STUDIECENTRUM VOOR KERNENERGIE

MEASUREMENT OF THE NATURAL RADIATION

OF THE BELGIAN TERRITORY

J. GILLARD - J.M. FLEMAL J.P. DEWORM - W. SLEGERS

BLG 607

Ministry oj Public Health and Environment

Institute of Hygiene and Epidemiology 14, Juliette Wytsman street 1050 ttrustels. PEASUfOTfT OF THE NATURAL RADIATION OF THE BaGIAN TERRITORY

J. GILLARD - J.M. FLEMAL

** J.P. DEWORM W. SLEGERS

IHE, Institut of Hygiene and Epidemiology Section Radioactivty Department of the Environment

Belgian Nuclear Research Centre. Department of Radiation Protection and Safety S.C.K.-C.E.t;. : Studiecentrum voor Kernenergie Centre d'étude et de l'Energie Nucléaire 1.

1. INTRODUCTION

The assessment of exposure to natural radiation to which the human being is submitted, is of particular importance as most of the collective dose received by the world population is of natural origin.

The Institute of Hygiene and Epidemiology (IHE) has been given the mission of controlling the radioactivity of the Belgian territory and of assessing the doses received by the Belgian population.

In this context, measurements of natural occuring radionuclides were per­ formed and the results written down in this report.

This study was carried out by the IHE and S.C.K./C.E.N, together. The purpose was the estimation of the doses received by the Belgian popula­ tion which were estimated on the basis of the above-mentioned measursments. The second purpose was the set up of a map of natural occuring radio­ nuclides and exposure rates.

The results derived from this study can also be compared to estimated contributions of artificial sources.

88-1019 2.

2. NATURAL RADIATION SOURCES

2.1. Cosmic radiation Cosutic-ray charged particles contribute significantly to man's dose from environmental radiation. The primary high energetic ccsmic radiation entering the atmosphere inter­ acts with the atomic nuclei in the air and produces secondary radiation 14 3 (neutrons, protons, kaons) as well as the cosmogenic radionuclides C, H, 22 7 Na and Be that contribute a measurable dose to man. The secondary cosmic radiation forms new secondary particles. At earth level the cosmic radiation has two components, one ionizing and one neutron component. The apparatus used for the measurements in this report detect only the ionizing components. At sea level the absorbed dose rate in air due to the -8 -1 -1 ionizing component amounts 3,2.10 Gy.h (3,2 urd.h ) (ref.l,Z). This value changes not much with latitude but with altitude; it doubles every 1500 m. (ref.1,2; fig.II; p.85). The cosmic radiation changes with the solar activity modulation as well as with changes in temperature in the upper layer of the atmosphere. The changes due to the solar activity are rare and of short duration. The influence on the yearly absorbed dose is thus very small. In this report the purpose was not to determine the cosmic component exactly. The values accepted can be found in different reports. 2.2. Terrestrial radiation Naturally occuring radionuclides in the earth represent a significant component of the background radiation exposure to the population. The radionuclides of primary importance, havina a long half live and present since the origin of the earth, are : 40K (T = 1,42.109 y) Ö/Rb (T = 4,8.10iU y) 238 9 U (T . = 4,47.10 y) + radioactive decay chain 232 10 Th (T . » 1,42.10 y) + radioactive decay chain 235 Other radionuclides, such as those present in the U decay series, have been neglected as they contribute very little to the total dose from natural background. 238 The radioactive decay chain of U is

J34u (4.«7 10'« «45 10sal S'y* 2Mm^ / 1 1 a| f 11.17 mul *! i7 1 2î*n. / 1 124.1 dl SO 10* il •I

11.823 c»

13.09 min» •% 11.(4 I0_'ll I1M.4»! 1? 1 3, V n- 3 i J» H»7tiirt» :5.01

232 The radioactive decay chain of Th is

23 »»Th V„ 11.41 I01,4P .7 It iljll J'

22» 4. c 1 J" '(.Uni

I5.76JI :3.66dl

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55 t)

ai

2tV T OISi) J-" 13.04 10* il M* i a : -f a: ,J/ 20.^ a;36% i 10.(4 XI / I10»iiiii|

In these two figures the radionuclides formed less than 1 % by the trans­ formation of the parent nuclides are omitted. 4.

The concentration of radionuclides in soil, which is directly relevant to the outdoor exposure, is largely determined by the activity concentration in the source rock. Igneous rock generally exhibit higher activity concen­ tration than sedimentary rocks, while metamorphic rocks have concentrations typical from which they were derived. However, certain sedimentary rocks, notably some shales and phosphate rocks, are highly active (ref.2). -8 -1 -1 The mean dose rate in air ranges from 3 to 7.10 Gy.h (3 to 7 urd.h ) -8 -1 -1 and the population - weighted mean amounts 4,9.10 Gy.h (4,9 urd.h ) (ref.2,3). 40 238 232 The average activity concentrations of K, U jind Th in soil and the corresponding dose rates in air 1 m above the ground surface, are cal- 238 232 culated on the assumption that all decay products of U and Th are in radioactive equilibrium with their precursors. This is only true for the source rocks, not for the sedimentary rocks (ref.3, p.44). 5.

3. INTEGRATED MEASUREMENTS NETWORK

3.1. Dosemeters network

3ilili_Definition End of 1979, a network of integrating thermoluminescent dosemeters was set up in . The section "Radioactivity" of IHE with the collaboration of the Royal Meteorological Institute selected 35 sites on the territory. This selection was based on the nature of the most prevalent soils in Belgium, on the density of population and on the ways o- approach and of supervision of these sites.

3.1.2. Description The exposure time of the dose meters is about one year. Their reading after this lapse of time gives the integrated yearly average doses absorbed in the atmosphere (together with a part of the absorbed doses in the atmosphere due to cosmic rays). The integrated dose which can be expected fluctuates between 0,4 to 1 mGy (40 to 100 mrds). Highly sensitive detectors are therefore not strictly necessary and detector TLD-700 was selected. These detectors are made of 3/3/0,9 mm patches composed of LiF enriched in Li-7 and they are practically insensitive to thermal neutrons. Their relative standard deviation for 40 mR is 5 %. The dosemeter holder is of type TNO (photo 1) containing 8 detectors placed behind a screen of 730 2 mg/cm thickness. This screen is made of 0,3 mm Pb, 1 mm Al and of plastic. The exposure rate is calculated by taking the average value of these 8 detectors. It is expressed in nSv.h

3.1.3. Calibration 60 The calibration of the detectors is carried out by means of a Co source in electronic equilibrium conditions. The exposure rate of this source is fixed by means of an ionization chamber. iLii4. i-E?. ü£iD2_ÜE All doseineters are set up in the same way on a PVC tube of about 6 cm diameter. 6.

