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1.
2.
M. J. Carson J. C. Davies E. Daw R. J. Hollingworth V. A. Kudryavtsev T. B. Lawson P. K. Lightfoot J. E. McMillan B. Morgan S. M. Paling M. Robinson N. J. C. Spooner D. R. Tovey 《Astroparticle Physics》2004,21(6):667-687
Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10−9–10−10 pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector. 相似文献
3.
Radiocaesium isotopes, discharged into the North-east Irish Sea from the Sellafield (formerly Windscale) nuclear fuel reprocessing plant in Cumbria, have been employed as flow monitors to update and extend the record of coastal water movement from the Irish Sea to the Clyde Sea area and, further north, to Loch Etive. The temporal trends in radiocaesium levels have been used to determine the extent of water mixing en route and to define mean advection rates. Flow conditions from the Irish Sea have changed considerably since the mid-1970s, the residence time of northern Irish Sea waters being ~12 months during 1978–1980 inclusive. Average transport times of four and six months are estimated for the Sellafield to Clyde and Sellafield to Etive transects respectively. Sellafield 137Cs levels in seawater were diluted by factors of 27 and 50 respectively during current movement to the Clyde and Etive areas. The decrease in salinity-corrected 137Cs concentrations between the Clyde and Etive suggests that dilution by Atlantic water occurs, the latter mainly entering the Firth of Lorne from the west. The majority (~94%) of the radiocaesium supply to Loch Etive enters the Firth of Lorne via the portion of the coastal current circulating west of Islay, only ~6% arriving via the Sound of Jura. 相似文献
4.
5.
地面核磁共振模型约束反演含水层参数 总被引:1,自引:1,他引:0
导电模型的地面核磁共振感应电动势是含水量的非线性函数.引入模型约束的迭代反演方法求解该非线性问题的反演.在反演过程中,根据理论公式计算迭代过程中灵敏度矩阵,并采用平坦模型和光滑模型两种约束.对均匀半空间、层状导电模型和实际数据进行了反演模拟,结果表明,模型约束迭代反演方法能从地面核磁共振感应电动势获得含水层较为合理的含水量及分布,且该结果可以从作为初始模型的均匀含水量分布反演得到.对无噪音数据,平坦模型和光滑模型约束对反演的含水量分布影响不大;但当数据存在一定的噪音时,平坦模型约束将比光滑模型约束获得更为精确的含水层参数. 相似文献
6.
Surface contamination with radioactive caesium introduced into the environment after the accident at the Chernobyl nuclear
plant was high enough in the Crimean Mountains to allow using radiocaesium as an indicator of penetration of radioactive contamination
into a karst system. Caesium concentrations have been studied in soils above Marble Cave, Tchatyrdag Plateau, in percolation
waters and in sediments transported by percolation waters within the cave. Contamination of the daylight surface with 137Cs is about 30 kqB m–2 which is approximately 13 times higher than the density of global fallouts. Besides 137Cs, almost all samples showed presence of 134Cs with the 137Cs/134Cs ratio close to that of Chernobyl contaminations.
Concentrations of 137Cs range from 9 to 15 mBq l–1 in the present percolation waters in the cave. In sediments related to percolation waters 134Cs is detected in some samples besides 137Cs, although the effect of 228Ac is not ruled out. Surprisingly, the highest concentrations of radiocaesium were measured in "old" sediments in the cave's
lower series. These sediments are not associated with modern percolation and are represented by a clay/moonmilk alternating
sequence deposited in an old dried cave lake. Moonmilk layers have higher caesium content than clay. It is assumed that Chernobyl
caesium was transported into the cave with aerosols which were then deposited mainly in areas where condensation occurs. The
sampling site is located just in the boundary between two microclimatic zones with a temperature gradient of 0.5 °C. Active
condensation processes occur in this area. Caesium was not detected in another similar sampling site (old lake deposits) located
within homogeneous microclimatic conditions. If the above interpretation is correct, these results show the geochemical significance
of the aerosol-condensation mechanism of mass transport and localisation.
Received: 1 June 1995 · Accepted: 4 December 1995 相似文献
7.
