P.K. Kuroda

Isolation of naturally occurring technetium

About l m mu g of Tc/sup 99/ was isolated from several kg of Belgian Congo pitchblende. The amount of Tc found in the ore appears to be in good agreement with the calculated value. The analytical procedure for the dissolution of the pitchblende, removal of Cu, Mo, Re, and Ru, and the final isolation of Tc is given. Counting results of two separate samples are tabulated. (P.C.H.)

Technetium in nature

Abstract A sample of African pitchblende was found to contain between 2·5–3·1 × 10−10 g of 99Tc per kilogram ore, but no other technetium isotopes were detected. The 99Tc/238U ratio in pitchblende was about the same as the 99Mo/238U ration in nonirradiated uranium. The experimental results suggest that the 99Tc is produced in the ore predominantly by 238U spontaneous fission.

THE OCCURRENCE OF MOLYBDENUM-99 IN NATURAL AND IN DEPLETED URANIUM SALTS AND THE SPONTANEOUS FISSION HALF-LIFE OF URANIUM-238

Abstract Measurements of the 99Mo/238U equilibrium ratios in aqueous solutions of non-irradiated uranium salts gave the following results: (4·4 ± 0·4) × 10−4 and (4·4 ± 0·3) × 10−4 disintegrations per second of 99Mo per gramme of 238U in natural uranium and in depleted uranium, respectively. A value of (8·0 ± 0·5) × 1015 years, which agrees with Segres value, is obtained from the above data for the spontaneous fission half-life of 238U, if one assumes that the yield of 99Mo is 6·4 per cent and the spontaneous fission of 238U is the only source of 99Mo.

The ratio of induced fission vs. spontaneous fission in pitchblende and natural occurrence of radiochlorine

Abstract Chlorine was isolated from kilogram quantities of both Canadian and African pitchblende, exhaustively purified, and counted. The specific activity of chlorine obtained from African pitchblende was found to be (7 ± 1) disintegrations per minute per gramme of chlorine, while that from Canadian pitchblende was (4 ± 1) disintegrations per minute per gramme of chlorine. The ratio of induced fission of 235U vs spontaneous fission of 238U in these minerals was calculated from the radiochlorine data. A value of 0·33 was obtained for the African pitchblende and a value of 0·19 for the Canadian pitchblende.

The occurrence of the short-lived iodine isotopes in natural and in depleted uranium salts☆☆☆

Abstract The occurrence of the short-lived iodine isotopes in non-irradiated uranium salts has been established. The equilibrium ratios of the short-lived iodine isotopes to 238U in depleted uranium agree, within the experimental error, with the ratios in natural uranium. The ratios expressed in terms of 10−4 disintegrations per second per gram of 238U are: 131I, 0·3 ± 0·1; 132I, 2·5 ± 0·3; 133I, 1·0 ± 0·2; 134I, 3·6 ± 0·4; 135I, 3·5 ± 0·4. The following values are obtained for the yields of the iodine isotopes, if Segres value for the spontaneous fission half-life of 238U, (8·04 ± 0·3) × 1015 years, is taken to be correct: 131I, 0·4 ± 0·1; 132I, 3·6 ± 0·4; 133I, 1·5 ± 0·3; 134I, 5·2 ± 0·5; 135I, 5·1 ± 0·5 per cent.

14·8 MeV neutron-induced (n, 2n), n, p) and (n, α) cross-sections for some closed shell nuclides

Abstract The activation cross-sections for 12 (n,p), (n,α) and (n,2n) reactions have been determined with 14·8 MeV neutrons using enriched sample materials and Ge(Li) γ-ray detection. The closed shell nuclides studied are 54Fe, 90Zr, 92Mo, 141Pr and 144Sm. The measured (n,2n) cross-section values are compared with those calculated by theoretical and empirical methods, and to plots of σ(n, 2n) vs the asymmetry parameter. A plot of the (n,2n) experimental data, which accounts for differences in nuclear radii and threshold energies for the same value of asymmetry parameter, is presented.

Radiochemical measurement of the natural fission rate of uranium and the natural occurrence of Ba140

Abstract Ba 140 was isolated from 4540 g of uranyl acetate. The equilibrium amount of Ba 140 in the uranium salt was found to be (1·6 ± 0·1) × 10 −14 c Ba 140 per gram U 238 , corresponding to an overall natural fission half-life of uranium of (5·9 ± 0·4) × 10 15 years, assuming a fission yield of 6·1% for Ba 140 .

Fallout of uranium isotopes from the 1980 eruption of Mount St. Helens

A marked increase in the concentration of238U in rain was observed at Fayetteville (36 °N, 94 °W), Arkansas, after the 18 May 1980 eruption of Mount St. Helens. The fallout of natural uranium observed during the summer months of 1980 can be attributed to the 18 May 1980 events, which ejected an amount of ash material on the order of 4 km3 or about 8·1015 grams into the atmosphere.234U and235U were found to be highly enriched relative to238U in several rain samples collected at Fayetteville, Arkansas, prior to the volcanic eruption. The anomalous uranium seems to have originated from the Soviet satellite Cosmos-954, which fell over Canada, on 24 January 1978. The effect of the 25th Chinese nuclear test, which occurred on 16 October 1980, on the concentrations of uranium isotopes in rain appears to have been insignificant.

Atmospheric residence times of strontium-90 and lead-210

The concentrations of89Sr,90Sr,210Pb and210Po were measured in a series of rain samples collected at Fayetteville (36°N, 94°W), Arkansas, after the 14th Chinese test of March 18, 1972, which occurred at Lop Nor (40°N, 90°E), China. Approximately concordant tropospheric residence times were obtained from the89Sr/90Sr and210Po/210Pb ratios in rain. The89Sr/90Sr ratios were also measured for the rain samples collected at Tokyo (36°N, 140°E), Japan, and at Ankara (40°N, 33°E), Turkey.

Mass distribution in 14·8 MeV neutron-induced fission of 232Th

Abstract In the 14·8 MeV neutron-induced fission of 232Th, the distribution of mass in the rare-earth region is studied by isolating radiochemically several fission products belonging to 13 mass chains. The absolute activities for these nuclides are determined by β− and γ-counting and the cumulative fission yields were determined relative to Mo99. Using these experimental data, the right side slope in the heavy peak of the mass yield curve for this fission process is clearly defined. Its significance with reference to the 14 MeV fission of 237Np and 238U is qualitatively discussed.