Herceg-Novi summer school, the starting point in the history of the International Committee for Radionuclide Metrology

This paper presents some of the most important points connected with the 1972 Herceg-Novi Radionuclide Metrology Summer School and its impact on the forthcoming evolution of the field. Topics of the conference, the state of the art at that time and recommendations for future developments as published in the journal Nuclear Instruments and Methods (Nim, 1973) are discussed. People and places, how a young participant perceived them then and remembers today, and the Romanian Laboratory of Radionuclide Metrology and its participation in ICRM activities are briefly presented.

60 years of absolute standardization of radionuclides by coincidence counting methods in the Romanian metrology laboratory

This review paper presents the contribution of the Radionuclide Metrology Laboratory (RML) to the development and practical application of the coincidence counting methods. It is also intended to pay tribute to Dr. Enric Leon Grigorescu, the founder of our school of radionuclide metrology. A synthetic treatment of the method, applied to some classes of radionuclides with their common and particular aspects in standardization, is presented: pioneering calculation of instrumental corrections, specific method corrections applied for various types of decay schemes in the variant of efficiency extrapolation, results obtained in international comparisons.

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)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)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.

Monte Carlo simulation of air sampling methods for the measurement of radon decay products

A stochastic model of the processes involved in the measurement of the activity of the ²²²Rn decay products was developed. The distributions of the relevant factors, including air sampling and radionuclide collection, are propagated using Monte Carlo simulation to the final distribution of the measurement results. The uncertainties of the ²²²Rn decay products concentrations in the air are realistically evaluated.

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.

Quality assurance for measurements of the radioactivity in the area of the"Horia Hulubei" National Institute for Physics and Nuclear Engineering, IFIN-HH

This paper presents one part of the activities deployed by the Laboratory for Environment and Personnel Dosimetry (LDPM) of IFIN-HH, namely the radiological monitoring of the environment within the Institute's area and its surrounding influence zone, according to the program approved by the National Regulatory Body for Nuclear Activities, CNCAN. The representative reports regard the radioactive content of soil, surface and underground water, cultivated and spontaneous vegetation, aerosols and atmospheric fallout, sediments. The common requirement is that the measured quantities be precise and the reported values be reliable and credible. This goal is achieved by maintaining a Quality System, verified within the obtaining and maintaining of the laboratory accreditation, according to the international standard ISO/IEC 17025:2005.The LDPM is accredited by the Romanian accreditation body, RENAR, member of the European Accreditation, EA and is designed by CNCAN as a notified testing laboratory. Many measurements were performed in collaboration with the Radionuclide Metrology Laboratory (RML) from IFIN-HH, RENAR accredited and CNCAN notified for calibration and for testing in the field of radioactivity measurement. This paper proposes a short presentation of the important aspects in our activity: i. description of equipment, samplingmethods, processing and measurement of environmental samples; ii. validation of equipment and methods by participation in international and national proficiency tests; iii. a five year follow chart, containing the results in measurement of samples; iv. a recent application, with a wide impact in Romanian mass media: the credible daily report on the possible influence of Fukushima accident over the Romanian environmental radioactivity.

Area dosimetry in the Praid-salt mine

The aim of the paper is to present a special application of the Romanian thermoluminescent dosemeters system, based on the use of the LiF:Mg,Cu,P, commercial GR-200A detectors, for the measurement of the ultra-low-level ambient dose equivalent rate values, situated within the interval of 1-100 nSv h(-1). The paper briefly describes the system and presents in detail the experimental procedure, including the corrections to be applied to the experimental values. The final characterisation of a Romanian salt mine, proposed to be used as an underground accelerator laboratory, is given. The comparison with the previous measurement results in the Slanic Prahova former salt mine and with the results obtained using the gamma-ray spectrometry method validates the results reported in this paper. The conclusion is that the system provides reliable results in the measurement of the ultra-low-level radiation background.

Standardization of 99mTc

The radioactivity of 99mTc was standardized by the 4piPC-gamma coincidence method with two different modes. One is using coincidences between (119.5-142.6)keV conversion electrons and K X-rays, and the other is coincidences between the 2.13 keV conversion electrons and 140.5 keVgamma-rays. The background of the K X-ray peak and the sensitivity of the proportional counter (PC) to 140 keV gamma-rays were the main sources of uncertainties in the first case and low detection efficiency for conversion electrons in the second case. General coincidence equations were written, with specific forms, for the three measurement variants, including literature variant. Comparison with the ionization chamber calibration is reported.

Standardization of 222Rn by LSC and comparison with - and -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.

Standardization of 65Zn by 4πPC-γ coincidence counting method with efficiency extrapolation

A 65Zn solution was standardized by the 4piPC-gamma efficiency-extrapolation coincidence counting method. Theoretical aspects of coincidence equations, efficiency equations and linearity conditions are reviewed. Experimental measurements were performed for two low level discrimination thresholds for the PC channel (counting K+L or K X-rays or Auger electrons from EC decay) and for three different settings of the gamma window. Requirements on gamma channel set-up for linear extrapolation were established by using a Pb absorber or by proper gamma window setting. The measured activity values were discussed and found in good agreement with those obtained with a calibrated ionization chamber.

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.

Precise measurement of the activity of 186Re, 188Re radiopharmaceuticals

The paper presents the results obtained in the assurance of traceability along the whole chain: production, distribution, use in hospitals, for the activity measurement of radiopharmaceuticals containing 186Re, 188Re and 186Re + 188Re mixtures. Standardization of the solutions, 4piPC-beta-efficiency relations and responses of a Centronic IG 12/20A ionization chamber and other radioisotope calibrators are presented. Gamma-ray and bremsstrahlung radiation contributions in the total response were evaluated. Some of the relevant results were compared with literature data.

Standardization of 152Eu

152Eu was standardized within the frame of a BIPM international comparison. The solution was prepared and bottled by PTB. The ampoules were measured at BIPM in the SIR ionization chambers and then dispatched to the participating laboratories. In the Radionuclide Metrology Laboratory of IFIN-HH, the solution was standardized using a coincidence method with "beta-efficiency extrapolation" by foil absorption. A simple 4pi beta-gamma-coincidence system was used, with NaI(Tl) and 4piPC detectors. No significant impurities were found apart for 0.5% 154Eu. To obtain linear extrapolation plots, a "gamma-window" of 180-1500 keV was chosen. Dead-times of 10 micros were used. A combined uncertainty of 0.24% was obtained, mainly from the extrapolation procedure component.

Standardization of 89Sr

Two methods were used for the standardization of the pure beta-emitter 59Sr solution received in the framework of the 2000 BIPM comparison of activity measurements. The first method was by scintillation counting using the triple to double coincidence ratio (TDCR) technique. The existing three detector-system was improved by the inclusion of a MAC-3 module produced by LNHB-Saclay. This module contains the circuits for the coincidence, dead time and gate functions. This was the first use of this equipment in an international comparison. The DETECSZ program (LNHB) was used to obtain the activity concentration, at the reference time, as 26.09+/-0.21 kBq g(-1). The second method was the efficiency tracer technique, using a 60Co standard solution and a 4pi beta-gamma-coincidence system. The radioactivity concentration was calculated from a general extrapolation curve, by using data from several sources. The value was 26.58+/-0.28 kBq g(-1) on the reference date 01.10.2000, 00 h UTC. The two results are in agreement within the limits of their combined uncertainties.

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.