They are hung at a height of about 1 m and are sheltered from rain and sun by a PVC cover (photo 2).

3.2. Soil sampling

111'ii_BS£iu^Si2D Soil samples were taken in the neighbourhood of most dosemeters except for Ostend and Felenne. They were also taken near the control stations of Doel, Tihange and Dion. On the whole a total of 35 soil samples were ta^en (map 1). In order to get a fairly good representative sample, 5 soil samples were taken round each dose meter : a central one and four other in different directions at about 4 m from the central point. The samples were then mixed together. All samples were taken up to a depth of 30 cm.

3.2.2^ Analyses of tha sanjgles In the laboratory the samples are weighted, dried at a tempérâttre of 108°C during 48 hours, mixed and weighted again to determine the evaporable moisture content. A sample of 2,7 liter was measured by gamma-spectrometry ^ „ ^ ^u ^- -^ ^ 40„ 226„ 232 _ . 137,, to determine the activity of K, Ra, Tmlh and Cs. Measuring time is 400 minutes; detection limit is about 0,15 mBq.g . The maximum relative standard deviation is about 10 %.

3.2.S. Exposure rate Th.- exposure rate at one meter above ground for natural emittors is de­ termined with the help of the following conversion factors calculated by BECK, H.L [4] for emittors uniformly distributed in the soil :

40K : 0,048 nSv.h"1/mBq.g"1 226 —1 •• 1 Ra + daughters : 0,49 nSv.h /mBq.g 232 -1 -1 Th + daughters : 0,76 nSv.h /mBq.g

The total exposure rate in nSv.h is : G - 0,048 C.. + 0,49 C + 0,76 C 40K 226Ra 232Th where C = concentration in mBq.g 137 The Cs activity was not taken into account because of the limited contribution to the total exposure rate. 7.

4. LOCAL GAMMA RAY MEASUREMENT NETWORK

4.1. Definition In order to get a good approach of the average exposure rate over the Belgian territory, the points of measurement were chosen so as to give the most possible regular response. 272 points of measurement were selected all over the territory (map 2) . They were taken far from built-up areas and roads so as to avoid any contribution of building material and of road coating.

The points of measurement were distributed in each province in the follo­ wing way. Antwerp 26 Brabant 30 Hainault 32 Limburg 27 Liège 41 Luxemburg 35 Namur 31 23 27 "272

The campaign was carried out by means of a truck equipped with a Nal 4"x4" crystal and with a Reuter-Stokes ionization chamber RSS-111. At each place 4 measurements were performed with the Nal crystal within a radius of about 25 m and a central measurement was taken with the ionization chamber. All measurements were carried out in similar conditions of temperature and hygrometry to minimize their influence or. the measured exposure rates. The study was performed during the years 1983 and 1984. 4.2. Nal-cristal 4"x4"

4.2.1. Description of the components - detector = 4"x4n Nal crystal with PM without preamplifier (one cable).

- a positive high voltage, 0 - 2000 V - 1 mA, with charge sensible pream­ plifier to avoid loss of signal (in cable).

- an adjustable monocanal analyzer to select incoming pulses; when the upper level is switched off, an integral counting is possible (0,1 à 2 MeV).

4 - a logaritmic rate meter : 0,1 à 10 cps.

- a mini-sealer with preset time and preset count possibility.

- a DC-source with transformer (24 V - 220 V) for using the instrument also with two 12 V batteries.

LOT HAItMCIEII neemt* aiui 0 - 100 mV

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M mANsroMcit MONOCANAL MM-SCAUER 24 V pone» suppir 1) 0 V < O. 11 M 1 MS* - 10

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Figure 1 : Components of the Nal - 4"x4" gamma detector.

4.2.2. Practical ^rangements The 4"x4" Nal-crystal is placed in a metal holder at a height of 30 cm above the soil (photo 3). On every place 5 different measurements were done : one central and four at a distance of about 25 m to control the homogenity of the soil. All measurements were done in the position "integral". The preset time on the mini-sealer was 100 seconds . The total counts per measurement varied from 16.000 to 800.000 so the statistical error is negligible. Ra, Co and Cs-sources are used to calibrate the crystal. 4.3. Ionization chamber

4;3;1. Description The ionization chamber used is a Reuter-Stokes RSS-111. It is a spherical chamber with a diameter of 13 cm filled to a pressure of 25 atmospheres with ultra-high purity argon. When radiation is incident upon the chamber, the ion pairs produced in the active volume are swept to the electrodes by a collecting potential. The resulting current is measured by an electrome­ ter and can be related directly to the free air exposure rate. The instru- 60 ment is calibrated for gamma ray response using a 37 MBq Co source. The relative response is shown in figure number 2.

2.0

>

z

<

0.01 0.1 0.2 0.3 0& 1 2 3 4 6 8

GAMMA ENERGY (MEV)

Figure 2 : Relative sensitivity of the RSS-111 at various energy points 60 relative to Co.

A portion of the ionization measured with the RSS-111 is due to cosmic rays secondaries, primarly high energy muons, photons and electrons. In typical measurement situations, the exposure rate due to cosmic radiation depends mainly on the mass of air above the chamber, i.e. the atmospheric pressure. Additionally, there are slight latitude variations and changes with time associated with the 11 year solar activity cycle. Table 1 gives the cosmic ray response at various atmospheric pressures as given by the ronstructor. 10.

Table 1 : Cosmic ray response of RSS-111

Atmospheric pressure -2 g.cm nSv.h"

1033 36 1000 38 950 43 900 50

4.3.2. Practical arrangements The ionization chamber was set up simultaneously with the Nal-crystal in the center of the measuring area at a height of 1 m abcve the soil.

