Y. Hatsukawa

RIKEN isotope separator on-line GARIS/IGISOL

Abstract This paper describes the fabrication and the characteristics of an isotope separator on-line (ISOL) which was constructed at the RIKEN Ring Cyclotron Facility. The ISOL consists of a gas-filled recoil separator and an ion-guide isotope separator on-line. Because of this combination the ISOL enables us to study short-lived isotopes of almost all elements.

Production of 99Mo for Nuclear Medicine by 100Mo(n, 2n)99Mo

We have proposed a new route to produce 99 Mo for nuclear medicine by the 100 Mo( n ,2 n ) 99 Mo reaction. The reaction cross section is known to be ∼1.5 b in the neutron energy, E n , range from 12 to 17 MeV: 10-times larger than the thermal-neutron capture cross section of 98 Mo. By irradiating an enriched 100 Mo target for 198 h with neutrons of ∼10 13 n/(cm 2 s) at E n ∼14 MeV, one can produce 79 GBq/g specific activity of 99 Mo. Since the cross sections for 100 Mo( n , p ) 100 Nb, 100 Mo( n , n p ) 99 Nb and 100 Mo( n ,α) 97 Zr at 12≤ E n ≤17 MeV are small, less than a few mb, radioactive waste during and/or after chemical processing of 99 Mo would not be a serious problem. The proposed route could bring a major breakthrough in the solution of ensuring a constant and reliable supply of 99 Mo without using highly enriched 235 U.

A γ-ray detector array for joint spectroscopy experiments at the JAERI tandem–booster facility

Abstract A compact array for γ-ray spectroscopy developed for the joint experiment at the Japan Atomic Energy Research Institute is described. It consists of an array of 11 Compton suppressed Ge detectors, a 4π silicon detector array for charged particle measurements, a position-sensitive silicon detector for experiments on Coulomb excitation and a conversion-electron spectrometer. The details of the detectors and new experimental results obtained with the compact array are also described.

Isomeric yield ratios of 134I and 136I in the proton-, 12C- and 19F-induced fission of 235U, 237Np and 238U

Short-lived nuclides of iodine produced in the proton-, 12C- and 19F-induced fission of 235U, 237Np and 238U were separated with a rapid chemical separation system SISAK. Relative yields of the nuclides were determined by γ -ray spectrometry to obtain the isomeric yield ratios of 134mI/134gI and 136mI/136gI. Angular momenta of the fission fragments, 134I and 136I, were derived from the measured isomeric yield ratios by the spin-dependent statistical model. In the light- and heavy-ion fission, variation of the observed angular momenta can be explained by the excitation energies of the fissioning nuclei and the spherical shell structure with N = 82.

Electromagnetic structure of 98Mo

Abstract The nucleus 98 Mo was multiply Coulomb excited using 20 Ne, 84 Kr and 136 Xe beams. Eighteen E2 and M1 reduced matrix elements connecting 7 low-lying levels have been determined using the least-squares code GOSIA. The results are compared with the predictions of an extended version of the IBM1 model. The quadrupole sum rules approach was used to determine the shape parameters in two 0 + (ground and first excited) states. The rotational invariants 〈Q 2 〉 and 〈 cos 3δ〉 obtained show the shape coexistence in 98 Mo nucleus: the triaxial ground state and the prolate first excited state.

Measurement of Thermal Neutron Cross Section and Resonance Integral of the Reaction137Cs(n, γ)138Cs

Abstract To obtain fundamental data for the research of the transmutation of nuclear waste, the thermal neutron cross section and the resonance integral of the reaction 137Cs(n, γ)138Cs have been measured by means of a modified Cd-ratio technique. Targets of about 0.4 MBq 137Cs were irradiated with neutrons in the JRR-4 swimming pool reactor by using a pneumatic tube equipped with a movable Cd shield, and neutron fluxes and their epithermal neutron fractions were monitored with activation detectors (Co/Al and Au/Al) whose sensitivity to epithermal neutrons differed from each other. After irradiation, the 137Cs samples were purified chemically and their γ-ray spectra were measured with a high purity Ge detector. The resulting yields of 138Cs for different neutron spectra and the neutron flux data have yielded that the thermal neutron cross section (for 2,200 m/s neutrons) is 0.25±0.02b and the resonance integral 0.36±0.07b. The results are consistent with the effective cross section (σ=0.250±0.013b) of our...

Mass separation of neutron-rich isotopes using a gas-jet coupled thermal ion source

A gas-jet coupled thermal ion source was installed in the isotope separator on line at the JAERI tandem accelerator. It was used for separation of neutron-rich isotopes produced in the reaction 238U(15 MeV-p, fission). The separation efficiencies of the whole system were measured to be 3.3% for 140Cs (T12 = 63.7 s), 2.0% for 144La (T12 = 40.8 s), 2.2% for 148Pr (T12 = 2.0 m), 1.2% for 156Pm (T12 = 26.7 s) and 1.0% for 160Eu (T12 = 44 s). A long sticking time of La atoms on the ionizer surface gave a low efficiency of about 0.1% for 148La (T12 = 1.05 s). The first observation of a new isotope 166Tb was carried out using its monoxide ions from this ion source: T12(166Tb) = 21±6 s.

Comparison Method for Neutron Activation Analysis with γ-γ Matrix

A comparison method, utilizing neutron activation analysis followed by multidimensional spectrum analysis was proven to provide accurate quantification of the multi-element samples. In this study, 23 elements were detected simultaneously in a sample containing standard elements for neutron activation analysis. The method presented here can be applied for about 50 elements.

A High-sensitivity and Non-destructive Trace Element Analysis Based on Multiple Gamma-ray Detection

A new trace-element quantification method has been developed by combining multiple gamma-ray detection and neutron activation analysis. This method is characterized by high sensitivity and simultaneous analysis for multielements. The quantification accuracy amounts to 3–20% depending on statistics. It has been successfully applied to the analyses of igneous rock samples, long-lived radionuclide, 129I, and geologic samples. Future perspectives for an innovative pulsed neutron source and a new detector system will be presented.

Multiple Coulomb excitation of a 76Ge beam

A multiple Coulomb excitation experiment on a 76Ge beam was performed using a natPb target. The relative excitation probabilities were measured as a function of the projectile scattering-angle. 15 E2 matrix elements, including diagonal ones, for seven low-lying states were determined using the least-squares search code GOSIA. The expectation values of centroid for the magnitude of the intrinsic frame E2 properties Q2 show that the ground state is weakly deformed, while the shape of the 02+ level is almost spherical. The 22+ state is found to be a band head of the γ vibrational band and the 42+ state is a member of this band.