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Measurements were made using the TDCR method. POLATOM prepared and distributed for the key comparison participants the 55Fe solution and 55Fe ready-to-measure sources in the Ultima Gold™ scintillator in polyethylene vials. The stability of the sources was confirmed. Source counting efficiency decreased proportionally with time by about 0.7% per month, possibly due to colour quenching. The POLATOM measurement result was consistent with the key comparison reference value. The nuclear data for 55Fe were adopted in accordance with the KCWG(II) recommendation. Measurement results obtained in non-diffusive (glass) vials were lower than in diffusive vials. [ABSTRACT FROM AUTHOR]

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. • Primary activity measurements of 60Co and 106Ru/106Rh are presented. • Activity assessment with the TDCR method depends on β-spectra computation. • For both radionuclides, the TDCR and 4πβ−γ coincidence results are compared. • Good agreement is obtained when the atomic effects are considered in the β-spectra calculation. [ABSTRACT FROM AUTHOR]

An activity standard for 212Pb in equilibrium with its progeny was realized, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. A Monte Carlo-based approach to estimating uncertainties due to nuclear decay data (branching ratios, beta endpoint energies, γ-ray energies, and conversion coefficients for 212Pb and 208Tl) led to combined standard uncertainties ≤ 0.20 %. Confirmatory primary measurements were made by LS efficiency tracing with tritium and 4παβ(LS)-γ(NaI(Tl)) anticoincidence counting. The standard is discussed in relation to current approaches to 212Pb activity calibration. In particular, potential biases encountered when using inappropriate radionuclide calibrator settings are discussed. • A solution of 212Pb in equilibrium with its progeny was standardized for activity • Triple-to-double coincidence ratio (TDCR) liquid scintillation counting was used • Efficiency tracing and anticoincidence provided confirmatory measurements • Settings for radionuclide calibrators are discussed • Earlier recommended radionuclide calibrator settings did not account for all progeny [ABSTRACT FROM AUTHOR]

An informal bilateral comparison of 14 C liquid scintillation (LS) counting at the National Research Council of Canada (NRC) and the National Institute of Standards and Technology (NIST) has been completed. Two solutions, one containing 14 C-labeled sodium benzoate and one containing 14 C-labeled n-hexadecane, were measured at both laboratories. Despite observed LS cocktail instabilities, the two laboratories achieved accord in their standardizations of both solutions. At the conclusion of the comparison, the beta spectrum used for efficiency calculations was identified as inadequate and the data were reanalyzed with different inputs, improving accord. [ABSTRACT FROM AUTHOR]

In this paper we describe experiments on two enriched 40K solutions to accurately determine decay data. The first solution was measured in 2004/2005 by means of a gamma-ray spectrometer with low background and a liquid scintillation (LS) counter to apply the CIEMAT/NIST efficiency tracing method. A combination of results yields an emission probability of the 1461 keV gamma-rays of P γ = 0.1030(11) which is lower than current results of data evaluations. The activity concentration of the second solution was also determined by means of LS counting, but here, the CIEMAT/NIST efficiency tracing method as well as the TDCR method were applied. Again, the result was combined with that of independent gamma-ray spectrometry and the gamma-ray emission probability was found to be P γ = 0.1029(9) in good agreement with the result obtained from the first solution. A combination of both experiments yields P γ = 0.1029(9). The spectra of a TriCarb LS counter were carefully analyzed and a beta minus emission probability P β − = 0.8954(14) was determined. The new results for P γ and P β − indicate that the overall probability of the decay via EC in recent data evaluations is overestimated. The LS counting efficiencies were computed with a stochastic model and up-to-date calculations of the beta spectrum and fractional EC probabilities were used. The final activity result of the second solution is combined with the outcome of a comprehensive isotopic analysis to determine the half-life of 40K which is found to be 1.2536(27) ·109 years. All above-stated uncertainties are standard uncertainties (k = 1). • Two enriched 40K solutions were measured by means of gamma-ray spectrometry. • Liquid scintillation counting was used for activity determination. • The TDCR method was used for the first time for this radionuclide. • Decay data were determined: P γ = 0.1029(9), P β − = 0.8954(14); (k = 1). • A combination with mass spectrometry yields the half-life: 1.2536(27) 109 years); (k = 1). [ABSTRACT FROM AUTHOR]

