The Mobile Analyzer of Radioactive Gases OuTflows (MARGOT): A promising environmental xenon radionuclides detection system

An ultra-compact and unshielded spectrometer for analysis of atmospheric xenon radionuclides has been developed: the MARGOT system. This system works at ambient temperature and high pressure, and has a 54.3 cm³ inner active volume. Atmospheric xenon radionuclide activities are determined with the electron-photon coincidence technique using both NaI(Tl) detectors and large pixellized Si-PIN detectors. The MARGOT system integrates an enhanced version of the PIPSBox™, Geant4 simulation and first calibration results are discussed.

Low-level laboratory measurement of xenon radionuclides: Electron-photon versus photon measurements

Radioactive xenon (mainly ^131mXe, ¹³³Xe, ^133mXe and ¹³⁵Xe) are tracked as markers of nuclear weapons testing. The CEA has developed the PIPSBox, a measurement cell able to detect electrons emitted by xenon nuclides. Combined with an ultra-low background γ spectrometer, electron detection capacities allow reaching minimum detectable activities (MDA) for a 3-day long measurement of about 0.5mBq for the four xenon radionuclides. Compared to a classical measurement cell, MDAs are improved by a factor of 2-4.

Ground surface ultralow background spectrometer: Active shielding improvements and coincidence measurements for the Gamma3 spectrometer

The ultralow background versatile spectrometer GAMMA³ has been optimized with the following shielding improvements: (i) optimized nitrogen injection flux of 300Lh^-1, and (ii) cosmic veto configuration with 9 scintillating plates. These improvements allow a reduction of 39% of the normalized integral background count rate down to 2.7±0.2min^-1kg_Ge^-1 (40-2500keV energy range). Minimum Detectable Activities when performing direct γ-ray spectrometry or γ-γ coincidence spectrometry are compared.

On the use of (127)Xe standards for the quality control of CTBTO noble gas stations and support laboratories

(127)Xe has a longer half-life than (131m)Xe, it can be easily purely produced and it is present in the environment at very low level. For these reasons, (127)Xe is supposed to be a convenient quality control radionuclide for remote noble gas stations of the International Monitoring System (IMS) network. As CEA/DAM has recently developed two new photon/electron setups for low-level detection of (131m)Xe, (133m)Xe, (133)Xe and (135)Xe, we took the opportunity to test these setups for the measurement of a (127)Xe standard. The results and a detailed description of these measurements are presented in this paper. They illustrate the complexity of (127)Xe decay, emitting simultaneously several γ, X-rays, conversion electrons and Auger electrons; this results in highly summated coincidence spectra. The measurements performed provide precise electron energy calibration of the setups. The count rate of electrons in coincidence with iodine Kα X-rays was found to be surprisingly low, leading to the study of electron-gated photon spectrum. Finally, a comparison of three photon/electron coincidence spectra obtained with three different setups is given. The use of (127)Xe as a standard for energy calibration of IMS noble gas station is possible, but it appears to be quite complicated for efficiency check of noble gas station equipped with β/γ detectors.

Improvements of low-level radioxenon detection sensitivity by a state-of-the art coincidence setup

The ability to quantify isotopic ratios of 135, 133 m, 133 and 131 m radioxenon is essential for the verification of the Comprehensive Nuclear-Test Ban Treaty (CTBT). In order to improve detection limits, CEA has developed a new on-site setup using photon/electron coincidence (Le Petit et al., 2013. J. Radioanal. Nucl. Chem., DOI : 10.1007/s 10697-013-2525-8.). Alternatively, the electron detection cell equipped with large silicon chips (PIPS) can be used with HPGe detector for laboratory analysis purpose. This setup allows the measurement of β/γ coincidences for the detection of (133)Xe and (135)Xe; and K-shell Conversion Electrons (K-CE)/X-ray coincidences for the detection of (131m)Xe, (133m)Xe and (133)Xe as well. Good energy resolution of 11 keV at 130 keV and low energy threshold of 29 keV for the electron detection were obtained. This provides direct discrimination between K-CE from (133)Xe, (133m)Xe and (131m)Xe. Estimation of Minimum Detectable Activity (MDA) for (131m)Xe is in the order of 1mBq over a 4 day measurement. An analysis of an environmental radioxenon sample using this method is shown.

