Radon surveys and effectiveness of remedial actions in spas on the Ischia island (Italy).

The possible damaging effects on human health of inhaled radon and its decay products are of interest to workers and the public. In particular, radon in thermal environments often occurs in high concentrations. Therefore, investigations and remedial actions are important to reduce activity concentration values and associated risk. This work concerns the analysis of two surveys of radon gas activity concentration carried out in 2006/2007 and 2019/2020 at twenty thermal spas on the island of Ischia (Italy). Annual measurements were carried out in workplaces located in the basement and ground floor using passive CR-39 detectors. In the spas involved in both surveys, the effectiveness of the remedial actions, implemented by the owners, was assessed obtaining an average percentage reduction of 74%. Considerations were made about the annual effective dose, and the location of the spas taking into account the geological setting of the volcanic nature of the island.

Development of radon transport model in different types of dwellings to assess indoor activity concentration.

The influence of different building types on the activity concentration of Radon indoor is studied through transport models in soil and building materials. The numerical solutions of the relevant transport equations are solved by the finite differences method (FDM) and used to evaluate the indoor Radon activity concentration. Several boundary conditions are introduced to simulate the Radon entry into the buildings from soils and to assess the Radon activity concentration at the different floors. The types of dwelling investigated differ in the position of the lower floor respect to the ground. Comparisons are made to modeling assessments obtained considering different soil characteristics underneath the building and building materials to simulate indoor Radon activity concentration. These investigations lead to the conclusion that, in addition to the nature of the soil and building materials, the position of lower floor of dwellings plays a significant role in determining the amount of radon entry into residential buildings. This work is effective to assess the health hazards coming from the Radon accumulation in living environments.

STUDY OF 222RN CONTINUOUS MONITORING TIME SERIES AND DOSE ASSESSMENT IN SIX EUROPEAN CAVES.

The present work aims to assess the effective doses from long-term continual radon monitoring in six European caves (Slovenia, Slovakia and the Czech Republic), including influencing environmental factors. Caves are important radiation protection subjects because of elevated radon activity concentration (~kBq/m3), mostly due to the low natural ventilation. The sources of radon gas are most often underground rock layers and clastic sediments. The radon activity concentrations show seasonal variations, for which the outside temperature is the main driving force. The human health impact due to the radon inhalation in monitored caves was estimated through the annual effective dose, using the methodology provided by the International Commission on Radiological Protection (ICRP Publication 137). The annual effective dose could reach several tens of mSv, depending on the working hours spent in the underground.

ANALYSIS BY SCANNER OF TRACKS PRODUCED BY RADON ALPHA PARTICLES IN CR-39 DETECTORS.

The most used passive detectors for Radon measurement are the CR39s, both for the good stability of the material and for the practicality of use. But, commercial reading systems are expensive and not always fast. The aim of the present work was the development of a method for a rapid, efficient and economic evaluation of the result of the indoor Radon measurement performed with CR39 detectors. The analysis and acquisition of detector images were performed using a photo scanner and the free ImageJ software. Several groups of CR-39 detectors were exposed, developed and analysed. Calibration curve was obtained in a wide range of exposure values (200-12 000 kBq·h·m -3) to allow the procedure to be applied in all possible measurement environments. Furthermore, a statistical study was carried out on the shape and size of nuclear tracks after chemical development. The dependence of the track size on Radon exposure was effective in showing the trace saturation effect as well.

Connection between 222Rn emission and geophysical-geochemical parameters recorded during the volcanic unrest at Campi Flegrei caldera (2011-2017).

Studies concerning 222Rn emission from soils are growing interest in the Earth Sciences, due to the gas potential as a tracer of natural phenomena. This paper presents a study of radon monitoring in two sites of Campi Flegrei caldera (Neaples, Italy) during the period July 1, 2011-December 31, 2017. This area was characterized by several phases of volcanic unrest. A hybrid method based on Multiple Linear Regression + Remote Radon Estimation method + Singular Spectrum Analysis (MLR + RRE + SSA) is developed for the trend extraction and the identification of anomalies in the time series of 222Rn. The results are compared with several routinely used geo-indicators of the caldera unrest. The comparisons show strong correlation among the signals. The present study proves the 222Rn is a potential indicator of the evolution of a volcanic crisis.