4.4. Correlation between exposure rate, measured with the Nal crystal and the ionization chamber The measuring of the ambient radiation was divided in two campaigns. During the first campaign in 1983 only the Nal crystal was used while in 1984 measurements were dono simultaneously with the crystal and the ionization chamber. The last campaign enclosed 120 points of measurement and with these results the correlation between the crystal and the ionization chamber was calculated : nSv.h"1 [RSS-111] = 0,113 cps (Nal] + 36 r = 0,99 All the results obtained with the Nal crystal in cps were converted in nSv.h with this characteristic equation. 11.

5. RESULTS

5.1. Integrated measurement network

51lil1_Dosemeters_ The average results of TLD dosemeters obtained during 4 years can be found in Table 2 together with those obtained with the cristal or the ionization chamber. Standard deviations are also mentioned. All results expressed in nSv.h are shown on map 1.

5.1.2. Soil sampling ~'T~" 7~~4Ô~~~?32„ 226„ . 137_ . .. . Activities in K, Th, Ra and Cs of the analysed soil samples are given in table 3. They are expressed in mBq.g of dry weight. Exposure rates (GV) calculated on the base of these activities are also mentioned in this table (cf. par. 3.2.3. & ref.5). These exposure rates expressed in nSv.h are also shown on map 1.

5.2. Local measurements network (crystal and ionization chamber) The 272 points of measurement are given in table 4. Lambert coordinates and dates of measurement are also mentioned. Some of the measurement were performed twice at different dates. All results are expressed in nSv.h and shown on map 3. 12.

6. INTERPRETATION

6.1. Integrated measurements network Comparison between measurements with dosemefers, soi] samples and ioniza­ tion chamber.

6.1.1. Average^exgosure rates The average of all exposure rates measured with TLD's is about 84 nSv.h and fluctuates from 55 to 107 nSv.h from North of the country to the Ardennes (table 2). The average of all exposure rates measured (round the TLD dosemeters) with the ionizing chamber amounts» 85 nSv.h and fluctuates from 59 r.. v.h in the North of t.he country to 108 nSv.h in the Ardennes (table 2) .

The correlation between TLD measurement methods and the ionization chamber method (IC) is TLD - IC - 2,2 nSv.h"1 r = 0,96 Exposure rates measured «rith TLD's as a function of those measured with the ionization chamber are shown in fig.3a. This figure shows a good agreement between both measurement methods. Measurements carried out by means of the ionization chamber are local measurements which may be influenced by atmospheric conditions, such as variation of the moisture in soil, depth of snow bed, wash-out of dust con­ taining decay products of Radon, temperature inversions, turbulences, etc... Therefore the measurements were performed as much as possible in similar atmospheric conditions. Somt. of the above mentioned variations cannot be detected by integrating TLD's, as their duration is relatively short compared to the global exposure time of the dosemeters.

The correlation between exposure rates given by TLD's and those calculated on the basis of soil samples activity (GV) (par. 5.1.2.) has also been 13.

calculated TLD = O,74.G + 46 nSv.h" v r = 0,92 This is shown in fig.3b

The correlation between exposure rates measured with the ionization chamber (IC) and those calculated on the basis of soil samples activity (GV) is : IC = 0,7. GV + 50 nSv.h"1 r = 0,95 This relation is shown in fig.3c. Assuming that in both last correlations, the exposure rate due to soil samples activity (GV) is 0, exposure rates g_ven by dosemeters and ioniza­ tion chamber are therefore respectively TLD = 40 and 52 nSv.h' X IC = 46 and 55 nSv.h"1 which can be assumed as being the exposure rate due to the ionizing compo­ nent of cosmic rays, to "Sky-Shining", to the presence of Radon in the atmosphere, and to artificial radionuclides as well a.s to a background component of the ionization chamber itself. Different figures have been reported for the assessment of the ionizing component of cosmic rays. These figures fluctuate between 32 and 40 nSv.h . Some experiments were conducted above large stretches of water with the ionization chamber. Measurements performed at Mol above abandoned water-covered sand quarries gave a value of 44 nSv.h . Measurements performed on board of a ship in the North Sea gave 41 and 43 nSv.h .

Consequently a good at_ roach of the terrestrial radiation can be obtained when subtracting 40 nSv.h from the results giv»n by the ionization chamber.

Average activities of soil samples expressed in mBq.g are summarized in table 5. They are classified following their geological underlying state. Exposure rates arising from these activities are also given in this table. This classification was made without a real geological study. Detailed reports on this matter can be easily found in littérature (réf.6). 14.

Relative contributions in K, ' Ra and Th of soil samples arranged following the main Belgian geological areas are shown in fig.4 as well as the total exposure rate calculated on the basis of these activities. A comparison between measurement results performed "in situ" with the ionization chamber, soil samples and the Ge-Li detector has been attempted in a separate study (ref.7). "In situ" spectra taken with the Ge-Li detector are summarized in fig.5 showing the contribution of the different nuclides.

6.2. Local measurements network : results obtained with the NaT crystal or wiih the ionization chamber A distinct evolution of exposure rates as a function of soil composition can be seen (table 5, fig.4) , whichever way the exposure rates are esta­ blished, either by calculation from the activities of isotopes (Beck) or by measurement with dosemeters or ionization chamber. All measurements performed with the Nal crystal or the ionization chamber are reported on map 3 (transpirent) and expressed in nSv.h . This map has to be read by putting it over the lithological map nr. 4 (ref.8). A fluctuation of dose rates from 54 to 120 nSv.h can be observed from the dunes of the coastal area and sands of Campine to the quartz and shales of the Ardennes. The exposure Late in Gaume where marl is the main soil constituent is about 90 nSv.h" .

When putting together similar points, the territory can be divided into different areas.

- North West of the river Leie and

A gradual decreasing exposure rate of 80 nSv.h to 60 nSv.h may be seen from South to North. As all these measurements were performed in the same period, this decrease can not ue due to measurement variations with time. The lowest values can be found above the sands of the coastal zone (54 nSv.h"1). The highest values are observed above the river deposits of the Polders (80 nSv.h" ). 15.

- North of the Demer river : area situated between the lowest course of the Scheldt and the Maas as border-river.

This area is mainly formed of sands called "Sands of Campine". Most of the data found fluctuate between 60 and 75 nSv.h . Lower values of 55 nSv.h can be observed above the moorland in the farthest North nf the country. Values between 80 and 90 nSv.h can be found above river d^oosits of tlvS Maas in the area situated North of Maastricht.

- Sand area situated South of the Demer and delimited by the Senne gnd the Maas Measured exposure rates fluctuate between 95 and 110 nSv.h .

