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Register a new userExploring atmospheric radon with airborne gamma-ray spectroscopy
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$^{222}$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.
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In this paper we present the results of a $sim$5 hour airborne gamma-ray survey carried out over the Tyrrhenian sea in which the height range (77-3066) m has been investigated. Gamma-ray spectroscopy measurements have been performed by using the AGRS_16L detector, a module of four 4L NaI(Tl) crystals. The experimental setup was mounted on the Radgyro, a prototype aircraft designed for multisensorial acquisitions in the field of proximal remote sensing. 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 it has been possible to split the measured count rate into a constant aircraft component and a cosmic component exponentially increasing with increasing height. The monitoring of the count rate having pure cosmic origin in the >3 MeV energy region allowed to infer the background count rates in the $^{40}$K, $^{214}$Bi and $^{208}$Tl photopeaks, which need to be subtracted in processing airborne gamma-ray data in order to estimate the potassium, uranium and thorium abundances in the ground. Moreover, a calibration procedure has been carried out by implementing the CARI-6P and EXPACS dosimetry tools, according to which the annual cosmic effective dose to human population has been linearly related to the measured cosmic count rates.
Based on cosmological rates, it is probable that at least once in the last Gy the Earth has been irradiated by a gamma-ray burst in our Galaxy from within 2 kpc. Using a two-dimensional atmospheric model we have performed the first computation of the effects upon the Earths atmosphere of one such impulsive event. A ten second burst delivering 100 kJ/m^2 to the Earth penetrates to the stratosphere and results in globally averaged ozone depletion of 35%, with depletion reaching 55% at some latitudes. Significant global depletion persists for over 5 years after the burst. This depletion would have dramatic implications for life since a 50% decrease in ozone column density results in approximately three times the normal UVB flux. Widespread extinctions are likely, based on extrapolation from UVB sensitivity of modern organisms. Additional effects include a shot of nitrate fertilizer and NO2 opacity in the visible providing a cooling perturbation to the climate over a similar timescale. These results lend support to the hypothesis that a GRB may have initiated the late Ordovician mass extinction (Melott et al. 2004).
Gamma-Ray Bursts (GRBs) are likely to have made a number of significant impacts on the Earth during the last billion years. We have used a two-dimensional atmospheric model to investigate the effects on the Earths atmosphere of GRBs delivering a range of fluences, at various latitudes, at the equinoxes and solstices, and at different times of day. We have estimated DNA damage levels caused by increased solar UVB radiation, reduction in solar visible light due to $mathrm{NO_2}$ opacity, and deposition of nitrates through rainout of $mathrm{HNO_3}$. For the ``typical nearest burst in the last billion years, we find globally averaged ozone depletion up to 38%. Localized depletion reaches as much as 74%. Significant global depletion (at least 10%) persists up to about 7 years after the burst. Our results depend strongly on time of year and latitude over which the burst occurs. We find DNA damage of up to 16 times the normal annual global average, well above lethal levels for simple life forms such as phytoplankton. The greatest damage occurs at low to mid latitudes. We find reductions in visible sunlight of a few percent, primarily in the polar regions. Nitrate deposition similar to or slightly greater than that currently caused by lightning is also observed, lasting several years. We discuss how these results support the hypothesis that the Late Ordovician mass extinction may have been initiated by a GRB.
We report results of air monitoring started due to the recent natural catastrophe on 11 March 2011 in Japan and the severe ensuing damage to the Fukushima Dai-ichi nuclear reactor complex. On 17-18 March 2011, we registered the first arrival of the airborne fission products 131-I, 132-I, 132-Te, 134-Cs, and 137-Cs in Seattle, WA, USA, by identifying their characteristic gamma rays using a germanium detector. We measured the evolution of the activities over a period of 23 days at the end of which the activities had mostly fallen below our detection limit. The highest detected activity amounted to 4.4 +/- 1.3 mBq/m^3 of 131-I on 19-20 March.
Since the formation of the terrestrial planets, atmospheric loss has irreversibly altered their atmospheres, leading to remarkably different surface environments - Earth has remained habitable while Venus and Mars are apparently desolate. The concept of habitability centres around the availability of liquid water which depends greatly on the composition of the atmosphere. While the history of molecular oxygen O$_2$ in Earths atmosphere is debated, geological evidence supports at least two major episodes of increasing oxygenation: the Great Oxidation Event and the Neoproterozoic Oxidation Event. Both are thought to have been pivotal for the development and evolution of life. We demonstrate through three-dimensional simulations that atmospheric O$_2$ concentrations on Earth directly control the evolution and distribution of greenhouse gases (such as O$_3$, H$_2$O, CH$_4$ and CO$_2$) and the atmospheric temperature structure. In particular, at $leq 1$% the present atmospheric level (PAL) of O$_2$, the stratosphere collapses. Our simulations show that a biologically ineffective ozone shield, lower than previously thought, existed during the Proterozoic, with a need for a Phanerozoic ozone shield to allow the emergence of surface life. We find that O$_2$ acts as a valve for the loss rate of atmospheric hydrogen through the exosphere. Estimated levels of hydrogen escape for the Proterozoic eon are all lower than present day, enabling us to establish Earths water loss timeline. Furthermore, we demonstrate how O$_2$ on terrestrial exoplanets determines their theoretical transmission spectra, challenging signal-to-nose ratio assumptions contributing to the design of next generation telescopes that will facilitate the characterisation of Earth-like worlds.
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