Development and applications of a miniature TDCR acquisition system for in-situ radionuclide metrology

This work presents the design and the basic features of a newly developed front-end digital pulse processing device for the application of the triple-to-double coincidence ratio (TDCR) method in liquid scintillation (LS) counting. The device (hereafter called nanoTDCR) allows coincidence counting of the signals from LS counters equipped with three photomultiplier tubes (PMT) and is designed for the primary standardization of radionuclides by the TDCR method. In contrast with other front-end TDCR acquisition systems developed by metrology institutes, it uses extendable dead-time systems in each PMT channel. The system allows simultaneous counting within two different base dead-time durations and two different coincidence windows. The important characteristics and the operation of the device are presented. The specific metrological features of the system are discussed, including the observed linearity of the system, tested up to 90 ks(-1) with more than 95% dead-time. Several applications of TDCR measurements with the nanoTDCR device are demonstrated: absolute standardization of pure beta radionuclides (H-3, Sr-90/Y-90), standardization of radionuclides decaying through electron-capture followed by gamma de-excitation (Pd-103, (103)mRh) and absolute activity measurements of Rn-222. The use of this system for the measurement of the decay of radionuclides is illustrated by the determination of the half-lives of (103)mRh, Ra-223 and the assessment of the concentration of a pure-beta impurity, P-33 in P-32.