- Sands and clay area situated between the Senne and the Scheldt Exposure rates fluctuate from 80 to 100 nSv.h" .

- South of the Sambre and the Maas There aren't many differences between the limestone-dolomites of Condroz and Famenne (90 to 120 nSv.h ) and the shales of the Ardennes (100 to 120 nSv.h ).

- Special areas Hautes Fagnes Above the marshy soil of the Hautes Fagnes, the measured exposure rates fluctuate between 80 and 90 nSv.h .

Gaume (extreme South of the Country) The soil in this region is mainly chalk-marl. The observed values range from 73 to 100 nSv.h .

Silt zones Exposure rates in silt zones come to about 80 nSv.h

On the whole the'exposure rates fluctuate between 50 to 120 nSv.h from North to South of the country. The Belgian territory can be roughly divided into 3 main exposure rate areas (map 5). 16.

7. CONCLUSIONS

The Institute of Hygiene and Epidemiology together with the Nuclear Centre of Mol started a systematic study of the radioactivity due to natural occuring nuclides throughout the whole national territory. Two networks were established : - a network of TLD's intended to integrate radiation doses over 1 year period. Instantaneous measurements of exposure rates were performed at the same locations with an ionization chamber or a Nal crystal. Moreover soil samples were taken in the neighbourhood of the dosemeters and their activity was measured. - a second network of 272 points of local measurements distributed all ovei the territory and performed with the ionization chamber and the Nal crystal.

The data obtained in that way lead to the following conclusions : - the average exposure rate on the whole of the territory may be estimated to 89 nSv.h (with a stanc.ard deviation of 17 nSv.h ), value which is well within the range of the average world estimations given in the Unscear report (ref.2). - there is a good agreement between the results of soil samples activity (expressed in exposure rates) and the exposure rate measured 1 m above ground surface with the integrating dosemeters. The différence between the data obtained by both methods gives an order of magnitude for the ionizing component of cosmic rays which could be estimated to approximately 40 nSv.h . - the local measurements performed all over the territory enabled to draw a map of exposure to natural radiation in Belgium (terrestrial and cosmic radiation together). This map shows a fluctuation of exposure rate of 50 to 130 nSv.h from the North to the South of the country. In some regions, the results must be considered as an indication only because of the relatively low number of measurement points. Such a network of 272 points of measurement constitutes a valuable reference for the estimation of possible supplementary radioactive pollution of the Belgian territory.

Besides/ the ionization chamber has proved to be a quick and easy instrument in order to draw a very detailed map of nn specific area when necessary. 17.

ACKNOWLEDGEMENTS

This work could be effected owing to the collaboration of :

- the Royal Meteorological Office for their willingness to get a place for the dose meters, as well as the water supply companies CIBE, SNDE, CIEAL, TMVW.

- Messrs. Robert Bollen (S.C.K./C.E.N.) and Moerman (IHE) for the technical support during the two campaigns.

- Messrs. Jacques Colard (S.C.K./C.E.N.) and Jean-Pierre Culot (CORAPRO) for the gamma-spectrometric analyses of the soil samples, and Guido Cosemans (S.C.K./C.E.N.) for the treatment of the results. 18.

8. REFERENCES

1. UNSCEAR 33° session Vienne 25-29 juin 1984 Exposition aux sources de rayonnement naturelles. A/AC.82R.420

2. UNSCEAR 1982 Report Ionizing radiation : sources and biological effects. United Nations publication Sales N° E.82.IX.8 06300 P

3. UNSCEAR 1977 Sources and effects of ionizing radiation. United Nations publication Sales N° E77.IX.I

4. H.L. Beck, J. De Campo and C. Gogolak In-situ Ge(Li) and Nal(Tl) gamma r;;y spectrometry. USAEC report HASL - 258 (1972)

5. W. Siegers, L. Ghoos, J. Gillard Metingen en resultaten van straling in de omgeving. Annalen van de Belgische vereniging voor Stralingsbescherming. Vol.8, n° 2 (1983)

6. J.M. Charlet, L. De Jonghe, SM. De Witte, B. Drumel J. Henry, A. Herbosch, J.P. Lefin, H. Martin Reconnaissance survey for uranium in the Belgian Paleozoic Ministerie van Economische Zaken, administratie der Mijnen, Geologische dienst van België. Professional paper 1983/1 n° 196

7. J.P. Deworm, J.P. Culot et al. In-situ measurements of Environmental Gamma radiation. Internal report August.3rd.1985.

8. Atlas van België. Table 2 : Environmental radiation in nSv/h, measured with TLD's and Nal crystal or RSS-111 ionization chamber.

Location TLD's Standard deviation Nal or RSS-111 nSv/h o nSv/h

Oostende (40) (3) (4) Koksijde 65 9 68 Beitem 73 9 81 Melle 77 6 86 Deurne 69 10 78 Brasschaat 60 5 64 Mol 55 8 59 Genk 57 6 61 Kleine Brogel 58 6 64 Schaffen 67 3 72 Florennes 96 4 97

ürustem 87 6 95 Zaventem 72 8 79 St. Genesius Rode 98 2 93 Chaumont Gistoux 66 6 64 Tienen 75 3 77 Bierset 97 3 92 Hollognes/Pierres 95 4 101 Hervé 88 4 95 Botrange 91 5 93 Sinsin 99 5 108

Ciney 107 7 96 96 1 99 Dourbes 86 4 77 Havre 87 5 88 Wasmuel 97 5 99 Gosselies 11 6 95 Chièvres 94 4 91 Hautrage 75 5 78 St. Hubert 99 3 91 Lacuisine 94 8 97 Libramont 96 3 100 88 3 94 Olenne 96 6

Mean 84 85 Table 3 : Activity in soil samples (mBq per gram dry weight) and corresponding exposure rate.

