Radionuclide deposition

NCRP. 1987. Use of bioassay procedures for assessment of internal radionuclide deposition. National Council on Radiation Protection and Measurements. Bethesda, MD. Report No. 87. 

Background Radiation—The amount of radiation to which a member of the general population is exposed from natural sources, such as terrestrial radiation from naturally occurring radionuclides in the soil, cosmic radiation originating from outer space, and naturally occurring radionuclides deposited in the human body. 

Smith, F.B. and MJ. Clark. 1986. Radionuclide deposition from the Chernobyl cloud. Nature 322 690-691. 

The dose of radiation delivered by an internally deposited radionuclide depends on the quantity of radioactive material residing in situ. This quantity decreases as a function of the physical half-life of the radionuclide and the rate at which the element is redistributed or excreted (i.e., its biological half-life). Because the physical half-life is known precisely and the biological half-life can be characterized within limits for most radionuclides, the dose to a tissue that will ultimately be delivered by a given concentration of a radionuclide deposited therein can be predicted to a first approximation. The collective dose to a population that will be delivered by the radionuclide—the so-called collective dose commitment—serves as the basis for assessing the relevant long-term health effects of the nuclide. 

Actinides were determined at the ultratrace level in moss samples collected from the eastern Italian Alps (1500 m a.s.l.). The frozen samples were cut into 1-2 cm sections and analyzed separately to obtain the distribution curves of the vertical concentrations. For plutonium and americium isotope analysis, 1-2 g of the samples were ashed, leached, separated with respect to analytes and analyzed by alpha spectrometry and LA-ICP-MS after the plutonium or americium had been electroplated on a stainless steel disk.23 Estimated limits of quantification of LA-ICP-MS for actinide radionuclides deposited on stainless steel plates after chemical separation are summarized in Table 9.45. For most of the long-lived radionuclides in moss samples, lower limits of determination were found at the 10 15gg 1 concentration level compared to those of a - spectrometry 23... 

Vented Underground Burst. An underground detonation which produces no visible fireball, but which results in the release of volatile radionuclides through fissures or other vents, produces a single particle class— atmospheric aerosol particles with condensable radionuclides deposited on their surface. Radionuclide abundance is independent of particle size. 

Data relating to radionuclide deposition (fallout) within a few miles of the Danny Boy, Sedan, and Palanquin nuclear cratering shots are examined for evidence of fractionation. The fractionation index is computed for several fission-product mass chains produced in each event. For the three events studied only Danny Boy showed unambiguous evidence of fractionation in the early fallout, and the degree of fractionation was small. In Danny Boy there was only a factor of four difference between most enriched and most depleted species, compared with the factors of several hundred that have been observed in many late time samples of airborne debris. If this small amount of fractionation proves to be true in general for cratering shots, predictions of early-fallout gamma-radiation patterns will be simplified. 

Table VIII shows the total storm rainfall and radionuclide depositions measured at each collection site. The storm description given earlier noted the diminishing rainfall as the frontal system moved down the coast. The total collected rainfall decreased from 86 mm. at Crescent City almost smoothly to the low of only 3 mm. at Piedras Blancas. The deposition of the three radionuclides follow a similar pattern the con-...

Hicks, H.G. (1982) Calculation of the concentration of any radionuclide deposited on the ground by offsite fallout from a nuclear detonation. Health Physics, 46, 585-610. 

Fig. 7-2. Summary of environmental pathways by which terrestrial plants may become contaminated with radionuclides. In the case of an input from atmosphere, or as a result of the process of resuspension , any external radionuclide burden may be reduced by field loss mechanisms conversely, an initially external radionuclide deposit (Rat) may become internalised (i int) following foliar absorption and translocation. Radioactive contaminants of soils may be derived either from atmospheric inputs or from seepage in ground waters. Partitioning of radionuclides in soil—soil water systems controls their availability for root absorption, which normally occurs exclusively from the liquid phase. The chemical speciation of the nuclide in this phase, however, provides a further control on bioavailability which is highly radionuclide specific.

An important parameter used to quantify dry deposition processes is the velocity of deposition (Kg) (Chamberlain, 1953). Vg is defined as the downward flux of aerosol or gas to a vegetation or soil surface, normalised to the ambient atmospheric gas or aerosol concentration above that surface. In the case of radionuclide deposition processes flux and concentration are, respectively, measured in units of radioactivity per unit area and volume, hence... 

Table 7-8. Retention half-lives of radionuclides deposited onto actively growing vegetation (Miller and Hoffman, 1983).

Sea bottom contamination depends on the rate of principal radionuclide deposition. In estimates the deposition coefficient 10" cm/s can be taken. 

