495 research outputs found
The imprint of thermally induced devolatilization phenomena on radon signal. Implications for the geochemical survey in volcanic areas
Thermal gradients due to magma dynamics in active volcanic areas may affect the emanating
power of the substrate and the background level of radon signal. This is particularly effective
in subvolcanic substrates where intense hydrothermal alteration and/or weathering processes
generally form hydrous minerals, such as zeolites able to store and release great amounts of
H2O (up to ∼25 wt.%) at relative low temperatures. To better understand the role played by
thermally induced devolatilization reactions on the radon signal, a new experimental setup has
been developed for measuring in real time the radon emission from a zeolitized volcanic tuff.
Progressive dehydration phenomena with increasing temperature produce radon emissions two
orders of magnitude higher than those measured during rock deformation, microfracturing and
failure. In this framework, mineral devolatilization reactions can contribute significantly to
produce radon emissions spatially heterogeneous and non-stationary in time, resulting in a
transient state dictated by temperature gradients and the carrier effects of subsurface gases.
Results from these experiments can be extrapolated to the temporal and spatial scales of
magmatic processes, where the ascent of small magma batches from depth causes volatile
release due to dehydration phenomena that increase the radon signal from the degassing host
rock material
Real-time setup to measure radon emission during rock deformation. Implications for geochemical surveillance
Laboratory experiments can represent a valid approach
to unravel the complex interplay between the geochemical
behaviour of radon and rock deformation mechanisms.
In light of this, we present a new real-time experimental
setup for analysing in continuum the alpha-emitting 222Rn
and 220Rn daughters over variable stress–strain regimes. The
most innovative segment of this setup consists of the radon
accumulation chamber obtained from a tough and durable
material that can host large cylindrical rock samples. The
accumulation chamber is connected, in a closed-loop configuration,
to a gas-drying unit and to a RAD7 radon monitor.
A recirculating pump moves the gas from the rock sample
to a solid-state detector for alpha counting of radon and
thoron progeny. The measured radon signal is enhanced by
surrounding the accumulation chamber with a digitally controlled
heating belt. As the temperature is increased, the number
of effective collisions of radon atoms increases favouring
the diffusion of radon through the material and reducing
the analytical uncertainty. The accumulation chamber containing
the sample is then placed into a uniaxial testing apparatus
where the axial deformation is measured throughout
a linear variable displacement transducer. A dedicated software
allows obtaining a variety of stress–strain regimes from
fast deformation rates to long-term creep tests. Experiments
conducted with this new real-time setup have important ramifications
for the interpretation of geochemical anomalies
recorded prior to volcanic eruptions or earthquakes
Indoor/outdoor air exchange affects indoor radon – the use of a scale model room to develop a mitigation strategy
Abstract. Indoor/outdoor air exchange on indoor radon concentration
was investigated. We evaluated the effect of air extraction versus air
introduction at different flow rates on equilibrium 222Rn activity
concentrations in a scale model room of 62 cm × 50 cm × 35 cm (inner length
x width × height), made of a porous, radium and thorium-rich lithoid
ignimbrite (Tufo di Gallese) from Vico volcano (Lazio, central Italy).
Experiments were carried either with the inner walls of the chamber covered
with a plasterboard shield or without any inner coating. Air introduction
was always more effective than air extraction to reduce indoor 222Rn
and, in both cases, higher flow rates produced higher 222Rn decreases.
The presence of the plasterboard enhanced 222Rn reduction when outdoor
air was introduced in the chamber. Main results were that, with
plasterboard, maximum reductions of 89.5 % and 25.0 % were obtained
introducing and extracting air, respectively; without plasterboard, we found
maximum radon decreases of 33.2 % and 26.6 %, namely with air
introduction or extraction. The diffusion of 222Rn through the walls of
the scale model room was modelled with a modified version of Fick's second
law, where a term considering air flow velocity was added. These findings
suggested that the combined use of proper coatings on the inner walls of a
house and outdoor air introduction at suitable rates are a good strategy to
approach radon mitigation actions
Use of commercial biochar for river water purification in the Lazio region, Italy
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Endokarst costero, niveles marinos y tectónica: el ejemplo de la costa oriental de Mallorca
Abstract not availabl
Testing the Properties of Radon Barrier Materials and Home Ventilation to Mitigate Indoor Radon
Indoor radon is the second cause of lung cancer. Mitigation strategies are based on (i) building protection with radon barrier materials, (ii) increasing home ventilation or (iii) room pressurization. A scale model room created with a porous ignimbrite rich in radon precursors was used as an analogue to test the indoor radon reduction ability of various radon barrier materials in a real room. The properties of these materials were tested with and without room pressurization by introducing outdoor air at different flow rates. The best materials reduced indoor radon up to 80% and, when the highest pressurization was applied, to 93%
Dataciones Th/U de espeleotemas freáticos controlados por el nivel marino, procedentes de cuevas costeras de Mallorca
