Vol. 48, 01, 05ok.qxd 117 ANNALS OF GEOPHYSICS, VOL. 48, N. 1, February 2005 Key words radon – atmosphere – uranium – thori- um – rock 1. Introduction Radon is released into the atmosphere main- ly from soils and underlying rocks, from ground waters (especially thermal ground waters), but also from oceans, natural gases, caves and mines (Gesell, 1983; Khatir Sam and Holm, 1995; Lozano et al., 2000; Jha et al., 2001; Papaste- fanou, 2001). Spatial variation of outdoor radon activity and its dependence on the geological conditions, on the type of cover of Earth surface (ocean, ice cap or snow cover) and on the varia- tions in soil moisture (Grasty, 1991) was investi- gated in many areas worldwide (Gesell, 1983; Gundersen, 1991). There is a large number of measurements of radon activity in the air above the ground surface, but due to the application of different methods, the results are not compara- Mailing address: Dr. Agnieszka Anna Ochmann, Institu- te of Geological Sciences Wroc l⁄ aw University, pl. M. Borna 9, 50-204 Wrocl⁄ aw, Poland; e-mail: ochmannn@yahoo.com Distribution of radon activity in the atmosphere above Wzgórza Niemczańsko-Strzelińskie (South-West Poland) and its dependence on uranium and thorium content in the underlying rock and indirect ground basement Agnieszka Anna Ochmann Institute of Geological Sciences Wrocl⁄ aw University, Wrocl⁄ aw, Poland Abstract Radon activity in the atmosphere and its behavior in the environment have been investigated using LR-115 nu- clear track detector. The complex geological structure of Wzgórza Niemczańsko-Strzelińskie (south-west Poland) enabled this problem to be studied in various geological conditions. The eU and eTh content in rocks and soil was measured by gamma-spectrometer GR-320. Uranium content of bedrock reached its maximum value of 15 ppm in the case of quartz-graphite schist. Thorium reached its maximum value of 35 ppm in the case of granodiorite. Radon activity was measured by means of long-term exposure of LR-115. The mean val- ue of atmospheric radon activity was 21 Bqm–3 in the air 2 m above the ground surface. The highest radon ac- tivities were measured in the area of granite and quartz-graphite schist outcrops and in the area of mylonitic rocks of the Niemcza Zone. Radon activity in close to ground cup detectors varies from 25 to 300 Bqm–3, these values depend on uranium and thorium content in indirect ground basement (soil and weathered rocks). Not only uranium and thorium content but also rock disintegration due to tectonic events (shear zones) influenced atmospheric radon activity. Seasonal variation is not strong, although higher values were measured in the au- tumn-winter period. 118 Agnieszka Anna Ochmann ble. Gesell (1983) compared the data from the area of United States, where the average radon activity in the air varies between 4-15 Bqm–3. In Canada outdoor radon activity, measured by one of the passive methods with an exposure period of 3 months, varied from 11 Bqm–3 to 67 Bqm–3 (the mean value for Manitoba is 59 Bqm–3 and Saskatchewan − 61 Bqm–3) (Grasty, 1991). Ac- cording to UNSCEAR (1983 fide Wilkening 1990) the typical radon activity in the air above the ground surface averages 10 Bqm–3. The aim of this investigation was to enrich the knowledge of radon behavior and to con- struct a map of spatial variation of radon activ- ity on the eastern area of Foresudetic Block. 2. Geological setting Wzgórza Niemczańsko-Strzelińskie are locat- ed in the eastern part of the Foresudetic bloc (SW part of Poland). This area includes the pe- riphery of the Sowie Góry Block, Niemcza Zone, metamorphic of Niemcza-Kamieniec Ząbkowicki, which is extended on the NE from the Niemcza Zone, and a crystalline massif of Wzgórza Strzelińskie (fig. 1). The North-East part of Sowie Góry Block is composed mainly of paragneisses and migmatic gneisses. In the gneisses small bodies of amphibolite, gabbro and serpentinite are inserted (Dziedzicowa, 1987). In the vicinity of the boundary of Niemcza Zone there are intrusions of quartz monzodiorite, which belongs to the plutonic rocks of Niemcza Zone (Dziedzicowa, 1987). Niemcza zone is extended along the east edge of Góry Sowie Block. It is the zone of dis- location