21 research outputs found
Exploring atmospheric radon with airborne gamma-ray spectroscopy
Rn is a noble radioactive gas produced along the U decay
chain, which is present in the majority of soils and rocks. As 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,
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 Rn as a source of background since
it affects the indirect estimate of equivalent U concentration. In this
work the AGRS method is used for the first time for quantifying the presence of
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 Rn. The refined statistical analysis provides not only a
conclusive evidence of AGRS Rn detection but also a (0.96 0.07)
Bq/m Rn concentration and a (1318 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
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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