78 research outputs found
Coastal upwelling in the Rias Bajas, NW Spain: Contrasting the benthic regimes of the Rias de Arosa and de Muros
Nutrient-rich North Atlantic water upwells off the NW coast of Spain and intermittently intrudes into the rias, coastal embayments, by displacement during periods of offshore winds. High primary production associated with the upwelling supports an intensive raft culture of the edible mussel, Mytilus edulis. This culture is most intensive (ca. 2000 rafts) in the Ria de Arosa, and results in one of the highest protein yields per unit area on earth...
A Mass Model for Estimating the Gamma Ray Background of the Burst and Transient Source Experiment
Orbiting x-ray and gamma ray instruments are subject to large background
count rates due to local particle fluxes in the space environment. The ability
of an instrument to make calibrated measurements of the flux from a source of
interest is highly dependent on accurately determining the background level. We
present here a method of calculating the energy dependent background flux for
any point in the complete data set recorded by the Burst and Transient Source
Experiment (BATSE) in its nine year mission. The BATSE Mass Model (BAMM) uses a
Monte Carlo mass modelling approach to produce a data base of the gamma ray
background which is then filtered to simulate the background count rate with a
2.048 second time resolution. This method is able to reduce the variations in
the background flux by a factor of 8 - 10, effectively `flat-fielding' the
detector response. With flat-fielded BATSE data it should be possible to use
the Earth occultation technique to produce a hard x-ray all sky survey to the
1-2 mCrab sensitivity limit. BAMM is also capable of estimating the
contribution to the spectra measured from gamma ray sources due to the
reprocessing of source photons in inactive material surrounding a gamma ray
detector. Possible applications of this aspect of the model in the area of
Gamma Ray Burst spectral analysis are discussed.Comment: 11 pages, 9 figures. Accepted for publication in Astronomy and
Astrophysics. Figures have been reduced to conform to astro-ph standard
Certified reference materials for radionuclides in Bikini Atoll sediment (IAEA-410) and Pacific Ocean sediment (IAEA-412)
The preparation and characterization of certified reference materials (CRMs) for radionuclide content in sediments collected offshore of Bikini Atoll (IAEA-410) and in the open northwest Pacific Ocean (IAEA-412) are described and the results of the certification process are presented. The certified radionuclides include: 40K, 210Pb (210Po), 226Ra, 228Ra, 228Th, 232Th, 234U, 238U, 239Pu, 239+240Pu and 241Am for IAEA-410 and 40K, 137Cs, 210Pb (210Po), 226Ra, 228Ra, 228Th, 232Th, 235U, 238U, 239Pu, 240Pu and 239+240Pu for IAEA-412. The CRMs can be used for quality assurance and quality control purposes in the analysis of radionuclides in sediments, for development and validation of analytical methods and for staff training
Developpement de la spectrometrie gamma ultra bas bruit de fond au laboratoire souterrain de modane - application aux decroissances double beta
Developpement de la spectrometrie gamma ultra bas bruit de fond au laboratoire souterrain de modane - application aux decroissances double beta
RĂ©flexion sur lâĂ©volution des concentrations en radionuclĂ©ides artificiels dans lâenvironnement français, les doses associĂ©es et lâadaptation des techniques dâanalyse aux besoins de la surveillance
La concentration de lâenvironnement français en radionuclĂ©ides artificiels et les techniques dâanalyses ont considĂ©rablement Ă©voluĂ© au cours des 50 derniĂšres annĂ©es. Au cours des annĂ©es 60 et 70, la surveillance effectuĂ©e par lâInstitut de protection et de sĂ»retĂ© nuclĂ©aire (IPSN) et par le service central de protection contre les rayonnements ionisants (SCPRI) permettait de connaĂźtre les niveaux des radionuclĂ©ides artificiels les plus abondants et qui contribuaient de façon prĂ©pondĂ©rante aux doses reçues par la population française. Depuis les annĂ©es 80, avec la fin des essais atmosphĂ©riques dâarmes nuclĂ©aires et la baisse des activitĂ©s de la plupart des radionuclĂ©ides concernĂ©s, les radionuclĂ©ides devenus prĂ©pondĂ©rants en activitĂ© et en doses sont : 3H, 14C, 85Kr et 133Xe. Or ces quatre radionuclĂ©ides ne font aujourdâhui lâobjet que dâun nombre trĂšs restreint dâanalyses dans le cadre de la surveillance effectuĂ©e par lâIRSN. La mise en relation des niveaux dâactivitĂ© des radionuclĂ©ides constituants le « bruit de fond » de la radioactivitĂ© artificielle environnementale, des activitĂ©s potentiellement ajoutĂ©es du fait des rejets des installations nuclĂ©aires, des doses correspondantes, ainsi que des limites de dĂ©tection obtenues au moyens des meilleures techniques disponibles, fournit des Ă©lĂ©ments de rĂ©flexion sur les enjeux de la surveillance radiologique de lâenvironnement et sur les possibilitĂ©s dâatteindre les objectifs correspondants. Ă lâexception de 14C et 3H, les activitĂ©s les plus basses prĂ©sentes dans lâenvironnement se trouvent dâores et dĂ©jĂ au niveau ou en-deçà des limites de dĂ©tection des techniques de mesure. 