Radon in the Living Environment,
19-23 April 1999, Athens, Greece
090
RADIUM DISTRIBUTION IN SOILS, ANALYSED WITH SEQUENTIAL EXTRACTION,
AND ITS EFFECT ON RADON EMANATION
Cecilia Edsfeldt
Royal Institute of Technology, Division of Engineering Geology, SE-100 44 Stockholm, Sweden.
Phone: +46 8 790 68 07; Fax: +46 8 790 68 10; e-mail: [email protected]
The radium distribution of the soil is one important parameter governing radon emanation. The
present study’s main objective is to investigate radium distribution in different Swedish soils, using
chemical selective sequential extraction, and to compare the outcome with the radon emanation of the
sampled soil types. Investigated samples were unconsolidated sediments (till, sand and clay) from the
Stockholm area. In the developed selective sequential extraction procedure, ammonium chloride and
hydrochloric acid were used to extract an exchangeable and an oxide-bound fraction from grain-size
separated samples. The soil residues were digested after extractions. Radium-226, uranium, iron,
manganese, calcium and barium were analysed from the extractant solutions and the digested samples.
Radon emanation was measured on unleached samples. In pedogenic soil phases concentrations of all
elements, as well as Rn emanation, increased with decreasing grain size and increasing specific
surface area. Radium was very well correlated with Ca and Ba, implicating an association between
these elements in the sampled soils. A major portion of the Ra was bound on the surfaces of grains.
Radium in oxide bound phase was the primary source of emanating radon, although exchangeable
radium was also important. Radium in the oxide bound was very well correlated with iron, which
indicates that this Ra was adsorbed to or co-precipitated with iron oxides. However, since iron in soils
can be well correlated with organic matter, it can not be ruled out that this Ra was partly associated
with organic matter that was leached in the same extraction. Radium bound in the crystal lattice of
minerals did not seem to contribute to the radon emanation. The sequential extraction method for
characterising radium distribution is promising. With the sequential extraction method, it is possible to
identify in which soil phase radium resides, and to gain information about the complicated soil system
that controls the emanation of radon.
Keywords: 222Rn, 226Ra, radium, radium distribution, radon emanation, radon risk, radon, sequential
extraction, soil, soil geochemistry
INTRODUCTION
Radon in indoor air is a recognised health-risk, which has led to extensive research in the area of
radon emanation. The actual mechanisms that control radon emanation are not totally understood.
The radium distribution of the soil is one important parameter governing radon emanation. Several
workers have presented theoretical calculations of how the radium distribution affects radon, e.g.
Morawska and Phillips, (1993). According to their formulae, the theoretical radon emanation
coefficient would be 0.00006 for a spherical sand-sized grain (0.5 mm) without inner porosity, with
a recoil range of 40 nm (222Rn) and a homogeneous Ra distribution, whereas it would be 0.5 for the
same grain assuming a surface radium distribution. Knowledge of the radium distribution is thus of
key importance in characterising emanation processes in different materials. Not many have studied
this in practice.
One approach towards characterising radium distribution is to use selective sequential extraction.
The same soil sample is extracted with a sequence of selective extractants, removing different soil
phases in each step, thus differentiating soil phases. The method has been used for characterisation
of uranium and radium distributions, e.g. on uranium mine tailings (Landa, 1984) and on natural
soils (Greeman and Rose, 1996; Greeman, et al., 1990). The aim of this study is to determine the
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radium-226 distribution in soils, and its effect on radon-222 emanation, using selective sequential
extraction. The major differences between this and previous work (e.g. Greeman and Rose 1990;
Greeman et al., 1999) is a different extraction procedure and the fact that the soil samples in the
present study were sieved prior to extractions. This was done in order to establish the influence of
grain-size on Ra adsorption and distribution.
MATERIALS
The stratigraphy of the sampling area (NV of Stockholm, Sweden) consists of basement
Precambrian migmatite-gneiss and granite-gneiss with pegmatite and aplite dikes, and younger
granites (Stålhös, 1969), overlain by Quaternary deposits; till, glaciofluvium, glacial and postglacial
clay (Möller and Stålhös, 1965). The granites (granite-gneisses) are enriched in uranium, why
samples collected in this area were expected to have a radium content that was somewhat higher
than normal. Soil Rn measurements close (~50 m) to the till sampling gave a Rn content of 70 000
Bq/m3 in till, and 150 000 Bq/m3 in clay, which is considered to be high radon ground. Gamma
spectrometry measurements at the same location gave a soil uranium content of 5-6 ppm.
