Akihiko Osa

Uptake and transport of positron-emitting tracer (18F) in plants☆

Abstract The transport of a positron-emitting isotope introduced into a plant was dynamically followed by a special observation apparatus called ‘Positron-Emitting Tracer Imaging System’ to observe the damage and recovery functions of plants in vivo. In the system, annihilation γ-rays from the positron emitter are detected with two planar detectors (5 × 6 cm2). The water containing ca. 5 MBq/ml of 18F was fed to the cut stem of soybean for 2 min and then the images of tracer activity were recorded for 30–50 min. When the midrib of a leaf near the petiole was cut just before measurement, the activity in the injured leaf was decreased but detected even at the apex. This result suggests that the damaged leaf recovered the uptake of water through the lamina. Maximum tracer activities in leaves of unirradiated plant were observed within 10 min, whereas those of irradiated plant at 100 Gy were observed after over 25 min. The final activity of irradiated plant after 30 min was lower than that of unirradiated plant. In case of beans, there was a difference in the absorption behavior of the 18F-labeled water between unirradiated and irradiated samples. These results show that the system is effective to observe the uptake and transportation of water containing positron emitting tracer for the study of damage and recovery functions of plants.

Production method of no-carrier-added186Re

No-Carrier-Added186Re was produced using the186W(p,n)186Re nuclear reaction with 13.6 MeV protons on thick targets of 99.79% isotopically enriched186WO3. The theoretical excitation functions for producing186Re, and possible radionuclidic impurities of182Re,183Re, and184Re were calculated using the ALICE code. Cross-sections of the186W(p,n)186Re reaction were measured up to 20 MeV using the stacked target method with thin foils of natural composition tungsten metal. The experimental and theoretical excitation functions were in good agreement. Targetry used at the TIARA cyclotron, and a radiochemical separation scheme for186Re are described.

Visualization of 15O-water flow in tomato and rice in the light and dark using a positron-emitting tracer imaging system (PETIS)

Abstract 15P-water flow from the roots to the top in tomato (Lycopersicon esculentum Mill.) and rice (Oryza sativa L.) plants was visualized with time using a positron-emitting tracer imaging system (PETIS). The 15O-water flow was switched on by light and completely stopped in the dark. The flow rate in the stem of tomato and the shoot of rice at a light intensity of 500 μmol·m−2·s−1 was 1.9 and 0.4 cm min−1, respectively.

Production of positron emitters and application of their labeled compounds to plant studies

The positron emitters11C,13N and18F and their labeled compounds have been produced for studies on plants using a newly developed positron emitting tracer imaging system. Although this system covers, at present, a limited area in a plant, the distribution of the positron emitter fed into the plant can be visualized dynamically. Further development of positron-emitter-labeled compounds is expected to elucidate the physiological function of plants in vivo.

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.

Production of positron emitters of metallic elements to study plant uptake and distribution

The metallic positron emitters 52Mn, 52Fe and 62Zn, the elements of which are essential nutrients for plants as well as for animals, have been produced for a new tracer method in plant physiology. The tracer method utilizes the detection of annihilation γ-rays, like PET in nuclear medicine, to obtain two-dimensional images on a plant as well as to obtain radioactivity counts at specified points in a plant; this method allows us to observe the tracer movement in a living plant without touching the test plant. The previously reported methods of radiochemical separation of these metallic positron emitters from targets were partly modified from the view of their use in plant physiology. Radionuclidic impurities remaining in the final solutions were examined by γ-ray spectrometry, and their influences on the above-mentioned measurements are discussed. From the experiments on a barley plant, the speeds of 52Mn2+ ion and 52Fe3+-mugineic-acid complex have been obtained for the first time to be 0.2 cm/min and 1.0 cm/min, respectively.

Ion source development for the JAERI on-line isotope separator

Abstract In accordance with the JAERI-KEK joint radioactive nuclear beam (RNB) project, we have installed a forced electron beam induced arc discharge (FEBIAD) type integrated-target–ion source in the JAERI-ISOL to produce heavy neutron-rich RNBs with particle-induced fission of 238 U. In the present ion source, a 2.6-g 238 UC 2 target is directly attached to a plasma chamber. RNBs of 8 Li, 18 F and 20 F are also planned to be used for the study of thermal diffusion in materials in the joint project. Release profiles of 7 Li have been studied using a cavity type thermal ion source. For mass-separation of F atoms, the molecular ion formations have been examined using the FEBIAD ion source.

Excitation Functions of Rhenium Isotopes on the natW(d, xn) Reactions and Production of No-carrier-added 186Re

Experimental cross sections for the reactions 186W(d, 2n)186Re, natW(d, xn)181-184Re and 186W(d, p)187W are measured up to 34 MeV using the stacked target method. The values obtained are compared with cross sections calculated using the ALICE code. The experimental and theoretical excitation functions are in reasonable agreement except for the l86W(d, p)187W reaction.

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.

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.