H. Iimura

Efficiency calibration of a Ge detector in the 0.1–11.0 MeV region

Abstract An efficiency curve was constructed for a large-volume Ge detector located at the thermal-neutron beam line of the JRR-3M reactor at the Japan Atomic Energy Research Institute (JAERI). The calibrations for γ-ray energies below 2754 keV were accomplished with a large number of radioactive sources and above 2754 keV with the 12 C(n,γ) and 14 N(n,γ) reactions. This detector and its efficiency curve were subsequently used to determine accurately the photon emission probabilities of γ rays from the decays of 56 Co (T 1/2 =77 d ) and 66 Ga (9.5 h ) and from the 35 Cl(n,γ) reaction. These radiation sources can serve as secondary standards for efficiency calibrations.

Selective mass separation of light lanthanoids by means of ionization of their monoxides

To strengthen elemental selectivity in isotope separation on-line, ionization of the monoxides of light lanthanoids in a thermal ion source has been studied. Currents of the monoxide ion MO+ and the metallic ion M+ were measured in off-line experiments using oxide reagents of the elements from Ba to Sm at ion-source temperatures from 1900 to 2730 K. The observed MO+M+ ratio was the highest for La and Ce, and decreased with increasing atomic number and temperature. In on-line experiments using heavy-ion fusion-evaporation reactions, La isotopes were mass-separated as La16O+, being well separated from the Cs and Ba isobars, while Pr isotopes were obtained at a higher temperature as Pr+ since the La and Ce isobars were still ionized favorably as MO+. Using this method, the isotope 121La was newly identified with a half-life of 5.3 ± 0.2 s.

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.

Rotational bands of 155Gd

Abstract High spin states of 155 Gd have been investigated using the 150 Nd( 12 C, α3n) reaction. Three rotational bands have been observed. Two of them have been extended up to (51/2) + and 45/2 − , respectively, and another band has been newly observed. The backbending and blocking effects are discussed in comparison with the calculation of cranked shell model. The routhians and the B (M1/BE2 ratio of the high-Ω rotational band are compared with the calculation by the tilted axis craking model. In addition the ground state rotational band of 156 Gd has been extended up to 22 + .

High-spin isomer and level structure of 145Sm

Abstract High-spin states of 145 Sm were studied by using the reactions 20 Ne( 136 Xe,α7n), 16 O( 136 Xe,7n), 139 La( 10 B,4n) and 138 Ba( 13 C,6n). The level scheme was extended up to the state at 14.6 MeV. The excitation energy and the spin-parity of the 0.96 μs high-spin isomer were determined to be 8.8 MeV and ( 49 2 + ), respectively. Experimental results were discussed comparing with the deformed independent particle model calculation. High-spin isomers observed in N = 83 isotones were interpreted to be caused by the sudden shape change from near spherical to oblate. The Z = 64 shell gap energy was found to decrease from 2.4 to 2.0 MeV as the proton number decreases from Z = 64 to 61.

High-spin states in148Tb

High-spin states of148Tb were studied by inbeam γ-ray spectroscopic techniques using141Pr(13C,6n)148Tb and27Al(130Te,9n)148Tb reactions. The level scheme of148Tb was established up to the excitation energy of 11.8MeV. The excitation energy of the high-spin isomer reported previously was revised to be 8.620MeV. The excited states below the isomer could be understood as resulted from the weak couplings of πh11/2 and νf7/2 to those of147Gd and147Tb, respectively.

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.

Development of a laser-enhanced ion-guide ion source

Abstract For the purpose of achieving a good efficiency and pulsed output of short-lived reaction products, we propose a laser-enhanced ion-guide ion source for an on-line isotope separator. Two-step resonant, three-color resonance ionization of Ba atoms was established in an off-line experiment and the ionization efficiency per pulse was measured to be 1.9%. In an on-line ion-guide experiment, it was found that the use of heavy gas was effective to stop the recoil atoms and that most of them remain in the gas until evacuation. While enhancement of the ionization efficiency by introduction of a laser beam to the ion-guide chamber has not been achieved so far, possible improvements are discussed.

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.