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First astatine-labeled compound shipped in the U.S.
The Department of Energy’s National Isotope Development Center (NIDC) on March 31 announced the successful long-distance shipment in the United States of a biologically active compound labeled with the medical radioisotope astatine-211 (At-211). Because previous shipments have included only the “bare” isotope, the NIDC has described the development as “unleashing medical innovation.”
R. M. Carroll, J. G. Morgan, R. B. Perez, O. Sisman
Nuclear Science and Engineering | Volume 38 | Number 2 | November 1969 | Pages 143-155
Technical Paper | doi.org/10.13182/NSE69-A19519
Articles are hosted by Taylor and Francis Online.
Two cylindrical specimens of UO2 were irradiated in the Oak Ridge Research Reactor at temperatures up to 1700°C. Both specimens were of natural enrichment uranium (0.7% 235U) but one specimen was a single crystal and the other had a fine-grain microstructure. The fission-gas release from these specimens were affected by the fission density, temperature, burnup, grain growth, and the cracking of the specimens. Concentrations of fission gas produced high local stresses which contributed to the cracking of the specimens. Spherical specimens of enriched (48.7% 235U), fused, polycrystalline UO2 were irradiated to study the effect of burnup and high fission density. The spherical specimens began breaking at 1.9% uranium burnup and continued to break into smaller fragments as the burnup continued to 4.6% uranium burnup. The primary cause of breaking was fission-gas pressure within the spheres rather than thermal stresses. Equiaxed grain growth in UO2 occurs at ∼1650°C and fission gas, normally trapped in a grain boundary, can then migrate along the mobile grain boundary. The fission-gas release rate is thus greatly increased during the time of grain growth but the increase in grain size has little influence on the subsequent gas release at lower temperatures. By the defect-trap model, the effect of an increase in fission density is to create more traps within the fuel and at the same time to generate more fission gas. Thus, although the concentration of fission gas within the specimen is proportional to the fission density (at equilibrium conditions) the escape rate of the fission gas is not proportional to the concentration, unless the fission density is very low. When the fission density is very high, however, the fission tracks will intersect and the fission gas may escape as if through interconnected diffusion pipes. The fission-gas release was found to increase exponentially with fission density above 1014 fissions/(cm3 sec).
