Measurement of the absolute gamma-ray emission intensities from the decay of 103Pd.

Palladium-103 decays through electron capture to excited levels of 103Rh, and especially to the 39.748-keV metastable state. A high activity palladium chloride solution was standardized by liquid scintillation, using the Triple-to-Double Coincidence Ratio method. The absolute photon emission intensities were determined by gamma-ray spectrometry using point sources prepared with the standard solution. Different detectors and measuring conditions were used to cross-reference the results. The most intense photon emission intensities are derived with about 1% relative combined standard uncertainty.

Methods for the experimental study of 220Rn homogeneity in calibration chambers.

This work presents two experimental methods for the evaluation of 220Rn homogeneity in calibration chambers. The first method is based on LSC of the 220Rn decay products captured in silica aerogel. The second method is based on application of solid state nuclear track detectors facing the air of the calibration chambers. The performances of the two methods are evaluated by dedicated experiments. The repeatability of the LSC-based method, estimated as relative standard deviation of the LSC measurements of ten silica aerogel samplers exposed under the same conditions is found to be 1.6%. Both methods are applied to study thoron homogeneity in the commercially available 50 L AlphaGuard emanation and calibration container, which was empty and its fan was turned on. It was found that the 220Rn distribution in this case is homogeneous within 10%. Both methods are also applied to test the thoron homogeneity in the BACCARA chamber at IRSN during a thoron calibration exercise. The results show that, at the centre of the chamber where the inputs of the sampling systems of the radon/thoron detectors were put close to each other, the thoron inhomogeneity is less than 10%. However, regions of higher thoron concentrations are clearly identified near the walls and the upper part of the chamber, with 220Rn concentrations being up to 60% higher compared to the concentration at the reference point. These results highlight the importance of the control and assessment of thoron homogeneity in thoron calibrations and in the cases when radon monitors are checked for thoron influence.

Study of two different coincidence counting algorithms in TDCR measurements.

This work presents a comparison of two different logics for imposing extending-type dead-time in TDCR measurements: the common dead-time (CDT) and the individual dead-time (IDT) counting logics. The CDT is implemented in the widely used MAC3 TDCR counting module and the IDT was recently implemented in the nanoTDCR counting device. The performance of the two counting algorithms is evaluated by three experimental setups and a dedicated Monte Carlo (MC) code for the simulation of realistic TDCR events. An excellent agreement is observed between the two counting logics for measurements of the pure ß-emitting radionuclides 3H, 14C, 63Ni and 90Sr/90Y for which the relative deviations in measured activities are in all cases less than 0.27%. For the measured 222Rn sources, we observe relative deviations up to 0.25% between the logical sum of double coincidences counting rates obtained with the two counting logics. The differences are in the double coincidence counting rate estimates which propagate to the estimates of the activity. Excellent agreement was observed between the CDT and IDT in MC simulated measurements of 3H where relative deviations are less than 0.24% for activities up to 70 kBq. The IDT counting algorithm seems to have an advantage in this particular case as it results in the same counting rates and calculated activities but with a significant reduction in the double coincidences dead-time.

Diffusion lengths and partition coefficients of 131mXe and 85Kr in Makrofol N and Makrofol DE polycarbonates.

This work presents the results of an experimental study of the Makrofol® N and Makrofol® DE polycarbonate foils absorption properties of 85Kr and 131mXe. The diffusion lengths of 85Kr and 131mXe in both types of foils are determined. The partition coefficients of 85Kr from air and water and that of 131mXe from air in Makrofol® N are determined. The partition coefficients of 85Kr from water and 131mXe from air in Makrofol® DE are also determined. The parameters are determined for T = 22°C and allow for the full characterization of sorption and desorption of 85Kr and 131mXe in the foils at this temperature. The results from this study highlight the remarkable absorption ability of Makrofol® and especially of the Makrofol® N foil and show that it surpasses the Makrofol DE® foil not only as a Rn absorber, but also as Kr and Xe absorber.

68Ga activity calibrations for nuclear medicine applications in Cuba.

