Nuclear reaction measurements for applied and basic nuclear science
Principle Investigator: Jolie Cizewski, Rutgers University
In environments such as nuclear reactors or nuclear devices, the materials, including the actinide fuel and short-lived products following nuclear fission, are exposed to an intense flux of neutrons. Understanding the performance of these devices has often been assessed by measuring the yields of long-lived daughters of prompt fission fragments or other products from neutron-induced reactions. However, the neutron-induced destruction or creation reactions on the parent fragments are very difficult to measure. Direct measurements of neutron-induced reactions, such as neutron capture, on radioactive isotopes, are limited to nuclei with half lives greater than hundreds of days. It is also difficult to predict neutron capture cross sections, in particular on neutron-rich nuclei where direct, rather than compound, capture may dominate. To inform neutron-capture reactions on radioactive nuclei, as well as to study the properties of neutron-rich nuclei, a program, supported in part by the DOE/NNSA Stewardship Science Academic Alliance, has been developed to study neutron transfer reactions with radioactive ion beams.Beams of fission fragments from the HRIBF interact with CD2 targets to induce (d,p) neutron transfer reactions. For light fission fragments, reaction protons are detected in arrays of silicon strip detectors at angles >100o in the laboratory. For heavier fission fragments, the back angle detector array was supplemented by position-sensitive silicon-strip detectors near 90o in the laboratory. Critical to the success of these measurements are new position-sensitive detectors implemented in the Oak Ridge Rutgers University Barrel Array (ORRUBA) [Pai07].
In neutron-rich nuclei with relatively low neutron separation energies (~3.5 MeV), neutron capture tends to be dominated by direct processes, which sensitively depend upon the single-neutron properties, measured directly in (d,p) reactions. However, in nuclei closer to the line of stability, with high (~7 MeV) neutron separation energies, neutron capture proceeds through a compound nucleus and the decay follows a statistical process. Recent studies [Hat08] have determined the constraints under which the (d,pγ) reaction can be used as a surrogate for (n,γ). The techniques to measure the (d,p) reaction in inverse kinematics in coincidence with reaction gamma rays have been developed [Ciz07]. A first measurement of a (d,pγ) reaction of importance to understanding the performance of a nuclear device, using beams of stable 75As, was performed in July 2008 [Pet08]. If this study is successful in reproducing the known 75As(n,γ) cross sections [NNDC], future experiments would involve radioactive ion beams of 73,74As.
Recent (d,p) reaction measurements include studies with 130,132Sn beams [Jon07], fission fragments that have been used in nuclear device modeling, such as the Foster and Arthur report [Fos82]. Future studies would include other fission products important for nuclear device modeling as well as light nuclei, such as 10Be and 26Al, products of neutron-induced reactions.
Additional information on this effort can be found at http://www.orau.org/stewardship/.
References
[Ciz07] J.A. Cizewski et al., Nucl. Instrum. and Meth. B261, 938 (2007).[Fos82] D.G. Foster and E.D. Arthur, LA-9168, February 1982 (unpublished, Los Alamos National Laboratory).
[Hat08] R. Hatarik et al., Compound-Nuclear Reactions and Related Topics, AIP Conference Proceedings 1005, 105 (2008), and to be published.
[Jon07] K.L. Jones et al., Acta. Phys. Pol. B38, 1205 (2007) and to be published.
[NNDC] http://www.nndc.bnl.gov/
[Pai07] S.D. Pain et al., Nucl. Instrum. Meth. Phys. Res. B261, 1122 (2007).
[Pet08] W.A. Peters et al., Bull. Am. Phys. Soc., October 2008.
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This file last modified Thursday January 08, 2009