九龙江河口区水体中的226Ra和228Ra

用ＭｎＯ２－纤维富集大体积水样中的Ｒａ同位素，并用直接射气法测定２２６Ｒａ和２２８Ａｃ的β计数法测定２２８Ｒａ的方法，研究了九龙江河口区２２６Ｒａ，２２８Ｒａ的行为，结果表明：在该河口区２２６Ｒａ，２２８Ｒａ均呈非保守行为，２２６Ｒａ，２２８Ｒａ的最高值分别在盐度为１９和９处测得。２２８Ｒａ／２２６Ｒａ）Ａ．Ｒ．值在盐度小于１９的区域约为３左右。与世界其他河口区相比，九龙江河口区的２２６Ｒａ，２２     

北太平洋亚热带环流区表层水中226Ra和228Ra的分布与变化

对1999年9～10月采自北太平洋亚热带环流区的19份表层海水样品的Ra同位素分析表明。研究海域表层水中的^226Ra、^228Ra放射性比度分别介于0．67～0．92、0．08～0．30Bq／m^3之间，平均值分别为0．74、0．11Bq/m^3．^226Ra/^228Ra)A．R．活度比的变化范围为0．11～0．44，平均值为0．19．上述数值明显低于近岸海域水体的相应值，表现为典型的开阔大洋水的特征．从空间分布的特征看，研究海域Ra同位素含量与^226Ra/^228Ra)A.R.值均呈均匀分布态势．将本研究结果与历史数据进行对比后发现，本研究获得的^226Ra、^228Ra放射性比度比20世纪60～80年代得到的数据来得低，可能与水体层化作用加强导致的Ra补充量的减少以及生物生产力升高导致的Ra迁出量的增加有关．北太平洋亚热带环流区表层水中Ra同位素的时间变化与文献报道的该海域叶绿素a、硅酸盐、磷酸盐含量与初级生产力的历史变化趋势相吻合．     

Distribution and mode of occurrences of radionuclides in phosphogypsum from the Aqaba and Eshidiya fertilizer plants, Jordan

Phosphogypsum is a waste by-product of the phosphate fertilizer industry that has relatively high concentrations of some U decay-series radionuclides such as ^226Ra and ^210Pb. The distribution and environmental mobility of radionuclides in phosphogypsum are an important concern because this gypsum by-product is used for wallboard, in agriculture and as a soil amendment. This study determined the distribution of ^226Ra, ^210Pb, within phosphogypsum stacks of varying age and among three size fractions （coarse： 〈0.212 mm; medium： 0.212-0.053 mm; fine： 〈0.053 mm）, in phosphogypsum derived from Aqaba and Eshidiya fertilizer plants. The results indicated that ^226Ra and ^210Pb were generally uniformly distributed in phosphogypsum stacks and showed no significant difference in the concentration of these elements with the age of stack. In the Aqaba phosphogypsum ^226Ra was slightly 10% enriched in the coarse fraction, while ^210Pb was 10% enriched in the free size fraction. In the Eshidiya phosphogypsum ^226Ra and ^210Pb contents were both relatively enriched （10%） in the fine size fraction.     

Mixing, sediment accumulation and focusing using 210Pb and 137Cs

The Portil lagoon is a natural freshwater reservoir located at the southwest of Spain, near the coast. In its surroundings an important tourist complex has been developed since the earlier 1970s. This has resulted in increased loads of nutrients, specially during summer months. In order to evaluate the impact from humans on the lagoon caused by anthropogenic activities, we have determined vertical profiles of excess ²¹⁰Pb and ¹³⁷Cs in a sediment core taken from its bottom. Vertical profile of excess ²¹⁰Pb seems to indicate that the sediment core was affected by large-scale mixing processes. Nevertheless this possibility was ruled out based on the shape of the ¹³⁷Cs vertical distribution after modelling the ¹³⁷Cs profile considering large-scale mixing. The chronology developed from ²¹⁰Pb and ¹³⁷Cs has allowed us to calculate the temporal evolution of the mass sedimentation rate during the last century. This mass sedimentation rate increased in 1973: from 0.08(2) g cm^-2 a^-1 in the period 1900-1973 to 0.17(5) g cm^-2 a^-1 in the period 1973-1995. This increase could be related to land-movements in the drainage area and to permitted sewage inputs into the lagoon, both with its origin in the growing/running of the surrounding tourist complex.     

