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Journal Articles

A Relativistic quantum approach to neutrino and antineutrino emission via the direct Urca process in strongly magnetized neutron-star matter

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

Journal Articles

Neutrinos in core-collapse supernovae and nucleosynthesis

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:20 Percentile:78.37(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 $$^{180}$$Ta and $$^{138}$$La and summarize the application of the neutrino -process chronometers, $$^{136,138}$$Ce, $$^{138}$$La, and$$^{92}$$Nb. We also consider other aspects.

Journal Articles

Supernova neutrino nucleosynthesis of the radioactive $$^{92}$$Nb observed in primitive meteorites

Hayakawa, 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:28 Percentile:63.21(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). $$^{92}$$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 $$^{92}$$Nb/$$^{93}$$Nb at the time of SSF cluster around two different values; one is near 10$$^{-3}$$, while the other is near 10$$^{-5}$$. Moreover, the astrophysical mechanism for the synthesis of $$^{92}$$Nb has remained an unsolved problem. Here we argue that conventional nucleosynthesis mechanisms cannot produce $$^{92}$$Nb and propose a new mechanism for the nucleosynthesis of this isotopebased upon neutrino induced reactions occurring during core-collapse supernova explosions.

Journal Articles

Reanalysis of the ($$J$$ = 5) state at 592 keV in $$^{180}$$Ta and its role in the $$nu$$-process nucleosynthesis of $$^{180}$$Ta in supernovae

Hayakawa, 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:14 Percentile:69.9(Physics, Nuclear)

We analyze the production and freeze-out of the isomer $$^{180}$$Ta in the $$nu$$-process. We consider the influence of a possible low-lying intermediate ($$J$$ = 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 $$^{138}$$La and $$^{180}$$Ta are coproduced by neutrino nucleosynthesis with an electron neutrino temperature of ${it kT}$ $$approx$$ 4 MeV.

Journal Articles

New estimate for the time-dependent thermal nucleosynthesis of $$^{180}$$Ta$$^{m}$$

Hayakawa, Takehito; Kajino, Toshitaka*; Chiba, Satoshi; Mathews, G. J.*

Physical Review C, 81(5), p.052801_1 - 052801_4, 2010/05

 Times Cited Count:48 Percentile:91.84(Physics, Nuclear)

The nucleosynthesis of $$^{180}$$Ta has remained an unsolved problem. The supernova neutrino process has been proposed as the origin of $$^{180}$$Ta but its model calculation overproduces the $$^{180}$$Ta solar abundance. This may originate from the unique feature that the naturally occurring abundance of $$^{180}$$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 $$^{180}$$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 $$^{180}$$Ta using the available nuclear data shows $$^{180}$$Ta can be produced by neutrino process and neutrino temperature of 4 MeV.

Oral presentation

Isomer residual ratio of odd-odd isotope $$^{180}$$Ta in supernova nucleosynthsis

Hayakawa, Takehito; Kajino, Toshitaka*; Chiba, Satoshi; Mathews, G. J.*

no journal, , 

The nucleosynthesis of an odd-odd isotope $$^{180}$$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 $$^{180}$$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 $$^{180}$$Ta can be reproduced by a supernova model with the neutrino temperature of 4 MeV.

Oral presentation

Excited states and $$gamma$$-ray transition probability on $$^{180}$$Ta and its effects to supernova neutrino process and s-process

Hayakawa, Takehito; Chiba, Satoshi; Kajino, Toshitaka*; Mathews, G. J.*; Mohr, P.*

no journal, , 

We have discuss nuclear structure of $$^{180}$$Ta, excited states and $$gamma$$ transition probabilities, and its effects to supernova neutrino nucleosynthesis and slow neutron capture reaction processes. The ground state of $$^{180}$$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 ($$gamma$$, $$gamma$$') reactions.

Oral presentation

Supernova neutrino nucleosynthesis of a radioactivity $$^{92}$$Nb

Hayakawa, 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 $$^{92}$$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.

Oral presentation

Synthesis of odd-odd nuclei by supernova neutrino process

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.

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