Development of portable Liquid Scintillation counters for on-site primary measurement of radionuclides using the Triple-To-Double Coincidence Ratio method
Abstract
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.
Keywords
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
Origin : Files produced by the author(s)