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Journal Articles

Model magnet development of D1 beam separation dipole for the HL-LHC upgrade

Nakamoto, Tatsushi*; Sugano, Michinaka*; Xu, Q.*; Kawamata, Hiroshi*; Enomoto, Shun*; Higashi, Norio*; Idesaki, Akira; Iio, Masami*; Ikemoto, Yukio*; Iwasaki, Ruri*; et al.

IEEE Transactions on Applied Superconductivity, 25(3), p.4000505_1 - 4000505_5, 2015/06

Recently, development of superconducting magnet system with high radiation resistance has been demanded for application in accelerator facilities such as CERN LHC. In order to realize superconducting magnet system with high radiation resistance, it is necessary to develop electrical insulator with high radiation resistance because the electrical insulator is made of organic materials whose radiation resistance is inferior to that of inorganic materials. We developed a glass fiber reinforced plastic with bismaleimide-triazine resin. The developed material showed excellent radiation resistance; the material evolved gases of 5$$times$$10 $$^{-5}$$mol/g and maintained flexural strength of 640MPa (90% of initial value).

Journal Articles

Safety requirements expected for the prototype fast breeder reactor "Monju"

Saito, Shinzo; Okamoto, Koji*; Kataoka, Isao*; Sugiyama, Kenichiro*; Muramatsu, Ken*; Ichimiya, Masakazu*; Kondo, Satoru; Yonomoto, Taisuke

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 10 Pages, 2015/05

Journal Articles

Distribution of supernova properties in the early universe

Tominaga, Nozomu*; Iwamoto, Nobuyuki; Nomoto, Kenichi*

AIP Conference Proceedings 1594, p.52 - 57, 2014/05

 Times Cited Count:1 Percentile:43.05

The first metal enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) III star. Chemical abundance in the early universe is recorded in abundance patterns of extremely metal-poor (EMP) stars. Increasing number of the EMP stars is now being discovered and allows us to statistically constrain explosion properties of Pop III SNe. We present Pop III SN models that reproduce well individual abundance patterns of 48 most metal-poor stars with [Fe/H] $$_sim^{<}$$ -3.5, and derive relations between abundance ratios and explosion properties of Pop III SNe.

Journal Articles

Abundance profiling of extremely metal-poor stars and supernova properties in the early universe

Tominaga, Nozomu*; Iwamoto, Nobuyuki; Nomoto, Kenichi*

Astrophysical Journal, 785(2), p.98_1 - 98_23, 2014/04

 Times Cited Count:54 Percentile:6.33(Astronomy & Astrophysics)

The first metal enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) III star and chemical evolution of the universe is recorded in abundance patterns of extremely metal-poor (EMP) stars. Increasing number of the EMP stars is now being discovered. This allows us to statistically constrain properties of SNe of Pop III stars (Pop III SNe). We investigate the properties of Pop III SNe by comparing their nucleosynthetic yields with the abundance patterns of the EMP stars. We focus on the most metal-poor stars with [Fe/H] $$_sim^{<}$$ 3.5 and present Pop III SN models that reproduce well their individual abundance patterns. From these models we derive relations between abundance ratios and properties of Pop III SNe: [(C+N)/Fe] vs. an ejected Fe mass, and [(C+N)/Mg] vs. a remnant mass. Using fitting functions, distribution of the abundance ratios of EMP stars is converted to those of the properties of Pop III SNe, which can be compared with SNe in the present day.