Development and calibration of a method for direct measurement of 220Rn (thoron) activity concentration.

The interest in the measurement of thoron (220Rn) activity concentration in air has recently increased, with the attention for the development of standards useful for the calibration of measuring instruments. Due to its short half-life (55.8 s), consolidated techniques for the realization and the use of controlled atmospheres of radon (222Rn) are not effective in the case of thoron. New adequate methodology are required. A method for the measurement of the thoron reference activity based on the direct detection of the alpha particles produced by the decay of 220Rn, from natural samples containing 232Th, is here proposed. The possibility of observing an acceptable spectrum is entrusted to the realization of measurement chambers small enough to reduce as much as possible the energy loss of the alpha particles before they reach the Silicon detector. Such a chamber was realized and used with a known thoron atmosphere in a controlled environment. The experimental results are compared with those obtained from the simulation with the Monte Carlo method: (i) the alpha spectra coming directly from thoron atoms exhibit similar shape with a linear trend plus an exponential trend on the left side of the 220Rn peak, depending from the distance between source and detector; (ii) the corresponding 220Rn detection efficiency values are compatible considering the uncertainties. An investigation was conducted to study the shape of the 220Rn spectra vs the different volume of chambers, through Monte Carlo simulations. The results show: (i) the linear part of the spectra shape goes to reduce with the increasing of the height of the chamber; (ii) the 220Rn detection efficiency decreases with the increasing of the height of the chamber.

Analysis of 7-years Radon time series at Campi Flegrei area (Naples, Italy) using artificial neural network method.

This paper reports the analysis of soil 222Rn data recorded over 7-years in the volcanic caldera of Campi Flegrei (Naples-Italy). The relationship between Radon activity concentration and several geophysical, geochemical and meteorological parameters, influencing the gas emissions, is estimated by the Artificial Neural Network (ANN) method. The analysis goals are: the estimation (replication) of the Radon time series from influencing parameters, the forecasting of an unknown part of it, and the search for anomalies. Results prove: (i) the effectiveness of the ANN method; (ii) Radon follow the periods of agitation of the caldera, demonstrated by the comparison with previous works using different methods.

Continuous radon monitoring during seven years of volcanic unrest at Campi Flegrei caldera (Italy).

This is a seven-year study (1/7/2011-31/12/2017) of radon monitoring at two sites of Campi Flegrei caldera (Neaples, Southern Italy) that in the last 70 years experienced repeated phases of volcanic unrest. The sites are equipped with devices for radon detection, based on the spectrometry analysis of the α-particles of radon daughters. A hybrid method, as combination of three known methods, is applied for the identification of residuals (anomalies) and trends of the time series of Radon. The results are compared with the following indicators of current caldera unrest: the tremor caused by the major fumarolic vent registered by a seismic station; the cumulative of background seismicity; the maximum vertical deformation acquired by GPS networks during the current phase of uplift; the temperature-pressure of the hydrothermal system estimated based on gas geo-indicators. The comparisons show strong correlation among independent signals and suggest that the extension of the area affected by current Campi Flegrei crisis is larger than the area of seismicity and of intense hydrothermal activity from which the radon stations are 1-4 km away. These results represent an absolute novelty in the study of a such calderic area and mark a significant step forward in the use and interpretation of the radon signal.

Analysis of geophysical and meteorological parameters influencing 222Rn activity concentration in Mladec caves (Czech Republic) and in soils of Phlegrean Fields caldera (Italy).

The present work concerns a detailed analysis of Radon time series to differentiate endogenous from exogenous phenomena which provide anomalous signals. Two-year data from two sites in Czech Republic and in Italy are analyzed in order to contribute to the prevention of natural hazards. A new hybrid forecasting method is implemented and tuned for the identification of Radon anomalies in the time series. It is based on the combination of Multiple Linear Regressions, Empirical Mode Decomposition and Support Vector Regression methods that decompose the signal and analyze the components to distinguish the variations due to Radon originated in depths from those due to environmental parameters. The possible correlations with fumarolic tremors in the Italian site and the faults microdisplacements in the Czech site have been studied, as well as with the earthquakes that have influence on two studied areas. Results show that: (i) the used method is very effective considering the calculated statistical uncertainties; (ii) the outer temperature is the main influencing Radon driving force; (iii) the extracted Radon anomalies due to endogenous phenomena are well correlated with fault displacements, fumarolic tremors, and with earthquakes under a characteristic delay time for each area; (iv) significant correlations among earthquake magnitude and depth with fault displacement and fumarolic tremor are found.

