Y. Sugiyama

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.

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.

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.

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.

Magnetic field measurement of the Jaeri heavy-ion spectrograph “ENMA”

Abstract A new magnetic spectrograph, named ENMA, for heavy-ion reaction studies was constructed. Magnetic field measurements for two dipoles, one quadrupole and three multipoles, of which the spectrograph consisted in the QMDMDM form, were performed. Almost perfect field distributions were obtained over a full range of the field strength in accordance with the two-dimensional calculation by the programs TRIM and LINDA. The fringing field distribution and the location of the effective field boundaries of the dipole magnets were quite stable against a change of the excitation current. The multipole magnets of the current sheet type were successfully constructed. The field strength of the quadrupole component of the multipole magnet M2 was enough for making the kinematic correction from k = −0.7 to 2.0.