Abstract
An attempt was made to reduce the background counting rate of γ-ray spectrometer commonly used. Additional setting of an inner shield made of oxygen free copper within the ordinary shield was found to work well. Remarkable reduction of spectral lines from radondaughters was observed by introducing N2-gas into the sample chamber to expel Rn together with the daughters existing there. Fluctuation in background also diminished sufficiently and was stabilized. It may be possible to employ the spectrometer of common use, even not to be designed for the low-level counting, for the measurement with high stability of low level radioactivity usig the present simple technique.