Space-time Bayesian analysis of the environmental impact of a dismissing nuclear power plant.

The assessment of the radiological impact of decommissioning activities at a nuclear power plant requires a detailed analysis of the distribution of radionuclides in the environment surrounding it. The present work concerns data of three campaigns carried out during the last twenty years in the plain of the Garigliano river surrounding the Garigliano Nuclear Power Plant (GNPP), which is located in Southern Italy and shut down in 1979. Moreover, some data from surveys held in the eighties, across the Chernobyl accident, have been taken in account. The results for the soil samples, in particular for 137Cs and 236U specific activity, were analyzed for their extension in space and in time. Some of the problems related to the classical analysis of environmental radiological data (non-normal distribution of the values, small number of sample points, multiple comparison and presence of values lesser than the minimum detectable activity) have been overcome with the use of Bayesian methods. The scope of the paper is threefold: (1) to introduce the data of the last campaign held in the Garigliano plain; (2) to insert these data in a larger spatio-temporal frame; (3) to show how the Bayesian approach can be applied to radiological environmental surveys, stressing out its advantages over other approaches, using the data of the campaigns. The results show that radionuclides specific activity in soil is dominated by the natural sources with the contribution of the atmospheric fallout. A detailed study was performed on the 137Cs data to evaluate both their statistical distribution and the trend over the space and the time. It results that (i) no new contribution there was in the last decades, (ii) specific activity values of the area surrounding the GNPP are consistent with those obtained in other farther areas, (iii) the effective depletion half-life factor for 137Cs is much lower than the half-life of the radionuclide.

AMS assessment of U-contamination of structural materials of the Garigliano NPP under decommissioning.

The assessment of the radiological impact of decommissioning activities at a Nuclear Power Plant requires a detailed mapping of the distribution of radionuclides both in the environment surrounding the NPP and in its structural material. The detection of long-lived actinide isotopes and possibly the identification of their origin is particularly interesting and valuable if ultrasensitive measurement of the relative abundance of U isotopes is performed via Accelerator Mass Spectrometry (AMS). In this paper we present an investigation carried out on the structural materials of the Garigliano NPP aiming to determine the abundance of 235,236,238U in the various compartments of the plant buildings under decommissioning. Since the expected values both for isotopic ratios and total U concentrations range over different orders of magnitude, we have developed a novel methodology for the measurement of 234,235U/238U isotopic ratios in low U concentration samples. This allowed a systematic investigation of the distribution of all U isotopes in concrete and metal matrices of the NPP. The behavior of 235,236U/238U isotopic ratios in the different compartments of the NPP is discussed. The correlation of these ratios with 60Co and 137Cs specific activities is also studied to show a different behavior for concrete and metal samples. These data represent a very valuable information to direct the decommissioning procedures under course.

SIGNAL DECOMPOSITION AND ANALYSIS FOR THE IDENTIFICATION OF PERIODIC AND ANOMALOUS PHENOMENA IN RADON TIME-SERIES.

This work concerns continuous monitoring of radon and thoron specific activity in soil gas within the framework of identifying possible anomalies. It is based on the analysis of a medium-term data record obtained from soil gas in an area of geophysical interest. The RaMonA spectrometric system is also used to measure the climatic parameters and a specific analysis of the alpha spectra is performed to better determine the alpha lines intensity. Since radon emission is also influenced by meteorological parameters, it is mandatory to differentiate the changes due to the deep phenomena. Different procedures are utilized to reach the above objective: statistical analysis using the Empirical Mode Decomposition technique, the Multiple Linear Regression method and the Remote Radon Estimation by using of the thoron trend to eliminate the locally produced radon fraction. The results of such methods are compared to recognize and to highlight radon anomalies.

Analysis of alpha particles spectra of the Radon and Thoron progenies generated by an electrostatic collection detector using new software.

A complete and detailed analysis of alpha spectra from the 222Rn and 220Rn progenies was performed by newly developed software. The software identifies the alpha peaks, performs appropriate fits and calculates the net area and its uncertainty, considering the entire background. The deconvolution of the overlapped peaks of 218Po and 212Bi allows us also to evaluate their minimum detectable area. The efficiency of the electrostatic detection method was recalculated and new useful considerations on the collected alpha emitters were made.

