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Journal Articles

$$E1$$ and $$E2$$ cross sections of the $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction at $$E_{rm{eff}}$$ $$sim$$ 1.2 MeV using pulsed $$alpha$$ beams

Makii, Hiroyuki; Ueda, Hitoshi*; Temma, Yasuyuki*; Nagai, Yasuki*; Shima, Tatsushi*; Fujimoto, Shinya*; Segawa, Mariko; Mishima, Kenji*; Nishiyama, Jun*; Igashira, Masayuki*

AIP Conference Proceedings 1269, p.283 - 288, 2010/10

https://doi.org/10.1063/1.3485149
 Times Cited Count：0 Percentile：0.02(Astronomy & Astrophysics)

The $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction cross section plays an important role in stellar evolution at the stage of helium-burning. However, the cross section at low energy still has a large uncertainty mainly due to the poor determination of the ratio of $$E2$$ cross section to $$E1$$ one. Hence, we have installed new system to make a precise measurement of the cross section. In this experiment, we used the high efficiency anti-Compton NaI(Tl) spectrometers with a large S/N ratio, an intense pulsed $$alpha$$ beams, and the monitoring system of target thickness. With use of the system we succeeded in removing a background due to neutron and could clearly detect the $$gamma$$-ray from the $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction with high statistics. We determined the $$E1$$ and $$E2$$ cross section down to $$E_{rm{eff}} sim $$ 1.2 MeV, and thus obtained results are compared to recent theoretical calculations.

Journal Articles

Neutron capture and inelastic scattering cross sections for $$^{186}$$Os, $$^{187}$$Os, and $$^{189}$$Os and the Re-Os chronology

Segawa, Mariko; Nagai, Yasuki*; Masaki, Tomohiro*; Temma, Yasuyuki*; Shima, Tatsushi*; Mishima, Kenji*; Igashira, Masayuki*; Goriely, S.*; Koning, A.*; Hilaire, S.*

AIP Conference Proceedings 1016, p.448 - 450, 2008/05

https://doi.org/10.1063/1.2943622

$$^{187}$$Re-$$^{187}$$Os pair is known as the most promising nuclear cosmochronometer with considerable potential. However, there remains non-trivial problems related to an excited neutron capture reaction of $$^{187}$$Os at a stellar temperature. Firstly, $$^{187}$$Os is produced and depleted by the slow process nucleosynthesis. Hence, it is necessary to obtain both the production and depletion rates of $$^{187}$$Os. Secondly, $$^{187}$$Os is depleted not only by its ground state neutron capture reaction but also by an excited state neutron capture reaction of $$^{187}$$Os in a stellar temperature. In the present study, we have measured the neutron capture reaction cross sections for $$^{186}$$Os, $$^{187}$$Os and $$^{189}$$Os accurately and neutron inelastic scattering reaction cross section for $$^{187}$$Os off the ground state of $$^{187}$$Os to its 9.75 keV first excited state in the neutron energy range from 10 to 100 keV.

Journal Articles

Neutron capture cross sections of $$^{186}$$Os, $$^{187}$$Os, and $$^{189}$$Os for the Re-Os chronology

Segawa, Mariko; Masaki, Tomohiro*; Nagai, Yasuki*; Temma, Yasuyuki*; Shima, Tatsushi*; Mishima, Kenji*; Igashira, Masayuki*; Goriely, S.*; Koning, A.*; Hilaire, S.*

Physical Review C, 76(2), p.022802_1 - 022802_5, 2007/08

https://doi.org/10.1103/PhysRevC.76.022802
 Times Cited Count：17 Percentile：72.66(Physics, Nuclear)

Discrete as well as continuum $$gamma$$-ray energy spectra from the neutron capture by $$^{186}$$Os, $$^{187}$$Os, and $$^{189}$$Os have been taken for the first time at 5 $$leq$$ En $$leq$$ 90 keV by an anti-Compton NaI(Tl) spectrometer. The detection of a weak discrete $$gamma$$-ray, about 0.5% of total $$gamma$$-ray strength, demonstrates the high sensitivity of the present measurement. The energy spectra enabled us to accurately determine the reaction cross sections with a small systematic uncertainty. Based on the new cross sections, we re-estimate on the basis of a careful reaction cross section calculation the correction factor F$$_{sigma}$$ for the neutron capture on the 9.75-keV first excited state in $$^{187}$$Os as a function of stellar temperature, as required to derive the age of the Galaxy within the Re-Os chronology.

