Exploring atmospheric radon with airborne gamma-ray spectroscopy

$^{222}$Rn is a noble radioactive gas produced along the $^{238}$U decay chain, which is present in the majority of soils and rocks. As $^{222}$Rn is the most relevant source of natural background radiation, understanding its distribution in the environment is of great concern for investigating the health impacts of low-level radioactivity and for supporting regulation of human exposure to ionizing radiation in modern society. At the same time, $^{222}$Rn is a widespread atmospheric tracer whose spatial distribution is generally used as a proxy for climate and pollution studies. Airborne gamma-ray spectroscopy (AGRS) always treated $^{222}$Rn as a source of background since it affects the indirect estimate of equivalent $^{238}$U concentration. In this work the AGRS method is used for the first time for quantifying the presence of $^{222}$Rn in the atmosphere and assessing its vertical profile. High statistics radiometric data acquired during an offshore survey are fitted as a superposition of a constant component due to the experimental setup background radioactivity plus a height dependent contribution due to cosmic radiation and atmospheric $^{222}$Rn. The refined statistical analysis provides not only a conclusive evidence of AGRS $^{222}$Rn detection but also a (0.96 $\pm$ 0.07) Bq/m$^{3}$ $^{222}$Rn concentration and a (1318 $\pm$ 22) m atmospheric layer depth fully compatible with literature data.Comment: 17 pages, 8 figures, 2 table

Training Future Engineers to Be Ghostbusters: Hunting for the Spectral Environmental Radioactivity

Although environmental radioactivity is all around us, the collective public imagination often associates a negative feeling to this natural phenomenon. To increase the familiarity with this phenomenon we have designed, implemented, and tested an interdisciplinary educational activity for pre-collegiate students in which nuclear engineering and computer science are ancillary to the comprehension of basic physics concepts. Teaching and training experiences are performed by using a 4" x 4" NaI(Tl) detector for in-situ and laboratory {\gamma}-ray spectroscopy measurements. Students are asked to directly assemble the experimental setup and to manage the data-taking with a dedicated Android app, which exploits a client-server system that is based on the Bluetooth communication protocol. The acquired {\gamma}-ray spectra and the experimental results are analyzed using a multiple-platform software environment and they are finally shared on an open access Web-GIS service. These all-round activities combining theoretical background, hands-on setup operations, data analysis, and critical synthesis of the results were demonstrated to be effective in increasing students' awareness in quantitatively investigating environmental radioactivity. Supporting information to the basic physics concepts provided in this article can be found at http://www.fe.infn.it/radioactivity/educational

Modelling soil water conent in a tomato field: proximal gamma ray spectroscopy and soil-crop system models

Proximal soil sensors are taking hold in the understanding of soil hydrogeological processes involved in precision agriculture. In this context, permanently installed gamma ray spectroscopy stations represent one of the best space-time trade off methods at field scale. This study proved the feasibility and reliability of soil water content monitoring through a seven-month continuous acquisition of terrestrial gamma radiation in a tomato test field. By employing a 1 L sodium iodide detector placed at a height of 2.25 m, we investigated the gamma signal coming from an area having a ~25 m radius and from a depth of approximately 30 cm. Experimental values, inferred after a calibration measurement and corrected for the presence of biomass, were corroborated with gravimetric data acquired under different soil moisture conditions, giving an average absolute discrepancy of about 2%. A quantitative comparison was carried out with data simulated by AquaCrop, CRITeRIA, and IRRINET soil-crop system models. The different goodness of fit obtained in bare soil condition and during the vegetated period highlighted that CRITeRIA showed the best agreement with the experimental data over the entire data-taking period while, in presence of the tomato crop, IRRINET provided the best results.Comment: 18 pages, 9 Figures, 3 Table

Accuracy of flight altitude measured with low-cost GNSS, radar and barometer sensors: Implications for airborne radiometric surveys

Flight height is a fundamental parameter for correcting the gamma signal produced by terrestrial radionuclides measured during airborne surveys. The frontiers of radiometric measurements with UAV require light and accurate altimeters flying at some 10 m from the ground. We equipped an aircraft with seven altimetric sensors (three low-cost GNSS receivers, one inertial measurement unit, one radar altimeter and two barometers) and analyzed ~3 h of data collected over the sea in the (35–2194) m altitude range. At low altitudes (H 80 m in terms of both altitude median standard deviation and agreement between the reconstructed and measured GPS antennas distances. Flying at 100 m the estimated uncertainty on the ground total activity due to the uncertainty on the flight height is of the order of 2%

Atmospheric Radon in a marine environment: a novel approach based on airborne gamma-ray spectroscopy

