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81.
We describe the science motivation and development of a pair production telescope for medium-energy (∼5–200 MeV) gamma-ray polarimetry. Our instrument concept, the Advanced Energetic Pair Telescope (AdEPT), takes advantage of the Three-Dimensional Track Imager, a low-density gaseous time projection chamber, to achieve angular resolution within a factor of two of the pair production kinematics limit (∼0.6° at 70 MeV), continuum sensitivity comparable with the Fermi-LAT front detector (<3 × 10−6 MeV cm−2 s−1 at 70 MeV), and minimum detectable polarization less than 10% for a 10 mCrab source in 106 s. 相似文献
82.
A 3-year study of indoor radon in more than 1000 homes in northern Virginia and southern Maryland was conducted using 3-month
exposure alpha-track monitors. In a study set of 200 homes, first-floor indoor radon concentrations, which most closely approximates
home exposure levels, averaged slightly more than 3 pCi/l. In a study set of 100 homes, sub-slab ventilation was used to reduce
indoor radon concentrations. Interest in remediation was related to public perception of the hazardous nature of radon; people
living in homes with indoor radon measurements of more than 4 pCi/l were more likely to participate in the remediation phase
of the project. Sub-slab ventilation was successful in more than 90% of the homes in reducing indoor radon from concentrations
as high as 30 pCi/ to less than 4 pCi/l, at least for the entire year of post-remediation radon measurements.
Received: 29 February 1996 · Accepted: 29 May 1996 相似文献
83.
J. Huang N. Hotta K. Kasahara I. Ohta S. Ozawa T. Saito M. Shibata X. W. Xu T. Yuda 《Astroparticle Physics》2003,18(6):637-648
We have done extensive Monte Carlo simulations using the new simulation codes of CORSIKA and COSMOS to compare with the gamma-family data obtained at Mts. Fuji (3750 m above sea level) and Kanbala (5500 m above sea level). Then, we estimated the primary proton and helium spectra around the knee energy region using a multiple-layered feed-forward neural network as a classifier of primary particle kind. The selection efficiency of proton-induced family events is estimated to be 82%. The flux value of protons at 2×1015 eV is (5.5±1.5)×10−14 (m−2 s−1 sr−1 GeV−1). The result suggests heavy-enriched primary composition around the knee region. 相似文献
84.
Koshi Nishimura Tatsuhiko Kawamoto Tetsuo Kobayashi Takeshi Sugimoto Shigeru Yamashita 《Bulletin of Volcanology》2005,67(7):648-662
Dacitic magma, a mixture of high-temperature (T) aphyric magma and low-T crystal-rich magma, was erupted during the 1991–1995 Mount Unzen eruptive cycle. Here, the crystallization processes of the low-T magma were examined on the basis of melt inclusion analysis and phase relationships. Variation in water content of the melt inclusions (5.1–7.2 wt% H2O) reflected the degassing history of the low-T magma ascending from deeper levels (250 MPa) to a shallow magma chamber (140 MPa). The ascent rate of the low-T magma decreased markedly towards the emplacement level as crystal content increased. Cooling of magma as well as degassing-induced undercooling drove crystallization. With the decreasing ascent rate, degassing-induced undercooling decreased in importance, and cooling became more instrumental in crystallization, causing local and rapid crystallization along the margin of the magma body. Some crystals contain scores of melt inclusions, whereas there are some crystals without any inclusions. This heterogeneous distribution suggests the variation in the crystallization rate within the magma body; it also suggests that cooling was dominant cause for melt entrapment. Numerical calculations of the cooling magma body suggest that cooling caused rapid crystal growth and enhanced melt entrapment once the magma became a crystal-rich mush with evolved interstitial melt. The rhyolitic composition of melt inclusions is consistent with this model.Editorial responsibility: H Shinohara 相似文献
85.
In radon mineral curative waters, according to Russian mineral water classification, the radon concentration should be greater than 185 Bq/l. There are about 30 mineral waters with high levels of radon in Russia. Radon-rich waters have high therapeutic effects. It is proven that natural background radiation stimulates the human immune system. Radon is a natural radioactive gas that has no taste, smell or color. Radon-222 is one of the heaviest elements in the zero groups of inert gases. It is a gaseous radioactive element. All radon isotopes are -emitters while the transformation of its decay products is accompanied by the emitting of -or -particles. The main products of radon decay are short-lived isotopes Po, Pb, Bi, and TL. Belonging to the uranium and thorium decay chain, radon isotopes form directly during the decay of radium isotopes. Therefore the radon concentration depends upon the concentration of its parent's isotope in water and rocks washed by it as well as upon the amount of radon emanation. Loose rocks or rocks with a great number of cracks are characterized by higher radon concentration (zones of tectonic disturbance, weathering crusts, etc.).Crystalline rocks usually have higher uranium concentrations than the average bedrock. Examples of rock types, which often have enhanced uranium concentration >5% ppm U includes the following: granites, syenites, pegmatite, acid volcanic rocks and acid gneisses. In the earth's crust radon migrates either in a gaseous or dissolved state. It can go to the surface without any chemical reaction. Formation of the radon-rich therapeutics waters of Russia has been analyzed, and most of them are genetically connected to crystalline acid rocks that have exceeded uranium-radium mineralization. The radon content in Russia reaches more than 8,000 Bq/l. Radon-rich waters of this type occur in the Altai, Karelia, St Petersburg and Trans-Baikal regions. Another type is connected to geodynamic activity of regions and secondary radioactivity. A well-known example of radon-rich waters of the second type is Pyatigorsk in the North Caucasus. Mixing confined carbon dioxide-hydrogen sulfide water and unconfined groundwater forms radon waters. The radon concentration is 1,170–2,430 Bq/l. The occurrence of radon-rich water deposits in other regions of Russia is described. Further investigation of the radon content in other geological environments will contribute to the environmental safety as well as to the solution to many genetic, hydrogeochronological, paleoreconstructive and prediction problems in hydrogeology. 相似文献
86.