Samples of glacial till (2 samples), sand and clay (1 sample each) were obtained. Sample material
was mainly granitic. Samples of till and sand were dried at room temperature and dry-sieved to
obtain the fine fraction, consisting of silt and clay particles (<0.063 mm). The coarser portion of the
samples were washed to remove remaining clay and silt particles, then dried at room temperature
and sieved. The clay was not sieved. Sedimentation analysis of clay and fine material (silt and clay)
of till and sand was performed according to Stål (1972). The clay sample consisted of 66 % claysized material (grain-size <0.002 mm) and negligible amounts of grains >0.06 mm.
METHODS
Sequential extractions, radon emanation measurements and chemical analysis of extraction fluids
are outlined in Figure 1. There are no general standards sequential extraction procedures, thus a new
procedure suitable for the goals of this project was developed after Landa (1984) and common
sequential extraction procedures (e.g. Förstner, 1993; Nordic Council of Ministers, 1988). The usual
sequential extraction scheme includes extraction agents for exchangeable cations, carbonates,
organic material, oxides (of Fe, Mn and Al), and residual. The source material for the sampled soils
was mainly granitic and the content of organic material was low; thus separate extractants for
carbonates and organic matter were excluded.
All chemicals used in the procedure were at least pro analysi (p. a.) grade. After extraction samples
were filtered through Munktells OOH paper filters. Filtrates and digested samples were acidified
with nitric acid (0.5 ml conc. HNO3 (suprapur)/100 ml solution) to ensure a low pH, in order to
reduce adsorption onto flasks and stabilise the solution. Soil residues were air-dried between
extractions. Sequential extractions were performed on three grain-sizes of sand (1-2 mm, 0.125-0.25
mm and <0.063 mm), on four grain-sizes of till (1-2 mm, 0.25-0.5 mm, 0.125-0.25 mm and <0.063
mm), and on unsieved clay (with the exception of the first extraction for dissolved elements).
Dissolved elements - This extraction step was performed on naturally moist clay and the air-dried
fine fractions of sand and till (not on coarser grain sizes, since they were washed prior to sieving).
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090
20 or 40 g of sample was equilibrated with 25 or 50 ml of deionised water for two hours, then
centrifuged and filtered. The filtrate was diluted to 100 ml and acidified.
Exchangeable elements (cation exchangeable elements, including elements weakly bound to
organic matter) – 25 g of air-dried sample was mixed with 100 ml of 1M NH4Cl (ammonium
chloride) and agitated on a shaker for two hours. If the leaching solution was cloudy after shaking,
it was centrifuged before filtration. The sample was washed with 1M NH4Cl to 100 ml of filtrate
and acidified.
Oxide bound elements (elements coprecipitated with Fe/Mn/Al oxides and elements strongly bound
to organic matter) - 2.5 g of soil residue was boiled with 100 ml of 1 M HCl (hydrochloric acid) for
15 minutes, then filtered. The sample was washed with deionised water until the filtrate volume
added up to 100 ml.
Residual (elements bound in the crystal lattice of minerals) – Soil residues from the preceding
leaching step were dried at 105 °C for 24 hours, ignited at 550 °C for 1 hour, and then ground in an
opal mortar. The powdered sample (0.25 g) was mixed with lithium metaborate (LiBO3, 0.75 g),
and fused by heating at 1000 °C for 45 minutes; resulting in a “glass” bead that was dissolved in 25
ml of 5 % HNO3 during shaking. The dissolution method is described by Potts (1987).
Radium in extractant solutions and digested samples was analysed with α-spectrometry by means of
liquid scintillation counting (LSC). Sample solutions were pre-treated in order to isolate 226Ra, and
analysed according to Suomela (1993). The procedure includes precipitation of Ra together with
barium sulphate and dissolution of the precipitate in EDTA. Samples with obvious content of humic
acids (yellow-brown colour) were digested with hydrogen peroxide (H2O2) prior to the pretreatment. Standard deviations ranged from 7-22 % in the dissolved phase, from 1-9 % in the
exchangeable phase (with the exception of Till 2 <0.063 mm: 25 %) and from 4-20 % in the oxide
bound phase. The concentrations of Ra in the residual were under the detection limit, thus the exact
Ra content in this phase is not known. The concentration can be estimated from the total
concentration of Ra subtracted by the total concentration of Ra in surface-bound fractions.
