Preparation of background samples for accurate low-level measurements by liquid-scintillation spectrometry

For precise measurement of low-level β-radioactivity by liquid-scintillation spectrometry, it is essential to prepare a so-called background sample, the count rate of which corresponds approximately to the background count rate of the source to be measured. A method for preparing such background samples is described in this paper. It has been successfully applied to the determination of 14C radioactivity as low as 30 mBq with a relative uncertainty of less than 5%.