Shin-Ichi Ichikawa

Simulation Study on the Measurements of Diffusion Coefficients in Solid Materials by Short-lived Radiotracer Beams

We have examined, by a computer simulation, an on-line measurement of diffusion coefficients by using a short-lived alpha particle emitter, 8Li (half life of 0.84 s), as a radiotracer. The energy spectra of alpha particles emitted from diffusing 8Li primarily implanted in the sample of LiAl are simulated as a measure of the diffusion of 8Li in the sample. As a possible time sequence for the measurement, a time cycle of 6 s, i.e. the implantation of 8Li for 1.5 s and subsequent diffusion for 4.5 s, is supposed. The sample is primarily set on a given temperature for the measurement. The time-dependent yields of alpha particles during the time cycle reveal the possibility to measure the diffusion coefficient with an accuracy of 10% if larger than 1×10-9 cm2/s, by the comparison with the experimental spectra measured at the temperature, i.e. at a certain diffusion coefficient.

A method for determination of the 152Eu activity

Abstract A new method for the absolute measurement of the 152 Eu activity was established based on the 4 πβ − γ spectroscopic coincidence method. It consists of a 4 πβ counter and a Ge(Li) detector, in which the effective counting efficiencies of the 4 πβ counter for β-rays conversion electrons, and Auger electrons were obtained by taking the intensity ratios for certain γ-rays between the single spectrum and the spectrum coincident with the pulses from the 4 πβ counter. First, in order to verify the method, three different methods of the absolute measurement were performed with a prepared 60 Co source to find excellent agreement among the results deduced by them. Next, the 4 πβ − γ spectroscopic coincidence measurement was applied to 152 Eu sources prepared by irradiating an enriched 151 Eu target in a reactor. The result was compared with that obtained by the γ-ray spectrometry using a 152 Eu standard source supplied by LMRI. They agreed with each other within an error of 1%.

First successful ionization of Lr (Z = 103) by a surface-ionization technique

We have developed a surface ionization ion-source as part of the JAEA-ISOL (Isotope Separator On-Line) setup, which is coupled to a He/CdI2 gas-jet transport system to determine the first ionization potential of the heaviest actinide lawrencium (Lr, Z = 103). The new ion-source is an improved version of the previous source that provided good ionization efficiencies for lanthanides. An additional filament was newly installed to give better control over its operation. We report, here, on the development of the new gas-jet coupled surface ion-source and on the first successful ionization and mass separation of 27-s (256)Lr produced in the (249)Cf + (11)B reaction.

Ground-state band of the neutron-rich transuranium nucleus 250Cm154

The ground-state band of the neutron-rich transuranium nucleus 250 Cm was established up to spin 12 by in-beam γ-ray spectroscopy using the two-neutron transfer reaction with a 248 Cm target and a 162 MeV 18 O beam. Deexcitation γ rays in 250 Cm were identified by selecting the kinetic energies of 16 O particles using Si Δ E – E detectors. The moment of inertia of 250 Cm 154 is considerably smaller than that of 248 Cm 152 , which supports the existence of the deformed subshell closure at N =152 in Cm isotopes.

Beta-Decay Energies of 121,123,125Ba and 121–124,126Cs

The β + -ray maximum energies of neutron-deficient 121,123,125 Ba and 121–124,126 Cs isotopes were measured using single HPGe-detector method, which does not need an annihilation-photon detection system. The radioactive sources were produced by bombarding Mo targets with 32 S 10+ and 35 Cl 11+ ions, followed by on-line mass-separation. The analysis of the experimental β + -ray spectra using response functions to monoenergetic positrons yielded β + -ray maximum energies and Q -values of orbital-electron capture ( Q EC -values) in the decay of these nuclides. The present experiment has extended the Q EC determination to 121,123 Ba isotopes in addition to improving the accuracy for the other nuclides.

Status report of the JAERI on-line isotope separator

Abstract A mass separator has been connected on line to the 20 MV tandem accelerator at JAERI/Tokai. Using a thermal ion source, decay spectroscopic studies have been carried out for neutron-deficient isotopes in the mass 120–130 region. A study with collinear laser spectroscopy has begun recently. The present paper describes the status of the mass separator facility together with some experimental results.

The KEK–JAERI joint RNB project

A new ISOL-based radioactive nuclear beam (RNB) facility has been constructed as a joint project of the High Energy Accelerator Research Organization (KEK) and the Japan Atomic Energy Research Institute (JAERI) at the Tandem accelerator of the Tokai site of JAERI. It uses heavy-ion linacs and related equipment of the presently closed KEK-RNB facility. Fission fragments with energy from 0.1 to 8 MeV/u will be available at this facility.

Triple neutron capture of 153Eu in a reactor: The cross sections of 154Eu and 155Eu

Successive neutron captures of 153Eu have been studied by means of an activation method. Samples of 153Eu enriched to 99.9% were irradiated in different reactor neutron spectra. The γ rays associated with the decays of 154Eu, 155Eu, and 156Eu produced respectively by one-, two-, and three-neutron captures of 153Eu were recorded and thermal neutron cross sections as well as resonance integrals were calculated for the reactions 154Eu(n, γ) 155Eu(σ0=(1840±90) barn I′0=(2100±2100) barn) and155Eu(n, γ) 156Eu(σ0= (3760±170) barn I′0=(15300±2700) barn).

Measurement of Hyperfine Structure of the 4f35d 5G-4f36p 5H in PrII by Collinear Laser-Ion-Beam Spectroscopy

The hyperfine structure of the transitions 4 f 3 ( 4 I o )5 d 5 G 2 o -4 f 3 ( 4 I o )6 p 5 H 3 (λ=601.94 nm) and 4 f 3 ( 4 I o )5 d 5 G 3 o -4 f 3 (^4I^o)6 p ^5H_3 (λ=604.83 n m ) o f P r I I h a s b e e n m e a s u r e d b y c o l l i n e a r l a s e r - i o n - b e a m s p e c t r o s c o p y . T h e m a g n e t i c - d i p o l e c o n s t a n t A a n d t h e e l e c t r i c - q u a d r u p o l e c o n s t a n t B o f t h e l e v e l s i n v o l v e d h a v e b e e n d e t e r m i n e d t o b e : A ( M H z ) B ( M H z ) 4f^3(^4I^o)5 d ^5G_2^o 1703.2±0.8 -14.1±5.8 4f^3(^4I^o)5 d ^5G_3^o 932.8±2.2 -15.1±6.6 4f^3(^4I^o)6 p ^5H_3 1028.7±1.0 -14.3±2.5.

Direct measurements of (α, n) and (p, n) reaction cross sections using light neutron-rich radioactive nuclear beams

Abstract A project to acquire directly nuclear cross sections of (α, n) and (p, n) reactions using low energy light neutron-rich radioactive nuclear beams (RNB) is in progress at JAERI-Tandem facility. The method of the production of neutron-rich RNB, an improvement of a gas counter (MSTPC) in order to work effectively under the high RNB-injection rate, and the feasibility of our experiments are discussed.