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The triple to double coincidence ratio method was used with a combined uncertainty of 1–2% to standardize tritiated water and a solution of 204Tl. The vial with liquid scintillator, in which the sample to be measured was dissolved, is optically coupled to three photomultipliers. The electronic module MAC-3 assures the selection of double and triple coincidences count rates, D and T, from the three counting channels. It contains the gating circuits, necessary to obtain the livetime value and the extended deadtime circuit. Specific computer programs were used to calculate the free parameter value, the efficiency of D and so, the value of the activity. The optimal value of the Birks ionisation-quenching parameter, kB, was evaluated by changing the detection efficiency with grey filters. Three types of liquid scintillators, namely InstaGel®, PPO+POPOP+Triton in toluene and Ultima Gold®, were employed. 204Tl was measured in the frame of an international comparison organized by BIPM. For tritiated water a comparison was made with LNHB-Saclay; the relative difference between the obtained values for the massic activity was only 0.2%. [Copyright &y& Elsevier]

Abstract: The “conventional” TDCR system was used for standardization of the tritiated water in the frame of the international comparison organized by CCRI(II). The prototype of the new TDCR realized at LNHB with three CPMs (Ivan et al., 2008) was improved by constructing at IFIN-HH, a system containing six channel photomultiplier tubes arranged symmetrically in a new optical chamber. The system was tested by measuring various pure beta emitters and for comparative measurements of tritiated water for validation studies. [Copyright &y& Elsevier]

A low-level gamma-ray spectrometry system was developed using a Ge(Li) detector with 6% relative efficiency coupled to a 2π beta plastic detector for coincidence selection and a massive NaI(Tl) detector for Compton suppression.The integral background count rate for (50–1500) keV was 0.5 s-1 kg-1 (Ge), using only beta coincidences. With Compton suppression, a value of 0.25 s-1 kg-1 (Ge) was obtained. Spectra with and without Compton suppression were studied for 60Co, 137Cs and 152Eu point sources. Considerations are made concerning the Compton suppression advantages in different situations. [Copyright &y& Elsevier]

Abstract: A new coincidence system, based on two thin NaI(Tl) crystals, 50×2mm2, with beryllium windows, 1.5mgcm−2, positioned approximately symmetrically from the source holder (at various distances) was constructed. The electronic chains of a classical 4πPC–γ system were utilized. A multichannel analyzer was employed for energy calibration, and an oscilloscope for visualization of the pulses. After calibration, the system was used for the standardization of an 125I solution. An energy window of 12–95keV containing the entire spectrum (single and sum peak) was employed, and a simple demonstration of Taylor''s equation [1967. X-ray–X-ray coincidence counting methods for the standardization of 125I and 197Hg. In: Standardization of Radionuclides: Proceedings of a International Atomic Energy Agency Symposium, Vienna, 1966, pp. 341–353, SM-79/65] for whole spectrum counting, was developed. The method and system were tested during the calibration of a LKB 2104 multi-gamma counter, by comparing the detection efficiency values obtained for this prepared standard solution and that utilized in the CIPM-CCRI(II) key comparison. The efficiency of the equipment was calculated as the mean of the two individual values. The result validates the method and demonstrates the accomplishment of the national traceability assurance in nuclear medicine for 125I. [Copyright &y& Elsevier]

This review paper presents the contribution of the Radionuclide Metrology Laboratory (RML) to the development and practical application of the coincidence counting methods. It is also intended to pay tribute to Dr. Enric Leon Grigorescu, the founder of our school of radionuclide metrology. A synthetic treatment of the method, applied to some classes of radionuclides with their common and particular aspects in standardization, is presented: pioneering calculation of instrumental corrections, specific method corrections applied for various types of decay schemes in the variant of efficiency extrapolation, results obtained in international comparisons. • Development of the coincidence method, efficiency extrapolation. • Pioneering original formulae for calculation of instrumental correction. • Adequate application of the method to various types of radionuclides. • Participation in international comparisons. [ABSTRACT FROM AUTHOR]

The radionuclide 68Ga is mainly a positron emitter (89.2%), with a half-life of 67.7min. It is used in nuclear medicine, being chemically extracted from the mixture 68(Ge+Ga); its precursor, 68Ge, disintegrates 100% by electron capture, with a half-life of 270.8d (Table of radionuclides, comments and Evaluation).A 4πβ–γ coincidence method was used for standardization, with a 4π proportional β-detector and a NaI(Tl) γ detector. Registration of the capture radiations was avoided using foil absorption and a high β threshold. Using supplementary foils for positron absorption, extrapolation graphs were obtained, with a mean slope of −4.4%. Care was taken to compensate for the loss of 68Ge during the preparation of solid sources for measurement. A combined uncertainty of 1.1% was estimated. [Copyright &y& Elsevier]