Uranium was analysed by ICP-MS (Induced Coupled Plasma - Mass Spectrometry; Potts, 1987).
Standard deviations were 0.2-5 % for the dissolved, oxide bound and residual phases and 4-12 %
for the exchangeable phase. Iron, manganese, calcium and barium were analysed with ICP-AES
(Induced Coupled Plasma - Atomic Emission Spectrometry). Standard deviations were generally
less than 1 %. For both types of ICP analyses four consecutive measurements were made on each
sample. Standard solutions with a matrix similar to the leachate matrix were used and potential
contamination was checked by analysing method blanks. Samples were analysed in a random order
to prevent false trends caused by instrument drift, which was checked by analysing control
standards after every 7th or 8th sample.
Total radium content of sieved, unleached samples was determined by gamma spectrometry at the
Kernfysisch Versneller Instituut (KVI), Netherlands. The analysis procedure is described in van der
Graaf et al. (1998a). Radon exhalation measurements were performed at the KVI, Netherlands, in a
sealed exhalation chamber, where nitrogen gas, flowing through the container, acted as a radon
carrier. After passing the container, the gas mixture was passed through activated charcoal, which
adsorbed the radon. The radon activity of the charcoal was then measured with a gamma
spectrometer. The measurement procedure is carefully described in van der Graaf et al. (1998b).
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Radon in the Living Environment,
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090
The exhalation measurements were performed on dry samples, excluding the influence of soil
moisture. The soil was arranged in layers with a thickness of about 0.3-3 cm, which is considerably
less than the Rn diffusion length in these materials (≈2 m). All Rn that emanated from the soil can
thus be assumed to have exhalated, and the Rn emanation coefficient can be calculated with the
knowledge of the total Ra content in the samples according to: Rnem=E/(Ra*λRn), where Rnem = Rn
emanation coefficient, E = Rn exhalation [Bq·kg-1·s-1], and λRn = Rn decay constant
[2.0985·10-6s-1].
RESULTS
Generally, concentrations of Fe, Mn, Ca, Ba, U and Ra in all surface-bound soil phases increased
with decreasing grain-size (Figures 2 and 3). The maximum concentration was most often attained
in the clay sample. Generally Ra correlated better with Ca than U did; and U correlated better with
Fe than Ra did.
Dissolved elements - Generally low concentrations of all analysed elements.
Exchangeable elements - Calcium was clearly most predominating in the exchangeable fraction,
with concentrations about two orders of magnitude greater than the other elements. More than 10 %
of total Ra was found in the exchangeable fraction, 1-16 % of total Ca, and less than 1 % of the
other elements (Figure 2).
Oxide bound elements - Iron predominated in the fraction that was extracted with hydrochloric acid.
Fe and Mn had the highest relative occurrence, 20-70 %, with the highest number corresponding to
the clay sample (Figure 3).
Residual - Regarding the residual fraction, the concentrations of elements were about equal in all
fractions, and did not increase with decreasing grain-size.
Radon exhalation (E), radon emanation coefficients and total 226Ra concentrations of unleached
samples are displayed in Table 1. The total Ra concentration corresponds closely to the sum of Ra
in surface bound fractions (exchangeable + oxide bound), indicating a low Ra content in the
residual. The Rn emanation increased with decreasing grain size. The Rn emanation coefficients are
rather low, depending on the fact that the Rn exhalation was measured on completely dry samples.
DISCUSSION
Expected, obtained and an interpretation of results from sequential extractions are summarised in
Table 2. Element concentrations in filtrates from all extractions were found to increase with
decreasing grain-size. This is to be expected, due to the increased adsorption/precipitation onto
smaller particles, resulting from the larger specific surface area (Megumi and Mamuro, 1974). In
accordance with the results of Greeman et al. (1999), this study shows that Ra has a better overall
correlation with Ca, while U correlates better with Fe. Ra was also well correlated with Ba, and it is
thus concluded that Ra was associated with Ca and Ba in the investigated soils.
The element distribution in the ammonium chloride extraction, with relatively high concentrations
of Ca and Ba, implies that cation-exchangeable elements were indeed extracted in this leaching
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Radon in the Living Environment,
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090
step. In the acid-leached fraction, all analysed elements correlated very well for all soil types and
grain-size fractions. The iron concentrations were much higher than the concentrations of the other
elements, indicating that the iron oxides were partly dissolved, liberating elements adsorbed to or
co-precipitated with these. The even concentrations in the residual was expected since this phase is
marginally affected by pedogenic processes.
