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

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%

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

Biomass water content effect on soil moisture assessment via proximal gamma-ray spectroscopy

Proximal gamma-ray spectroscopy supported by adequate calibration and correction for growing biomass is an effective field scale technique for a continuous monitoring of top soil water content dynamics to be potentially employed as a decision support tool for automatic irrigation scheduling. This study demonstrates that this approach has the potential to be one of the best space–time trade-off methods, representing a joining link between punctual and satellite fields of view. The inverse proportionality between soil moisture and gamma signal is theoretically derived taking into account a non-constant correction due to the presence of growing vegetation beneath the detector position. The gamma signal attenuation due to biomass is modelled with a Monte Carlobased approach in terms of an equivalent water layer which thickness varies in time as the crop evolves during its life-cycle. The reliability and effectiveness of this approach is proved through a 7 months continuous acquisition of terrestrial gamma radiation in a 0.4 ha tomato (Solanum lycopersicum) test field. We demonstrate that a permanent gamma station installed at an agricultural field can reliably probe the water content of the top soil only if systematic effects due to the biomass shielding are properly accounted for. Biomass corrected experimental values of soil water content inferred from radiometric measurements are compared with gravimetric data acquired under different soil moisture levels, resulting in an average percentage relative discrepancy of about 3% in bare soil condition and of 4% during the vegetated period. The temporal evolution of corrected soil water content values exhibits a dynamic range coherent with the soil hydraulic properties in terms of wilting point, field capacity and saturation

Investigating the potentialities of Monte Carlo simulation for assessing soil water content via proximal gamma-ray spectroscopy

Proximal gamma-ray spectroscopy recently emerged as a promising technique for non-stop monitoring of soil water content with possible applications in the field of precision farming. The potentialities of the method are investigated by means of Monte Carlo simulations applied to the reconstruction of gamma-ray spectra collected by a NaI scintillation detector permanently installed at an agricultural experimental site. A two steps simulation strategy based on a geometrical translational invariance is developed. The strengths of this approach are the reduction of computational time with respect to a direct source-detector simulation, the reconstruction of 40K, 232Th and 238U fundamental spectra, the customization in relation to different experimental scenarios and the investigation of effects due to individual variables for sensitivity studies. The reliability of the simulation is effectively validated against an experimental measurement with known soil water content and radionuclides abundances. The relation between soil water content and gamma signal is theoretically derived and applied to a Monte Carlo synthetic calibration performed with the specific soil composition of the experimental site. Ready to use general formulae and simulated coefficients for the estimation of soil water content are also provided adopting standard soil compositions. Linear regressions between input and output soil water contents, inferred from simulated 40K and 208Tl gamma signals, provide excellent results demonstrating the capability of the proposed method in estimating soil water content with an average uncertainty <1%

Studio della quota di volo mediante GNSS, altimetro radar e barometro per rilievi di spettroscopia gamma da velivolo

The study of the distribution of the terrestrial radionuclides (238U, 232Th e 40K), performed by using airborne gamma-ray spectroscopy techniques, is influenced by the height of the detector with respect to the ground. An uncertainty of 10% at a flight height of 100 m originates an estimation error of the order of 7% in 208Tl gamma signal, a daughter isotope of the 232Th decay chain. The use of a new class of spectrometers mounted on board of UAV (Unmanned Aerial Vehicle), for refined measurements in hostile places and boondocks, necessitates an accurate real-time estimation of the flight height. The Radgyro is an aircraft dedicated to multiparameter surveys and it is able to carry a set of instruments for a maximum payload of 120 kg, among which four NaI(Tl) gamma-ray spectrometers. An inertial station with an integrated GNSS (Global Navigation Satellite System) receiver provides the aircraft trim with a maximum frequency of 400 Hz. The aircraft is equipped with a network of three GNSS receivers positioned on the extremities of the hull of aircraft. A 24 Ghz radar altimeter detects the height with a frequency of 60 Hz. The measurement of pressure and temperature permit to infer the barometric height at 2 Hz. With the aim to study the uncertainties related to the flight height through the measurements acquired by the altimeters in comparison with the GNSS data, three flights were performed on the sea with a flight height range of 31-249 m, for a total time of 4702 seconds of effective flight. At the end of this study, we can affirm that the abundances error of K, U and Th increases of the 7.7%, 0.5% and 2.7% respectively, as a result of uncertainties related to the flight altitude