Baklanov A, Sprensen JH (2001) Parameterisation of radionuclide deposition in atmospheric long-range transport modelling. Phys Chem Earth (B) 26(10) 787-799 Bott A (1989a) A positive definite advection scheme obtained by non-linear renormalization of the advective fluxes. Mon Weather Rev 117 1006—1015 Bott A (1989b) Reply. Mon Weather Rev 117 2633-2636... 

Aquatic sediments are formed in all surface waters by the settling of coarse and fine inorganic and organic particles. They are present in rivers, in lakes and in the oceans, and radionuclides deposited on the surface of the earth will sooner or later come into contact with these sediments. They may enter the sediments by sorption of molecularly-dispersed species (ions, molecules), by precipitation or coprecipitation, by coagulation of colloids (in particular carrier colloids) followed by sedimentation of the particles formed, or by sedimentation of coarse particles (suspended matter). By desorption, the radionuclides may be remobilized and released again into the water. 

After a radionuclide intake has occurred, any radionuclide remaining within the organ of intake will irradiate that organ or tissue. The rate at which the radionuclide leaves the site of intake by dissolution and absorption into the blood depends on the physical and chemical properties of the materials present. The term uptake is used to describe the quantity of the radionuclides that is absorbed into the blood after an intake has occurred. After absorption, portions of the radionuclide will be deposited in, and irradiate other organs and tissues as illustrated in Fig. 6.5. Fractions of the radionuclide uptake are excreted by various routes, such as in urine or faeces. A portion of radionuclide deposited in an organ may be recycled (i.e., returned to the blood) so that it is again available for deposition in an organ or excretion from the body. 

A variety of in-vitro bioassay samples can be collected from an individual for the purpose of ascertaining whether an internal radionuclide deposition has occurred previously. Samples that may be collected and analysed for such a purpose include urine, faeces, hair, teeth, breath, tissue etc. 

Each of these samples provides an indirect measure of the internal radionuclide deposition because the organ and tissues of main concern related to the radionuclide are not being sampled. Thus, proper interpretation of these results requires knowledge of the relationships between the presence of a radionuclide in the various bioassay samples and organ radionuclide burdens of interest. 

Following a nuclear accident, deposited radionuclides may be present in different physico-chemical forms, ranging from mobile low molecular mass (LMM) ionic species to inert high molecular mass (HMM) colloidal forms or particles. Even in areas far from the actual site, the relative fraction of radionuclides associated with HMM formed in rain-water may be substantial (Salbu, 1988). The size distribution patterns of radionuclides deposited, the composition of the fallout, level of activities and the activity ratios, will depend on the accident scenario, course of event, distance from the source, wind dispersion and climatic or microclimatic conditions. Spatial and temporal variations in the behaviour of deposited radionuclides with respect to mobility and bioavailability are to be expected and may in part be attributed to differences in the physico-chemical forms of radionuclides in the fallout, at least during the first years after deposition (Salbu et al., 1994). 

Analysis of herbage (of forage) has sometimes been used to detect and identify radionuclides deposited from the atmosphere (Jackson et al., 1981). However, the problem arises that when the deposition rate is low, large areas of vegetation need to be sampled for detection. In the case of plutonium, an alternative is to collect the faeces of grazing animals such as cows, sheep and rabbits. Plutonium is very poorly absorbed by the mammalian gut and so virtually all that is ingested by an animal will appear in its faeces. Also, if the species selected obtains its food entirely by grazing, then the isotopic ratio Pu will be the same in the faeces as deposited on the... 

Baklanov, A., and S0rensen, J.H. (2001) Parameterisation of radionuclide deposition in atmospheric dispersion models, Phys. Chem. Earth 26, 787-799. 

In a liquid scintillation (LS) system, the sample is mixed with a cocktail that consists of an organic scintillator dissolved in an organic solvent. The cocktail and the usual aqueous sample form an emulsion. The radiation emitted by the intimately mixed radionuclide deposits its energy in the solvent, which transfers it to the scintillator. The scintillations are then detected by the PMT. The LS counter is useful for detecting alpha particles and low-energy beta particles from samples that... 

Carrier addition is widely used, not only for yield determination, but because the added mass avoids problems of radiocolloidal behavior. Other advantages of added carrier are the ability to use precipitation for radionuclide separation and purification, and avoidance of unintended coprecipitation during scavenging. When carrier is not added because no stable isotope is available or the counting source must be very thin, radionuclide deposition on container walls or on suspended solids must be avoided by applying the techniques discussed in Section 4.4, notably use of nonisotopic carrier or low pH. 

Effective haif-iife— The time required for the amount of a radionuclide deposited in a living organism to be diminished by 50% as a result of the combined action of radioactive decay and biologic elimination. 

This document presents analyses of accidents in a Mark 1 BWRthat show revaporisation releases of radionuclides deposited in the reactor coolant system and in the drywell can continue at significant rates for up to 50 hours. 

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