Utility of 222Rn as a passive tracer of subglacial distributed system drainage

This paper is not subject to U.S. copyright. The definitive version was published in Earth and Planetary Science Letters 462 (2017): 180-188, doi:10.1016/j.epsl.2016.12.039.Water flow beneath the Greenland Ice Sheet (GrIS) has been shown to include slow-inefficient (distributed) and fast-efficient (channelized) drainage systems, in response to meltwater delivery to the bed via both moulins and surface lake drainage. This partitioning between channelized and distributed drainage systems is difficult to quantify yet it plays an important role in bulk meltwater chemistry and glacial velocity, and thus subglacial erosion. Radon-222, which is continuously produced via the decay of 226Ra, accumulates in meltwater that has interacted with rock and sediment. Hence, elevated concentrations of 222Rn should be indicative of meltwater that has flowed through a distributed drainage system network. In the spring and summer of 2011 and 2012, we made hourly 222Rn measurements in the proglacial river of a large outlet glacier of the GrIS (Leverett Glacier, SW Greenland). Radon-222 activities were highest in the early melt season (10–15 dpm L−1), decreasing by a factor of 2–5 (3–5 dpm L−1) following the onset of widespread surface melt. Using a 222Rn mass balance model, we estimate that, on average, greater than 90% of the river 222Rn was sourced from distributed system meltwater. The distributed system 222Rn flux varied on diurnal, weekly, and seasonal time scales with highest fluxes generally occurring on the falling limb of the hydrograph and during expansion of the channelized drainage system. Using laboratory based estimates of distributed system 222Rn, the distributed system water flux generally ranged between 1–5% of the total proglacial river discharge for both seasons. This study provides a promising new method for hydrograph separation in glacial watersheds and for estimating the timing and magnitude of distributed system fluxes expelled at ice sheet margins.U.S. National Science Foundation Arctic Natural Sciences Program (ANS-1256669); Woods Hole Oceanographic Institution Arctic Research Initiative, Ocean Ventures Fund, and Ocean Climate Change Institute; United Kingdom Natural Environment Research Council studentship (NE/152830X/1); the Carnegie Trust, Edinburgh University Development Trust

Natural radionuclides and radiation risk assessment in southern Thailand soils

The natural radioactivity and uranium activity ratio in soil samples from four provinces in southern Thailand have been studied. These four selected provinces are proposed as potential sites to set up thermal power plants by Thai government, since the government has planned to construct nuclear power plants (NPPs) as well as coal-fired thermal power plants to generate adequate and reliable electricity for supply a rapidly growing industrialization. It is important to focus not only on security and adequacy of power system but also on environmental protection and monitoring and risk assessment. To carry out environmental monitoring and radiation risk assessment, the concentration of natural radionuclides and radiation hazard parameter play significant roles. These data should be established and available before construction and during operation of power plants. For this reason, a total number of thirty-seven soil samples were collected from those four provinces. The concentration of natural radionuclides including 226Ra, 228Ac and 40K were determined by using gamma spectroscopy. Activity concentrations of 226Ra, 228Ac and 40K vary from 3–160 Bq/kg with an average of 50 Bq/kg, 5–225 Bq/kg with an average of 70 Bq/kg and 0–1425 Bq/kg with an average of 330 Bq/kg, respectively. We have notice that most of the soil samples corrected from one of the four provinces show higher activity concentrations of radionuclides than others. This province is one of the high uranium and thorium level area in Thailand, reported by the Department of Mineral Resource, Thailand. The radiation hazard parameters including absorbed dose rate (D), annual effective dose equivalent (AEDE), radium equivalent activity (AGDE) and external hazard index (Hex) were calculated and compared with the international recommended values. Concentration of uranium was determined using the inductively coupled plasma mass spectrometry (ICP-MS) and isotopic composition of 234U/238U and 235U/238U were determined using thermal ionization mass spectrometry (TIMS). Concentrations of U vary from 1.5–32 μg/g with an average of 9.0 μg/g. Activity ratio of uranium will be presented for the first time in southern Thailand soils.Second International Conference on Radiation and Dosimetry in Various Fields of Research