222Rn is a naturally occurring noble gas produced via alpha decay of 226Ra and it is the only gaseous daughter product of the decay chain of 238U, a radioisotope present in the majority of soils and rocks. 222Rn is almost chemically inert, it exhales into the atmosphere and migrates by diffusion and convection: as it runs out mainly through radioactive decay characterized by a 3.82 days half-life, it is a widespread atmospheric tracer, particularly effective for gathering insights into air vertical mixing processes in the atmospheric boundary layer. Understanding 222Rn distribution in the environment is also of great concern for investigating the health impacts of low-level radioactivity and for supporting regulation of human exposure to ionizing radiation in modern society. Airborne Gamma-Ray Spectroscopy (AGRS) always treated 222Rn as a source of background: its decay product 214Bi is the main gamma-emitter in the 238U decay chain and, since it binds to airborne aerosols, it is responsible for the measured radon background. For the first time we exploit the AGRS method for quantifying the presence of 222Rn in the atmosphere and assessing its vertical profile. AGRS measurements have been performed in the (70 – 3000) m altitude range during a ~4 hours survey over the Tyrrhenian sea. The experimental setup, made up of four 4L NaI(Tl) crystals, was mounted on the Radgyro, a prototype aircraft designed for multisensorial acquisitions in the field of proximal remote sensing. A theoretical model accounting for the presence of atmospheric 222Rn has been developed in order to reconstruct experimental radiometric data over the entire altitude range: the overall count rate recorded in the 214Bi photopeak is fitted as a superposition of a constant component due to the radioactivity of the aircraft and of the equipment plus a height dependent contribution due to cosmic radiation and atmospheric 222Rn. Modeling the latter component requires a radon vertical profile, which is in turn directly connected with the dynamics of the atmospheric boundary layer. Thanks to the large elevation extent, it has been possible to explore the presence of radon in the atmosphere via the modeling of the count rate in the 214Bi photopeak energy window according to two analytical models which respectively exclude and account for the presence of atmospheric radon. The refined statistical analysis provides not only a conclusive evidence of AGRS 222Rn detection but also a (0.96 ± 0.07) Bq/m^3 222Rn concentration and a (1318 ± 22) m atmospheric layer depth fully compatible with literature data

Cosmic radiation in the lower atmosphere with airborne gamma-ray spectroscopy

The frontiers of Airborne Gamma-Ray Spectroscopy (AGRS) are continuously pushed forward thanks to the development of innovative instrumentation and to advances in data analysis and interpretation. The employment of new unmanned aerial vehicles, together with the need for real-time identification of anthropogenic radionuclides for homeland security purposes, are reawakening the interest in detectors efficiencies and minimum detectable activities, which can be estimated provided an adequate understanding of the background contributions. In this context, cosmic radiation is an ever-present spectral component whose characterization can supply significant insights to multiple disciplines (e.g. environmental contamination assessment, radioprotection). For the first time a dedicated offshore AGRS survey of ~5 hour has been performed in the (70 – 3000) m altitude range with the specific objective of answering the following questions: 1) how can an AGRS detector be calibrated for the cosmic background signal? 2) what is the shape of a gamma-ray cosmic spectrum in the (0.8 – 7) MeV energy range? 3) is it possible to calibrate an AGRS detector for the electromagnetic shower component of the cosmic effective dose by means of dosimetry software? By acquiring high-statistics spectra over the sea (i.e. in the absence of signals having geological origin) and by spanning a wide spectrum of altitudes we can split the constant contribution coming from the radioactivity of the aircraft from the height dependent contributions associated with cosmic radiation and with atmospheric radon. A statistical analysis provided the parameters that linearly relate the count rates in the 40K, 214Bi and 208Tl photopeaks with the count rate recorded in the (3 – 7) MeV energy window in which no event coming from terrestrial radioactivity is expected. By applying the obtained linear relations it is possible to calculate for every spectrum the background count rates that need to be subtracted in order to estimate the K, eU and eTh abundances in the ground. This approach also provides additional constraints in the < 3 MeV energy range for the fitting of the polynomial energy dependence of the gamma cosmic spectral shape. Moreover, the AGRS detector has been calibrated for the electromagnetic shower component of the cosmic effective dose (CED^EMS) to human population by using as calibrating reference dose rate values obtained separately with the CARI-6P and the EXPACS (EXcel-based Program for calculating Atmospheric Cosmic Ray Spectrum) dosimetry software. The relation between the count rate in the (3 – 7) MeV energy window and the CED^EMS has been found to be linear. Although this approach is clearly model dependent, the results are in agreement at ~10% level, similarly to accuracies obtained with traditional approaches

Filling the gap between punctual and satellite soil moisture measurements through proximal gamma-ray spectroscopy