The realization and dissemination of the 68Ga activity measurement unit in Cuba is presented. Firstly, the implementation of the Triple to Double Coincidence Ratio (TDCR) method is described for the calibration of the activity concentration of a 68Ga solution using a Hidex™ commercial liquid scintillation counter and a FORTRAN code developed for the calculation of the 68Ga counting efficiencies in the given measurement system. The relative expanded uncertainty (k = 2) associated with the 68Ga activity concentration obtained with the TDCR method is equal to 2%. With the aim to validate this measurement uncertainty estimate, the method is also applied to an Amersham standard solution of 22Na - a positron emitter with a similar decay mode to the 68Ga disintegration scheme from the point of view of type of emitted particles detected in the measurement system. The observed difference between the measured 22Na activity concentration by the TDCR method and the corresponding reference value traceable to NIST is equal to 0.16%. Outcomes of transferring the 68Ga activity standard, realized with the TDCR method, to the secondary standard radionuclide calibrator Capintec CRC™ 15R and to three radionuclide calibrators used for 68Ga PET applications in a hospital are also shown.

Measurement of absolute K X-ray emission intensities in the decay of 103mRh.

A new experiment was designed to measure the photon emission intensities in the decay of 103mRh. The rhodium samples were activated in the ISIS experimental nuclear reactor at CEA Saclay. The procedure includes an absolute activity measurement by liquid scintillation counting using the Triple-to-Double Coincidence Ratio method, followed by X-ray spectrometry using a high-purity germanium detector to determine the photon emission intensities. The new result (IX = 0.0825 (17)) is derived with a significant reduction of the uncertainty.

Results of an international comparison of activity measurements of 68Ge.

An international key comparison, identifier CCRI(II)-K2.Ge-68, has been performed. The National Institute of Standards and Technology (NIST) served as the pilot laboratory, distributing aliquots of a 68Ge/68Ga solution. Results for the activity concentration, CA, of 68Ge at a reference date of 12h00 UTC 14 November 2014 were submitted by 17 laboratories, encompassing many variants of coincidence methods and liquid-scintillation counting methods. The first use of 4π(Cherenkov)ß-γ coincidence and anticoincidence methods in an international comparison is reported. One participant reported results by secondary methods only. Two results, both utilizing pure liquid-scintillation methods, were identified as outliers. Evaluation using the Power-Moderated Mean method results in a proposed Comparison Reference Value (CRV) of 621.7(11)kBqg-1, based on 14 results. The degrees of equivalence and their associated uncertainties are evaluated for each participant. Several participants submitted 3.6mL ampoules to the BIPM to link the comparison to the International Reference System (SIR) which may lead to the evaluation of a Key Comparison Reference Value and associated degrees of equivalence.

Bias in the measurement of radon gas using ionization chambers: Application to SIR.

Two main non-destructive techniques can be used to measure standard 222Rn gas ampoules: well-type ionization chambers and gamma-ray spectrometry, the former being used in the Système International de Référence (SIR) for international comparison purposes. The reliability of these techniques requires that the variability of the flame-sealed gas glass ampoules used have a negligible influence on the detector response. This variability is studied in this work by considering three parameters: the volume of the ampoule, the position of the sealing point and the thickness of the glass. Results showed that variability of the gas ampoules induced measurement bias larger than the uncertainty of the standard sources.

An absolute radon 222 activity measurement system at LNE-LNHB.

A good metrological traceability of radon and progenies is necessary to accurately measure the radon concentration. In 1995, at the LNE-LNHB, J.L. Picolo developed a reference method using a defined-solid-angle (DSA) alpha spectrometer to measure a frozen radon source. With this method it was possible to measure radon standards with a relative standard uncertainty of 0.5%. This paper presents the design and the characterization of a new upgraded measurement system; all parameters and their uncertainties are discussed. This new system allows the measurement of radon sources from 100Bq to 4MBq with a relative standard uncertainty of 0.3%.

Determination of (222)Rn absorption properties of polycarbonate foils by liquid scintillation counting. Application to (222)Rn measurements.

This work demonstrates that a Liquid Scintillation Counting (LSC) technique using a Triple to Double Coincidence Ratio counter with extending dead-time is very appropriate for the accurate measurement of (222)Rn activity absorbed in thin polycarbonate foils. It is demonstrated that using a toluene-based LS cocktail, which dissolves polycarbonates, the (222)Rn activity absorbed in thin Makrofol N foil can be determined with a relative standard uncertainty of about 0.7%. A LSC-based application of the methodology for determination of the diffusion length of (222)Rn in thin polycarbonate foils is proposed and the diffusion length of (222)Rn in Makrofol N (38.9±1.3µm) and the partition coefficient of (222)Rn in Makrofol N from air (112±12, at 20°C) and from water (272±17, at 21°C) are determined. Calibration of commercial LS spectrometers for (222)Rn measurements by LSC of thin polycarbonate foils is performed and the minimum detectable activities by this technique are estimated.

