H. Ohnuma

Spin-Isospin Resonances Observed in the (d,2He) and (12C,12N) Reactions at E/A = 135 MeV

Abstract The (d, 2 He) and ( 12 C, 12 N) charge-exchange reactions have been studied at E/A = 135 MeV using the high resolution spectrograph SMART at RIKEN. The similarities were found in the energy spectra of both reactions, indicating the strong selectivity of ΔS = 1 and ΔT = 1 transitions. The 12 C( 12 C, 12 N) 12 B reaction has been studied using the microscopic DWBA calculation, suggesting that the reaction predominantly goes thorough a one-step process. The dominance of the L = 0 component was also found.

Proton single-particle states in [sup 21,23]Na through the ([ital d],[ital n]) reaction

Proton single-particle states in [sup 21,23]Na were studied through the ([ital d],[ital n]) reaction on [sup 20,22]Ne at [ital E][sub [ital d]]=25 MeV. Angular distributions of the emitted neutrons leading to the final states up to [ital E][sub [ital x]]=15 MeV were measured. Spectroscopic information has been obtained from an analysis with the adiabatic deuteron breakup approximation, where [ital s]-wave deuteron breakup effects have been included. Proton unbound transitions were analyzed by means of Vincent and Fortunes method. It was found that the observed proton single-particle states in [sup 21,23]Na exhausted almost all the strength for the 2[ital s]1[ital d] shell. The distributions of the 2[ital s]1[ital d] strength were reasonably reproduced by recent 2[ital s]1[ital d] shell model calculations. The occupation probabilities and single-particle energies of the proton orbits near Fermi levels in the ground states of [sup 20,22]Ne were deduced in a framework of combined analysis of the stripping and pickup data on the same target nucleus.

Charge-exchange reaction 12C(12C, 12N)12B at EA = 135 MeV

Abstract The charge-exchange reaction 12 C( 12 C, 12 N) 12 B has been studied at E A = 135 MeV . The elastic scattering of 12 C from 12 C was also measured to determine the optical potential parameters. The differential cross sections for the charge-exchange reaction leading to the 12 B ground state (1 + ) were well described byh the microscopic DWBA calculation, suggesting the dominance of the one-step process. The L = 0 component was found to be about five times stronger than the L = 2 component at 0°.

Tensor analyzing power of the (d, 2He) reaction at 270 MeV

Abstract The tensor analyzing power of the (d, 2He) reaction has been measured at 270 MeV. Its usefulness for spectroscopic studies, particularly in identifying the Jπ of spin-flip dipole states, is demonstrated for a 12C target. The data are reasonably well reproduced in terms of the distorted-wave Born approximation theory for the three-body reaction.

Spectroscopy of 24Al through the 24Mg(p, n)24Al reaction at Ep = 35 MeV

Abstract An experimental study of the 24 Mg(p, n) 24 Al reaction at E p = 35 MeV was carried out. High-resolution neutron time-of-flight spectra were measured at 17 angles in a range of 0°–110°. Neutron peaks corresponding to seventeen states in 24 A1 have been resolved. A number of spin-parity assignments have been made based on distorted-wave Born-approximation (DWBA) analyses for the measured angular distributions, using microscopic transition amplitudes obtained from the 1s0d shell model for positive-parity states and those from the 0s0p-1s0d-1p0f open-shell randomphase approximation (OSRPA) for negative-parity states. Reasonable correlation between the low-energy (p, n) cross section and the β-decay strength has been found for the observed 0 + →1 + Gamow-Teller transitions leading to the 0.439, 1.116 and 3.023 MeV states in 24 Al. The 1.56 MeV 5 + state has been identified as a 0 h ω stretched state, in addition to the 5.54 MeV, 6 state of 1 h ω character. Candidates for the 1 h ω negative-parity transitions leading to the 2, 3, 4 states are also presented.

