H. Ikezoe

Α-nucleus potential for α-decay and sub-barrier fusion

The set of parameters for {alpha}-nucleus potential is derived by using the data for both the {alpha}-decay half-lives and the fusion cross sections around the barrier for reactions {alpha}+{sup 40}Ca, {alpha}+{sup 59}Co, and {alpha}+{sup 208}Pb. The {alpha}-decay half-lives are obtained in the framework of a cluster model using the WKB approximation. The evaluated {alpha}-decay half-lives and the fusion cross sections agreed well with the data. Fusion reactions between {alpha} particles and heavy nuclei can be used for both the formation of very heavy nuclei and spectroscopic studies of the formed compound nuclei.

Two deformation paths in proton-induced fission of 232Th☆

Abstract Velocities of complementary fission fragments have been accurately measured by a double velocity time-of-flight method in the proton-induced fission of 232 Th with incident energies from 12.0 to 14.7 MeV. The results experimentally demonstrate for the first time the correlation among the threshold energy, the total fragment kinetic energy, and the mass division mode in fission: one type of the fission process has a lower threshold energy and leads to a compact scission configuration with reflection asymmetry, and the other type has a higher threshold energy and leads to a symmetric elongated scission configuration.

Niobium superconducting quarter-wave resonators as a heavy ion accelerating structure

Abstract A superconducting quarter-wave resonator with an optimum beam velocity of 0.1 c has been developed for the JAERI tandem heavy-ion booster. The resonator structure is made of niobium and copper. A prototype resonator and two resonators for the buncher of the booster have been built. The buncher resonators generated accelerating field gradients of 6 MV/m at an rf loss of about 4 W and 6.8–7.0 MV/m at maximum. The result was confirmed with CI beams of β (= v / c ) = 0.1.

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.

In-beam α- and γ-ray spectroscopy for 216Ra

Abstract By a simultaneous observation of α-particle decays and γ-rays in the 208 Pb( 12 C, 4n) and 207 Pb( 12 C, 3n) reaction we have found extremely short-lived long-range α-particle decays from high-spin states in 216 Ra and established their decay properties. The level sequence of 216 Ra was established up to 11 − (possibly 14 + ).

JAERI magnetic spectrograph for heavy-ion research

Abstract The design of a magnetic spectrograph for heavy-ion reaction studies with the JAERI 20 MV tandem accelerator is described. The spectrograph consists of a quadropole (Q), a multipol (M1), a dipole (D1), a multipole (M2), a dipole (D2) and a multipole (M3). In order to obtain a unique mass identification over a wide mass range in combination with the time-of-flight measurement, the pain length difference ΔL is kept small: L/ΔL is designed to be larger than 210 for a horizontal angular spread of 5 mrad. A momentum resolving power P/ΔP of 7000 is obtainable for solid angles up to 16 msr. The M2 magnet is used to correct the kinematic effect in the range from k= −0.4 to 1.0. The dispersion is variable from 10 to 15.5 m along the focal plane for k = 0 by use of the M3 magnet.

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.

TRANSPORT EFFICIENCY OF JAERI RECOIL MASS SEPARATOR

Abstract Solid angles and transport efficiencies of the JAERI recoil mass separator were measured by using three procedures, that is, by using (1) α-particles from an 241 Am source, (2) elastic recoils of 197 Au produced in the bombardments of 28 Si beams on 197 Au targets and (3) evaporation residues produced in the fusion reaction of 30 Si+ 141 Pr. The solid angles of 11 and 21 msr were obtained for the focus conditions of the mass dispersion (x | δ m )=−1.1 and 0 cm /% respectively. The measured transport efficiency was compared with the ion-optical calculation of GIOS and a good agreement between the calculation and the present data was obtained. The charge state distributions of low-energy heavy recoils 167 Ta and 197 Au were also measured and compared with the various calculations. It was found that the empirical formula by Shima et al. well reproduced the present data.

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.