Evidence against solar influence on nuclear decay constants.

The hypothesis that proximity to the Sun causes variation of decay constants at permille level has been tested and disproved. Repeated activity measurements of mono-radionuclide sources were performed over periods from 200 days up to four decades at 14 laboratories across the globe. Residuals from the exponential nuclear decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ from one data set to another and are attributable to instabilities in the instrumentation and measurement conditions. The most stable activity measurements of alpha, beta-minus, electron capture, and beta-plus decaying sources set an upper limit of 0.0006% to 0.008% to the amplitude of annual oscillations in the decay rate. Oscillations in phase with Earth's orbital distance to the Sun could not be observed within a 10-6 to 10-5 range of precision. There are also no apparent modulations over periods of weeks or months. Consequently, there is no indication of a natural impediment against sub-permille accuracy in half-life determinations, renormalisation of activity to a distant reference date, application of nuclear dating for archaeology, geo- and cosmochronology, nor in establishing the SI unit becquerel and seeking international equivalence of activity standards.

Assessment of measurement result uncertainty in determination of (210)Pb with the focus on matrix composition effect in gamma-ray spectrometry.

Reference materials were used to assess measurement result uncertainty in determination of (210)Pb by gamma-ray spectrometry, liquid scintillation counting, or indirectly by alpha-particle spectrometry, using its daughter (210)Po in radioactive equilibrium. Combined standard uncertainties of (210)Pb massic activities obtained by liquid scintillation counting are in the range 2-12%, depending on matrices and massic activity values. They are in the range 1-3% for the measurement of its daughter (210)Po using alpha-particle spectrometry. Three approaches (direct computation of counting efficiency and efficiency transfer approaches based on the computation and, respectively, experimental determination of the efficiency transfer factors) were applied for the evaluation of (210)Pb using gamma-ray spectrometry. Combined standard uncertainties of gamma-ray spectrometry results were found in the range 2-17%. The effect of matrix composition on self-attenuation was investigated and a detailed assessment of uncertainty components was performed.

Measurement of ²²6Ra in soil from oil field: advantages of γ-ray spectrometry and application to the IAEA-448 CRM.

The analytical performance of gamma-ray spectrometry for the measurement of (226)Ra in TENORM (Technically Enhanced Naturally Occurring Radioactive Material) soil was investigated by the IAEA. Fast results were obtained for characterization and certification of a new TENORM Certified Reference Material (CRM), identified as IAEA-448 (soil from oil field). The combined standard uncertainty of the gamma-ray spectrometry results is of the order of 2-3% for massic activity measurement values ranging from 16500 Bq kg(-1) to 21500 Bq kg(-1). Methodologies used for the production and certification of the IAEA-448 CRM are presented. Analytical results were confirmed by alpha spectrometry. The "t" test showed agreement between alpha and gamma results at 95% confidence level.

IAEA-447: a new certified reference material for environmental radioactivity measurements.

The environment program of the International Atomic Energy Agency (IAEA) includes activities to produce and certify reference materials for environmental radioactivity measurements. This paper describes methodologies applied in preparation and certification of the new IAEA-447 moss-soil certified reference material. In this work, the massic activities and associated standard uncertainties of (40)K, (90)Sr, (137)Cs, (208)Tl, (210)Pb, (210)Po, (212)Pb, (214)Pb, (214)Bi, (226)Ra, (228)Ac, (234)Th, (234)U, (238)U, (238)Pu, (239+240)Pu, (241)Pu and (241)Am were established. Details of the analytical methods including radiochemical procedures were reported. Analytical challenges and lessons learned from the reported results in the worldwide IAEA proficiency test using this material was summarized and best analytical practices to improve the performance for environmental radioactivity determinations were recommended. IAEA-447 is an important reference material for quality control and method validation of gamma-ray spectrometry and radiochemical analytical procedures.

Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry--part II (volume sources).

