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- and 
-processes following 
-process in the collapsar jetHe, Z.*; Kajino, Toshitaka*; Kusakabe, Motohiko*; Zhou, S.-G.*; Koura, Hiroyuki; Chiba, Satoshi*; Li, H.*; Lin, Y.*
Astrophysical Journal Letters, 966(2), p.L37_1 - L37_7, 2024/05
Times Cited Count：7 Percentile：47.33(Astronomy & Astrophysics)Maruyama, Tomoyuki*; Baha Balantekin, A.*; Cheoun, M.-K.*; Kajino, Toshitaka*; Kusakabe, Motohiko*; Mathews, G. J.*
Physics Letters B, 824, p.136813_1 - 136813_8, 2022/01
Times Cited Count：8 Percentile：67.70(Astronomy & Astrophysics)
Cd(
)
Cd reaction in an -process branching pointHayakawa, Takehito*; Toh, Yosuke; Kimura, Atsushi; Nakamura, Shoji; Shizuma, Toshiyuki*; Iwamoto, Nobuyuki; Chiba, Satoshi*; Kajino, Toshitaka*
Physical Review C, 103(4), p.045801_1 - 045801_5, 2021/04
Times Cited Count：1 Percentile：11.25(Physics, Nuclear)Cd()Cd reaction using neutron beams at J-PARCHayakawa, Takehito*; Toh, Yosuke; Huang, M.; Shizuma, Toshiyuki*; Kimura, Atsushi; Nakamura, Shoji; Harada, Hideo; Iwamoto, Nobuyuki; Chiba, Satoshi*; Kajino, Toshitaka*
Physical Review C, 94(5), p.055803_1 - 055803_6, 2016/11
Times Cited Count：4 Percentile：29.80(Physics, Nuclear)
NbHayakawa, Takehito; Kajino, Toshitaka*; Chiba, Satoshi*
Nihon Butsuri Gakkai-Shi, 70(11), p.824 - 829, 2015/11
The isotope Nb decays to Zr with a half-life of 34.7 Myr. The initial abundance ratios for Nb/
Nb at the time of solar system formation (SSF) have been measured in primitive meteorites. The astrophysical origin of this material, however, has remained unknown. We have proposed a novel origin of Nb via neutrino-induced reactions in core-collapse supernovae.
-decay half-lives of 110 neutron-rich nuclei across the 
=82 shell gap; Implications for the mechanism and universality of the astrophysical processLorusso, G.*; Nishimura, Shunji*; Xu, Z. Y.*; Jungclaus, A.*; Shimizu, Y.*; Simpson, G. S.*; S
derstrm, P.-A.*; Watanabe, H.*; Browne, F.*; Doornenbal, P.*; et al.
Physical Review Letters, 114(19), p.192501_1 - 192501_7, 2015/05
Times Cited Count：183 Percentile：97.79(Physics, Multidisciplinary)
SiKomatsubara, Tetsuro*; Kubono, Shigeru*; Hayakawa, Takehito; Shizuma, Toshiyuki; Osawa, Akira*; Ito, Yuta*; Ishibashi, Yoko*; Moriguchi, Tetsuro*; Yamaguchi, Hidetoshi*; Kahl, D.*; et al.
European Physical Journal A, 50, p.136_1 - 136_9, 2014/09
Times Cited Count：15 Percentile：66.39(Physics, Nuclear)The level scheme above the proton threshold in Si is crucial for evaluating the 
Al(p,
)Si stellar reaction, which is important for understanding the astrophysical origin of the long-lived cosmic radioactivity Al(T
=7.17
10
y) in the Galaxy. The excited states in Si have been studied using an in-beam -ray spectroscopy technique with the 
Mg(
He,n)Si reaction. The spin-parity of one of the most important states reported recently at 5890.0 keV has been assigned as 0
by - angular correlation measurements.