40 232 226 137 G-l SN/ GV_! I-GV_L Number Ka Th Ra Cs nSv. h SU nSv- h nSv. h nSv-h Location

59 560 42 42 8 80 1.21 66 96 30 TIHANGE 237 310 14 14 6 32 1.07 30 68 38 K0KSIJDE 238 410 23 23 7 48 1.07 45 81 36 BEITEM 239 440 29 33 9 60 1.17 51 86 35 HELLE 240 330 20 23 7 43 1.15 37 78 41 DEURNE 241 170 11 14 9 23 1.17 20 64 44 BRASSCHAAT 242 185 7 11 6 19 1.04 18 61 43 GENK 243 190 9 12 4 22 1.07 21 64 43 KLEINE BR0GEL 244 470 17 15 3 43 1.11 39 72 33 SCHAFFEN 245 600 47 47 8 87 1.22 71 97 26 FLORENNES 246 540 38 41 7 75 1.18 64 95 31 BRUSTEH 247 320 19 25 10 42 1.09 39 78 39 ZAVENTEM 248 590 42 46 11 82 1.18 69 93 24 ST GENESIUS RODE 249 80 6 6 < 1 12 1.04 12 55 43 CHAUMONT GISTOUX 250 390 23 25 2 49 1.01 49 77 28 TIEllEN 251 olO 44 44 6 85 1.18 72 92 20 BIERSET 252 510 43 46 11 79 1.20 66 101 35 HOLLOGNES/PIERRES 253 410 41 47 16 74 1.30 57 95 38 254 470 47 41 34 78 1.60 49 93 44 BOTRANGE 255 720 44 28 18 82 1.28 64 108 44 SINSIN 256 470 51 41 14 81 1.21 67 96 29 CINEY 257 430 48 56 11 84 1.24 68 99 31 HODAVE 258 1000 44 31 11 97 1.20 81 112 31 DOURBES 259 380 28 29 9 54 1.15 47 88 41 HAVRE 260 550 47 55 9 89 1.15 77 99 22 WASMUEL 261 530 39 44 9 77 1.13 68 95 27 GOSSELIES 262 520 42 39 12 76 1.10 69 91 22 CHIEVRES 263 330 15 21 9 38 1.07 36 78 42 HAUTRAGE 264 550 42 33 21 75 1.36 55 91 36 SAINT HUBERT 265 640 53 40 27 91 1.32 69 97 28 LACUISINE 266 620 44 28 21 77 1.37 56 100 44 LIBRAMONT 267 330 47 29 16 65 1.27 51 94 43 VIRTON 268 ISO 8 13 11 20 1.24 16 59 43 HOL 269 790 47 38 9 92 1.31 70 101 31 DION 270 470 26 23 8 53 1.13 47 82 35 DOEL

* G = exposure rate calculated from the different radionuclides with Beck's formula (par. 3.2.3) SN = specific weight of original sample; SD = specific weight of dried sample GV = exposure rate corrected for moisture content I = exposure rate measured with the ionization chamber Table 4.1. : Results of the measurements with the Nal crystal and the ionization chamber.

Lanbert Mai RSS-111 . Number Date - 1 co-ordinates cps nSv.h" ! nSv.h" Location I i 1 198.55 203.90 4-10-83 247 64 j MEERH0UT 2 184.95 193.30 4-10-83 271 66 ! HERSELT 3 170.00 194.85 4-10-83 240 63 PUTTE 4 169.50 202.80 4-10-83 353 76 ! - KESSEL 5 170.70 210.10 4-10-83 290 68 I Z ANDHOVEN 6 183.50 204.90 4-10-83 350 75 ' OLEN 7 186.40 210.80 4-10-83 246 64 j - LICHTAART 8 199.00 217.35 4-10-83 256 65 ! - RETIE 9 198.60 227.00 5-10-33 154 53 ARENDONK 10 192.10 232.70 5-10-83 190 57 - VEELTE 11 188.70 224.45 5-10-83 258 65 - TURNHOUT 12 184.65 225.75 5-10-83 280 67 - MERKSPLAS 13 179.50 239.40 5-10-83 183 56 - MEERLE 14 169.10 231.40 5-10-83 220 61 - LOENH0UT 15 171.90 223.05 5-10-83 313 71 - WESTMALLE 16 204.55 219.50 2-12-83 232 62 - POSTEL 17 207.95 198.40 2-12-83 204 59 - OOSTHAM 18 153.00 193.00 6-10-83 311 71 - HEFFEN 19 154.60 200.70 6-10-83 383 79 - KONTICH 20 139.50 194.30 6-10-83 338 74 - SINT AMANDS 21 147.80 210.70 6-10-83 331 73 - BURCHT 22 150.80 223.00 6-10-83 221 61 - STABR0EK 23 15 '). 60 229.60 6-10-83 179 56 - KALMTHOUT 24 214.00 190.00 7-10-83 240 63 - ZOLDER 25 220.10 204.10 7-10-83 251 64 - HECHTEL 26 217.50 213.00 7-10-83 236 62 - LOMMEL 27 233.00 2:4.20 7-10-83 269 66 - HAMONT ! 28 239.10 20'». 35 7-10-83 2/8 67 - BREE 29 246.60 204.20 7-10-83 324 73 - KINROOI I 30 245.401 191.00 7-10-83 473 89 - DILSEN ! 31 234.601 191.40 7-10-83 187 57 - OPGLABBEEK 32 199.451 184.80 11-10-83 327 73 - DIEST 33 201.551 191.55 11-10-33 7.00 58 - OEURNE 34 207.251 175.15 11-10-83 309 71 - NIEUWERKERKEN 35 205.351 163.20 11-10-83 590 102 - VELM 35 205.35i 163.20 26-4-84 609 105 107 VELM 36 213.75! 159.95 11-10-84 567 100 - B0VELIN6EN 37 219.30 163.25 11-10-33 567 100 - HEXS 38 233.70 165.90 11-10-33 586 102 - MILLEN 39 222.05 179.10 12-10-83 299 70 - DIEPENBEEK 40 223.85 173.85 12-10-83 423 83 - VLIERMAAL 41 216.15 182.35 12-10-83 245 63 - KURINGEN 42 225.90 199.25 12-10-83 280 67 - LINDE 43 227.00il90.10 12-10-83 242 63 - ZWARTBERG 44 243.OOi183.20 12-10-83 418 83 - MAASMECHELEN 45 242.30!182.30 12-10-83 391 80 - MAASMECHELEN 46 235.951181.95 12-10-33 222 61 - ZUTENDAAL 47 233.001174.10 12-10-83 534 96 - WALTVILDER 48 200.751154.50 13-10-83 552 98 - (BERTREE) 48 200.751154.50 26-4-84 574 101 103 KANNUT(BERTREE) Table 4.2. : Results of the measurements with the Nal crystal and the ionization chamber.

