Expected geoneutrino signal at JUNO

Constraints on the Earth's composition and on its radiogenic energy budget come from the detection of geoneutrinos. The KamLAND and Borexino experiments recently reported the geoneutrino flux, which reflects the amount and distribution of U and Th inside the Earth. The KamLAND and Borexino experiments recently reported the geoneutrino flux, which reflects the amount and distribution of U and Th inside the Earth. The JUNO neutrino experiment, designed as a 20 kton liquid scintillator detector, will be built in an underground laboratory in South China about 53 km from the Yangjiang and Taishan nuclear power plants. Given the large detector mass and the intense reactor antineutrino flux, JUNO aims to collect high statistics antineutrino signals from reactors but also to address the challenge of discriminating the geoneutrino signal from the reactor background.The predicted geoneutrino signal at JUNO is 39.7 $^{+6.5}_{-5.2}$ TNU, based on the existing reference Earth model, with the dominant source of uncertainty coming from the modeling of the compositional variability in the local upper crust that surrounds (out to $\sim$ 500 km) the detector. A special focus is dedicated to the 6{\deg} x 4{\deg} Local Crust surrounding the detector which is estimated to contribute for the 44% of the signal. On the base of a worldwide reference model for reactor antineutrinos, the ratio between reactor antineutrino and geoneutrino signals in the geoneutrino energy window is estimated to be 0.7 considering reactors operating in year 2013 and reaches a value of 8.9 by adding the contribution of the future nuclear power plants. In order to extract useful information about the mantle's composition, a refinement of the abundance and distribution of U and Th in the Local Crust is required, with particular attention to the geochemical characterization of the accessible upper crust.Comment: Slight changes and improvements in the text,22 pages, 4 Figures, 3 Tables. Prog. in Earth and Planet. Sci. (2015

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

Perceiving the crust in 3D: a model integrating geological, geochemical, and geophysical data

Regional characterization of the continental crust has classically been performed through either geologic mapping, geochemical sampling, or geophysical surveys. Rarely are these techniques fully integrated, due to limits of data coverage, quality, and/or incompatible datasets. We combine geologic observations, geochemical sampling, and geophysical surveys to create a coherent 3-D geologic model of a 50 x 50 km upper crustal region surrounding the SNOLAB underground physics laboratory in Canada, which includes the Southern Province, the Superior Province, the Sudbury Structure and the Grenville Front Tectonic Zone. Nine representative aggregate units of exposed lithologies are geologically characterized, geophysically constrained, and probed with 109 rock samples supported by compiled geochemical databases. A detailed study of the lognormal distributions of U and Th abundances and of their correlation permits a bivariate analysis for a robust treatment of the uncertainties. A downloadable 3D numerical model of U and Th distribution defines an average heat production of 1.5$^{+1.4}_{-0.7}$$\mu$W/m$^{3}$, and predicts a contribution of 7.7$^{+7.7}_{-3.0}$TNU (a Terrestrial Neutrino Unit is one geoneutrino event per 10$^{32}$ target protons per year) out of a crustal geoneutrino signal of 31.1$^{+8.0}_{-4.5}$TNU. The relatively high local crust geoneutrino signal together with its large variability strongly restrict the SNO+ capability of experimentally discriminating among BSE compositional models of the mantle. Future work to constrain the crustal heat production and the geoneutrino signal at SNO+ will be inefficient without more detailed geophysical characterization of the 3D structure of the heterogeneous Huronian Supergroup, which contributes the largest uncertainty to the calculation.Comment: 25 pages, 9 figures, 6 table

A century of oil and gas exploration in Albania: assessment of Naturally Occurring Radioactive Materials (NORMs)

Because potential Naturally Occurring Radioactive Materials (NORMs) generated from oil and gas extractions in Albania have been disposed without regulatory criteria in many decades, an extensive survey in one of the most productive regions (Vlora-Elbasan) has been performed. Among 52 gamma-ray spectrometry measurements of soil, oil-sand, sludge, produced water and crude oil samples, we discover that relatively low activity concentrations of 226Ra, 228Ra, 228Th and 40K, which are 23 +/- 2 Bq/kg, 23 +/- 2 Bq/kg, 24 +/- 3 Bq/kg and 549 +/- 12 Bq/kg, respectively, come from oil-sand produced by hydrocarbon extraction from molasses formations. The mineralogical characterization together with the 228Ra/40K and 226Ra/40K ratios of these Neogene deposits confirm the geological and geodynamic model that predicts a dismantling of Mesozoic source rocks. The average activity concentrations (+/- standard deviations) of the radium isotopes (226Ra, 228Ra) and of the 228Th and 40K radionuclides in soil samples are determined to be 20 +/- 5 Bq/kg, 25 +/- 10 Bq/kg, 25 +/- 9 Bq/kg and 326 +/- 83 Bq/kg, respectively. Based on these arguments, the future radiological assessment of other fields in the region can be strategically planned focusing on the oil-sands from molasses sediments. No disequilibrium in the 228Ra decay segment has been observed in soil, sludge and oil-sand samples within the standard uncertainties. After a detailed radiological characterization of the four main oilfields, we can conclude that the outdoor absorbed dose rate never exceeds the worldwide population weighted average absorbed dose rate in outdoor air from terrestrial gamma radiation.Comment: 21 pages, 5 figures, 2 tables, Chemosphere 201

