Y. Tomita

Observation of Airy oscillation for the 16O+16O system at Elab = 145 MeV

Abstract We have measured elastic scattering angular distribution at E lab = MeV for the 16 O+ 16 O system, for which nuclear rainbow scattering has been observed recently at E lab = 350 MeV. Analysis of the present data shows that the observed dip at θ cm ≅ 54° and the modulated peak at θ cm ≅62° are an Airy minimum and an Airy maximum, respectively. We found several discrete sets of optical potentials which fit the data. One of them provides a real volume integral which agrees with the previously proposed energy dependence.

The level structure of 50V and the 5.255 MeV isobaric analog resonance in 51V studied by 50Ti(p, n) and (p, nγ) reactions

Abstract The 50Ti(p, n) and (p, nγ) reactions have been studied at proton energies between 3.8 and 5.4 MeV. Excitation functions and angular distributions have been measured for both neutrons and γ-rays. The results have been analyzed by statistical theories. For most of the levels in 50V below 1.9 MeV, spins have been determined. The branching ratios and the mixing ratios for the γ-rays deexciting these levels have also been obtained. The 5.255 MeV analog resonance has been observed in the (p, n) reaction and has been assigned to be 9 2 + .

Fast-neutron scattering from 139La, 141Pr, Er and 209Bi

Abstract The angular distributions of neutrons scattered from 139La, 141Pr, Er and 209Bi were measured at incident energies from 1.5 to 3.5 MeV in 500 keV steps. The results were compared with calculations using both the spherical optical model and the coupled-channels theory. The optical-potential parameters used in both the calculations were determined from comparison of the theoretical calculations with the measured values for 209Bi. The angular distributions for 139La, 141Pr and Er calculated with the coupled-channels theory fit the experiments better than those calculated with a spherical potential, except for the case of the lowest energy for 139La and 141Pr.

Energy dependence of the nuclear level density below the neutron binding energy

Abstract The energy spectra of neutrons inelastically scattered from Co, Ag, In, Ta and Au have been measured in the energy range 3.5–8.5 MeV (every 0.5 MeV step) of incident neutrons by means of the time-of-flight technique with pulsed-beam Van de Graaff accelerators and an ion buncher of the Mobley type. The relations between the level density and the excitation energy are obtained in the 2–8 MeV range. The inverse compound nucleus formation cross sections for several forms of the optical model potential are used in the derivation. For Co and Ag, the relations agree with the prediction of the Fermi gas model. For In, Ta and Au, there are obvious breaks in the observed relations at 4–5 MeV excitation. Below the breaks the observed points fit to the curves calculated by the constant temperature model. Above the breaks they fit those based on the Fermi gas or constant temperature model.

Development of the JAERI tandem superconducting booster

Abstract A heavy-ion superconducting booster project is in progress at JAERI. The booster linac will consist of 40 quarter wave resonators made of niobium and copper. Its buncher and de-buncher have been built, which have resonators identical to those for the linac. With the resonators, we obtained field levels of 5 to 6 MV/m with an rf input of 4 W and a maximum field level of 7 MV/m. The resonators, the proposed bunching system, linac structure and refrigeration system are described.

Transfer cross sections for 28Si + 58,62Ni

Abstract Quasielastic reaction cross sections have been measured for 28 Si + 58,62 Ni at an energy ≈ 40% above the Coulomb barrier. A strong isotope dependence in the transfer cross sections, which are dominated by the one-neutron pickup reaction, has been observed. A simple DWBA analysis can give a consistent description of the experimental results.

Incomplete fusion of the 16O + 27Al reaction

Abstract Velocity spectra of fusion-like residues produced in the reactions of 90 MeV and 150 MeV 16 O with 27 Al were measured. At 90 MeV the velocity spectra were well reproduced by a statistical model calculation. At 150 MeV the observed centroids of the velocity spectra deviate from the statistical model predictions. The centroid shifts as a function of the atomic and mass numbers of evaporation residues were analyzed by two different model calculations based on the assumption that incomplete fusion is (a) a peripheral process, or (b) independent on the angular momentum of the entrance channel, respectively. The later assumption is in better agreement with the presented data.

Performance of the heavy-ion magnetic spectrograph “ENMA” on the kinematic correction

Abstract A magnetic spectrograph, named ENMA, has been successfully put into operation for heavy-ion reaction studies at the JAERI tandem accelerator. The spectrograph consists of two dipoles, a quadrupole and three multipoles arranged in the form of Q-M1-D1-M2-D2-M3. The kinematic broadening has been well compensated for over the kinematic parameter range from k = 0.4 to 1.15 mainly with a quadrupole field produced by the multipole magnet M2. The energy resolution obtained as a function of the kinematic parameter k is consistent with the value estimated from the contributions due to the target effects, the beam emittance and the intrinsic energy resolution of the spectrograph.

Magnetic substate population in 12C + 12C inelastic scattering

Abstract Using the λ-ray recoil method we have measured the spin alignment for the single 2 + excitation in 12 C+ 12 C inelastic scattering over the energy range 19⩽ E cm ⩽55 MeV. The angular distribution of the magnetic substate population has been obtained. As quantization axis for the description of the magnetic substate has been chosen the direction of the center-of-mas scattering angle of a decaying nucleus. The all-over behavior of the angular distribution is satisfactorily reproduced by a simple DWBA calculation.

A 5.5-Mev ION BUNCHER OF MOBLEY TYPE

Abstract An ion buncher of Mobley type, a system for producing ion bursts of high intensity and of nanosecond duration, has been constructed for proton and deutron beams from a 5.5-MV Van de Graaff accelerator and has been successfully used in fast-neutron time-of-flight experiments. In the system an rf resonator is employed in order to obtain a high voltage (50 kV) of 24 Mc which is supplied to the deflector. The Mobley magnet has a mass-energy product of 17. Bunched pulses of 1.0–2.8 ns duration at the target for proton and deuteron beams with energies of 1.2–5.5 MeV were observed on a sampling oscilloscope. The bunching ratio larger than 10 was obtained for the proton pulses of energies higher than 3 MeV and for the deuterons higher than 4 MeV. It was found that the inherent beam spread was almost canceled out at the target by the linear-acceleration effect which was caused by the change in potential between the deflector plates.