The kinetics of the aqueous phase reactions of NO3 radicals with HCOOH/HCOO– and CH3COOH/CH3COO– have been investigated using a laser photolysis/long-path laser absorption technique. NO3 was produced via excimer laser photolysis of peroxodisulfate anions (S2O
8
2–
) at 351 nm followed by the reactions of sulfate radicals (SO
4
–
) with excess nitrate. The time-resolved detection of NO3 was achieved by long-path laser absorption at 632.8 nm. For the reactions of NO3 with formic acid (1) and formate (2) rate coefficients ofk
1=(3.3±1.0)×105 l mol–1 s–1 andk
2=(5.0±0.4)×107 l mol–1 s–1 were found atT=298 K andI=0.19 mol/l. The following Arrhenius expressions were derived:k
1(T)=(3.4±0.3)×1010 exp[–(3400±600)/T] l mol–1 s–1 andk
2(T)=(8.2±0.8)×1010 exp[–(2200±700)/T] l mol–1 s–1. The rate coefficients for the reactions of NO3 with acetic acid (3) and acetate (4) atT=298 K andI=0.19 mol/l were determined as:k
3=(1.3±0.3)×104 l mol–1 s–1 andk
4=(2.3±0.4)×106 l mol–1 s–1. The temperature dependences for these reactions are described by:k
3(T)=(4.9±0.5)×109 exp[–(3800±700)/T] l mol–1 s–1 andk
4(T)=(1.0±0.2)×1012 exp[–(3800±1200)/T] l mol–1 s–1. The differences in reactivity of the anions HCOO– and CH3COO– compared to their corresponding acids HCOOH and CH3COOH are explained by the higher reactivity of NO3 in charge transfer processes compared to H atom abstraction. From a comparison of NO3 reactions with various droplets constituents it is concluded that the reaction of NO3 with HCOO– may present a dominant loss reaction of NO3 in atmospheric droplets. 相似文献
8.
M. Catherine Eimers Andrew M. Paterson Peter J. Dillon Sherry L. Schiff Brian F. Cumming Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109
Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in
the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~
20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ 34S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment
were relatively low (1.9–5 mg S g−1 dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in
δ 34S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally
reciprocal depth pattern between total S concentration and δ 34S ratios. While initial shifts in total S and δ 34S were likely due to enhanced SO4 reduction of newly available anthropogenic SO4, both the magnitude and pattern of up-core S enrichment and shifts in δ 34S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and
δ 34S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake
characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S
deposition in this region, likely due to redox-related mobility of S in upper sediment. 相似文献
9.
The evolution of groundwater chemistry along the direction of groundwater flow was studied using hydrochemical data from samples collected along a flow line in the Neogene Aquifer, Belgium. Infiltrating water was found to have a very low mineral content and low pH because the sediments are strongly decalcified. Increasing SiO2 and cation concentrations along the groundwater flow line indicate silicate-weathering processes, confirmed with the aid of saturation indices, calculated with PHREEQC, and stability diagrams. A classification system based on redox sensitive species was developed and shows that an extensive redox sequence is present in the aquifer. At a shallow depth, pyrite oxidation has caused an increase in sulphate, while iron is precipitated as hydroxides. Elevated arsenic concentrations are related to the reduction of these iron hydroxides at a relatively shallow depth and to the dissolution of siderite at greater depth. Dissolution of carbonate in the aquifer material, present in deep layers and to the north, has lead to increased Ca2+ and HCO3 ? concentrations. The Ca2+ from the groundwater is exchanged for Na+, Mg2+ and K+ adsorbed to the clay surfaces at the bottom of the groundwater reservoir. Although the Neogene Aquifer is well flushed, there are still some marine influences present in the deepest parts. 相似文献
10.
PPGIS及其在加拿大安大略省核废料处理选址项目中的应用 总被引:9,自引:0,他引:9
刘政荣 《武汉大学学报(信息科学版)》2005,30(1):82-85
介绍了公众参与地理信息系统,给出了一个应用项目——加拿大安大略省核废料处理设施选址公众参与地理信息系统。 相似文献