Scintillation Spectrometer Studies on the Beta-activity of K⁴⁰

Abstract

The beta-ray spectrum of potassium-40 has been studied using the scintillations from the crystal of potassium iodide activated with thallium iodide. The Kurie plot of the spectrum gave the forbidden shape, which was straightened from the end-point 1320±20 kev down to well below 300 kev by the third forbidden tensor (or axial vector) correction factor. Measurement on the specific activity has also been carried out and resulted in the value λ(β)=5.0±0.2×10⁻¹⁰ per year. This value is in good agreement with recent determinations.