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

Reference worldwide model for antineutrinos from reactors

Antineutrinos produced at nuclear reactors constitute a severe source of background for the detection of geoneutrinos, which bring to the Earth's surface information about natural radioactivity in the whole planet. In this framework we provide a reference worldwide model for antineutrinos from reactors, in view of reactors operational records yearly published by the International Atomic Energy Agency (IAEA). We evaluate the expected signal from commercial reactors for ongoing (KamLAND and Borexino), planned (SNO+) and proposed (Juno, RENO-50, LENA and Hanohano) experimental sites. Uncertainties related to reactor antineutrino production, propagation and detection processes are estimated using a Monte Carlo based approach, which provides an overall site dependent uncertainty on the signal in the geoneutrino energy window on the order of 3%. We also implement the off-equilibrium correction to the reference reactor spectra associated with the long-lived isotopes and we estimate a 2.4% increase of the unoscillated event rate in the geoneutrino energy window due to the storage of spent nuclear fuels in the cooling pools. We predict that the research reactors contribute to less than 0.2% to the commercial reactor signal in the investigated 14 sites. We perform a multitemporal analysis of the expected reactor signal over a time lapse of 10 years using reactor operational records collected in a comprehensive database published at www.fe.infn.it/antineutrino.Comment: Slight changes and improvements in the text, added references. 17 pages, 6 figures, 8 tables; Physical Review D 201

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%

New challenges in the spectral reconstruction of terrestrial gamma rays and reactor antineutrinos

