Technical note: Quantifying Uranium-series disequilibrium in natural samples for dosimetric dating – Part 1: gamma spectrometry

Dosimetric dating techniques rely on accurate and precise determination of environmental radioactivity. Gamma spectrometry is the method of choice for determining the activity of 238U, 232Th and 40K. With the aim to standardise gamma-spectrometric procedures for the purpose of determining accurate parent nuclide activities in natural samples, we outline here basics of gamma spectrometry and practical laboratory procedures. This includes gamma radiation and instrumentation, sample preparation, finding the suitable measurement geometry and sample size for a given detector and using the most suitable energy peaks in a gamma spectrum. The issue of correct efficiency calibration is highlighted. The procedures outlined are required for estimating contemporary parent nuclide activity. For estimating changing activities during burial specific data analyses are required and these are also highlighted.

Factors affecting the minimum detected activity of the GAMMAVISION software report protocol

The article presents the results of a gamma- spectrometer study with a low- capacity scintillation (NaI(Tl)) detection unit, with software GammaVision v.8, adopted to solve certification problems, including for measuring activities close to zero. The list of factors influencing the presentation of the minimum detected activity (MDA) in the report protocol is analyzed software GammaVision v.8. To perform the measurements, the company´s ORTEC gamma-spectrometer with a low-capacity detection unit a type digiBASE-RH, in which a high-voltage power supply unit, amplifier, digital multi-channel analyzer with USB-connection to a computer with the installed driver are installed, was used. The peak search in the library was performed using a compressed version of the library, which contains two nuclides 137Cs and 40K. Methods of calculating MDA are based on the intensity of accounts. Nuclide activity is calculation for all peaks in the library, the energy of which is in the selected energy ranges for analysis. Measurements and calculations MDA under the given conditions of research for five methods depending on time of measurement and geometry of measurements are carried out. It is shown that the level of MDA can be reduced by choosing the optimal conditions, time of measurement and geometry of measurements. Recommendations are given for the use of capacity for counting sample, which will reduce the amount of substance required for analysis and optimize the time spent on measuring the counting sample. In a prospect it is expedient to undertake a study of dependence of MDA from the physical properties and radionuclide composition of the substance for the counting sample and the dependence from the uncertainty in the equation MDA.

Natural and anthropogenic radioactivity of feedstuffs, mosses and soil in the Belgrade environment, Serbia

By gamma spectroscopic measurement a content of natural radio-nuclides (40K, 238U, 226Ra, 232Th) and 137Cs was determined in samples of soil, alfalfa, maize and moss on six sites in the surroundings of Belgrade. Natural radionuclides in the soil were at the level characteristic for Serbia, whereas a relatively high level of activity of 137Cs (around 30 Bq kg-1) was determined. On the other hand, in plant samples mostly used as feed (such as alfalfa and maize) the concentration of natural radio-nuclide activity and 137Cs was relatively low, i.e. below the range of detection. The content of natural radio-nuclides in moss was within the standard range of values specific for Serbia. However, the activity level of 137Cs in moss gathered from the wider area around Belgrade, was high, the highest measured level being in the Avala-Zuce area (158-221 Bq kg-1). Our results show that this radio-nuclide is still present in the living environment of Belgrade even 20 years after the Chernobyl disaster, and that moss is a good indicator of living environment 137Cs contamination.