of the mass of rocks and is built of my- lonites originated from deformations of gneiss- es of Góry Sowie (Scheumann, 1937 fide Dziedzicowa, 1987; Mazur et al., 1995). The mylonitic rocks include the small bodies of am- phibolites, quartz-graphite schist, the enclaves of gneisses and intrusions of plutonic rocks (Mazur et al., 1995). In the south part of Niem- cza Zone there are vast outcrops of serpentinite and gabbro (Puziewicz and Radkowska, 1990). The eastern edge of Niemcza Zone adjoins the series of mica schist or more general series of metamorphic rocks. This area is known as a metamorphic of Niemcza-Kamieniec Ząbkow- icki and its contact with the crystalline massif of Wzgórza Strzelińskie (Strzelińskie Hills) in the eastern part is covered with Quaternary sedi- ments (Dziedzicowa, 1966). Metamorphic of Niemcza-Kamieniec Ząbkowicki is built mainly of mica schist with the inserts of quartz-felds- pathic schist, quartz-graphite schist, amphibo- lites and marbles (Dziedzicowa, 1966). Between the metamorphic of Niemcza-Ka- mieniec Ząbkowicki and Wzgórza Strzelińskie, near Górka Sobocka village, there are outcrops of granite intrusion and its southern metamorphic cover – gneisses of Wzgórza Lipowe (Lipowe Hills) (Wojnar, 1977; Bartz and Puziewicz, 1999). According to Oberc-Dziedzic and Szczepanski (1995) the granite from Górka Sobocka is the westernmost part of the crystalline massif of Wzgórza Strzelińskie. The series of crystalline rocks of the Wzgórza Strzelińskie massif can be divided into four groups (Oberc-Dziedzic, 1991): gneisses, the elder schist series, the younger schist series and plutonic rocks. The most common are gneisses. The rocks of the elder schist series (amphibolites, mica schist, limestone and mar- bles) appear in gneisses and are crimped with the rocks of younger series. The younger schist series, named Jeglowa series, is composed of quartzite, quartz-sericite schist, mica-silliman- ite-quartz schist. The youngest group of rocks are plutonic rocks: quartz diorite, tonalitie, gra- nodiorite and granite. Granite predominates in the northen part of massif (Oberc-Dziedzic, 1991). On the whole area of investigation there are the intrusions of Tertiary basalts. Complex geological structure of this area, a wide variety of types of rocks and the presence of tectonic zone between Sowie Góry Block and crystalline massif of Wzgórza Strzelińskie (Mazur et al., 1995), enabled the discussed problem to be studied in various geological conditions. 3. Methods The fundamental equipment of this investi- gation was the LR-115 detector (production of Kodak), which is one of many types of solid 119 Distribution of Rn activity in the atmosphere and its dependence on U and Th content in the ground state nuclear track detectors. The application of solid state nuclear track detectors is based on the creation of structural defects on the sensi- tive surface of the detector due to alpha-particle hit against it (Fleischer et al., 1965). The struc- tural defects were enlarged during the process of etching, which enabled us to observe them even at slight magnification. A LR-115 detector was used for measuring the radon activity in the air (both in the open air and inside of a closed can). According to the in- formation of its manufacturer, the LR-115 detec- tor records the alpha-particles in a range of 1.2- 4.8 MeV, meaning that the alpha-particles emit- ted in a well-defined distance from the detector could be registered. This characteristic facilitates the elimination of recording alpha-particles emit- ted from the solid products of radon decay. In order to carry out the measurements of radon activity in the outdoor air, the detectors were fixed to the inner surface of a black plastic cup (of 8 cm diameter). The plastic cups provided shelter from the sun light and precipitations. We chose 27 monitoring points were situated on the outcrops of the different types of rocks. Each monitoring point consisted of 4 cups fixed 2 m, 1 m, 0.5 m and 0.05 m above the ground surface (fig. 2a,b). The higher the level above the ground surface where the detector was fixed the more representative the measure was for the more ex- Fig. 1. Geological scheme of Wzgórza Niemczańsko-Strzelińskie (scheme prepared on the basis of the geo- logical maps made by Badura, Berezowska, Cwojdzinski, Dziemianczuk, Gawronski, Gazdzik, Jerzmanski, Oberc, Trepka, Walczak-Augustyniak, Wòjcik). 