Kajino, Toshitaka*; Mathews, G. J.*; Hayakawa, Takehito
Journal of Physics G; Nuclear and Particle Physics, 41(4), p.044007_1 - 044007_34, 2014/04
Times Cited Count：29 Percentile：81.65(Physics, Nuclear)Neutrino interactions are a key component of the mechanism for supernova explosions. They also play an important role in the associated nucleosynthesis. Nevertheless, a number of issues remain to be resolved. In this review we summarize research by our group and others on some of these issues. Much effort is now invested in understanding the transport of neutrinos from the core and the role of neutrino heated convection in the outer envelopes. In addition to the neutrino transport issues, we review some current topics in neutrino induced nucleosynthesis (the neutrino and p processes). We review some current issues regarding the synthesis of the neutirno-process isotopes 
Ta and 
La and summarize the application of the neutrino -process chronometers, 
Ce, La, and Nb. We also consider other aspects.
Nb observed in primitive meteoritesHayakawa, Takehito; Nakamura, Ko*; Kajino, Toshitaka*; Chiba, Satoshi; Iwamoto, Nobuyuki; Cheoun, M. K.*; Mathews, G. J.*
Astrophysical Journal Letters, 779(1), p.L9_1 - L9_5, 2013/12
Times Cited Count：35 Percentile：63.32(Astronomy & Astrophysics)Short-lived radioactivities are used as nuclearcosmochronometers for understanding the free decay time from the last nucleosynthesis episode until the time of solar system formation (SSF). Nb (half-life of 34.7 Myr) is one of a short-lived isotope existed at SSF. However, there is a controversy in that the inferred initial abundance ratios for Nb/Nb at the time of SSF cluster around two different values; one is near 10
, while the other is near 10
. Moreover, the astrophysical mechanism for the synthesis of Nb has remained an unsolved problem. Here we argue that conventional nucleosynthesis mechanisms cannot produce Nb and propose a new mechanism for the nucleosynthesis of this isotopebased upon neutrino induced reactions occurring during core-collapse supernova explosions.
Suzuki, Toshio*; Yoshida, Takashi*; Chiba, Satoshi; Kajino, Toshitaka*
Nihon Butsuri Gakkai-Shi, 67(1), p.49 - 54, 2012/01
Neutrino processes play important roles in synthesis of 
Li, 
B, La, Ta and other elements in explosive environments realized in supernovae. In order to understand better the neutrino processes, we constructed new shell model Hamiltonians based on recent progress of physics in unstable nuclei near the neutron drip-line. We then applied these Hamiltonians to calculate the neutrino-nucleus reaction cross sections through detailed and careful comparison of nuclear properties with those of relevant experimental data. We can thus carry out precise and reliable theoretical estimate of supernova nucleosynthesis of 
Li, B, etc including the neutrino processes. Finally we propose a new method to determine unknown neutrino oscillation parameters, namely the mixing angle 
and the mass hierarchy, by making use of strong dependence of the yields of Li, B on these parameters.
Suzuki, Toshio*; Yoshida, Takashi*; Chiba, Satoshi; Kajino, Toshitaka*
Nihon Butsuri Gakkai-Shi, 67(1), p.49 - 54, 2012/01
Neutrino-nucleus reaction processes play important roles in synthesis of Li, B, La, Ta and other elements in explosive environments realized in supernovae. We have constructed new shell model Hamiltonians based on recent progress of physics in unstable nuclei near the neutron drip-line. The spin responses of nuclei are found to be remarkably improved by the new Hamiltonians. We then applied these Hamiltonians to calculate the neutrino-nucleus reaction cross sections, and obtained more precise and reliable theoretical estimate of supernova nucleosynthesis of Li, B, etc including the neutrino processes. Finally we propose a new method to determine unknown neutrino oscillation parameters, namely the mixing angle and the mass hierarchy, by making use of strong dependence of the yields of Li and B on these parameters.
