Low-Energy Standards for Gamma-Ray Spectrometry

Abstract

A simple type of low-energy calibration standard for gamma -ray spectrometry has been developed for the range 5 to 75 kev. Standards are made by placing a target of a single element over a pure beta emitter, such as promethium- 147 or strontium-90. Characteristic x rays of the target element are generated, usually the K alpha radiation, although L x rays are predominant for very thin targets. For energy calibrations greater than 17 to 20 kev it is best to use thin metallic foil targets or pressed oxide disks. Standards for energies less than 17 kev are best prepared by mixing a solution of the beta emitter with a few milligrams of a salt of the target element, and evaporating to dryness on a micro cover glass. By this technique, the lowest energy K alpha x ray clearly observed was that of vanadium at 4.96 kev, using a 1 1/2 x 1/2 inch thallium-activated sodium iodide crystal equipped with a 0.005-inch beryllium window. The use of these standards affords a simple and convenient technique for checking nonlinear response in the low-energy region for scintillation detector systems, measuring the noise level of multiplier phototubes, and identifying radioactive elements which emit convertedmore » gamma rays.« less