[Dominant Research Contribution of Dr. Eiichi Tanaka in the Field of Very Weak Radioactivity Measurements].

This article gives dominant research contributions of the late Dr. Eiichi Tanaka in the field of very weak radioactivity measurements with a new type of an extremely low background β-ray scintillation spectrometer, which consists of a large plastic scintillator and a gas-flow GM counter located in the small hollow in the bottom part of the plastic scintillator. The pulse signals from plastic scintillator are coincidence-gated by the pulses from the GM counter. Dominant background signals due to the energetic muons still appear in the higher region than 3.5 MeV even with coincidence gating mode, but extreme reduction of background can be attained in the 0～3 MeV region which is essentially important in the β-ray spectrometry for most of radionuclides.