Journal Articles

Manufacture of the winding pack and development of key parts for the JT-60SA poloidal field coils

Tsuchiya, Katsuhiko; Kizu, Kaname; Murakami, Haruyuki; Yoshida, Kiyoshi; Kurihara, Kenichi; Hasegawa, Mitsuru*; Kuno, Kazuo*; Nomoto, Kazuhiro*; Horii, Hiroyuki*

IEEE Transactions on Applied Superconductivity, 22(3), p.4202304_1 - 4202304_4, 2012/06

 Times Cited Count:6 Percentile:53(Engineering, Electrical & Electronic)

no abstracts in English

Journal Articles

Production of the $$p$$-process nuclei in the carbon-deflagration model for type Ia supernovae

Kusakabe, Motohiko*; Iwamoto, Nobuyuki; Nomoto, Kenichi*

Astrophysical Journal, 726(1), p.25_1 - 25_11, 2011/01

 Times Cited Count:37 Percentile:20.57(Astronomy & Astrophysics)

We calculate nucleosynthesis of proton-rich isotopes in the carbon deflagration model for Type Ia supernovae (SNe Ia). When the deflagration wave passes through the outer layer of the CO white dwarf, $$p$$-nuclei are produced by photodisintegration reactions on s-nuclei in a region with the peak temperature ranging from 1.9 to 3.6$$times$$10$$^{9}$$ K. We find that about 50% of $$p$$-nuclides are co-produced when normalized to their solar abundances in all adopted cases of seed distribution. Mo and Ru, which are largely underproduced in Type II supernovae (SNe II), are produced at a level similar to other $$p$$-nuclides. The ratios between $$p$$-nuclei and iron in the ejecta are larger than the solar ratios by a factor of 1.2. We also compare the yields of oxygen, iron, and $$p$$-nuclides in SNe Ia and SNe II, and suggest that SNe Ia could make a larger contribution than SNe II to the solar system content of $$p$$-nuclei.

Journal Articles

Empirical abundance scaling laws and implications for the $$gamma$$ process in core-collapse supernovae

Hayakawa, Takehito; Iwamoto, Nobuyuki; Kajino, Toshitaka*; Shizuma, Toshiyuki; Umeda, Hideyuki*; Nomoto, Kenichi*

Astrophysical Journal, 685(2), p.1089 - 1102, 2008/10

 Times Cited Count:20 Percentile:43.82(Astronomy & Astrophysics)

no abstracts in English

Journal Articles

Supernova nucleosynthesis in the early universe

Tominaga, Nozomu*; Umeda, Hideyuki*; Maeda, Keiichi*; Nomoto, Kenichi*; Iwamoto, Nobuyuki

Proceedings of the International Astronomical Union, Volume 4, Symposium S255, p.189 - 193, 2008/06

The first metal enrichment in the universe was made by supernova (SN) explosions of population (Pop) III stars. The trace remains in abundance patterns of extremely metal-poor (EMP) stars. We investigate the properties of nucleosynthesis in Pop III SNe by means of comparing their yields with the abundance patterns of the EMP stars. We focus on (1) jet-induced SNe with various energy deposition rates [$$dot{E}_{rm dep}=(0.3-1500)times 10^{51}$$ ergs s$$^{-1}$$], and (2) SNe of stars with various main-sequence masses ($$M_{rm ms}=13-50M_odot$$) and explosion energies [$$E=(1-40)times10^{51}$$ ergs]. The varieties of Pop III SNe can explain varieties of the EMP stars: (1) higher [C/Fe] for lower [Fe/H] and (2) trends of abundance ratios [X/Fe] against [Fe/H].

Journal Articles

Supernova nucleosynthesis and extremely metal-poor stars

Tominaga, Nozomu*; Umeda, Hideyuki*; Maeda, Keiichi*; Iwamoto, Nobuyuki; Nomoto, Kenichi*

AIP Conference Proceedings 1016, p.49 - 54, 2008/05

We investigate hydrodynamical and nucleosynthetic properties of the jet-induced explosion of a population III 40M$$_odot$$ star with a two-dimensional special relativistic hydrodynamical code and compare the abundance patterns of the yields with those of the metal-poor stars. We conclude that (1) the ejection of Fe-peak products and the fallback of unprocessed materials can account for the abundance patterns of the extremely metal-poor stars and that (2) the jet-induced explosion with different energy deposition rates can explain the difference of the abundance patterns of the metal-poor stars.