Abstract: The NMISA participated in the international key comparison of the pure beta-emitter Technetium-99, CCRI(II)-K2.Tc-99. The comparison solution was standardized using three methods, namely the TDCR efficiency calculation method, the CIEMAT/NIST efficiency tracing method and the 4π(LS)β–γ coincidence tracing method with Co-60 as tracer. Excellent agreement between results obtained with the three methods confirmed the applicability of the beta spectral shape given by the latest (2011) DDEP evaluation of Tc-99 decay data, rather than the earlier (2004) evaluation. [Copyright &y& Elsevier]

Abstract: The triple-to-double-coincidence ratio method (TDCR) is an important method for activity standardization in metrology institutes worldwide. There is an increasing interest in portable systems that allow activity determination outside of specialized laboratories with high accuracy. Within the framework of the EMRP “MetroFission” project, several portable systems using different designs were developed. The PTB system described here is based on channel photomultipliers incorporated in a portable detection module, a separate electronics bin and a computer for data acquisition and storage. This miniature TDCR system was extensively tested and compared to the PTB reference TDCR system that is very well characterized and has been used in several intercomparisons. [Copyright &y& Elsevier]

Abstract: A 85Sr solution was measured in two liquid scintillation (LS) counters. Scintillation pulses from the delayed transitions in the 85Sr decay were by and large lost as the dead time of the LS-counter was much longer than the lifetime of the 85Rb excited level. The registration probability of these pulses has been defined and introduced into the counting efficiency calculation. The results of the 85Sr solution standardization by the CIEMAT/NIST and the TDCR methods relative to the results from the 4π(LS)-γ coincidence and anticoincidence method were 0.997±0.012 and 0.971±0.019, respectively. [Copyright &y& Elsevier]

Abstract: Beta-emitters 36Cl and 63Ni, and the electron capture radionuclide 55Fe were used to calibrate a secondary standardization instrument Quantulus-1220TM. An external standard technique was applied to assess the quenching level of samples. Nitromethane as an artificial quencher was used for sample preparation at different quenching levels. The dependence of the counting efficiency on the quenching level was determined. Samples of beta-emitters were re-measured with the triple-to-double coincidence ratio (TDCR) primary standardization instrument. The specific activities of beta-emitters were determined with the help of the software TDCRB-02 and compared with known values. It was found that for 36Cl and 63Ni the discrepancy was 0.9% and 2.7%, respectively, within the specified uncertainty limits. A new sample with 90Sr was prepared and measured with the TDCR device. In this case, the divergence from the expected value was 1.7%. Results suggest the suitability of the TDCR techniques for low-level counting. [Copyright &y& Elsevier]

Abstract: The nuclide 241Am decays by alpha emission to 237Np. Most of the decays (84.6%) populate the excited level of 237Np with energy of 59.54keV. Digital coincidence counting was applied to standardize a solution of 241Am by alpha–gamma coincidence counting with efficiency extrapolation. Electronic discrimination was implemented with a pressurized proportional counter and the results were compared with two other independent techniques: Liquid scintillation counting using the logical sum of double coincidences in a TDCR array and defined solid angle counting taking into account activity inhomogeneity in the active deposit. The results show consistency between the three methods within a limit of a 0.3%. An ampoule of this solution will be sent to the International Reference System (SIR) during 2009. Uncertainties were analysed and compared in detail for the three applied methods. [Copyright &y& Elsevier]

