INSTITUTE OF PHYSICS PUBLISHING

JOURNAL OF RADIOLOGICAL PROTECTION

J. Radiol. Prot. 24 (2004) A35–A62

PII: S0952-4746(04)88490-8

Absorbed dose rate conversion coefficients for reference terrestrial biota for external photon and internal exposures

12:03 pm, Mar 18, 2005

V Taranenko1 , G Pr¨ohl1 and J M G´omez-Ros2 1 Institute of Radiation Protection, GSF—National Research Centre for Environment and Health, Ingolst¨adter Landstraße 1, D-85764 Neuherberg, Germany 2 Radiation Dosimetry Group, CIEMAT, Avenida Complutense 22, 28040 Madrid, Spain

E-mail: [email protected]

Received 3 December 2003, accepted for publication 29 October 2004 Published 3 December 2004 Online at stacks.iop.org/JRP/24/A35 doi:10.1088/0952-4746/24/4A/003

Abstract The paper describes dosimetric models that allow the estimation of average radiation exposures to terrestrial biota due to environmental sources in the soil as well as internal uniform distributions of radionuclides. Simple threedimensional phantoms for 13 faunal reference organisms are specified. The calculation of absorbed dose per unit source strength for these targets is based on photon and electron transport simulations using the Monte Carlo method. The presented absorbed dose rate conversion coefficients are derived for terrestrial reference species. This allows the assessment of internal exposure as well as external photon exposure depending on the nuclide, habitat, target size and environmental contamination. To enable the application of specific radiation weighting factors for α-, low energy β- (E 0 < 10 keV), β- and γ -radiations, their partial contributions to the total absorbed dose are provided separately. The coefficients for external exposure are listed for organisms living above the ground for an infinite plane source 3 mm deep in soil,as well as for a horizontally infinite volume source uniformly distributed to a depth of 10 cm. Furthermore, the coefficients are also presented for organisms living in a contaminated 50 cm thick soil layer. A multi-layer canopy model for plants is also described. The conversion coefficients are given for 3 H, 14 C, 40 K, 36 Cl, 59,63 Ni, 89,90 Sr, 94 Nb, 99 Tc, 106 Ru, 129,131 I, 134,135,137 Cs, 210 Po, 210 Pb, 226 Ra, 227,228,230,231,232,234 Th, 234,235,238 U, 238,239,240,241 Pu, 241 Am, 237 Np and 242,243,244 Cm, together with their progeny. 1. Introduction Traditionally, scientific and administrative activities of radiation protection focused on the radiation exposure of humans, due to both artificial and natural sources. However, in recent 0952-4746/04/04A0035+28$30.00

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years, the limitation to human health protection has been increasingly questioned and the possible impact of ionising radiation on non-human biota has attracted more and more attention from both the professional radiation and environmental protection communities (Pentreath 2002, NEA 2002). The requirement for an internationally agreed rationale for the protection of the environment from exposure to ionising radiation has been recognised (IAEA 1999). This paper focuses on the development of dosimetric models that enable the assessment of radiation doses to a broad range of target organisms from both internal and external irradiation. Input quantities for the assessment are measured or calculated activity concentrations in biota or in their immediate environment. Nuclide-specific dose rate conversion coefficients are derived as a function of habitat, target size and exposure route (internal or external). Radionuclides distributed in the environment lead to external radiation exposure of organisms living in or close to a contaminated medium. The external exposure of biota is the result of complex and sometimes non-linear interactions of various factors: • the geometrical relation between the radiation source and the target; • the level of contamination in the environment; • the materials present and their shielding properties with respect to both environmental media and the organism; • the radionuclide-specific decay properties characterised by the radiation type, the energies emitted and the yield; • the size of the target organism (self-shielding). The geometric relationship between radiation source and the exposed organism is a very important factor. The intensity of the radiation field around a source decreases with distance and is influenced by the material between the radiation source and the target. The number of possible situations is enormous; therefore a limited number of representative situations have been selected for detailed calculations. The exposure conditions were selected so that they allow the determination of exposures also for those conditions for which explicit calculations were not made. Recent approaches to estimating exposures to biota from radionuclides in the environment have been based on a number of simplifying assumptions that potentially lead to overestimation (US DOE 2002, Amiro 1997, IAEA 1992). For internal exposure, it is complete energy absorption. For external exposure, it is homogeneity and infinite extent of the surrounding contaminated medium. These conditions are in general adequate for aquatic ecosystems, where the differences in density of water and the exposed biota are very limited. However, in terrestrial habitats with pronounced heterogeneities in materials and densities, analytical approaches are associated with considerable uncertainties. In the case of internal exposure, it is often assumed that the whole energy of γ -radiation is absorbed within organisms, although the range of photon radiation is in general much longer than the organism size. This causes considerable overestimation, especially for small biota. Some authors (e.g. Thorne et al 2002) have used elsewhere precalculated absorption energy fractions for photons and electrons in order to give more realistic values of internal dose. Thorne et al (2002) note that internal exposure of animals has been estimated by calculating the dose at the centre of a uniformly contaminated sphere of unit density material. Obviously, such a positioning of a receptor has a tendency to overestimate the dose. In the terrestrial environment, the radiation source may be in air or in soil and the exposure targets live in the soil (e.g. mouse, earthworm), on the soil (e.g. rabbit, cattle) or in the air (birds). However, the air as a relevant source of radiation is in general a temporary and local phenomenon, since processes such as fallout, rain-out and wash-out cause an

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effective deposition to soil. The most relevant radiation source subsequent to a release in the environment is therefore the contamination of the soil, which causes—depending on the half-life—a persistent radiation source for all terrestrial biota. The estimation of external exposures in the terrestrial environment is more complex than in the aquatic environment. Soil, air and organic matter differ considerably in composition and density, which cannot, in general, be adequately taken into account by analytical solutions. Therefore, radiation transport is simulated by means of a Monte Carlo technique, which provides several advantages: • • • •

materials differing in composition and density can be considered; complex geometries of sources and targets can be simulated; all relevant physical processes that control radiation transport are precisely treated; self-shielding is implicitly considered.

Due to the complexity of the processes and the enormous variability of organisms and their natural habitats, it is impossible to cover all exposure conditions. Therefore, typical energies, contaminated media and organism sizes were selected for detailed consideration. Exposure conditions for which detailed calculations are not available are then determined by interpolation between those cases. The exposure conditions for this purpose were defined taking into account the following criteria: • Dose rate conversion coefficients (DCCs) are calculated for β- and γ -emitters. Due to the short range of α-radiation, external exposure from α-particles is not relevant (except for very small organisms or organs such as bacteria and fungal hyphae for which the equilibrium dose in a surrounding medium can be used). • For the calculation of DCCs for species in the soil, a uniformly contaminated volume source was assumed. • For the calculation of DCCs for species on the ground, a planar radiation source on top of the soil with a surface roughness of 3 mm and a volume source with a depth of 10 cm were assumed. Extensive tabulations for other soil source configurations are not shown here, since it is believed that the selected variants are of primary importance. 1.1. Dose concept and RBE The concept of equivalent dose may be applied to biota only cautiously and with limitations. The radiation quality factors were derived for application in dose assessments for humans, for whom stochastic effects are of primary importance. However, in the assessment of exposures to biota different end-points are frequently considered, as well as the emphasis being shifted to higher doses that may even cause deterministic effects. Therefore, the radiation quality factors used for dose assessments for humans may not be applicable to dose assessments for biota. Before the concept of equivalent dose is applied to biota, appropriate radiation weighting factors have to be derived for the relevant end-points. According to these considerations, absorbed dose will be the key quantity for the exposure assessment of biota. The estimations made in FASSET (framework for assessment of environmental impact) and presented here have been made on the basis of absorbed dose. To account for the radiation quality, the possible impact of the radiation weighting factor on the exposures to biota is illustrated. 1.1.1. Relative biological effectiveness. For the calculation of the equivalent dose, ICRP recommends a radiation weighting factor for α-radiation of 20. However, for humans,

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V Taranenko et al Table 1. Exposure models for the calculation of dose rate conversion coefficients for the reference organisms.

Radiation Radiation target Exposure type Source

Fauna

Flora

Target location

Target size

Geometry

External

γ

Volume, upper 50 cm In soil, at 25 cm depth Plane, at 0.3 cm depth; Above soil, 1 cm–1.5 m Simple phantoms volume, upper 10 cm at height 0–10 m

Internal

α, β, γ

Whole body



External

γ

Plane, at 0.3 cm depth; volume, upper 10 cm

Above soil, at height 0–5 m

0.5–1 cm

Horizontal layers

stochastic radiation effects are the major concern, whereas for biota deterministic effects such as morbidity, mortality, reduced reproductive success and mutations are of primary interest. UNSCEAR (1996) suggests a value for the RBE of α-radiation of 5 for the use in impact assessment for biota. Kocher and Trabalka (2000) suggest a RBE factor of 5–10 for biota. This range has been derived on the basis of the analysis given by the ICRP for deterministic effects. However, there are several experiments that also suggest higher values for RBE. In some of the experiments, end-points are investigated that are especially important for the consideration of doses to biota (IAEA 1999). NCRP (1991) summarises RBE values for internal α-emitters of 15–50 for the induction of bone sarcomas, lung cancer and liver chromosome aberrations. The last end-point is particularly relevant for the consideration of effects on biota. These examples highlight the large variability of RBE values and the uncertainty that is associated with their application. The investigations cover a range of about 5–50; however, in some cases even higher values are reported. Due to the complex dependence of RBE on dosimetric and environmental factors as well as on the end-point considered, the derivation of a generally applicable RBE value for internal α-emitters appears currently not to be possible. A number of investigations suggest that low energy β-radiation with energies below 10 keV has a higher biological effectiveness than electrons with energies above 10 keV (Straume and Carsten 1993, Moiseenko et al 2000). Moiseenko et al consider a RBE value for tritium (mean β-energy less than 10 keV) between 2 and 3 as appropriate. 2. Materials and methods Several exposure models have been assumed. Table 1 summarises the different source–target combinations, in which the habitat of the exposure target is listed against the location of the radiation source. 2.1. Description of reference organisms Clearly, it is impossible to consider all species of flora and fauna during the course of an environmental impact assessment even within limited geographical boundaries. Instead, reference organism types are selected to represent typical species for ecosystems, for which models are adopted for the purpose of deriving organism, tissue or organ dose rates. The selection of reference organisms is described in Strand et al (2001). The reference organisms are selected from four terrestrial ecosystems, i.e. forest, semi-natural, agricultural and wetlands.

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Table 2. Specification of the faunal reference organisms. Example animal

3D shape

Fulla : length, width, height (cm)

Mass (g)

Shielding layer (cm)

Woodlouse Earthworm Mouse/bird, small Mole Snake Rabbit/bird, large Fox Deer Cattle Bird egg, small Bird egg, large

Ellipsoid Cylinder Ellipsoid Ellipsoid Cylinder Ellipsoid Ellipsoid Ellipsoid Ellipsoid Ellipsoid Ellipsoid

1.7, 0.6, 0.3 12, 0.8, 0.8 7, 3, 3 11, 4, 4 100, 3, 3 30, 11, 11 40, 15, 20 60, 27, 27 160, 70, 90 2.4, 1.7, 1.7 4.5, 3, 3

0.17 6 35 97 740 2 × 103 6.6 × 103 2.4 × 104 5.5 × 105 4 22

0 0 0.1 0.1 0 0.1 0.1 0.1 0.3 0.1 0.1

a

For an ellipsoid the dimensions are the lengths of the major axes; for a cylinder width equals height and represents diameter. The triplet corresponds to x-, y- and z-dimensions of the phantom in Monte Carlo simulations.