Journal Articles

Spectroscopic studies of extremely metal-poor stars with the subaru high-dispersion spectrograph, 4; The $$alpha$$-element-enhanced metal-poor star BS 16934-002

Aoki, Wako*; Honda, Satoshi*; Beers, T. C.*; Hidai, Masahide*; Iwamoto, Nobuyuki; Tominaga, Nozomu*; Umeda, Hideyuki*; Nomoto, Kenichi*; Norris, J. E.*; Ryan, S. G.*

Astrophysical Journal, 660(1, Part1), p.747 - 761, 2007/05

 Times Cited Count:39 Percentile:25.02(Astronomy & Astrophysics)

A detailed elemental abundance analysis has been carried out for the very metal-poor ([Fe/H] = -2.7) star BS 16934-002, which was identified in our previous work as a star exhibiting large overabundances of Mg and Sc. A comparison of the abundance pattern of this star with that of the well-studied metal-poor star HD 122563 indicates excesses of O, Na, Mg, Al, and Sc in BS 16934-002. Of particular interest, no excess of C or N is found in this object, in contrast to CS 22949-037 and CS 29498-043, two previously known carbon-rich, extremely metal-poor stars with excesses of the $$alpha$$ elements. No established nucleosynthesis model exists that explains the observed abundancepattern. A supernova model, including mixing and fallback, assuming severe mass loss before explosion, is discussed as a candidate progenitor of BS 16934-002.

Journal Articles

The Connection between $$gamma$$-ray bursts and extremely metal-poor stars; Black hole-forming supernovae with relativistic jets

Tominaga, Nozomu*; Maeda, Keiichi*; Umeda, Hideyuki*; Nomoto, Kenichi*; Tanaka, Masaomi*; Iwamoto, Nobuyuki; Suzuki, Tomoharu*; Mazzali, P. A.*

Astrophysical Journal, 657(2, Part2), p.L77 - L80, 2007/03

 Times Cited Count:100 Percentile:6.48(Astronomy & Astrophysics)

Long-duration $$gamma$$-ray bursts (GRBs) are thought to be connected with luminous and energetic Type Ic supernovae [SNe, called hypernovae (HNe)] resulting from the black-hole (BH) forming collapse of massive stars. For GRBs 060505 and 060614, however, the expected SNe have not been detected. The upper limits to the SN brightness are about 100 times fainter than GRB-associated HNe (GRB-HNe), corresponding to the upper limits to the ejected $$^{56}$$Ni masses of $$M(^{56}$$Ni)$$sim 10^{-3}M_odot$$. SNe with a small amount of $$^{56}$$Ni ejection are observed as faint Type II SNe. HNe and faint SNe are thought to be responsible for the formaion of extremely metal-poor (EMP) stars. A relativistic jet-induced BH forming explosion of the 40$$M_odot$$ star is investigated and hydrodynamic and nucleosynthetic models are presented. These models can explain both GRB-HNe and GRBs without bright SNe in a unified manner. We suggest that GRBs without bright SNe are likely to synthesize $$M(^{56}$$Ni)$$sim 10^{-4}-10^{-3}M_odot$$ or $$sim 10^{-6}M_odot$$.

Journal Articles

Principle of universality of $$gamma$$-process nucleosynthesis in core-collapse supernova explosions

Hayakawa, Takehito; Iwamoto, Nobuyuki; Kajino, Toshitaka*; Shizuma, Toshiyuki; Umeda, Hideyuki*; Nomoto, Kenichi*

Astrophysical Journal, 648(1, Part2), p.L47 - L50, 2006/09

 Times Cited Count:17 Percentile:52.25(Astronomy & Astrophysics)

Using core-collapse supernova explosion models, we investigate the principle of the universality of the $$gamma$$-process that the s/p abundance ratios produced by individual nucleosynthesis are almost constant in the wide region of the atomic number. The universality originates from the weak $$s$$-process in pre-supernovae, the independence of the s/p abundance ratios of the nuclear reactions, and the shift of the $$gamma$$-process layers. Our calculations further suggest an extended universalitythat the s/p ratios in the $$gamma$$-process layers are not only constant but also centered around a specific value 3. To verify this, we propose an astronomical observation of Indium isotopic abundance fractions.

