George A. Cowan

The variability of the natural abundance of 235U

The possibility that the atomic ratio 235u/238U may be slightly variable due to natural nuclear chain reactions such as have been identified in Gabon, West Africa, has prompted a re-examination of very precise gas mass spectrometric isotopic ratio data from a number of laboratories. Two modal values of the isotopic ratio exist in the data. Their relative difference, 0.03%, is statistically significant. The lower mode is due principally to ores from the Colorado Plateau. This difference was recognized in 1963 by the U.S. Atomic Energy Commission but the substantiating data have not been openly published. Insufficient data presently exist to attribute this difference to chemical differentiation of the uranium isotopes, presumably in the ‘sandstone’ type deposits of the Colorado Plateau, or to dilution with Precambrian ore deposits, depleted in 235U by nuclear reactions.

Double beta decay of U-238

The half-life for the decay of {sup 238}U to {sup 238}Pu has been measured to be (2.0{plus minus}0.6){times}10{sup 21} yr by chemically isolating and measuring from the resultant alpha particles the amount of plutonium that had accumulated in 35 yr from 8.4 Kg of purified uranyl nitrate. Other sources of {sup 238}Pu have been studied and found negligible.

Solar neutrino production of technetium-97 and technetium-98

It may be possible to determine the boron-8 solar neutrino flux, averaged over the past several million years, from the concentration of technetium-98 in molybdenite. The mass spectrometry of this system is greatly simplified by the absence of stable technetium isotopes, and the presence of the fission product technetium-99 provides a monitor of uiranium-induced backgrounds. This geochemical experiment could provide the first test of nonstandard solar models that suggest a relation between the chlorine-37 solar neutrino puzzle and the recent ice age.

Heavy Methanes as Atmospheric Tracers

Methane-21 (13CD4) is potentially a useful nonradioactive tracer for testing atmospheric transport and diffusion models on a continental scale. In an experiment to demonstrate this long-range utility, the release of 84 grams of methane-21 was detected at distances of 1500 to about 2500 kilometers at concentrations of about 1 part in 2 x 1016 parts (by volume) in the air by a technique in which methane was separated and the methane-21 content was measured with a mass spectrometer.

Double-beta decay of 238U.

The half-life for the decay of {sup 238}U to {sup 238}Pu has been measured to be (2.0{plus minus}0.6){times}10{sup 21} yr by chemically isolating and measuring from the resultant alpha particles the amount of plutonium that had accumulated in 35 yr from 8.4 Kg of purified uranyl nitrate. Other sources of {sup 238}Pu have been studied and found negligible.

Double-beta decay of sup 238 U

The half-life for the decay of {sup 238}U to {sup 238}Pu has been measured to be (2.0{plus minus}0.6){times}10{sup 21} yr by chemically isolating and measuring from the resultant alpha particles the amount of plutonium that had accumulated in 35 yr from 8.4 Kg of purified uranyl nitrate. Other sources of {sup 238}Pu have been studied and found negligible.

Double-beta decay ofU238

The half-life for the decay of {sup 238}U to {sup 238}Pu has been measured to be (2.0{plus minus}0.6){times}10{sup 21} yr by chemically isolating and measuring from the resultant alpha particles the amount of plutonium that had accumulated in 35 yr from 8.4 Kg of purified uranyl nitrate. Other sources of {sup 238}Pu have been studied and found negligible.

A proposed geological solar neutrino measurement

It may be possible to measure the boron‐8 solar neutrino flux, averaged over the past several million years, from the concentration of technetium‐98 inmolybdenum‐rich ore. This geochemical experiment could provide the first test of nonstantard solar models that suggest a relation between the chlorine‐37 solar neutrino puzzle and the most recent glacial epoch. The necessary conditions for achieving a meaningful measurement are identified and discussed.