LAMBERT Nal RSS-111 Number Date J 1 co-ordinates cpS nSv. h" nSv.h* Location

49 204.15 142.95 13-10-33 612 105 . 0TEPPE 49 204.15 142.95 25-4-84 613 105 104 0TEPPE 50 203.00 136.70 13-10-33 437 35 - COUTHUIN 51 218.80 121.60 13-10-33 571 VO - BOIS ET B0RSU 52 223.05 133.25 13-10-33 650 109 - 52 223.05 133.25 26-4-84 686 114 119 MANDRIN 53 218.30 144.55 13-10-33 595 103 - SAINT GEORGES 53 218.30 144.55 26-4-34 628 107 110 SAINT GEORGES 54 221.05 152.05 13-10-83 630 107 - REMIC0URT 54 221.05 152.05 26-4-34 612 105 106 REMIC0URT 55 234.20 154.45 13-10-33 605 104 - LIERS 56 236.40 139.95 14-10-33 583 101 - TILFF 1 56 236.40 139.95 26-4-34 660 111 110 TILFF 57 236.50 133.15 14-10-83 592 102 - POULSEUR 57 236.50 133.15 26-4-34 617 106 J 05 P0ULSEUR 58 233.90 124.45 14-10-33 591 102 - 59 211.00 134.55 25-4-34 - - 96 TIHANGE 60 248.80 113.30 14-10-83 670 Ill - 1 61 253.00 123.00 19-10-33 652 109 - ST0UM0NT 62 248.30 145.00 20-10-83 545 97 - SOUHAGNE 63 251.65 141.55 20-10-33 573 100 - PEPINSTER 64 247.10 126.50 20-10-33 524 95 - QUAREUX 65 251.60 132.00 20-10-83 456 87 - LA REID 66 260.90 134.65 20-10-83 476 89 - SART 67 261.25 139.60 20-10-83 594 103 - JALHEY 68 263.85 146.30 21-10-33 618 105 - 69 266.15 151.25 21-10-83 443 86 - 70 256.20 156.20 21-10-33 376 78 - 71 246.60 158.75 21-10-33 539 96 - BOMBAYE 72 244.75 158.30 21-10-83 569 100 - VISE 73 243.55 155.90 21-10-33 507 93 - ARGENTEAU 74 266.00 123.20 24-10-83 561 99 - 75 268.20 115.60 24-10-33 588 102 - RECHT 76 272.20 103.30 24-10-83 510 93 - THOMMEN 77 274.90 98.75 24-10-83 594 103 - REULAND 78 279.30 114.90 24-10-83 539 96 - MEYRODE 79 284.30 122.70 24-10-83 522 94 - BULLINGEN 30 281.10 129.40 24-10-33 573 100 - ELSENBORN 81 270.20 135.45 24-10-84 454 87 - BARACQUE MICHEL 82 74.50 163.50 25-10-83 543 97 - BELLEGEM 83 74.50 172.50 25-10-83 409 82 - KUURNE 84 74.05 180.95 25-10-83 330 73 - MEULEBEKE 35 73.85 195.70 25-10-33 314 71 - WINGENE 86 71.15 206.50 17-4-84 275 67 64 OOSTKAMP 36 71.15 206.50 25-10-83 291 69 - OOSTKAMP 87 74.85 216.10 25-10-83 342 74 - DAMME 88 78.00 225.15 25-10-83 369 77 - KNOKKE 89 77.10 227.90 25-10-83 160 54 - KNOKKE(STRAND) 90 49.40 215.10 17-4-84 230 62 63 OOSTENDE 90 49.40 215.10 25-10-83 228 62 — OOSTENDE Table 4.3. : Results of the measurements with the Nal crystal and the ionization chamber.

LAMBERT Nal -, RSS-111 | Number co-ordinates Date cps nSv.h nSv.h"1 Location

91 41.701208.60 17-4-84 400 31 80 MIDDELKERKE 91 41.201208.60 26-10-83 440 85 - MIDDELKERKE 92 25.35i201.10 26-10-83 152 53 - DE PANNE(STRAND) 93 27.OOi191.55 26-10-83 374 78 - H0UTEM 94 30.00 183.50 26-10-83 439 35 - STAVELE 95 26.95 174.70 26-10-83 495 92 - WATOU 96 39.40 172.90 26-10-33 452 87 - VLAMERTINGE 97 44.20 182.70 26-10-83 349 75 - MERKEM 98 45.30!194.50 26-10-33 400 81 - BEERST 99 43.801202.30 26-10-83 410 32 - SPERMALIE 100 61.501208.90 26-10-33 248 64 - JABBEKE 101 54.451202.80 27-10-83 281 68 - EERNEGEM 102 38.30 in?. 60 27-10-33 309 71 - K0RT7.MARK 103 53 OOi182.50 27-10-33 389 80 - OOSTNIEUWKERKE 104 62.05i173.60 27-10-33 439 85 - LEDEGEM 105 57.601166.20 27-10-83 473 89 - WERVIK 106 187.15 ! 183.90 8-11-33 372 78 - RILLAAR 107 170.501184.25 8-11-83 500 92 - HAACHT 108 164.00 1180.50 8-11-33 484 90 - NEDEROKKERZEEL 109 155-70 1183.80 8-11-83 485 90 - EPPEGEM 110 157.501172.70 8-11-33 606 104 - KRAAINEM 111 172.601171.50 8-11-83 478 90 - HEVERLEE 112 186.10 1174.10 8-11-33 347 75 - BINKOM 113 201.151172.75 8-11-83 430 84 - BUDINGEN 114 141.60 il82.90 9-11-83 534 96 - MERCHTEM 115 137.90i173.80 9-11-33 525 95 - TERNAT 116 134.801167.20 9-11-33 588 102 - LENNIK 117 144.60 163.00 9-11-33 512 94 - RUISBROEK 118 124.001155.10 9-11-33 621 106 - ST PIETERSKAPELLE 119 140.451x53.60 9-11-83 624 106 - TUBIZE 120 158-801145.70 9-11-83 480 90 - GENAPPE 121 156.60*154.80 9-11-83 553 98 - OHAIN 122 159.10 1163.05 9-11-83 620 106 - HOEILAART 123 188.20 1162.60 10-11-83 Ó61 HI - HOEGAARDEN 124 196.75 160.75 10-11-33 648 109 - NEERWINDEN 124 196.75 1160.75 26-4-84 615 105 106 NEERWINDEN 125 188.50 1153.80 10-11-83 619 106 - HUPPAYE 126 174.u0jl45.10 10-U-83 630 107 - WALHAIN 127 169.00i155.00 10-11-83 625 107 - WAVER 128 174.40 Ü62.70 10-11-33 561 99 - MILLE 129 220.10 1146.80 26-4-34 605 104 105 SAINT GEORGES 130 229.45 1134.40 26-4-84 570 100 101 TAVIER 131 185.70Î131.SO 24-5-84 460 38 34 VEDRIN 132 204.601124.20 24-5-34 485 91 92 OHEY 133 199.70 1127.75 24-5-84 571 101 108 HALTINNE 134 202.55 113.75 24-5-84 593 103 108 EMPTINNE 135 185.90jl23.65 5-6-84 453 38 89 WEPION 136 187.05 illl.00 5-6-84 428 94 86 YVOIR 137 187.30 104.00 5-6-84 406 82 82 DINANT 138 189.00 ' 94.65 5-6-84 585 103 106 FESCHAUX Table 4.4. : Results of the measurements with the Nal crystal and the ionization chamber.