This thesis faces the spectral reconstruction of gamma-rays coming from the Earth and antineutrinos produced by nuclear reactors, interpreted as fundamental background in geoneutrino measurements. The multiform nature of radioactivity manifestations populates a kaleidoscope of spectral structures that can be deciphered as a superposition of fundamental shapes. As in gamma-ray spectroscopy the ∼1 MeV energy range is the theater where the ensemble of 40K, 238U and 232Th rehearse, in electron antineutrino measurements the same energy range is inhabited by reactor antineutrinos and geoneutrinos. The contents of this thesis are included in 8 publications, both peer-reviewed papers and conference proceedings. I took an active part in a wide community of scientists from different disciplines and international institutions. I presented the results of these studies as invited speaker to 4 international conferences (JPGU in 2014 and Neutrino Geoscience, TAUP and AAP in 2015). Getting insights into the Earth’s surface and interior requires to provide for gamma-ray and geoneutrino measurements an adequate understanding of different spectral components. A worldwide reference model for predicting reactor antineutrino signals and spectra was elaborated, which is fundamental for inferring the geoneutrino component from measured inverse beta decay events. I addressed the problem of the uncertainty propagation and I performed a reactor signal analysis over 10 years for the KamLAND (Japan), Borexino (Italy) and SNO+ (Canada) detectors by using reactor data collected in a comprehensive database published at www.fe.infn.it/antineutrino. I estimated the variability of the SNO+ reactor spectral shape caused by the temporal evolution of the reactor fissile inventory, related to the poor knowledge on the functioning of CANDU reactors, responsible for ∼55% of the SNO+ signal. The Huronian Supergroup geological reservoir is the major source of uncertainty in the prediction of the local contribution to the SNO+ geoneutrino signal. In the light of better constraining the geochemical model of this reservoir, I took care of HPGe spectroscopy measurements on collected rock samples and I defined the statistical distributions describing the U and Th content of the reservoir. For this scope, having refined measurements of natural radionuclides abundances was mandatory, which required an accurate instrumental calibration for the different spectral components. The full efficiency calibration of the HPGe detector was performed using certified reference materials and estimating correction factors, which allowed to quantify for the main gamma lines the individual contribution each input quantity has on the uncertainty budget. The reliability of the HPGe performances is fundamental for facing the challenges of scintillation detectors calibration. The Full Spectrum Analysis with Non Negative Least Square constraint was applied to the sensitivity calibration of in-situ and airborne NaI detectors to determine the 40K, 238U, 232Th and 137Cs fundamental spectra. These studies highlighted the importance of performing dedicated instrumental calibrations, which involve experimental measurements characterized by different sources of uncertainty and different fields of view. The modeling of background spectral components of airborne gamma-ray measurements required dedicated calibration flights at different heights above the sea, which allowed to assess the contributions originating from the radioactivity of the aircraft materials and from cosmic rays. Airborne gamma-ray measurements suffer also for the presence of a phantom source in the atmosphere, 222Rn. I studied the feasibility of quantifying the presence of 222Rn in the atmosphere by applying a refined statistical analysis describing the expected count rate in the 214Bi energy window. These studies reflect the melting of close disciplines in which my research activities will point in the next years.In questa tesi è affrontata la ricostruzione spettrale dei raggi gamma provenienti dalla Terra e degli antineutrini prodotti dai reattori nucleari, intesi come background nelle misure di geoneutrini. La natura multiforme delle manifestazioni della radioattività popola un caleidoscopio di forme spettrali decodificabili come sovrapposizioni di forme fondamentali. Così come nella spettroscopia gamma l’intervallo di energie vicino al MeV è il teatro in cui si esibiscono 40K, 238U e 232Th, nelle misure di antineutrini di tipo elettronico lo stesso range di energie ospita gli antineutrini prodotti dai reattori nucleari unitamente ai geoneutrini. I contenuti di questa tesi sono inclusi in 8 pubblicazioni, sia su riviste indicizzate che come proceedings di conferenze. Ho collaborato con un’ampia comunità di scienziati afferenti a diverse discipline e istituti di ricerca internazionali. Ho presentato i risultati delle mie ricerche come speaker a 4 congressi internazionali (JPGU nel 2014 e Neutrino Geoscience, TAUP e AAP nel 2015). Per studiare cosa avviene sulla superficie e all’interno della Terra è necessaria sia per quanto riguarda i raggi gamma che per i geoneutrini una conoscenza raffinata delle diverse componenti spettrali. Ho elaborato un modello su scala globale per la stima dei segnali e degli spettri degli antineutrini da reattore, fondamentale per estrapolare dal segnale misurato gli eventi prodotti dai geoneutrini. Ho affrontato il problema della propagazione delle incertezze e, adottando i dati pubblicati alla pagina www.fe.infn.it/antineutrino, ho condotto un’analisi su un lasso di tempo di 10 anni del segnale atteso a KamLAND (Giappone), Borexino (Italia) e SNO+ (Canada). Ho stimato la variabilità dello spettro da reattore per l’esperimento SNO+, che è causata dall’evoluzione temporale delle frazioni di fissione ed è legata alla scarsa conoscenza del funzionamento dei reattori CANDU, responsabili del ~55% del segnale a SNO+. Con l’obiettivo di raffinare la caratterizzazione geochimica del reservoir geologico Huronian Supergroup, principale sorgente di incertezza nella stima del segnale locale di geoneutrino a SNO+, ho condotto misure di spettroscopia gamma in laboratorio su campioni di roccia e modellato le distribuzioni statistiche che descrivono le abbondanze di U e Th del reservoir. Raffinate misure di radioattività sono state realizzate con il rivelatore HPGe la cui calibrazione in efficienza ha previsto l’impiego di materiali certificati e la stima di fattori di correzione da applicare alle attività misurate. Ciò ha permesso di quantificare per le principali linee gamma il peso che ogni quantità di input ha sull’incertezza complessiva. L’affidabilità delle misure condotte con il rivelatore HPGe è il fondamento su cui poggia la calibrazione in efficienza di rivelatori a scintillazione. La Full Spectrum Analysis con vincolo di non negatività è stata applicata alla calibrazione di rivelatori NaI(Tl) destinati a misure di radioattività in-situ e airborne, la quale restituisce gli spettri fondamentali di 40K, 238U, 232Th e 137Cs. Questi studi hanno evidenziato l’importanza di calibrazioni dedicate, in cui è spesso necessario confrontare misure aventi diverse sorgenti di incertezza e campi di visione. Sono stati realizzati voli di calibrazione sul mare in un ampio range di quote per stimare le componenti spettrali di background nelle misure airborne. Ciò ha permesso di separare il contributo originato dalla radioattività dei materiali dal contributo dovuto alla radioattività cosmica. Le misure airborne sono affette dalla presenza di 222Rn in atmosfera. Ho studiato la possibilità di quantificare il 222Rn atmosferico grazie a un’analisi statistica basata sulla modellazione del rate di conteggio nella regione energetica associata al fotopicco del 214Bi. Questi studi riflettono l’interazione di discipline vicine, campo in cui indirizzerò le mie future attività di ricerca