Calculation of the detection limits with the least-squares method in gamma-ray spectrometry: A simple procedure.

A metrologically consistent procedure for assessing the detection limits of activity measurements for gamma-ray emitters with high-resolution spectrometers using the LSQ method is described and tested. As the input to the assessment, besides the measured contents of the spectral channels, the results of the peak analysis, i.e.

Decision threshold as a gauge of the measurement quality in gamma-ray spectrometric measurements.

We show that in gamma-ray spectrometric measurements the decision threshold depends on the observed value of the measurand. Since the decision threshold is intended to describe the sensitivity of the measurement, this dependence restricts its application to measurements where the indication is not expressive. To extend the direct applicability of the decision threshold to expressive indications in gamma-ray spectrometric measurements, where mainly the Region-of-Interest method is used to evaluate the isolated peaks, a recalculation of the decision thresholds to the peak widths corresponding to the inexpressive peaks is proposed.

Influence of the solar activity on the background of a high-resolution gamma-ray spectrometer.

The count rate in the peak of a gamma-ray spectrum at 2223 keV was measured over a period of 25 years. The peak is produced by neutron capture on hydrogen, a constituent of the spectrometer's shield. Since the neutrons are produced by cosmic rays, the count rate in the peak is correlated with the solar activity via the interaction between the solar wind and the cosmic rays.

Comparison of different approaches of soil sampling uncertainty determination.

The ISO/IEC 17025 standard requires that all significant contributions have to be propagated to the measurement uncertainty, including also sampling uncertainties. We evaluated soil sampling uncertainties for gamma-ray spectrometry by using in-house and split-sample methods. By in-house method, the sampling uncertainty was determined by comparing standard deviations of measurement results and average analytical uncertainty.

Calculation of decision thresholds according to the standard ISO 11929-3 in case of presence of the peaked background.

The method of calculation of the decision threshold with the Least Squares Method, described in the standard ISO 11929, is presented for the case when the sources of peaked background contribute to the peak holding the indication. The decision threshold is calculated from spectral data corresponding to the indication zero; therefore, the observed indication must be removed from the spectrum. When the peaked background is present, the indication completely overlaps with the peaked background, so it can't be unfolded directly.

Influence of solar activity on ambient dose equivalent *(10) measured with thermoluminescent dosimeters in Slovenia.

Ambient dose equivalent *(10) is measured to assess general population exposure to ionising radiation. From its spatial and time variations it is possible to identify sources of exposure. In Slovenia, semi-annual *(10) is measured routinely with thermoluminescence dosimeters at 66 locations around the Nuclear Power Plant (NPP) Krško and at 50 other locations covering the rest of Slovenian territory.

Negative correlation between the number of sunspots and the occurrence of 7Be and 22Na in the surface air and their contribution to radiation doses.

This article presents yearly mean concentrations of cosmogenic radionuclides 7Be and 22Na occurring in dry and wet depositions (fallout) and aerosols. Time dependencies negatively correlated with the yearly mean number of sunspots. Activity concentrations of 7Be and 22Na in aerosols in the surface air had a correlation of near-unity.

Empirical determination of the correlation coefficient between the number of counts in a peak in a gamma-ray spectrum and the number of counts in the continuum where the peak is superimposed.

An account is given on the value of the correlation coefficient between the number of counts in a peak in a gamma-ray spectrum and the number of counts in the background, where the peak resides. It is supposed that the decomposition of the spectrum in the peak and in the background is performed by using the Least Squares method. The values of the correlation coefficient were determined empirically from measurements of gamma-ray spectra under repeatable conditions and from analyses of these spectra using four different kinds of peak-analysis software.

Measurement uncertainty arising from sampling of environmental samples.

In 2017, a new revision of the ISO/IEC 17025 standard was issued. One of the important changes is that the uncertainty arising from sampling has to be evaluated. Based on this new requirement, we evaluated the contribution of the sampling procedure to the total uncertainty budget of the high-resolution gamma-ray spectrometry of environmental soil, tap water and aerosol filter samples.

Determining the probability of locating peaks using computerized peak-location methods in gamma-ray spectra as a function of the relative peak-area uncertainty.

The probabilities of locating peaks with a high relative peak-area uncertainty were determined empirically with nine types of peak-location software used in laboratories engaged in gamma-ray spectrometry measurements. It was found that it is not possible to locate peaks with a probability of 0.95, when they have a relative peak-area uncertainty in excess of 50%.

The effect of stabilization on the utilization of municipal sewage sludge as a soil amendment.

This study assesses the potential use of different types of stabilized sewage sludge as a soil amendment by considering their physicochemical characteristics, nutritional status, and their trace metal and radionuclide content. The concentrations of trace metals and radionuclides were determined using ICP-OES and gamma-ray spectrometry, respectively. For determining nutritional status and chemical characterization, this study followed standard ISO-recommended procedures.

Calculation of the detection limits for radionuclides identified in gamma-ray spectra based on post-processing peak analysis results.

A new method for calculating the detection limits of gamma-ray spectrometry measurements is presented. The method is applicable for gamma-ray emitters, irrespective of the influences of the peaked background, the origin of the background and the overlap with other peaks. It offers the opportunity for multi-gamma-ray emitters to calculate the common detection limit, corresponding to more peaks.