LAMBERT Nal RSS-111 n -1 Nuttier co-ordinates Date cps I nSv .h nSv.h Location

139 189.751 36.65 5-6-84 501 93 91 JAVINGUE 140 202.901 92.65 5-6-34 529 96 98 VILLERS/LESSE 141 198.95:104.50 5-6-84 615 106 107 C0NNEUX 142 155.351 95.85 5-6-84 582 102 103 SENZEILT£ 143 154.801 82.30 6-6-84 598 104 104 DAILLY 144 156.25, 73.15 6-6-84 515 94 95 CUL DES SARTS 145 171.25i 79.80 6-6-34 550 98 100 LE MESNIL 146 170.801 90.75 6-6-34 611 106 106 R0MEREE 147 185.65i141.95 3-7-84 442 36 85 MEHAIGNE 148 171.25 133.55 3-7-84 575 101 102 MAZY 149 170.30'122.50 3-7-84 564 100 103 AISEM0NT 150 167.25 >'111.80 3-4-85 - - 99 üIiiSMES 151 172.35'103.40 3-7-84 609 104 104 ROSEE 152 189.60! 75.20 21-8-84 624 107 111 153 187.55; 63.40 21-8-84 632 107 106 30H.W 154 187.55' 57.40 21-8-84 550 98 101 S'JGNY 155 219.20:111.60 23-8-84 860 133 130 SOMME-LEUZE 156 153.90H12.90 4-7-84 591 103 100 NALINNES 157 141.15i104.35 4-7-84 555 98 97 BEAUMONT 158 138.15. 95.75 4-7-34 502 93 91 SIVRY 159 136.101 75.40 4-7-84 577 101 97 MACQUEN0ISE 160 137.55' 81.05 4-7-84 645 109 106 MACON 161 136.55.112.50 4-7-84 687 114 107 LA3ÜISSIERE 162 117.20'115.20 5-7-84 594 103 101 AULNOIS 163 103.301114.40 5-7-34 660 111 105 ROISIN 164 106.35 122.20 5-7-34 627 107 101 ELOUGES 165 103.25|133.85 3-4-85 - - 83 STAMBRUGES 166 90.20 j133.85 5-7-84 468 89 77 WIERS 167 79.70j137.00 5-7-84 613 105 90 WEZ-VELVAIN 168 76.30 144.90 5-7-84 650 109 99 MARQUAIN 169 78.85 153.70 6-7-84 344 75 72 PECQ 170 91.20 153.30 6-7-84 340 131 93 CORDES 171 91.75i145.15 6-7-84 900 138 96 MAULDE 172 107.20)152.60 6-7-84 S80 101 85 OSTICHES 173 117.80il49.75 9-7-84 770 123 119 SILLY 174 111.95 144.35 9-7-84 - - 99 ATTRE 175 120.301144.00 9-7-84 - - 92 THORICOIJRT 176 116.65!135.50 3-4-85 - - 76 ERBAUT 177 138.40 142.25 3-4-85 - - 99 ECAUSSINNES 178 139.25 134.45 11-7-84 570 100 100 FAMILLEUREUX 179 122.60 123.35 11-7-84 471 89 119 SPIENNES 180 132.85 121.85 3-4-85 - - 71 ESTINNES 181 147.20 121.10 3-4-85 - - 104 LEERNES 182 i;2.50 133.50 11-7-84 612 105 104 LUTTRE 183 123.85 184.30 12-7-84 464 88 85 LEDE 184 125.70 174.00 12-7-84 597 103 102 DENDERHOUTEM 185 117.15 164.70 12-7-34 500 92 89 186 106.40 165.55 12-7-84 520 95 92 3RAKEL 187 105.00 174.20 12-7-84 520 95 92 ZVALM 188 107.30 183.60 12-7-84 378 79 79 BOTTELAERE Table 4.5. : Results of the measurements with the Nal crystal and the ionization chamber.

