Y. Ishizaki

Level structure of 116Sn and 117Sn from (p, d), (p, t) and (p, p′) reactions

Abstract The level structure of 116 Sn has been investigated by the reactions 117 Sn(p, d), 118 Sn(p, t), and 116 Sn(p, p′) with 55 MeV incident protons and that of 117 Sn by 118 Sn(p, d) and 117 Sn(p, p′) reactions. The emitted particles have been analysed with a broad-range magnetic spectrometer. Angular distributions of emitted particles in the (p, d), (p, t) and (p, p′) reactions are analysed in terms of the DWBA method. A strong similarity between the 117 Sn(p, d) and 118 Sn(p, t) reactions is found in the excitation of all of the observed states in 116 Sn. Three new 2 + states in 118 Sn are identified both from the (p, d) and (p, t), and two excited 0 + states are established. Spectroscopic factors for 25 states extracted from the 117, 118 Sn (p, d) reactions are compared with theoretical predictions based on the pairing interaction plus quadrupole-quadrupole and octupole-octupole interactions. The agreement is reasonably good except for the 2 + states at E x ≈ 4 MeV in 116 Sn.

Ground-state transition strengths of the (p, t) reactions for nuclei with A = 23−238

Abstract Differential cross sections at the first peak of L = 0 angular distributions of ground-state transitions in (p, t) reactions have been measured with a 51.9 MeV proton beam for target nuclei with A = 23–238. Distinct shell-closure effects were observed at N = 28, 50, 82 and 126, but not discernible at N = 20. The transition strengths exhibit maxima at the middle of the major shells except for the region of well-deformed nuclei, where the strengths are appreciably smaller than those for the spherical or vibrational nuclei. The results are compared with the predictions of the interacting boson approximation model (IBA) and with DWBA calculations using form factors deduced from the BCS wave functions.

The single-hole states in the 50 < N ≦ 126 shell with (p, d) reactions

The neutron single-hole states in the 50 < N ≦ 82 shell have been studied by the 140Ce(p, d) reaction at 55 MeV incident energy, and those in the 82 < N ≦ 126 shell by 208, 206Pb(p, d) reactions. Emitted deuterons have been analysed with a broad-range magnetic spectrometer. Angular distributions are analysed in terms of the DWBA method. The l-values for all deuteron groups are assigned, and the jπ value and the spectroscopic factor for each state are obtained. The single-hole energies in 58139Ce81 obtained are d32 − 0; s12 − 0.25; h112 − 0.75; d52 − 1.58; g72 − 2.81 MeV (in excitation energies). These results are much different from those of the Pittsburgh group with the (d, t) reactions. The new result that the g72 state jumps below the d52state is interpreted by considering the interaction between the g72 neutrons and the last eight protons in the g72 orbit of 139Ce. The single-hole energies in 82207Pb125 are: p12 − 0; f52 − 0.57; p32 − 0.90; i132 − 1.63; f72 − 2.34; h92 − 3.41 MeV. The correspondence of the states in 205Pb with those in 207Pb is obtained from the angular distribution analysis. No evidence is found for the J-dependence of angular distributions in either the l = 3 or l = 1 Pb(p, d) transitions. The Q-dependence is discussed.

Study of the ηπ− system in the π−p reaction at 6.3 GeV/c

Abstract Data of the ηπ− system were obtained in the reaction π−p → ηπ−p at 6.3 GeV/c beam momentum. About 17 k events of ηπ− were collected in the mass range 0.8 ⩽ Mηπ- ⩽ 1.8 GeV/c2 and in the range of the momentum transfer squared 0.075 ⩽ |t′| ⩽ 0.60 (GeV/c)2. A large forward-backward asymmetry was observed around 1.3 GeV/c2 in the Gottfried-Jackson frame of the ηπ− system. A partial wave analysis of the data was performed. A peak of the D+ wave attributed to a2 (1320) is clearly seen. An enhancement is observed around 1.3 GeV/c2 in the P+ wave.

Excited 0+ states in 52Fe, 54Fe, 56Ni and 58Ni from the (p, t) reaction

Abstract Excited 0 + states have been observed at 4.14, 2.54, 4.99 and 2.94 MeV in 52 Fe, 54 Fe, 56 Ni and 58 Ni, respectively, in the (p, t) reaction. A shell model interpretation of these 0 + levels is given in terms of four particle(hole) - m hole(particle) configurations.

