Contribución a la caracterización de aerosoles radiactivos derivados del radón

La existencia de una relación entre el riesgo a desarrollar un cáncer de pulmón y la exposición al radón y descendientes presentes en el aire se puso de manifiesto hace ya bastante tiempo en la población minera. Desde aquellas fechas se han desarrollado numerosos estudios encaminados a determinar el riesgo radiológico por unidad de exposición. En la actualidad, se pueden distinguir dos grandes vías para su evaluación: a) los estudios epidemológicos, y b) la utilización de modelos dosimétricos del sistema respiratorio. La utilización de dichas vías en la evaluación del riesgo radiológico por unidad de exposición en la población minera muestran factores de riesgo que se diferencian en un factor de 2 a 3. En la utilización de los modelos dosimétricos del sistema respiratorio, las incertidumbres que se introducen se pueden atribuir a cuatro orígenes: a) características fisico-químicas del aerosol, b) parámetros utilizados para describir el modelo dosimétrico, c) hipótesis utilizadas en las células irradiadas, y d) factores de ponderación utilizados en dosimetría.La finalidad de este trabajo de investigación ha sido la determinación de parámetros que caracterizan a los descendientes del radón de vida corta en recintos cerrados para analizar en primer lugar su comportamiento físico-químico y así mejorar la estimación del riesgo radiológico debido a su inhalación mediante la utilización de modelos dosimétricos del tracto respiratorio. Para alcanzar este fin se han puesto a punto diversas técnicas que permiten analizar, tanto en una instalación de laboratorio como en espacios habitados, el factor de equilibrio, la fracción libre y el espectro dimensional de descendientes del radón en estado libre. En referencia a los dos primeros parámetros se ha desarrollado un equipo portátil que permite realizar medidas de campo con una gran precisión. En cuanto al sistema de medida del espectro dimensional de los descendientes del radón en estado libre se ha realizado el diseño y construcción de un nuevo sistema basado en las técnicas de tubos de difusión, que presenta un gran número de mejoras respecto a otros prototipos. Con este sistema se ha establecido, en una intercomparación realizada en la cámara de radón, construida para este estudio, que el tamaño más probable del espectro dimensional de los descendientes en estado libre está comprendido entre 0.8 nm y 0.9 nm. Con el sistema de media del factor de equilibrio y la fracción libre se han llevado a cabo medidas experimentales de campo en cuatro lugares de la costa catalana. Se estableció que dicho parámetros varían de forma significativa, (0.03) y fp (0-0.72), en los distintos emplazamientos de acuerdo con sus características del lugar y su clima. que Las medidas de F y fp muestran una correlación de tipo inversa mediante una ecuación del tipo logarítmico potencial, Ln(1/fp)=1.90*(Ln(1/F))-0.68, que puede ser utilizada para todo el rango de F, en lugar de la ecuación del tipo potencial sugerida por diversos autores, que sólo se ajusta correctamente para un reducido rango de F.Los resultados de campo y de laboratorio obtenidos se han introducido en dos modelos dosimétricos del tracto respiratorio de manera a evaluar su riesgo radiológico. Estos resultados muestran que no existe un factor de dosis por unidad de exposición de radón constante sino que para una precisa estimación de dicha dosis es necesario la medida de los descendientes del radón. La mejor estimación que se ha obtenido con los modelos dosimétricos, suponiendo como valor más probable del factor de equilibrio de 0.4, es de 10 nSv por Bq m-3 h que difiere en un factor 3 respecto a los resultados epidemiológicos tal como ya se recogía en otros trabajos anteriores.The knowledge of a relationship between the probability of develop a lung cancer and the exposure to radon and radon progeny in the air has been established years ago in the miner population. From this date different studies have been developed in order to determine the radiological risk per unit exposure. Nowadays, two different ways are used for its evaluation: a) epidemiologic studies and b) the use of dosimetric models of the respiratory tract. The use of these ways shows a difference of a factor 2 -3. In the use of dosimetric models, the uncertainties arise from four origins: a) physico-chemical aerosol properties, b) parameters used in the dosimetric model, c) hypothesis in the irradiated cells and d) weighted factors used in dosimetry.The aim of this research is the evaluation of different parameters that characterise indoors short-lived radon progeny in order to analyse its physico-chemical behaviour and therefore, improve the estimation in the radiological risk evaluation using respiratory tract dosimetric models.In order to achieve this objective different systems have been developed for determining the equilibrium factor, the unattached fraction and the unattached activity size distribution. Regarding the two first parameters a portable monitor has been developed in order to measure high accuracy field measurements. A new system based in the tube diffusion technology has been developed for measuring continuously the unattached activity size distribution. Intercomparison with the aerosol group of Brest in a radon-walk-chamber developed in this work has been carried out. The most probable value for the unattached activity size distribution has been established in the range from 0.8 nm and 0.9 nm.Continuous measurements of F and fp have been carried out in four dwelling of the Mediterranean Catalan Coast. It has been established that these parameters vary widely, F(0.03-0.87) and fp (0-0.72), from one site to another and with time, according to the characteristics of the site and climate. The measurements of F and fp show that fp is negatively correlated to F by a log-power equation, Ln(1/fp)=1.90*(Ln(1/F))-0.68 , which can be used in all the F range, instead of the commonly used power equation fp=a*Fb suggested other authors, which fits well for a reduced range of F.Both, laboratory and field measurements have been introduced in two dosimetric models in order to evaluate the radiological risk. The results show that there is variability in the risk estimation per unit exposure depending on the environmental conditions and therefore, an accurate estimation of radon progeny activity concentration should be measured. The best estimation, for an equilibrium factor of 0.4, is 10 nSv per Bq m-3 h, which still differs by a factor of 3 from the epidemiological estimation

