K. Hatanaka

Facility for the (p, n) polarization transfer measurement

Abstract We have designed and constructed a facility to measure the complete polarization transfer coefficient Dij for the (p, n) reaction at intermediate energies. The facility consists of a beam swinger dipole magnet used for angular distribution measurements and a 100 m tunnel for the neutron energy measurement by the time-of-flight method. Typical neutron energy resolution is about 1.85 MeV for 290 MeV neutrons including a contribution of 1 MeV due to the target thickness. The background associated with this tunnel system was carefully investigated and found to be negligibly small. A dipole magnet for the neutron spin rotation is installed in the neutron flight path to measure the longitudinal polarization as well as the induced polarization. The neutron polarimeter which consists of 6 planes of the two-dimensional position-sensitive neutron detectors with a size of 1 m × 1 m × 0.1 m has been constructed. Its effective left-right analyzing power 〈Ayeff〉 has been calibrated at 194, 290 and 384 MeV. The figure-of-merit value defined by 〈Ayeff〉2 × eDS at 290 MeV is 4.05 × 10−4, where eDS is the double scattering efficiency.

Realization of matching conditions for high-resolution spectrometers

For precise measurements of nuclear-reaction spectra using a beam from an accelerator, a high-resolution magnetic spectrometer is a powerful tool. The full capability of a magnetic spectrometer, however, can be achieved only if the characteristics of the beam coming from the accelerator are matched to those required by the spectrometer by properly adjusting the beam line conditions. The matching methods, lateral dispersion matching, focus matching and also the kinematic correction compensate the spectrum line-broadening effects caused by the beam momentum spread and reaction kinematics. In addition, angular dispersion matching should be performed if good resolution of the scattering angle is important. Diagnostic methods developed to realize these matching conditions for the spectrometers K600 at IUCF and Grand Raiden at RCNP are presented.

Attenuation of neutrons in the atmosphere and a thick carbon target

Abstract A neutron beam dump experiment has been carried out using the accelerator beam at RCNP, Osaka University. Neutrons with energies Tn=100– 400 MeV were allowed to bombard a carbon target (density 1.8 g / cm 3 ) which had a thickness varying from 0 to 300 cm , and the attenuation of the neutrons was measured in the range from 0 to 540 g / cm 2 . The experimental data were well reproduced by the Monte Carlo calculation by the Shibata model. Using these results, the attenuation of neutrons in the Earths atmosphere was obtained by means of a simulation. The results are useful not only for cosmic ray experiments but also for radiation protection experiments since the target does not contain hydrogen.

Gamow–Teller transitions in exotic pf-shell nuclei relevant to supernova explosion

Gamow–Teller (GT) transitions starting from unstable pf-shell nuclei are of interest not only in nuclear physics, but also in astrophysics, e.g. in violent neutrino induced reactions at the core-collapse stage of type II supernovae. In the β-decay study of these pf-shell nuclei, half-lives can be measured rather accurately. On the other hand, in high-resolution (3He, t) charge-exchange reactions at 0°, individual GT transitions up to high excitations can be studied. Assuming the isospin symmetry for the strengths of Tz = ±1 → 0 analogous GT transitions, we present a unique merged analysis for the determination of absolute B(GT) values.

Gamow-Teller transitions in the Ni-64(He-3, t)Cu-64 reaction

In order to study the Gamow–Teller (GT) transitions in the fp-shell nucleus 64Cu, the 64Ni(3He, t)64Cu charge-exchange reaction was investigated at MeV/nucleon [1]. The outgoing tritons were momentum analysed by the Grand Raiden spectrometer at 0°. The very high energy resolution of 35 keV (FWHM) allowed the separation of individual levels in the excitation energy region from 0 to 3.5 MeV. An angular distribution analysis was performed for the observed transitions to these states. In addition to the ground state (g.s.), known to be a Jπ = 1+ GT state, several excited states showed L = 0 nature, making them candidates of GT states. At higher excitation energies, the level density becomes very high and a bump-like structure, the so-called GT Giant Resonance, dominates the spectrum.