A new thoron atmosphere reference measurement system.

A new thoron reference ((220)Rn) in air measurement system is developed at the LNE-LNHB with the collaboration of the IRSN. This measurement system is based on a reference volume with an alpha detector which is able to directly measure thoron and its decay products at atmospheric pressure. In order to improve the spectrum quality of the thoron progenies, we have applied an electric field to catch the decay products on the detector surface. The developed system is a portative device which can be used to measure reference thoron atmosphere such as the BACCARA chamber at IRSN (Picolo et al., 1999). As this system also allows the measurement of radon ((222)Rn) in air, it was validated using the radon primary standards made at the LNE-LNHB. This thoron measurement system will be used, at IRSN, as a reference instrument in order to calibrate the thoron activity concentration in the BACCARA facility.

Development of a primary thoron activity standard for the calibration of thoron measurement instruments.

The LNHB and IRSN are working on a reference atmosphere for thoron ((220)Rn) instrument calibration. The LNHB, as the national metrology institute for activity measurement in France, has to create a new thoron reference standard in order to estimate with accuracy the thoron concentration of a reference atmosphere. The measurement system presented in this paper is based on a reference volume using an alpha detector, which is able to measure thoron and its decay products to define the thoron concentration of a thoron reference atmosphere. This paper presents the first results with this new system using a well-known radon ((222)Rn) atmosphere and a thoron ((220)Rn) atmosphere.

Experimental study of the influence of the counter and scintillator on the universal curves in the cross-efficiency method in LSC.

The cross-efficiency method in LSC is one of the approaches proposed for the extension of the Système International de Référence (SIR) to radionuclides emitting no gamma radiation. This method is based on a so-called "universal cross-efficiency curve", establishing a relationship between the detection efficiency of the radionuclide to be measured and the detection efficiency of a suitable tracer. This paper reports a study at LNHB on the influence of the scintillator and of the LS counter on the cross-efficiency curves. This was done by measuring the cross-efficiency curves obtained for (63)Ni and (55)Fe vs. (3)H, using three different commercial LS counters (Guardian 1414, Tricarb 3170 and Quantulus 1220), three different liquid scintillator cocktails (Ultima Gold, Hionic Fluor and PicoFluor 15 from Perkin Elmer(®)), and for chemical and colour-quenched sources. This study shows that these cross-efficiency curves are dependent on the scintillator, on the counter used and on the nature of the quenching phenomenon, and thus cannot definitively be considered as "universal".

Measurement of the French national tritiated-water standard by helium-3 mass spectrometry.

The (3)He ingrowth technique is based on the detection of the tritium radioactive daughter, (3)He, by mass spectrometry. Over the last three decades it has been used extensively in oceanography and groundwater studies for measurements of very low to ultra-low levels of tritium. To compare it with the best available methods of radioactive counting, we applied this method to measure the massic activity of a tritiated-water primary standard prepared by the French Laboratoire National Henri Becquerel (LNHB). One liter of a low-level tritium solution was prepared from a small aliquot of the LNHB standard by two-step gravimetric dilution with tritium-free groundwater. Sixteen samples of this solution were analyzed at the LSCE-Saclay noble gas facility, using the (3)He ingrowth method. The massic activity of the prepared solution was also measured by Liquid Scintillation Counting using the Quantulus LNHB counter and an internal calibration method with the LNHB tritiated water standard. All results agree within their standard uncertainty.

Standardization of xenon-127 and measurement of photon emission intensities.

Xenon-127 was standardized by internal gas counting using three proportional counters in a differential arrangement to eliminate edge effects. The detection efficiency of the proportional counters was calculated by considering the cascade of events following the electron capture and associated gamma transitions. Activity per unit volume was measured with 0.7% relative standard uncertainty. Gamma-ray spectrometry was performed and absolute photon emission intensities were derived. This study shows that (127)Xe could be a surrogate for (133)Xe for the calibration of remote radio-xenon monitoring stations.

