H. Orihara

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.

Improvement of time resolution in a TOF PET system with the use of BaF2 crystals

Abstract In the course of the construction of a new type of time-of-flight positron emission tomograph (TOF PET), the time resolution of a system with BaF 2 crystals has been tested. It was found that low-viscosity silicon oil is one of the best optical coupling media between the BaF 2 crystal and the photomultiplier tube, and that the time resolution is less sensitive to the geometry between the detector and the source position. The dependence of the time resolution on the size of the BaF 2 crystal has been determined as well. Absorption and attenuation of photons in the detector system are expected to be of particular importance for the better performance of the TOF PET.

Preparation of Thin Polycarbonate Film and Its Application to PIXE Analysis of Anionic Elements in Water Samples

A polycarbonate film of thin and uniform thickness was prepared. A casting solution for film-formation was made up by diluting a solution of poly (bisphenol A carbonate) in chloroform by a factor of two to three with benzene. A uniform film was created by dropping 0.2-0.3 cm3 of the casting solution slowly on a water surface within an aperture (20 mm diameter) of Mylar target frame floating on 50 wt% sucrose aqueous solution. Films of 0.14-0.27 mg/cm2 thickness thus prepared offer a good combination of mechanical strength and low continuum backgrounds. To test PIXE analysis of anionic species in water, targets containing SO42-, Cr2O72-, AsO43-, and Ga3+-internal standard were prepared by depositing 100 μl of the test solutions onto the polycarbonate film, and irradiated in vacuum by 3 MeV proton beams. The difference between the nominal and the analyzed concentrations seldom exceeded ± 15 % in the range from 10 to 2000 ppb.

Determination of Heavy-Metal Concentrations in Water by PIXE Analysis Using Zr as an Internal Standard

A metal-preconcentration procedure, which consists of a combination of chelation by dibenzyldithiocarbamate ions with subsequent condensation into dibenzylidene-D-sorbitol gels, has been reformed by using Zr as an internal standard. The colloidal gels formed in solutions were collected on a nuclepore filter for direct irradiation by 3 MeV proton beams in a system of vertical beam type in-air PIXE. The methodology was tested for simultaneous determination of the concentrations of seven metals (Fe, Co, Ni, Cu, Cd, Hg, Pb) in 25 ml of an aqueous sample. A good linear relationship was obtained between the nominal concentration and the elemental X-ray yields normalized with Zr-Kα ones. Absolute values of concentration in the sample solutions can be determined with an experimental error less than ±14 % in the 5-100 ppb range by employing published data pertinent to the inner shell ionization and subsequent X-ray emission of the heavy metals.

FACILITY OF PIXE ANALYSIS AT TOHOKU UNIVERSITY

PIXE research at the 4.5-MV Dynamitron laboratory of the Faculty of Engineering, Tohoku University started as a joint project between Cyclotron and Radioisotope Center(CYRIC), Tohoku University, and the Dynamitron laboratory. The PIXE equipments including vertical beam in air PIXE system called ViaPIXE was installed at a vacant beam course of the Dynamitron laboratory. Some PIXE experiments conducted at this facility as well future PIXE research in this laboratory are briefly described.

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.

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.

The (p, n) reaction on cadmium isotopes leading to the ground- and excited-state analogs

Abstract The (p, n) reactions to ground- and excited-state analogs on 110,114,116 Cd have been studied at a bombarding energy of 25 MeV. Angular distributions of emitted neutrons leading to ground-state analogs, and 2 + , 3 − and 4 + excited-state analogs were obtained for each target. Angular distributions of differential cross sections to the ground-state analog agree with the predictions obtained from macroscopic DWBA calculations in which a Lane potential is employed. Coupled-channel calculations indicate the importance of two-step processes in the (p, n) transition to an excited-state analog. Further, the calculation using a larger value for the deformation parameter of the isovector part than of the isoscalar one fairly well describes the 2 + excited-state analog.