Search

Abstract: A procedure has been developed to calibrate photon-emitting wide area reference sources in terms of activity, surface emission rate and uniformity considering the requirements introduced by the recent revision of ISO standard 8769. The method makes use of a large volume NaI detector with a cross table scanning system, a radiography system and it applies Monte Carlo techniques to assess the surface emission rate. The method was successfully applied to sources of 241Am, 57Co, 137Cs and 60Co. In addition, problems with definitions and the practical use of standard are highlighted. [Copyright &y& Elsevier]

Abstract: The radionuclide 113mCd was extracted from a Cd component, which has been irradiated in a research reactor during its routine operation. A validated separation procedure was then used to obtain a 113mCd solution of high radiochemical purity. The solution was measured by means of liquid scintillation counting for activity determination. To this end, the CIEMAT/NIST efficiency tracing method as well as the triple-to-double coincidence (TDCR) counting technique were used. Measurements in a low-background gamma-ray spectrometer were applied to identify any potential photon-emitting impurities and to measure the 263.7keV photons from the isomer transition. A gamma emission probability of 0.01839(29)% was determined for this line. The liquid scintillation measurements were also used to evaluate the half-life of 113mCd. The decay was followed for about 11 months and a half-life T 1/2=13.97(13) years was obtained. [ABSTRACT FROM AUTHOR]

Abstract: The activity of a 22Na solution was measured by means of two 4πβ−γ coincidence-counting techniques. The first method corresponds to the classical 4πβ−γ coincidence counting and requires the β+-branching ratio. The second procedure is based on a variation of the distance between source and gamma detector. The efficiency for detecting the sum peak is then extrapolated to zero, giving the total source activity. The combination of both methods yields the β+ branching ratio. In addition, liquid scintillation counting using the CIEMAT/NIST-method as well as a secondary standardization by means of calibrated ionization chambers were used for activity determination. The results were checked for consistency and an ampoule was submitted to the BIPM to have the activity result entered into the database of the International Reference System (SIR). [Copyright &y& Elsevier]

Abstract: A triple-to-double coincidence ratio (TDCR) liquid scintillation counting system (; ) was set up at the Physikalisch-Technische Bundesanstalt (PTB) to be used as an additional technique for primary activity standardization. The optical chamber of the system was designed in our laboratory, expending great effort to achieve maximum light transmission to the photomultiplier tubes (PMT) and, consequently, a maximum counting efficiency and low uncertainties. A programme to compute the counting efficiencies and to analyse the measurement data was developed and tested. The software can also be used to allow for PMT asymmetries. The system and recently developed analysis procedures were used for the activity standardization of a tritiated water solution within the scope of an international comparison under the auspices of the Bureau International des Poids et Mesures (BIPM). [Copyright &y& Elsevier]

Some authors have raised doubt about the invariability of decay constants, which would invalidate the exponential-decay law and the foundation on which the common measurement system for radioactivity is based. Claims were made about a new interaction – the fifth force – by which neutrinos could affect decay constants, thus predicting changes in decay rates in correlation with the variations of the solar neutrino flux. Their argument is based on the observation of permille-sized annual modulations in particular decay rate measurements, as well as transient oscillations at frequencies near 11 year −1 and 12.7 year −1 which they speculatively associate with dynamics of the solar interior. In this work, 12 data sets of precise long-term decay rate measurements have been investigated for the presence of systematic modulations at frequencies between 0.08 and 20 year −1 . Besides small annual effects, no common oscillations could be observed among α, β - , β + or EC decaying nuclides. The amplitudes of fitted oscillations to residuals from exponential decay do not exceed 3 times their standard uncertainty, which varies from 0.00023 % to 0.023 %. This contradicts the assertion that 'neutrino-induced' beta decay provides information about the deep solar interior. [ABSTRACT FROM AUTHOR]

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 68 Ge/ 68 Ga solution. Results for the activity concentration, C A , of 68 Ge 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)β-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) kBq g −1 , based on 14 results. The degrees of equivalence and their associated uncertainties are evaluated for each participant. Several participants submitted 3.6 mL 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. [ABSTRACT FROM AUTHOR]

Abstract: The triple-to-double coincidence ratio (TDCR) method is frequently used to measure the activity of radionuclides decaying by pure β emission or electron capture (EC). Some radionuclides with more complex decays have also been studied, but accurate calculations of decay branches which are accompanied by many coincident γ transitions have not yet been investigated. This paper describes recent extensions of the model to make efficiency computations for more complex decay schemes possible. In particular, the MICELLE2 program that applies a stochastic approach of the free parameter model was extended. With an improved code, efficiencies for β−, β+ and EC branches with up to seven coincident γ transitions can be calculated. Moreover, a new parametrization for the computation of electron stopping powers has been implemented to compute the ionization quenching function of 10 commercial scintillation cocktails. In order to demonstrate the capabilities of the TDCR method, the following radionuclides are discussed: 166mHo (complex β−/γ), 59Fe (complex β−/γ), 64Cu (β−, β+, EC and EC/γ) and 229Th in equilibrium with its progenies (decay chain with many α, β and complex β−/γ transitions). [Copyright &y& Elsevier]

Abstract: An international exercise, registered as EUROMET project no. 907, was launched to measure both the activity of a solution of 124Sb and the photon emission intensities of its decay. The same solution was sent by LNE-LNHB to eight participating laboratories, six of which sent results for photon emission intensities both in absolute and in relative terms. From these results and including previous published values, a consistent decay scheme was worked out, proving that problems in activity measurements have not been due to decay scheme data. [ABSTRACT FROM AUTHOR]

Abstract: An international exercise, registered as EUROMET project no. 907, was launched to measure both the activity of a solution of 124Sb and the photon emission intensities of its decay. The same solution was sent by LNE-LNHB to eight participating laboratories. In order to identify possible biases, the participants were asked to use all possible activity measurement methods available in their laboratory and then to determine their reference value for comparison. Thus, measurement results from 4πβ–γ coincidence/anti-coincidence counting, CIEMAT/NIST liquid-scintillation counting, 4πγ counting with well-type ionization chambers and well-type crystal detectors were given. The results are compared and show a maximum discrepancy of about 1.6%: possible explanations are proposed. [Copyright &y& Elsevier]

The aim of the European Metrology Research Project MetroBeta is to improve the knowledge of the shapes of beta spectra, both in terms of theoretical calculation and measurement. The precise knowledge of beta spectra is required for the activity standardisation of pure beta emitters. Metallic magnetic calorimeters (MMCs), a type of cryogenic detectors, with the beta emitter embedded in the absorber have proven to be among the best beta spectrometers, in particular for low-energy beta transitions. Within this project, new designs of MMCs optimized for five different beta energy ranges were developed and a new detector module was constructed. The beta spectra of 151Sm, 14C and 99Tc have been measured so far; additional measurements with 36Cl are under preparation. Improved theoretical calculation methods and complementary measurement techniques complete the project. • Beta spectrometry using metallic magnetic calorimeters was developed in the European Metrology Research Project MetroBeta. • New source/absorber preparation techniques and a new detector module have been developed. • High statistics measurements of the beta spectra of 151Sm, 14C and 99Tc were performed; measurements of 36Cl will follow. [ABSTRACT FROM AUTHOR]