基于克里格法刻画砂岩型铀矿U、Ra和U-Ra平衡系数垂向分布规律——以二连盆地芒来铀矿床为例

砂岩型铀矿是绿色经济可采的重要能源矿种,目前是世界上重要的铀矿勘探类型之一。二连盆地芒来铀矿床、鄂尔多斯盆地纳岭沟铀矿床铀矿体多呈板状产出,板状铀矿体成因备受关注。为研究砂岩型铀矿内部U、Ra和铀镭平衡系数（Kp）分布的垂向分布规律,本文以二连盆地芒来铀矿床为例,采用具有网格精度高优点的克里格插值法研究U、Ra和Kp垂向分布规律,分别利用放射性样品分析数据和定量伽马测井五点式反褶积法反演U含量数据,通过克里格法精细刻画砂岩型矿体中U、Ra和Kp分布的垂向分布规律。研究发现,该矿床板状矿体内部具有卷状的特征,Kp分布形态可以用来判断含氧含铀水的运移方向以及氧化强弱。该方法对研究铀矿体形态、铀矿成矿规律和后续地浸开采具有重要意义。     

Determination of residence time and mixing processes of the Ubatuba,Brazil, inner shelf waters using natural Ra isotopes

Coastal waters contain elevated dissolved activities of short-lived radium isotopes, ²²³Ra and ²²⁴Ra, having half-lives of 11.4 and 3.66 days, respectively. The input of these isotopes near the coast must be balanced by decay and mixing into the open ocean, where excess activities are zero. Since the decay rate is known, in the ideal case the mixing rate may be determined from the offshore distribution of these isotopes. This study found that samples collected in June 2000 followed the expected exponential decrease with distance offshore. We assign a dispersion coefficient of 28–39 m² s⁻¹ for this study. During January 2002 and November 2003, there was not a consistent decrease of activity with distance offshore. This is likely due to the ruggedness of the coastline, where many bays and small islands interrupt simple mixing patterns. To estimate exchange rates during 2002 and 2003, we used a model based on the decrease in the ²²⁴Ra/²²³Ra activity ratio (AR) with time for samples isolated from fresh inputs of Ra. This model yielded residence times of 1–2 weeks for samples collected within 20 km of the coast. We used this residence time to calculate the flux of ²²⁸Ra (half-life = 5.7 years) to the study area necessary to maintain the enrichment relative to ocean water. This enrichment is a factor of ten greater than the flux of ²²⁸Ra expected from submarine groundwater discharge (SGD) occurring within 50 m of shore.     

北黄海水体的226Ra和228Ra

用锰纤维富集-射气法测定了北黄海海水中的镭同位素226Ra和228Ra,研究了该海域水体中镭同位素的含量和分布.研究结果表明北黄海水体夏季226Ra的比活度为1.80～4.35 Bq/m3,平均值为3.06 Bq/m3;冬季226Ra的比活度为2.08～5.20 Bq/m3,平均值为3.28 Bq/m3.北黄海夏季228Ra的比活度为3.85～25.60 Bq/m3,平均值为10.60 Bq/m3;冬季228Ra的比活度为3.14～15.60Bq/m3,平均值为7.66 Bq/m3.该数据范围和中国近海其他海域、孟加拉湾、泰国昭披耶河口、濑户内海等海域相近.北黄海东北部海域,渤海海峡靠近山东半岛的海区和中北部海区表层镭同位素活度较高.C1断面镭同位素的分布特征从镭同位素的方面证实了渤海海峡水交换表现为北进南出特征这一结论的正确性.226Ra和228Ra的垂直分布较为复杂,大部分站位呈现出底层活度变高的趋势,其他少数站位呈现出中间层活度高的分布特征,不同来源的镭同位素输入至该海域形成了这样的分布特征.     