120 Agnieszka Anna Ochmann tensive area. Furthermore, detectors situated 0.05m above the ground registered thoron Rn220 beside the radon Rn222. The time of exposure was 6 months, twice a year: October-March (autumn- winter period) and April-September (spring-sum- mer period). A long measurement period enables us to obtain the average values for the time of ex- posure and reduces the effect of diurnal fluctua- tions of pressure and temperature. The two sets of measurements were repeated the following year and the values obtained were similar to these which had been taken the year before. The radon activity in the outdoor air was cal- culated dividing the number of traces on 1 cm2 of the detector surface by the number of days of ex- posure and the result obtained multiplied by the calibration coefficient (in case of the atmospher- ic air it is 13.8), this model was elaborated by Srivastawa et al. (1995). The LR-115 detector was also used during the measurement of the radon emanation from different types of rocks from the investigated area. To measure the radon emanation a modi- fied method of the «can technique» was ap- plied. The «can technique» was developed by Alter and Prize (1974 fide Azam et al., 1995) and then applied with some modification, among others, by Karamadoust (1988), Azam et al. (1995) and Solecki (1999). The basis of this method is that the total amount of radon in the investigated material con- sists of two parts, one – the atoms of radon stuck in the mineral crystals, the other – the radon atoms free to migrate in the interstitial spaces. The second part of radon atoms is the part which can get out of the rock material, enter the air above and could be registered by the detector. The ratio of these parts is defined by the emana- tion coefficient. The emanation coefficient was calculated introducing the total radium activity (content) CtRa and effective radium activity CeRa k C Ce eRa Rat= . The total radium activity Ct Ra is the total amount of radon in the rock material calculated on the basis of gamma-spectrometric analysis of radium activity. In this case the analysis was made by Radiometric Laboratory of GIG in Ka- towice, using semi-conductor detector HPGe, according to the Polish norm PN-89/Z-70073. The effective radium content CeRa is the fraction of radium which corresponds to the part of radon which has emanated from the sample. Ef- fective radium activity is expressed in Bq/kg unit and can be calculated from the equation C KMT V e e Ra = t where ρ is the track density on cm2 of the detec- tor surface, V the volume of free space in the can, K a calibration constant (0.0245 track on cm2 in one day), M the mass of sample in kg and Te the time of exposure in days (Azam et al., 1995). Crushed rock material (grain size of 3.5- 1 cm) was closed in a hermetic can of the known Fig. 2a,b. The measurements of radon activity in the outdoor air, a) a plastic cup with detector; b) diagram presenting the construction of the monitoring point. a b Fig. 3. The instrument for measuring radon emana- tion from the rock material by «can technique» method; 1 – magnet, 2 – detector, 3 – metal plate. 121 Distribution of Rn activity in the atmosphere and its dependence on U and Th content in the ground volume. On the inner surface of the cap, there was fixed a detector to register the alpha parti- cles of radon in the air above the sample of rock (fig. 3). The important element is to start expo- sure after stabilization of the secular equilibrium between Ra226 and Rn222. The equilibrium (of 98%) between them stabilizes after 3 weeks in the closed space. Because of this period of sta- bilization, 3 weeks after closing the can, the de- tector was covered by metal plate, which was held by a magnet from outside of the can. After this period the metal plate was removed by tak- ing away the magnet and the detector starts to be exposed. This is a modification of the Azam method introduced by Solecki (1999). The de- tector mainly registers the alpha particles which come