The component ecosystems were selected to be typical for Europe. The selected reference organisms and their descriptive parameters should be considered as a useful first-order approximation that may require refining in specific contexts. 2.1.1. Fauna. Simple three-dimensional (3D) phantoms, i.e. ellipsoids and cylinders, have been defined as model geometric equivalents of reference organisms according to average characteristics of mass and size. Such representation is sufficient since the primary objective of the study is to quantify the whole body dose. More detailed calculation of dose distribution within the body, namely for critical organs and tissues, would require the application of detailed anatomical data. As well as the issue of the unification of reference phantoms, the question of intercommunication with the other stages of system for dose assessment arises: whether the knowledge on the radionuclide partitioning among the organs is available in full, or whether there is a representative amount of information on the effects for organs considered. These are nine ground-dwelling organisms with dimensions in a range in size from approximately one millimetre to one metre and with respective masses ranging from 0.2 g to 550 kg, plus a small and a large bird, having the same geometry as a mouse and rabbit, respectively, and two bird eggs (table 2). The organisms are located near the ground–air interface. In addition, two reference bird phantoms are also located at 3 and 10 m heights above the ground. The material composition of the reference organisms is taken to be the same as for skeletal muscle (ICRU 1992a) with a density 1 g cm −3 . The shielding layer representing fur and skin is approximated by keratin with density 1 g cm−3 , except for the eggs where calcium carbonate, CaCO3 , with density 2.4 g cm−3 was used as the eggshell. 2.1.2. Flora. For the calculation of external exposure to photon radiation, three horizontal layers—characterised as a homogeneous mixture of vegetation biomass and air—are defined according to the estimated biomass per unit area (table 3). The layers overlie one another, bottom up: herbaceous vegetation, shrub and tree. The density decreases with height, but it is assumed to be constant within the layer. The most important parameter—the biomass per unit area—can vary substantially. Therefore, an interval estimate is applied for the biomass of the tree and the shrub layers. For each layer, the approximate material composition has been calculated according to the biomass density and taking its composition to be that of water.

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V Taranenko et al Table 3. Three vegetation layers considered as receptors for the calculation of the external photon exposure of plants.

Vegetation layer

Layer height (m)

Vegetation mass per unit area (kg m−2 )

Layer densitya (kg m −3 )

Target organ

Location of the target layer

Tree

9

Min 10 Max 15

Min 2.3 Max 2.9

Bud Meristem

Middle of canopy, at 5.5 m, 1 cm thick

Shrub

0.9

Min 2 Max 5

Min 3.4 Max 6.8

Bud Meristem

Middle of canopy, at 0.55 m, 1 cm thick

Herb

0.1

1.25

13.7

Meristem

On the ground, 5 mm thick

a

Including the air component.

The target organs, the meristem and the buds, are described as layers parallel to the ground surface. These organs are characterised by very intensive cell division, which may cause high radiosensitivity. They are key components for vegetative and floral reproduction. 2.2. Internal exposure of fauna For the calculation of average absorbed dose due to internal exposure, the assumption has been made that the radiation emitters are uniformly distributed within the body of the reference organism. The range of α-particles in tissue is 16–130 µm for 3–10 MeV energy respectively. Therefore, it is assumed for all organisms that all emitted energy is absorbed. For γ - and β-radiations, the average absorbed dose per unit source strength (photons or int , for a target T , radiation R (photon or electron) and initial electrons per unit mass), DT,R,E 0 particle of energy E 0 (expressed in joules) is derived as int DT,R,E ≡ 0

E 0 × f T,R,E0 × mT , mT

(1)

where f T,R,E0 is the fraction of energy emitted as a specified radiation type R in a body of target T and which is absorbed within it, and m T is the body mass of target T , kg. Here the multiplication by target mass is needed for the normalisation to unit source strength, i.e. the absorbed dose is per one source particle emitted from 1 kg of source being the same as target. The average absorbed dose per unit source strength has units of Gy kg. To account for the energy leakage from the target, a series of Monte Carlo models has been constructed according to the specification of the faunal reference organisms (table 2). In these model geometries, the target phantom is surrounded by air. Test simulations showed little influence of the surrounding material composition and density on particle backscattering. The test calculations were done for surrounding soil of 1 and 1.6 g cm −3 densities. The simulations were performed for 19 discrete energies, E 0 , in the range from 10 keV to 10 MeV. The coupled electron–photon transport mode was used. As a result, the absorbed dose per starting particle, denoted as a quotient in equation (1), and its kerma analogue have been estimated along with statistical uncertainties. 2.3. External exposure of fauna in the ground In the dosimetric model for the reference organisms in the soil, it is assumed that the target organism is at a depth of 25 cm in a uniformly contaminated soil layer of 50 cm.

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Table 4. Composition of materials assumed in the Monte Carlo simulations. Mass fraction (%) Element

Organism tissuea

Shielding layer

H C N O Na Al Si P S Cl Ar K Ca Fe

10.2 14.3 3.4 71.0 0.1

7 50 16 24

Density (g cm −3 ) a b

Eggshell

Soilb

12

2.1 1.6

48

57.7

Air 0.064 0.014 75.09 23.56

5.0 27.1 0.2 0.3 0.1

3 1.28

0.4 40 1.05

1.0

2.4

1.3 4.1 1.1 1.6

1.2 × 10−3

Skeletal muscle (ICRU 1992a). Typical silty soil, on a wet mass basis (Eckerman and Ryman 1993).

Since the densities of soil and tissue are similar, the photon transport for the specified configuration can be simulated directly for the finite source surrounding the target. Hence, the Monte Carlo model geometry consists of a soil compartment which is the isotropic source (with effectively infinite horizontal dimensions, varying for different source energies) and the target in the middle as a receptor. It is assumed that the reference organisms of mouse, mole, rabbit and fox are surrounded by a shielding layer of 0.1 cm and an air layer of 0.5 cm to take into account of the fact that the corresponding burrowing animals are not in direct contact with the contaminated soil. Woodlice and earthworms fully fill their burrows and are not surrounded by air. For a complete description see table 2 for the geometry and table 4 for material compositions. The orientation of organisms in the model geometry was as stated in table 2, i.e. the first two size parameters (length and width) define horizontal dimensions while the height specifies the vertical extent. Using the photon transport mode, under the assumption of charged-particle equilibrium, the average absorbed dose was approximated by the scored kerma. The simulations were performed for seven initial energies in the range from 10 keV to 3 MeV. The results were normalised to unit source strength (one photon per unit source mass). 2.4. External exposure of fauna and flora above the ground 2.4.1. Fauna. In this part, the dosimetric model for external exposure to photon radiation, originating from horizontally infinite soil sources, is described. The sources considered are: planes at various depths, including a depth of 3 mm, which represents superficial deposition of radionuclides, taking into account the effect of surface roughness; and a volume source uniformly distributed to a depth of 10 cm. In the model geometry, most of the faunal organisms are located on the ground, i.e. at zero height. The phantoms of deer and cattle are located at heights of 0.5 and 1 m, respectively. The small and large birds are located at heights of 0, 3 and 10 m. Despite the availability of modern computers, the Monte Carlo simulations can be very lengthy, especially for exposure above the ground where the direct solution implies a

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horizontally extended source of large size. Due to the long range of photons in air, a large area around the organism has to be considered as a source. In such a simulation, a small target scores only a few photons, because the probability of the target being hit by an uncollided photon is in inverse proportion to the square of the distance from source to target. Hence, very many photon tracks have to be simulated in the direct solution method to achieve results with an acceptable statistical uncertainty. Therefore, a two-step method has been developed in order to optimise the estimation of the average absorbed body dose for faunal targets exposed to photon radiation emitted from soil. In this procedure, the body-averaged absorbed dose per unit source strength (photons per ext,S , for a target T , source S (plane or volume) in the soil and initial unit area or mass), DT,E 0 photon energy E 0 is estimated by ext,S S DT,E ≡ K aT ,E 0 r T,E 0 A S , 0

(2)

S is the air kerma at the height of the target T per source photon of energy E 0 where K aT,E 0 emitted from the soil source S, Gy; r T,E0 is the ratio of the body-averaged absorbed dose for the target reference organism T to the air kerma at its height calculated for the photon source energy E 0 ; and A S is the area of the source plane or the mass of the source volume, m 2 or kg. S In the first step, the air kerma (free in air), K aT,E , at the height of the target reference 0 organism T (average over its height) is calculated for various sources S of monoenergetic photons E 0 on or in the soil. The source–target inversion method (Saito and Jacob 1995) was adopted for application at the heights of faunal reference organisms. The model universe consisted of a vertical cylinder of sufficient radius and height (3 km) to account for photon multi-scattering in air. The horizontal plane at z = 0 divided the air and soil compartments; the soil was 5 m thick. As a receptor, an air slab of appropriate thickness and at the appropriate height parallel to the air–soil interface was specified for each target reference organism. The isotropic model sources were: points at 0.3 cm depths and a vertical line from 0 to 10 cm. The Monte Carlo calculations were performed for 19 energies in the range from 10 keV to 10 MeV. The kerma values were scored via the track length estimator in two ways: directly in the code using the heating number (amount of photon energy imparted per collision); as well as by using air kerma coefficients (ICRU 1992b). In the second step, the ratio of the tissue absorbed dose in an organism to the air kerma, r T,E0 , was calculated for the different organisms and five energies from 50 keV to 3 MeV. In this Monte Carlo model, the calculation of energy deposition was done for a horizontally extended source in the soil with a reduced radius, e.g. 20 m for the targets at low height and 60 m for the elevated ones. Cross-check calculations were made with enlarged radii to test the stability of the results. The photon transport mode was chosen for the simulations. With the assumption of charged-particle equilibrium, the tallied tissue kerma approximates the tissue absorbed dose. Since the selected reference organisms of large size have shapes similar to a sphere, the dependence of the ratio, r T,E0 , on the source depth was found to be of minor importance.

2.4.2. Flora. In order to calculate the kerma for three prescribed receptors, i.e. the meristem and buds of herb, shrub and tree, due to photon emitters in the ground, a horizontally infinite source was considered in this dosimetric model. Two sources were examined: a plane isotropic source at a depth of 3 mm, which represents the initial superficial deposition of radionuclides taking surface roughness into account; and a volume source uniformly distributed to a depth of 10 cm. The model universe consisted of a vertical cylinder of sufficiently large radius and height to account for photon multi-scattering. The horizontal plane at z = 0 divided the air and soil

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compartments; the soil was 3 m thick. The space above the ground was divided into three slabs according to the description of the vegetation layers (table 3). Within each vegetation layer, an appropriate slab receptor was specified parallel to the air–soil interface. In these direct Monte Carlo simulations, the isotropic sources (plane or cylinder) had various radii depending on the mean free path length. The radius of the effectively infinite horizontal source has been estimated for different source energies and varies from 200 m to 1.4 km. As the receptors, the central core cylinders were specified with various radii (5–200 m) depending on the source size. The Monte Carlo calculations were performed for 17 energies in the range from 10 keV to 5 MeV. The kerma values were scored via the track length estimator. The results were normalised per unit source strength—one photon per unit source mass and per unit source area for the volume and plane sources, respectively. 2.5. Monte Carlo modelling The simulations of radiation transport from the source throughout the model geometry to the points of interest were performed using the MCNP general purpose Monte Carlo code version 4c3 (Briesmeister 2000) as well as the PENELOPE code system version 2003 (Salvat et al 2003) for the internal exposure simulations only. The photon transport mode with detailed interaction treatment was chosen. It includes coherent and incoherent scattering, photoelectric absorption, production of photons by the photoeffect and a thick target bremsstrahlung model for electrons. Detailed electron transport was simulated only in the series of calculations for internal exposure. The materials used in the simulations are described in table 4. In models with a photon source, the scoring of energy deposition was made in two different ways depending on the interaction density (which is in turn proportional to the density of the target medium): track length estimation of energy deposition for the air and tissue equivalent targets, and energy balance estimation only for tissue equivalent targets. The first estimate gives the kerma value; the second yields the absorbed dose. Whereas in dense media such as tissue the uncertainty of the energy balance estimate is generally low, this is not the case for low density media such as air. The track length estimate is reliable in general, since there are many tracks in the scoring region. However, in tissue the density of collisions is rather high. As a termination condition for the simulations, the cut-off on the number of histories was the requirement to provide a good precision of the result, i.e. approximately 5% in relative error (corresponding to one standard deviation). 2.6. Derivation of conversion coefficients The results of Monte Carlo simulations are expressed in units of absorbed dose per unit source strength. They are dependent on target, source configuration, radiation type and discrete energy. However, the conversion coefficient that relates the dose rate to the activity concentration in the body or in the environment for a specific radionuclide is found to be a quantity of more practical utility. There are a large range of anthropogenic and natural radionuclides which need to be considered within environmental impact assessments and in this initial investigation of a framework it is not possible to consider them all. Therefore, a subset of radionuclides of 22 elements was selected (Strand et al 2001). These are the 37 radionuclides: 3 H, 14 C, 40 K, 36 Cl, 59,63 Ni, 89,90 Sr, 94 Nb, 99 Tc, 106 Ru, 129,131 I, 134,135,137 Cs, 210 Po, 210 Pb, 226 Ra, 227,228,230,231,232,234 Th, 234,235,238 U, 238,239,240,241 Pu, 241 Am, 237 Np and 242,243,244 Cm.

