H. Schrader

Standardisation and decay data of 177Lu and 188Re.

The activity values of 177Lu and 188Re standard sources were measured using the 4pibeta-gamma-coincidence method and by liquid scintillation counting. The X- and gamma-ray emission probabilities per disintegration were determined by means of photon spectrometry with calibrated Ge and Si(Li) detectors and using the pertinent activity values. The half-lives were measured with ionization chambers, yielding T(1/2)(177Lu) = 6.646(5) d and T(1/2)(188Re) = 0.70848(9) d.

Half-life measurements of long-lived radionuclides—New data analysis and systematic effects

Half-lives of long-lived radionuclides, for example, (85)Kr, (90)Sr, (108m)Ag, (133)Ba, (137)Cs, (152)Eu and (154)Eu, were measured at the Physikalisch-Technische Bundesanstalt (PTB) by ionization chamber measuring systems, for some nuclides, during a period of about 30 years. In particular, the relative residuals of fitted raw data from current measurements by a modified Townsend balance (compensation method) showed small periodic yearly fluctuations. The interpretation of these fluctuations is discussed. To solve problems of instrument instabilities (fluctuations), a new method of data analysis is applied using least-squares fits of combinations of the current ratios of the various radionuclide sources with corresponding data points measured each at nearly the same time. The data are corrected for instabilities similarly to when using current ratios with a (226)Ra reference source. The new method of data analysis excludes possible systematic effects due to disequilibrium of the (226)Ra decay chain. The limits of the method are discussed including the elimination of outliers due to systematic errors. An uncertainty budget is presented with the corresponding uncertainty components. Relative residuals of the fits in the best cases of the order of +/-5x10(-4) have been achieved. The results comprise data until the end of 2008. They agree within the limits of their relative uncertainties, typically better than 1.5x10(-3), with those published earlier by PTB authors.

STANDARDIZATION AND DECAY DATA OF 153SM

Abstract The activity concentration of a 153 Sm solution was determined by 4 πβ – γ coincidence measurements and by liquid scintillation counting (LSC). Both methods yielded results which differ by only 0.1%, the relative standard uncertainty being 0.1 and 0.2%, respectively. X-ray and gamma-ray emission probabilities of several transitions were measured; they were used to calculate beta transition probabilities. The emission probabilities of the 69.7 and the 103.2 keV gamma rays were found to be 0.0465±0.0005 and 0.2923±0.0018, respectively; and the half-life was found to be (46.274±0.007) h.

Calibration and consistency of results of an ionization-chamber secondary standard measuring system for activity

Calibration in terms of activity of the ionization-chamber secondary standard measuring systems at the PTB is described. The measurement results of a Centronic IG12/A20, a Vinten ISOCAL IV and a radionuclide calibrator chamber for nuclear medicine applications are discussed, their energy-dependent efficiency curves established and the consistency checked using recently evaluated radionuclide decay data. Criteria for evaluating and transferring calibration factors (or efficiencies) are given.

Standardization and decay data of 68Ge/68Ga

Abstract A gamma and an x-ray spectrometer, 4πβ—γ-coincidence equipment, liquid-scintillation counting (LSC) equipment and a calibrated ionization chamber (IC) have been used to determine the decay scheme parameters of 68Ga and the specific activity of a 68Ge/68Ga solution. The transition probability of the positron branch and the EC branch to the ground state of 68Zn, b1 and e1, the corresponding branches to the 1077 keV level of 68Zn, b2 and e2, the total emission probability of annihilation radiation from the 68Ga decay, pann, and the gamma-ray emission probabilities of the quanta corresponding to the 1077 keV transition (p1077) and to some weak transitions were redetermined. The results are b1 = 0.8785 ± 0.0012, e1 = 0.0892 ± 0.0012, b2 = 0.0129 ± 0.004, e2 = 0.0193 ± 0.0004, pann = 1.7829 ± 0.0022, p1077 = 0.0322 ± 0.0003. The specific activity of a 68Ge/68Ga solution was determined with a relative uncertainty of 1% (1σ) using 4πβ—γ coincidence, LSC and IC measurements. A half-life of T 1 2 = (270.99 ± 0.19) d for 68Ge was obtained by measurements with an ionization chamber.