= 5) state at 592 keV in Ta and its role in the 
-process nucleosynthesis of Ta in supernovaeHayakawa, Takehito; Mohr, P.*; Kajino, Toshitaka*; Chiba, Satoshi; Mathews, G. J.*
Physical Review C, 82(5), p.058801_1 - 058801_4, 2010/11
Times Cited Count：21 Percentile：72.08(Physics, Nuclear)We analyze the production and freeze-out of the isomer Ta in the -process. We consider the influence of a possible low-lying intermediate ( = 5) state at 592 keV using a transition width estimated from the measured half-life. This more realistic width is much smaller than the previous estimate. We find that the 592 keV state leads only to a small reduction of the residual isomer ratio from the previous result. The isomer ratio changes from 0.39 to 0.38, whereas previously it was estimated that this transition could reduce the ratio to R = 0.18. This finding strengthens the evidence that La and Ta are coproduced by neutrino nucleosynthesis with an electron neutrino temperature of 
4 MeV.
La and Ta via charged and neutral currents by the quasiparticle random-phase approximationCheoun, M. K.*; Ha, E.*; Hayakawa, Takehito; Kajino, Toshitaka*; Chiba, Satoshi
Physical Review C, 82(3), p.035504_1 - 035504_7, 2010/09
Times Cited Count：39 Percentile：86.85(Physics, Nuclear)We investigate neutrino-induced reactions on heavy nuclei. Charged current (CC) reactions,Ba(
, 
)La and Hf(, )Ta are calculated by a quasi-particle random phase approximation (QRPA) with pairing correlations. For neutral current (NC) reactions, 
La(
)La
and 
Ta()Ta, we generate ground and excited states of odd-even target nuclei, La and Ta, by operating one quasi-particle to even-even nuclei. Numerical results for CC reactions are shown to be consistent with recent semi-empirical data deduced from the Gamow-Teller strength distributions measured in the (
He,
) reaction. Results for NC reactions are estimated to be smaller by a factor about 4 to 5 rather than those by CC reactions. Finally, cross sections weighted by the incident neutrino flux in the core collapsing supernova are presented for further applications to the network calculations for relevant nuclear abundances.
Ta
Hayakawa, Takehito; Kajino, Toshitaka*; Chiba, Satoshi; Mathews, G. J.*
Physical Review C, 81(5), p.052801_1 - 052801_4, 2010/05
Times Cited Count：52 Percentile：91.12(Physics, Nuclear)The nucleosynthesis of Ta has remained an unsolved problem. The supernova neutrino process has been proposed as the origin of Ta but its model calculation overproduces the Ta solar abundance. This may originate from the unique feature that the naturally occurring abundance of Ta is actually a meta-stable isomer, while the ground state is beta-unstable. We have made a new time-dependent calculation of the supernova production ratio of the long-livedisomer in Ta. Such a time-dependent solution is crucial for understanding the production and survival of this isotope. We find that the explicit time evolution of the synthesis of Ta using the available nuclear data shows Ta can be produced by neutrino process and neutrino temperature of 4 MeV.
Cd isomer and 
process contribution to rare 
nuclide 
SnHayakawa, Takehito; Shizuma, Toshiyuki; Chiba, Satoshi; Kajino, Toshitaka*; Hatsukawa, Yuichi; Iwamoto, Nobuyuki; Shinohara, Nobuo; Harada, Hideo
Astrophysical Journal, 707(2), p.859 - 865, 2009/12
Times Cited Count：7 Percentile：21.88(Astronomy & Astrophysics)no abstracts in English
La-Ce-
Ce nuclear cosmochronometer of supernova neutrino process'"Hayakawa, Takehito; Shizuma, Toshiyuki; Kajino, Toshitaka*; Ogawa, Kengo*; Nakada, Hitoshi*
Physical Review C, 79(5), p.059802_1 - 059802_2, 2009/05
Times Cited Count：0 Percentile：0.00(Physics, Nuclear)We have proposed a new nuclear cosmochronometer La(T=102 Gyr)-Ce-Ce for measuring the time elapsed from a supernova process episode. La is synthesized by the process. If a 1
excited state exists at energy lower than 72 keV, the 1 state may be a unstable isomer and La synthesized by the process is destroyed via the isomer. Recently, Byelikov et al. have measured Gamow-Teller strength distributions in La. It has been presented that this experiment shows that the existence of a low-energy 1 state in La is extremely unlikely. Our calculated result is consistent with their result and we conclude that there is no evidence that suggests the existence of the 1 isomer in La.