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V Taranenko et al Table 5. The list of progeny radionuclides included along with the predecessor in the dose rate conversion coefficient tabulations. Predecessor radionuclide

Progeny radionuclide included with the predecessor

90 Sr

90 Y

106 Ru

106 Rh

137 Cs

137m Ba

210 Pb

210 Bi

226 Ra

222 Rn, 218 Po, 218 At, 214 Pb, 214 Bi, 214 Po

228 Th

224 Ra, 220 Rn, 216 Po, 212 Pb, 212 Po, 212 Bi, 208 Tl

234 Th

234m Pa, 234 Pa

235 U

231 Th

241 Pu

237 U

In order to derive nuclide-specific absorbed dose rate conversion coefficients the following calculations have been made. 2.6.1. Internal exposure of fauna  int int ≡ yi DT,R (E i ), C T,N R

(3)

i

int where C T,N is the average absorbed dose rate conversion coefficient for target reference organism T , due to incorporated uniformly distributed radionuclide N, (µGy h−1 ) (Bq kg−1 )−1 ; R is the radiation type (alpha, electron or photon); yi is the yield for the i th int (E i ) is the absorbed dose per unit radiation emission; i is the radiation emission index; DT,R int source strength interpolated for the energy E i from the DT,R,E matrix, Gy kg. 0 In the case of β − -emission, E i was taken as the average energy of the spectrum. To allow the application of radiation weighting factors, the values of internal sums are reported separately for four groups: α-radiation, low energy β-radiation (E 0 < 10 keV), β-radiation (E 0  10 keV) and γ -radiation.

2.6.2. External photon exposure of fauna and flora  ext,S ≡ y j DText,S (E j ), C T,N

(4)

j ext,S where C T,N is the average absorbed dose rate conversion coefficient for target reference organism T , due to uniformly distributed (in the soil volume or on the plane) radionuclide N forming a source S, (µGy h−1 ) (Bq kg−1 )−1 or (µGy h−1 ) (Bq m−2 )−1 for volume and plane sources respectively; y j is the yield for the j th photon emission; j is the photon emission index; DText,S (E j ) is the absorbed dose per unit source strength interpolated for the energy E j ext,S from the DT,E matrix. 0 The radionuclide transformation data were taken from the ICRP Publication 38 (ICRP 1983). Radioactive progeny are included in the calculation of the DCCs if their half-lives are shorter than ten days (table 5). One-dimensional linear interpolation in energy was applied. In the derivation of internal DCCs, a fresh mass basis was used; for external DCCs, the soil mass density includes the water content.

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Figure 1. The energy dependence of the absorbed energy fraction for source photons, f γ , uniformly distributed within the body of faunal reference organisms.

3. Results 3.1. Internal exposure of fauna 3.1.1. γ -radiation. The absorbed energy fractions of photons are shown in figure 1, depending on the initial photon energy for a number of organisms. The mean free path of photons is considerably longer than the range of electrons. Therefore, the absorbed fractions cover a wide range of several orders of magnitude from nearly one for low energy γ -radiation and large organisms to 10−4 for small organisms and high photon energies. The absorption is a non-linear function of target size and energy. The main processes causing absorption of photon energy are the Compton effect and the photoeffect; their contributions to absorption depend on the energy of the photon emitted. As a result, the absorbed fraction decreases in the energy range from 10 to 100 keV by a factor of 20–100 for small organisms, whereas it is relatively constant between 100 keV and 1 MeV. Beyond energies of 1 MeV, the decrease of the absorbed fractions with energy is steeper. This steep decrease in the high energy region is not present for the large organisms for which the electron leakage is of minor importance. A slight peak around 0.5 MeV in the case of small organisms is due to increased energy transfer from first-collision Compton scattering. 3.1.2. β-radiation. The absorbed fractions of electrons are summarised in figure 2,depending on the initial electron energy for a number of organisms. The organisms were chosen to cover a wide range of sizes. For electron energies below 100 keV, the absorbed fraction is approximately one even for very small organisms. The range of electrons in living tissue increases from 160 µm for 100 keV to 5 mm for 1 MeV. The absorbed fraction is close to unity if the diameter of the target is well above the range of the electron. Only for very small targets and high energies is the absorbed fraction of electrons considerably smaller than 0.5. 3.2. External exposure of fauna in the ground Figure 3 shows the absorbed dose for the smallest and largest in-soil reference organisms, as a function of the photon energy. The dose increases in proportion to the photon energy except

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Figure 2. The energy dependence of the absorbed energy fraction for source electrons, f e , uniformly distributed within the body of faunal reference organisms.

Figure 3. The energy dependence of the absorbed dose per unit source strength (photons per unit mass), Dext:vol−50 , for a woodlouse (full circles) and fox (open triangles) located in soil at a depth of 25 cm for photon volume source in the top 50 cm of soil (1.6 g cm −3 soil wet bulk density). The results for the other in-soil reference organisms lie in between the two presented.

at very low energies in the largest organism. The dose varies by a factor of five orders of magnitude or three orders of magnitude between the photon energies of 10 keV to 3 MeV for fox and woodlouse reference organisms, whereas its variation between the organisms does not exceed a factor of hundred even for the lowest energy of 10 keV. Over an energy of 100 keV, the difference is approximately constant—the dose to the woodlouse is higher by 50% than that to the fox due to the effect of self-shielding in the case of a larger target. 3.3. External exposure of fauna above the ground The air kerma at different heights at the locations of the reference organisms has been calculated by Monte Carlo simulations. The height varies from almost ground level up to 10 m for a bird. Two methods of kerma estimation were used: direct, MCNP in the code, using the heating number (Briesmeister 2000) and using air kerma coefficients (ICRU 1992b). The two sets of

Absorbed dose rate conversion coefficients

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Figure 4. The energy dependence of the absorbed dose per unit source strength (photons per unit area), Dext:plane−0 , for photon plane source on top of the ground, for reference organisms above the ground: woodlice (full circles), deer (open triangles) and cattle (full boxes). The results for the other above-soil reference organisms lie in between the presented curves.

results were found to be in a good agreement. They agreed within 5% in general, or within 10% in some cases in the low energy region of 10–30 keV. The results for kerma are found to be in a good agreement with those previously reported (Saito and Jacob 1995, Eckerman and Ryman 1993): for the conventional height of 1 m for a plane source at zero depth and two volume sources of 10 and 15 cm thickness the difference is less than 3%; for detection heights of 0.1, 0.5, 2, 5 and 10 m and a plane source at zero depth, the difference is generally less than 5%, except for low energy region of 10–30 keV, where it reaches 20%. The latter discrepancy can be attributed to averaging over the target height. Furthermore, slightly different detection heights and soil composition were used in the comparative study of Saito and Jacob (1995). The ratios of the absorbed dose averaged over the body of the reference organism to the air kerma at the location of the organism have been estimated using Monte Carlo simulations for finite plane sources in the soil at depths of 0, 5 and 20 cm (1.6 g cm −3 soil wet bulk density). Within the statistical uncertainty of less than 10%, the ratio was found to be independent of the source depth. Therefore, a unified set of ratios was used for all soil source configurations studied, i.e. planes at 0 and 3 mm depth and volumes of 5, 10 and 15 cm thickness (results are given here only for selected configurations). The ratio decreases as the target size increases owing to the effect of self-shielding. The tendency is more pronounced for low source energies: for 50 keV the ratio has a value of one for most reference organisms, but with lower values of 0.6 and 0.1 for deer and cattle, respectively. At 3 MeV the value is slightly higher than one for most reference organisms. For deer and cattle, it is 0.8 and 0.4, respectively. The absorbed dose for three reference organisms located above the ground is given as a function of the photon source energy in figure 4 for the plane source at zero depth. The exposure of smaller animals is higher than for large ones due to the more effective self-shielding of large organisms; such differences are more pronounced at low energies—two orders of magnitude at 10 keV and a factor of four at 5 MeV. Within the range from 10 to 50 keV, the dose increases (as the energy decreases) by a factor of approximately 14 for the smallest target (woodlouse) and by a factor of two for the largest (cattle). This increase is due to a rise of the energy absorption at low energies. Beyond 50 keV, the absorbed dose increases by approximately two orders of magnitude for the large targets whereas the targets of small size experience a less steep increase.

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ext , as function of Figure 5. The absorbed dose per unit source strength (photons per unit area), Dcattle the source energy and depth of the source in the soil for a cattle reference organism. The sources are: a plane at zero depth (full circles), a plane at 3 mm depth (open triangles) to take account of surface roughness and a volume uniformly distributed to a depth of 10 cm (1.6 g cm −3 soil wet bulk density).

The doses given in figure 4 are for a source on the ground at zero depth. This is the ideal case of a smooth plane source. In figure 5, absorbed doses for the cattle are given for different source configurations, such as plane and volume sources. The doses at low energies are much lower for the shielded sources. For energies of 100 keV and above, the ratio of doses due to a plane source at zero depth to one at 3 mm depth is a constant of approximately three, while at 50 keV the ratio is approximately 20; the ratio increases rapidly as the energy decreases and at 10 keV the dose to cattle is four orders of magnitude lower for the shielded source than for the unshielded one. 3.4. External exposure of flora above the ground Direct Monte Carlo calculations of the kerma in plant receptors were performed for the previously described configuration of the exposure model. Under the assumption of chargedparticle equilibrium, the results for kerma approximate the absorbed doses for all of three receptors. As a function of the source energy, the values of absorbed dose per unit source strength are shown in figure 6 for two sources: a plane source at zero depth, as well as for a volume source uniformly distributed to a depth of 10 cm. The values presented in the figure are for minimum biomass density (table 3). The curves for both sources have a shape similar to those for the kerma in air, but the values are lower, especially in the low energy region. The vegetation layers attenuate the photons more than air, particularly for the photons having near-horizontal directions, i.e. for shallow sources. For a plane source, the difference in dose to the herb receptor and the tree receptor, for energies over 60 keV, is approximately constant and amounts to a factor of three, whereas for 10 keV it is five orders of magnitude. For the volume source, the difference in dose is less. At energies over 70 keV, the dose in the herb receptor is higher by approximately 20% than the dose in the tree receptor, whereas at 10 keV it is five orders of magnitude higher. In order to study the influence of biomass density on the dose in receptors, additional simulations were performed for models with increased biomass in shrub and tree layers, in accordance with table 3. The resulting doses are reduced from the minimum case, as illustrated

Absorbed dose rate conversion coefficients

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Figure 6. The energy dependence of the absorbed dose per unit source strength (photons per unit area), Dext , for three floral receptors: meristem of herb (full circles), meristem and buds of shrub and tree (open triangles and full boxes, respectively); for two photon sources: a plane on top of the ground (full curves) and a volume uniformly distributed to a depth of 10 cm (broken curves) for 1.6 g cm −3 soil wet bulk density. The values are provided for minimum assumed biomass densities of shrub and tree layers (see table 3).

