Yttrium ENDF/B-VII Data from Theory and LANSCE/GEANIE Measurements and Covariances Estimated using Bayesian and Monte-Carlo Methods
- Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
- CEA DAM Ile-de-France, Departement de Physique Theorique et Appliquee, Service de Physique Nucleaire, BP 12, 91680 Bruyeres-le-Chatel (France)
- Dept. of Physics, University of Guelph, Guelph, Ontario, N1G 2W1 (Canada)
- Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States)
Yttrium plays an important role as a radiochemical dosimetry detector for determining high energy 14 MeV neutron fluences, through measurement of (n,2n) activation products. The total (n,2n) cross section is known rather well from extensive activation measurements on the stable {sup 89}Y isotope, and from a previous activation measurement on the unstable {sup 88}Y ground state. However, until now the branching ratios to the ground state and excited isomers in {sup 88}Y via the {sup 89}Y (n,2n) reaction were not well known, and furthermore, uncertainty estimates were not available for these cross sections and branching ratios. This paper describes how gamma-ray transitions between states in (n,2n) and (n,n') reactions measured using the GEANIE detector at Los Alamos' LANSCE facility, together with theory predictions using the GNASH code, enable us to determine these quantities for the ENDF/B-VII evaluation. A previous measurement by Dietrich, at Livermore, provided important complementary information to the GEANIE analysis. We describe an uncertainty quantification analysis that uses the GNASH-KALMAN approach to evaluate cross sections for the {sup 89}Y (n,2n) population of the {sup 88}Y ground state and two meta-stable isomers (m1 and m2), along with their uncertainties. Our new results agree with Arthur's historic Los Alamos evaluated cross sections within a few percent below 15 MeV (with larger differences above 15 MeV). The (n,2n) cross sections to the {sup 88}Y ground state and m1, m2 isomers impact the average {sup 88}Y(n,2n){sup 87}Y cross section at leading-order; we determine this 14.1 MeV average cross section {sup 88}Y(n,2n){sup 87}Y = 1107 mb ({+-} 4%), which agrees with the value obtained from Arthur's evaluation to 0.7%. An alternative method to predict cross sections, uncertainties, and covariance data, is described that uses the European TALYS reaction modeling code and a Backward-Forward Monte-Carlo uncertainty quantification technique. This approach uses a microscopic optical model, together with Hauser-Feshbach and preequilibrium reaction mechanisms, and the underlying model parameters and their uncertainties and correlations are determined through a Monte-Carlo filtering method based on comparisons with measured cross section data. We compare the results obtained using this approach with the GNASH-KALMAN method. The evaluated cross sections are rather similar in the two approaches. We show how the uncertainty information, as embodied in the resulting covariance matrices, is also qualitatively similar in both approaches.
- OSTI ID:
- 21028330
- Journal Information:
- Nuclear Data Sheets, Vol. 108, Issue 12; Other Information: DOI: 10.1016/j.nds.2007.11.004; PII: S0090-3752(07)00100-7; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0090-3752
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BRANCHING RATIO
CROSS SECTIONS
EVALUATED DATA
GAMMA RADIATION
GROUND STATES
ISOMERS
MEV RANGE 10-100
MONTE CARLO METHOD
NEUTRON REACTIONS
NUCLEAR DATA COLLECTIONS
OPTICAL MODELS
RADIOCHEMISTRY
REACTION KINETICS
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