Alpha-particle Activity Research Articles

The uranium geochemistry of latten Volcanic National Park, California

The uranium contents and relative alpha-particle activities have been determined on thirty-nine samples from Lassen Volcanic National Park. Sodium and potassium were also determined on nineteen of the samples. Secular radioactive equilibrium to within sampling and analytical error was found between the uranium values and the radium values of other workers. The K 2 O U ratio was found to be constant over a fourfold variation in uranium. The relative alpha-particle activity to uranium ratio was also found to be constant in the main Lassen sequence. There is some evidence that zircon crystals contain a proportion of the uranium in the Lassen volcanic rocks.

Alpha-Particle Assay and the Measurement of the Thorium-Uranium Ratio in Radioactive Ores

The measurement of the alpha-particle activity of a `thick' radioactive source containing the natural radioactive series is discussed critically. Two methods of determining the thorium-uranium ratio are considered for use in ore or mineral assays. The energy discrimination method is simple in procedure and can take account of lack of secular equilibrium between members of a series in the radioactive sample. The beta-alpha coincidence method, making use of the difference in the disintegration constants of radium C' and thorium C', is more complicated. Initial experimental verification of the theory has been obtained. The estimated statistical error in determining the thorium-uranium ratio by the energy discrimination method is ±5% in the region of Th/U = 1, with a 4% sample (U3O8 equivalent concentration) in 4 minutes counting. A similar accuracy is obtainable in the coincidence method with a counting period 10 times greater

DISTRIBUTION OF RADIOACTIVITY IN GRANITES AND POSSIBLE RELATION TO HELIUM AGE MEASUREMENT*

Granulated samples of acidic igneous rocks have been found to give a much higher rate of emission of alpha particles than corresponds to the known total contents of uranium and thorium. Abnormally large residual ranges of the alpha particles suggest a surficial distribution of the radioactive elements on the surfaces of the granules in the form of secondary mineral coatings. Most of the alpha-particle activity can be removed by dilute hydrochloric acid, leaving an activity corresponding to the low content of uranium and thorium found in sandstones and arkoses, in which the essential mineral grains of granites have been rounded and cleaned by attrition. The proportion of surficial activity appears to be less for granite samples taken from considerable depth below the surface than for samples from the zone of surface-water saturation. Losses of activity by acid treatment appear to be related to the degree of retentivity of helium in different igneous rock types. Determination of the helium age ratio before and after acid treatment suggests that the essential rock minerals contain as much helium as they should commensurate with their age and with the quantity of radioelements uniformly distributed within them, and not removable by acid. The low ratio of helium to radioactivity for the rock as a whole may be due either to loss of helium from highly radioactive areas that are easily affected by acid and thus also probably by ground waters, or to actual supergene enrichment of radioelements late in the history of the rock.

Determination of the Thorium Content of Rocks

A new method for the determination of thorium in quantities of the order of 10—5 to 10—6 g is employed to complete the data necessary for the calculation of the age of geological material. The alpha-particle activity of thoron in a streaming gas is measured with a counter, a procedure which is shown to be superior to the usual ionization measurements on the thoron deposit. Simultaneously, the Pa/Ra ratio in common rocks can be determined.