Search

The β+/EC decay of 126 La produced by the 94 Mo( 36 Ar, 3pn) reaction has been studied using the on-line isotope separator connected to an AVF cyclotron. Gamma-ray singles, γ–γ angular correlation and internal conversion electron measurements were carried out. From analysis of these data, 33 new levels in 126 Ba were found and the decay scheme containing 137 γ-rays and 50 excited states was constructed. The probable spin and parity of the two β-decaying states in 126 La were found to be 4±, 5± for the high-spin isomer with a half-life of 54(2) s and 0−, 1±, 2− for the low-spin isomer with a half-life shorter than 50 s.

The ALICE code was used to calculate the excitation functions for proton induced reactions on 100Mo that lead to the production of Nb, Mo and Tc isotopes. The ALICE code predicts a maximum cross section of the order of 100 mb for the 100Mo(p,pn)99Mo nuclear reaction. ALICE predicts that the production of a few Curies of 99Mo is feasible if high intensity (mA) protons are degraded from 50→30 MeV in a target of highly isotopically enriched 100Mo. The ALICE code cannot be used to predict the cross sections for the isomeric states for the 100Mo(p, 2p)99m+gNb→99Mo reactions. However, the predicted cross section for protons on 100Mo to yield 99Nb suggests that the (p,2p) reaction channel does not contribute significantly to the thick target yield of 99Mo. Several considerations suggest that accelerator production of 99Mo→99mTc generators is not a practical economic alternative to fission produced 99Mo. Considerations for the cyclotron production of 99mTc are discussed.

A coronary stent was made radioactive by implantation of 133Xe ions for the purpose of suppressing the re-narrowing of the part of blood vessel in which the stent is implanted. Electrons of relatively low energies emitted in the decay of 133Xe may give an antiproliferative effect of ionizing radiation to the intimal cells within a limited range of 1 mm. A 133Xe+ beam accelerated at 40 or 60 keV was directed to several stainless steel stents mounted on a target-holder table that could revolve and move up and down to distribute the 133Xe+ ions within a stent as well as among the stents. The radioactive stents produced contained up to 100 kBq of 133Xe and were implanted into the abdominal aortas of rabbits. Neointimal thickening was analyzed by histomorphometry for samples taken 4 weeks after stent implantation. The results indicate that the radioactive stents have a potential to suppress neointimal hyperplasia in rabbits.

Beta-ray endpoint energies of the neutron-deficient nuclide of 126La have been measured with an HPGe detector. The 126La activities were produced by the 94Mo(36Ar, 3pn) reaction and mass-separated on-line. From the β-γ coincidence measurements, QEC values of the high- and low-spin isomers of 126La were determined for the first time to be 7700 ± 100 keV and 7910 ± 400 keV, respectively. The experimental atomic masses were compared with predicted values of mass formulas.

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.

No-carrier-added tantalum-183 was produced free of radiotantalum impurities by the 186 W(p,α) 183 Ta nuclear reaction using 13.6 MeV protons on thick targets of isotopically enriched 186 WO 3 . The proton energy was optimum for the simultaneous production of 186 Re and 183 Ta. The ALICE code was used to theoretically determine the optimum irradiation conditions for the production of 183 Ta with proton and deuteron nuclear reactions. A Bio-imaging analyser was used to illustrate the migration of 183 Ta species into a grass plant ( Cyperus microiria steud). 183 Ta has potential applications as a tracer for ecotoxicity studies, and for developmental studies for radiotantalum pharmaceuticals.