The Uranium 234 Content of Natural Uranium and the Specific Alpha-Activities of the Isotopes

Abstract

The uranium 234 content of natural uranium was determined, by a combination of alpha-counting and mass spectrometer techniques, to be 0.005481 ±0.000012 weight percent, the precision being expressed on the basis of 95 percent probability. This corresponds to a half-life of (2.522±0.008) X10 5 years. Considering possibilities of bias, these figures are believed to lie within one percent of the true values. In conjunction with this determination, the half-lives of the other natural uranium isotopes were also measured. P REVIOUS determinations of the weight percent of uranium 234 in natural or "normal" uranium have all involved measurement by the mass spectrometer. Nier first used such an instrument to determine the relative abundance of uranium 238 and uranium 234 in normal uranium. 1 Chamberlain, Williams, and Yuster used two related methods. 2 The first method was identical in principle to Nier's method in that they used the mass spectrometer for a direct measurement of normal uranium. In the second method the specific activity of uranium 234 was determined from the total alpha-activity and relative isotopic abundance of enriched uranium samples, assuming the specific activities of uranium 238 and 235 from the data of others. From their data on the alpha-activity of enriched samples, together with a specific activity figure for uranium 238, 3 it is possible to deduce a value for the content of uranium 234 in natural uranium by computation of the uranium 234 alpha-emission enrichment factor.By using pure samples of uranium 234 grown from UX h Knight, Goldin, P. A. Macklin, and R. L. Macklin of this laboratory have determined the specific activity of uranium 234 from which they calculated, using the specific activity of uranium 238 given in this report, the weight percent of uranium 234 in normal uranium. Their normal abundance figures of 0.005805±0.00008 weight percent is significantly different from that reported in this paper, but the cause of the difference is not yet known.This report is concerned with a re-determination of the weight percent of uranium 234 in normal uranium by a method similar to the second method used by Chamberlain, Williams, and Yuster, and also an independent re-determination of the specific alpha-activities of the three isotopes. The uranium 234 content of uranium highly enriched in the 234 isotope can be determined with greater accuracy by the use of the mass spectrometer than that achieved in measurements on normal uranium, since the ratio of the uranium 234 to the sum of uranium 235 and 238 in greatly enriched uranium has been increased many times. The alpha- Nier, Phys. Rev. 55, 150 (1939). 2 Chamberlain, Williams, and Yuster, Phys. Rev. 70, 580 (1946). 3 G. T. Seaborg and I. Perlman, Rev. Mod. Phys. 20, 637 (1948). activities of the enriched and normal uranium can then be measured by the use of counting equipment.

New measurement of the 238U decay constant with inductively coupled plasma mass spectrometry

“…Figure 5 shows our preliminary result, converted to a halflives of 4.452(27) 9 10 9 or 4.456(21) 9 10 9 years, respectively, along with previously reported and evaluated a-counting results (adapted from [5]). Of these, only our measurement, Kienberger [24] and Jaffey et al [1] are not correlated with assumed natural uranium isotope ratios because they included measurements of enriched 238 U. Our results indicate slightly faster decay of 238 U than those obtained by medium-geometry a-counting but overlap with the evaluated (k = 2) uncertainty envelope [6] (shaded light blue in Fig.…”

Mesure du rapport des sections efficaces de fission par neutrons thermiques de 239Pu et de l'uranium naturel

“…2 X 75I (X.mn-l.mg-1 d'uranium ordinaire à 0,1 pour 10o près [4]; 2 X 68 030 (X. mn-l . Ig-1 de 239PU à o,4 pour o0 près [5] -(ces valeurs ayant été obtenues par numération des particules « dans des chambres d'ionisation à géométrie 2 7r après correction de la rétrodiffusion).…”

“…Des valeurs précises des activités spécifiques « par unité de masse ayant été publiées [4], [5], les valeurs des 91 s'en déduisent immédiatement.…”

Mesure du rapport des sections efficaces d'activation du manganèse et de fission de l'uranium en neutrons thermiques. Redétermination de la densité neutronique étalon de Chatillon

“…Cependant, la prévision des corps stables exigesans doute moins de précision que celle des énergies disponibles. C'est peut-être pour cela que la formule de Bethe-Fermi a la réputation d'annoncer les corps stables dans l'ensemble du tableau périodique [2].…”