Figure 7. The energy dependence of the ratio of kerma calculated for low biomass per unit area (2 kg m −2 for the shrub and 10 kg m −2 for the tree layer) to the kerma calculated for high biomass per unit area (5 kg m −2 for the shrub and 15 kg m −2 for the tree layer). The results are for a plane photon source at a 3 mm depth in the soil (1.6 g cm −3 soil wet bulk density). Shown are results for three receptors: meristem of herb (full circles), buds and meristem of shrub and tree (open triangles and full boxes, respectively). The error whiskers represent 95% confidence intervals.

in figure 7. The receptor at the highest position of 5 m is shielded most, so its dose is most sensitive to biomass variation. 3.5. Conversion coefficients Internal exposure of faunal reference organisms (table 6). The values are given for radionuclides that are uniformly distributed in the body of the organism. In the table, the

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contributions for α-radiation, low energy β-radiation (E 0 < 10 keV), β-radiation (E 0  10 keV) and γ -radiation are differentiated in order to enable the application of assessmentspecific radiation weighting factors, w R , for the different radiation types. In this way, the equivalent dose for faunal reference organisms can be readily calculated. External exposure for soil faunal reference organisms (table 7). The values are given for radionuclides uniformly distributed in the upper 50 cm of soil; target organisms were positioned at 25 cm depth. Only the contribution due to photon radiation was considered. External exposure for faunal reference organisms above the soil. In table 8, the values are given for a plane source at a depth of 3 mm. In table 9, the values are given for a volume source uniformly distributed in the top 10 cm. Only the contribution due to photon radiation was considered. External exposure for critical organs of plants (table 10). The values are given for meristems of grass and for meristems and buds of a shrub and a tree. The values are given for a plane source with a surface roughness of 3 mm and a volume source uniformly distributed in the top 10 cm. Only the contribution due to photon radiation was considered. 4. Discussion and conclusions This paper has described dosimetric models that enable the assessment of exposures to a broad range of terrestrial target organisms due to both internal and external exposures from contaminated soil. Input quantities for the assessment are the measured or the calculated activity concentrations in biota or in soil. Nuclide-specific dose rate conversion coefficients have been derived taking into account habitat, target size and exposure route (internal and external exposure). The following points have been considered: • Selection of radionuclides. The DCC were derived for a number of selected radionuclides relevant in the case of radioactive releases from nuclear installations and for the natural radiation background. • Selection of reference organisms. Due to the enormous variability of species and habitats, it was impossible to consider all species explicitly. Therefore, a set of reference organisms of various sizes and habitats was defined for further detailed considerations that allow the assessment of exposures to a wide range of possible species. • Definition of geometries. Selected terrestrial reference organisms were approximated by simple three-dimensional phantoms. • Calculation of the average absorbed dose. For each target reference organism, the bodyaveraged absorbed dose per unit source strength was calculated using the Monte Carlo method of photon and electron radiation transport for monoenergetic radiation sources of various configurations. • Calculations of nuclide-specific dose rate conversion coefficients. On the basis of absorbed dose estimates, nuclide-specific DCCs were derived for different exposure models. The DCCs for external exposure in the terrestrial environment are given for organisms living on the soil, for planar radiation sources with a surface roughness of 3 mm and a volume source due to the uniform contamination of the top 10 cm of soil. For organisms living in the soil, it was assumed that they reside in the centre of a uniformly contaminated layer extending 50 cm below the ground surface. The DCCs for internal exposure were derived, assuming uniform distribution of the radionuclides in the organism. General dependences of the DCCs. The dose rate conversion coefficients for external exposure decrease with the size of the animal due to the increasing self-shielding effect.

Dose rate conversion coefficient ((µGy h−1 ) (Bq kg−1 )−1 ); contribution from different radiations Radio- Radia- Woodnuclide tion louse 3H 14 C 40 K

36 Cl 59 Ni

63

Ni

89 Sr 90 Sr + 94

Nb

99 Tc 106 Ru+

129 I

131

I

Low β β 2.8 × 10−5 2.0 × 10−4 β 100% γ β 1.4 × 10−4 3.6 × 10−6 Low β 73% γ 27% β β 2.3 × 10−4 β 3.6 × 10−4 9.6 × 10−5 β 95% γ 5% β 5.7 × 10−5 2.5 × 10−4 β 100% γ 3.7 × 10−5 Low β 12% β 86% γ 2% 1.0 × 10−4 β 98% γ 1%

Earthworm

Small egg

Large egg

Mouse, small bird

2.8 × 10−5 2.6 × 10−4 2.8 × 10−4 100% 99% 1% 1.5 × 10−4 1.5 × 10−4 3.8 × 10−6 3.9 × 10−6 69% 68% 31% 32%

2.9 × 10−4 99% 1% 1.5 × 10−4 3.9 × 10−6 67% 33%

2.9 × 10−4 99% 1%

2.9 × 10−4 5.1 × 10−4 1.1 × 10−4 88% 12%

3.2 × 10−4 6.0 × 10−4 1.3 × 10−4 73% 27%

3.2 × 10−4 6.0 × 10−4 1.4 × 10−4 71% 29%

5.0 × 10−4 6.1 × 10−4 7.0 × 10−4 100% 100% 99% 1% 3.8 × 10−5 3.9 × 10−5 4.0 × 10−5 12% 12% 11% 85% 84% 81% 3% 5% 7% 1.1 × 10−4 1.1 × 10−4 1.2 × 10−4 97% 95% 92% 3% 5% 8%

7.1 × 10−4 99% 1% 4.0 × 10−5 11% 81% 8% 1.2 × 10−4 91% 8%

3.1 × 10−4 5.6 × 10−4 1.1 × 10−4 83% 17%

3.9 × 10−6 67% 33%

Mole

Snake

Rabbit, large bird

Fox

3.3 × 10−6 2.9 × 10−5 2.9 × 10−4 2.9 × 10−4 3.1 × 10−4 3.2 × 10−4 98% 98% 96% 94% 2% 2% 4% 6% 1.6 × 10−4 4.0 × 10−6 66% 66% 66% 66% 34% 34% 34% 34% 9.9 × 10−6 3.2 × 10−4 3.2 × 10−4 3.3 × 10−4 3.3 × 10−4 6.2 × 10−4 6.1 × 10−4 6.4 × 10−4 6.4 × 10−4 1.5 × 10−4 1.5 × 10−4 2.4 × 10−4 3.0 × 10−4 64% 65% 41% 32% 36% 35% 59% 68% 5.8 × 10−5 7.4 × 10−4 7.3 × 10−4 8.1 × 10−4 8.3 × 10−4 99% 99% 98% 97% 1% 1% 2% 3% 4.1 × 10−5 4.1 × 10−5 4.5 × 10−5 4.7 × 10−5 11% 11% 10% 10% 79% 79% 72% 69% 10% 9% 18% 21% 1.2 × 10−4 1.2 × 10−4 1.5 × 10−4 1.6 × 10−4 89% 89% 75% 68% 11% 11% 24% 32%

Deer

Cattle

3.3 × 10−4 3.6 × 10−4 92% 85% 8% 15%

66% 34%

65% 35%

3.3 × 10−4 6.5 × 10−4 4.0 × 10−4 24% 76%

3.4 × 10−4 6.5 × 10−4 6.8 × 10−4 14% 86%

8.5 × 10−4 95% 5% 4.8 × 10−5 9% 67% 23% 1.9 × 10−4 59% 41%

8.9 × 10−4 91% 9% 5.0 × 10−5 9% 65% 26% 2.6 × 10−4 43% 57%

Absorbed dose rate conversion coefficients

Table 6. Nuclide-specific absorbed dose rate conversion coefficients for internal exposure of faunal reference organisms due to activity uniformly distributed in the body. Radionuclides with a plus sign denote the inclusion of progeny.

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Table 6. (Continued.) Dose rate conversion coefficient ((µGy h−1 ) (Bq kg−1 )−1 ); contribution from different radiations Radio- Radia- Woodnuclide tion louse 134 Cs

135 Cs 137 Cs+

210 Po 210 Pb+

226

Ra+

227 Th

Earthworm

Small egg

Large egg

Mouse, small bird

1.0 × 10−4 1.1 × 10−4 1.3 × 10−4 1.3 × 10−4 1.5 × 10−4 1.5 × 10−4 87% 82% 72% 70% 63% 64% 13% 18% 27% 30% 37% 36% 3.9 × 10−5 1.4 × 10−4 1.4 × 10−4 1.5 × 10−4 1.6 × 10−4 1.6 × 10−4 1.6 × 10−4 96% 95% 91% 90% 87% 88% 4% 5% 9% 10% 13% 12% 3.1 × 10−2 −4 −4 −4 −4 2.3 × 10 2.4 × 10 2.4 × 10 2.4 × 10 2.4 × 10−4 2.4 × 10−4 2% 2% 2% 2% 2% 2% 98% 98% 98% 98% 98% 98% 1% 1% 1% 1% 1% 1.4 × 10−2 1.4 × 10−2 1.4 × 10−2 1.4 × 10−2 1.4 × 10−2 1.4 × 10−2 97% 96% 96% 96% 96% 96% 3% 3% 4% 4% 4% 4%

α 98% β 2% α 9.6 × 10−5 Low β 9% β 89% γ 2% α

98% 2%

97% 2%

97% 3%

97% 3%

9.8 × 10−5 9% 88% 3%

9.9 × 10−5 9% 87% 4%

1.0 × 10−4 9% 86% 5%

1.0 × 10−4 9% 86% 6%

3.4 × 10−2

232 Th

1.9 × 10−2 97% 3% 2.7 × 10−2 1.0 × 10−4 9% 85% 6% 2.3 × 10−2

Rabbit, large bird

Fox

Deer

Cattle

2.4 × 10−4 3.0 × 10−4 4.0 × 10−4 6.7 × 10−4 40% 31% 24% 14% 60% 69% 76% 86% 2.0 × 10−4 2.2 × 10−4 2.6 × 10−4 3.5 × 10−4 73% 65% 56% 40% 27% 35% 44% 60% 2.5 × 10−4 2% 98% 1% 1.5 × 10−2 95% 4% 1%

2.5 × 10−4 2% 97% 1% 1.5 × 10−2 95% 4% 1%

2.5 × 10−4 2% 97% 1% 1.5 × 10−2 94% 4% 2% 3.5 × 10−2

2.5 × 10−4 2% 97% 1% 1.5 × 10−2 92% 4% 4% 3.5 × 10−2

97% 3%

97% 3%

96% 3%

96% 3%

95% 3%

1.0 × 10−4 9% 85% 6%

1.0 × 10−4 8% 83% 8%

1.0 × 10−4 8% 83% 9%

1.1 × 10−4 8% 82% 10%

1.1 × 10−4 8% 80% 12%

V Taranenko et al

231 Th

Snake

9.1 × 10−5 β 95% γ 5% β 3.8 × 10−5 1.2 × 10−4 β 98% γ 2% α 2.0 × 10−4 Low β 2% β 98% γ 1.4 × 10−2 α 97% β 3% γ α

228 Th+

230 Th

Mole

Dose rate conversion coefficient ((µGy h−1 ) (Bq kg−1 )−1 ); contribution from different radiations Radio- Radia- Woodnuclide tion louse 234 Th+ 234 U 235 U+

238

U

238 Pu 239 Pu 240 Pu 241 Pu+

241 Am 237

Np

242 Cm 243 Cm

244 Cm

Earthworm

Small egg

Large egg

Mouse, small bird

Mole

β 2.9 × 10−4 4.1 × 10−4 4.4 × 10−4 4.7 × 10−4 4.7 × 10−4 4.8 × 10−4 α 2.8 × 10−2 2.7 × 10−2 α 95% 95% 95% 95% 95% 95% β 4% 4% 4% 4% 4% 4% α 2.4 × 10−2 α 3.2 × 10−2 α 3.0 × 10−2 α 3.0 × 10−2 3.1 × 10−6 α 2% 2% 2% 2% 2% 2% Low β 98% 98% 98% 98% 98% 98% α 3.2 × 10−2 α 2.8 × 10−2 α 3.5 × 10−2 −2 3.4 × 10 α 98% 98% 98% 98% 97% 97% β 2% 2% 2% 2% 2% 2% α 3.3 × 10−2

Snake

Rabbit, large bird

Fox

Deer

Cattle

4.8 × 10−4 5.0 × 10−4 5.1 × 10−4 5.1 × 10−4 5.2 × 10−4

95% 4%

94% 4%

94% 4%

94% 4%

93% 4%

2% 98%

2% 98%

2% 98%

2% 98%

2% 97%

97% 2%

97% 2%

97% 2%

3.5 × 10−2 3.5 × 10−2 97% 96% 2% 2%

Absorbed dose rate conversion coefficients

Table 6. (Continued.)

