Begoña Quintana

Coincidence summing corrections for the natural decay series in γ-ray spectrometry

Using a Monte Carlo code and a Markov formalism to describe the decay schemes, coincidence-summing correction factors can be calculated with a suitable accuracy. For two dierent measuring geometries and an HPGe detector, calculated and experimental correction factors have been shown to closely agree for 152 Eu. The simulation method has subsequently been applied in assessing the need for coincidence-summing corrections for members of the uranium, thorium and actinium series measurable by g-spectrometry. Correction factors were calculated for predominant g emissions significantly aected by coincidence-summing eects and the correctness of our calculations tested for environmental samples. The test makes it evident that in order to obtain reliable and unbiased activity values for some natural radionuclides coincidence summing cannot be neglected in environmental measurements at small source‐ detector distances. # 2001 Elsevier Science Ltd. All rights reserved.

Towards a proper modeling of detector and source characteristics in Monte Carlo simulations

We performed a systematic study on the influence of different source configurations on the reliability of Monte Carlo calculations for the response of Ge detectors. Calculated full-energy peak efficiencies are compared to experimental values in the energy range 46-1800 keV. Setups with different characteristics are considered, from point-like to volume sources. Among the latter there are filters and aqueous matrices and sediments in Petri boxes or Marinelli beakers. The analysis of the deviations between experimental and calculated results for the different configurations enables us to detect inaccuracies in the description of detector and source characteristics and to improve them. By means of this procedure satisfactory results of the efficiencies were obtained in the whole energy range. For all setups, the deviations average 1.5%, except for the sediment sources where they are up to 3.3%.

Studies on radioactivity in aerosols as a function of meteorological variables in Salamanca (Spain)

Abstract Ambient concentrations of aerosol radioactivity in ground-level air were measured weekly in a low-industrialized city (Salamanca, Spain). Means of about 6.9×10−5 and 4.83×10 −4 Bq m −3 were found for gross α and β activities, respectively, averaged over three years. The measured activities, which include contributions from several radionuclides in the ground atmosphere, were evaluated to determine the relationship between the meteorology and the aerosol activities in air. We have studied the influence of diverse meteorological parameters such as temperature, pressure and wind direction, as well as the effect of the less often considered terrestrial electrostatic field. Concentrations of gross α and β activities were greatly affected by the meteorological conditions, showing pronounced differences between seasons. The study reveals that much of the variability (approximately 50%) in the activities is explained by the electrostatic field, its influence being higher in winter. About 40% of the α and β variability is explained by both the temperature and the humidity. The influence of the wind direction is only statistically significant for α radioactivity. A simple mathematical model based on these variables is developed to describe globally the dynamics in air of radioactive particles enabling us to estimate the air radioactive background level.

Effects of gamma radiation on the biological, physico-chemical, nutritional and antioxidant parameters of chestnuts – A review

Gamma radiation has been used as a post-harvest food preservation process for many years. Chestnuts are a seasonal product consumed fresh or processed, and gamma irradiation emerged recently as a possible alternative technology for their post-harvest processing, to fulfil the requirements of international phytosanitary trade laws. After harvest and storage, several problems may occur, such as the presence of infestations and development of microorganisms, namely rotting and fungi. These diminish the quality and safety of the product, decreasing the yield along the production chain. In fruits, gamma irradiation treatment is for two main purposes: conservation (ripening delay) and insect disinfestation (phytosanitary treatment). In this review, the application of gamma irradiation to chestnuts is discussed, including production data, the irradiated species and the effects on biological (sprouting, rotting, respiration rate, insects, worms and fungi), physico-chemical (color, texture, and drying rate), nutritional (energetic value, proteins, sugars and fatty acids) and antioxidant (tocopherols, ascorbic acid, phenolics, flavonoids and antioxidant activity) parameters. These changes are the basis for detecting if the food product has been irradiated or not. The validation of standards used for detection of food irradiation, as applied to chestnuts, is also discussed.

An empirical method to determine coincidence-summing corrections in gamma spectrometry

We propose an empirical method to calculate coincidence-summing corrections in γ-spectroscopy by comparing the measured areas from the same γ-ray emissions in two different geometries. The method is simple and avoids complicated calculations needed in usual procedures. The applications to two experimental arrangements used frequently for measuring environmental samples is developed and the efficiency calibration in the energy range [46.54, 1410] keV of a HPGe detector is performed for these specific experimental setups.

Summing-coincidence corrections with Geant4 in routine measurements by γ spectrometry of environmental samples

In this work, we describe a method to quantitatively evaluate true-coincidence-summing effects by making use of the Geant4 toolkit, which incorporates an emulation of the radionuclide disintegration scheme. To check the capabilities of the method, we firstly validated the simulated corrections using the ones obtained experimentally for radionuclides such as (60)Co, (152)Eu and (133)Ba. Secondly, we evaluated the effect of summing corrections of some radionuclides included in two intercomparison exercises to conclude that the results were improved when utilising the method described here.

Gamma-ray spectral analysis with the COSPAJ continuum fitting routine

We present a method to fit γ-ray full-energy peaks. Instead of performing a local fit to a limited number of channels around full-energy peaks simultaneously to the peak fit, it uses a spectral continuum fitting program, COSPAJ, to determine the peak base-line independently to the peak fitting. Full-energy peaks are described by the sum of two exponential distributions convoluted with a Gaussian. The method produces consistent results, accurate determinations of peak areas and it induces relative area uncertainties down to 0.02%.

Low-level gamma spectrometry for pollution assessment in San Simón Bay (Vigo, Spain)*

A gamma spectrometer with HPGe detector of 50% relative efficiency and 1 cps total background has been dedicated to the measurement of an intertidal sediment core from a coastal environment at the Ria de Vigo (Spain). The area is affected by lead pollution and the source identification needs of a precise dating of the sediment core. Such a precise dating requires the measurement not only of the radionuclides directly involved in time calculation, as 210 Pb and 226 Ra, but also of ancillary radionuclides which inform about the dating model to apply and about the validity of its time estimation. Gamma spectrometry with Ge detectors performs a simultaneous measurement of the full content in γ-emitters of the sample. However, its use is limited by its high spectral background. We present the characteristics of our low- level background gamma spectrometer and also of Galea, the computing tool for the expert analysis of natural radionuclides. Both make possible to get the proper experimental results to reach a suitable dating. The results allowed us to detect a change in the sedimentation dynamics in the area under study, to verify the impact of lead pollution in the 210 Pb level, to obtain a sedimentation rate by using the CF:CS model with a suitable correction factor and, finally, to validate the sediment dating.

AUTOMATIC ANALYSIS OF CONTINUUM PHENOMENA IN GAMMA SPECTRA

Abstract A method to fit the continuum of gamma spectra, developed to determine the baseline below full-energy peaks, is applied to the study of structures contained within the continuum. Specifically, we analyze the two spectral lines which appear in the background spectra of a low-level germanium gamma-ray spectrometer due to the inelastic scattering of cosmic-ray, tertiary fast-neutrons on 72 Ge and 74 Ge. The automatic analysis of the continuum it makes possible to characterize completely the cosmic-ray induced background and to study the environmental fast-neutron flux.

A method for the complete analysis of NORM building materials by γ-ray spectrometry using HPGe detectors

A methodology including software tools for analysing NORM building materials and residues by low-level gamma-ray spectrometry has been developed. It comprises deconvolution of gamma-ray spectra using the software GALEA with focus on the natural radionuclides and Monte Carlo simulations for efficiency and true coincidence summing corrections. The methodology has been tested on a range of building materials and validated against reference materials.