Yoichi Kawase

A helium-jet type ISOL at the Kyoto University reactor

Abstract A He-jet type ISOL was constructed and installed at the Kyoto University Reactor as a test apparatus of the ISOL for a planned new high flux reactor. The results of the test experiments on the performances of the He-jet rapid transport system, ion sources and mass analyzing system are presented together with the construction details. Nuclear spectroscopic studies are now being performed on short-lived alkali elements down to 0.38 s 95 Rb which are obtained with sufficient intensities.

A multicounter goniometer for gamma-gamma angular correlation measurements

Abstract A multicounter goniometer for gamma-gamma angular correlation measurements was newly designed and constructed. It consists of 12 photomultipliers with NaI(Tl) crystals placed radially at intervals of 30° and a 12 × 12 coincidence matrix circuit which follows 12 linear amplifiers and 2 × 12 single channel pulse height analyzers. Coincidence counts at 11 angles between 30° and 330° are taken simultaneously for each of the 12 counters, so that with this method angular correlation measurements can be made within a time reduced by a factor 12 × 11, as compared with the ordinary method.

Characteristics of a mixed-gas jet system in KUR-ISOL

Abstract The characteristics of N2- and He-N2 mixed-gas jet systems have been investigated when a target chamber was located in a strong radiation field at KUR-ISOL. The ion yields have been much enhanced using the He-N2 mixed-gas jet coupled with PbI2 as aerosol material. The characteristics of these gas jet systems have been studied by measuring the amount of transported activities and by detecting representative γ-rays from mass-separated fission products. The dependence of the ion yields on the aerosol materials (DOP, NaCl and PbI2) and on the volumetric mixing ratio of He and N2 gases has been investigated.

The oxidation technique for efficient ionization of lanthanides by a helium-jet loaded on-line isotope separator

Abstract The oxidation technique has successfully been developed for efficient ionization of lanthanides by a He-jet type on-line isotope separator for fission products. By introducing a small amount of oxygen to the helium-jet, monoxides of lanthanides (LaO, CeO, PrO, NdO and PmO) can be ionized with a very high efficiency (40–86%) by a surface ionization ion source. The ionization characteristics have been studied by detecting representative γ-rays from radioactive isotopes of relevant elements as functions of the temperature of the ionizer and the oxygen flow rate. Applying this method to the ionization of praseodymium, a new isotope, 154Pr, has been identified. The ionization mechanism of the lanthanide monoxide is discussed in relation to the work function of the tungsten surface and the first ionization potential of the monoxide compounds.

Low-spin states in 110Cd and 112Cd

Abstract Gamma-transitions in the decays of 24.7 sec 110g Ag and 13.3 min 112g In have been studied with Ge(Li) detectors and a multi-counter goniometer to elucidate low-spin excited states in 110 Cd and 112 Cd. Five new levels at 1732, 2079, 2287, 2332 and 2662 keV in 110 Cd and three new levels at 2124, 2155 and 2300 keV in 112 Cd have been established from the decays of 1 + states of parent nuclei. The 0 + assignments to the levels at 1473, 2079 and 2662 keV in 110 Cd and at 1224 and 1870 keV in 112 Cd have been confirmed by angular-correlation measurements. Mixing ratios of the 2 3 + −2 1 + transitions have been determined. Log ft values of allowed β-decays from the 1 + states are presented. Discussions on the low-spin states of the Cd isotopes are given in the light of the collective model.

IMPROVEMENT OF A MULTICOUNTER GONIOMETER FOR GAMMA--GAMMA ANGULAR CORRELATION MEASUREMENTS.

Abstract A multicounter goniometer previously reported has been improved to increase the efficiency of the system and was successfully applied for gamma-gamma angular correlation measurements of short-life nuclei such as 43 sec 104Rh.

Target and ion source developments for a helium-jet type ISOL at the Kyoto University reactor

Abstract A target system and ion sources for a He-jet type ISOL have been successfully constructed and the characteristics have been studied. The beam intensities of short-lived fission products have been much improved by increasing the He gas pressure owing to a range effect of fission products in the He gas and a short transport time effect of aerosols in a target chamber and a capillary. An oscillating electron ion source has been coupled with the He-jet system and ten kinds of elements have been ionized with efficiencies of 0.4–2.4%. A high temperature thermal ion source has been studied to ionize the alkali, alkaline-earth and rare-earth elements. The effects of the He-jet on the ion source have been discussed.

Half-life measurements of 93Sr, 94Sr, 95Sr, 139Cs, 141Cs and 143Ba mass-separated by KUR-ISOL

Abstract The half-lives of 93Sr, 94Sr, 95Sr, 139Cs, 141Cs and 143Ba have been measured with a Ge(Li) detector using sources mass-separated by KUR-ISOL. The results of the measurements are 93Sr, 7.41 ± 0.04 min; 94Sr, 75.3 ± 0.2 s ; 95 Sr , 23.8 ± 0.3 s ; 139 Cs , 9.27 ± 0.16 min ; 141 Cs , 24.98 ± 0.13 s ; 143 Ba, 14.33 ± 0.08 s . These results compare favourably with the previously reported values except that for the 95Sr half-life.

Qβ Measurements of Neutron-Rich Isotopes in the Mass Region 147≤A≤152

The systematic Q β measurements of 14 neutron-rich nuclei in the mass region from A =147 to A =152 have been performed with an HPGe detector. Neutron rich nuclei were mass separated from the thermal neutron induced fission of 235 U using a He-jet type on-line isotope separator which has been developed at the Kyoto University Reactor (KUR). From β-ray singles and β-γ coincidence measurements, the Q β values of 147 La, 147-150 Ce, 147-152 Pr, 152 Nd and 152 Pm have been determined. The Q β values of 152 Pr and 152 Nd have been measured for the first time. The atomic masses derived from the Q β values are compared with the predictions of theoretical mass calculations.

Characteristics of a gas-jet transport system for an on-line isotope separator☆

Abstract Basic characteristics of a gas-jet transport system for an on-line isotope separator have been investigated using a 252Cf source and a 235U fission source. The transport efficiency of fission products through a capillary has been measured to be about 60% for the 235U fission source. The sweep-out time of fission products through a target chamber and the transit time through a capillary have been measured for He, N2 and CO2 gases at several pressures. The measured sweep-out times have been almost equal to the exchange over time of the gas. The transit times have been found to be reasonably predicted by calculations. The transport system has been incorporated into the KUR-ISOL and is used for the study of short-lived nuclei.