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V Taranenko et al Table 7. Nuclide-specific absorbed dose rate conversion coefficients for external photon exposure of faunal reference organisms inside the soil for a uniform volume source uniformly distributed to a depth of 50 cm in the soil and having effectively infinite horizontal dimensions (1.6 g cm −3 soil wet bulk density). The organisms are located at a depth of 25 cm. Non-photon emitting radionuclides have been excluded. Radionuclides with a plus sign denote the inclusion of progeny. Dose rate conversion coefficient ((µGy h−1 ) (Bq kg−1 )−1 )

Radionuclide 40 K 36 Cl 59 Ni 89 Sr 90 Sr + 94 Nb 106 Ru+ 129

I

131 I 134 Cs 137 Cs+ 210 Po 210 Pb+ 226 Ra + 227 Th 228 Th+ 230 Th 231

Th

232 Th 234 Th+ 234

U

235 U+ 238 U 238

Pu

239 Pu 240 Pu 241 Pu+ 241 Am 237 Np 242 Cm 243 Cm 244 Cm

Woodlouse

Earthworm

Mouse

Mole

Snake

Rabbit

Fox

8.1 × 10−5 8.0 × 10−8 1.5 × 10−7 4.5 × 10−8 1.6 × 10−10 8.4 × 10−4 1.1 × 10−4 3.6 × 10−6 1.9 × 10−4 8.3 × 10−4 3.1 × 10−4 4.6 × 10−9 6.3 × 10−7 9.1 × 10−4 4.6 × 10−5 7.9 × 10−4 2.2 × 10−7 4.6 × 10−6 1.5 × 10−7 1.1 × 10−5 1.9 × 10−7 6.7 × 10−5 1.3 × 10−7 1.8 × 10−7 9.4 × 10−8 1.7 × 10−7 1.7 × 10−9 6.3 × 10−6 7.8 × 10−6 1.9 × 10−7 5.0 × 10−5 1.7 × 10−7

8.5 × 10−5 7.6 × 10−8 7.9 × 10−8 4.7 × 10−8 1.4 × 10−10 8.5 × 10−4 1.1 × 10−4 3.6 × 10−6 1.8 × 10−4 8.2 × 10−4 2.9 × 10−4 4.6 × 10−9 5.2 × 10−7 9.2 × 10−4 4.5 × 10−5 7.9 × 10−4 1.9 × 10−7 4.2 × 10−6 1.3 × 10−7 1.2 × 10−5 1.5 × 10−7 6.4 × 10−5 1.1 × 10−7 1.5 × 10−7 8.0 × 10−8 1.4 × 10−7 1.6 × 10−9 5.6 × 10−6 7.4 × 10−6 1.6 × 10−7 4.9 × 10−5 1.5 × 10−7

8.1 × 10−5 7.7 × 10−8 2.1 × 10−8 4.5 × 10−8 8.2 × 10−11 8.3 × 10−4 1.0 × 10−4 2.5 × 10−6 1.9 × 10−4 8.1 × 10−4 2.9 × 10−4 4.5 × 10−9 3.4 × 10−7 8.9 × 10−4 4.4 × 10−5 7.7 × 10−4 1.5 × 10−7 3.6 × 10−6 8.9 × 10−8 1.1 × 10−5 1.0 × 10−7 6.2 × 10−5 6.5 × 10−8 9.2 × 10−8 5.5 × 10−8 8.8 × 10−8 1.6 × 10−9 4.5 × 10−6 6.8 × 10−6 9.9 × 10−8 4.8 × 10−5 8.9 × 10−8

8.0 × 10−5 7.4 × 10−8 1.5 × 10−8 4.3 × 10−8 6.6 × 10−11 7.9 × 10−4 1.0 × 10−4 2.3 × 10−6 1.8 × 10−4 7.8 × 10−4 2.8 × 10−4 4.3 × 10−9 3.2 × 10−7 8.8 × 10−4 4.3 × 10−5 7.7 × 10−4 1.4 × 10−7 3.4 × 10−6 7.9 × 10−8 1.1 × 10−5 8.6 × 10−8 6.1 × 10−5 5.3 × 10−8 7.5 × 10−8 4.8 × 10−8 7.2 × 10−8 1.5 × 10−9 4.3 × 10−6 6.5 × 10−6 8.1 × 10−8 4.6 × 10−5 7.3 × 10−8

7.9 × 10−5 7.5 × 10−8 2.2 × 10−8 4.3 × 10−8 7.3 × 10−11 8.0 × 10−4 1.0 × 10−4 2.4 × 10−6 1.8 × 10−4 7.9 × 10−4 2.8 × 10−4 4.3 × 10−9 3.6 × 10−7 8.7 × 10−4 4.2 × 10−5 7.5 × 10−4 1.4 × 10−7 3.3 × 10−6 8.3 × 10−8 1.1 × 10−5 9.2 × 10−8 6.0 × 10−5 5.9 × 10−8 8.3 × 10−8 5.1 × 10−8 7.9 × 10−8 1.5 × 10−9 4.5 × 10−6 6.2 × 10−6 8.9 × 10−8 4.5 × 10−5 8.0 × 10−8

6.8 × 10−5 6.5 × 10−8 5.6 × 10−9 3.7 × 10−8 2.8 × 10−11 6.9 × 10−4 8.8 × 10−5 1.5 × 10−6 1.6 × 10−4 6.8 × 10−4 2.4 × 10−4 3.7 × 10−9 2.5 × 10−7 7.6 × 10−4 3.7 × 10−5 6.6 × 10−4 1.0 × 10−7 2.8 × 10−6 5.3 × 10−8 9.4 × 10−6 4.9 × 10−8 5.3 × 10−5 2.5 × 10−8 3.5 × 10−8 3.0 × 10−8 3.3 × 10−8 1.3 × 10−9 3.7 × 10−6 5.6 × 10−6 3.8 × 10−8 4.1 × 10−5 3.3 × 10−8

5.9 × 10−5 5.4 × 10−8 1.5 × 10−9 3.2 × 10−8 1.1 × 10−11 5.8 × 10−4 7.4 × 10−5 1.1 × 10−6 1.3 × 10−4 5.7 × 10−4 2.1 × 10−4 3.2 × 10−9 2.2 × 10−7 6.4 × 10−4 3.2 × 10−5 5.6 × 10−4 8.2 × 10−8 2.3 × 10−6 3.9 × 10−8 8.0 × 10−6 3.1 × 10−8 4.5 × 10−5 1.2 × 10−8 1.6 × 10−8 2.1 × 10−8 1.5 × 10−8 1.1 × 10−9 3.3 × 10−6 4.8 × 10−6 1.7 × 10−8 3.5 × 10−5 1.4 × 10−8

The differences in DCCs for external exposure among organisms are more pronounced for low energy photons, since for such photons the effect of self-shielding is more important. The exposure of small organisms (e.g. mice) from high energy photon emitters is higher for underground organisms, compared to organisms above the ground, whereas the reverse applies for larger organisms (e.g. foxes). The external exposure to low energy photon emitters is in general higher for above-ground organisms, since the shielding effect of the soil is less pronounced. For internal exposure to γ -emitters, DCCs increase in proportion to the mass of the organism due to the higher absorbed fractions. This dependence is more pronounced for high energy photon emitters (e.g. 137 Cs and 137m Ba). For α- and β-emitters, the DCCs for internal exposure are nearly size independent.

Dose rate conversion coefficient ((µGy h−1 ) (Bq m −2 )−1 ) Mouse, large Earthworm, egg, small

Radio-

nuclide Woodlouse small egg × 10−7

40 K

4.8

36 Cl

5.3 × 10−10

59

−12

4.8

× 10−7

5.2

× 10−10 −12

bird h = 0 4.8

× 10−7

5.2

× 10−10 −12

Rabbit, large bird

Small bird

Snake

h=0

Fox

4.7

× 10−7

4.6 × 10−7

4.3 × 10−7

4.1 × 10−7

5.2

× 10−10

5.0 × 10−10

4.6 × 10−10

4.3 × 10−10

−12

−12

−12

−12

Mole

Deer

h =3m

Cattle

3.2

× 10−7

3.3

× 10−10 −12

1.4

× 10−7

1.3

× 10−10 −13

h = 10 m

4.1

× 10−7

3.0

4.5

× 10−10

3.2 × 10−10

−13

× 10−7

Large bird h =3m

h = 10 m

4.1 × 10−7

3.0 × 10−7

4.5 × 10−10

3.2 × 10−10

−13

2.7 × 10 2.7 × 10 2.7 × 10 2.7 × 10 2.6 × 10 2.4 × 10 2.2 × 10 1.4 × 10 2.1 × 10 6.8 × 10 Negligible 6.8 × 10 Negligible 2.8 × 10−10 2.8 × 10−10 2.8 × 10−10 2.8 × 10−10 2.7 × 10−10 2.5 × 10−10 2.3 × 10−10 1.8 × 10−10 7.5 × 10−11 2.4 × 10−10 1.7 × 10−10 2.4 × 10−10 1.7 × 10−10

Ni

89 Sr

94 Nb

1.8 × 10−12 1.8 × 10−12 1.8 × 10−12 1.7 × 10−12 1.7 × 10−12 1.6 × 10−12 1.4 × 10−12 8.8 × 10−13 1.6 × 10−13 1.2 × 10−12 4.3 × 10−13 1.2 × 10−12 4.3 × 10−13 5.3 × 10−6 5.3 × 10−6 5.3 × 10−6 5.2 × 10−6 5.0 × 10−6 4.7 × 10−6 4.4 × 10−6 3.4 × 10−6 1.4 × 10−6 4.5 × 10−6 3.2 × 10−6 4.5 × 10−6 3.2 × 10−6

106 Ru+

7.0 × 10−7 7.0 × 10−7 6.9 × 10−7

90 Sr +

× 10−8

129 I 131 I 134 Cs 137

Cs

Absorbed dose rate conversion coefficients

Table 8. Nuclide-specific absorbed dose rate conversion coefficients for external photon exposure of faunal reference organisms above the soil for a uniform plane source at the depth of 3 mm in the soil (1.6 g cm −3 soil wet bulk density). Non-photon emitting radionuclides have been excluded. Radionuclides with a plus sign denote the inclusion of progeny.

