Keiichi Kisamori

Candidate Resonant Tetraneutron State Populated by the He 4 (He 8, Be 8) Reaction

A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction ^{4}He(^{8}He,^{8}Be) at 186  MeV/u. The energy of the state is 0.83±0.65(stat)±1.25(syst)  MeV above the threshold of four-neutron decay with a significance level of 4.9σ. Utilizing the large positive Q value of the (^{8}He,^{8}Be) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently.

Sharaq Spectrometer: High-resolution Spectroscopy Using Exotic Beams And Reactions

We introduce the recent development for increasing the performance of the SHARAQ spectrometer, which was operated at RI Beam Factory in RIKEN, Japan. The paper contains main achievements of our developments, which are detector developments, improvements of high-resolution performance at SHARAQ, and developments of new reaction probes to explore new kinds of nuclear responses. By using those new experimental technique, we recently performed various nuclear experiments at SHARAQ. We described here the preliminary results of the experiments together with their brief details.

Heavy-Ion Double-Charge Exchange Study via a 12 C( 18 O, 18 Ne) 12 Be Reaction

Motonobu Takaki! (CNS, The University of Tokyo)! ! H. Matsubara2, T. Uesaka3, N. Aoi4, M. Dozono1, T. Hashimoto4, T. Kawabata5, 
 S. Kawase1, K. Kisamori1, Y. Kubota1, C.S. Lee1, J. Lee3, Y. Maeda6, S. Michimasa1,
 K. Miki4, S. Ota1, M. Sasano3, T. Suzuki4, K. Takahisa4, T.L. Tang1, A. Tamii4, 
 H. Tokieda1, K. Yako1, R. Yokoyama1, J. Zenihiro3, and S. Shimoura1! ! 1CNS, The University of Tokyo! 2National Institute of Radiological Science (NIRS)! 3RIKEN Nishina Center! 4Research Center for Nuclear Physics, Osaka University! 5Department of Physics, Kyoto University! 6Department of Applied Physics, University of Miyazaki

Spin-Isospin Response of the Neutron-Rich Nucleus 8He via the \((p,n)\) Reaction in Inverse Kinematics

A systematic study of the nucleon density distributions of finite nuclei is important for understanding the isospin dependence of the nuclear many-body system. For example, the neutron skin thicknesses are known to be strongly correlated with the density-dependent term of the symmetry energy, and the isospin-dependent term of the nuclear equation of state. In previous works, we have succeeded in extracting the neutron density distributions of stable nuclei such as Sn and Pb isotopes via proton elastic scattering. At the same time we have launched a new project aimed at measuring the Elastic Scattering of Protons with RI beams (ESPRI) with the purpose of the extraction of proton and neutron density distributions of unstable nuclei. We have newly developed and tested unique devices for the ESPRI measurements at NIRSHIMAC in Chiba and GSI in Germany. Finally, we have successfully performed the ESPRI experiment at RIBF in April, 2013. Unlike the case of stable nuclei, however, we have no information on the nuclear charge densities of unstable nuclei. Thus, we have proposed a new method to extract proton and neutron densities via two-energy proton elastic scattering. This method is based on the large difference between the energy dependences of the p-p and p-n interactions. Recently, we performed an experiment to demonstrate this new method using real data of Zr isotopes. In this report, we show the preliminary results of Zr only. For other isotopes (Zr), the analysis is still ongoing. The experiment was performed at RCNP, Osaka University. Polarized proton elastic scattering from Zr and Ni at 200 and 300 MeV was measured by using the Grand Raiden magnetic spectrometer. Figure 1 shows the angular distributions of cross sections (dσ/dΩ) and the analyzing powers (Ay) of Zr(p⃗,p) at 200 and 300 MeV and of Ni(p⃗,p) at 200 MeV. The red lines denote the result of relativistic impulse approximation (RIA) with relativistic-Hartree (RH) densities. The Ni data was used to determine the effective interaction at 200 MeV (solid lines). Using the effective interaction, the proton and neutron densities of Zr were simultaneously searched and the results are denoted by the solid lines in Fig. 1 and 2. The

Measurement of the 8 He( p,n ) 8 Li Reaction at Intermediate Energy in Inverse Kinematics

We performed the first measurement of the He(p, n)Li reaction at a beam energy of 190A MeV in inverse kinematics at the RIKEN RI Beam Factory (RIBF). It is well known that (p, n) measurements at intermediate energies are powerful tools to study spin-isospin responses of nuclei. A facility for (p, n) measurements in inverse kinematics was constructed at RIBF to extend the field of spin-isospin physics to unstable nuclei. The main component of this facility is the neutron detector WINDS, which was recently developed for detection of recoil neutrons with low kinetic energies. A fundamental study on the structure of He is its β-decay, for which the Q-value is 10.7 MeV. In contrast to β-decay, charge-exchange reactions, such as (p, n) reactions, do not suffer from the Q-value limitation and can be used to study transitions to highly-excited states. Figure 1 shows a preliminary spectrum of the He(p, n)Li reaction by tagging the Li isotopes. Two loci are observed in this spectrum. The locus at low excitation energy is most likely the Ex = 0.98 MeV state with B(GT) = 0.24, which has been observed in previous β-decay studies. A large transition strength is found at around Ex ∼ 8 MeV, which is a candidate for the Gamow-Teller state. In the present work, the angular distribution of the differential cross sections will be analyzed to clarify the nature of this state.