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

The analysis of multichannel airborne gamma-ray spectra

The conventional processing of airborne gamma-ray spectrometric data uses 3 broad energy windows to estimate the ground concentrations of K U and Th. This thesis investigates the potential for using the full gamma-ray spectrum in an attempt to increase the amount of information currently extracted from airborne gamma-ray data. The observed spectrum is considered as the sum of 3 terrestrial and 3 background components. Given the shapes of the component spectra, the airborne gamma-ray spectrometric inverse problem is to determine the relative contributions of the components to the observed spectrum. The component spectra are determined through suitable airborne and ground calibrations. The limitations of the component spectra have necessitated a model-based approach to multichannel fitting. The components are fit to real data, and only those energies over which a good fit is achieved are used for multichannel processing. A parametric model based on a principal component analysis of the terrestrial component spectra as functions of simulated detector height is used to find the K, U and Th terrestrial component spectra that best fit the background-corrected airborne data. The simulated heights are mapped onto actual heights using airborne calibrations over a calibration range. This enables the terrestrial component spectra to be used for the calibration of multichannel background estimation methods. The component spectra are then fit to the background-corrected observed spectra to obtain elemental count rates. This strategy ensures the best possible fit between model and data, and minimizes the propagation of statistical errors in the observations into the estimates of the elemental count rates. The analysis of multichannel spectra using this model produces 3 new parameters - the effective height of the detector above K, U and Th sources. These effective heights may be useful for regolith mapping and for refining the data processing procedures. The multichannel processing results in significant reductions in the fractional errors associated with the estimated elemental count rates. For 3 surveys processed using the new methodology, the average deviations of the K, U and Th elemental count rates from the estimated mean elemental count rates at each observation point are reduced by 12.4%, 26.5% and 20.3%, respectively, when compared to the conventional 3-channel method. This results in a better structural resolution of small anomalies in enhanced images of the processed data

Proof-of-Principle Experiment for FEL-Based Coherent Electron Cooling,”

Abstract Coherent electron cooling (CEC) has a potential to significantly boost luminosity of high-energy, highintensity hadron-hadron and electron-hadron colliders. In a CEC system, a hadron beam interacts with a cooling electron beam. A perturbation of the electron density caused by ions is amplified and fed back to the ions to reduce the energy spread and the emittance of the ion beam. To demonstrate the feasibility of CEC we propose a proof-of-principle experiment at RHIC using SRF linac. In this paper, we describe the setup for CeC installed into one of RHIC's interaction regions. We present results of analytical estimates and results of initial simulations of cooling a gold-ion beam at 40 GeV/u energy via CeC

Analysis of aqueous matrices using supercritical fluid extraction in conjunction with chromatographic, spectroscopic and mass spectometric techniques

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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