+

210 Po

6.9 × 10−7 6.6 × 10−7 6.1 × 10−7 5.7 × 10−7 4.5 × 10−7 1.8 × 10−7 6.0 × 10−7 4.2 × 10−7 6.0 × 10−7 4.2 × 10−7

× 10−8

9.4 9.4 9.4 1.3 × 10−6 1.3 × 10−6 1.3 × 10−6

9.3 × 10−8 9.0 × 10−8 8.4 × 10−8 7.6 × 10−8 5.0 × 10−8 1.0 × 10−8 8.2 × 10−8 5.2 × 10−8 8.2 × 10−8 5.2 × 10−8 1.3 × 10−6 1.2 × 10−6 1.1 × 10−6 1.1 × 10−6 8.3 × 10−7 3.2 × 10−7 1.1 × 10−6 8.0 × 10−7 1.1 × 10−6 8.0 × 10−7

5.3 × 10−6 5.3 × 10−6 5.2 × 10−6

5.2 × 10−6 5.0 × 10−6 4.6 × 10−6 4.3 × 10−6 3.4 × 10−6 1.4 × 10−6 4.5 × 10−6 3.2 × 10−6 4.5 × 10−6 3.2 × 10−6

−6

× 10−8

−6

−6

1.9 × 10 1.9 × 10 1.9 × 10 1.9 × 10−6 1.8 × 10−6 1.7 × 10−6 1.6 × 10−6 1.2 × 10−6 5.0 × 10−7 1.7 × 10−6 1.2 × 10−6 1.7 × 10−6 1.2 × 10−6 −11 −11 −11 2.9 × 10 2.8 × 10 2.8 × 10 2.8 × 10−11 2.7 × 10−11 2.5 × 10−11 2.4 × 10−11 1.8 × 10−11 7.5 × 10−12 2.4 × 10−11 1.7 × 10−11 2.4 × 10−11 1.7 × 10−11

226 Ra +

7.1 × 10−9 7.0 × 10−9 7.0 × 10−9 5.6 × 10−6 5.6 × 10−6 5.6 × 10−6

7.0 × 10−9 6.7 × 10−9 6.3 × 10−9 5.7 × 10−9 3.8 × 10−9 8.1 × 10−10 6.1 × 10−9 4.2 × 10−9 6.1 × 10−9 4.2 × 10−9 5.5 × 10−6 5.3 × 10−6 5.0 × 10−6 4.7 × 10−6 3.7 × 10−6 1.6 × 10−6 4.8 × 10−6 3.5 × 10−6 4.8 × 10−6 3.5 × 10−6

227 Th

3.5 × 10−7 3.5 × 10−7 3.5 × 10−7

3.5 × 10−7 3.3 × 10−7 3.1 × 10−7 2.9 × 10−7 2.2 × 10−7 7.5 × 10−8 3.1 × 10−7 2.2 × 10−7 3.1 × 10−7 2.2 × 10−7

210 Pb+

228 Th+ 230 Th

× 10−6

× 10−6

× 10−6

4.6 4.6 4.6 1.9 × 10−9 1.9 × 10−9 1.9 × 10−9

4.5 × 10−6 4.4 × 10−6 4.2 × 10−6 3.9 × 10−6 3.1 × 10−6 1.4 × 10−6 4.0 × 10−6 2.9 × 10−6 4.0 × 10−6 2.9 × 10−6 1.9 × 10−9 1.8 × 10−9 1.7 × 10−9 1.6 × 10−9 1.0 × 10−9 2.4 × 10−10 1.5 × 10−9 9.4 × 10−10 1.5 × 10−9 9.4 × 10−10

A55

A56

Table 8. (Continued.) Dose rate conversion coefficient ((µGy h−1 ) (Bq m −2 )−1 ) Mouse, large RadioEarthworm, egg, small nuclide Woodlouse small egg bird h = 0

Rabbit, Mole

Snake

large bird h=0

Small bird Fox

Deer

Cattle

h =3m

h = 10 m

Large bird h=3m

h = 10 m

232 Th

5.7 × 10−8 5.7 × 10−8 5.7 × 10−8 1.3 × 10−9 1.3 × 10−9 1.3 × 10−9

5.6 × 10−8 5.4 × 10−8 5.0 × 10−8 4.6 × 10−8 3.1 × 10−8 6.9 × 10−9 4.8 × 10−8 3.1 × 10−8 4.8 × 10−8 3.1 × 10−8 1.3 × 10−9 1.3 × 10−9 1.2 × 10−9 1.1 × 10−9 6.8 × 10−10 1.4 × 10−10 9.8 × 10−10 5.3 × 10−10 9.8 × 10−10 5.3 × 10−10

234 Th+

8.4 × 10−8 8.4 × 10−8 8.3 × 10−8

8.2 × 10−8 7.9 × 10−8 7.4 × 10−8 6.9 × 10−8 5.2 × 10−8 1.9 × 10−8 7.2 × 10−8 5.2 × 10−8 7.2 × 10−8 5.2 × 10−8

231 Th

−9

2.0 × 10 2.0 × 10 1.9 × 10 5.6 × 10−7 5.5 × 10−7 5.5 × 10−7

1.9 × 10−9 1.9 × 10−9 1.7 × 10−9 1.6 × 10−9 1.0 × 10−9 2.0 × 10−10 1.4 × 10−9 6.5 × 10−10 1.4 × 10−9 6.5 × 10−10 5.4 × 10−7 5.2 × 10−7 4.9 × 10−7 4.5 × 10−7 3.2 × 10−7 9.7 × 10−8 4.8 × 10−7 3.5 × 10−7 4.8 × 10−7 3.5 × 10−7

238 Pu

1.4 × 10−9 1.4 × 10−9 1.4 × 10−9 2.3 × 10−9 2.3 × 10−9 2.3 × 10−9

1.4 × 10−9 1.3 × 10−9 1.2 × 10−9 1.1 × 10−9 7.1 × 10−10 1.3 × 10−10 9.7 × 10−10 4.0 × 10−10 9.7 × 10−10 4.0 × 10−10 2.3 × 10−9 2.2 × 10−9 2.1 × 10−9 1.9 × 10−9 1.2 × 10−9 2.2 × 10−10 1.6 × 10−9 6.8 × 10−10 1.6 × 10−9 6.8 × 10−10

239 Pu

1.1 × 10−9 1.1 × 10−9 1.0 × 10−9

1.0 × 10−9 1.0 × 10−9 9.3 × 10−10 8.4 × 10−10 5.5 × 10−10 1.2 × 10−10 7.7 × 10−10 3.7 × 10−10 7.7 × 10−10 3.7 × 10−10

240 Pu 241 Pu+

2.2 × 10−9 2.2 × 10−9 2.2 × 10−9 2.2 × 10−9 2.1 × 10−9 2.0 × 10−9 1.8 × 10−9 1.1 × 10−9 2.1 × 10−10 1.6 × 10−9 6.6 × 10−10 1.6 × 10−9 6.6 × 10−10 1.7 × 10−11 1.7 × 10−11 1.6 × 10−11 1.6 × 10−11 1.6 × 10−11 1.5 × 10−11 1.3 × 10−11 9.4 × 10−12 2.6 × 10−12 1.4 × 10−11 1.0 × 10−11 1.4 × 10−11 1.0 × 10−11

241 Am

8.4 × 10−8 8.4 × 10−8 8.3 × 10−8

234

U

235 U+ 238 U

−9

−9

8.3 × 10−8 8.0 × 10−8 7.4 × 10−8 6.7 × 10−8 4.5 × 10−8 9.9 × 10−9 7.2 × 10−8 5.1 × 10−8 7.2 × 10−8 5.1 × 10−8 9.0 × 10−8 8.7 × 10−8 8.1 × 10−8 7.3 × 10−8 5.0 × 10−8 1.2 × 10−8 7.9 × 10−8 5.5 × 10−8 7.9 × 10−8 5.5 × 10−8 2.7 × 10−9 2.7 × 10−9 2.5 × 10−9 2.2 × 10−9 1.4 × 10−9 2.7 × 10−10 2.0 × 10−9 8.7 × 10−10 2.0 × 10−9 8.7 × 10−10

4.2 × 10−7 4.2 × 10−7 4.2 × 10−7 2.6 × 10−9 2.6 × 10−9 2.5 × 10−9

4.1 × 10−7 4.0 × 10−7 3.7 × 10−7 3.4 × 10−7 2.5 × 10−7 7.9 × 10−8 3.6 × 10−7 2.6 × 10−7 3.6 × 10−7 2.6 × 10−7 2.5 × 10−9 2.4 × 10−9 2.3 × 10−9 2.0 × 10−9 1.3 × 10−9 2.4 × 10−10 1.8 × 10−9 7.9 × 10−10 1.8 × 10−9 7.9 × 10−10

243 Cm 244 Cm

V Taranenko et al

Np 9.1 × 10−8 9.1 × 10−8 9.1 × 10−8 242 Cm 2.8 × 10−9 2.8 × 10−9 2.8 × 10−9 237

Dose rate conversion coefficient ((µGy h−1 ) (Bq kg−1 )−1 ) Mouse, large Radio-

nuclide Woodlouse small egg

bird h = 0

3.0 × 10−5 3.0 × 10−5 3.0 × 10−5

40 K

Rabbit,

Earthworm, egg, small Mole

Snake

h=0

Fox

Deer

Cattle

h=3m

h = 10 m

h =3m

h = 10 m

3.0 × 10−5 2.9 × 10−5 2.7 × 10−5 2.6 × 10−5 2.1 × 10−5 9.4 × 10−6 2.8 × 10−5 2.3 × 10−5 2.8 × 10−5 2.3 × 10−5

59 Ni

3.1 1.5 × 10−7 1.5 × 10−7 1.5 × 10−7

3.1 × 10−8 3.0 × 10−8 2.8 × 10−8 2.6 × 10−8 2.0 × 10−8 8.1 × 10−9 2.9 × 10−8 2.3 × 10−8 2.9 × 10−8 2.3 × 10−8 1.4 × 10−7 1.4 × 10−7 1.2 × 10−7 1.0 × 10−7 3.5 × 10−8 4.9 × 10−9 9.3 × 10−9 Negligible 9.3 × 10−9 Negligible

89 Sr

1.7 × 10−8 1.7 × 10−8 1.7 × 10−8

1.7 × 10−8 1.6 × 10−8 1.5 × 10−8 1.4 × 10−8 1.1 × 10−8 4.7 × 10−9 1.6 × 10−8 1.3 × 10−8 1.6 × 10−8 1.3 × 10−8

1.1 × 10 1.1 × 10 1.0 × 10 3.2 × 10−4 3.2 × 10−4 3.2 × 10−4

1.0 × 10−10 1.0 × 10−10 9.0 × 10−11 8.0 × 10−11 4.3 × 10−11 7.6 × 10−12 4.1 × 10−11 1.0 × 10−11 4.1 × 10−11 1.0 × 10−11 3.2 × 10−4 3.0 × 10−4 2.8 × 10−4 2.7 × 10−4 2.1 × 10−4 8.7 × 10−5 3.0 × 10−4 2.4 × 10−4 3.0 × 10−4 2.4 × 10−4

129 I

4.2 × 10−5 4.2 × 10−5 4.2 × 10−5 1.7 × 10−6 1.7 × 10−6 1.7 × 10−6

4.1 × 10−5 4.0 × 10−5 3.7 × 10−5 3.4 × 10−5 2.7 × 10−5 1.1 × 10−5 3.9 × 10−5 3.1 × 10−5 3.9 × 10−5 3.1 × 10−5 1.7 × 10−6 1.6 × 10−6 1.5 × 10−6 1.3 × 10−6 8.7 × 10−7 1.7 × 10−7 1.4 × 10−6 8.8 × 10−7 1.4 × 10−6 8.8 × 10−7

131 I

7.7 × 10−5 7.7 × 10−5 7.7 × 10−5

7.6 × 10−5 7.3 × 10−5 6.7 × 10−5 6.3 × 10−5 5.0 × 10−5 1.9 × 10−5 7.2 × 10−5 5.7 × 10−5 7.2 × 10−5 5.7 × 10−5

