Monte Carlo simulation of muon-induced background of an anti-Compton gamma-ray spectrometer placed in a surface and underground laboratory

Simulations of cosmic ray muon induced background of an HPGe detector placed inside an anti-Compton shield on the surface and in shallow underground is described. Investigation of several model set-ups revealed some trends useful for design of low-level gamma-ray spectrometers. It has been found that background spectrum of an HPGe detector can be scaled down with the shielding depth. No important difference is observed when the same set-up of the anti-Compton spectrometer is positioned horizontally or vertically. A cosmic-muon rejection factor of at least 40 (at around 1 MeV) can be reached when the anti-Compton suppression is operational. The cosmicmuon background can be reduced to such a level that other background components prevail, like those from the residual contamination of the detector and shield materials and/or from radon, especially for the underground facilities

Background and summary: a new focus on groundwater-seawater interactions

Water and chemical fluxes across the sea floor provide an important linkage between terrestrial and marine environments. Oceanographers recognize that these fluxes may act as a source of nutrients or other harmful contaminants to marine systems (e.g. Johannes, 1980; Valiela et al., 1990). These fluxes may also act as a beneficial source of freshwater for coastal marine estuaries that require relatively low salinities. Hydrologists and hydrogeologists recognize that fluxes across the sea floor comprise an important part of the water balance for coastal aquifers. Most fresh groundwater discharge to the ocean is derived from terrestrial aquifer recharge. Management of coastal aquifers requires careful estimates of recharge and other hydrological components, such as groundwater discharge. These estimates are commonly combined into a comprehensive water budget to evaluate how much groundwater might be available for municipal uses and whether saltwater intrusion may be a potential concern. Excessive groundwater withdrawals can cause saltwater intrusion by intercepting the seaward flux of freshwater that prevents saltwater from intruding a coastal aquifer. Quantitative estimates of fresh groundwater discharge toward the coast can provide a basis for determining safe withdrawal rates. Oceanographers, marine scientists, and those studying and managing saltwater intrusion in coastal aquifers, share a common goal of quantification and understanding of groundwater and seawater interactions. Submarine groundwater discharge, or SGD, has become a popular term in the literature for describing the flux of water across the sea floor. Burnett et al. (2003) specifically define SGD as the discharge of aquifer porewater across the sea floor and into the ocean. They define flow in the opposite direction as submarine groundwater recharge (SGR). SGR is the recharging flux of seawater into the aquifer. The presence of SGR does not necessarily indicate saltwater intrusion, which occurs when saline water moves into parts of the aquifer previously occupied by freshwater. A conceptual model of the types of flow patterns that are expected to exist in many coastal aquifers at the terrestrial–marine boundary is shown. Through a detailed field study, Kohout (1960) showed that as fresh groundwater flows seaward, it meets and mixes with saline groundwater before discharging into the ocean. Because of this mixing and subsequent discharge to the ocean, seawater is drawn into the aquifer to replace the saline groundwater that discharged to the ocean. Seawater drawn into the aquifer is sometimes referred to as recirculated seawater. Michael et al. (2005) suggest that the seasonality of terrestrial recharge may also act as a mechanism for recirculating seawater through a coastal aquifer. As the mixing zone moves landward and seaward in response to seasonal fluctuations in recharge, seawater may be drawn in and flushed out of the aquifer over the course of a year. SGD can also occur at the bottom of the open ocean, even in the absence of a terrestrial connection. Waves, tides, and ocean currents can create hydraulic gradients that pump seawater across the sea floor. Interest in groundwater–seawater interactions continues to receive a significant amount of attention in the literature. Saltwater intrusion, freshwater deliveries to marine estuaries, and nutrient loading are persistent problems of global importance. The problems are difficult to address, however, because of the elusive nature of SGD. Fortunately, the science is advancing. The journal Biogeochemistry, dedicated the entire November 2003 issue to the subject of SGD as did the journal Ground Water, in the December 2004 issue. Zektser & Dzhamalov (2007) released a comprehensive review on the subject of SGD and groundwater–seawater interactions in a new book: Submarine Groundwater. In their book, they suggest that SGD and related studies should be categorized into a new field called “Marine Hydrogeology”. The concentrated efforts of numerous researchers from a wide range of disciplines have led to substantial advancements in characterizing SGD, but there is still more work to be done

Preface

Water and chemical fluxes across the sea bottom provide an important linkage between terrestrial and marine environments. From the marine perspective, these water fluxes, commonly referred to as submarine groundwater discharge (SGD), may contain elevated nutrient concentrations or high levels of other potentially harmful contaminants. Terrestrially derived SGD can also be an important source of freshwater for estuarine ecosystems that require relatively low salinities. For these reasons, the past decade has shown a rapid increase in the level of interest from estuary and marine scientists toward a better understanding of SGD. From the terrestrial perspective, SGD has also been a topic of interest to those studying saltwater intrusion and management of coastal aquifers. Saltwater intrusion studies commonly employ some form of a water balance method, whether through numerical modelling or volumetric calculations, to explain intrusion patterns and develop predictions and management plans. In developing a water balance for a coastal aquifer, estimates for all of the key components, including SGD, are synthesized. Although the motivation may be different depending on whether one works from the marine or terrestrial perspective, both groups have a common goal of obtaining accurate SGD estimate

