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Journal Articles

Production of $^{256}$ Lr in the $^{248}$ Cm + $^{14}$ N reaction

Sato, Nozomi; Sato, Tetsuya; Asai, Masato; Toyoshima, Atsushi; Tsukada, Kazuaki; Li, Z.*; Nishio, Katsuhisa; Nagame, Yuichiro; Schdel, M.; Haba, Hiromitsu*; et al.

RIKEN Accelerator Progress Report, Vol.46, P. 237, 2013/00

http://www.rarf.riken.jp/researcher/APR/Document/ProgressReport_vol_46.pdf

Due to the strong relativistic effects, the weakly-bound outermost electron results in a significantly low first ionization potential (IP) of Lr as compared with its neighboring heavy actinides. The isotope $^{256}$ Lr, with a relatively long half-life of 27 s, is the suitable candidates for the IP measurement of Lr through the surface ionization method. In the present study, we measured the cross section of the $^{248}$ Cm( $^{14}$ N, 6) $^{256}$ Lr reaction to evaluate the production rate of $^{256}$ Lr. A $^{248}$ Cm target with 960 60 g/cm $^{2}$ thickness was bombarded with a $^{14}$ N $^{5+}$ beam from the RIKEN AVF Cyclotron. The beam energy was 91 MeV in the middle of the target. The average beam intensity was 1.2 particle-A. Reaction products were transported to the rotating wheel -particle detection system with a He/KCl gas-jet system. The $^{256}$ Lr cross section of 271 nb was calculated based on the -particle events between 8.3 and 8.7 MeV.

Journal Articles

New decay properties of $^{264}$ Hs, $^{260}$ Sg, and $^{256}$ Rf

Sato, Nozomi*; Haba, Hiromitsu*; Ichikawa, Takatoshi*; Ideguchi, Eiji*; Kaji, Daiya*; Koura, Hiroyuki; Kudo, Yuki*; Morimoto, Koji*; Morita, Kosuke*; Ozawa, Akira*; et al.

RIKEN Accelerator Progress Report, Vol.42, P. 16, 2009/00

http://www.rarf.riken.jp/researcher/APR/Document/2008.pdf

New Decay Properties of $^{264}$ Hs and its -decay daughter nuclei were studied by using reactions of $^{208}$ Pb( $^{58}$ Fe,2n) and $^{207}$ Pb( $^{58}$ Fe,n) by using a gas-filled recoil ion separator, GARIS at RIKEN. We observed three correlated events in irradiation of $^{58}$ Fe on $^{208}$ Pb, and eight events in irradiation of $^{58}$ Fe on $^{207}$ Pb. A half-life was deduced to be 0.90 $^{+0.40}_{-0.20}$ . We assigned these eleven events to be the decays of $^{264}$ Hs. We found different decay-chain events of $^{264}$ Hs from a previous report. One is a long-lived -decay of $^{260}$ Sg with 180 $^{150}_{-60}$ ms of half-life. Another is a long-lived -decay of $^{256}$ Rf with 10.4 $^{8.4}_{-3.2}$ s of half-life. For $^{260}$ Sg and $^{256}$ Rf, the decay of such a long-lived state have not been reported. These are the first observations of isomerism in $^{260}$ Sg and $^{256}$ Rf.

Journal Articles

Attempt to produce the 3rd chain of $^{278}$ 113

Morimoto, Koji*; Morita, Kosuke*; Kaji, Daiya*; Akiyama, Takahiro*; Goto, Shinichi*; Haba, Hiromitsu*; Ideguchi, Eiji*; Katori, Kenji*; Koura, Hiroyuki; Kudo, Hisaaki*; et al.

RIKEN Accelerator Progress Report, Vol.42, P. 15, 2009/00

http://www.rarf.riken.jp/researcher/APR/Document/2008.pdf

In 2003-2007, we had performed an experiment to synthesize an element 113 by a $^{209}$ Bi $^{70}$ Zn reaction using a gas-filled recoil ion separator (GARIS) at RIKEN Nishina-Center. In a total of 241 days of net irradiation time experiment, two decay chains were observed and assigned from an isotope $^{278}$ 113. The cross section of the $^{209}$ Bi( $^{70}$ Zn,n) $^{278}$ 113 reaction was determined to be 31 $^{+40}_{-20}$ fb at that time. In order to increase the statistics of the decay property, we continued to produce more decay chains. The experiment was carried out from January 7 to March 31, 2008. The experimental conditions were identical to those used in the previous experiment. $^{70}$ Zn ion beam of 353 MeV was extracted from RILAC. The net irradiation time was 83 days and the total dose of $^{70}$ Zn was 2.28 $times10^{19}$ . In the present expriment any candidate of $^{278}$ 113 was not observed. Then combining the results of the present and previous experiments, the production cross section of $^{278}$ 113 was determined to be 22 $^{+29}_{-19}$ fb.

Journal Articles

First-principles electron dynamics simulation for optical breakdown of dielectrics under intense laser field

Otobe, Tomohito; Yamagiwa, Mitsuru; Iwata, Junichi*; Yabana, Kazuhiro*; Nakatsukasa, Takashi*; Bertsch, G. F.*

RIKEN Accelerator Progress Report, Vol.41, P. 185, 2008/00

We simulate the optical breakdown process of dielectrics under the intense laser field employing the first-principle method. Our result for the diamond, which is typical dielectrics, shows the saturation of the energy absorption and electron excitation. We found also the induced field by the surface charge becomes out of phase to the applied field.

Journal Articles

Decay modes of heavy and superheavy nuclei predicted by KTUY mass formula

Koura, Hiroyuki; Tachibana, Takahiro*

RIKEN Accelerator Progress Report, Vol.39, P. 30, 2006/05

no abstracts in English

Journal Articles

Decay modes of heavy and superheavy nuclei

Koura, Hiroyuki

RIKEN Accelerator Progress Report, Vol.38, P. 9, 2005/05

We calculate proton-emission partial half lives and discuss dominant decay modes in the heavy and superheavy nuclidic region. The proton-emission partial half-lives are calculated from the one-dimensional WKB method with single-proton potentials and a mass formula that our group has developed. The calculated half lives well reproduce experimental ones in order of 100 or 1/100 which is similar predictability to other predictions as the alpha decay and the beta decay. We apply this result to calculation of branching ratios of nuclear decays considered the alpha decay, beta decay and spontaneous fission in the heavy and superheavy nuclide region. In this analysis we point out that proton-emitting nuclei are expected to be in the unknown proton-rich nuclidic region with . On the other hand, proton-rich nuclei with have much shorter spontaneous-fission half-lives than ones of proton emissions on this calculation, therefore we conclude that ground-state proton emissions would not occur in that region.