from the decay of Rn222 and not from Rn220. Taking into account diffusion coefficients of radon in the air and in the crushed rock mate- rial, the half-life time of the thoron Rn220 and the distance between the detector and the surface of the sample, it was estimated that alpha particles of thoron could be registered in 10%. The ema- nation coefficients of 14 different types of rocks were measured and estimated. Moreover the emanation coefficient was measured for a grain size smaller than 1 cm and for a moisture con- tent of 13% and 24% wt for each type of rock. These variations of conditions changed the ke values but the relative differences of ke between the different types of rocks remained the same. In this paper ke values are presented which were obtained for dry rock material of grain size of 3.5-1 cm. The field measurements of the uranium and thorium content in rocks and soil were per- formed using gamma-spectrometer GR-320. The gamma-spectrometer GR-320 is equipped with a detector, with a source Cs of 0.5 mCi (18.5 kBq). The gamma-spectrometer GR-320 measures contents of Bi214 and Tl208 and on this basis, it estimates the contents of U238 and Th232. Therefore the results are presented as an equiv- alent content of uranium (eU) and thorium (eTh). A few zero values of measurements ob- tained on the outcrops of gabbro and serpen- tinites prove that the cosmic radiation does not influence the results of measurements. The 29 sets of measurements (in each place – 30 single measurements, each one lasting 300s) were collected above the out- crops of different type of rocks and above the soils which cover them. 4. Results 4.1. The eU and eTh content in soil and underlying rocks The mean eU contents in the rocks of inves- tigated area vary from values close to zero (gab- bro, serpentinite) up to 12 ppm, in the quartz- graphite schist in the south part of Niemcza Zone (fig. 4). The quartz-graphite schist which crops out in the north part of metamorphic of Niem- cza-Kamieniec Ząbkowicki, contains 7 ppm eU. The mean values for granitoides are 3-6 ppm eU, in mica schist of metamorphic of Niemcza- Kamieniec Ząbkowicki and schist of Wzgórza Lipowe the measured contents are 2-4 ppm eU. A relatively high value was obtained for basalt in the north-east part of the metamorphic of Niem- 122 Agnieszka Anna Ochmann cza-Kamieniec Ząbkowicki – 3.2 ppm. The low- est values of uranium content were measured on amphibolites, quartzite, quartz-feldspathic schist and some basalts. The thorium content has a decisive impact the thoron activity in the environment. The rela- tively high eTh contents (> 20 ppm) were meas- ured on the outcrops of some granite and schist of Wzgórza Lipowe (fig. 4). The highest mean value – 32 ppm, was found on granodiorite near Niemcza. The slightly lower thorium contents (20-15 ppm) were recorded in quartz-feldspath- ic schist of metamorphic of Niemcza-Kamieniec Ząbkowicki, mica schist of Wzgorza Lipowe and mica-sillimanite schist in south part of Wz- gorza Strzelinskie. The high value eTh of the basalt in the north-east part of the metamorphic of Niemcza-Kamieniec Ząbkowicki – 12.9 ppm is noteworthy. The uranium and thorium content in soil usu- ally corresponds to the contents in the underlying rocks. In most places the eU and eTh contents in soil (mean values: 2 ppm eU and 8 ppm eTh) are slightly reduced in relation to the contents in un- derlying rocks (mean: 3 ppm eU and 12 ppm eTh), but not in every place. On the areas com- posed of amphibolite, serpentinite, gabbro and quartzite the values measured on soil are higher than the values measured on the underlying rocks. It could be explained by the presence of loess ma- terial in the soil, which contains, after Solecki (2000), 2-3 ppm eU and about 10 ppm eTh. Fig. 4. The mean eU and eTh contents in the rocks of Wzgórza Niemczańsko-Strzelińskie. 