An alternative approach to the decision threshold.

Two effects were identified that induce the dependence of the decision threshold on the uncertainty of the conversion factor. With the first effect, the conversion factor influences the decision threshold directly, through its variability. With the second effect, the variability of the conversion factor influences the decision threshold only when it is not evaluated for the null measurement.

Systematic influences on the areas of peaks in gamma-ray spectra that have a large statistical uncertainty.

A method is presented for calculating the expected number of counts in peaks that have a large relative peak-area uncertainty and appear in measured gamma-ray spectra. The method was applied to calculations of the correction factors for peaks occurring in the spectra of radon daughters. It was shown that the factors used for correcting the calculated peak areas to their expected values decrease with an increasing relative peak-area uncertainty.

Advancements in NORM metrology - Results and impact of the European joint research project MetroNORM.

The results of the three years European Metrology Research Programme's (EMRP) joint research project 'Metrology for processing materials with high natural radioactivity' (MetroNORM) are presented. In this project, metrologically sound novel instruments and procedures for laboratory and in-situ NORM activity measurements have been developed. Additionally, standard reference materials and sources for traceable calibration and improved decay data of natural radionuclides have been established.

Calculation of the detection limits by explicit expressions.

A method for calculating the approximate value of the detection limit for measurements of ionizing radiation is presented. The method can be applied when the indication corresponding to the detection limit and its uncertainty are given as explicit functions. Then also the detection limit can be calculated explicitly, which means that the iteration procedure for its calculation can be avoided.

Determination of the measurement threshold in gamma-ray spectrometry.

In gamma-ray spectrometry the measurement threshold describes the lover boundary of the interval of peak areas originating in the response of the spectrometer to gamma-rays from the sample measured. In this sense it presents a generalization of the net indication corresponding to the decision threshold, which is the measurement threshold at the quantity value zero for a predetermined probability for making errors of the first kind. Measurement thresholds were determined for peaks appearing in the spectra of radon daughters Pb and Bi by measuring the spectrum 35 times under repeatable conditions.

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.

Calculation of the correlation coefficients between the numbers of counts (peak areas and backgrounds) obtained from gamma-ray spectra.

Two simple methods for calculating the correlations between peaks appearing in gamma-ray spectra are described. We show how the areas are correlated when the peaks do not overlap, but the spectral regions used for the calculation of the background below the peaks do. When the peaks overlap, the correlation can be stronger than in the case of the non-overlapping peaks.

(60)Co in cast steel matrix: A European interlaboratory comparison for the characterisation of new activity standards for calibration of gamma-ray spectrometers in metallurgy.

Two series of activity standards of (60)Co in cast steel matrix, developed for the calibration of gamma-ray spectrometry systems in the metallurgical sector, were characterised using a European interlaboratory comparison among twelve National Metrology Institutes and one international organisation. The first standard, consisting of 14 disc shaped samples, was cast from steel contaminated during production ("originally"), and the second, consisting of 15 similar discs, from artificially-contaminated ("spiked") steel. The reference activity concentrations of (60)Co in the cast steel standards were (1.

Evaluation of comparison and proficiency test results of gamma ray spectrometry at Jožef Stefan Institute from 1986 to 2014.

One of the best ways to demonstrate the performance and capabilities of testing laboratories is to participate successfully in different international comparison schemes and proficiency tests. The overview of all results of such schemes in the field of high resolution gamma-ray spectrometry where the Laboratory for Radioactivity Measurements (LMR) of the Jožef Stefan Institute (JSI), Slovenia, participated in years 1986-2014 is presented. Different schemes are compared, strong points and drawbacks of different providers and schemes regarding evaluation procedures, determination of reference values, reporting time, sets of radionuclides included in the samples and range of activities of different radionuclides are discussed.

Measurement function for the activities of multi-gamma-ray emitters in gamma-ray spectrometric measurements.

In gamma-ray spectrometric measurements the background is usually taken into account by conducting measurements on a blank sample. However, this method is not appropriate if many different kinds of samples are measured and several types of detectors are used. In such cases it is easier to measure accurately the activities of the blank materials separately and then to subtract the activities of the blank sample from the total sample activities.

Calculation of the decision threshold in gamma-ray spectrometry using sum peaks.

In the presence of radon daughters, gamma rays from (88)Y with energies at 898.0keV or 1836.1keV appear on a high, continuous background or overlap with other peaks.

Reliability of the peak-analysis results in gamma-ray spectrometry for high relative peak-area uncertainties.

When measurement results with values near the decision threshold are being considered, a relative uncertainty of 60% is expected. Since such measurement results can be reported, the performance of the peak-analysing software for gamma-ray spectra needs to be examined for peaks that have a large relative uncertainty. The investigation was performed on a series of spectra measured with a HPGe detector under identical counting conditions.

Precise measurement of the half-life of ⁶¹Cu.

The decay characteristics of (61)Cu allow for a precise determination of its half-life. In order to search for a possible influence of the chemical environment on the decay rate, the half-life of (61)Cu in nickel and nickel-oxide was measured with high precision. The results show a small difference in the half-life that can be explained by the differences in electron density at the site of the nucleus.