A new set of electronic modules (NIM standard) for a coincidence system using the pulse mixing method

Activity standardization of 60Co and 106Ru/106Rh by means of the TDCR method and the importance of the beta spectrum

Atomic and nuclear data represent an important input for the accuracy of primary activity measurements based on liquid scintillation. In particular, the reliability of β-spectrum computation has been investigated for several years through experimental and theoretical studies providing solid evidence for the need to consider the atomic effects. In the present study, the activity standardization of two β-emitting radionuclides (60Co, 106Ru/106Rh) was carried out by means of the 4πβ-γ coincidence and Triple-to-Double Coincidence Ratio (TDCR) methods. The comparison between the activity concentrations given by both primary techniques presents new evidence that a better agreement is obtained when the exchange and screening effects are included in the β-spectra implemented in the model of light emission for TDCR measurements. A new development of a stochastic model based on Geant4 simulations for TDCR calculations is also presented.

Cross-validation of standardisation techniques at ANSTO using cobalt-60 and learnings from the presence and identification of non-gamma-ray emitting impurities

To fulfil the technical requirements for accreditation to ISO/IEC 17025, the end-to-end validation of all processes associated with standardising 60Co, including gravimetric source dispensing, primary standardisation by the 4π(LS)β-γ coincidence and live-timed anti-coincidence extrapolation techniques, and impurity determination were performed and documented. Pure-beta-emitting impurities in a 60Co stock solution were identified. The impact of such impurities on measurement by liquid scintillation counting and comparison in the ESIR are discussed. A fresh 60Co source was produced, standardised, and compared using the SIR.

Measurement of the absolute gamma-ray emission intensities from the decay of 147Nd

The 2011 Decay Data Evaluation Project (DDEP) evaluation for ¹⁴⁷Nd includes recommended absolute emission intensities for the two main gamma-rays at 91.105 (2) keV and 531.016 (22) keV of 0.284 (18) and 0.127 (9) respectively, i.e. with uncertainties of 6.3% and 7.1%. These large uncertainties stem from inconsistencies in the published data and are unfit for modern purposes, since the production of ¹⁴⁷Nd is used as an important neutron flux dosimeter. The LNE-LNHB has undertaken new absolute gamma-ray emission intensity measurements. The results of these measurements will be presented, along with a full uncertainty budget, and their effect on the recommended data uncertainties will be discussed.

Activity measurements and determination of nuclear decay data of 166Ho in the MRTDosimetry project

Holmium-166 is a high-energy β^--emitter radionuclide (~ 1.8 MeV) with a short half-life (~26.8h) that offers great potential as an alternative to ⁹⁰Y for the treatment of liver cancer based on radioembolization. The possibility of quantitative Single Photon Emission Computed Tomography (SPECT) imaging of the main γ-ray emission at 80.6 keV, in addition to strong paramagnetic properties suitable for Magnetic Resonance Imaging (MRI), complement this therapeutic potential. The present paper describes the measurements carried out in three European radionuclide metrology laboratories for primary standardization of ¹⁶⁶Ho and new determinations of X- and γ-ray photon-emission intensities in the framework of the European EMPIR project MRTDosimetry. New half-life measurements were also performed.

The half-life of 129I

The radionuclide ¹²⁹I is a long-lived fission product that decays to ¹²⁹Xe by beta-particle emission. It is an important tracer in geological and biological processes and is considered one of the most important radionuclides to be assessed in studies of global circulation. It is also one of the major contributors to radiation dose from nuclear waste in a deep geological repository. Its half-life has been obtained by a combination of activity and mass concentration measurements in the frame of a cooperation of 6 European metrology institutes. The value obtained for the half-life of ¹²⁹I is 16.14 (12) × 10⁶ a, in good agreement with recommended data but with a significant improvement in the uncertainty.

Standardization of 68Ge/68Ga using the 4πβ-γ coincidence method based on Cherenkov counting

In the framework of an international BIPM comparison (Bureau International des Poids et Mesures), the activity standardization of ⁶⁸Ge in a solution of ⁶⁸Ge/⁶⁸Ga in equilibrium provided by NIST was carried out at LNHB. This exercise was organized to meet the growing interest in ⁶⁸Ga as a radiopharmaceutical in nuclear medicine services (e.g. as a surrogate of ¹⁸F for PET imaging). Due to the volatility of germanium, the activity standardization of ⁶⁸Ge was investigated at LNHB by means of 4πβ-γ coincidence counting based on Cherenkov measurements. This technique was applied to take advantage of the Cherenkov threshold (~ 260keV in aqueous solutions) in order to prevent counting from electron-capture events associated with ⁶⁸Ge disintegrations. Cherenkov counting was performed using glass and polyethylene vials and the resulting activity concentrations were compared with 4πβ-γ coincidence measurements based on liquid scintillation. The efficiency-extrapolation curve obtained with Cherenkov measurements in glass vials was compared to Monte Carlo simulations based on the Geant4 code.