LAMBERT Nal RSS-111 Nimber co-ordinates Date cps nSv.h" nSv.h Location

189 108.75 188.60 12-7-84 324 72 69 HELLE 190 95.80 170.50 13-7-34 355 76 78 191 91.70 164.10 13-7-84 477 90 86 192 92.051187.55 13-7-84 305 70 69 193 91.35i193.10 13-7-84 420 84 84 NEVELE 194 134.70:182.50 19-7-84 448 87 85 8AARDEGEM 195 132.80!191.05 19-7-84 336 74 73 196 137.001201.30 19-7-84 377 79 77 TIELRODE 197 137.501213.50 19-7-84 381 79 - VRASENE 198 128.301212.00 19-7-84 275 67 - 199 121.60:202.00 19-7-84 276 67 - L0KEREN 200 119.90i193.80 19-7-84 246 64 - 0VERMERE 201 36.60:201.60 20-7-84 249 64 - URSEL 202 92.00:215.00 20-7-84 248 64 - SINT LAURENS 203 105.10'212.65 20-7-84 286 68 - 204 104.75 201.40 20-7-84 246 63 - 205 203.50! 86.65 21-8-34 6J7 110 112 206 204.75i 81.25 21-8-84 520 95 96 207 207.20. 73.85 21-8-84 620 106 110 MAISSIN 208 196.50 54.10 21-8-84 600 104 109 209 200.00 64.10 21-8-84 525 95 97 CARLSBOURG 210 229.60 23.10 22-8-84 637 108 110 TORGNY 211 228.35 35. U0 22-8-84 416 83 87 GERONVILLE 212 221.75 42.40 22-3-84 451 87 87 IZEL 213 219.00 55.40 22-3-84 646 109 114 SINT MEDARD 214 221.55 68.65 22-8-84 636 1C3 110 LIBRAMONT 215 216.45 84.80 22-8-84 743 120 120 AWENNE 216 216.301 92.05 22-8-84 694 114 114 FORRIERES 217 223.10 104.45 23-8-84 693 i!4 117 MARCHE 218 235.45 112.90 23-8-84 586 102 101 MORMONT 219 233.65 105.85 23-8-84 623 106 107 BEFFE 220 233.50 95.40 23-8-84 745 120 118 BEAUSAINT 221 238.00 81.45 28-3-84 637 108 114 FLAMIERGE 222 231.70 i 76.00 28-3-84 547 98 102 REMAGNE 223 234.70i 65.15 28-3-84 669 112 102 JUSERET 224 234.30 1 55.60 28-8-84 696 115 104 L'EGLISE 225 236.35 45.15 28-3-84 575 101 83 RULLES 226 249.50 | 34.53 28-8-84 670 112 94 HABERGY 227 250.551 44.15 28-3-84 627 107 73 HEINSCH 228 251.201 51.50 28-8-84 770 123 96 NOTHOMB 229 249.201 64.30 28-8-84 787 125 119 TIN^ANGE 230 251.10! 76.70 29-8-84 705 116 112 WARDIN 231 249.55; 84.90 29-8-84 718 117 118 NOVILLE 232 251.15 92.60 29-8-84 802 127 121 H0UF7ALIZE 233 261.10 102.75 29-8-84 650 109 106 BOVIGNY 234 253.50 105.40 29-3-84 700 115 114 BIHAIN 235 259.65 108.70 29-S-84 787 125 121 236 48.80 215.40 17-4-84 45 41 41 OOSTENDE(STAXETFSL 237 29.50 199.20 26-9-83 290 68 68 KOKSIJDE 238 62.50 177.60 26-9-83 400 81 - BEITEM Table 4.6. : Results of the measurements with the Nal crystal and the ionization chamber.

LAM' Mai RSS-11L Number co-ordinctes Date cps nSv.h" nSv.hT1 Location 1 1 239 U1.20ll85.70 26-9-83 440 86 . MELLE 240 156.00 209.00 26-9-83 368 78 - DEURNE 241 159.30 225 • 20 26-9-83 244 64 - BRASSCHAAT 242 230.00 180.00 26-9-83 220 61 - GENK 243 227.20 207.90 26-9-83 250 64 - KLEINE BR0GEL 244 197.95 187.55 26-9-83 320 72 - SCHAFFEN 245 169.80 102.60 23-9-81 540 97 - FLCRENNES 246 207.00 164.00 25-9-81 523 95 - BRUSTEM 247 158.00 177.00 25-9-81 380 79 - ZAVENTEM 248 149.00 159.00 23-9-81 501 93 - ST GENESIUS RODE 249 174.80 152.80 25-9-81 240 63 6

40 232„. -^Radionuclides K 226Ra Th Total

Soil ^--^ mBq .g nSv .h"1 mBq.g" nSv.h"1 mBq- g~ nSv-H" nSv.h

Sand of the campine 170 8 13 6 9 7 21

Polder clay, dune sand 370 18 20 10 20 15 43

Sand, clay, sandstone 430 21 31 15 27 20 56

Clay, chalk, marl, limestone r.oo 24 43 21 41 31 76

Shales, dolomite, quartzite 610 20 38 18 47 36 83

REMARK : The contribution of Cs is not raken into account. 0C

IMIIfllllllllipiliJIII'IMll!Fltl|IMIIIIM|llll|llll|IIMllltl|*

PHOTO 1 : Holder for thermoluminescent dosemeters with 8 LIF detectors :: '&ÏZ

À

PHOTO 2 : Support for dosemeter ,1

/1 \J '\J -^ s. ai. T>

•V'V^ 'V' .<-;;*{«fjF

PHOTO 3 : Measurement with the Nal crystal •A

:'*• ~-W.fl

PHOTO 4 : Measurement with ionization chamber -1 100 nSv.h 110 nSv.h 100 pSv.h TLD TLD IC

90 ' 80

70 . 60

50 TLD = 0.74.GV + 46 40 IC = 0, 70.GV + 50 r = 0,92 r = 0,95

30 20 -1 GV nSv.h 10 nSv.h 0 20 40 60 80 100 0 20 40 60 80 100 GV GV Fig. 3b Fig. 3c

Fig. 3 : Correlations bet»>*>en the different methods - IC : ionization chamber - TLD : thermoluminescent dosemeter - GV : soil samples ^K-40 Ro-226 E^ Th-232

1 1 21 nSv.» h - 43 nSv.- h.- i a 6 nSv.- h--

361 381 421

27Ï Polder day, Sand.clay, Sond of Compine dune sand sandstone

7 6 nSv.h-1 8 3 nSv.h -1

35! 411 431 -,

22! Clay.chalk, Shales,dolomite, marljimestone quartzite

fig. 4 : Environmental radiation calculated from soil samples Fig. 5 In-sdu gamma-ray spectra at MOL ( S.C.K.-C.E.N.) June 11, 1984 HP Ge detector at 1 meter above the ground ( counting tune 180 minutes )

X 1Q

i : s 1 S 2 s « s S 2 es ta M M m 3 S

S3 è3 = K CM CM f3 f3 S3 I! 111 11 11 I I J s

O * c

CO

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J> MAP 1

• Location of the TLD-network over the Belgian territory.

— Exposure rate in nSv-h calculated from soil samples. o Exposure rate in nSv.h measured with TLD-dosemeter. LOENHOU HRINTHO

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l.l.NI-.MIiOl H<; MAP 4 KAART 1

CARTEL K 0A5 - 0,70 mSv/year

0,70 - 0,90 mSv/year

0,90 - 1J0 mSv/year MAP 5 : Exposure rate measured with Nal crystal or ionization chamber.