Low-level 226Ra determination in groundwater by SF-ICP-MS: optimization of separation and pre-concentration methods

Inductively coupled plasma mass spectrometry (ICP-MS) techniques have been widely used for analysis of long-lived environmental radionuclides. In this paper, we present an optimization of the sector field (SF)-ICP-MS technique for the analysis of 226Ra in groundwater samples using a method of pre-concentration of radium in water samples. The separation protocol and a sequential application of ion exchange and extraction chromatography have been optimized, and related polyatomic interferences and matrix effects affecting the 226Ra signal were investigated. Analyzing 12 replicates (water spiking at 22 fg g−1 of 226Ra), the 226Ra recovery efficiency close to 100 % has been obtained. The instrumental 226Ra detection limit of 0.09 fg g−1 (3σ criterion) and the absolute detection limit of 0.05 fg in a 25-mL groundwater sample have been reached. An optimization of the radium separation method and a pre-concentration of radium in groundwater samples led to high radium recoveries, almost up to 100 %. The same could be said with respect to the separation of the interfering elements, important for the quantitative 226Ra analysis by SF-ICP-MS. The improvements in the separation and pre-concentration techniques also helped to improve the 226Ra detection limit down to 0.05 fg/25 mL of groundwater sample

Reference material for radionuclides in sediment IAEA-384 (Fangataufa Lagoon sediment)

Author Posting. © Springer, 2007. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Radioanalytical and Nuclear Chemistry 273 (2007): 383-393, doi:10.1007/s10967-007-6898-4.A reference material designed for the determination of anthropogenic and natural radionuclides in sediment, IAEA-384 (Fangataufa Lagoon sediment), is described and the results of certification are presented. The material has been certified for 8 radionuclides (40K, 60Co, 155Eu, 230Th, 238U, 238Pu, 239+240Pu and 241Am). Information values are given for 12 radionuclides (90Sr, 137Cs, 210Pb (210Po), 226Ra, 228Ra, 232Th, 234U, 235U, 239Pu, 240Pu and 241Pu). Less reported radionuclides include 228Th, 236U, 239Np and 242Pu. The reference material may be used for quality management of radioanalytical laboratories engaged in the analysis of radionuclides in the environment, as well as for the development and validation of analytical methods and for training purposes. The material is available from IAEA in 100 g units

A century of warfare shoots holes in anti-Caulerpa campaign

Effort to have all varieties of the marine alga Caulerpa taxifolia listed as noxious weeds hinges on the argument that the alga's proliferation in the Mediterranean Sea is a cause and not a consequence of environmental degradation. Until now, the occurrence of two populations in a pristine part of the northern Mediterranean near the island of Porquerolles has upheld this claim. Here we show that the alga's development at Porquerolles is indeed a consequence of environmental degradation caused by military weapons' impacts on seagrass beds during the last century. The available data show that substratum enrichment plays a key role in fostering development of Caulerpa, irrespective of whether this results directly from pollution or from the impacts of pollution and other anthropogenic factors on benthic vegetation cover

Beryllium-7 analyses in seawater by low background gamma-spectroscopy

Author Posting. © Akadémiai Kiadó, 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Radioanalytical and Nuclear Chemistry 277 (2008): 253-259, doi:10.1007/s10967-008-0739-y.7Be is a cosmogenic isotope produced in the stratosphere and troposphere. 7Be has a half-life of 53.4 days and decays to 7Li emitting a 477 keV gamma line with a branching ratio of 0.104. It is predominantly washed out of the atmosphere through wet deposition. It is a tool for oceanographers to study air sea interaction and water mass mixing. Beryllium’s largely non-reactive nature in the open ocean makes it an excellent conservative tracer. Its conservative nature and extreme dilution in seawater also makes it difficult to concentrate and analyze. Early experiments at WHOI with Fe(OH)3 cartridges to directly collect 7Be by insitu underwater pumps proved ineffective. Collection efficiencies of the cartridges were too low to be consistently useful. At sea chemistry of whole water samples became the method of choice. The use of stable 9Be as a yield monitor further improved the accuracy of the procedure. The method was optimized at WHOI in 2005 using a seawater line that enters WHOI’s coastal research lab. The procedure was then used on an oceanographic cruise on the R/V Oceanus out of Bermuda in the oligotrophic Sargasso Sea.The authors would like to thank DOE, ONR and NSF for funding of this research

Estimation of the time-dependent radioactive source-term from the Fukushima nuclear power plant accident using atmospheric transport modelling

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Ground gamma-ray survey of the Solforata gas discharge area, Alban Hills-Italy: A comparison between field and laboratory measurements

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