134 Cs 137 Cs+

3.2 × 10−4 3.2 × 10−4 3.2 × 10−4 1.2 × 10−4 1.1 × 10−4 1.1 × 10−4

3.1 × 10−4 3.0 × 10−4 2.8 × 10−4 2.6 × 10−4 2.1 × 10−4 8.5 × 10−5 3.0 × 10−4 2.4 × 10−4 3.0 × 10−4 2.4 × 10−4 1.1 × 10−4 1.1 × 10−4 1.0 × 10−4 9.5 × 10−5 7.6 × 10−5 3.1 × 10−5 1.1 × 10−4 8.6 × 10−5 1.1 × 10−4 8.6 × 10−5

210 Po

90

Sr

+

94 Nb 106 Ru+

−10

3.1 × 10−8

Large bird

3.1 × 10−8

36 Cl

× 10−8

Small bird

large bird

−10

−10

1.7 × 10−9 1.7 × 10−9 1.7 × 10−9

1.7 × 10−9 1.6 × 10−9 1.5 × 10−9 1.4 × 10−9 1.1 × 10−9 4.7 × 10−10 1.6 × 10−9 1.3 × 10−9 1.6 × 10−9 1.3 × 10−9

Pb+ 3.5 × 10−7 3.5 × 10−7 3.4 × 10−7 226 Ra + 3.4 × 10−4 3.4 × 10−4 3.4 × 10−4

3.4 × 10−7 3.3 × 10−7 2.9 × 10−7 2.6 × 10−7 1.5 × 10−7 2.8 × 10−8 1.8 × 10−7 1.2 × 10−7 1.8 × 10−7 1.2 × 10−7 3.4 × 10−4 3.3 × 10−4 3.1 × 10−4 2.9 × 10−4 2.3 × 10−4 1.0 × 10−4 3.2 × 10−4 2.6 × 10−4 3.2 × 10−4 2.6 × 10−4

2.0 × 10−5 2.0 × 10−5 2.0 × 10−5 2.9 × 10−4 2.9 × 10−4 2.9 × 10−4

1.9 × 10−5 1.9 × 10−5 1.7 × 10−5 1.6 × 10−5 1.2 × 10−5 4.3 × 10−6 1.8 × 10−5 1.4 × 10−5 1.8 × 10−5 1.4 × 10−5 2.9 × 10−4 2.8 × 10−4 2.6 × 10−4 2.5 × 10−4 2.0 × 10−4 9.5 × 10−5 2.7 × 10−4 2.2 × 10−4 2.7 × 10−4 2.2 × 10−4

210

227 Th 228 Th+

Absorbed dose rate conversion coefficients

Table 9. Nuclide-specific absorbed dose rate conversion coefficients for external photon exposure of faunal reference organisms above the soil for a uniform volume source formed by the upper 10 cm of soil (1.6 g cm −3 soil wet bulk density). Non-photon emitting radionuclides have been excluded. Radionuclides with a plus sign denote the inclusion of progeny.

A57

A58

Table 9. (Continued.) Dose rate conversion coefficient ((µGy h−1 ) (Bq kg−1 )−1 ) Mouse, large Earthworm, egg, small

Radio-

nuclide Woodlouse small egg 230 Th

1.2

× 10−7

1.2

bird h = 0 1.2

× 10−6

× 10−7

Mole 1.2

× 10−7

1.2

h=0

× 10−7

1.1 × 10−7

× 10−6

× 10−6

Fox 9.5

Deer

× 10−8

5.6 × 10−8

× 10−6

× 10−6

Cattle 1.2

h=3m

× 10−8

× 10−8

7.0

× 10−7

1.8 × 10−6

h = 10 m 4.2

× 10−8

h =3m 7.0

× 10−8

h = 10 m 4.2 × 10−8

2.4 2.4 2.4 9.5 × 10−8 9.5 × 10−8 9.3 × 10−8

2.3 2.3 2.1 1.9 1.2 2.8 1.3 1.8 1.3 × 10−6 −8 −8 −8 −8 −8 −9 −8 −8 −8 9.2 × 10 8.9 × 10 8.1 × 10 7.1 × 10 4.0 × 10 7.7 × 10 4.3 × 10 2.1 × 10 4.3 × 10 2.1 × 10−8

234 Th+

4.6 × 10−6 4.6 × 10−6 4.6 × 10−6

× 10−6

4.6 × 10−6 4.4 × 10−6 4.1 × 10−6 3.8 × 10−6 2.9 × 10−6 1.1 × 10−6 4.3 × 10−6 3.4 × 10−6 4.3 × 10−6 3.4 × 10−6

× 10−7

235 U+

1.2 1.2 1.1 3.0 × 10−5 3.0 × 10−5 3.0 × 10−5

1.1 × 10−7 1.1 × 10−7 9.9 × 10−8 8.8 × 10−8 4.8 × 10−8 9.0 × 10−9 5.0 × 10−8 2.0 × 10−8 5.0 × 10−8 2.0 × 10−8 2.9 × 10−5 2.8 × 10−5 2.6 × 10−5 2.4 × 10−5 1.8 × 10−5 5.4 × 10−6 2.7 × 10−5 2.2 × 10−5 2.7 × 10−5 2.2 × 10−5

238 U

8.7 × 10−8 8.6 × 10−8 8.5 × 10−8

8.3 × 10−8 8.1 × 10−8 7.3 × 10−8 6.5 × 10−8 3.5 × 10−8 6.0 × 10−9 3.2 × 10−8 9.4 × 10−9 3.2 × 10−8 9.4 × 10−9

234 U

238 Pu 239 Pu

× 10−7

× 10−6

Large bird

232 Th

× 10−7

× 10−6

Snake

Small bird

× 10−6

231 Th

× 10−6

× 10−7

Rabbit, large bird

× 10−7

× 10−7

× 10−7

1.1 1.1 1.1 5.7 × 10−8 5.7 × 10−8 5.6 × 10−8

1.1 × 10−7 1.1 × 10−7 9.8 × 10−8 8.7 × 10−8 4.8 × 10−8 8.4 × 10−9 4.7 × 10−8 1.5 × 10−8 4.7 × 10−8 1.5 × 10−8 5.5 × 10−8 5.3 × 10−8 4.8 × 10−8 4.3 × 10−8 2.4 × 10−8 5.2 × 10−9 2.6 × 10−8 1.2 × 10−8 2.6 × 10−8 1.2 × 10−8

241 Pu+

1.1 × 10−7 1.1 × 10−7 1.1 × 10−7 1.1 × 10−7 1.0 × 10−7 9.3 × 10−8 8.3 × 10−8 4.5 × 10−8 8.1 × 10−9 4.5 × 10−8 1.4 × 10−8 4.5 × 10−8 1.4 × 10−8 8.2 × 10−10 8.2 × 10−10 8.1 × 10−10 8.1 × 10−10 7.8 × 10−10 7.2 × 10−10 6.6 × 10−10 4.6 × 10−10 1.3 × 10−10 7.3 × 10−10 5.7 × 10−10 7.3 × 10−10 5.7 × 10−10

241 Am

2.9 × 10−6 2.9 × 10−6 2.9 × 10−6

240 Pu

242 Cm

3.9 3.9 3.9 1.2 × 10−7 1.2 × 10−7 1.1 × 10−7

3.8 × 10−6 3.7 × 10−6 3.4 × 10−6 3.1 × 10−6 2.1 × 10−6 5.3 × 10−7 3.3 × 10−6 2.5 × 10−6 3.3 × 10−6 2.5 × 10−6 1.1 × 10−7 1.1 × 10−7 9.9 × 10−8 8.8 × 10−8 4.9 × 10−8 8.9 × 10−9 5.2 × 10−8 1.7 × 10−8 5.2 × 10−8 1.7 × 10−8

243 Cm

2.3 × 10−5 2.3 × 10−5 2.2 × 10−5

2.2 × 10−5 2.1 × 10−5 2.0 × 10−5 1.8 × 10−5 1.4 × 10−5 4.4 × 10−6 2.1 × 10−5 1.6 × 10−5 2.1 × 10−5 1.6 × 10−5

1.1

× 10−7

× 10−6

1.1

× 10−7

1.0

× 10−7

1.0 × 10−7 1.0 × 10−7 9.1 × 10−8 8.1 × 10−8 4.5 × 10−8 8.0 × 10−9 4.7 × 10−8 1.5 × 10−8 4.7 × 10−8 1.5 × 10−8

V Taranenko et al

244 Cm

× 10−6

2.8 × 10−6 2.8 × 10−6 2.5 × 10−6 2.3 × 10−6 1.5 × 10−6 3.3 × 10−7 2.3 × 10−6 1.7 × 10−6 2.3 × 10−6 1.7 × 10−6

× 10−6

237 Np

Dose rate conversion coefficient for plane source ((µGy h−1 ) (Bq m −2 )−1 ) Shrub Radionuclide

Dose rate conversion coefficient for volume source, ((µGy h−1 ) (Bq kg−1 )−1 )