Contribución a la caracterización de aerosoles radiactivos derivados del radón

La existencia de una relación entre el riesgo a desarrollar un cáncer de pulmón y la exposición al radón y descendientes presentes en el aire se puso de manifiesto hace ya bastante tiempo en la población minera. Desde aquellas fechas se han desarrollado numerosos estudios encaminados a determinar el riesgo radiológico por unidad de exposición. En la actualidad, se pueden distinguir dos grandes vías para su evaluación: a) los estudios epidemológicos, y b) la utilización de modelos dosimétricos del sistema respiratorio. La utilización de dichas vías en la evaluación del riesgo radiológico por unidad de exposición en la población minera muestran factores de riesgo que se diferencian en un factor de 2 a 3. En la utilización de los modelos dosimétricos del sistema respiratorio, las incertidumbres que se introducen se pueden atribuir a cuatro orígenes: a) características fisico-químicas del aerosol, b) parámetros utilizados para describir el modelo dosimétrico, c) hipótesis utilizadas en las células irradiadas, y d) factores de ponderación utilizados en dosimetría.La finalidad de este trabajo de investigación ha sido la determinación de parámetros que caracterizan a los descendientes del radón de vida corta en recintos cerrados para analizar en primer lugar su comportamiento físico-químico y así mejorar la estimación del riesgo radiológico debido a su inhalación mediante la utilización de modelos dosimétricos del tracto respiratorio. Para alcanzar este fin se han puesto a punto diversas técnicas que permiten analizar, tanto en una instalación de laboratorio como en espacios habitados, el factor de equilibrio, la fracción libre y el espectro dimensional de descendientes del radón en estado libre. En referencia a los dos primeros parámetros se ha desarrollado un equipo portátil que permite realizar medidas de campo con una gran precisión. En cuanto al sistema de medida del espectro dimensional de los descendientes del radón en estado libre se ha realizado el diseño y construcción de un nuevo sistema basado en las técnicas de tubos de difusión, que presenta un gran número de mejoras respecto a otros prototipos. Con este sistema se ha establecido, en una intercomparación realizada en la cámara de radón, construida para este estudio, que el tamaño más probable del espectro dimensional de los descendientes en estado libre está comprendido entre 0.8 nm y 0.9 nm. Con el sistema de media del factor de equilibrio y la fracción libre se han llevado a cabo medidas experimentales de campo en cuatro lugares de la costa catalana. Se estableció que dicho parámetros varían de forma significativa, (0.03) y fp (0-0.72), en los distintos emplazamientos de acuerdo con sus características del lugar y su clima. que Las medidas de F y fp muestran una correlación de tipo inversa mediante una ecuación del tipo logarítmico potencial, Ln(1/fp)=1.90*(Ln(1/F))-0.68, que puede ser utilizada para todo el rango de F, en lugar de la ecuación del tipo potencial sugerida por diversos autores, que sólo se ajusta correctamente para un reducido rango de F.Los resultados de campo y de laboratorio obtenidos se han introducido en dos modelos dosimétricos del tracto respiratorio de manera a evaluar su riesgo radiológico. Estos resultados muestran que no existe un factor de dosis por unidad de exposición de radón constante sino que para una precisa estimación de dicha dosis es necesario la medida de los descendientes del radón. La mejor estimación que se ha obtenido con los modelos dosimétricos, suponiendo como valor más probable del factor de equilibrio de 0.4, es de 10 nSv por Bq m-3 h que difiere en un factor 3 respecto a los resultados epidemiológicos tal como ya se recogía en otros trabajos anteriores.The knowledge of a relationship between the probability of develop a lung cancer and the exposure to radon and radon progeny in the air has been established years ago in the miner population. From this date different studies have been developed in order to determine the radiological risk per unit exposure. Nowadays, two different ways are used for its evaluation: a) epidemiologic studies and b) the use of dosimetric models of the respiratory tract. The use of these ways shows a difference of a factor 2 -3. In the use of dosimetric models, the uncertainties arise from four origins: a) physico-chemical aerosol properties, b) parameters used in the dosimetric model, c) hypothesis in the irradiated cells and d) weighted factors used in dosimetry.The aim of this research is the evaluation of different parameters that characterise indoors short-lived radon progeny in order to analyse its physico-chemical behaviour and therefore, improve the estimation in the radiological risk evaluation using respiratory tract dosimetric models.In order to achieve this objective different systems have been developed for determining the equilibrium factor, the unattached fraction and the unattached activity size distribution. Regarding the two first parameters a portable monitor has been developed in order to measure high accuracy field measurements. A new system based in the tube diffusion technology has been developed for measuring continuously the unattached activity size distribution. Intercomparison with the aerosol group of Brest in a radon-walk-chamber developed in this work has been carried out. The most probable value for the unattached activity size distribution has been established in the range from 0.8 nm and 0.9 nm.Continuous measurements of F and fp have been carried out in four dwelling of the Mediterranean Catalan Coast. It has been established that these parameters vary widely, F(0.03-0.87) and fp (0-0.72), from one site to another and with time, according to the characteristics of the site and climate. The measurements of F and fp show that fp is negatively correlated to F by a log-power equation, Ln(1/fp)=1.90*(Ln(1/F))-0.68 , which can be used in all the F range, instead of the commonly used power equation fp=a*Fb suggested other authors, which fits well for a reduced range of F.Both, laboratory and field measurements have been introduced in two dosimetric models in order to evaluate the radiological risk. The results show that there is variability in the risk estimation per unit exposure depending on the environmental conditions and therefore, an accurate estimation of radon progeny activity concentration should be measured. The best estimation, for an equilibrium factor of 0.4, is 10 nSv per Bq m-3 h, which still differs by a factor of 3 from the epidemiological estimation.Postprint (published version