3H et 14C sont donc les seuls radionuclĂ©ides toujours mesurables dans lâenvironnement et pour lesquels une influence des rejets atmosphĂ©riques des installations nuclĂ©aires est potentiellement dĂ©celable dans tous les milieux
Anti-Compton gamma spectrometry for environmental samples
The results of the low-level performance of an anti-Compton device are presented. The anti-coincidence action of the NaI detectors lowers the total background of the HPGe detector integrated on the energy range 30 keV to 2730 keV by a factor 8.1 and suppresses the continuum above 300 keV by a factor larger than 10. Qualitative and quantitative results on environmental samples are described to illustrate the improvement of uncertainties determination and the significant reduction of detection limits. This provides ever more accurate and precise data on natural and anthropogenic radionuclides often used as tracers for environmental studies
Impact of an exceptional Saharan dust outbreak in France: PM10 and artificial radionuclides concentrations in air and in dust deposit
The present study focuses on the exceptional Saharan dust event that affected most of France in February 2004. Activity levels of various artificial radionuclides (90Sr, 137Cs, uranium, thorium and plutonium isotopes, 241Am) were examined. Activity or isotopic ratios are discussed in the context of atmospheric nuclear weapons tests, among them French tests performed in Sahara in the 1960s. The daily evolution of 137Cs activity levels in the atmosphere was compared to daily PM10 change. A link between airborne 137Cs and PM10, is given. It is estimated that this 2-day event deposited as much 137Cs as would be deposited on average over a 10-month period. The amount of deposited 137Cs and 239+240Pu represents respectively about 0.1 and 1% of the activity already present in the soil. Such Saharan dust events correspond to an extreme type of " feeder" process of artificial radionuclides in the atmosphere. Therefore, they contribute to the long term background level of artificial radionuclides kept at trace levels in the atmosphere. © 2010 Elsevier Ltd
Experience acquired on environmental sample combustion for organically bound tritium measurement
In order to determine organically bound tritium (OBT) concentrations, environmental samples are generally first freeze-dried. This first step is to remove tritiated water. Then, the dry residue is burnt in a special furnace with oxygen. Finally, the tritiated water fraction obtained is measured using a liquid scintillation counter. Our laboratory has developed a "pyroxydiser" tubular furnace for a computer controlled combustion. This paper presents the different improvements of the equipment. For three years, the analysis of each sample has been replicated. The experience acquired on the environmental matrices analysed using this setup is shown. © 2009 Elsevier Ltd. All rights reserved
SpectromĂ©trie bĂȘta appliquĂ©e aux mesures de la radioactivitĂ© dans lâenvironnement
Les techniques employĂ©es pour quantifier les Ă©metteurs bĂȘta purs (3H, 14C, 90Sr, 36Cl, 63NiâŠ) dans les matrices environnementales sont basĂ©es sur une sĂ©lectivitĂ© physico-chimique de lâĂ©lĂ©ment suivi dâune mesure par scintillation liquide ou comptage proportionnel. Nous avons Ă©tudiĂ© une configuration de mesure simple, basĂ©e sur des dĂ©tecteurs silicium minces (PIPS), afin dâobtenir une sĂ©lectivitĂ© spectromĂ©trique couplĂ©e ou non Ă une sĂ©lectivitĂ© physico-chimique. La quantification de sources pures montre que les limites de dĂ©tection sont du mĂȘme ordre de grandeur que celles obtenues par les mĂ©thodes conventionnelles avec lâavantage de prĂ©ciser la prĂ©sence dâinterfĂ©rents rĂ©siduels. De mĂȘme, pour des mesures de surveillance ou de contrĂŽle rĂ©glementaire, excluant une prĂ©paration chimique importante, la contribution des radionuclĂ©ides naturels est souvent Ă la base de la mise en Ćuvre de mesures complĂ©mentaires. Cette contribution des naturels peut ĂȘtre observĂ©e afin dâexclure la nĂ©cessitĂ© de ces mesures complĂ©mentaires mĂȘme si les seuils globaux rĂ©glementaires sont dĂ©passĂ©s
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