Low-activity Samples Research Articles

Large Thin-Wall Geiger Counter

A new thin-wall Geiger counter of large area sensitive to soft beta-radiation has been developed. The sensitive area can be as large as desired and the wall thin enough for C14 (2 mg/cm2). The cylindrical geometry renders the counter especially suitable for accurate assays of large solid samples of low specific activity and low energy.

Scintillation counting equipments

Two types of scintillation counter, employing the VX 5045 multiplier photocell and a phosphor, are described. The alpha scintillation counting equipment is a complete instrument for counting samples of low activity over an area of 10 cm2, at background rates of less than 2 counts per hour. A counting efficiency of 35% is obtained from a thin alpha-particle source with a comparative accuracy of ±1%. The scintillation gamma counter is designed as a probe unit for routine measurement of gamma-ray flux. Methods are given for the preparation of suitable phosphors. Using a thallium-activated sodium iodide phosphor, a counting efficiency of 22.5% was measured for 1.2-MeV gamma rays stable over long periods to ± 1%.

Preparation of Silver Bromide Precipitates for Radioactivity Measurements

RADIOACTIVE tracer studies in progress at this Laboratory employing insecticides labelled with bromine-82 have involved activity measurements on liquid and solid samples, and on gaseous samples in certain cases. Liquid samples (usually as soluble bromide) were assayed in a Geiger–Muller counter of the type described by Veall1, whereas solids (usually as silver bromide) were assayed under a thin mica end-window counter of conventional design. For bromine-82 activities (Eβ-max. = 0·46 MeV., Eγ = 0·55, 0·79 and 1·35 MeV.) the use of liquid samples proved the more convenient ; but that of prepared precipitates was some fifteen times more efficient. The higher efficiency was a decisive factor with samples of low specific activity.

An Internal Geiger Counter for the Assay of Low Specific Activity Samples of Carbon 14 and other Weak Beta Emitters in Biological Samples

An Internal Geiger Counter for the Assay of Low Specific Activity Samples of Carbon 14 and other Weak Beta Emitters in Biological Samples