Neutron Cross Section Measurements Using the ORELA: exp 40 Ar(N,X), exp 40 Ca(N,X), exp 22 Ne(N, gamma ), exp 187 Os(N,N') exp 186 exp 187 exp 188 Os(N,Nn' gamma ), the Stable Tellurium Isotopes (N, gamma ), and exp 205 Tl(N,N gam

摘要

The research performed during this reporting period consisted primarily of (1) measurement, analysis, and publication of the exp 187 Os(n,n') cross section near 30 keV, (2) measurement and analysis of the exp 148 exp 149 exp 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 exp 60 Ni(n, gamma ) data discussed in a paper included with this report. The major result of the exp 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 exp 187 Re implies exp 187 Os beta decay, is estimated to be (8.9 +- 2.0) x 10 exp 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 exp 8 neutrons/cm exp 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. (ERA citation 08:056655)