Comparison of methods for H*(10) calculation from measured LaBr3(Ce) detector spectra

The Universitat Politecnica de Catalunya (UPC) and the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) have evaluated methods based on stripping, conversion coefficients and Maximum Likelihood Estimation using Expectation Maximization (ML-EM) in calculating the H*(10) rates from photon pulse-height spectra acquired with a spectrometric LaBr3(Ce)(1.5¿ × 1.5¿) detector. There is a good agreement between results of the different H*(10) rate calculation methods using the spectra measured at the UPC secondary standard calibration laboratory in Barcelona. From the outdoor study at ESMERALDA station in Madrid, it can be concluded that the analysed methods provide results quite similar to those obtained with the reference RSS ionization chamber. In addition, the spectrometric detectors can also facilitate radionuclide identification.Postprint (author's final draft

Dose calculations in aircrafts after Fukushima nuclear power plant accident – Preliminary study for aviation operations

There is little information to decision support in air traffic management in case of nuclear releases into the atmosphere. In this paper, the dose estimation due to both, external exposure (i.e. cloud immersion, deposition inside and outside the aircraft), and due to internal exposure (i.e, inhalation of radionuclides inside the aircraft) to passengers and crew is calculated for a worst-case emergency scenario. The doses are calculated for different radionuclides and activities. Calculations are mainly considered according to International Commission on Radiological Protection (ICRP) recommendations and Monte Carlo simulations. In addition, a discussion on potential detectors installed inside the aircraft for monitoring the aerosol concentration and the ambient dose equivalent rate, H*(10), for during-flight monitoring and early warning is provided together with the evaluation of a response of a generic detector. The results show that the probability that a catastrophic nuclear accident would produce significant radiological doses to the passengers and crew of an aircraft is very low. In the worst-case scenarios studied, the maximum estimated effective dose was about 1¿mSv during take-off or landing operations, which is the recommended yearly threshold for the public. However, in order to follow the ALARA (As Low As Reasonably Achievable) criteria and to avoid aircraft contamination, the installation of radiological detectors is considered. This would, on one hand help the pilot or corresponding decision maker to decide about the potential change of the route and, on the other, allow for gathering of 4D data for future studiesPostprint (published version