Journal Articles

Explosive nucleosynthesis in different ${it Y$_{e}$}$ conditions

Iwamoto, Nobuyuki; Umeda, Hideyuki*; Nomoto, Kenichi*; Tominaga, Nozomu*; Thielemann, F. K.*; Hix, W. R.*

AIP Conference Proceedings 847, p.409 - 411, 2006/07

The observations of metal-poor stars with metallicity [Fe/H] $$<-2.5$$ have been extensively performed. The abundance patterns of these stars are well explained by supernova models with extensive material mixing and fallback onto the compact remnant. Nevertheless important deficiencies of odd elements (especially Sc and K) are present in most investigations. Recent simulations of core collapse supernovae showed that innermost ejecta undergo large amounts of neutrino flux and neutrino interactions with materials in these ejecta change electron fraction to ${it Y$_{e}$}$ $$>0.5$$. Nucleosynthesis in the proton-rich environments allows Sc and Zn (which are less produced in normal supernova models) to be enriched. Therefore, it is interesting to investigate the influence of a large variation of ${it Y$_{e}$}$ on explosive nucleosynthesis. We calculate nucleosynthesis with ${it Y$_{e}$}$ ranging from 0.48 to 0.58 in complete and incomplete Si burning layers in Pop III supernovae. We discuss the production of some important nuclei and compare the abundance patterns with those in observed extremely metal-poor stars.

Journal Articles

The $$p$$-process in the carbon deflagration model for type Ia supernovae and chronology of the solar system formation

Kusakabe, Motohiko*; Iwamoto, Nobuyuki; Nomoto, Kenichi*

AIP Conference Proceedings 847, p.424 - 426, 2006/07

We consider nucleochronology with four $$p$$-process radioactive nuclides $$^{53}$$Mn, $$^{92}$$Nb, $$^{97}$$Tc and $$^{146}$$Sm which are produced in a carbon deflagration model for type Ia supernovae. We apply the result of the $$p$$-process nucleosynthesis to simple galactic chemical evolution models and discuss the circumstances of the solar system formation.

Journal Articles

Chemical abundances in the secondary star of the black hole binary V4641 Sagittarii (SAX J1819.3-2525)

Sadakane, Kozo*; Arai, Akira*; Aoki, Wako*; Arimoto, Nobuo*; Hidai, Masahide*; Onishi, Takashi*; Tajitsu, Akito*; Beers, T. C.*; Iwamoto, Nobuyuki; Tominaga, Nozomu*; et al.

Publications of the Astronomical Society of Japan, 58(3), p.595 - 604, 2006/06

 Times Cited Count:8 Percentile:70.86(Astronomy & Astrophysics)

We report detailed spectroscopic studies performed for the secondary star in the black hole binary (micro-quasar) V4641 Sgr in order to examine its surface chemical composition and to see if its surface shows any signature of pollution by ejecta from a supernova explosion. We obtain abundances of 10 elements and find definite over-abundances of N (by 0.8 dex or more) and Na (by 0.8 dex) in V4641 Sgr. From line-by-line comparisons of eight other elements (C, O, Mg, Al, Si, Ti, Cr, Fe) between V4641 Sgr and the two normal late B-type stars, which have been reported to have solar abundances. An evolutionary model of a massive close binary system has been constructed to explain the abundances observed in V4641 Sgr. The model suggests that the BH forming supernova in this system was a dark one.

