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.

Standardization of 67Cu and calibration of the ionization chamber. Impurities and decay scheme problems.

This paper describes the standardization of 67Cu by the 4πß(PC)-γ coincidence method, and the calibration of ionization chamber. The difficulties were. (i) One of the excited levels of 67Zn has a half life of 9.10µs. (ii) A recent publication reconsiders the decay scheme parameters. (iii) The solution had a significant content of impurities. The conclusions were that the result of absolute standardization is less influenced by the decay scheme parameters and impurities than the measurements by ionization chamber.

Measurement of liquid scintillation sources of (210)Pb obtained from (222)Rn decay.

Liquid scintillation samples were filled with (222)Rn and the activity was measured with good precision after reaching the secular equilibrium with the progeny (218)Po, (214)Pb, (214)Bi and (214)Po. After decay of most of (222)Rn activity, the samples contain (210)Pb and progeny. The activities of (210)Pb and progeny can be calculated as a function of time using the initial (222)Rn activity. The samples were measured in a TDCR counter and the experimentally determined counting efficiencies are in accordance with previously published results.

Measurement of (124)I.

The paper describes the measurements performed at IFIN-HH regarding the creation of a Romanian (124)I standard, consisting of: absolute standardization of the solution by the application of the 4πß(PC)-γ coincidence method; Calibration of the CENTRONIC IG12/20A ionization chamber with a standardised solution and comparison with a calculated efficiency; γ-ray spectrometry activity measurement and determination of the impurity levels; Comparison of the results of the three methods.

Assessment of derived emission limits for radioactive effluents resulted from the decommissioning activities of the VVR-S nuclear research reactor.

This paper presents complex studies on establishment of derived emission limits for potential radionuclides emitted as gaseous and liquid effluents, during the decommissioning activities (2nd and 3rd phases) of a nuclear research reactor, cooled and moderated with distilled water, type VVR-S, owned by the IFIN-HH. In the present paper there are described: the analysis methods and equipment used, the methodologies for calculating doses and the Derived Emission Limits (DEL), the experimentally measured activities of the representative radionuclides found in gaseous and liquid effluents resulted from decommissioning activities, as well as the effective derived limits of liquid and gaseous effluents, applying the calculation methodologies, specific to critical categories of exposed subjects. A constraint effective dose limit for a person from the critical group of 50 µSv/year was considered in calculations. From the comparison of the two series of values, measured released activities and DELs, there has been concluded that for the gaseous effluents they comply with the DELs, while in the case of liquid effluents they are higher and consequently they must be treated as liquid radioactive wastes.

Standardization of Tc-99 by two methods and participation at the CCRI(II)-K2. Tc-99 comparison.

The work accomplished within the participation at the 2012 key comparison of Tc-99 is presented. The solution was standardized for the first time in IFIN-HH by two methods: LSC-TDCR and 4π(PC)ß-γ efficiency tracer. The methods are described and the results are compared. For the LSC-TDCR method, the program TDCR07c, written and provided by P. Cassette, was used for processing the measurement data. The results are 2.1% higher than when applying the TDCR06b program; the higher value, calculated with the software TDCR07c, was used for reporting the final result in the comparison. The tracer used for the 4π(PC)ß-γ efficiency tracer method was a standard (60)Co solution. The sources were prepared from the mixture (60)Co+(99)Tc solution and a general extrapolation curve, type: N(ßTc-99)/(M)(Tc-99)=f [1-ε(Co-60)], was drawn. This value was not used for the final result of the comparison. The difference between the values of activity concentration obtained by the two methods was within the limit of the combined standard uncertainty of the difference of these two results.

Standardization of ¹8F and its use for the Romanian PET metrological traceability chain assurance.

This paper presents the work performed at IFIN-HH and at the users' sites, aimed to establish the (18)FDG Romanian PET traceability chain. It summarizes the operations: (i) Absolute standardization of a (18)F solution, by the 4πß(PC)-γ coincidence method; (ii) Control of gamma-ray impurity content and measurement of the activity by gamma ray spectrometry; (iii) Measurement of the half life, for detection of some short/long life positron emitter impurities; (iv) Calibration of the CENTRONIC IG12/20A ionization chamber; (v) Calibration of commercial radionuclide calibrators.

