RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics(γ,n) and (γ,2n) cross sections in Coulomb breakup reactions of79
Se,80 Se at 200 MeV/nucleon
A. Hirayama,∗1,∗2 S. Takeuchi,∗1∗2 T. Nakamura,∗1∗2 Y. Kondo,∗1∗2 Y. Togano,∗1∗2 M. Shikata,∗1∗2J. Tsubota,∗1∗2 T. Ozaki,∗1∗2 A. T. Saito,∗1∗2 T. Tomai,∗1∗2 H. Wang,∗2 H. Otsu,∗2 H. Sakurai,∗2 S. Kawase,∗3N. Watanabe,∗3 and the ImPACT collaboration
SAMURAI magnet to measure the scattering angle ofcharged particles. At the exit of the magnet, FDC2(MWDC) was installed to measure the bending angles
and trajectories of the charged fragments. A plastichodoscope was placed behind the FDC2 to measure
ΔE and timing information. The hodoscope consistsof seven slats of plastic scintillators with a thicknessesof 5 mm.
An analysis for charged particles is now ongoing.
Identiﬁcation of the atomic number was performed using the plastic hodoscope. By correcting the x- andy-position dependence of the light output in the scintillator, 4σ separation for atomic number has beenachieved. To obtain mass-to-charge ratio, magnetic
rigidities will be deduced by tracking information fromthe FDC1 and FDC2. Further analysis is in progress
to deduce the inclusive and exclusive cross sections ofthe Coulomb breakup reactions.
This research was funded by ImPACT Program ofCouncil for Science, Technology and Innovation (Cabinet Oﬃce, Government of Japan).

High-level radioactive wast, generated at nuclear
power plants contain long lived ﬁssion products(LLFPs). Dumping LLFPs is still diﬃcult becauseof their long lifetime. One way to reduce or reuse
the LLFPs is the transmutation of the LLFPs into a
short-lived or stable nucleus using nuclear reactions.
For this transmutation, basic nuclear reaction data on
LLFPs are important. Therefore, we performed nuclear reaction experiments using the LLFPs produced
as secondary beams. In this report, we focus on the(γ,n) and (n,γ) reactions for the LLFPs and 79,80 Se.
The 79 Se nucleus is an LLFP with a lifetime of 0.3M
years. The (n,γ) reaction of LLFPs is important fortransmutation ; however, experiments on the (n,γ)
reaction have several diﬃculties. Therefore, we havemeasured the (γ,n) reaction as an alternative way todeduce the (n,γ) reaction cross section by introducing
the Coulomb breakup reactions of 79,80 Se in inverse
kinematics.
The experiment was performed using the SAMURAI spectrometer1) at the RIKEN Nishina Center.
Secondary beams of 79,80 Se with an energy of 200
MeV/nucleon were produced by the in-ﬂight ﬁssionof a 238 U primary beam with 345 MeV/nucleon on a9Be production target. Particle identiﬁcation of thesecondary beams was performed using BigRIPS. The
momentum slit at the F1 focus was set to 0.1%, andthe ΔE-TOF method using F7 and F13 plastic scintillators and the ionization chamber (ICB) at F13 wasenough to identify secondary beams without Brho reconstruction. Figure 1 shows the particle identiﬁcation of the secondary beams for the 79 Se setting. Thesecondary beam intensities are 2,700 and 2,500 cps atF13, beam energies were 216 and 218 MeV/nucleon,
and beam purities were 54 % and 49 % for 79 Se and80Se, respectively. Beam directions and positions weremeasured by BDC (MWDC), which was placed upstream of the secondary target. Secondary targets ofPb and C with thickness of 0.54 g/cm2 and 0.26 g/cm2 ,respectively, were placed at the F13 focus and surrounded by DALI2 to detect de-excitation γ rays forreaction identiﬁcation. Neutrons decaying from the excited states were detected by NeuLAND2) and NEBULA.3) Charged fragments produced in the breakup
reactions were analyzed by the SAMURAI spectrometer. FDC1 (MWDC) was placed at the entrance of the∗1∗2∗3Fig. 1. Particle idetiﬁcation of the secondary beam (for the79Se setup)

References
1) T. Kobayashi et al. , Nucl. Instrum. Methods Phys. Res.
Sect. B317, 294 (2013).
2) https://www.gsi.de/work/fairgsi/rareisotopebeams/
r3b/neuland.htm
3) T. Nakamura et al. , Nucl. Instrum. Methods Phys. Res.
Sect. B376, 156 (2016)

Department of Physics, Tokyo Institute of Technology
RIKEN Nishina Center
Faculty of Engineering and Science, Kyushu University- 48 -