Fitting methods for constructing energy-dependent efficiency curves and their application to ionization chamber measurements

An ionization chamber without and with an iron liner (absorber) was calibrated by a set of radionuclide activity standards of the Physikalisch-Technische Bundesanstalt (PTB). The ionization chamber is used as a secondary standard measuring system for activity at the Slovak Institute of Metrology (SMU). Energy-dependent photon-efficiency curves were established for the ionization chamber in defined measurement geometry without and with the liner, and radionuclide efficiencies were calculated. Programmed calculation with an analytical efficiency function and a nonlinear regression algorithm of Microsoft (MS) Excel for fitting was used. Efficiencies from bremsstrahlung of pure beta-particle emitters were calibrated achieving a 10% accuracy level. Such efficiency components are added to obtain the total radionuclide efficiency of photon emitters after beta decay. The method yields differences of experimental and calculated radionuclide efficiencies for most of the photon-emitting radionuclides in the order of a few percent.

An ionization chamber as a secondary standard for activity

A commercially-available radionuclide calibrator is used to maintain the unit of activity in the Slovak Institute of Metrology (SMU) and to check and verify activity meters in the field of nuclear medicine. The calibration of the instrument is described. The long-term stability is checked at regular intervals by means of 137Cs and 226Ra reference sources. A slow decrease of efficiency of about 2% per year has been observed, which has to be corrected for. An energy-dependent efficiency curve of the ionization chamber is established by transfer of calibration factors from a similar instrument at the Physikalisch-Technische Bundesanstalt (PTB). The curve has been checked by measurements with activity standards of 60Co, 54Mn, 22Na, 85Sr, 65Zn, 88Y, 57Co, 139Ce, 137Cs, 125I, 241Am, 210Pb and 109Cd. The established curve permits one to calculate calibration factors for additional short-lived radionuclides used in nuclear medicine. An overall uncertainty was obtained for activity measurements with calculated calibration factors under standard measurement conditions of better than 1.8%.

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.

Standardization and decay data of 186Re

Abstract The specific activity of a 186 Re solution was measured using 4πβ—γ-coincidence and liquid scintillation counting techniques to within a relative uncertainty of 0.4% (1σ). Efficiency-calibrated semiconductor spectrometers were used to measure the emission probabilities of the X- and gamma rays. A half-life of 186 Re of (3.7183±0.0011) d was measured using an ionization chamber and a 4π proportional counter, and the transition probabilities for the beta and EC transitions were deduced from the measured data.

Seasonal variations of decay rate measurement data and their interpretation.

Measurement data of long-lived radionuclides, for example, (85)Kr, (90)Sr, (108m)Ag, (133)Ba, (152)Eu, (154)Eu and (226)Ra, and particularly the relative residuals of fitted raw data from current measurements of ionization chambers for half-life determination show small periodic seasonal variations with amplitudes of about 0.15%. The interpretation of these fluctuations is a matter of controversy whether the observed effect is produced by some interaction with the radionuclides themselves or is an artifact of the measuring chain. At the origin of such a discussion there is the exponential decay law of radioactive substances used for data fitting, one of the fundamentals of nuclear physics. Some groups of physicists use statistical methods and analyze correlations with various parameters of the measurement data and, for example, the Earth-Sun distance, as a basis of interpretation. In this article, data measured at the Physikalisch-Technische Bundesanstalt and published earlier are the subject of a correlation analysis using the corresponding time series of data with varying measurement conditions. An overview of these measurement conditions producing instrument instabilities is given and causality relations are discussed. The resulting correlation coefficients for various series of the same radionuclide using similar measurement conditions are in the order of 0.7, which indicates a high correlation, and for series of the same radionuclide using different measurement conditions and changes of the measuring chain of the order of -0.2 or even lower, which indicates an anti-correlation. These results provide strong arguments that the observed seasonal variations are caused by the measuring chain and, in particular, by the type of measuring electronics used.