Susan A. Casso

Determination of thorium isotopes in seawater by nondestructive and radiochemical procedures

Abstract Procedures have been developed for the analyses of dissolved and particulate 234Th, 228Th, 230Th and 232Th in seawater. Large volume samples (>1000 1) are collected using in situ pumps. Seawater is pumped sequentially through a filter cartridge and two MnO2 adsorbers for the collection of particulate and dissolved Th, respectively. Both filters adsorbers are analysed for 234Th using a simple gamma counting technique. This newly developed 234Th procedure can be conducted at sea, and thus provides an easy and efficient method for 234Th analyses on large volume samples. Subsequent radiochemical purification procedures and low-level alpha counting techniques are used in the laboratory for the analyses of 228Th, 230Th and 232Th on these same samples.

DETERMINATION OF FISSION-PRODUCTS AND ACTINIDES IN THE BLACK SEA FOLLOWING THE CHERYNOBYL ACCIDENT

Radiochemical procedures are discussed for the isolation and determination of a suite of radionuclides in samples from the Black Sea following their input from the Chernobyl reactor accident. The samples analyzed include discrete water samples and both suspended and dissolved phases collected by in-situ chemisorption techniques. The radiochemical scheme permits the separation and analysis of134Cs,137Cs,90Sr,144Ce,147Pm,106Ru,239Pu,240Pu, and in some instances242Cm,238Pu, and241Am. The detection techniques employed include various instrumental gamma spectrometric methods, low-level beta counting, alpha spectrometry, and mass spectrometry.The methods developments are described and data are presented on some representative samples from the Black Sea. The sensitivity of the analysis for the various nuclides and sample types is summarized and questions of radiochemical interferences are addressed.

In situ chemisorption of radiocesium from seawater

A novel approach to in situ extraction of Cs radionuclides from seawater is described which offers many advantages over previous methods. Cesium (stable and radioactive) is partially stripped from seawater as it passes in series through a tandem cartridge consisting of twin beds of ion exchange resin impregnated with cupric ferrocyanide. It is demonstrated that, when seawater passes through this cartridge at a constant flow-rate, collection efficiencies of each bed are the same, allowing the calculation of the seawater Cs nuclide concentration. The cartridge is made of inexpensive, readily available, PVC pipe fittings and is easily deployed under various field conditions. Procedures are described for resin preparation and desorption and radiochemical purification of the collected Cs. Thousands of liters of seawater can be stripped of Cs in this way, permitting substantial improvement in the sensitivity of measurement of 134Cs and 137Cs.

Fallout nuclides in Atlantic and Pacific water columns : GEOSECS data

Funding was provided by the United States Department of Energy under Contract DE-AC02-EV03563.

Particle and solution phase depth distributions of transuranics and 55Fe in the North Pacific

In situ large volume filtration and chemisorption techniques were used to collect samples from the North Pacific for radiochemical analyses of fallout transuranics and 55Fe in filterable and filtered phases. The data cover several locations for surface collections and a detailed depth profile north of Hawaii at 30°N. The observed partition of these nuclides between suspended particulate and filtered phases is directly linked to the rates at which they are moved downward through the water column in association with sinking particles. Particulate phases in open ocean surface waters contain higher Pu (12–35%) than subsurface particulates (which average about 6%). 241Am was found to exhibit much stronger particle association—typically close to 50% in both surface and subsurface waters—in accord with its known greater particle reactivity. In the high Pu deep water layer, particle associated Pu dropped to close to 1% of total Pu concentration. Together with a correlated increase in the proportion of oxidized Pu in this layer close to the sediment-water interface, this is taken as clear evidence of remobilization Pu from particles at, or near to, the interface. 55Fe distributions on filtered particulates indicate a much deeper depth distribution relative to the transuranics. This may reflect both a higher particle association reactivity in respect to scavenging and a longer exposure history to scavenging (especially relative to 241Am—produced by in situ decay).

