Development of portable Liquid Scintillation counters for on-site primary measurement of radionuclides using the Triple-To-Double Coincidence Ratio method

Philippe Cassette (1) , M. Capogni (2) , L. Johansson (3) , K. Kossert (4) , O. Nahle (4) , J. Sephton (3) , P. de Felice (2)

1 LNHB (CEA, LIST) - Laboratoire National Henri Becquerel (CEA, LIST)
2 ENEA-INMRI - Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti
3 NPL - National Physical Laboratory [Teddington]
4 PTB - Physikalisch-Technische Bundesanstalt [Braunschweig]

The Triple-to-Double Coincidence Ratio (TDCR) method in Liquid Scintillation counting (LSC) is a primary radionuclide standardization method widely used in National Metrology laboratories and was primarily developed for the activity measurement of beta emitters. It is based on liquid scintillation: the light is detected by three photomultipliers (PM) and the detection efficiency is evaluated by using a model which uses the ratio of triple-to-double coincidences between the PM tubes. Up to now, most of current TDCR systems were locally-made metrology instruments neither aimed at nor suitable for in-situ measurements. In the framework of the European Metrofission project, a work package was dedicated to the realisation of miniature self-calibrated primary TDCR systems, which are state-of-the-art, for use on-site. The challenge was to develop a versatile portable, table-top designed instrument, from this metrology device. This implied improvements for the miniaturisation of the detection chamber, for the miniaturisation of electronic modules by exploring the possibilities of digital treatment, and for the validation of models and extension of them to nuclides with special beta spectrum shapes, to nuclides with complex decay schemes including many gamma-rays and to nuclides with higher atomic number decaying by electron capture. Four prototypes of counters were built by the Metrofission partners ENEA (Italy), LNHB (France), NPL (UK) and PTB (Germany) using various technical approaches. The paper describes these prototypes and provides some details on the choice of the technical options concerning the design of the optical chamber, of the photodetectors and of the acquisition system.

Mots clés: Optical reflection; Mathematical model; Electron tubes; Photonics; coincidence techniques; liquid scintillation detectors; photodetectors; radioactivity; ionizing radiation; instrumentation; nuclear instrumentation; beta-rays; photomultipliers; radioisotopes; standardisation; portable liquid scintillation counters; triple to double coincidence ratio (TDCR); radionuclide standardization method; beta emitters; photomultiplier tubes; locally-made metrology instruments; European Metrofission project; table-top designed instrument; Metrology device; detection chamber; electronic modules; digital treatment; beta spectrum shapes; complex decay scheme; gamma-rays; atomic number; electron capture; Liquid scintillation; Metrology; TDCR counter

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Instrumentations et Détecteurs [physics.ins-det]

Philippe Cassette, M. Capogni, L. Johansson, K. Kossert, O. Nahle, et al.. Development of portable Liquid Scintillation counters for on-site primary measurement of radionuclides using the Triple-To-Double Coincidence Ratio method. 2013 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and their Applications (ANIMMA), Jun 2013, Marseille, France. pp.06727876, ⟨10.1109/ANIMMA.2013.6727876⟩. ⟨cea-01822354⟩