That Rn emanation increases with decreasing grain size is explained partly by the recoil theory (e.g.
Fleischer, 1980), but it primarily depends on the fact that the smaller grains tend to have a larger
total concentration of Ra, due to the larger surface area (Figure 4). The Rn emanation (E) was very
well correlated with Ra concentrations in the acid-leached fraction. The correlation was also good
with Ra in the exchangeable, but the total amount of Ra in this phase was smaller. Results from
multiple regression point to Ra in oxide bound phase as the variable that was most important with
respect to the radon emanation. It can thus be assumed that the Ra contributing to Rn emanation
was primarily associated with iron oxides (or strongly bound to organic matter) on the surface of
soil grains. Ra in the exchangeable phase was also important, while radium in the crystal lattice of
minerals seems to have been of minor importance.
Research results from Greeman et al. (1999) and Hogue et al. (1997) suggest that radium that
contributes to radon emanation is primarily bound to organic matter and to the exchangeable
fraction, while uranium, to a large extent, is bound to Fe oxides. Since the present study did not
have a separate extractant for the organic phase, Ra bound to organic matter was leached at either
the salt (weakly bound) or the acid extraction step (strongly bound). The very good correlation
between Ra and Fe in the acid extraction step does not suggest that the organic phase contribute
significantly to the result in this phase, thus the results of this study indicate a larger importance of
the Fe oxide phase than does the results of Greeman et al. (1999). However, there is a possibility
that the Ra is connected with Fe-organo-metallic complexes that also might have been leached in
this extraction, rather than with Fe oxides, which would then be more in accordance with Greeman
et al. (1999). This possibility is supported by the results of Karltun and Gustafsson (1993) that show
a good correlation between Fe and Al oxides and organic matter in soils.
The developed sequential extraction method worked well, the intended soil phases were extracted in
the extraction steps designed for them. However, an improved resolution would have been
advantageous, and thus a separate extractant for organic matter would have been desirable. All the
elements analysed from the extractant solutions gave valuable information. Ca is a typically
exchangeable element, while Fe precipitates as iron oxides. They give essential information on what
soil phase have really been extracted. Mn precipitates as oxides, as Fe does, and Ba is interesting
because Ba2+ behaves similarly to Ra2+ in most environments. However, an analysis of silica (Si;
possible dissolution of crystalline matter), aluminium (Al; presence of Al oxides), thorium (Th;
comparison with other work) and organic carbon (C; extraction of organic matter) would also have
been desirable. The method will be revised prior to further use. The present study is an initial study
to test the sequential extraction method for different Swedish soil types. Further studies will be
performed in order to establish if the method gives results that are representative of the investigated
soils.
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CONCLUSION
Determining radium distribution using sequential extraction gives information about the radon risk
potential of a soil. The present and previous studies (e.g. Landa, 1984; Greeman and Rose, 1996;
Greeman et al., 1999) show that Ra that can be extracted from soil by simple methods is the primary
source of emanating radon. The sequential extraction method can be used to gain valuable
knowledge concerning Ra geochemistry, which can be taken into account when radon risk models
are developed.
ACKNOWLEDGEMENTS
I would like to thank Emiel van der Graaf and the others at the Kernfysisch Versneller Instituut,
Groningen, Netherlands, for the opportunity to perform radon exhalation measurements at their
laboratory. This work was funded by the Swedish Radiation Protection Institute, and the Royal
Institute of Technology, Stockholm.
REFERENCES
[1]
Fleisher, R. L. Isotopic Disequilibrium of Uranium: Alpha-Recoil Damage and Preferential Solution
Effects. Science 1980; 207: 979-981.
[2]
Förstner, U. Metal speciation - General concepts and applications. Int J Environ Anal Chem 1993; 51:
5-23.
[3]
Graaf, E. R. van der, Cozmuta, I., Edsfeldt, C. Determination of the radioactivity, radon exhalation and
emanation of 12 Swedish soil samples. KVI intern report S40. Kernfysisch Versneller Instituut,
Groningen, 1998a, 9 pp.
[4]
Graaf, E. R. van der, Cozmuta, I., van der Spoel, W. H. Calibration of the KVI instrument to measure
radon exhalation rates from building materials under controlled conditions. KVI report R99.
Kernfysisch Versneller Instituut, Groningen, 1998b, 46 pp.