Li(d,t)Li reactionHashimoto, Takashi; Ishiyama, Hironobu*; Watanabe, Yutaka*; Hirayama, Yoshikazu*; Imai, Nobuaki*; Miyatake, Hiroari; Jeong, S.-C.*; Tanaka, Masahiko*; Yoshikawa, Nobuharu*; Nomura, Toru*; et al.
Physics Letters B, 674(4-5), p.276 - 280, 2009/04
Times Cited Count：7 Percentile：45.71(Astronomy & Astrophysics)The excitation function of the Li(d,t)Li reaction was directly measured using Li beams at E
= 0.3, 0.4, 0.5, 0.7, 0.8, 1.0, 1.1, and 1.2 MeV with CD
targets. The beam energies covered the Gamow peaks for 1
310
K. Large cross sections were observed at around E = 0.8 MeV, implying a resonance state located at 22.4 MeV in 
Be. The present astrophysical reaction rate is higher in one order magnitude than the presently adopted rate at around 110 K.
Yoshida, Takashi*; Suzuki, Toshio*; Chiba, Satoshi; Kajino, Toshitaka*; Yokomakura, Hidekazu*; Kimura, Keiichi*; Takamura, Akira*; Hartmann, D. H.*
Astrophysical Journal, 686(1), p.448 - 466, 2008/10
Times Cited Count：104 Percentile：89.96(Astronomy & Astrophysics)The neutrino-nucleus reaction cross sections of 
He and 
C are evaluated using new shell model Hamiltonians. The new cross sections enhance the yields of Li and B produced during the supernova explosion of a 16.2 
star model compared to the case using the conventional cross sections by about 10%. On the other hand, the yield of B decreases by a factor of two. The yields of 
Li, Be, and the radioactive nucleus Be are found at a level of 
. The temperature of 
- and 
-neutrinos inferred from the supernova contribution of B in Galactic chemical evolution models is constrained to be in the range 4.3 MeV to 6.5 MeV. The increase in the Li and B yields due to neutrino oscillations is demonstrated with the new cross sections.
process in core-collapse supernovaeHayakawa, Takehito; Iwamoto, Nobuyuki; Kajino, Toshitaka*; Shizuma, Toshiyuki; Umeda, Hideyuki*; Nomoto, Kenichi*
Astrophysical Journal, 685(2), p.1089 - 1102, 2008/10
Times Cited Count：32 Percentile：60.69(Astronomy & Astrophysics)no abstracts in English
Yoshida, Takashi*; Suzuki, Toshio*; Chiba, Satoshi; Kajino, Toshitaka*; Yokomakura, Hidekazu*; Kimura, Keiichi*; Takamura, Akira*; Hartmann, D.*
Astrophysical Journal, 686(1), p.448 - 466, 2008/10
The neutrino-nucleus reaction cross sections of He and C are evaluated using new shell model Hamiltonians. Branching ratios of various decay channels are calculated to evaluate the yields of Li, Be, and B produced through the -process in supernova explosions. The new cross sections enhance the yields of Li and B produced during the supernova explosion of a 16.2 M
star model compared to our previous study by factors of 1.3 and 1.2, respectively. On the other hand, the yield of B decreases by a factor of three. The yields of 
Li, 
Be, and the radioactive nucleus Be are found at a level of 10 to 11 M. The temperature of 
- and 
-neutrinos inferred from the supernova contribution of B in Galactic chemical evolution models is constrained to be in the range 4.5 MeV to 6.4 MeV. The increase in the Li and B yields due to neutrino oscillations is demonstrated with the new cross sections.
