Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
W, 
Re and 
Os; Implications for the Re-Os cosmochronologyShizuma, Toshiyuki; Utsunomiya, Hiroaki*; Mohr, P.*; Hayakawa, Takehito; Goko, Shinji*; Makinaga, Ayano*; Akimune, Hidetoshi*; Yamagata, Tamio*; Ota, Masahisa*; Ogaki, Hideaki*; et al.
Physical Review C, 72(2), p.025808_1 - 025808_9, 2005/08
Times Cited Count：43 Percentile：90.03(Physics, Nuclear)Cross sections of the W, Re, Os(
) reactions were measured using quasi-monochromatic photon beams from laser Compton scattering (LCS) with average energies from 7.3 to 10.9 MeV. The results are compared with the predictions of Hauser-Feshbach statistical calculations using four different sets of input parameters. In addition, the inverse neutron capture cross sections were evaluated by constraining the model parameters, especially the 
strength function, on the basis of the experimental data. The present experiment helps to further constrain the correction factor 
for the neutron capture on the 9.75 keV state in Os. Implications of to the Re-Os cosmochronology are discussed with a focus on the uncertainty in the estimate of the age of the Galaxy.
W, Re and Os for cosmochronologyShizuma, Toshiyuki; Utsunomiya, Hiroaki*; Goko, Shinji*; Mohr, P.*; Hayakawa, Takehito; Makinaga, Ayano*; Hara, Kaoru*; Ogaki, Hideaki*; Lui, Y.-W.*; Goriely, S.*
Nuclear Physics A, 758, p.561c - 564c, 2005/07
Photodisintegration experiments were carried out for W, Re, and Os using quasi-monochromatic 
-ray beams from laser Compton scattering (LCS) at the National Institute of Advanced Industrial Science and Technology. The excitation function of (,n) cross sections was measured for the three nuclei near neutron thresholds, taking advantage of the intense peaking of the energy-tunable LCS beam in the energy region of astrophysical importance. Neutron capture cross sections for 
W, Re, and Os are evaluated from the photodisintegration data with the Hauser-Feshbach statistical model. We quantitatively discuss the two corrections factors for the s-process branchings and the neutron capture on the 9.75 keV state.
Taira, Yoshitaka*; Fujimoto, Masaki*; Fujimori, Kosuke*; Kitaura, Mamoru*; Zen, H.*; Okano, Yasuaki*; Hosaka, Masahito*; Yamazaki, Junichiro*; Kato, Masahiro*; Hirade, Tetsuya; et al.
no journal, ,
For general positron sources, radioisotopes such as 
Na are often used. However, there is a problem that positrons cannot probe the deep region of metal materials with a thickness of 1 mm or more. Gamma-ray induced positron annihilation lifetime measurement (GiPALS) is a method for generating positrons in bulk samples with a thickness of several centimeters and samples placed in vessels such as high temperature and/or pressure furnaces. The annihilation lifetime of positrons is about 200 ps for metal materials, so it is important to use gamma rays with a shorter pulse width for GiPALS in order to accurately measure the positron lifetime. We have succeeded in the proof-of-principle experiment for GiPALS of ultra-short pulse gamma rays with a pulse width of 2 ps, which was originally developed using 90
collision laser Compton scattering at UVSOR.
Taira, Yoshitaka*; Fujimoto, Masaki*; Fujimori, Kosuke*; Kitaura, Mamoru*; Zen, H.*; Okano, Yasuaki*; Hosaka, Masahito*; Yamazaki, Junichiro*; Kato, Masahiro*; Hirade, Tetsuya; et al.
no journal, ,
For general positron sources, radioisotopes such as Na are often used. However, there is a problem that positrons cannot probe the deep region of metal materials with a thickness of 1 mm or more. Gamma-ray induced positron annihilation lifetime measurement (GiPALS) is a method for generating positrons in bulk samples with a thickness of several centimeters and samples placed in vessels such as high temperature and/or pressure furnaces. The annihilation lifetime of positrons is about 200 ps for metal materials, so it is important to use gamma rays with a shorter pulse width for GiPALS in order to accurately measure the positron lifetime. We have succeeded in the proof-of-principle experiment for GiPALS of ultra-short pulse gamma rays with a pulse width of 2 ps, which was originally developed using 90 collision laser Compton scattering at UVSOR.
Yabuuchi, Atsushi*; Awaji, Ryo*; Hirade, Tetsuya; Fujinami, Masanori*; Oshima, Nagayasu*; Takai, Kenichi*; Taira, Yoshitaka*
no journal, ,
In situ measurements of positron annihilation lifetimes have been performed at the UVSOR synchrotron radiation facility to evaluate defects formed during tensile deformation in pure iron using the gamma-ray induced positron annihilation spectroscopy technique. A 66 MeV gamma-ray pulse beam with a diameter of 3 mm was irradiated to the centre of the sample while stretching it to a nominal strain of 7 or more at a strain rate of 2.2
10
/s. The positron lifetime change during the tensile deformation of iron specimens was observed. Positron lifetime measurements have often been performed after the deformation of the sample. Unlike these results, it was found that the lifetime change at the initial deformation stage was very small in these In situ measurements.