Inflow of Chernobyl 90Sr to the Black Sea from the Dnepr River

Following the Chernobyl reactor accident in April 1986, studies of radionuclides in aquatic systems in general, and in the Black Sea in particular, have focused primarily on the fate and behaviour of direct fallout deposition (Buesseler et al. , in press; Livingston et al. , 1988; Polikarpov et al. , 1991). In this paper we present an evaluation of riverine 90 Sr input and its use as a tracer for circulation studies of Chernobyl labelled shelf waters. We describe how 90 Sr measurements in the Dnepr River in the period 1986–89 can be used to determine the amount and timing of the subsequent 90 Sr inflow to the northwest Black Sea. Comparison of these data with measurements made in the Danube River in 1988 demonstrates that the Dnepr 90 Sr flux to the Black Sea is about one order of magnitude higher than that of the Danube.

Radiocesium and other nuclides in the Norwegian-Greenland Seas, 1981-1982

This report contains data obtained from measurements of various artificial radiotracers in seawater samples from the Norwegian-Greenland Seas and adjacent seas during 1981-82. The radionuclides measured include /sup 137/Cs, /sup 134/Cs, /sup 90/Sr and /sup 3/H. The sampling and analytical work result from the efforts of several laboratories. The data set includes a large number of measurements in surface water in the region and a substantial number of vertical profiles in the various water masses. The radiotracers in the region originate from nuclear fallout from atmospheric nuclear-weapons tests and from low-level releases of liquid waste to European coastal waters in association with the reprocessing of nuclear fuel.

Cesium and strontium isotopes in the northwestern North Atlantic and Arctic Ocean, 1981-1985

The report contains (137)Cs and (90)Sr data from seawater samples collected on four cruises in the northwestern North Atlantic, Arctic Ocean, and Barents Sea during 1981 to 1985, and radionuclide data (137)Cs, (90)Sr and (239)Pu from samples collected on a cruise to the Norwegian-Greenland Seas in 1979. Also included are data from four ice stations in the Arctic from 1979 to 1985. The sample collections were made possible through collaborative efforts with several laboratories. The radionuclide analyses were done at the Woods Hole Oceanographic Institution.

Ruthenium-106 in the Black Sea

Profiles of Chernobyl 106Ru and137 Cs were obtained at margin and interior sites in the Black Sea between 1986 and 1988. The data show a vertical separation in the activity distributions of these two tracers. Ruthenium-106 is found at depths below the Chernobyl 137Cs, indicating that 106Ru is removed via particle scavenging processes, unlike the Cs isotopes which serve primarily as tracers of physical mixing. In 1988, more detailed measurements at depths near the oxic/anoxic interface suggest that a subsurface maximum in 106Ru occurs at the same depth as the paniculate Mn maximum above oxygen zero, with perhaps a secondary peak below. Inventory calculations indicate that while 106Ru has been significantly scavenged from the upper 50m, the net loss of 106Ru from the upper 200m has been relatively small since its input in 1986. This implies that substantial 106RU is remineralized from sinking particles, and returns to the dissolved pool, thus limiting net export and increasing the apparent residence time of Ru. Relatively high deep water 106Ru inventories (50% of total) suggest that a substantial fraction of the 106Ru transient tracer reaches the deep waters as a pulse shortly after delivery. This is analogous to what has been seen for the weapons testing fallout radionuclide, 239,240Pu.

Studies of Chernobyl 90Sr and Cs Isotopes in the Northwest Black Sea (Poster)

During 1990, an oceanographic cruise was conducted to study the fate of Chernobyl fallout radionuclides in the Black Sea. The focus of this program was a study of the waters and sediments in the Danube fan region. Work was conducted aboard the R/V Professor Vodjanitsky, operated by the Institute of Southern Seas Biology, Sevastopol (U.S.S.R.), with participation by scientists from the Woods Hole Oceanographie Institution and the U.S. Environmental Protection Agency. As part of this program, samples of marine sediments, waters and biota were analyzed by the three labs in an intercomparison of radioanalytical techniques.