222Rn+220Rn monitoring by alpha spectrometry.

Controlled 222Rn+220Rn mixed atmospheres have been realised introducing calibrated sources in a stainless steel chamber. An electrostatic alpha monitor internal to the chamber has been used for an accurate discrimination of alpha peaks due to the products of the two isotopes. In the chamber, different specific activities are achieved in order to test the response of the internal reference instrument and to evaluate the possible interferences due to contemporary presence of both radon isotopes. Results show that: (i) the atmospheres are very stable, (ii) the monitor is adequate for their control because the various alpha lines are well evaluated and (iii) using Tyvek® filter, the efficiency of monitor is stable and constant vs. activity.

Track counting and thickness measurement of LR115 radon detectors using a commercial image scanner.

An original optical method for track counting and film thickness determination of etched LR115 radon detectors was developed. The method offers several advantages compared with standard techniques. In particular, it is non-destructive, very simple and rather inexpensive, since it uses a commercial scanner and a free software. The complete analysis and the calibration procedure carried out for the determination of radon specific activity are reported. A comparison with the results of spark counting defines the accuracy and the precision of the new technique.

Dependence of the LR-115 radon detector calibration factor on track density.

The reliability and accuracy of the methodology based on using LR-115 track detectors for radon measurements have been studied by determining the dependence of their calibration factors on radon exposure at levels reaching 13 MBq m(-3) h. This factor results not constant and demonstrated a decreasing exponential trend vs. exposure that has been explained in terms of the saturation effect and verified using a numerical simulation. This dependence does not affect the parameter that normalizes track density vs. film thickness. This parameter results constant and equal to - 0.30±0.02 cm(-2)/µm in the 300-8000 kBq h m(-3) exposure range.

Realization and characterization of a ²²°Rn source for calibration purposes.

The recent interest for measuring (220)Rn activity in air and the following development of the corresponding measurement techniques require the improvement of standards for the calibration and characterization of the measurement devices. Due to the short half-life of the (220)Rn, the adopted techniques for the production of (222)Rn sources are not always reliable. In this paper a methodology for realizing a thoron known activity starting from a (232)Th source will be presented and discussed.

The first use of (236)U in the general environment and near a shutdown nuclear power plant.

We present a first effort to investigate (236)U in the environment near a shutdown nuclear power plant far away from highly contaminated sites, by using accelerator mass spectrometry. The detection limit of about 1pg (236)U allowed us to identify a minimal increase of the (236)U/(238)U isotopic ratio correlated to a peak of (137)Cs in river sediments downstream of the nuclear power plant, and to detect anthropogenic (236)U also upstream, where it is probably not related to the power plant but to global fallout. The (236)U content shoved variations of the (236)U/(238)U isotopic ratio in relation to the chemical-physical characteristics of the sediments. This demonstrates the potential of (236)U as an environmental tracer, and as an indicator for releases from nuclear facilities.

A radon facility at Naples University: features and first tests.

A radon calibration facility was developed at Naples University (Italy). It consists of an exposure chamber, a radon reference monitor and an apparatus suitable for radon circulation and air climatic control. The parameters that are possible to change and control are carrier gas, radon activity, gas pressure, temperature, and humidity. The characterization of the facility is actually underway to verify its reliability and stability with respect to various parameters of interest.

The influence of environmental parameters in electrostatic cell radon monitor response.

To better understand the influence of air parameters such as pressure, humidity and temperature on the counting efficiency of a radon monitor based on solid state silicon detectors and radon daughter electrostatic collection, a number of experimental and theoretical studies have been performed. This study has been carried out using a multiparameter acquisition system used to monitor radon, temperature, pressure and relative humidity. Results show that air humidity and temperature inside the cell influence radon daughter collection in a significant way. For the tested cell, a decrease of the 218Po counting efficiency vs. humidity and temperature increase was measured in the ranges from 10% to 90% and from 15 degrees C to 35 degrees C, respectively. These effects were also theoretically studied by using Monte-Carlo software, which takes into account electrostatic collection of radon daughters in the cell, by considering the recombination process as a function of climatic parameters. A satisfactory agreement was obtained between experimental measurements and theoretical calculations.