Jacques Bouchard

The design of a liquid scintillation counter based on the triple to double coincidence ratio method

In Liquid Scintillation Counting (LSC), the Triple to Double Coincidence Ratio method (TDCR) is an absolute activity measurement method, especially developed for pure β- and pure EC-emitters activity standardisation. In this method, the detection efficiency is calculated using a physical and statistical model of the photon distribution emitted by the source. The application of this method requires the use of a specific three-photodetector Liquid Scintillation (LS) counter, which is not commercially available. When designing such a counter, the fundamental basis of the LSC phenomena and TDCR method must be taken into account. The key points of this design are presented in this paper.

Measurements of high-activity sources with a 4πβ-γ coincidence system

Abstract A 4πβ-γ coincidence system (IMPECC) working with cumulative dead times is described. The main features of the electronics of that system are presented, and its capability of measuring accurately sources of very high activity is demonstrated experimentally with a set of 60Co sources. Results are coherent, and no bias is observed with increasing activities, even for the source of 1.3 MBq which was measured with a relative uncertainty that did not exceed 0.25%. A method derived from selective sampling was also tested successfully with the sources of highest activity.

A simple, powerful 4πβ/γ coincidence system based on the pulse-mixing method

An improved version of a simple and powerful 4πβ/γ coincidence system based on the pulse-mixing method is described. It is based on the use of extendable dead-times measured by the live-time technique. The coincidence channel is replaced by a “virtual” common channel where pulses coming from both beta and gamma detectors are mixed and counted together. The basic property of this common channel is to register no more than one pulse per coincident pair of pulses. A single channel-analyzer or an analog-to-digital converter (ADC) can be incorporated in the gamma channel. If an ADC is used, coincident and non-coincident spectra can be deduced from the recording. All the major problems (dead-time, accidental coincidences corrections) encountered in conventional systems are eliminated. An important feature of this system is its insensitivity to the delay between beta and gamma pulses. This coincidence method has been tested successfully for several radionuclides (60Co, 134Cs, 85Sr and 169Yb) presenting different measurement difficulties, including metastable states (85Sr and 169Yb). It is now used routinely for activity measurements.

Standardization of iodine-129 by the TDCR liquid scintillation method and 4π β-γ coincidence counting

Abstract Iodine-129 is a long-lived fission product, with physical and chemical properties that make it a good candidate for evaluating the environmental impact of the nuclear energy fuel cycle. To avoid solid source preparation problems, liquid scintillation has been used to standardize this nuclide for a EUROMET intercomparison. Two methods were used to measure the iodine-129 activity: triple-to-double-coincidence ratio liquid scintillation counting and 4π β-γ coincidence counting; the results are in good agreement.

Properties of a 4πβ-γ coincidence system with a cumulative dead-time circuit

Abstract A coincidence measuring system working with cumulative dead times is presented. The principles of counting for beta, gamma and coincident pulses are developed and the formulae to be applied are derived. A method inspired from selective sampling is also described. All the formulae have been checked with Monte Carlo simulations, showing the ability of accurate measurements even at high count rates.