Filling the gap between punctual (∼cm^2) and catchment (∼10 ha) soil moisture measurements is an urgent open issue that recently boosted the development of nuclear based monitoring techniques hinging on the detection of cosmic-ray neutrons and gamma-rays. Indeed, despite the increasing number of satellite missions and the growing availability of open access satellite images repositories, calibration ground-truth measurements are required for a comprehensive interpretation of hyperspectral data. The fate of the sparse and sporadic punctual measurements performed with electromagnetic and gravimetric methods is to be overcome by innovative technologies for a non-invasive, contactless and continuous monitoring of soil moisture at field scale. In this scenario, proximal gamma-ray spectroscopy is identified as a promising tool for a full exploitation of high quality satellite data, with the perspective of realizing tangible applications in the field of sustainable agriculture, threatened by relentless effects due to climate changes. The terrestrial gamma signal measured with a spectrometer installed at a few meters above the ground is inversely correlated with soil water content and is basically insensitive to variations in cosmic radiation and soil chemical composition. With a dedicated experiment carried out in a tomato agricultural test field, we hourly collected gamma-ray spectra over a period of 7 months covering the entire crop growing season. We obtained reliable non-stop estimates of top soil (∼ 30 cm) moisture levels with a ∼2·10^3 m^2 footprint by calibrating and correcting with a Monte Carlo based approach the gamma signal due to the naturally occurring potassium radioisotope (40K) detected during the entire crop season. Proximal gamma-ray spectroscopy with permanent stations is one of the best space-time trade-off methods which can provide accurate time series of soil moisture, concurrently minimizing time costs and manpower thanks to the employment of real-time and remotely controlled sensors. This proof of concept experiment demonstrates that networks of proximal gamma-ray spectroscopy stations can potentially fulfill the spatiotemporal requirements for the calibration of satellite observations, as well as provide a support decision tool for a rational use of water resources

Challenges, solutions and benefits of natural radioactivity mapping

The spatial interpolation of punctual radiometric data for the realization of natural radioactivity maps poses several challenges associated to the integration of information referred to different measurement techniques, measurement errors, detectors’ field of view and morphological features. Indeed, the elaboration of a unique cartographic product with an appropriate descriptive legend from laboratory, in-situ and airborne gamma-ray spectroscopy data cannot be pursued without critically dealing with some delicate issues. Gamma ray surveys allow for monitoring the spatial distribution of terrestrial radioelements (K, U and Th) and in turn provide valuable insights on geological mapping, structural geology and soil surveying. The high efficiency and relatively good spectral resolution make Sodium Iodide (NaI) detectors particularly suitable for real-time insitu and airborne measurements, respectively characterized by a spatial footprint of ∼m^2 and ∼10^5 m^2. On the other hand, Hyper Pure Germanium (HPGe) detectors, thanks to the optimal spectral resolution combined with low radiation background, are ideal for achieving very low uncertainties in gamma-ray measurements performed in laboratory on rock and soil samples. We dealt with these problematic aspects proposing operative solutions regarding the statistical treatment of analyzed datasets, the heterogeneous experimental uncertainties and the spatial resolution of the measurements. The results obtained from the rigorous study of statistical distributions and the spatial correlation were integrated based on appropriated geostatistical interpolators. Taking on the challenge to treat heterogeneous input uncertainties data, the degree of confidence associated with two different gamma-ray techniques is considered, giving value to the spatial data represented in the map. Multivariate spatial interpolation enhances the estimation of radioelements distribution taking advantage of the correlation existing between the under-sampled gamma-ray measurements and the continuous distributions of geological formations. The described methods were validated through several surveys that cover approximately 50000 km^2 of the Italian territory: specific case studies will be presented and discussed

Radon daughters rain-induced activity

Abstract not availabl

Airborne gamma-ray spectrometry for investigating radon vertical profile

222Rn gas has always been recognized as a sizable source of systematic uncertainty for the estimation of terrestrial 238U concentration by means of Airborne Gamma-Ray Spectroscopy (AGRS) measurements. 238U ground abundance is conventionally retrieved by monitoring the 1765 keV Energy Window (BEW) associated to the decay of 214Bi, a daughter isotope that occurs after 222Rn in the 238U decay series. This prevents to distinguish the gamma signal generated by 214Bi in the ground from the one emitted by 214Bi attached to airborne aerosols and produced after the decay of 222Rn exhaled into the atmosphere. A deep interest exists in understating the 222Rn distribution as it has implications in tracing air vertical mixing processes, studying the dynamics of the atmospheric boundary layer and investigating health impacts of human exposure to low-level ionizing radiation. We present the results of a dedicated off-shore AGRS campaign which led to the acquisition of 14688 1-second radiometric measurements performed in the (70 – 3000) m altitude range with a 16L NaI(Tl) detector. Experimental data were tested against a theoretical model describing the overall count rate recorded in the BEW (nBEW) as a superposition of a constant component due to the radioactivity of the aircraft plus a height dependent contribution due to cosmic radiation and atmospheric 222Rn. The altitude profile of the 222Rn component of the nBEW outlines the combination of a detector field of view effect, reflecting the 1765 keV photon mean free path in air (~ 175 m), and of the vertical distribution of 222Rn itself. The latter has been modeled as a single air layer extending up to a cutoff altitude s and having uniform 222Rn concentration aRn located at the bottom of a radon-free layer. Thanks to the large flight altitude range covered during the data taking and to the adoption of a refined χ2 based statistical analysis we obtained not only a conclusive evidence of AGRS 222Rn detection but also a 222Rn concentration aRn = (0.96 ± 0.07) Bq/m^3 and an atmospheric layer depth s = (1318 ± 22) m fully compatible with literature data