Nuclear medicine progress report for quarter ending December 31, 1987

The production of osmium-191 by thermal neutron irradiation of enriched osmium-190 has been further evaluated at neutron flux values from 4 /times/ 10/sup 14/ to 2.5 /times/ 10/sup 15/ neutrons/cm/sup 2//center dot/sec. In order to obtain osmium-191 with a specific activity of 250 mCi per mg of enriched osmium-190, irradiation periods at neutron flux values lower than 2.5 /times/ 10/sup 15/ neutrons/cm/sup 2//center dot/sec have to be extended up to 2--4 weeks. This results in significantly increased levels of the undesirable iridium-192. The iridium-192 is produced by capture of a neutron by iridium-191, which is formed by decay of the short-lived 4.96 sec iridium-191m daughter produced by ..beta../sup /minus// decay of osmium-191. Elution of even small levels of iridium-192 from the Os-191/Ir-191m generator results in a large portion of the total absorbed radiation dose from the generator eluate. Two efficient methods for purification of osmium-191 by conversion to osmium tetroxide and isolation by both distillation and solvent extraction methods have been developed for removal of iridium-192. During this period, iodination of model nucleoside substrates has also been pursued. The reaction of iodine monochloride with imidazole nucleoside, 5-amino-1-(2,3,5-tri-O-acetyl-..beta..-D-ribofuranosy) imidazole-4-carboxamide, provided the unexpected 2-chloroimidazolenucleoside in good yield. This could be a usefulmore » method for preparation of other chlorinated imidazoles. 23 refs., 7 figs., 7 tabs.« less