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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：2 Percentile：39.49(Astronomy & Astrophysics)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：23 Percentile：78.34(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：32 Percentile：63.99(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.
= 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：18 Percentile：70.71(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.
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：51 Percentile：91.70(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.
NbHayakawa, Takehito; Kajino, Toshitaka*; Nakamura, Ko*; Chiba, Satoshi; Iwamoto, Nobuyuki; Cheoun, M. K.*; Mathews, G. J.*
no journal, ,
Relatively short-lived radioactivities are used as nuclear cosmochronometers for determining the free decay time from the last nucleosynthesis episode strongly affecting to the material of the solar system to the solar system formation. An unstable isotope of Zr with a half-life of 34.7 Myr is extinct in the present solar system, which can be used as a new cosmochronometer. We discuss the contribution of the neutrino-process.
-ray transition probability on Ta and its effects to supernova neutrino process and s-processHayakawa, Takehito; Chiba, Satoshi; Kajino, Toshitaka*; Mathews, G. J.*; Mohr, P.*
no journal, ,
We have discuss nuclear structure of Ta, excited states and transition probabilities, and its effects to supernova neutrino nucleosynthesis and slow neutron capture reaction processes. The ground state of Ta beta decays with a half-life of about 8 hours, whereas an isomer at 77 keV is meta-stable state. In hot temperature environments in stars, the ground state and the isomer are linked through highly excited states by (, ') reactions.
Ta in supernova nucleosynthsisHayakawa, Takehito; Kajino, Toshitaka*; Chiba, Satoshi; Mathews, G. J.*
no journal, ,
The nucleosynthesis of an odd-odd isotope Ta has remained an unsolved problem and as its origin many nucleosynthesis mechanisms have been proposed. We have made a new time-dependent calculation of Tameta-stable isomer residual ratio after supernova neutrino-inducedreactions. This isomer residual ratio is crucial for understanding the production and survival of this isotope. We include the linking between the isomer and all known excited states. We find that the relative solar abundance of Ta can be reproduced by a supernova model with the neutrino temperature of 4 MeV.
Hayakawa, Takehito; Nakamura, Ko*; Kajino, Toshitaka*; Chiba, Satoshi; Cheoun, M. K.*; Mathews, G. J.*; Iwamoto, Nobuyuki
no journal, ,
Huge amount of neutrinos are generated from proto neutron stars in early phase of supernova explosions. They produce new isotopes from pre-existing isotopes by neutrino-nucleus interactions in outer layers of supernovae. In general, odd-odd isotopes have rare isotopic abundance compared with other isotopes and thus synthesis by neutrino can contribute its abundance. Such odd-odd isotopes are observed in the solar abundances and meteorites. We discuss nucleosynthesis by neutrino-induced reactions with a supernova model.