[5]
Greeman, D. J., Rose, A. W. Factors controlling the emanation of radon and thoron in soils of the
eastern USA. Chem Geol 1996; 129: 1-14.
[6]
Greeman, D.J., Rose, A.W., Washington, J.W., Dobos, R.R., Ciolkosz, E.J. Geochemistry of radium in
soils of the Eastern United. Appl Geochem 1999; 14: 365-385.
[7]
Greeman, D. J., Rose, A. W., Jester, W. A. Form and behaviour of radium, uranium and thorium in
Central Pennsylvania soils derived from dolomite. Geophys Res Lett 1990; 17(6): 833-836.
[8]
Hogue, J. R., Rose, A. W., Jester, W. A. Patterns of disequilibrium among 238U, 234U, 230Th and 226Ra
in total soil and soil phases in two soil profiles. In: Rose A. W., editor. Generation and mobility of
radon in soils. Final Report to U.S. Dept. of Energy, Contract DE-FG02-87ER60577. Appendix B.
Pennsylvania State University, Department of Geosciences, 1997. 43 pp.
[9]
Karltun, E., Gustafsson, J. P. Interference by organic complexation of Fe and Al on the SO42 −
adsorption in Spodic B horizons in Sweden. J Soil Sci 1993; 44: 625-632.
[10] Landa, E. R. Geochemical and radiological characterisation of soils from former radium processing
sites. Health Phys 1984; 46(2): 385-394.
[11] Megumi, K., Mamuro, T. Emanation and Exhalation of Radon and Thoron Gases from Soil Particles. J
Geophys Res 1974; 79: 3357-3360.
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[12] Möller H., Stålhös, G. Beskrivning till geologiska kartbladet Stockholm NO. SGU Ae Nr 2 (in
Swedish). Swedish Geological Survey, Stockholm, 1964, 148 pp.
[13] Morawska, L., and Phillips, C. R. Dependence of the radon emanation on radium distribution and
internal structure of the material. Geochim Cosmochim Acta 1993; 57: 1783-1797.
[14] Nordic Council of Ministers. Soil Chemistry Monitoring. In: Guidelines for integrated monitoring. The
steering body for environmental monitoring, Nordic Council of Ministers 1988; pp 27-31.
[15] Potts, P. J. A handbook of silicate rock analysis. Blackie & Son Limited, Glasgow 1987, 622 pp.
[16] Stål, T. Kornfördelning – förslag till geotekniska laboratorieanvisningar, del 4. Byggforskningens
informationsblad B2:1972 (in Swedish). Statens institut för byggnadsforskning, Stockholm, 1972, 23
pp.
[17] Stålhös, G. Beskrivning till Stockholmstraktens berggrund. SGU Ba Nr 24 (in Swedish). Swedish
Geological Survey, Stockholm, 1969, 190 pp.
[18] Suomela, J. Method for determination of radium-226 in water by liquid scintillation counting. SSIreport 93-12. Swedish Radiation Protection Institute, Solna, 1993, 9 pp.
767
Radon in the Living Environment,
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090
Table 1:
Radon exhalation (E), activity concentrations of
(Rn eman) of unleached soil samples.
SAMPLE
Till 1
Till 2
Sand
Clay
Grain size [mm]
>1
>0.25
>0.125
<0.063
>1
>0.25
>0.125
<0.063
>1
>0.125
<0.063
<0.063
E [Bq/(kg s)] 1)
1.2E-05
1.48E-05
5.76E-05
8E-06
1.03E-05
4.05E-05
7E-06
1.05E-05
3.85E-05
4.7E-05
226
226
Ra, and Rn emanation coefficients
Ra [Bq/kg] 2)
33.4
32.9
36.7
121.4
32.2
31.7
32
101.8
32.7
32.7
167.1
100.8
Rn eman3)
0.171
0.192
0.227
0.115
0.153
0.189
0.099
0.153
0.108
0.223
1)
Uncertainties due to counting statistics and variation in total efficiency (1 standard deviation) are 2-5 %. Systematical
uncertainties in absolute calibration are at maximum 4 %.
2)
Uncertainties due to counting statistics (1 standard deviation) are 2-5 %. Systematical uncertainties in absolute
calibration are at maximum 10 %.
3)
Uncertainties due to counting statistics and variation in total efficiency (1 standard deviation) are 3-5 %. Systematical
uncertainties in absolute calibration are not included and are at maximum 11 %.
Table 2:
Summary of expected outcome, results and interpretation of results from the sequential
extraction procedure.