Results of an international comparison for the activity measurement of 177Lu.

An international Key Comparison of (177)Lu has recently been carried out. Twelve laboratories performed assays for radioactivity content on aliquots of a common master solution of (177)Lu, leading to eleven results submitted for entry into the Key Comparison Database of the Mutual Recognition Arrangement. A proposed Comparison Reference Value (CRV) was calculated to be 3.288(4)MBq/g using all eleven results. Degrees of equivalence and their uncertainties were calculated for each laboratory based on the CRV. Most of the values reported by the participating laboratories were within 0.6% of the CRV.

Standardization of 64Cu and 68Ga by the 4π(PC)ß-γ coincidence method and calibration of the ionization chamber.

The paper treats the application of the 4π(PC)ß-γ coincidence method for the standardization of the radionuclides (64)Cu and (68)Ga. The general coincidence equations are written. Two types of extrapolation were described and used in measurement: the positron-annihilation coincidence, and the counting of all emitted radiations; both methods are compared with respect to results, advantages and drawbacks. The impurities' content correction was applied. The standardized solutions were used to calibrate the ionization chamber CENTRONIC IG12/20A and to determine the gamma-rays emission intensities.

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.

International exercise on 124Sb activity measurements.

An international exercise, registered as EUROMET project no. 907, was launched to measure both the activity of a solution of (124)Sb 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 4pibeta-gamma coincidence/anti-coincidence counting, CIEMAT/NIST liquid-scintillation counting, 4pigamma 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.

International exercise on 124Sb photon emission intensities determination.

An international exercise, registered as EUROMET project no. 907, was launched to measure both the activity of a solution of (124)Sb 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.

The 222Rn standard system established at IFIN-HH, Romania.

The paper presents the (222)Rn Standard System realized at the Radionuclide Metrology Laboratory from IFIN-HH, Romania. It contains a Pylon solid (226)Ra source, and a glass circuit for circulation and recovery of (222)Rn in glass ampoules, at the 77K temperature. The radon can be recovered both in ampoules with liquid scintillator (LS), for absolute standardization of (222)Rn by liquid scintillation counting (LSC) (Cassette et al., 2006), and in evacuated ampoules as gas, simultaneously or by the transfer of radon from gas into LS ampoules, in order to establish the traceability chain. The absolute standardization consists in the registration of the double coincidence counting rate in LS, due to the whole sequence of short life components of the (222)Rn chain, in equilibrium conditions. The main correction applied to the measurement results is due to the decay of (214)Po during the extendable dead time of the system. The following procedure was applied to take it into account. The value of the base duration of the dead time was precisely measured and used for the data corrections. The measurements of each source were repeated during a period of several days, and the decay curve parameters were calculated. If the dead time value and the correction formulae, presented throughout the paper, were adequate, then the re-determination of the (222)Rn half life, T(1/2)=(3.8232+/-0.0008) d, using the decay curve of the corrected counting rates should be correct. On the other hand, the effective dead time values obtained by parallel calculations were compared. The paper presents the results obtained in the standardization of several sources, by LSC, and the evaluation of the uncertainties associated to the method.

IFIN-HH ionization chamber calibration and its validation; electrometric system improvement.

The paper presents the results obtained in the calibration of the CENTRONIC IG12/20A ionization chamber for 18 gamma ray emitters, and its improvement with a Keithley 6517A electrometer. The calibration figures were determined either directly in pA MBq(-1) units, or calculated from old units, by using the system capacity value. The calibration figures, determined with RML's standards, are compared with those deduced from the KCRV or the mean of the comparisons, and the values determined at PTB-Germany.

Activity measurements of technically enhanced naturally occurring radionuclides (TENORM) in phosphogypsum.

Phosphogypsum is a by-product of the phosphoric acid based fertilizer industry; it can be used in agriculture and to make building materials. Phosphogypsum is radioactive due to the presence of technically enhanced naturally occurring radionuclides (TENORM) and its environmental impact is a major concern of the public authorities. The Radionuclide Metrology Laboratory from IFIN-HH participated at the IAEA-CU-2007-06-CCRI(II)-S5 Supplementary Comparison for the Determination of TENORM in phosphogypsum. The measurement procedures and the discussion of results and problems encountered are presented.

