A. Osa

Test results of 18 GHz ECR charge breeder for KEK–JAERI RNB facility

Some of the test results of KEK ECR charge breeder made for KEK–JAERI RNB facility are presented and discussed. The charge breeding efficiencies for singly charged ions of noble gases have been measured; typically 13.5% of Ar9+, 10.4% of Kr12+, and 6.8% of Xe20+ with a global efficiency of about 50%. By injecting pulsed Xe1+ ion beam into the charge breeder, the time necessary for charge breeding has been also measured and found to be about 60 ms for Xe21+ ions. As an effort to reduce the residual gas ions incidentally existing in the plasma chamber of the charge breeder a nonevaporable getter has been tested, and the preliminary results are discussed.

KEKCB electron cyclotron resonance charge breeder at TRIACa)

The KEKCB is an electron cyclotron resonance (ECR) ion source for converting singly charged ions to multicharged ones at Tokai Radioactive Ion Accelerator Complex. By using the KEKCB, singly charged gaseous and nongaseous ions were converted to multicharged ones of A/q approximately 7 with efficiencies of 7% and 2%, respectively. The conversion efficiency was found to be independent of the lifetime of the radioactive nuclei having lifetimes of the order of one second. Three collimators located at the entrance and the exit of the KEKCB defined the beam axis and facilitated beam injection. Grinding and washing the surfaces of aluminum electrode and plasma chamber dramatically reduced impurities originating from the ECR plasma of the KEKCB.

Prolate and Oblate Shape Coexistence in 188Pt

A standard in-beam γ-spectroscopy experiment for 188Pt is performed via the 176 Yb(18O, 6n) reaction at beam energies of 88 and 95MeV, and the level scheme for 188Pt is established. Prolate and oblate shape coexistence has been demonstrated to occur in 188Pt by applying the projected shell model. The rotation alignment of i13/2 neutrons drives the yrast sequence changing suddenly from prolate to oblate shape at angular momentum 10h, indicating likely a new type of shape phase transition along the yrast line in 188Pt.

The development of an ECR charge breeder for KEK-JAERI joint RNB project

For the construction of an electron cyclotron resonance (ECR) charge breeder (CB) at KEK-JAERI radioactive nuclear beam facility, we have made a pilot charge breeding system consisting of two compact-sized ECR ion sources. In order to find the necessary conditions for an ECRCB with high efficiency, the charge breeding efficiency for Ar ions in nitrogen plasma has been measured and compared with the results from the simulation of the trajectories of the ions in the plasma. By explicitly taking into account the cumulative small angle scattering of charged ions as well as the confinement magnetic field of the pilot CB, the simulation predicts the stopping efficiency. This is defined as a probability that the injected ions are still within the plasma volume when their initial directional motions have become randomized. Incorporating the ionization efficiency for the ions, the overall breeding efficiency has been estimated. Finally, the characteristics of the ECRCB recently installed for tests at KEK is described.

QEC Measurement of 124,125,127-130La

For neutron-deficient 124,125,127-130 La, Q EC measurement has been performed by determining β + -ray maximum energies. The radioactive sources were prepared by on-line mass-separation following the fusion-evaporation reactions 92, nat Mo( 36 Ar, 3 p x n ). The β + -rays were measured with an HPGe detector in β-γ coincidence mode in which γ-rays were detected with another HPGe detector for specifying an excited state in daughter nucleus. By unfolding the β + -ray spectra using experimental response functions, the Q EC -values of 124, 125, 127, 130 La were newly obtained, and those of 128, 129 La were improved in their accuracy. The Q EC -values obtained and the resulting atomic masses are compared with theoretical predictions. The results of half-life calculation and two-neutron separation energies using the experimental Q EC -values are also discussed.

Toward Online Nanoscale Diffusion Measurements Using Radioactive 8Li Tracer

We have examined the feasibility of a new online nanoscale diffusion measurement method using a radioactive 8Li tracer by computer simulations. We have found that the detection limit of the lithium diffusion coefficient can be improved to a low value of 1×10-12 cm2/s by detecting α particles emitted at a small angle relative to a sample surface that is irradiated with a low-energy 8Li beam of about 8 keV.

Nanoscale diffusion tracing by radioactive 8Li tracer

We have developed a nanoscale diffusion measurement method using an α-emitting radioactive 8Li tracer. In this method, while implanting a pulsed 8 keV 8Li beam, the α particles emitted at a small angle (10°) relative to the sample surface were detected as a function of time. The method has been successfully applied to measuring lithium diffusion coefficients for an amorphous Li4SiO4–Li3VO4 (LVSO) thin film with a thickness of several hundred nanometers, demonstrating that the present method is sensitive to diffusion coefficients down on the order of 10−12 cm2/s, which is more sensitive by about two orders of magnitude than that previously achieved.

Development of radioactive ion beam production systems for Tokai Radioactive Ion Acceleration Complex-High temperature ion source for short-lived isotopes.

We have developed a new ion source system in the isotope separator on-line at Japan Atomic Energy Agency, for separation of short-lived isotopes produced by proton-induced fission of (238)U. The ion source system is a forced electron beam induced arc discharge version E type ion source with a target container. We successfully operated this system at 2000 degrees C as a result of reductions in volume of the ion source and the target container, introduction of heating method by electron bombardment, and improvement to the heat shield. This new ion source system was tested using (238)U of 640 mg/cm(2) with a proton primary beam of 30 MeV, 350 nA. Release times were measured for Kr, In, and Xe. The values of release times are 2.6 s for Kr, 1.8 s for In, and 4.6 s for Xe. In this work, the ion source system enabled us to mass-separate short-lived isotopes such as (93)Kr(T(1/2)=1.286 s), (129)In(T(1/2)=0.61 s), and (141)Xe(T(1/2)=1.73 s) with intensity of 10(3) ions/s.

An automatic liquid-nitrogen filling system for multiple Ge detectors

In order to reduce the time and effort of the daily task of refilling Dewar vessels of Ge detectors with liquid nitrogen (LN(2)), we have developed an automatic LN(2) filling system equipped with a LN(2) plant. With this system, we were freed from the work of LN(2) filling. Such an LN(2) filling system is useful for moderate-scale Ge detector arrays consisting of fewer than 20 Ge detectors.

Performance of a new signal processing system for a detector array

To measure neutron cross-section data of minor actinides, we construct a 4-pi Ge-spectrometer utilizing multiple gamma-ray detection method. This spectrometer consists of 30 Ge crystals (40 detector outputs) and 128 BGO anti-Compton shields. Generally, a data acquisition system for such a big Ge spectrometer consists of many NIM modules; it requires large space and huge cost. To overcome these problems, we developed a new data acquisition system with digital signal processing techniques. This system is mounted in a 19 inches VME sub-rack, and the cost of this system is greatly reduced. Obtained FWHMs (2.5~2.8 keV at 1.33 MeV) show good performances as normal MCA even with short shaping time and much higher channel density. The dead time of this system is only 3.2 micro sec per event. Thus good energy resolution is achieved with short shaping time and short dead time