Distribution of <Superscript>226</Superscript>Ra in the Arctic Ocean and the Bering Sea and its hydrologic implications

Radium-226 (²²⁶Ra) activities were measured in the surface water samples collected from the Arctic Ocean and the Bering Sea during the First Chinese National Arctic Research Expedition. The results showed that ²²⁶Ra concentrations in the surface water ranged from 0.28 to 1.56 Bq/m³ with an average of 0.76 Bq/m³ in the Arctic Ocean, and from 0.25 to 1.26 Bq/m³ with an average of 0.71 Bq/m³ in the Bering Sea. The values were obviously lower than those from open oceans in middle and low latitudes, indicating that the study area may be partly influenced by sea ice meltwater. In the Bering Sea, ²²⁶Ra in the surface water decreased northward, probably as a result of the exchange between the ²²⁶Ra-deficient sea ice meltwater and the ²²⁶Ra-rich Pacific water. In the Arctic Ocean, ²²⁶Ra in the surface water increased northward and eastward. This spatial distribution of ²²⁶Ra reflected the variation of the ²²⁶Ra-enriched river component in the water mass of the Arctic Ocean. The vertical profiles of ²²⁶Ra in the Canadian Basin showed a concentration maximum at 200 m, which could be attributed to the inputs of the Pacific water or/and the bottom shelf water with high ²²⁶Ra concentration. This conclusion was consistent with the results from ²H, ¹⁸O tracers.     

南极普里兹湾及其邻近海域表层水镭同位素的分布及应用

中国第27次南极科学考察期间(2010年12月30日至2011年1月16日),对普里兹湾及其邻近海域表层海水进行了226Ra和228Ra的分析,结果表明:226Ra和228Ra比活度的变化范围分别为1.47—2.43Bq/m3和0.17—0.45Bq/m3,平均值分别为2.13Bq/m3和0.29Bq/m3,228Ra/226Ra)A.R.(228Ra与226Ra的活度比)的变化范围为0.08—0.20,平均值为0.14。根据盐度和226Ra的质量平衡方程,计算出研究海域表层水中冰融水、南极夏季表层水和普里兹湾中深层水的份额。研究海域表层水中温度、盐度、226Ra、228Ra、228Ra/226Ra)A.R.和冰融水份额的空间分布显示,在埃默里冰架前沿海域,西侧海域较东侧海域具有低温、高盐、高226Ra、低228Ra、低228Ra/226Ra)A.R.、低冰融水份额的特征,证实埃默里冰架下水体东进西出的运动规律。根据埃默里冰架前沿东、西侧水体228Ra/226Ra)A.R.的差异,估算出埃默里冰架下表层水体东进西出所经历的时间为1.85a。此外,在普里兹湾湾口中部海域(66.5—67.5°S,72°—74°E),观察到次表层水的上升通风作用,该区域较高的228Ra含量和228Ra/226Ra)A.R.证明这些表层水体并非来自湾外绕极深层水的上涌,而可能来自湾内埃默里冰架输出水体。     

Under the shadow of the Magellanic Bridge: A measurement of the extragalactic background at ∼ 0.7 keV

We measured the extragalactic 0.7 keV X-ray background by observing the X-ray shadow of a neutral gas cloud in the Magellanic Bridge region. Two ROSAT PSPC observations of total 104 ks were complemented by a detailed H I mapping of the cloud with both the Parkes 64 m telescope and the Australia Telescope Compact Array. From the detected anti-correlation between the observed background intensity and the H I column density of the cloud, we derived the unabsorbed extragalactic background intensity as ∼ 28 keV s⁻¹ cm⁻² keV⁻¹ sr⁻¹ at ∼ 0.7 keV. The 95% confidence lower limit 18 keV s⁻¹ cm⁻² keV⁻¹ sr⁻¹ is greater than the expected point-like source contribution ? 14 keV s⁻¹ cm⁻² keV⁻¹ sr⁻¹, constrained by the mean source spectrum together with the total background intensity in the 1-2 keV band. A significant fraction of the 0.7 keV background likely arises in a diffuse hot intergalactic medium of a few million degrees, as has been predicted in hydrodynamic simulations of cosmological structure formation.Richard McCray