Abstract: Samples containing high-energy beta emitters in hydrochloric acid were measured in an in-house built triple-to-double coincidence counter. For the analysis of the results, a new method was developed that is based on a free parameter model. Formulas for the determination of the counting efficiencies were derived assuming a Poisson distribution for the generation of photoelectrons at the photocathodes and applying the Frank and Tamm theory to the production of Čerenkov light. The anisotropy effect for the emission of Čerenkov light was taken into account. The activities determined with the new method were compared with the results from other primary standardization techniques. The following radionuclides were successfully studied: 32P, 89Sr, 90Y, 204Tl and 106Rh. [Copyright &y& Elsevier]

Abstract: Recent liquid scintillation (LS) measurements at the National Institute of Standards and Technology (NIST) and at the Laboratoire National Henri Becquerel (LNHB) on a standardized 63Ni solution that has been tracked for nearly 40 years have resulted in several important findings: (i) a 63Ni half-life value of 101.2±1.5a has been determined with the present decay data. This value is consistent with a previous specific activity determination and with an earlier value from decay measurements; and it appears to be more satisfactory than a recent data evaluator''s recommended value of 98.7a. (ii) All solution standards of 63Ni as disseminated by NIST for the past 38+ years are internally consistent with past and recent standardizations. (iii) Primary LS standardizations of 63Ni by the triple-to-double coincidence ratio (TDCR) method and by CIEMAT/NIST 3H-standard efficiency tracing (CNET) appear to be comparable, although the latter methodology is believed to be inherently inferior. (iv) There is excellent measurement agreement between NIST and LNHB for 63Ni primary standardizations. [Copyright &y& Elsevier]

A description of the triple-to-double coincidence ratio (TDCR) spectrometer recently constructed at NIST and results of tests to assess its operating characteristics are presented. Measured activities for previously calibrated solutions of 3H (tritiated water) and 63Ni agreed with certified activity values to within 0.04% and 0.2%, respectively. Agreement between measurements of solutions containing 90Y using the TDCR and the CIEMAT/NIST efficiency tracing method was achieved to within 0.7% and within the respective experimental uncertainties. A difference of 5.3% was observed between TDCR measurements and the certified massic activity value for a calibrated solution containing 54Mn, but because of the large uncertainty on the TDCR result (3.6% relative standard uncertainty), the values agree to within the experimental uncertainties. Agreement to within experimental uncertainties (2%) for 103Pd was achieved with the TDCR and CIEMAT/NIST methods, but not between TDCR and isothermal calorimetric measurements. TDCR results for a 204Tl solution were in excellent agreement (maximum difference of 0.2% with any other method, with combined standard uncertainty of 0.45% on TDCR result) with results obtained using three other methods. [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]

Abstract: The “conventional” TDCR system was used for standardization of the tritiated water in the frame of the international comparison organized by CCRI(II). The prototype of the new TDCR realized at LNHB with three CPMs (Ivan et al., 2008) was improved by constructing at IFIN-HH, a system containing six channel photomultiplier tubes arranged symmetrically in a new optical chamber. The system was tested by measuring various pure beta emitters and for comparative measurements of tritiated water for validation studies. [Copyright &y& Elsevier]

A standard for activity of 224Ra in secular equilibrium with its progeny has been developed, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. The standard was confirmed by efficiency tracing and 4παβ(LS)-γ(NaI(Tl)) anticoincidence counting, as well as by 4πγ ionization chamber and NaI(Tl) measurements. Secondary standard ionization chambers were calibrated with an expanded uncertainty of 0.62% (k = 2). Calibration settings were also determined for a 5 mL flame-sealed ampoule on several commercial reentrant ionization chambers (dose calibrators). • A solution of 224Ra was standardized for activity by triple-to-double coincidence ratio (TDCR) liquid scintillation counting. • Efficiency tracing and anticoincidence provided confirmatory measurements. • Radionuclide calibrator settings determined with typical expanded (k = 2) uncertainties < 1%. [ABSTRACT FROM AUTHOR]