M. Fujioka

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.

Diffusion of radioisotopes from solids in the form of foils, fibers and particles

Abstract We summarize the formula for the diffusion of a radioactive product from a solid target or catcher material in the form of foils, fibers and particles for the case of vanishing surface density of the diffusing isotopes, in which the analytical expression for the diffusion yield, i.e., the probability for radioisotope to escape before decaying is newly obtained for diffusion from a solid in the form of a fiber.

The mass of the electron neutrino from electron capture in 163Ho

Abstract Using an M X-ray spectrum from electron capture in 163Ho together with M X-ray fluorescence spectra of the Dy atom, the partial decay constants of 163Ho, λM1 and λM2 were measured. With λM1, λM2 and λt (total decay constant) as three constraints, the mass of the electron neutrino, mVe, the Q-value, and log(ft) of the 163Ho decay were simultaneously determined. Results obtained are m V e = 110 − 110 + 350 e V , Q = 2.710 − 0.500 + 0.100 k e V , and log ( f t ) = 4.993 − 0.001 + 0.030 .

A new EMIS facility at the Tohoku University cyclotron

Abstract An EMIS facility has begun operation at one of the beam lines of a multipurpose cyclotron of K = 50 MeV. The separator is of a Scandinavian type of 55° deflection and 1500 mm dispersion, and is equipped with three beam-transport lines to which are connected a tape-transport system for ISOL study, a retardation system for implantation work and an optical spectrometer for surface analysis. The status and developments of this facility are reported here for the first time.

Isomeric yield ratios of fission products in the system of 24 MeV proton-induced fission of238U

Isomeric yield ratios of 30 fission products in 24 MeV proton-induced fission of238U were measured by the use of the ion-guide isotope separator on-line. The obtained isomeric yield ratios were converted to the angular momenta of primary fission fragments based on the statistical model. The deduced angular momenta were examined from various aspects. It is found that in general the angular momentum continuously increases with the fragment mass number including the region of symmetric mass division. However, there are some exceptions. For Sn isotopes the deduced angular momenta are quite small due to the spherical shape of the nuclear shell configuration. It is also concluded from the consideration of the charge distribution that the angular momentum of fission product scatters considerably within the narrow range of mass division. The dependence of the angular momentum on the available energy of fragments at scission point indicates that the individual fragment possesses a characteristic deformation at scission and/or the deduced angular momentum is seriously affected by the particle excitation after scission.

An Upper Limit for the Mass of the Electron Anti-neutrino From the Ins Experiment

Abstract The β-spectrum in 3 H decay has measured at INS with an energy resolution of 10–16 eV. The overall response function of the spectrometer system was reliably obtained with a reference 109 Cd source having the same chemical structure as the 3 H source. An upper limit of 32 eV has been obtained for the mass of the electron anti-neutrino with statistical and systematic errors.

The mass of the electron neutrino using electron capture in 163Ho

Abstract By reconstructing an M X-ray spectrum from 163 Ho per atom per second using two spectra S M1 and S M2 , the M X-ray spectra of dysprosium when there is one vacancy in the M 1 and M 2 subshell, the partial decay constants λ M1 and λ M2 were determined. Using λ M1 , λ M2 and λ 1 (total decay constant), an upper limit of 550 eV was obtained for the mass of the electron neutrino.

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.

Determination of the change of nuclear charge radius of the119Sn Mössbauer transition by internal conversion

Radioactive119Sb was implanted into six host matrices (CaSnO3, Pt, Y, Au,Β-Sn, Pb) and internal conversion electrons of the 23.87 keV transition in119Sn were measured with an iron-free magnetic spectrometer as well as Mössbauer spectra. In the analysis of the conversion spectra of outermost electrons, the overlapping K-LM Auger lines were subtracted using the Auger spectrum of tin measured with another source of117mSn, and the shake-off effect accompanying the conversion process was considered. From the correlation between the Mössbauer isomer shifts and the intensity ratios of O-shell to N1-shell conversion electrons, the change of the nuclear charge radius of the 23.87 keV transition of119Sn was deduced to be δR/R=(0.87 ± 0.25) × 10−4 for a uniform charge distribution ofR= 1.2 ×A1/3 fm or, equivalently, δ 〈r2>—=(3.6 ± 1.0) ×10−3 fm2.

The mass of the electron neutrino and electron capture in 163Ho

Abstract To determine the mass of the electron neutrino, electron capture in 163 Ho was studied. From the intensity of M X-rays and the total number of 163 Ho atoms in a source, as determined by the PIXE method, the partial M-capture half life of 163 Ho was estimated to be (4.5 ± 1.5) × 10 4 yr. A relation between the Q -value of 163 Ho and the mass of the electron neutrino was obtained.