Neutron cross section measurements using the ORELA: /sup 40/Ar(n,x), /sup 40/Ca(n,x), /sup 22/Ne(n,. gamma. ), /sup 187/Os(n,n') /sup 186/ /sup 187/ /sup 188/Os(n,nn'. gamma. ), the stable tellurium isotopes (n,. gamma. ), and /sup 205/Tl(n,n. gamma. ). Progress report, September 1, 1982-August 31, 1983
Description: The research performed during this reporting period consisted primarily of (1) measurement, analysis, and publication of the /sup 187/Os(n,n') cross section near 30 keV, (2) measurement and analysis of the /sup 148/ /sup 149/ /sup 159/Sm(n,..gamma..) cross sections, (3) development and publication of a significantly better approximation to the average neutron scattering function as determined by total cross section measurements at the Oak Ridge Electron Linear Accelerator (ORELA), and (4) providing support for the neutron capture facility at ORELA as in the corrections made to the /sup 60/Ni(n,..gamma..) data discussed in a paper included with this report. The major result of the /sup 187/Os(n,n') cross section measurement was the 30 keV average value for that cross section anti sigma/sub nn'/ approx. = 1.5 +- 0.2 b and the implication that the duration of stellar nucleosynthesis, as derived from the /sup 187/Re ..-->.. /sup 187/Os beta decay, is estimated to be (8.9 +- 2.0) x 10/sup 9/ year consistent with an earlier estimate reported by Winters and Macklin. The Sm(n,..gamma..) measurement has already resulted in an estimate of the importance of branching in the s-process in the samarium mass region. We estimate the average neutron density during s-process nucleosynthesis in the vicinity of the solar system to be between less than or equal to (1.1 + 0.7) and (1.1 - 0.6) x 10/sup 8/ neutrons/cm/sup 3/. In the optical model analysis of neutron total cross sections we continue to find that orbital angular momentum dependent well depths are required if the spherical optical model is used to describe the neutron-nucleus interaction at low neutron energies.
Date: September 1, 1983
Creator: Winters, R.R.
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