Speaker
Mariko Segawa
(Research Center for Nuclear Physics, Osaka University, Japan)
Description
187Re-187Os pair is known as the most promising nuclear cosmochronometer with
considerable potential. This is because 187Re beta decays with the half-life of
42.3+/- 1.3 Gyr,187Re is produced only by the rapid neutron capture process
nucleosynthesis, and both 186Os and 188Os are produced only by the slow neutron
capture process nucleosynthesis.
However, there remains a non-trivial problem related to an excited neutron capture
reaction of 187Os at a stellar temperature. Namely, 187Os is produced and depleted
by the slow process nucleosynthesis. Hence, it is necessary to obtain both the
production and depletion rates of 187Os to derive the excess abundance of 187Os,
which can be attributable to beta-decay from 187Re. While, 187Os is depleted not
only by its ground state neutron capture reaction but also by an excited state
neutron capture reaction of 187Os. Note that 187Os has a low-lying excited state at
Ex = 10 keV, and the state could be significantly populated at a stellar
temperature kT ~ 30 keV [1. Hence, it is necessary to know the excited state
neutron capture cross section for 187Os* to estimate the depletion rate of 187Os
[2].
In order to deduce neutron capture cross section for 187Os*, it has been suggested
to measure the neutron inelastic scattering cross section for 187Os off the ground
state of 187Os to its excited 10 keV state. The measurement of the inelastic
scattering cross section of the ground state in 189Os has been also suggested to
derive the neutron capture cross section for the first excited state of 187Os*,
since the spin-parities of the ground state in 189Os is the same as that of the
first excited in 187Os.
In the present study, we have measured the neutron capture reaction cross sections
for 186Os, 187Os and 189Os accurately and neutron inelastic scattering reaction
cross-section for 187Os in the neutron energy range from 10 to 100 keV. The
measurements of the neutron capture reactions have been carried out by detecting a
prompt γ-ray from the reaction by means of an anti-Compton NaI(Tl) spectrometer.
The (n, n’) reaction cross section for 187Os has been measured by means of 6Li-
glass scintillation detectors. Theses results will be discussed.
[1] D. D. Clayton, Astrophys. J. 139, 637 (1964)
[2] W. A. Fowler, Revs. Mod. Phys, Vol. 56, No2. Part1. April 1984.
Author
Mariko Segawa
(Research Center for Nuclear Physics, Osaka University, Japan)
Co-authors
Mr
Akira Nakayosi
(Research Center for Nuclear Physics, Osaka University, Japan)
Mr
Jun Nishiyama
(Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Japan)
Prof.
Masayuki Igashira
(Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Japan)
Dr
Tatushi Shima
(Research Center for Nuclear Physics, Osaka University, Japan)
Mr
Tomohiro Masaki
(Physics department, Kobe University, Japan)
Prof.
Yasuki Nagai
(Research Center for Nuclear Physics, Osaka University, Japan)
Mr
Yasuyuki Temma
(Research Center for Nuclear Physics, Osaka University, Japan)
Mr
takeshi Ohta
(Research Center for Nuclear Physics, Osaka University, Japan)