123 Distribution of Rn activity in the atmosphere and its dependence on U and Th content in the ground 4.2. The emanation coefficient of the samples of selected rocks Emanation coefficient (ke) is interpreted as a ratio of the amount of radon that emanated to the air above the sample to the whole radon which was generated in the sample. Emanation coeffi- cient is a feature of the material and quantifies the ability of this material to emanate radon-gas. The emanation coefficient of samples of 14 selected rocks vary in the range 0.003-0.13 (table I). According to UNSCEAR, the emanation coefficient varies in range of 0.01 – 0.8 (1988 fide Robé and Labed, 1995; Markkanen and Arvela, 1992). The emanation coefficients of investigated rocks fit in the lower range of the values published by UNSCEAR. The lower ema- nation coefficients were measured for basalts and the highest values of emanation coefficient were obtained for quartz-feldspathic schist, quartz-graphite schist and granite (Górka Sobocka). Solecki (1999) measured for the metamorphic schist an emanation coefficient of 0.29. The higher emanation coefficient of meta- morphic schist than that of the magmatic rocks could be explained by the textures of metamor- phic schist, which were formed as a result of numerous transformations and deformations. Therefore it could be presumed that the migra- tion inside these rocks will be faster than in the solid magmatic rock. Effective radium activity (content) (CeRa) quantifies the radon that come out to the atmos- phere from the definite quantity of crushed rock. Effective radium activity is the result of the total activity of Ra228 and Ra226 in rock and the emanation coefficient of this rock. The measurements inside the closed can partially in- clude the thoron emanation, however in the at- mosphere the presence of thoron is limited up to the height of 30-40 cm. Therefore in the case of atmospheric radon the effective Ra226 activity should by taken in consideration. The effective Ra226 activity for the investigated samples is shown in the last column of table I. 4.3. Atmospheric radon activity in the air 2 m above the ground surface The radon activity distribution above the area of Wzgórza Niemczańsko-Strzelińskie is illustrated in fig. 5, the values are year-aver- age. The highest radon activity, above 20 Bq m3, is observed above the area of the out- crops of mylonite of Niemcza Zone, where the maximum values were measured above the outcrops of mylonitic gneisses, granodiorite and quartz-graphite schist. Another area of high values is the region of Górka Sobocka, Wzgórza Lipowe and North-West part of Wzgórza Strzelińskie, with the maximum val- ues above the outcrops of granites near Górka Sobocka and Strzelin. These two geological situations of the higher radon activity in the at- mosphere demonstrate the two general factors Table I. Emanation coefficient (ke) and effective Ra226 activity of selected rocks from investigated area. Type of rock ke CeRa226 [Bq/kg] Gabbro 0.01 0.03 Serpentine 0.03 0.13 Quartzite (Wzgórza Strzelińskie) 0.07 0.45 amphibolite (NE part 0.06 0.80 of Sowie Góry) Basalt (E periphery of Góry 0.007 0.26 Sowie) Basalt (metamorphic of Niemcza- 0.003 0.17 -Kamieniec Ząbkowicki) Basalt (S part of Wzgórza 0.003 0.08 Lipowe) Quartz-feldspathic schist 0.13 3.39 (metamorphic of Niemcza -Kamieniec Ząbkowicki) Quartz-graphite schist 0.11 6.80 (Niemcza Zone) Gneisses (Wzgórza Strzelińskie) 0.01 0.55 Quartz monzodiorite 0.01 0.51 (NE part of Sowie Gory) Granodiorite (Niemcza Zone) 0.06 4.43 Granite (Górka Sobocka) 0.09 5.25 Granite (Strzelin) 0.03 1.90 124 Agnieszka Anna Ochmann that influence the radon exhalation: uranium/ radium content in the rocks and their emana- tion coefficient. The influence of the high con- tents of uranium in rocks on the radon activity in the atmosphere is obvious. Much more in- teresting seems to be the influence of the my- lonitisation, fracturating and weathering of rocks in the tectonic zone, which can be ob- served above the Niemcza Zone. The in- creased migration of radon from fractured and weathered rocks was described among others by Gates et al. (1990), Ball et al. (1991), Gun- dersen (1991), Dubois et al. (1995) and Ciężkowski and Przylibski (1997). Faults and cracks increase the surface of contact between rock and ground water, what promotes the pos- sibility of radon migration too (Ball et al., 1991; Strzelecki and Wolkowicz, 1993). The mean value of atmospheric radon activ- ity, measured 2 m above the ground, on the area of Wzgórza Niemczańsko-Strzelińskie was 21 Bqm–3. This value corresponds to the radon ac- tivity measured above the central mountainous areas of the USA. The mean radon activity in the atmosphere on the area of USA varies in the range of 4-15 Bqm–3, on the Colorado Plateau these values reach 18.5-27.8 Bqm–3 (Gesell, 1983). In Canada outdoor radon activity meas- ured 3 m above the ground surface reached the mean values for the provinces of Manitoba 59 Bqm–3 and Saskatchewan 61 Bqm–3 (Grasty, 1991). Fig. 5. Atmospheric radon activity distribution above the area of Wzgórza Niemczańsko-Strzelińskie. 