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White, Morgan C.

Publications and source records attributed to White, Morgan C..

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Templates of expected measurement uncertainties for prompt fission neutron spectra

In this paper, we provide templates of uncertainty sources expected to appear for three measurement types of prompt fission neutron spectra (PFNS): (1) shape measurements, (2) clean-ratio shape, that is the monitor PFNS are measured in nearly exactly the same surrounding as the PFNS of interest, and (3) indirect ratios, where the detector efficiency is backed out from PFNS monitor measurements. Information is also listed that is needed to faithfully include PFNS in nuclear data evaluations to guide experimenters on how to best report data and metadata for their measurements. These templates also suggest a typical range of pertinent uncertainty values and their correlations in case realistic uncertainties cannot be estimated from information on the measurement itself. The templates were based on a literature review, information found in EXFOR for 252 Cf, 235, 238 U, and 239 Pu PFNS, and enhanced by expertise from experimenters contributing to these PFNS templates.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Evaluations of Energy Spectra of Neutrons Emitted Promptly in Neutron-induced Fission of 235 U and 239 Pu

The energy spectra of neutrons emitted promptly in the neutron-induced fission reactions of 235 U and 239 Pu were re-evaluated for ENDF/B-VIII.0. The evaluations presented here are based on a careful modeling of all relevant physics processes, an extensive analysis of experimental data and a detailed quantification of pertinent uncertainties. Energy spectra of neutrons emitted in up to fourth chance fission are considered and both compound and pre-equilibrium processes are included. Also, important nuclear model parameters, such as the average total kinetic energy of the fission fragments and the multiple chance fission probabilities, and their uncertainties are estimated based on experimental knowledge, model information and evaluated data. In addition to experimental information already available for ENDF/B-VII.1, these new evaluations make use of recently published experimental data either of high precision or spanning a broad incident energy range, information on legacy measurements explaining discrepancies and recently measured data of the average total kinetic energy as a function of incident neutron energy. The resulting evaluated data and covariances agree well with the experimental database used for the evaluation. However, the evaluated spectra are softer than the 235 U and 239 Pu ENDF/B-VII.1, JENDL-4.0 and JEFF-3.2 evaluations for incident neutron energies E inc ≤ 1.5 MeV and E inc ≤ 5 MeV, respectively. For E inc > 5 MeV, the evaluated spectra show structures due to the improved modeling which are not present in ENDF/B-VII.1 and JEFF-3.2 but can be observed in JENDL-4.0 evaluations. Part of these new evaluations were adopted for ENDF/B-VIII.0, while the ENDF/B-VII.1 239 Pu PFNS was retained for E inc ≤ 5 MeV awaiting more conclusive experimental evidence.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

The LANL/LLNL Prompt Fission Neutron Spectrum Program at LANSCE and Approach to Uncertainties

New data on the prompt fission neutron spectra (PFNS) from neutron-induced fission with higher accuracies are needed to resolve discrepancies in the literature and to address gaps in the experimental data. The Chi-Nu project, conducted jointly by LANL and LLNL, aims to measure the shape of the PFNS for fission of {sup 239}Pu induced by neutrons from 0.5 to 20 MeV with accuracies of 3–5% in the outgoing energy from 0.1 to 9 MeV and 15% from 9 to 12 MeV and to provide detailed experimental uncertainties. Neutrons from the WNR/LANSCE neutron source are being used to induce fission in a Parallel-Plate Avalanche Counter (PPAC). Two arrays of neutron detectors are used to cover the energy range of neutrons emitted promptly in the fission process. Challenges for the present experiment include background reduction, use of {sup 239}Pu in a PPAC, and understanding neutron detector response. Achieving the target accuracies requires the understanding of many systematic uncertainties. The status and plans for the future will be presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Listing of Available ACE Data Tables

This document is divided into multiple sections. Section 2 lists some of the more frequently used ENDF/B reaction types that can be used with the FM input card. The remaining sections (described below) contain tables showing the available ACE data tables for various types of data. These ACE data libraries are distributed by the Radiation Safety Information Computational Center (RSICC) with MCNP6.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2014

Testing for the Photon Doppler Broadening Data Sampling Bug in MCNP5/X

MCNP5/X has the capability to perform photon Doppler broadening to incorporate the effect of bound electrons on photon scattering. This effect is generally important if energy spectra or detector responses are desired for photons in the tens to hundreds of keY energy range. In the Fall of 2011, a diligent MCNP user noticed that the sampling routines in MCNP were inconsistent with t he data for sampling which atomic shell t he electron is bound. The data are provided in probability density function (PDF) format, whereas MCNP sampled the data as if they are in a cumulative density function (CDF) format, leading to erroneous results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

The Los Alamos CP2011 ACE Format Charged Particle Transport Library for MCNP6

Twenty-five ACE tables for MCNP6 are given for the various combinations of incident protons, deuterons, tritons, helions (He-3), and alphas onto targets of protons, deuterons, tritons, helions, alphas, Li-6 and Li-7. An appropriate xsdir file is also included. The usual convention has been followed that the lighter charged particle is defined to be the incident particle and the heavier is defined to be the target.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

IER 153: Measure the Fission Neutron Spectrum Shape Using Threshold Activation Detectors - CEDT Phase-1 Preliminary Design

The critical assembly chosen to perform these irradiation experiments is the Planet assembly. The purpose of this experiment is to determine more precisely the fission neutron spectrum. According to recent measurements of neutron cross section data performed in Russia, Hungary, and some other countries, the data suggest that ENDF/B fission neutron spectra has too few neutrons emitted below 1 MeV. In addition, measurements at TA-18 Los Alamos Critical Experiment Facility (LACEF) suggest that the fission spectrum may be too low (between 10-30%) for energies above 10 MeV. These proposed deficiencies in the tails of the fission spectrum may have repercussions in our mission applications related to nuclear energy and global security and need to be resolved. To measure the fission neutron spectrum, threshold activation foils will be used in the center of a highly enriched uranium assembly that will be assembled on the Planet vertical assembly machine.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2014

Advancing the Fundamental Understanding of Fission: 2014 LDRD 20120077DR Review

The following slides were presented as part of the LDRD 20120077DR Progress Appraisal Review held Tuesday, February 4, 2014. This is part of an ongoing project assessment the previous of which was documented in LA-UR-13-21182. This presentation documents the progress made against the goals agreed to as part of the 2013 review.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

Nuclear Data

PowerPoint presentation targeted for educational use. Nuclear data comes from a variety of sources and in many flavors. Understanding where the data you use comes from and what flavor it is can be essential to understand and interpret your results. This talk will discuss the nuclear data pipeline with particular emphasis on providing links to additional resources that can be used to explore the issues you will encounter.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