The 12C(d, p)13C reaction at Ed = 30MeV and positive-parity states in 13C

Abstract The 12 C(d, p) 13 C reaction has been studied at E d = 30MeV. All the known positive-parity states of 13 C below 10 MeV in excitation energy, including the 7 2 + and 9 2 + states, are observed in this reaction. The angular distributions for these positive-parity bound and unbound states are analyzed in CCBA framework. The 13 C wave functions, which reproduce the resonant and nonresonant scattering of neutrons from 12 C, also give good accounts of the experimentally observed angular distributions and energy spectra of outgoing protons in the 12 C(d, p) 13 C reaction. In most cases the cross-section magnitude and the angular distribution shape are primarily determined by the 0 + ⊗ j component, even if it is only a small fraction of the total wave function. An exception is the 7 2 + state, where the main contribution comes from the 2 + ⊗ d 5 2 component. The inclusion of the 4 + state in 12 C and the g 9 2 and g 7 2 neutron components in the n + 12 C system has a very small effect on the low-spin states, but is indispensable for a good fit to the 7 2 + and 9 2 + angular distributions. The transitions to the negative-parity states, 1 2 1 − , 3 2 1 − , 5 2 − , 7 2 − and 1 2 3 − , are also observed experimentally, and are analyzed by DWBA.

12C(p, n)12N and 16O(p, n)16F reactions at Ep = 35 and 40 MeV: Reliability of the information obtained from DWBA analysis of low-energy (p, n) data

Abstract A high-resolution study of the 12C(p, n)12N and 16O(p, n)16F reactions was made at Ep = 35 and 40 MeV. The low-lying states in 12N(1+, 2+ and 2−) and in 16F(0−, 1−, 2− and 3−) were clearly resolved, and their angular distributions were measured. Extensive DWBA analysis was made and compared with the data. The calculated angular distribution shapes are found to be in agreement with the data and insensitive to the choice of the parameters involved. On the other hand, the magnitudes of the DWBA cross sections depend strongly on the bound state parameters in the case of a transition from a tightly bound state to a loosley bound state. In the other cases the overall uncertainty of the DWBA cross section magnitudes was estimated to be about ±30%. Within this uncertainty the experimental cross sections for the 12C(p, n) reaction were explained by the calculation, but those for the 16O(p, n) reaction were not: the observed strengths were about a half of the calculated values. Since these results agree with those at intermediate energies, the origin of the discrepancy is considered to be in the structure of the mass 16 nuclei rather than in reaction dynamics. In general, the present results compare well with those at intermediate energies, indicating that the structure information extracted from low-energy, high-resolution (p, n) data is basically sound if careful analysis of the data is made.

A comparative study of the 13C(p, p′)13C and 13C(p, n)13N reactions at Ep = 35 MeV☆

Abstract Differential cross sections were measured at Ep = 35 MeV for the 13C(p, n) and 13C(p, p′) reactions leading to the four low-lying states in the mirror nuclei 13N and 13C. In addition, the analyzing powers were measured for the 13C(p, p′) reaction. The data are generally well accounted for by DWBA calculations except for the 13 C(p, p′) 13 C (3.09 MeV , 1 2 + ) reaction, for which the calculations cannot even reproduce the qualitative features of the data. A comparison of the (p, n) and the (p, p′) results suggests that the isoscalar part of the 13 C ( g.s. , 1 2 − ) → 13 C (3.09 MeV , 1 2 + ) transition is not correctly described by currently available shell-model wave functions.

Isovector deformation parameters from the (p, n) reactions on 54, 56Fe and 58, 60, 62, 64Ni at 35 MeV

Abstract The (p, n) reactions on 54, 56 Fe and 58, 60, 62, 64 Ni have been studied at E p = 35 MeV. Angular distributions of emitted neutrons leading to ground-state analogs and 2 + excited-state analogs were obtained for each target. Differential cross sections have been found to be consistent with the predictions obtained from DWBA calculations in which the Lane potential was employed. It was found that the direct process dominates at E p = 35 MeV for the excitation of 2 + analogs. Their isoveetor deformation parameters are extracted from these isotope sets by comparison with the DWBA calculations. The magnitudes of the isoveetor deformation parameters are larger than the isoscalar parameters by a factor of 3 to 5, and are consistent with the calculated results in terms of the core polarization.

Energy-dependent measurements of the pp elastic analyzing power and narrow dibaryon resonances

Abstract The energy dependence of the pp elastic analyzing power has been measured using an internal target during polarized beam acceleration. The data were obtained in incident-energy steps varying from 4 to 17 MeV over an energy range from 0.5 to 2.0 GeV. The statistical uncertainty of the analyzing power is typically less than 0.01. A narrow structure is observed around 2.17 GeV in the two-proton invariant mass distribution. A possible explanation for the structure with narrow resonances is discussed.