Masses of Stable Nuclei fromNe20toFe57

Abstract

80 120 160 200 240 TIME IN MINUTES FIG. 1. Growth of 2.3-day 93 239 from 23-minute U 239 . The points indicate the activities of successive fluoride extractions, plotted at the times of extraction. Decay measurements were made a day later on the first six fractions, and the resulting slopes are shown on the plot.experiments showed that in the reduced state with a thorium carrier it precipitates with iodate, and in the oxidized state with uranium as sodium uranyl acetate. It also precipitates with thorium on the addition of H2O2. It precipitates in basic solution if carbonate is carefully excluded. These properties indicate that the two valence states are very similar to those of uranium (U ++++ and U0 2 ++ or U2O7 ), the chief difference from that element being in the value of the oxidation potential between the two valences, such that the lower state is more stable in the new element. It is interesting to note that the new element has little if any resemblance to its homolog rhenium; for it does not precipitate with H2S in acid solution, is not reduced to the metal by zinc in acid solution, and does not have an oxide volatile at red heat. This fact, together with the apparent similarity to uranium, suggests that there may be a second "rare earth" group of similar elements starting with uranium.The final proof that the 2.3-day substance is the daughter of the 23-minute uranium is the demonstration of its growth from the latter. For this experiment activated uranium was purified twice by precipitation as sodium uranyl acetate, which was dissolved in HF and saturated with S0 2 . Then equal quantities of cerium were added at twenty-minute intervals and the precipitates filtered out. The first precipitate, made immediately after purification, carried all the fluoride-precipitable contaminations and was discarded; its weakness indicated a very good purification. The activities of the others are plotted in Fig. 1.A preliminary study of the radiations from 93 239 shows that it emits continuous negative beta-particles with an upper limit of 0.47 Mev, and a weak complex spectrum of low energy gamma-rays (<0.3 Mev) and probably x-rays. The question of the behavior of its daughter product 94239 immediately arises. Our first thought was that it should go to actinouranium by emitting an alpha-particle.We sought for these by preparing a strong sample (11 millicuries) of purified 93 and placing it near a linear amplifier in a magnetic field to deflect the beta-particles. From this experiment we conclude that, if alpha-particles are emitted, their half-life must be of the order of a million years or more; the same experiment showed that if spontaneous fission occurs its half-life must be even greater. We wish to express our gratitude to the Rockefeller Foundation and the Research Corporation, whose financial support made this work possible.

Mass-spectrometer study of the rare gases

“…The comparative data are again those of Vaughan , W illiams, a nd Tate [5], and thE' weight calculated from their values is 39.950, The accepted value is 39.944. The chemical weigh t compu ted from th e abundance and the isotopic weigh ts given by Pollard [10] is 39.949' Table 4 lists the krypton isotop es and their respective abundance. Nier's values [3] converted from r elative to percentage abundan ce are also inclu ded.…”

“…The accuracy is believed to b e of th e order of 1 percent of th e a bundance for isotop ic n,b und an ces greater than 10 p ercent. With th e n eon isotopic masses listE'd by Pollard [10] Table 3 lists the argon isotopes n,nd their r espective p ercentage itbundance. The comparative data are again those of Vaughan , W illiams, a nd Tate [5], and thE' weight calculated from their values is 39.950, The accepted value is 39.944.…”