Oral presentation

Neutron induced reaction and Re/Os cosmochronometer, 3

Segawa, Mariko; Nagai, Yasuki*; Masaki, Tomohiro*; Shima, Tatsushi*; Makii, Hiroyuki; Mishima, Kenji*; Ueda, Hitoshi*; Temma, Yasuyuki*; Igashira, Masayuki*; Osaki, Toshiro*; et al.

no journal, , 

no abstracts in English

Oral presentation

Nuclear astrophysics study with pulsed neutrons

Segawa, Mariko; Nagai, Yasuki*; Masaki, Tomohiro*; Temma, Yasuyuki*; Shima, Tatsushi*; Mishima, Kenji*; Igashira, Masayuki*; Goriely, S.*; Koning, A.*; Hilaire, S.*

no journal, , 

The $$^{187}$$Re nucleus is known to be a good chronometer to derive the stellar duration of the r-process nuceosyntheis and deduce the age of universe. However, there are several problems inherent to this chronometer. In order to solve these problems, one must know both the production and depletion rates (via the excited state as well as the ground state) of $$^{187}$$Os and inelastic scattering cross section off the ground state (J$$^{pi}$$= 1/2$$^{-}$$) of $$^{187}$$Os to its excited 10 keV state (J$$^{pi}$$= 3/2$$^{-}$$) are needed. Hence, in the present study we aimed to accurately measure the neutron capture cross sections of $$^{186}$$Os, $$^{187}$$Os and $$^{189}$$Os, and the inelastic scattering cross section for $$^{187}$$Os for neutrons between 10 and 90 keV by developing a new experimental method.

Oral presentation

Neutron induced reaction and Re/Os chronometer

Segawa, Mariko; Nagai, Yasuki*; Masaki, Tomohiro*; Temma, Yasuyuki*; Shima, Tatsushi*; Makii, Hiroyuki*; Mishima, Kenji*; Ueda, Hitoshi*; Nakayoshi, Akira*; Ota, Takeshi*; et al.

no journal, , 

$$^{187}$$Re-$$^{187}$$Os pair is known as the most promising nuclear cosmochronometer with considerable potential. However, there remains non-trivial problems related to an excited neutron capture reaction of $$^{187}$$Os at a stellar temperature. Firstly, $$^{187}$$Os is produced and depleted by the slow process nucleosynthesis. Hence, it is necessary to obtain both the production and depletion rates of $$^{187}$$Os. Secondly, $$^{187}$$Os is depleted not only by its ground state neutron capture reaction but also by an excited state neutron capture reaction of $$^{187}$$Os in a stellar temperature. In the present study, we have measured the neutron capture reaction cross sections for $$^{186}$$Os, $$^{187}$$Os and $$^{189}$$Os accurately and neutron inelastic scattering reaction cross section for $$^{187}$$Os off the ground state of $$^{187}$$Os to its 9.75-keV first excited statein the neutron energy range from 10 to 100 keV. The measurements of the neutron capture reactions have been carried out by detecting a prompt $$gamma$$-ray by means fan anti-Compton NaI(Tl) spectrometer. The (n, n') reaction cross section for $$^{187}$$Os has been measured with use of four $$^{6}$$Li-glass scintillation detectors. Based on these new capture cross sections, we reestimate on the basis of a careful reaction cross section calculation the correction factor F for the neutron capture on the 9.75-keV first excited state in $$^{187}$$Os as a function of stellar temperature, as required to derive the age of the galaxy within the Re-Os chronology.

Oral presentation

Measurement of the E1 and E2 partial cross sections of the $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction at E$$_{cm}$$ = 1.2 and 1.5 MeV using pulsed $$alpha$$ beam

Makii, Hiroyuki; Ueda, Hitoshi*; Nagai, Yasuki*; Segawa, Mariko; Temma, Yasuyuki*; Shima, Tatsushi*; Mishima, Kenji*; Igashira, Masayuki*

no journal, , 

The $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction plays an important role in stellar evolution at the stage of He-burning. However the cross section at the stellar temperature still has a large uncertainty mainly due to the poor determination of the cross section ratio, $$sigma_{E2}/sigma_{E1}$$. In order to make a precise measurement of the $$sigma_{E2}/sigma_{E1}$$, we have installed a new measurement system of the $$gamma$$-ray angular distributions of the $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction. In this experiment, we used high efficiency anti-Compton NaI(Tl) spectrometers to detect $$gamma$$-rays from the reaction with a large S/N ratio, an intense pulsed $$alpha$$ beams, and the monitoring system of the target thickness. With use of the system we succeeded in removing a background due to neutrons and could clearly detect the $$gamma$$-ray from the reaction with high statistics. We determined the E1 and E2 cross section down to E$$_{cm}$$ = 1.2 MeV, and thus obtained results are compared to recent theoretical calculations.

7 (Records 1-7 displayed on this page)
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