Long-term performances of the ⁹⁵ZR/⁹⁵Nb chronometer for nuclear events dating

The present work reports on a long-term analysis of the performances of the (95)Zr/(95)Nb chronometer for dating a nuclear event. Taking benefit of a recent Profiency Test Exercise, a sample containing a standardized mixture of fission products has been measured repeatedly with a low background HPGe spectrometer during a period extending up to one year with the aim of assessing the accuracy of the various zero-time determinations. Evaluation of the uncertainties associated to these evaluations was performed using a Monte Carlo approach. Input parameters sensitivity has been investigated, especially the influence of the (95m)Nb decay branch. The (95)Zr/(95)Nb chronometer was found to be accurate for zero-time determination within one day and one week for a decay of 3 months and 10 months respectively. Sub-day uncertainties are achievable for a two months old sample whereas sub-week uncertainties are reached after a decay of six months. Limitations of the technique for dating a real event are investigated.

Innovative concept for a major breakthrough in atmospheric radioactive xenon detection for nuclear explosion monitoring

The verification regime of the comprehensive test ban treaty (CTBT) is based on a network of three different waveform technologies together with global monitoring of aerosols and noble gas in order to detect, locate and identify a nuclear weapon explosion down to 1 kt TNT equivalent. In case of a low intensity underground or underwater nuclear explosion, it appears that only radioactive gases, especially the noble gas which are difficult to contain, will allow identification of weak yield nuclear tests. Four radioactive xenon isotopes, ^131mXe, ^133mXe, ¹³³Xe and ¹³⁵Xe, are sufficiently produced in fission reactions and exhibit suitable half-lives and radiation emissions to be detected in atmosphere at low level far away from the release site. Four different monitoring CTBT systems, ARIX, ARSA, SAUNA, and SPALAX™ have been developed in order to sample and to measure them with high sensitivity. The latest developed by the French Atomic Energy Commission (CEA) is likely to be drastically improved in detection sensitivity (especially for the metastable isotopes) through a higher sampling rate, when equipped with a new conversion electron (CE)/X-ray coincidence spectrometer. This new spectrometer is based on two combined detectors, both exhibiting very low radioactive background: a well-type NaI(Tl) detector for photon detection surrounding a gas cell equipped with two large passivated implanted planar silicon chips for electron detection. It is characterized by a low electron energy threshold and a much better energy resolution for the CE than those usually measured with the existing CTBT equipments. Furthermore, the compact geometry of the spectrometer provides high efficiency for X-ray and for CE associated to the decay modes of the four relevant radioxenons. The paper focus on the design of this new spectrometer and presents spectroscopic performances of a prototype based on recent results achieved from both radioactive xenon standards and air sample measurements. Major improvements in detection sensitivity have been reached and quantified, especially for metastable radioactive isotopes ^131mXe and ^133mXe with a gain in minimum detectable activity (about 2 × 10⁻³ Bq) relative to current CTBT SPALAX™ system (air sampling frequency normalized to 8 h) of about 70 and 30 respectively.

Certified reference material for radionuclides in fish flesh sample IAEA-414 (mixed fish from the Irish Sea and North Sea)

A certified reference material (CRM) for radionuclides in fish sample IAEA-414 (mixed fish from the Irish Sea and North Seas) is described and the results of the certification process are presented. Nine radionuclides (40K, 137Cs, 232Th, 234U, 235U, 238U, 238Pu, 239+240Pu and 241Am) were certified for this material. Information on massic activities with 95% confidence intervals is given for six other radionuclides (90Sr, 210Pb(210Po), 226Ra, 239Pu, 240Pu 241Pu). Less frequently reported radionuclides (99Tc, 129I, 228Th, 230Th and 237Np) and information on some activity and mass ratios are also included. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in fish sample, for the development and validation of analytical methods and for training purposes. The material is available from IAEA, Vienna, in 100 g units.