Bk and Cf chromatographic separation and ²49Bk/²48Cm and ²49Cf/²48Cm elemental ratios determination by inductively coupled plasma quadrupole mass spectrometry.

The French Atomic Energy Commission has carried out several experiments for the study of minor-actinide transmutation processes in high intensity thermal neutron flux. In this context a Cm sample enriched in (248)Cm (∼97%) was irradiated in a thermal neutron flux at the High Flux Reactor (HFR) of the Laue-Langevin Institute (ILL). The precise and accurate determination of Cf isotope ratios and of (249)Bk/(248)Cm and (249)Cf/(248)Cm elemental ratios in the (248)Cm irradiated sample is crucial for the calculation of actinide neutron capture cross-sections. This work describes an analytical procedure for the separation and the isotope ratio measurement of Bk and Cf in the irradiated sample. The Bk and Cf separation is based on a lanthanides separation protocol previously developed by the laboratory. Well-defined retention times for Bk and Cf were obtained by coupling the Ionic Chromatography (IC) with an ICP-QMS. All conditions of element separation by IC and the different steps of the analytical protocol in order to obtain the isotopic and elemental ratios are presented. Relative uncertainties of Cf isotopic ratios range from 0.3% to 0.5% and the uncertainty of the (249)Bk/(248)Cm and (249)Cf/(248)Cm elemental ratios are respectively 6.1% and 3.2%. This level of uncertainty for both isotopic and elemental ratios is in perfect agreement with the requirement for transmutation studies.

Standardization, decay data measurements and evaluation of 64Cu.

The purposes of this study were to create national activity standards of (64)Cu, to make possible the definition of an international key comparison reference value and to determine the decay data in order to improve the decay scheme. Four laboratories measured the activity of a (64)Cu solution; these results were compared through the International Reference System. Moreover, the laboratories carried out new measurements of the photon emission intensities and of the half-life. A new decay scheme was derived from these new values and the previously published ones.

Monte-Carlo simulations of the new LNHB manganese bath facility.

The new manganese bath facility of the Laboratoire National Henri Becquerel has been modeled by using three Monte-Carlo codes: MCNPX, GEANT4, and FLUKA, in order to determine the correction factors needed in the neutron source calibration process. The most realistic source geometry has been determined, and the most reliable cross sections library has been chosen. The models were compared, and discrepancies between the codes have been pointed out. Potential causes of deviations between results were assessed and discussed using additional models. Finally, an experimental process is proposed to validate the accuracy of the different codes and their abilities in simulating the neutron capture by the manganese bath.

Decay scheme study of 126Sn and 126Sb.

To study the decay scheme of (126)Sn, two samples of a purified solution were measured by gamma-ray spectrometry and the relative photon emission intensities were determined. The (126)Sb(m) isomeric branching ratio was derived to be 18.6 (6) %. The maximum beta energy of the (126)Sn decay was checked by liquid scintillation. The Kbeta/Kalpha intensity ratio of Sb was determined being 0.226 (11). These new experimental results were used to re-examine the whole decay scheme of (126)Sn and its daughters.

Study of the influence of the liquid scintillator in the Compton efficiency tracing method.

The principle of the Compton source efficiency tracing method (CET) in liquid scintillation counting (LSC) is to use, as a tracer, a Compton electron source temporarily created inside the source being measured. The tracer source and the source to measure have thus exactly the same chemical composition. A main advantage anticipated for this measurement method is its low sensitivity to the kB factor and insensitivity to the chemical composition and quenching of the source, which would obviate the necessity to develop a reference liquid scintillator cocktail in the framework of an international reference system for the measurement of pure-beta emitters by LSC. We took the opportunity of a tritiated water international activity measurement in comparison to prepare LS sources using various commercial liquid scintillator cocktails. Tritium is assumed to be a good candidate for testing the LSC activity measurement method, as the detection efficiency is rather low and the effect of the ionization quenching parameter, kB, on the detection efficiency calculation by the TDCR method is known to be important. The sources were measured using a TDCR counter equipped with a Compton spectrometer in order to apply the CET method. The measurements are analyzed using both the TDCR method and CET method in order to deduce the optimal calculation parameters. The detection efficiency range covered by these experiments is from 0.4 to 0.6, allowing a good test of the validity of the physical assumptions included in the calculation model. The paper will conclude on the advantages and drawbacks of using this CET method in the framework of an international reference system for low-energy pure-beta radionuclides.