The second part of an intercomparison of the coincidence summing correction methods is presented. This exercise concerned three volume sources, filled with liquid radioactive solution. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing corrective factors for several energies of (152)Eu and (134)Cs, and different source-to-detector distances. They are presented and discussed.

Results of an international comparison for the determination of radionuclide activity in bilberry material.

Radioactivity found in wild food products has assumed greater importance when assessing the total exposure of the population. For this reason, IRMM has been developing a reference material for the activity concentration of three radionuclides in bilberry samples. In order to characterise this new material, a CCRI(II) supplementary comparison was organised. The difficulties encountered in this comparison are discussed, in particular the efficiency calibration for volume sources of gamma-ray emitters, and comparison reference values for (137)Cs and (40)K are calculated.

Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry.

A comparison of the coincidence summing correction methods is presented. Since there are several ways for computing these corrections, each method has advantages and drawbacks that could be compared. This part of the comparison was restricted to point sources. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing correction factors for several energies of (152)Eu and (134)Cs, and three source-to-detector distances. They are presented and discussed.

Development of simulated air filters for gamma-ray spectrometry proficiency testing.

A set of 60 spiked simulated air filter sources was developed for the 2004-2005 proficiency test of the Italian radioactivity surveillance network. Each simulated filter source was prepared by reproducible volumetric dispensing of 19 drops of a mixed radioactive solution containing Co-57, Cs-134, Cs-137, Co-60 and Eu-152. The spiking pattern was investigated and optimized by numerical simulations. The filter sources were checked by double counting on HPGe and NaI(Tl) detectors. The standard deviation (SD) of activity values was 1.5%.

A new experimental procedure for determination of photoelectric efficiency of a NaI(Tl) detector used for nuclear medicine liquid waste monitoring with traceability to a reference standard radionuclide calibrator.

To determine photopeak efficiency for (99m)Tc of the NaI(Tl) detector used for liquid waste monitoring at the Nuclear Medicine Unit of IRCCS Paediatric Hospital Bambino Gesù in Rome, a specific experimental procedure, with traceability to primary standards, was developed. Working with the Italian National Institute for Occupational Prevention and Safety, two different calibration source geometries were employed and the detector response dependence on geometry was investigated. The large percentage difference (almost 40%) between the two efficiency values obtained showed that geometrical effects cannot be neglected.

Experimental determination of calibration settings of a commercially available radionuclide calibrator for various clinical measurement geometries and radionuclides.

Following the approach of the National Primary Laboratory of the UK (NPL) for the calibration of radionuclide calibrators, but using a commercially available instrument with no data available in the literature, the radionuclide calibrator response was investigated as a function of different measurement geometries at the "Regina Elena" National Cancer Institute (IRE) in Rome. Working with Italian National Metrology Institute for ionising radiation quantities (ENEA-INMRI), specific calibration factors with traceability to national primary standards were determined for different types of glass vials, solid capsules and plastic syringes, investigating three radionuclides with different energy spectra (Tc-99m, In-111, I-131). For each kind of syringe, calibration correction factors for different filling volumes were calculated. For Tc-99m and I-131 the difference between measured and true activity was in the range 2-7%, depending on measurement geometry. For In-111 a large percentage deviation from the true activity value was found in each geometry considered, reaching 35%. The magnitude of this difference is particularly dependent on the energies of the emitted photons.

Random-summing correction and pile-up rejection in the sum-peak method.

The sum-peak counting method was applied for 125I absolute activity measurement. Count rate-dependent corrections for random summing and dead time effects were experimentally determined at different count rates and in several experimental conditions. Two NaI(Tl) crystals of different volumes were used. They were connected to pulse recording systems with different characteristics, with or without pile-up rejection live-time corrector circuits (PUR/LTC). A theoretical model was proposed to explain the different behaviours found experimentally. It is shown that count rate-dependent effects are drastically reduced by the use of PUR/LTC.