Effects of the anisotropy of β-ray emission from a sealed source on the detection efficiency

Angular distributions of the low-energy β-ray emission from a sealed standard β-source are calculated by a simple method, resulting in an anisotropic angular distribution. Effects of the anisotropy are evaluated on the determination of detection efficiency of a β-ray detector for various thicknesses of the sealing layer of the standard source. A method to correct for these effects is developed. It is found that the anisotropy of the angular distributions is required to be considered for evaluating the detection efficiency of a β-ray detector, particularly for the measurement of low-energy β-rays.