T. Ishimatsu

The ion-guide isotope separator on-line at the Tohoku University Cyclotron

Abstract The status of the ion-guide isotope separator on-line at the Tohoku University Cyclotron is reported. The optimum ion-guide parameters were determined from test experiments using atomic and molecular ions ionized with an electric discharge inside the target chamber as well as using 64 Ga(T 1 2 = 2.6 m ) ions produced by the 64Zn(p, n) reaction. Using the present system together with a ΔE−E plastic counter telescope and a germanium detector we identified 16 short-lived nuclei including the first mass-separated nuclei 57Cu and 45V. The efficiency of mass separation for 64Ga was ϵ ∼ 1%, where ϵ is defined as the number of atoms collected at the end of the separator divided by that recoiling from the target. Application of IGISOL to nuclear physics is being performed for nuclei in the f 7 2 -P 3 2 shell regions and medium-mass neutron-rich nuclei produced by the proton-induced fission reaction with a uranium target.

Highly excited spin-1 levels in52Cr and56Fe by the (γ, γ) reaction

Abstract The resonance scattering of electron bremsstrahlung from natural chromium and iron targets has been studied for photon energies up to 12 MeV. Seven γ-transitions of energies higher than 7 MeV were observed for each of the targets, which suggests seven resonant levels in each of52Cr and56Fe at excitation energies above 7 MeV. The spins of these levels were all assigned to be 1 from the relative yields at scattering angles of 125° and 150°. Radiative widths of these levels were obtained. A discussion is made about the possibility that these levels are T

The mirror transition of the Tz = −12 nucleus 59Zn

The mirror transition of the Tz = −12 nucleus 59Zn was studied by using an isotope separator on-line. The half-life and Emaxβ+ were measured to be 182.0 ± 1.8 ms and 8100 ± 100 keV, respectively. The ft values and the Gamow-Teller matrix elements to the low-lying states of 59Cu were determined and compared with the shell-model values. The masses of neutron-deficient Zn isotopes were calculated from the Kelson-Garvey mass relation.

A systematic study of the (p, d) strength for transitions to deeply bound hole states

Abstract The (p, d) reactions on 95, 98Mo, 112, 116Cd, 115In, 124Sn, 130Te and 141Pr have been studied with 52 MeV protons. In each deuteron spectrum, a giant-resonance-like gross structure was observed at excitation energies where those deuterons are expected to appear which result from direct neutron pickup from the outermost inner shell in these nuclei, consisting of the 1 g 9 2 , 2 p 1 2 , 2 p 3 2 and 1 f 5 2 subshells. A DWBA analysis of the angular distribution of the gross structure suggests that the structure contains a substantial part of the whole strength or shell-model limit of the outermost inner shell and no significant contribution of processes other than the direct neutron pickup.

The reaction 26Mg(3He, n)28Si at 23 and 45 MeV

Abstract Angular distributions of neutron groups from the 26 Mg( 3 He, n) 28 Si reaction have been measured at bombarding energies of 23.1 and 45.5 MeV. The experimental results are compared with DWBA and coupled-channel calculations. The zero-range DWBA calculation using shell-model two-nucleon spectroscopic amplitudes explains rather well most of the experimental data of the lowest four states in 28 Si, but it is necessary to take two-step processes into account to reproduce all of them satisfactorily. A strong neutron group observed at about 6.9 MeV in residual excitation is described as one composed of unresolved four groups, of which three are attributed to positive-parity states in 28 Si predicted in this energy region by the shell-model calculation and one to the 6.88 MeV 3 − state in 28 Si.

In-beam spectroscopic study of 107In

Abstract The nuclear level structure of 107In has been studied with the 106Cd(α, p2n)107In and 106Cd(3He, pn)107In reactions. In addition to the ordinary in-beam measurements of γ-rays and conversion electrons, p-γ coincidence measurements were performed in order to identify the γ-transitions in 107In. The experimental data of positive parity states are compared with predictions of a hole-phonon coupling model, in which a g 9 2 proton hole couples to the quadrupole core vibration. This simple model appears to be inadequate to describe the observed level properties of 107In.

Highly excited spin-1 states in 88Sr by the (γ, γ) reaction

Abstract The resonant scattering of bremsstrahlung γ-rays by a SrCO 3 target has been studied for γ-ray energies of 5–11 MeV. Six γ-transitions of energies between 6–8 MeV, which indicate six resonant states in 88 Sr, were observed. The relative intensities of the resonantly scattered γ-rays at 125 and 150° were found to be compatible only with the assignment of spin 1 to the six states. Radiative widths of the resonant states were deduced. The possibility that these states are components of the giant M1 resonance in 88 Sr is discussed.

The 59Co (d, 3He)58Fe reaction and 58Fe levels in the particle-vibration coupling model

Abstract The 59Co(d, 3He)58Fe reaction at a deuteron energy of 33.3 MeV was used to populate proton hole states in 58Fe. Angular distributions were measured for the states up to 6 MeV excitation. From DWBA analysis, l-values and spectroscopic factors were extracted. The particle-vibration coupling model was used to interpret the positive-parity states observed in the present experiment as well as the related properties of 58Fe established so far. The model calculation has reproduced rather well the level properties of 58Fe.

Nuclear g-factor of the 172+ isomeric state in 63Cu

Abstract The nuclear g-factor of the 4498 keV 17 2 + isomeric state in 63Cu was measured with the in-bearn perturbed angular distribution method, through the 62Ni(α, p2nγ)63Cu reaction, to be gexp = 0.184 ± 0.012. This value is in good agreement with a semiempirical g-factor for the three-quasiparticle configuration [π2p 3 2 (v1f 5 2 , 1g 9 2 )7] 17 2 + calculated using the experimental single-particle g-factors of neighbouring nuclei. At the same time the internal magnetic field at the Cu nuclei in Ni metal was obtained to be Bint = −46.6 ± 1.3 kG.

Precision half‐life measurements of the mirror nuclei in the f7/2‐shell using an IGISOL

The half‐lives of Tz=−1/2 mirror nuclei in the f7/2‐shell region were measured with a new on‐line separator, IGISOL of Tohoku University. The deduced experimental Gamow‐Teller (GT) matrix elements were compared with the results of large‐scale shell‐model calculations. As an average quenching factor of the GT matrix elements for the mirror β‐decay in the f7/2‐shell a value of 0.844±0.042 (simple average) was obtained.