[cat] Actualment és possible constatar la formació d'espeleotemes freà tics en la superfÃcie dels llacs salobrosos de nombroses coves costaneres de l’illa de Mallorca (Espanya); la seva presència registra amb precisió l’altura mitjana del nivell marà en el moment de la deposició d'aquests carbonats freà tics. Per tant, els dipòsits antics d'espeleotemes freà tics poden ser utilitzats per a reconstruir les fluctuacions de la Mediterrà nia durant el Pleistocè ja que existeixen, en diverses coves de l’à rea en estudi, abundants alineacions elevades d'aquests espeleotemes que delimiten paleonivells assolits per les aigües freà tiques. S'han datat alguns espeleotemes freà tics, usant el mètode Th/U, amb la intenció de determinar la posició del nivell marà durant el Pleistocè mitjà i superior. Han estat reconegudes tres estabilitzacions altes de la Mediterrà nia a diferents altures -entre 1,4 i 2,5 metres per damunt de l’actual nivell de fa mar -en coves localitzades en distints sectors de la costa oriental de Mallorca. Les esmentades estabilitzacions es remunten a edats entorn dels 83, 108 i 124 ka B.P. i poden ser relacionades amb diversos events menors dins de l’estadi 5 del registre marà d’isòtops d'oxigen. Aixà mateix, s'inclouen en aquesta nota algunes dades mineralògiques sobre els espeleotemes datats. Es poden observar diferències d'altura de fins 1 metre en mostres pertanyents al mateix paleonivell marÃ. Hi són particularment ben documentades les corresponents al subestadi isotòpic 5e, el qual es presenta registrat a altituds majors en les localitats mes septentrionals. Aquestes anomalies altimètriques han de ser explicades en base a una deformació tectònica recent de l’à rea investigada.[eng] Phreatic speleotherns form today at the surface of the brackish pools existing inside littoral caves of Mallorca island (Spain); their occurrence directly identifies the height of the sea level at the time of carbonate deposition. Therefore, ancient phreatic speleothems can be used to reconstruct Mediterranean fluctuations during the Pleistocene, since many raised alignments of these deposits are present in several caves of the studied area. Some phreatic speleothems have been dated using the Th/U method in order to determine the position of the sea level during the Middle and Upper Pleistocene. Three high sea-stands have been recognized at different heights -bemeen 1.4 and 2.5 meters above current sea level- in caves located in various sectors of the eastern coast of Mallorca. They date back to around 83, 108 and 124 ka B P and can be related to several minor events within stage 5 of the marine oxygen isotope record. Some mineralogical data about the analyzed samples are also included in this paper. Differences in height of about 1 meter can be observed in samples corresponding to the same sea paleolevel. Those which are particularly well-documented pertain to substage 5e, with higher elevations towards the northernmost localities. These altimetrical disturbances could be explained in terms of a tectonic tilt of the investigated area
Sea level change at Capo Caccia (NW Sardinia) and Mallorca (Balearic Islands) during oxygen isotope substage Se, based on Th/U datings of phreatic overgrowths on speleothems
Sea level changes during Last Interglacial (substage Se) have been documented in two sites of the Western Mediterranean area: Mallorca Island (Balearic Archipelago) and Capo Caccia area (NW Sardinia). Past sea stands have been recorded by overgrowths of phreatic crystallizations developing around previously formed vadose speleothems. These carbonate coatings have been U-series dated, mostly using multicollector inductively coupled mass spectrometry. Two high sea stands have been recognised along the eastern coast of Mallorca at about 1.5 - 3 metres a.p.s.l, from 135 to 109 ka B.P., with a rapid episode of regression around 125 ka. The average duration of the older high stand episode can be estimated at 9.5 ka and that of the younger at 12.8 ka. So far only the younger stand has been found in Capo Caccia area at 4.3 m a.p.s.l., with a minimum duration of 3 ka. The difference in elevation of late Se high stand, recorded at Mallorca and Capo Caccia, can be only partly justified by neotectonic activity and is probably the result of different responses of the two areas, (owing to their different crustal thickness) to the change in the water loading characterising the glacial-interglacial cycles.Els canvis del nivell de la mar durant el darrer interglacial (subestadi isotòpic Se) han estat documentats en dues à rees de la Mediterrà nia occidental: l'illa de Mallorca (Illes Balears) i la zona de Capo Caccia, a I' Alguer (NW de Sardenya). A les coves costaneres d'aquestes illes, antigues estabilitzacions del nivell marà es troben enregistrades mitjançant sobrecreixements de cristal·litzacions freà tiques que es desenvoluparen al voltant d'espeleotemes vadosos preexistents. Aquests recobriments de carbonats s'han datat amb el mètode de les sèries de l'Urani, majorità riament usant tècniques MC-ICPMS (multicollector inductively coupled mass spectrometry). Al llarg de la costa oriental de Mallorca, ha estat possible reconèixer dos episodis transgressius que assoleixen 1,5 - 3 m per sobre de I' actual nivell marÃ, ocorreguts entre 135 i 109 ka BP, separats per una rà pida regressió al voltant dels 125 ka. La durada de la pulsació transgressiva més antiga pot ésser estimada en 9,5 ka, mentre que la duració de la més recent seria de 12,8 ka. Fins al moment, tans sols la transgressió més recent es troba documentada a l'à rea de Capo Caccia a +4,3 m amb una durada mÃnima de 3 ka. La diferència d'altitud de l'episodi transgressiu més recent dins el subestadi Se, enregistrat a Mallorca i a Capo Caccia (Sardegna), pot ésser tan sols parcialment justificada per l'activitat neotectònica i és probablement el resultat de respostes diferents de les dues à rees (atribuïbles a les distintes gruixes de l'escorça continental) als canvis en la cà rrega d'aigua marina que caracteritzen els cicles climà tics pleistocènics
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