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Title: Determining neutron capture cross sections via the surrogate reaction technique

Abstract

Indirect methods play an important role in the determination of nuclear reaction cross sections that are hard to measure directly. In this paper we investigate the feasibility of using the so-called surrogate method to extract neutron capture cross sections for low-energy compound-nuclear reactions in spherical and near-spherical nuclei. We present the surrogate method and develop a statistical nuclear reaction simulation to explore different approaches to utilizing surrogate reaction data. We assess the success of each approach by comparing the extracted cross sections with a predetermined benchmark. In particular, we employ regional systematics of nuclear properties in the 34{<=}Z{<=}46 region to calculate (n,{gamma}) cross sections for a series of Zr isotopes and to simulate a surrogate experiment and the extraction of the desired cross section. We identify one particular approach that may provide very useful estimates of the cross section, and we discuss some of the limitations of the method. General recommendations for future (surrogate) experiments are also given.

Authors:
 [1];  [2]; ; ; ;  [3]
  1. Fundamental Physics, Chalmers University of Technology, SE-41296 Goeteborg (Sweden)
  2. (United States)
  3. Lawrence Livermore National Laboratory, P.O. Box 808, L-414, Livermore, California 94551 (United States)
Publication Date:
OSTI Identifier:
20995336
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevC.75.055807; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; BENCHMARKS; CAPTURE; CROSS SECTIONS; EXTRACTION; NEUTRON REACTIONS; NUCLEAR PROPERTIES; NUCLEI; SIMULATION; SPHERICAL CONFIGURATION; ZIRCONIUM ISOTOPES

Citation Formats

Forssen, C., Lawrence Livermore National Laboratory, P.O. Box 808, L-414, Livermore, California 94551, Dietrich, F. S., Escher, J., Hoffman, R. D., and Kelley, K. Determining neutron capture cross sections via the surrogate reaction technique. United States: N. p., 2007. Web. doi:10.1103/PHYSREVC.75.055807.
Forssen, C., Lawrence Livermore National Laboratory, P.O. Box 808, L-414, Livermore, California 94551, Dietrich, F. S., Escher, J., Hoffman, R. D., & Kelley, K. Determining neutron capture cross sections via the surrogate reaction technique. United States. doi:10.1103/PHYSREVC.75.055807.
Forssen, C., Lawrence Livermore National Laboratory, P.O. Box 808, L-414, Livermore, California 94551, Dietrich, F. S., Escher, J., Hoffman, R. D., and Kelley, K. Tue . "Determining neutron capture cross sections via the surrogate reaction technique". United States. doi:10.1103/PHYSREVC.75.055807.
@article{osti_20995336,
title = {Determining neutron capture cross sections via the surrogate reaction technique},
author = {Forssen, C. and Lawrence Livermore National Laboratory, P.O. Box 808, L-414, Livermore, California 94551 and Dietrich, F. S. and Escher, J. and Hoffman, R. D. and Kelley, K.},
abstractNote = {Indirect methods play an important role in the determination of nuclear reaction cross sections that are hard to measure directly. In this paper we investigate the feasibility of using the so-called surrogate method to extract neutron capture cross sections for low-energy compound-nuclear reactions in spherical and near-spherical nuclei. We present the surrogate method and develop a statistical nuclear reaction simulation to explore different approaches to utilizing surrogate reaction data. We assess the success of each approach by comparing the extracted cross sections with a predetermined benchmark. In particular, we employ regional systematics of nuclear properties in the 34{<=}Z{<=}46 region to calculate (n,{gamma}) cross sections for a series of Zr isotopes and to simulate a surrogate experiment and the extraction of the desired cross section. We identify one particular approach that may provide very useful estimates of the cross section, and we discuss some of the limitations of the method. General recommendations for future (surrogate) experiments are also given.},
doi = {10.1103/PHYSREVC.75.055807},
journal = {Physical Review. C, Nuclear Physics},
number = 5,
volume = 75,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Cross sections for radiative neutron capture on unstable nuclei at low energies are difficult to calculate with high precision, and can be impossible to measure directly. It is therefore important to explore alternative methods. The prospects of one such method, the Surrogate Nuclear Reaction Technique, is currently being investigated at Lawrence Livermore National Laboratory. The purpose of this paper is to outline the strategy for combining the results from a surrogate experiment with theoretical calculations in order to extract the desired cross section.
  • Neutron-induced reaction cross sections are sometimes difficult to measure due to target or beam limitations. For two-step reactions proceeding through an equilibrated intermediate state, an alternate ''surrogate reaction'' technique can be applicable, and is currently undergoing investigation at LLNL. Measured decay probabilities for the intermediate nucleus formed in a light-ion reaction can be combined with optical-model calculations for the formation of the same intermediate nucleus via the neutron-induced reaction. The result is an estimation for overall (n,{gamma}/n/2n) cross sections. As a benchmark, the reaction {sup 92}Zr({alpha},{alpha}'), surrogate, for n+{sup 91}Zr, was studied at the A.W. Wright Nuclear Structure Laboratory atmore » Yale. Particles were detected in the silicon telescope STARS (Silicon Telescope Array for Reaction Studies) and {gamma}-ray energies measured with germanium clover detectors from the YRAST (Yale Rochester Array for SpecTroscopy) ball. The experiment and preliminary observations will be discussed.« less
  • An indirect method for determining cross sections of reactions proceeding through a compound nucleus is presented. Some applications of the Surrogate nuclear reaction approach are considered and challenges that need to be addressed are outlined.
  • The surrogate reaction method is a powerful tool to infer neutron-induced data of short-lived nuclei. After a short overview of the experimental techniques employed in the present surrogate experiments, we will concentrate on a recent measurement to determine neutron-induced fission cross sections for the actinides {sup 242,243}Cm and {sup 241}Am. The latest direct neutron-induced measurement for the {sup 243}Cm fission cross section is questioned by our results, since there are differences of more than 60% in the 0.7 to 7 MeV neutron energy range. Our experimental set-up has also enabled us to measure for the first time the fission fragmentmore » ''pseudo-mass'' distributions of {sup 243,244,245}Cm and {sup 242}Am compound nuclei in the excitation energy range from a few MeV to about 25 MeV.« less
  • The 92Mo(n, ) cross section was obtained using both the absolute surrogate approach and surrogate ratio method (SRM), relative to the 94 Mo(n, ) cross section, in an equivalent neutron energy range of 80 to 890 keV. Excited 93Mo and 95Mo nuclei were populated using the 92Mo(d, p) and 94Mo(d, p) reactions, respectively. Both discrete and statistical tagging approaches were employed to identify the -decay channel and were examined in terms of their sensitivity to the initial angular momentum population distribution. The absolute surrogate 92 Mo(n, ) cross sections disagree with evaluated neutron capture cross section data by as muchmore » as a factor of 4, whereas the results obtained using the SRM trend more favorably with the evaluated result. Experimental results suggest that discrete and statistical tagging approaches may sample different contributions of the cascade for near-spherical nuclei. This work uses the surrogate method in the determination of neutron capture cross sections on spherical and quasispherical nuclei in the mass-90 region and provides a possible pathway to extend the SRM to a broader mass range.« less