125 Distribution of Rn activity in the atmosphere and its dependence on U and Th content in the ground 4.4. Radon activity in the air close to ground, 0.05 m above the ground surface The year-average values of radon activity close to the ground are shown in table II. The values are not interpolated over the whole area because this parameter varies strongly, depending on the exhalation from the limited local ground. Moreover, because of the way the cups with detectors are positioned (they were placed directly on the ground), the meas- urements were not influenced by dispersion in the atmosphere. The measurements carried out close to the ground include Rn222 and Rn220, so the radon activity values are influ- enced by both uranium and thorium content in soil and underlying rocks. The highest values of radon activity (>200 Bqm–3) in air close to the ground were measured on granodiorite and granite, a little lower values (100-200 Bqm–3) were measured on mylonitic gneisses of Niemcza Zone, on mica schist and quartz-feldspathic schist of metamorphic of Niemcza-Kamieniec Ząbkowicki and on some basalts. The high values of radon activity are caused by the relatively high uranium and thori- um content in soil (2-3 ppm eU and 7-18 ppm eTh) and underlying rocks (3-6 ppm eU and 11- 26 ppm eTh) in these places. The lowest activities (25-45 Bqm–3) were measured on serpentinite and gneisses of Góry Sowie, where the uranium and thorium contents are: close to zero for eU and 2- 3 ppm eTh. The relatively low radon activity of 52 Bqm–3 on quartz-graphite schist, where the contents of eU and eTh in rock are 13 ppm and 6.6 ppm respectively, results from the unavoid- able location of the detector outside of the old quarry, near the gneiss outcrops. The high values of radon activity in the air in relation to the low uranium and thorium contents in underlying rocks, were measured on amphibolites, gabbros and quartz. In these places the soil contains more radioactive elements (1.5-2 ppm eU and 6-9 ppm eTh) than the rocks (0.1-0.5 ppm eU and 0.7-3.7 ppm Th), which could result from the uranium and thorium concentration during the soil genesis process and from addition of loess material. 4.5. Seasonal variation of radon activity in the air It is possible to observe slight seasonal vari- ations of radon activity in the air at a height of 2 m (fig. 6). In spite of the fact that the modal value is located in the same range of activity val- Table II. Radon activity in the air close to the ground above the outcrops of different rocks. Number of Type of Rn activity monitoring underlying 0.05 m above point rock the ground (fig. 1) [Bqm–3] 1 Mylonitic gneisses 193 of Niemcza Zone 2 Basalt 171 3 Granodiorite 303 4 Mica schist 90 of Niemcza Zone 5 Amphibolite 118 6 Quartz-graphite schist 52 7 Gneisses of Sowie Góry 25 8 Quartz monzodiorite 66 9 Serpentinite 45 10 Granodiorite 212 11 Serpentinite 37 12 Gabbro 85 13 Amphibolite 165 14 Mica schist 67 15 Quartz-feldspathic schist 131 16 Mica schist 137 17 Mica schist 180 18 Mica schist 155 19 Basalt 87 20 Basalt 101 21 Granite 240 22 Granite 200 23 Gneisses 48 of Wzgórza Strzelińskie 24 Gneisses 47 of Wzgórza Strzelińskie 25 Quartzite and quartz schist 40 26 Granite 145 27 Erlanes 75 126 Agnieszka Anna Ochmann ues for the autumn-winter and spring-summer period (10-20 Bqm–3), in the autumn-winter pe- riod there are more measurements in the range of 20-30 and 30-40 Bqm–3 than in the range of 0-10 Bqm–3, the opposite situation is observed on the histogram for the spring-summer period. The slightly higher values in the autumn-win- ter period could be explained by increased exha- lation in the conditions of temperature