Journal Articles

Evidence for p-process nucleosynthesis recorded at the solar system abundances

Hayakawa, Takehito; Iwamoto, Nobuyuki; Shizuma, Toshiyuki; Kajino, Toshitaka*; Umeda, Hideyuki*; Nomoto, Kenichi*

European Physical Journal A, 27(S1), p.123 - 128, 2006/03

 Percentile:100(Physics, Nuclear)

no abstracts in English

Journal Articles

Enrichment of very metal poor stars with both $$r$$-process and $$s$$-process elements from $$8-10M_odot$$ stars

Wanajo, Shinya*; Nomoto, Kenichi*; Iwamoto, Nobuyuki; Ishimaru, Yuri*; Beers, T. C.*

Astrophysical Journal, 636(2, Part1), p.842 - 847, 2006/01

 Times Cited Count:33 Percentile:31.76(Astronomy & Astrophysics)

Recent spectroscopic studies have revealed the presence of numerous carbon-enhanced, metal-poor stars with [Fe/H]$$<-2$$ that exhibit enhancements of $$s$$-process elements. These stars are believed to be the result of a binary mass-transfer episode from a former asymptotic giant-branch (AGB) companion that underwent $$s$$-process nucleosynthesis. However, several such stars exhibit significantly lower Ba/Eu ratios than solar $$s$$-process abundances. We propose a model in which the double enhancements of $$r$$- and $$s$$-process elements originate from a former $$8-10M_odot$$ companion in a wide binary system, which may undergo $$s$$-processing during an AGB phase, followed by $$r$$-processing during its subsequent supernova explosion. The mass of Eu captured by the secondary through the wind from the supernova is estimated. We find that the estimated mass is in good agreement with a constraint on the Eu yield per supernova event, when the initial orbital separation is taken to be $$sim$$ 1 year.

Journal Articles

Scaling relations for the supernova $$gamma$$-process and the $$^{176}$$Lu nuclear cosmochronometer

Hayakawa, Takehito; Iwamoto, Nobuyuki; Shizuma, Toshiyuki; Kajino, Toshitaka*; Umeda, Hideyuki*; Nomoto, Kenichi*

Nuclear Physics A, 758, p.525c - 528c, 2005/07

no abstracts in English

Journal Articles

The $$p$$-process nucleosynthesis in the carbon deflagration model for type Ia supernovae

Kusakabe, Motohiko*; Iwamoto, Nobuyuki; Nomoto, Kenichi*

Nuclear Physics A, 758, p.459c - 462c, 2005/07

We calculate nucleosynthesis of proton-rich isotopes in the Carbon deflagration model for Type Ia supernova. We investigate the influence of variations int he C/O ratios and $$^{22}$$Ne abundances left in accreting CO white dwarf on the $$p$$-process nucleosynthesis. We compare the yields of $$^{56}$$Fe and $$p$$-nuclei in Type Ia and Type II supernovae, and obtain a result that C-deflagration supernovae can contribute to the galactic evolution (and the solar system) of the $$p$$-nuclei.

Journal Articles

The First chemical enrichment in the universe and the formation of hyper metal-poor stars

Iwamoto, Nobuyuki; Umeda, Hideyuki*; Tominaga, Nozomu*; Nomoto, Kenichi*; Maeda, Keiichi*

Science, 309(5733), p.451 - 453, 2005/07

 Times Cited Count:189 Percentile:2.36(Multidisciplinary Sciences)

The recent discovery of a hyper-metal-poor (HMP) star, with a metallicity Fe/H smaller than 1/100,000 of the solar ratio, together with one earlier HMP star, has raised a challenging question whether these HMP stars are the actual first-generation, low-mass stars of the universe. We argue that these HMP stars are the second-generation stars formed from gases that were chemically enriched by the first-generation supernovae. The key to this solution is the very unusual abundance patterns of these HMP stars and the similarities and differences between them. We can reproduce these abundance features with core-collapse "faint" supernova models that include extensive matter mixing and fallback during explosions.

33 (Records 1-20 displayed on this page)