Observation of two-hole states at high excitation energy in (p, t) reactions

Abstract Bumps of two-hole states at high excitation energies were observed systematically in the triton spectra from (p, t) reactions with 52 MeV protons on nuclei in a broad range of masses. The cross sections of the bumps are almost equal for various targets with the same deep major shells. These cross sections vary discontinuously with variation of the corresponding deep major shell. About 20 to 50 % of the total expected strength is observed experimentally, if the bumps are assumed to arise from two-neutron pickup from the deep major shells. The centres of gravity of the bumps are located at excitation energies of about 7 to 9 MeV in all cases. On the other hand, the widths of the bumps change from about 3 MeV for 66 Zn to about 9 MeV for 230 Th.

Vector resonances around 1.6 GeV of the ηπ+π− system in the π−p charge exchange reaction at 8.95 GeVc

Abstract High statistics data of the ηππ system in π − p → ηπ + π − n were obtained. A partial wave analysis was performed in the mass region between 1.37 and 1.85 GeV. Resonant structures were observed in the IJ PC = 11 −− wave around 1.6 GeV and in 13 −− around 1.7 GeV. The structure in 11 −− was fitted with a single Breit-Wigner and also fitted with two Breit-Wigners. The result suggests the possible existence of two vector resonances around 1.6 GeV. The structure in 13 −− is considered to be the π 3 (1690).

Core-excited states of 54Fe from the 56Fe(p, t)54Fe reaction at 52 MeV

Abstract The (p, t) reaction on 56 Fe has been studied at a bombarding energy of 51.9 MeV using a broad-range magnetic spectrometer. States of 54 Fe were identified up to an excitation energy of 7.6 MeV. Differential cross sections were obtained for 16 triton groups. From the shapes of angular distributions J π = 0 + , 2 + , 3 − and 4 + were assigned for 11 levels. The 0 + state at 2.56 MeV was strongly excited (≈ 27% of the ground state transition). Comparison with the DWBA calculation was made based on the shell-model calculation on 54 Fe with ( f 7 2 ) −(n+2) ( p 3 2 , f 3 2 , p 1 2 ) n configurations for the low-lying even-parity states. The agreement with the experimental results was satisfactory for most of the states with appreciable (p, t) strengths which were interpreted as core-excited states mostly with 3h-lp and 4h-2p configurations. An empirical normalization constant of 12.5 was derived from the L = 0 ground state transition.

The l = 3 and 4 transitions in inelastic scattering of protons from 66Zn

Abstract Elastic and inelastic scatterings of protons from 66 Zn have been studied at 55.01 MeV incident energy. Scattered protons have been analysed and detected by a broad-range magnetic spectrometer with a 200 proportional counter system. No strongly excited states have been observed in the excitation energy E x > 6 MeV. Angular distributions are analysed in terms of the DWBA method. In addition to the well-known first 2 + and 3 − states, six l = 3 transitions with reduced transition rates of 2 ∼ 1 in a single particle unit are observed for excitation energies in the 4.1–5.7 MeV region. Two l = 4 transitions are also observed for excitation energies of 3.08 and 4.70 MeV.

Neutron single-hole states in 149Sm, 157Gd and 196Au investigated by (p, d) reactions

Abstract In order to continue studies of neutron single-hole states in nuclei of 50 ≦ N ≦ 126, (p, d) reactions on 150 Sm, 158 Gd and 197 Au have been investigated by the use of a proton beam of 55 MeV. Emitted particles were analysed with a broad-range magnetic spectrometer and detected with a 200 proportional counter system. Angular distributions of 39 deuteron groups are analysed with the aid of the DWBA method. The l -values are assigned, and J π values and the spectroscopic factor for each state are obtained. Many new excited states have been found and their J π values are given. Energy shifts of the neutron single-hole states of 3p 1 2 ., 2f 5 2 , 3p 3 2 , li 13 2 , 2f 7 2 and 1h 9 2 observed between 207,205 Pb and 196 Au are interpreted on the basis of effective proton-neutron interactions. The observed energy shifts are reproduced rather well by the use of the interaction V pn = ( V 0 + V 1 σ p · σ n ) δ (r p − r n ) and of the harmonic-oscil except for the case of the p 1 2 state. In order to explain the shift of the p 1 2 state relative to the p 3 2 state, it is necessary to introduce some spin-dependent interactions such as tensor interactions and/or two-body spin-orbit interactions.