Intercomparison study of atmospheric 222Rn and 222Rn progeny monitors

The use of the noble gas radon (222Rn) as a tracer for different research studies, for example observation-based estimation of greenhouse gas (GHG) fluxes, has led to the need of high-quality 222Rn activity concentration observations with high spatial and temporal resolution. So far a robust metrology chain for these measurements is not yet available. A portable direct atmospheric radon monitor (ARMON), based on electrostatic collection of 218Po, is now running at Spanish stations. This monitor has not yet been compared with other 222Rn and 222Rn progeny monitors commonly used at atmospheric stations. A 3-month intercomparison campaign of atmospheric 222Rn and 222Rn progeny monitors based on different measurement techniques was realized during the fall and winter of 2016–2017 to evaluate (i) calibration and correction factors between monitors necessary to harmonize the atmospheric radon observations and (ii) the dependence of each monitor's response in relation to the sampling height and meteorological and atmospheric aerosol conditions. Results of this study have shown the following. (i) All monitors were able to reproduce the atmospheric radon variability on a daily basis. (ii) Linear regression fits between the monitors exhibited slopes, representing the correction factors, between 0.62 and 1.17 and offsets ranging between -0.85 and -0.23¿Bq¿m-3 when sampling 2¿m above ground level (a.g.l.). Corresponding results at 100¿m¿a.g.l. exhibited slopes of 0.94 and 1.03 with offsets of -0.13 and 0.01¿Bq¿m-3, respectively. (iii) No influence of atmospheric temperature and relative humidity on monitor responses was observed for unsaturated conditions at 100¿m¿a.g.l., whereas slight influences (order of 10-2) of ambient temperature were observed at 2¿m¿a.g.l. (iv) Changes in the ratio between 222Rn progeny and 222Rn monitor responses were observed under very low atmospheric aerosol concentrations. Results also show that the new ARMON could be useful at atmospheric radon monitoring stations with space restrictions or as a mobile reference instrument to calibrate in situ 222Rn progeny monitors and fixed radon monitors. In the near future a long-term comparison study between ARMON, HRM, and ANSTO monitors would be useful to better evaluate (i) the uncertainties of radon measurements in the range of a few hundred millibecquerels per cubic meter to a few becquerels per cubic meter and (ii) the response time correction of the ANSTO monitor for representing fast changes in the ambient radon concentrations.Postprint (published version

Variability of methane fluxes at the Ebro Delta due to rice field: comparison between inventories and Radon Tracer Method based results.

The Ebro River Delta, in the northwestern Mediterranean basin, has an extension of 320 km2 and is mainly covered by rice fields. Rice fields are known to be one of the main sources of anthropogenic methane emissions, and a better estimation of its temporal variability in relation to the different rice cultivation phases is important to help with the implementation of emission reduction strategies (Àgueda et al., 2017), In the framework of the ClimaDat network, an atmospheric station was installed in the middle of the Ebro Delta in 2012. A Picarro G2301 for greenhouse gases (GHG) atmospheric concentrations and an ARMON (Atmospheric Radon Monitor) for atmospheric 222Rn concentrations were collocated among other instruments. Nocturnal hourly atmospheric observations of CH4 and 222Rn measured between 2013 and 2019 were used to apply the Radon Tracer Method (RTM) for retrieving CH4 fluxes over the footprint area. The Ebro River Delta has a reduced dimension and a complex meteorological regime highly influenced by the Ebro channelled winds and the sea breezes, making it difficult to calculate GHG fluxes using global or regional inversion models. However, the use of high-resolution backtrajectories (model WRF-Flexpart) coupled with the traceRadon daily radon flux maps for Europe (Karsten et al., 2022), with a resolution of 0.05 degrees, has allowed the use of the RTM in this complex area. Methane fluxes estimated by RTM were compared with fluxes directly measured with chambers in past studies (Martínez-Eixarch et al., 2018) and with data obtained by the EDGAR inventory (Crippa et al., 2022). Results show a promising agreement between methane fluxes obtained with different methods, and a variability clearly governed by the rice crop cycle which is not reflected in the methane emissions values reported in EDGAR inventories.Peer ReviewedPostprint (published version

Metrology for low-cost CO2 sensors applications: the case of a steady-state through-flow (SS-TF) chamber for CO2 fluxes observations

