Proposed New Method for Separating Isotopes
RECENTLY1 a double mercury discharge vessel was used (Fig. 1), in which a large current running in the outer vessel irradiated the small current discharge in the inner vessel with 2537 Å resonance radiation. This irradiation caused the running voltage and electron temperature in the inner discharge to be reduced appreciably over the non-irradiated mode of operation. The explanation offered was that the neutral Hg atoms in the inner vessel absorbed the resonance radiation and entered the 63P1 state (see Fig. 2), and from this level the atom was ionized by electron impact. In addition the 63P0 and 63P2 metastable levels are populated from the 63P1 level by electron collisions and by cumulative absorption and radiative decay of higher levels. Because the radiation field is doing approximately half the ionization work, the electron temperature drops correspondingly.
Ionization of U, UO, and UO2 by Electron Impact
The first ionization potential of uranium and the first appearance potentials of UO and UO2 by electron impact have been measured in a mass spectrometer, using the retarding potential difference (RPD) method. Small modifications of the RPD source are described. Crucibles of zirconium diboride were found to be preferable to tantalum crucibles for vaporization of uranium metal. Correction is made to the uranium appearance potential for thermally excited low‐lying levels of the uranium atom, and for the several possible ionization paths. The ionization potential for uranium is 6.11±0.05 eV; for UO and UO2 the appearance potentials are 5.72±0.06 eV and 5.5±0.1 eV. Ionization probability curves were determined for U and UO.
Geomagnetic Polarity Epochs: Sierra Nevada Data, 3
Available paleomagnetic and radiometric results for about 60 igneous rocks 3.6 m.y. old or less are consistent with the following geomagnetic polarity epoch time scale: Brunhes normal polarity epoch, 0.0 to 0.85±0.15 million years; Matuyama reversed polarity epoch, 0.85±0.15 to 2.4±0.1 million years; Gauss normal polarity epoch, 2.4±0.1 to 3.35±0.1 million years; Gilbert reversed polarity epoch, 3.35±0.1 million years to (?). A brief interval of normal polarity (the Olduvai event) occurs within the Matuyama reversed epoch at about 1.9 m.y., and a brief interval of reversed polarity (the Mammoth event) occurs within the Gauss normal epoch at about 3.06 m.y. Data for twelve units from eastern California and Nevada, reported here for the first time, are particularly useful in defining the Gauss-Gilbert boundary and for recognizing the Mammoth event.