difference between the air in the ground and air above the ground surface. In the autumn-winter period the air temperature above the ground usually is low- er than that in the ground, which causes convec- tion of the air from ground to the atmosphere. These phenomena were described by Wilkening (1990), Hakl et al. (1995) and Robé and Labed (1995). The snow cover, described as a factor which decreases the radon activity in the atmos- phere (Juzdan et al., 1985; Somogyj et al., 1986; Feichter and Crutzen, 1989; Dörr and Münnich, 1990; Jacob and Prather, 1990; Ennemoser et al., 1995), is not the dominant factor because on this area the period of snow cover is very short. 5. Conclusions The mean value of radon activity in the air 2 m above ground surface was 21 Bqm–3. The highest values were measured in the area of granite and quartz-graphite schist outcrops (rocks of the high eU content) and in the area of mylonitic rocks of the Niemcza Zone. These ob- servations confirm that the radon activity in the atmosphere depends on uranium/radium content in the rocks and their emanation coefficient and on the mylonitisation and fracturating grade of rocks in the tectonic zone. The slight seasonal variation of radon activity in the air is the result of weather conditions which control radon mi- gration from soil-gas to atmosphere. Radon activity close to the ground surface varies from 25 to 300 Bqm–3 and accurately re- flects the uranium and thorium content in the indi- rect ground basement (soil and weathered rocks). REFERENCES AZAM, A., A.H. NAQVI and D.S. SRIVASTAVA (1995): Radi- um concentration and radon exhalation measurements using LR-115 type II plastic track detectors, Nucl. Geophys., 9 (6), 653-657. BALL, T.K., D.G CAMERON, T.B. COLMAN and P.D. ROBERTS (1991): Behaviour of radon in the geological environ- ment: a review, Quart. J. Eng. Geol., 24, 169-182. BARTZ, W. and J. PUZIEWICZ (1999): Orientotion of quartz axes in the quartz-graphite schist of niemcza Zone and the Niemcz-Kamieniec Ząbkowicki metamorphic unit (Lower Silesia, Poland) as an indicator of metamor- phism and deformation conditions, Arch. Miner., LII (l), 113-129 (in Polish). CIĘŻKOWSKI, W. and T.A. PRZYLIBSKI (1997): Radon in wa- ters from health resorts of the Sudety Mts. (SW Poland), Appl. Radiat. Isot., 48 (6), 855-856. DÖRR, H. and K.O. MÜNNICH (1990): Rn-222 flux and soil air concentration profiles in West-Germany. Soil Rn- 222 as tracer for gas transport in the unsaturated soil zone, Tellus, 42B, 20-28. DUBOIS, C., A. ALVAREZ CALLEJA, S. BASSOT and A. CHAM- BAUDET (1995): Modelling the 3-dimensional microfis- sure network in quartz in a thin section of granite, in Gas Geochemistry, edited by C. DUBOIS, D. KLEIN, A. CHAMBAUDET and M. REBETEZ (Northwood: Science Reviews), 357-368. DZIEDZICOWA, H. (1966): The schist series east of the Niem- cza Zone in the light of new investigations, Z geologii Ziem Zachodnich, Wroc l⁄ aw, 101-118 (in Polish). DZIEDZICOWA, H. (1987): Structural evolution and meta- morphism of eastern border of the Góry Sowie, Acta Univ. Wrat. No. 788, Prace Geologiczno-Mineralog- iczne, X, 221-247 (in Polish). Fig. 6. Distribution of radon activity values, meas- ured in the air 2 m above the ground surface in the two periods of the year, which demonstrates slight seasonal variation. 127 Distribution of Rn activity in the atmosphere and its dependence on U and Th content in the ground ENNEMOSER, O., S.M.G. GIACOMUZZI, P. BRUNNER, P. SCHNEI- DER, V. STIGL, F. PURTSCHELLER and W. AMBACH (1995): Radon measurements in soil to predict indoor radon con- centrations in new buildings in an area with unusually high radon levels, Sci. Total Environ., 162, 209-213. FEICHTER, J. and P.J. CRUTZEN (1990): Parameterization of vertical tracer transport due to deep cumulus convec- tion in a global transport model and its evaluation with Radon-222 measurements, Tellus, 42B, 100-117. FLEISCHER, R.L., P.B. PRICE and R.M. WALKER (1965): Sol- id-state track detectors: applications to nuclear science and geophysics, Ann. Rev. Nuc. Sci., 15, 1-28. GATES, A.E., L.C.S. GUNDERSEN and L.D. MALIZZI (1990): Comparison of radon in soil over faulted crystalline terranes: glaciated versus unglaciated, Geophys. Res. Lett., 