J. Bouchard

First results in the development of an on-line digital counting platform dedicated to primary measurements.

This paper describes the first step in the development of a digital platform dedicated to primary radionuclide measurements. In order to validate the implementation of an on-line processing based on extendable dead-times, a FPGA-based digital system has been programmed for liquid scintillation counting. After a description of the hardware, TDCR (Triple to Double Coincidence Ratio) measurements are presented. Comparisons of activity measurements with the classical system operating at LNHB are used to validate the new system; coincidence counting differences observed when increasing the resolving time in the digital platform are discussed.

Performance and applications of cooled composite bolometers in the field of ionizing radiation metrology

Two major limitations met in the field of ionizing radiation metrology, i.e. energy resolution and detection energy threshold, may be improved by one or two orders of magnitude by using composite bolometers cooled below 300 mK and operating in the pulse mode. The major advantages are: possibility of choosing the absorber (from diamond to BGO: Al2O3, Ge, Si, BaF2, LiF, etc), the absence of statistical noise (phonon quanta are in the 10−4 eV range) and ultimate resolution in the 10−1 eV range for small bolometers. The theoretical and experimental limits are analyzed and solutions for extraneous noise limitations in a complete system are described. The most recent results in alpha-particle and gamma-ray spectrometry using a new design, the composite-composite bolometer, are given. In these, a resolution of 10.5 keV was obtained for 6 MeV alpha particles and < 2.5 keV for241Am 18 keV X rays using a 24 sapphire bolometer. The ideal bolometer concept is also discussed. In this, the simultaneous detection of quanta (due to ionization, fluorescence, ballistic phonons) and thermal energies will make it possible to have lower thresholds by amplification in the target. It should thus be possible to determine the characteristics of the particles (their precise arrival time and the positions of the impacts) and provide improvements in the field of integral counting for the absolute measurement of radioactivity.

Validation study of a new technique for absolute activity measurement with 4π solid angle metallic magnetic calorimeters

In this paper we present a prototype of a new class of detectors, metallic magnetic calorimeters operating at cryogenic temperatures, which we are developing for absolute activity measurement of low-energy-emitting radionuclides. We explain the detection principle and give a detailed description of the realisation of the prototype, containing an (55)Fe source inside the detector absorber. The analysis of first data taken with this detector is presented and the result of activity measurement compared with liquid scintillation counting. Some ways for reducing the uncertainty that can be achieved with this new technique are proposed.

Further investigations of thermal cryogenic detectors in the field of ionizing radiation metrology

Abstract Thermal cryogenic detectors (bolometers, microcalorimeters) have been operated in the pulse mode to quantify ionizing radiation. These detectors exhibit considerable promise for applications in high resolution spectrometry and integral counting. A compact cryogenic system has been developed that can easily be operated for 15 h at 300 mK. This temperature is probably low enough for α-particle spectrometry. We have recently installed a composite-composite bolometer into this cryostat. The detector consists of two cubic crystals (a sapphire target and a diamond scatterer) coupled to a chemically doped Ge temperature sensor. The time constants of the bolometric signal are such that processing and digital filtering of the pulses is required. Careful examination and processing of the recorded pulses permits the elimination of some causes of the loss in energy resolution (pile-up, microphonics, collection defect). Moreover, the very strong dependence of the gain on the temperature has led us to define stability criteria and to select, a posteriori, measurement periods showing sufficient stability.

A new absolute method for the standardization of radionuclides emitting low-energy radiation.

Microcalorimeters (or bolometers) operated at temperatures below 100 mK allow individual counting of photons and electrons with a very low energy detection threshold. The physics is based on the pulse temperature increase of the target (or absorber) of the detector due to the complete absorption of both electrons and photons. Since this target can be constructed with a perfect 4-pi geometry, a bolometer offers potentially a new method for absolute activity measurements of radionuclides emitting low-energy radiation. In this paper we present our first results of a feasibility study of activity standardization of a 55Fe solution with a prototype 4-pi bolometer.

DUPLICATE: Digital instrumentation and management of dead time: First results on a NaI well-type detector setup

The Publisher regrets that this article is an accidental duplication of an article that has already been published, doi:10.1016/j.apradiso.2010.01.040. The duplicate article has therefore been withdrawn.

Bolometer characterisation with a specially developed cryogenic source having more than five peaks in the 1–6 keV range

At very low temperature (10–50 mK), and at relatively low energy (typically 100 eV–10 keV), the linearity and resolution of bolometers need to be carefully tested. Commercially available sources below 6 keV are rare and difficult to cool down. We have developed a specially designed compact X-ray source where 55Fe is combined with an ion-exchanged membrane containing more than three fluorescent elements. More than five peaks can be identified form 1 keV to 6.5 keV. A spectrum obtained with a 0.5 mg composite diamond bolometer, allowing a good measurement of linearity and resolution as a function of energy is presented. It is compared with a spectrum of the same source measured with a classical germanium detector. Since bolometer detectors have neither window, nor dead layer effects, bolometer spectra obtained with these sources could be used to directly calibrate the efficiency response of classical detectors at very low energy.