Radionuclides enrichment

Walter HJ, Geibert W, Rutgers van der Loeff MM, Fischer G, Bathman U (2001) Shallow vs. deep-water scavenging of Pa and °Th in radionuclide enriched waters of the Atlantic sector of the Southern Ocean. Deep-Sea Res 148 471-493... 

Fanning K.A., Byrne R.H., Breland II, J.A. and Betzer P.R. (1981) Geothermal springs of the west Florida continental shelf Evidence for dolomitization and radionuclide enrichment. Earth and Planet. Sci. Lett. 52, 345-354. 

The metallic and Ionic cleaning procedures studied by Kern were evaluated by radiotracer methods. This technique requires the use of radionuclide enriched reagents. Recently, a procedure utilizing secondary Ion mass spectrometry (SIMS) has been developed for studying very low levels of contamination on silicon surfaces (18). 

The main scale minerals present and associated radionuclide enrichments are common to a number of the key NORM industries shown in Table 1. 

This removal may also include diffusion of soluble U(VI) from seawater into the sediment via pore water. Uranium-organic matter complexes are also prevalent in the marine environment. Organically bound uranium was found to make up to 20% of the dissolved U concentration in the open ocean." ° Uranium may also be enriched in estuarine colloids and in suspended organic matter within the surface ocean. " Scott" and Maeda and Windom" have suggested the possibility that humic acids can efficiently scavenge uranium in low salinity regions of some estuaries. Finally, sedimentary organic matter can also efficiently complex or adsorb uranium and other radionuclides. 

While great public protection is provided by these barriers, accidents can happen. Regardless of the cause of an accident, the core cannot overheat while in contact with liquid water. Furthermore it cannot be critical in the absence of water (because of the low enrichment of the fuel) thus, any accident involves a subcritical core that is heal by decaying radionuclides with inadequate cooling. Figure 8.1-1 shows the rate of heat evolution as a function of time after shutting down a 3,0(K3-MW reactor (Cohen, 1982). Even after an hour, th leat production is about 40 MW. 

Heussner S, Cherry RD, Heyraud M (1990) Po-210 and Pb-210 in sediment trap particles on a Mediterranean continental margin. Cont. Shelf Res 10 989-100 Heyraud M, Cherry RD (1983) Correlation of Po-210 and Pb-210 enrichments in the sea-surface microlayer with neuston biomass. Cont Shelf Res 1 283-293 Honeyman BD, Santschi PH (1989)The role of particles and colloids in the transport of radionuclides and trace metals in the oceans. In Environmental particles. Buffle J, van Leewen HP (eds) Lewis Publishers, Boca Raton, p 379-423... 

Linked Systems Isotopic Enrichment. The power of advanced measurement techniques can often be extended by linking them with other techniques. Such is the case for the detection of trace quantities of natural radionuclides and isotope enrichment. We have already found this extremely valuable for gas proportional counting of 37Ar and accelerator atom counting of 14C [8,9]. The first nuclide was enriched by means of thermal diffusion (Ar) the... 

Measurements of radionuclides and metals in marine sediments and particulate matter are conducted for a variety of purposes, including the determination of sedimentation rates, trace metal and radionuclide fluxes through the water column, enrichment of metals in specific phases of the sediments, and examination of new sedimentary phases produced after sediment deposition. Such studies address fundamental questions concerning the chronology of deep-sea and near-shore sedimentary deposits, removal mechanisms and cycling of metals in the ocean, and diagenesis within deep-sea sediments. 

The distribution of the product radionuclides was studied as a function of irradiation periods of from 2-14 days (Table I). These data show that irradiation periods of greater than three or four days do not result in large increases in Os-191 yield but do lead to rapid increases in the Os-193, Ir-192, and Ir-194 impurities. As a result, a three day irradiation period has been chosen as a compromise between Os-191 yield and increasing levels of isotopic impurities. The rapid approach of Os-191 yield to a maximum value during a 14-day irradiation period suggests a maximum attainable specific activity of approximately 600 mCi/mg of enriched 0s-190 target. 

Isotope dilution using enriched isotope tracers or long-lived radionuclides (e.g., I)... 

Conventional radiochemical methods for the determination of long-lived radionuclides at low concentration levels require a careful chemical separation of the analyte, e.g., by liquid-liquid, solid phase extraction or ion chromatography. The chemical separation of the interferents from the long-lived radionuclide at the ultratrace level and its enrichment in order to achieve low detection limits is often very time consuming. Inorganic mass spectrometry is especially advantageous in comparison to radioanalytical techniques for the characterization of radionuclides with long half-lives (> 104 a) at the ultratrace level and very low radioactive environmental or waste samples. 

A major topic in isotope mass spectrometry is the determination of the half-lives of long-lived radionuclides. De Bievre and Verbruggen34 determined the half-life of 241 Pu for 3-decay in the isobaric radionuclide 241 Am on material from Oak Ridge that had initially been about 93% isotopically enriched. Due to the isobaric interference of 241 Pu and 241 Am radionuclides during mass spectrometric measurements by TIMS, Am had to be removed by chemical separation immediately (less than 48 h) prior to measurements as described in reference 34. On the basis of all the measurements performed over an extended period of more than 20 years and after considering the possible effects of systematic errors during these measurements, a half-life for the 3 decay of 241 Pu of (ti/2 = 14.290 0.006 a) was reported.34... 

Long-lived radionuclides occur at extremely low concentrations, especially in environmental samples, therefore several authors have proposed matrix separation and enrichment of the analytes before analysis.21,24,26,3 39 Radiochemical methods often require very careful and time consuming separation and enrichment processes and measurement procedures of a-, (3- and -emitting radioactive species at the trace and ultratrace level using conventional radioanalytical techniques 40-43 Trace/matrix separation, which is performed offline or online in order to avoid possible isobaric interferences, matrix effects and to reduce the detection limits for the determination of long-lived radionuclides, is also advantageous before ICP-MS measurements as the most widely applied mass spectrometric technique. 

The greatest Cs/Mn ratio observed in the fallout tray samples was 0.1 at 16,500 feet or 10 times that seen in the crater lip ejecta. Air filter samples, on the other hand, exhibited the expected enrichment in the volatile fission product, 137Cs, relative to the highly refractory 54Mn. The relationships of crater ejecta and fallout materials to volatile and refractory nuclear detonation products, shown in Figures 14 and 15, conform to the generally accepted theories on the contrasting behavior of these two radionuclides. 

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