Measurement of (55)Fe solution activity by LSC-TDCR method.

A solution of (55)Fe was measured by using liquid scintillation counting (LSC)-TDCR method. The measurement was performed within the frame of the CIPM CCRI(II)-K2.Fe-55 comparison during the year 2006. Two computation codes were used for the calculation of detection efficiency, the difference between the results being analyzed. The photomultipliers asymmetry and its influence on the results, as well as the long-term stability are also analyzed. The influence of the variation of kB value over the activity value is compared with the case of (3)H standardization.

Standardization of 222Rn by LSC and comparison with alpha- and gamma-spectrometry.

Liquid scintillation counting (LSC) was used for the measurement of 222Rn in equilibrium with its daughters, with detection efficiency close to 5. The appropriate corrections were considered, including one related to the probability that the 165-micros half-life 214Po decays during the dead time of the counter initiated by the disintegration of his parent nuclide, 214Bi. The dead-time determination of a commercial LS counter is also presented using a 222Rn standard source. The LSC 222Rn sources were prepared by transfer of 222Rn produced by a solid 226Ra source into LSC cocktail frozen at 77K, flame-sealed afterwards. They were measured using the LNHB triple coincidence counter with adjustable extending-type dead-time unit, between 8 and 100 micros; two different procedures were used to calculate an effective dead time and then to deduce the counting rate extrapolated to zero dead-time value. The LSC results were compared with those obtained by cryogenic alpha-particle spectrometry (LNHB system) and by gamma-ray spectrometry for the same radon source in the LSC vial; the geometry transfer coefficient was calculated using the ETNA software. Measurement results and uncertainties are discussed.

Results obtained in the metrological certification of a commercially available radionuclide calibrator.

The paper presents the results obtained at IFIN-HH during a metrological certification of the commercially available radionuclide calibrator, the CURIEMENTOR2. Its performance was tested for the radionuclides: 57Co, 99mTc, 131I and 137Cs. The calibration factors determined by the manufacturer and those obtained at IFIN-HH differed by less than 3.5%. New calibration factors were determined for 60Co and 188Re, which have, until now, not been distributed by the manufacturer to the users. Furthermore, the linearity of instrument response and the dependence of measuring geometry were checked and found in accordance with the international accepted standards and legal requirements.

The standardization of a 204Tl solution

Two methods were used for the standardization of the 204Tl solution received in the framework of the 1997 BIPM comparison. The first method, 4pi liquid scintillation (LS), consisted of the extrapolation of the 4pi counting rate to the zero discrimination level. A home-made, single channel instrument and a commercial Packard INSTA-GEL scintillator were used. The radioactivity concentration on the reference date 1 April 1997 was 63.1+/-1.3 kBq g(-1). The second method was the efficiency tracer technique, using a 60Co standard solution; the radioactivity concentration was calculated as the mean of several extrapolated values of the curve NbetaTl-204 = N0Tl-204f(1 - epsilon(betaCo-60)). The preliminary reported value was 62.8+/-0.8 kBq g(-1); the revised value is 61.8+/-1.2 kBq g(-1), in good agreement with other 4pi (p.c.) tracer results in the comparison. Some remarks are made regarding our measurements and the comparison results.

Standardization of 169Yb by the 4pibeta-gamma method

169Yb was standardized in the framework of an EUROMET international comparison. Two solutions, with approximately activity concentrations of 16 MBq g(-1) and 1.6 MBq g(-1) were distributed to the participants by BNM-LPRI-(France). In the Radionuclide Metrology Laboratory of INFIN-HH, the weak solution was standardized using a coincidence method, applying the 'beta-efficiency extrapolation' variant. A simple 4pi beta-gamma coincidence equipment was used. Due to the presence of a metastable state with a half-life of 0.66 micros in the decay scheme of 169Tm, a resolution time of 5.1 micros was chosen for the coincidence module. A gamma threshold of 150 keV was used. A second degree extrapolation graph was used, providing an activity concentration value of 1.18 MBq g(-1) at 15 November 1997, 12 h UT. The combined uncertainty was 0.9%. Using the dilution factor provided by BNM-LPRI, the corresponding activity concentration for the strong solution is 11.989 MBq g(-1) (uA = 0.110MBq g(-1); 0.92%).