Soil CO2 emissions are one of the largest contributions to the global carbon cycle, and a full understanding of processes generating them and how climate change may modify them is needed and still uncertain. Thus, a dense spatial and temporal network of CO2 flux measurements from soil could help reduce uncertainty in the global carbon budgets. In the present study, the design, assembly, and calibration of low-cost air enquirer kits, including CO2 and environmental parameters sensors, is presented. Different types of calibrations for the CO2 sensors and their associated errors are calculated. In addition, for the first time, this type of sensor has been applied to design, develop, and test a new steady-state through-flow (SS-TF) chamber for simultaneous measurements of CO2 fluxes in soil and CO2 concentrations in air. The sensors’ responses were corrected for temperature, relative humidity, and pressure conditions in order to reduce the uncertainty in the measured CO2 values and of the following calculated CO2 fluxes based on SS-TF. CO2 soil fluxes measured by the proposed SS-TF and by a standard closed non-steady-state non-through-flow (NSS-NTF) chamber were briefly compared to ensure the reliability of the results. The use of a multiparametric fitting reduced the total uncertainty of the CO2 concentration measurements by 62 %, compared with the uncertainty that occurred when a simple CO2 calibration was applied, and by 90 %, when compared to the uncertainty declared by the manufacturer. The new SSTF system allows the continuous measurement of CO2 fluxes and CO2 ambient air with low cost (EUR ~ 1200), low energy demand (< 5 W), and low maintenance (twice per year due to sensor calibration requirements).Peer ReviewedPostprint (published version

An unmanned aircraft system to detect a radiological point source using RIMA software architecture

Unmanned Aircraft Systems (UASs), together with the miniaturisation of computers, sensors, and electronics, offer new remote sensing applications. However, there is a lack of hardware and software support to effectively develop the potential of UASs in different remote sensing applications, such as the detection of radioactive sources. This paper presents the design, development and validation of a UAS for the detection of an uncontrolled and point radioactive source. The article describes a flexible and reusable software architecture for detecting the radioactive source (NaTcO 4 , containing 99m Tc) with a gamma-ray Cadmium Zinc Telluride (CZT) spectrometer as a proof of concept. The UAS is equipped with multichannel air-ground communications to perform missions beyond line of sight and onboard computation to process samples in real time and thus react to any anomaly detected during the mission. An ad hoc ground control station (GCS) has also been developed for the correct interpretation of the radioactive samples taken by the UAS. Radiological spectra plots, contour mapping and waterfall plots are some of the elements used in the ad hoc GCS. The article shows the results obtained in a flight campaign performing different flights at different altitudes and speeds over the radiological source, demonstrating the viability of the system.Peer ReviewedPostprint (published version

REFLECT – Research flight of EURADOS and CRREAT: Intercomparison of various radiation dosimeters onboard aircraft

Aircraft crew are one of the groups of radiation workers which receive the highest annual exposure to ionizing radiation. Validation of computer codes used routinely for calculation of the exposure due to cosmic radiation and the observation of nonpredictable changes in the level of the exposure due to solar energetic particles, requires continuous measurements onboard aircraft. Appropriate calibration of suitable instruments is crucial, however, for the very complex atmospheric radiation field there is no single reference field covering all particles and energies involved. Further intercomparisons of measurements of different instruments under real flight conditions are therefore indispensable. In November 2017, the REFLECT (REsearch FLight of EURADOS and CRREAT) was carried out. With a payload comprising more than 20 different instruments, REFLECT represents the largest campaign of this type ever performed. The instruments flown included those already proven for routine dosimetry onboard aircraft such as the Liulin Si-diode spectrometer and tissue equivalent proportional counters, as well as newly developed detectors and instruments with the potential to be used for onboard aircraft measurements in the future. This flight enabled acquisition of dosimetric data under well-defined conditions onboard aircraft and comparison of new instruments with those routinely used. As expected, dosimeters routinely used for onboard aircraft dosimetry and for verification of calculated doses such as a tissue equivalent proportional counter or a silicon detector device like Liulin agreed reasonable with each other as well as with model calculations. Conventional neutron rem counters underestimated neutron ambient dose equivalent, while extended-range neutron rem counters provided results comparable to routinely used instruments. Although the responses of some instruments, not primarily intended for the use in a very complex mixed radiation field such as onboard aircraft, were as somehow expected to be different, the verification of their suitability was one of the objectives of the REFLECT. This campaign comprised a single short flight. For further testing of instruments, additional flights as well as comparison at appropriate reference fields are envisaged. The REFLECT provided valuable experience and feedback for validation of calculated aviation doses.Postprint (published version

Metrology for the mobile detection of ionising radiation following a nuclear or radiological incident - “Preparedness”

Postprint (published version