K. Ideno

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.

Airy minimum crossing θcm = 90° at Elab = 124 MeV for the 16O + 16O system

We have measured the elastic scattering angular distribution for the 16O + 16O system at Elab = 124 MeV, where a prominent minimum has been observed in the θcm = 90° excitation function. The measured angular distribution shows modulated Airy structures at large angles with a dip at θcm = 90°. It is concluded that the prominent minimum in the excitation function is due to an Airy minimum, most likely to be the third member, crossing 90° at that energy.

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.

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.

Pre-scission sup 4 He multiplicity in the sup 19 F+ sup 197 Au reaction

Pre- and post-scission {sup 4}He particle multiplicities for the {sup 19}F+{sup 197}Au reaction in the excitation energy range of 43 to 90 MeV have been measured in coincidence with fission fragments. The coincident {sup 4}He particles measured at backward angles are accounted for by evaporation from a compound nucleus and fission fragments. The most probable center-of-mass energy of the {sup 4}He particles measured at backward angles is shifted towards lower energies by {approx}2 MeV compared to a statistical model calculation performed by assuming {sup 4}He emission from a spherical compound nucleus. The observed pre-scission {sup 4}He multiplicity as a function of excitation energy is compared to a set of statistical-model calculations which also included the delayed onset of fission. The comparison shows that the observed energy dependence of the pre-scission {sup 4}He multiplicity is reproduced by the calculation without taking into account the delayed onset of fission if the reduced emission barrier for {sup 4}He is assumed in the calculation. The emission mechanism of the pre-scission {sup 4}He is discussed.

Charged particle emissions in fission process

Abstract Pre- and post-scission multiplicities of proton and α particle have been measured in the reactions of 19 F + 181 Ta, 197 Au, 208 Pb and 28 Si + 197 Au, 208 Pb and 16 O + 197 Au. Pre-scission data show no systematic deviation from statistical model calculations if measured emission barriers for charged particles are taken into account in the transmission coefficient calculations. This suggests that the transient time during which fission widths reach a stationary value at saddle point is less than about 10 −20 sec. Post-scission multiplicities of proton and α particle show steep increases with compound nucleus excitation energies.

Statistical emission of complex fragments produced in the reaction 37Cl + 68Zn

Abstract Kinetic energy, angular and charge distributions have been measured for complex fragments (5 ⩽ Z ⩽ 29) produced in the 37 Cl induced reactions on 68 Zn at laboratory bombarding energies of 156, 166 and 177MeV. The characteristics of the fragments observed at backward angles are consistent with those of the decay products from an equilibrium compound nucleus. The charge distributions of these products are reproduced by the statistical model calculation which takes account of the potential energy associated with mass asymmetry and angular momentum. The influence of angular momentum on the width of the charge (mass) distributions for symmetric mass division is discussed.

Symmetric mass division process in the reactions 37Cl+68Zn and 16O+89Y

Abstract To investigate a feature of the symmetric mass division at high angular momentum, distributions of mass, angular and total kinetic energy have been measured with a time-of-flight telescope for the products of symmetric mass division in the 37 Cl+ 68 Zn and 16 O+ 89 Y reactions. The widths of the mass and totalkinetic energy distributions are broader than those expected from the liquid drop model.