Determination of X- and gamma-ray emission intensities in the decay of (131)I

The activity per unit mass of an iodine-131 solution was absolutely standardized by both the 4πβ-γ coincidence method and the 4πγ counting technique. The calibrated solution was used to prepare point sources after a preliminary deposit of AgNO3 to prevent the loss of volatile iodine. Relative and absolute photon emission intensities of 15 sgamma-rays and those of the two K X-rays of xenon were determined by gamma-ray spectrometry, with relative uncertainties of 0.8% for the three main emissions.

Standardization of 67Ga, 51Cr and 55Fe by live-timed anti-coincidence counting with extending dead time

In this work, the activity standardization of 51Cr, 55Fe and 67Ga by live-timed anti-coincidence counting with extending dead time is described. The difficulties of the method, the uncertainties of the results of the measurements and the comparison of these results with others measurement methods are discussed.

Standardization of 67Ga using a 4π(LS)β–γ anti-coincidence system

(67)Ga is an interesting radionuclide as it is widely used in nuclear medicine. The meta-stable level related to the 93.3keV gamma-transition represents the main difficulty when using the coincidence method to standardize this radionuclide. The 4pi(LS)beta-gamma anti-coincidence system implemented at LNHB is based on the use of electronic modules specifically designed for radioactivity metrology. On the contrary to classical coincidence systems, activity measurements of (67)Ga are carried out as for prompt beta-gamma emitters; indeed, when using a live-timed anti-coincidence system with extendable dead times, the problem due to the excess of counting generated by the meta-stable level is avoided. Considering that the standardization of (67)Ga does not depend on the decay scheme parameters (except for the half-life), the measurement of the gamma-emission intensities has been performed. The standardization of this radionuclide was also a good opportunity for a new participation of our laboratory in the SIR of (67)Ga (International Reference System); the result obtained with the 4pi(LS)beta-gamma anti-coincidence system is compared with those submitted by other National Metrology Institutes (NMIs). The non-extendable dead times used in most of the participations could be one of the causes responsible for the abnormal dispersion of the results. The optimization of the standard solution of (67)Ga for the radioactive source preparation is also discussed.

A 4pi(LS)beta-gamma coincidence system using a TDCR apparatus in the beta-channel

This article is an overview of the capabilities of a 4 pi(LS)beta-gamma coincidence counting system based on a liquid scintillation detector in the beta-channel. Equipped with a three-photomultiplier apparatus designed for the triple to double coincidence ratio (TDCR) method, the 4 pi(LS)beta-gamma coincidence system developed at LNHB combines the two techniques. The 4 pi(LS)beta-gamma counting setup records the different types of scintillation events between photomultipliers (double and triple coincidences) and the associated gamma-spectra according to a bi-dimensional configuration. When measuring the activity of a (54)Mn solution, the extrapolation method is carried out by defocusing the photomultipliers; this procedure allows the measurement of gamma-ray sensitivity of the scintillation cocktail in the 835 keV energy region. In addition, in the framework of a (65)Zn standardization, 4 pi(LS)beta-gamma measurements are compared with standard 4 pi(PC)beta-gamma anticoincidence counting using a proportional counter in the beta-channel.

Freeze-drying applied to radioactive source preparation

In the framework of R&D studies for the improvement of radioactive source efficiencies prepared on thin films for 4pibeta-gamma coincidence counting, a comparative study on two drying methods has been undertaken in our laboratory (BNM-Laboratoire National Henri Becquerel, France). The standard method of evaporation at atmospheric pressure and a method based on freeze-drying using commercial equipment are compared. The preliminary results of this study obtained with 65Zn sources are presented and a significant improvement of the detection efficiencies to the electron emission for freeze-dried sources is shown. In the course of validation of this method, other radionuclides were studied and, up to now, the results confirm the better crystallization homogeneity achieved for freeze-dried sources.

Study of XK and gamma photon emission following decay of 154Eu

A joint project has been established between VNIIM (D.I. Mendeleyev Institute for Metrology) and LNHB (Laboratoire National Henri Becquerel) to determine as accurately as possible the X- and gamma-ray emission probabilities of 154Eu. Point sources were prepared by VNIIM, and absolute measurements of activity per unit mass were undertaken by both laboratories using coincidence, anti-coincidence and 4pi-gamma counting methods. Other point sources and one aliquot were also prepared for precise gamma-ray spectrometry measurements. Absolute photon emission probabilities were determined with a maximum uncertainty of 0.5% for the most intense lines, supporting the development of this nuclide as a multigamma standard.