17 (6), 813-816. GESELL, T.F. (1983): Background atmospheric 222Rn con- centrations outdoors and indoors. A review, Health Phys., 45, 289-302. GRASTY, R.L. (1991): A cross Canada radon survey, in Pro- ceedings of the Fifth International Symposium on the Natural Radiation Environment, Salzburg Austria. GUNDERSEN, C.L.S. (1991): Radon in sheared igneous and metamorphic rocks, U.S. Geol. Surv. Bull. (on line: http://sedwww.cr.usgs.gov:8080/radon/shearl-6). HAKL, J., I. HUNYADI and A. VARHEGYI (1995): The study of subsurface radon transport dynamics based on moni- toring in caves, in Gas Geochemistry, edited by C. DUBOIS, D. KLEIN, A. CHAMBAUDET and M. REBETEZ (Northwood: Science Reviews), 391-398. JACOB, D.J. and M.J. PRATHER (1990): Radon-222 as a test of convective transport in a general circulation model, Tellus, 42B, 118-134 . JHA, S., A.H. KHAN. and U.C. MISHRA (2001): A study ofthe technologically modified sources of 222Rn and its envi- ronmental impact in an Indian U mineralised belt, J. Environ. Radioact., 53 (2), pp. 183-197. KARAMADOUST, N.A., S.A. DURRANI and J.H. FREMLIN (1988): An investigation of radon exhalation from fly ash pro- duced in the combustion of coal, Nucl. Tracks, 15, pp. 667. KHATIR SAM, A.K. and E. HOLM (1995): The natural ra- dioactivity in phosphate deposits from Sudan, Sci. To- tal Environ., 162, 173-178. LOZANO, J.C., F. VERA TOME, V. GOMEZ ESCOBAR and P. BLANCO RODRIGUEZ (2000): Radiological characteriza- tion of uranium mine with no mining activity, Appl. Radiat. Isot., 53, 337-343. MARKKANEN, M. and H. ARVELA (1992): Radon emanation from soils, Radiat. Prot. Dosimetry, 45 (1/4), 269-272. MAZUR, S., J. PUZIEWICZ and D. JÓZEFIAK (1995): The Niemcza zone – A regional-scale shear zone between two areas of contrasting tectono-metamorphic evolu- tion, in Przewodnik LXVI Zjazdu PTG «Geologia i Ochrona Środowiska Bloku Przedsudeckiego», Wro- c l⁄ aw, 221-240 (in Polish). OBERC-DZIEDZIC, T. (1991): Geological setting of the Strzelin granitoids, Acta Univ. Wratisl., 1375, Prace Geol. Miner., XXIX, pp. 295-324 (in polish). OBERC-DZIEDZIC, T. and J. SZCZEPAŃSKI (1995): Geology of the Wzgórza Strzelińskie cristalline massif, in Przewodnik LXVI Zjazdu PTG «Geologia i Ochrona Środowiska Bloku Przedsudeckiego», Wroc l⁄ aw, 111-126 (in Polish). PAPASTEFANOU, C. (2001): Radiological impact from atmos- pheric releases of 238U and 226Ra from phosphate rock processing plants, J. Environ. Radioact., 54, pp. 75-83. PUZIEWICZ, J. and M. RADKOWSKA (1990): Morphology of the crystals of zircon from plutonic rocks of the Niem- cza Zone (Sudetes, SW Poland), Arch. Miner., XLVI (1-2), 124-139 (in Polish). ROBÉ, M.C. and V. LABED (1995): Explaining the variation in soil radon concentrations: a study of the influence of some intrinsic properties of a rock matrix on the radon emission factor, in Gas Geochemistry, edited by C. DUBOIS, D. KLEIN, A. CHAMBAUDET and M. REBETEZ (Northwood: Science Reviews), 535-542. SOLECKI, A.T. (1999): Radon emanation of selected Sudet- ic rocks, in 5th International Conference on Rare Gas Geochemistry, August 30-September 3, 1999, Debre- cen, Hungary. SOLECKI, A.T. (2000): Radiometric anomalies of the central part of the Sudetic Foreland and their relation with geological environment, Acta Univ. Wrat. No. 2210, Prace Geologiczno-Mineralogiczne, LXIX, 1-91 (in Polish). SOMOGYJ, G., A.F. HAFEZ, I. HUNYADI and M. TÓTH-SZILÁ- GYJ (1986): Measurement of exhalation and diffusion parameters of radon in solids by particle track detec- tors, Int. J. Radiat. Appl. Instrum., Part D, Nucl. Tracks Radiat. Meas., 12 (1/6), 701-704 SRIVASTAVA, D.S., P. SINGH, N.P.S. RANA, A.H. NAQVI, A. AZAM, T.V. RAMACHANDRAN and M.C. SUBBA RAMU (1995): Calibration factor for LR-115 type II track de- tectors for environmental radon measurements, Nucl. Geophys., 9 (5), 487-495. STRZELECKI, R. and S. WOLKOWICZ (1993): Geological con- trol on radon emanations, Nukleonika, 38 (4), 109-120. WILKENING, M. (1990): Radon in the environment, Studies in Environmental Science No. 40, pp. 138. WOJNAR, B. (1977): Petrography of granite from Górka Sobocka in the Foresudetic block, Acta Univ. Wrat. No. 378, Prace Geologiczno-Mineralogiczne, VI, 139-156 (in Polish).