed by LANL. The nPod uses fifteen 15-inch-long, 1-inch-diameter, 10 atm, 3 He proportional counters embedded in an HDPE moderator block 16.6 inches tall, 16-30/32 inches wide, and 4 inches deep. The moderator is wrapped in 1/32-inch-thick cadmium to minimize the nPod's sensitivity to neutrons reflected by the floor and walls.…”

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confidence: 99%

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Simulations of neutron multiplicity measurements with MCNP-PoliMi.

Mattingly¹,

Pozzi

Clarke

et al. 2010

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Issued b y S andia Na tional Laboratories, o perated for the Un ited States Department of En ergy b y Sandia Corporation. NOTICE:This report was prepared as an account of work sponsored by an agency of the United States G overnment. Neither th e Un ited S tates Government, n or a ny a gency th ereof, n or a ny o f their employees, n or a ny o f th eir contractors, subcontractors, or th eir employees, make any warranty, e xpress o r i mplied, o r a ssume a ny l egal li ability o r responsibility for th e a ccuracy, completeness, or us efulness of a ny i nformation, a pparatus, pr oduct, or process di sclosed, o r represent that its use would not infringe privately o wned rights. Reference herein to any specific commercial p roduct, p rocess, o r se rvice b y trad e n ame, trad emark, m anufacturer, o r o therwise, does not necessarily c onstitute or im ply it s e ndorsement, re commendation, o r f avoring b y th e United States Government, any agency thereof, or any of their contractors or subcontractors. The views and o pinions expressed herein do not n ecessarily state or reflect those o f th e United States Government, any agency thereof, or any of their contractors. AbstractThe heightened focus on nuclear safeguards and accountability has increased the need to develop and verify simulation tools for modeling these applications. The ability to accurately simulate safeguards techniques, such as neutron multiplicity counting, aids in the design and development of future systems. This work focuses on validating the ability of the Monte Carlo code MCNPX-PoliMi to reproduce measured neutron multiplicity results for a highly multiplicative sample. The benchmark experiment for this validation consists of a 4.5-kg sphere of plutonium metal that was moderated by various thicknesses of polyethylene. The detector system was the nPod, which contains a bank of 15 3He detectors. Simulations of the experiments were compared to the actual measurements and several sources of potential bias in the simulation were evaluated. The analysis included the effects of detector dead time, sourcedetector distance, density, and adjustments made to the value of ν-bar in the data libraries. Based on this analysis it was observed that a 1.14% decrease in the evaluated value of ν-bar for 239Pu in the ENDF-VII library substantially improved the accuracy of the simulation. 4

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Section: Dead Timementioning

confidence: 99%

Section: Simulationmentioning

confidence: 99%

Section: Simulationmentioning

confidence: 99%

mentioning

confidence: 99%

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Simulations of neutron multiplicity measurements with MCNP-PoliMi.

Mattingly¹,

Pozzi

Clarke

et al. 2010

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“…The response is the total neutron leakage from a spherical system. The system is the polyethylenereflected BeRP ball [7,8] described in Table 1. The density of the polyethylene is perturbed.…”

Section: Neutron Reflector Polyethylene Densitymentioning

confidence: 99%

Using the MCNP Taylor series perturbation feature (efficiently) for shielding problems

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2017

EPJ Web Conf.

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Abstract. The Taylor series or differential operator perturbation method, implemented in MCNP and invoked using the PERT card, can be used for efficient parameter studies in shielding problems. This paper shows how only two PERT cards are needed to generate an entire parameter study, including statistical uncertainty estimates (an additional three PERT cards can be used to give exact statistical uncertainties). One realistic example problem involves a detailed helium-3 neutron detector model and its efficiency as a function of the density of its high-density polyethylene moderator. The MCNP differential operator perturbation capability is extremely accurate for this problem. A second problem involves the density of the polyethylene reflector of the BeRP ball and is an example of first-order sensitivity analysis using the PERT capability. A third problem is an analytic verification of the PERT capability.

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