Low-level activity measurement of 131Xem, 133Xem, 135Xe and 133Xe in atmospheric air samples using high-resolution dual X–γ spectrometry

High-resolution dual X and gamma spectrometry has been optimized to improve the sensitivity in analyzing radioxenon from environmental samples, especially for the metastable isotopes (131Xem and 133Xem). The full-energy peak (FEP) efficiency curve in the 20-700 keV range has been established with a global uncertainty better than +/-3% using a Monte Carlo simulation. The minimum detectable activity concentrations (MDC) achievable at the laboratory for 131Xem, 133Xem, 133Xe and 135Xe are presented and the influence of 133Xe activity on the metastable radioxenon MDCs is evaluated.

Activity measurement of a 176Lu sample using coincidence peaks and Monte Carlo simulations

We present the results of the activity measurement of a sample of the rare isotope 176Lu, obtained by gamma-ray spectrometry through the use of 22 peaks in an energy spectrum acquired with a 300 cc well-type HPGe detector located in the Modane underground facility below the French Alps. Of the above peaks, 17 are coincidence peaks between two or three gamma-rays or X-rays. True coincidence summing corrections were made using our Coincal code. Monte Carlo simulations were carried out for calibration purposes.

The absolute and relative bioavailability of dipyridamole from different preparations and the in vitro-in vivo comparison

The in vitro liberation and the bioavailability (BV) of dipyridamole (D) in three different brands (A, B, C) were determined in a three way cross-over study on 12 healthy subjects. Also, the pharmacokinetics of D given intravenously was investigated. The in vitro liberation of B is only to be achieved by repeated touching. The tmax for the preparations, expressed as mean +/- s mean amounts as follows: A: 0.8 +/- 0.06; B: 1.1 +/- 0.1; C: 0.8 +/- 0.09 hours and is in the case of B significantly different (p less than 0.05) from the others. The cmax values (A: 1.01 +/- 0.25; B: 1.16 +/- 0.15; C: 1.51 +/- 0.3 mumol X l-1) and the AUC values (A: 3.8 +/- 0.9; B: 3.1 +/- 0.5; C: 3.8 +/- 0.7 mumol X h X l-1) are not different. The absolute BV of D is 27 +/- 5.5% (range: 11-44%) independent of the used brand. In 4 subjects a second tmax at the 4th-6th hour is to be observed irrespective of the way of dosing. An enterohepatic circulation is assumed. It is concluded that the determination of the in vitro liberation is a necessary and useful parameter, but cannot be used alone for characterization of the BV in every case, as e.g., for problem drugs.

The in vitro liberation and the bioavailability of different brands of griseofulvin in plasma and urine in man

The bioavailability of griseofulvin in three different brands, two microfine forms (Gricin = G, Likuden = L), and one ultramicrofine form (Gris-PEG = GP), was determined in plasma and urine in six healthy volunteers in a crossover study and compared with in vitro liberation data. GP shows a higher AUCo infinity (140 +/- 24 mumol . h . l-1) and Cmax (4.5 +/- 0.1 mumol . h-1) than the microsize brands of griseofulvin (AUCo infinity:58 +/- 7, and 45 +/- 6 mumol . h . l-1; Cmax:1.7 +/- 0.2, and 1.5 +/- 0.2 mumol . l-1; G and L, resp.), but the same tmax at the third hour. There results correspond with the in vitro liberation data. Contradictory results of the bioavailability are found by determining the amount of 6-Demethylgriseofulvin eliminated in urine. The elimination of this main metabolite after dosing with L is lower (0.18 +/- 0.02 mmol) than those of the other two brands, which do not differ (0.31 +/- 0.04; 0.32 +/- 0.02 mmol, G and GP, resp.). It is concluded that the determination of bioavailability only by means of the eliminated amount of a metabolite in urine may produce false results.