JIANG Chunming YU Guirui CAO Guangmin LI Yingnian ZHANG Shichun FANG Huajun 《大气科学进展》2010,27(6):1372-1379
CO2 efflux was estimated using different regression methods in static
chamber observation from an alpine meadow on the Qinghai-Tibetan Plateau.
The CO2 efflux showed a seasonal pattern, with the maximun flux
occurring in the middle of July. The temperature sensitivity of CO2
efflux (Q10> was 3.9, which was at the high end of the range of
global values. CO2 emissions calculated by linear and nonlinear
regression were significantly different (p<0.05). Compared with the linear
regression, CO2 emissions calculated by exponential regression and
quadratic regression were 12.7% and 11.2% larger, respectively.
However, there were no significant differences in temperature sensitivity
values estimated by the three methods. In the entire growing season, the
CO2 efflux estimated by linear regression may be underestimated by up
to 25% compared to the real CO2 efflux. Consequently, great caution
should be taken when using published flux data obtained by linear regression
of static chamber observations to estimate the regional CO2 flux in
alpine meadows on the Qinghai-Tibetan Plateau. 相似文献
87.
David S. Vinson Avner Vengosh Daniella Hirschfeld Gary S. Dwyer 《Chemical Geology》2009,260(3-4):159-171
Naturally-occurring radionuclides (uranium, radium, and radon), major dissolved constituents, and trace elements were investigated in fresh groundwater in 117 wells in fractured crystalline rocks from the Piedmont region (North Carolina, USA). Chemical variations show a general transition between two water types: (1) slightly acidic (pH 5.0–6.0), oxic, low-total dissolved solids (TDS) waters, and (2) near neutral, oxic to anoxic, higher-TDS waters. The uranium, radium, and radon levels in groundwater associated with granite (Rolesville Granite) are systematically higher than other rock types (gneiss, metasedimentary, and metavolcanic rocks). Water chemistry plays a secondary role on radium and radon distributions as the 222Rn/226Ra activity ratio is correlated with redox-sensitive solutes such as dissolved oxygen and Mn concentrations, as well as overall dissolved solids content including major divalent cations and Ba. Since 224Ra/228Ra activity ratios in groundwater are close to 1, we suggest that mobilization of Ra and Rn is controlled by alpha recoil processes from parent nuclides on fracture surfaces, ruling out Ra sources from mineral dissolution or significant long-distance Ra transport. Alpha recoil is balanced by Ra adsorption that is influenced by redox conditions and/or ion concentrations, resulting in an approximately one order of magnitude decrease (~ 20,000 to ~ 2000) in the apparent Ra distribution coefficient between oxygen-saturated and anoxic conditions and also across the range of dissolved ion concentrations (up to ~ 7 mM). Thus, the U and Th content of rocks is the primary control on observed Ra and Rn activities in groundwater in fractured crystalline rocks, and in addition, linked dissolved solids concentrations and redox conditions impart a secondary control. 相似文献
88.
由相对地热梯度推断的腾冲火山区现存岩浆囊 总被引:15,自引:6,他引:15
为利用温泉来研究和监测腾冲火山区的现今岩浆分布并探讨其活动性,提出相对地热梯度的概念:假设各热田或水热活动区的热储深度相等,则热储温度与地表温泉温度之差为该地相对地热梯度。通过对前人在该地区获得的温泉的基本要素和温泉水化学分析数据分析,选取了159个温泉计算相对地热梯度。用这159个数据,通过克里金插值方法获得了腾冲火山区的相对地热梯度平面分布。结果发现腾冲火山区有3个相对地热梯度在100℃以上的高值区域。结合其他资料,认为腾冲火山区现今存在3个岩浆囊,它们的几何尺度为19~28kin,深度为4~12km或更深,并且目前的活动性各不相同。 相似文献
89.
90.