Leaching agent
Deionised
water
1M NH4Cl
Expected outcome
Dissolved
elements.
Cation
exchangeable ions,
e.g. Ca, Ba and Ra,
and ions weakly
bound to organic
matter.
1M HCl
Elements
coprecipitated with
Fe /Mn /Al oxides
and elements
strongly bound to
organic matter.
Digestion
of Elements bound in
soil residues
the crystal lattice of
minerals.
Outcome
Generally
low
concentrations.
Ca predominated. Ra
correlated well with
Ca (and Ba). Very
little Fe and U.
Interpretation
Dissolved elements.
Fe predominated.
Good correlation
between all analysed
elements. More Ra in
this fraction than in
the preceding one.
Concentrations did not
vary much between
samples. Ra analysis
failed.
Fe oxides dissolved,
elements bound to
these liberated.
Possibly also
elements associated
with organic matter.
Elements bound in the
crystal lattice of
minerals. Marginal
effects of soil
formation processes.
768
Cation exchangeable
elements. Ra
associated with Ca
and Ba.
Radon in the Living Environment,
19-23 April 1999, Athens, Greece
090
SAMPLES FOR ANALYSIS:
TILL: >1 mm, >0.25 mm, >0.125 mm, <0.063 mm,
SAND: >1mm, >0.125 mm, <0.063 mm,
CLAY: <0.063 mm
RADON
EMANATION
ANALYSIS
SEQUENTIAL
EXTRACTIONS
SAND and TILL >0.125 mm
CLAY, SAND and TILL <0.063 mm
DEIONISED
WATER
RADON
EMANATION
MEASUREMENT
SOIL RESIDUE
AMMONIUM
CHLORIDE
TOTAL Ra
ANALYSIS
SOIL RESIDUE
HYDROCHLORIC
ACID
SOIL RESIDUE
FILTRATE
DIGESTION
DISSOLVED SAMPLES
CHEMICAL
ANALYSIS
LSC ANALYSIS
OF Ra
ICP-MS
ANALYSIS OF U
ICP-AES
ANALYSIS OF Fe,
Mn, Ca AND Ba
Figure 1:
Flow chart outlining sequential extractions, radon emanation measurements and
chemical analysis of extraction fluids.
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Radon in the Living Environment,
19-23 April 1999, Athens, Greece
090
Fe [ppm]
Mn [ppm]
Till1
Figure 2:
<0,063
>0,25
>0,5
>1
0
<0,063
40
30
20
10
0
Till2
Sand
Concentrations in the exchangeable phase.
770
ClayCla
yClay
<0,063
5
50
<0,063
10
60
>0,25
15
Ra [Bq/kg]
8
7
6
5
4
3
2
1
0
>0,5
20
>0,25
<0,063
100
25
U [ppb]
100
>1
Ba [ppm]
0
>0,25
0
>0,5
0
500
>1
1
>0,5
2
1000
>1
2
<0,063
4
>0,25
3
2000
1500
>0,5
6
12
>1
4
>0,25
8
>0,5
5
>1
10
Ca [ppm]
Radon in the Living Environment,
19-23 April 1999, Athens, Greece
090
3000
20000
200
2000
10000
100
1000
0
0
0
U [ppb]
Ra [Bq/kg]
214
100
5000
80
4000
20
0
0
0
Till1
Figure 3:
<1
Till2
<1
1000
>0,063
20
<0,125
40
<0,25
2000
>0,063
40
<0,125
60
<0,25
3000
<1
60
Sand
Clay
Concentrations in the oxide bound phase.
771
>0,063
80
<0,125
100
<1
<1
Ba [ppm]
>0,063
300
>0,063
30000
<0,125
4000
<0,25
400
>0,063
40000
<0,125
5000
<0,25
500
<1
50000
<0,125
Ca [ppm]
<0,25
Mn [ppm]
<0,25
Fe [ppm]
Radon in the Living Environment,
19-23 April 1999, Athens, Greece
8.E-05
Rn exhalation
[Bq/(kg.s)]
Rn exhalation
[Bq/(kg.s)]
090
6.E-05
4.E-05
2.E-05
0.E+00
0
50
100
6.E-05
4.E-05
2.E-05
0.E+00
0.001 0.01
150
Surface bound Ra [Bq/kg]
Figure 4:
8.E-05
0.1
1
log Surface area [m2/kg]
Scatter plots of radon exhalation vs. surface bound Ra and surface area.
772
10