Tree

Shrub

Tree

Herb

Low density

High density

Low density

High density

Herb

Low density

High density

Low density

High density

36 Cl

4.5 × 10−7 5.0 × 10−10

4.0 × 10−7 4.4 × 10−10

3.8 × 10−7 4.3 × 10−10

2.9 × 10−7 3.2 × 10−10

2.7 × 10−7 3.0 × 10−10

2.9 × 10−5 3.1 × 10−8

2.7 × 10−5 2.9 × 10−8

2.7 × 10−5 2.8 × 10−8

2.4 × 10−5 2.4 × 10−8

2.2 × 10−5 2.3 × 10−8

59 Ni

1.7 × 10−9

8.6 × 10−10

6.4 × 10−10

8.4 × 10−11

2.7 × 10−11

1.8 × 10−7

1.3 × 10−8

2.9 × 10−9

3.9 × 10−12

9.8 × 10−14

89

2.7 × 10−10 2.2 × 10−12

2.3 × 10−10 1.4 × 10−12

2.3 × 10−10 1.2 × 10−12

1.7 × 10−10 3.2 × 10−13

1.6 × 10−10 1.8 × 10−13

1.7 × 10−8 1.3 × 10−10

1.6 × 10−8 5.1 × 10−11

1.5 × 10−8 3.7 × 10−11

1.3 × 10−8 7.0 × 10−12

1.3 × 10−8 3.5 × 10−12

94 Nb 106 Ru+

5.0 × 10−6 6.6 × 10−7

4.4 × 10−6 5.8 × 10−7

4.3 × 10−6 5.6 × 10−7

3.2 × 10−6 4.2 × 10−7

3.0 × 10−6 4.0 × 10−7

3.1 × 10−4 4.1 × 10−5

2.9 × 10−4 3.9 × 10−5

2.9 × 10−4 3.8 × 10−5

2.5 × 10−4 3.3 × 10−5

2.3 × 10−4 3.1 × 10−5

129 I

1.1 × 10−7

9.4 × 10−8

9.1 × 10−8

5.5 × 10−8

4.4 × 10−8

1.9 × 10−6

1.6 × 10−6

1.4 × 10−6

8.9 × 10−7

7.7 × 10−7

131 I 134 Cs

1.3 × 10−6 5.0 × 10−6

1.1 × 10−6 4.4 × 10−6

1.1 × 10−6 4.3 × 10−6

8.2 × 10−7 3.2 × 10−6

7.7 × 10−7 3.0 × 10−6

7.6 × 10−5 3.1 × 10−4

7.2 × 10−5 2.9 × 10−4

7.0 × 10−5 2.9 × 10−4

6.1 × 10−5 2.5 × 10−4

5.7 × 10−5 2.3 × 10−4

137 Cs+

1.8 × 10−6

1.6 × 10−6

1.6 × 10−6

1.2 × 10−6

1.1 × 10−6

1.1 × 10−4

1.1 × 10−4

1.0 × 10−4

9.0 × 10−5

8.5 × 10−5

210

2.7 × 10−11 9.6 × 10−9

2.4 × 10−11 7.6 × 10−9

2.3 × 10−11 7.3 × 10−9

1.7 × 10−11 4.8 × 10−9

1.6 × 10−11 4.2 × 10−9

1.7 × 10−9 4.0 × 10−7

1.6 × 10−9 2.1 × 10−7

1.6 × 10−9 1.9 × 10−7

1.4 × 10−9 1.3 × 10−7

1.3 × 10−9 1.1 × 10−7

226 Ra + 227 Th

5.3 × 10−6 3.5 × 10−7

4.7 × 10−6 3.1 × 10−7

4.5 × 10−6 3.0 × 10−7

3.4 × 10−6 2.3 × 10−7

3.2 × 10−6 2.1 × 10−7

3.3 × 10−4 2.0 × 10−5

3.2 × 10−4 1.9 × 10−5

3.1 × 10−4 1.8 × 10−5

2.7 × 10−4 1.6 × 10−5

2.5 × 10−4 1.5 × 10−5

228 Th+

4.4 × 10−6

3.9 × 10−6

3.7 × 10−6

2.9 × 10−6

2.7 × 10−6

2.8 × 10−4

2.7 × 10−4

2.6 × 10−4

2.3 × 10−4

2.2 × 10−4

230 Th

2.4 × 10−9

1.8 × 10−9

1.6 × 10−9

9.8 × 10−10

8.5 × 10−10

1.4 × 10−7

8.0 × 10−8

7.1 × 10−8

4.5 × 10−8

4.2 × 10−8

40 K

Sr 90 Sr +

Po 210 Pb+

Absorbed dose rate conversion coefficients

Table 10. Nuclide-specific absorbed dose rate conversion coefficients for three vegetation receptors and two uniform sources in the soil. The values are given for meristem of grass and for buds of a shrub and a tree for a plane source at the depth of 3 mm and a volume source uniformly distributed to a depth of 10 cm (1.6 g cm −3 soil wet bulk density). The values are attributable to photon radiation only. Non-photon emitting radionuclides have been excluded. Radionuclides with a plus sign denote the inclusion of progeny.

A59

A60

Table 10. (Continued.) Dose rate conversion coefficient for plane source

Dose rate conversion coefficient for volume source

((µGy h−1 ) (Bq m −2 )−1 )

((µGy h−1 ) (Bq kg−1 )−1 )

Shrub

Tree

Shrub

Tree

Radionuclide

Herb

231 Th

6.5 × 10−8

Low density

High density

Low density

High density

Herb

× 10−8

5.0 × 10−8

3.2 × 10−8

2.8 × 10−8

2.7 × 10−6

232 Th

1.7 × 10−9

× 10−9

1.2 7.3 × 10−8

1.1 × 10−9

5.3 × 10−10

4.4 × 10−10

1.1 × 10−7

234 Th+

8.3 × 10−8

7.1 × 10−8

5.3 × 10−8

234 U

5.0

2.5 × 10−9

1.7 × 10−9

1.5 × 10−9

5.9 × 10−10

4.3 × 10−10

−7

−7

−7

5.3

Low density

High density

1.9 × 10−6

1.4 × 10−6

1.3 × 10−6

× 10−8

× 10−8

4.6 × 10−6

5.1 4.3 × 10−6

4.2 4.2 × 10−6

2.1 × 10−8 3.6 × 10−6

1.9 × 10−8 3.4 × 10−6

1.4 × 10−7

6.1 × 10−8

4.8 × 10−8

1.9 × 10−8

1.5 × 10−8

−5

−5

−5

−5

5.6 × 10 1.9 × 10−9

5.0 × 10 1.2 × 10−9

4.8 × 10 1.0 × 10−9

3.6 × 10 3.4 × 10−10

3.4 × 10 2.2 × 10−10

3.1 × 10 1.0 × 10−7

2.8 × 10 4.1 × 10−8

2.8 × 10 3.0 × 10−8

2.4 × 10 7.9 × 10−9

2.3 × 10−5 4.9 × 10−9

238 Pu 239 Pu

3.0 × 10−9 1.3 × 10−9

2.0 × 10−9 9.3 × 10−10

1.7 × 10−9 8.2 × 10−10

5.7 × 10−10 3.3 × 10−10

3.5 × 10−10 2.4 × 10−10

1.4 × 10−7 6.6 × 10−8

6.0 × 10−8 3.1 × 10−8

4.5 × 10−8 2.6 × 10−8

1.2 × 10−8 1.2 × 10−8

7.5 × 10−9 9.7 × 10−9

240 Pu

2.9 × 10−9

1.9 × 10−9

1.7 × 10−9

5.5 × 10−10

3.4 × 10−10

1.3 × 10−7

5.7 × 10−8

4.3 × 10−8

1.2 × 10−8

7.3 × 10−9

241 Pu+

1.7 × 10−11

1.1 × 10−11

× 10−11

6.3 × 10−10

7.7 × 10−8

5.5 × 10−8

3.3 × 10−6

7.7 2.7 × 10−6

7.5 × 10−10

9.5 × 10−8

1.0 4.9 × 10−8

8.7 × 10−10

241 Am

1.5 8.0 × 10−8

1.5 × 10−11

2.6 × 10−6

1.9 × 10−6

6.0 × 10−10 1.8 × 10−6

237 Np

1.0 × 10−7

8.5 × 10−8

8.2 × 10−8

5.8 × 10−8

5.2 × 10−8

4.2 × 10−6

3.6 × 10−6

3.5 × 10−6

2.8 × 10−6

2.6 × 10−6

−9

−9

−9

−7

−8

−8

−8

9.1 × 10−9 1.7 × 10−5

U

238 U

242

Cm

243 Cm

3.5 × 10 4.2 × 10−7

× 10−11

2.4 × 10 3.7 × 10−7

2.1 × 10 3.6 × 10−7

−10

7.3 × 10 2.7 × 10−7

−7

2.0

High density

× 10−6

+

235

−7

× 10−8

Low density

−10

4.6 × 10 2.6 × 10−7

1.4 × 10 2.3 × 10−5

× 10−10

6.5 × 10 2.1 × 10−5

5.0 × 10 2.1 × 10−5

1.4 × 10 1.8 × 10−5

V Taranenko et al

Absorbed dose rate conversion coefficients

A61

The DCCs allow the assessment of exposures for a wide range of organisms and habitats. Although—compared to the variability of the environment—only relatively few situations were considered in detail, the data allow interpolation to other exposure situations. Comparing the dose rate conversion coefficients for external exposure provided in this paper with similar evaluations (US DOE 2002, Amiro 1997), it is important to bear in mind that the external doses presented here are attributable only to photon radiation. Neglecting external electron radiation results in underestimation of dose for small organisms. The calculation of external doses due to electrons is very sensitive to the description of the shielding layer of reference phantoms. Therefore, justification of the latter is seen as one of the primary tasks for future improvements. Other potential enhancements are: • Concerning fauna internal exposure, the simple geometric phantoms used for the presented dose calculations are easy to describe, but they are irrelevant for dose estimation to specific organs and tissues as well as for the calculation of the dose responses for nonuniform distributions of radiation emitters. This shortcoming can be bypassed in future by construction of modified, more realistic phantoms with embedded simplified organs of interest. • An additional exposure model for radionuclides deposited on the surface of reference fauna and flora would enhance the system for quantitative assessment of external exposure. • For external exposure of fauna, the aspect of target shielding by vegetation requires more consideration. It is planned to provide results for other source depths in soil as well. • Development of a model for underground exposure of flora. • Extension of the radionuclide list using updated decay data. Acknowledgment This work was supported by the European Union FASSET project: ‘Framework for assessment of environmental impact’, contract No FIGE-CT-2000-00102. References Amiro B D 1997 Radiological dose conversion factors for generic non-human biota used for screening potential ecological impacts J. Environ. Radioact. 35 37–51 Briesmeister J F (ed) 2000 MCNP—A General Monte Carlo N-Particle Transport Code Version 4C Manual (Los Alamos: Los Alamos National Laboratory) Eckerman K F and Ryman J C 1993 External exposure to radionuclides in air, water, and soil Federal Guidance Report No. 12 (Washington, DC: Environmental Protection Agency) International Atomic Energy Agency (IAEA) 1992 Effects of ionizing radiation on plants and animals at levels implied by current radiation protection standards Technical Report Series No. 332 (Vienna: International Atomic Energy Agency) International Atomic Energy Agency (IAEA) 1999 Protection of the environment from the effects of ionising radiation IAEA-TECDOC-1091 (Vienna: International Atomic Energy Agency) International Commission on Radiation Units and Measurements (ICRU) 1992a Photon, electron, proton and neutron interaction data for body tissues ICRU Report 46 (Bethesda, MD: International Commission on Radiation Units and Measurements) International Commission on Radiation Units and Measurements (ICRU) 1992b Measurement of dose equivalents from external photon and electron radiations ICRU Report 47 (Bethesda, MD: International Commission on Radiation Units and Measurements) International Commission on Radiological Protection (ICRP) 1983 Radionuclide transformations. Energy and intensity of emissions ICRP Publication 38 (Ann. ICRP 11–13) (Oxford: International Commission on Radiological Protection) Kocher D C and Trabalka J R 2000 On the application of radiation weighting factors for alpha particles in protection of environment Health Phys. 79 407–11

A62

V Taranenko et al

Moiseenko V V, Waker A J, Hamm R N and Prestwich W V 2000 Calculation of radiation induced DNA damage from photons and tritium beta particles Radiat. Environ. Biophys. 40 33–8 National Council on Radiation Protection and Measurements (NCRP) 1991 Effects of ionizing radiation on aquatic organisms NCRP Report 109 (Bethesda, MD: National Council on Radiation Protection and Measurements) Nuclear Energy Agency (NEA) 2002 Radiological protection of the environment: the path forward to a new policy? Workshop Proc. (Taormina, Italy, Feb. 2002) (Paris: Nuclear Energy Agency) Pentreath R J 2002 Radiation protection of people and the environment: developing a common approach J. Radiol. Prot. 22 45–56 Saito K and Jacob P 1995 Gamma ray fields in the air due to sources in the ground Radiat. Prot. Dosim. 58 29–45 Salvat F, Fern´andez-Varea J M and Sempau J 2003 PENELOPE—A Code System for Monte Carlo Simulation of Electron and Photon Transport (Paris: Nuclear Energy Agency, Organisation for Economic Co-operation and Development) ISBN 92-64-02145-0 Strand P, Beresford N, Avila R, Jones S R and Larsson C-M (ed) 2001 Identification of candidate reference organisms from a radiation exposure pathways perspective Framework for Assessment of Environmental Impact (FASSET) Deliverable 1 www.fasset.org Straume T and Carsten A L 1993 Tritium radiobiology and relative biological effectiveness Health Phys. 71 347–63 Thorne M C, Kelly M, Rees J H, S´anchez-Freira P and Calvez M 2002 A model for evaluating radiological impacts on organisms other than man for use in post-closure assessments of geological repositories for radioactive wastes J. Radiol. Prot. 22 249–77 United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 1996 Effects of Radiation on the Environment. Sources and effects of ionizing radiation (Report to the General Assembly) (New York: United Nations Scientific Committee on the Effects of Atomic Radiation) United States Department of Energy (US DOE) 2002 A graded approach for evaluating radiation doses to aquatic and terrestrial biota DOE Standard DOE-STD-1153-2002 (Washington, DC: US Department of Energy)

Absorbed dose rate conversion coefficients for ...

Dec 3, 2004 - photon and electron transport simulations using the Monte Carlo method. The presented .... has a higher biological effectiveness than electrons with energies above 10 keV (Straume and. Carsten 1993 .... Hence, the Monte Carlo model geometry consists of a soil compartment which is the isotropic source.

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