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Radon measurements in different types of natural waters in Jordan
Pergamon
Radiation Measurements, Vol. 28, Not I-6, pp. 591-594, 1997 O 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 1350-4487/97 $17.00 + 0.00 PII: S 1350-4487(97)00146-7
R A D O N M E A S U R E M E N T S IN D I F F E R E N T T Y P E S O F N A T U R A L W A T E R S IN J O R D A N
B. A. AL-BATAINA, A.M. ISMAIL, M.K. KULLAB, K.M. ABUMURAD AND H. MUSTAFA* Physics Department, *Earth Sciences Department, Yarmouk University, Irbid-Jordan ABSTRACT Results on radon (~Rn) conomtration for different natural water resources in Jordan, using CR-39 plastic detectors are presented. The activity density of 222Rn ranges from 3.3-10.7 Bq/l (cold spring water), 3.2-5.5 Bq/1 (hot spring water), 3.1-5.7 Bq/l (well water), 2.5-4.7 Bq/l (drinking water) and 4.3-6.3 Bq/1 (sea water). Thus, no unusual radon levels in Jordanian water were observed.
KEYWORDS Radon; water resources; closed can technique; SSNTD's; dosimeter; aquifer; activity density. INTRODUCTION Due to its long half-life time relative to other isotopes, radon ( 222Rn, Tt/2 = 3.82 d) which is a descendent of 23SU is considered to be the most significant isotope of radon problem in the environmental studies. Trace particles of 238Uare found in most natural rocks. The acidic magmatic rocks such as granite contain, in general, more radioactive elements than sedimentary rocks, and the latter contain more than basic magmatic rocks such as basalt. Uranium has affinity to some materials such as phosphates, coal, oil shale etc. Jordan has rich phosphate deposits and thus it is likely to have high values of uranium and radon. Once radon is formed, a proportion of it will escape from its immediate environment into air or water-filled pore-spaces via the process of alpha recoil from its parent, 226Ra, (Tanuer, 1964). Water which is percolating and flowing through pores of the soil and rocks dissolves radioactive elements, especially radium and radon out of these rocks. Radon is subsequently diffused or transported with water, which becomes radioactive. Radon in water presents a dual pathway for exposure of individuals: by ingestion from direct water consumption, and by inhalation exposure when radon emanates from water. The dose to the respiratory system outweighs the dose to the digestion system (Cross et al., 1985). Activities of Z~2Rn in natural water are usually measured by different techniques such as liquid scintillation counter, ionization chamber and gamma ray spectrometry. However, the results obtained by these methods are not always accurate (Kenshuh et al., 1991). This study of radon activity in natural waters is being carried out for the first time in Jordan by using super grade quality of CR=39 solid state nuclear track detectors (SSNTD's), which has proved to be a very economical and reliable method. These detectors have a unique registration sensitivity for alpha particles with energies of ~100 keV. EXPERIMENTAL TECHNIQUE In this work, a variety of water samples from different locations of Jordan were collected and analyzed by using closed can technique; details about sites' locations are shown in Table 1. Water samples were taken in clean plastic bottles from a depth of 0.5 m under the surface of the water whenever possible. In order to prevent radon leakage, the bottles were closed tightly at the site and
591
592
PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE
carried gently to minimize degassing. 50 g samples of water from each bottle were poured into plastic cups. Each sample cup was covered and glued tightly by an inverted passive radon dosimeter cup, see Figure I. A circular hole was made in the dosimeter lid, and covered by a piece of sponge with dimensions 5 cm x 5 cm x 0.5 cm glued onto the interior surface of the lid. This configuration was necessary to maintain the same calibration conditions, also to make sure that thoron (22°Rn, Ttr2 = 55.6 s) cannot reach the detector and to minimize the evaporation from water samples. Atter an exposure time of 90 days, the dosimeter cups were separated from the sample cups. Fortunately no water droplets were formed on the surface of the detectors. The detectors were removed and chemically etched, using a 30% solution of KOH at a temperature of 70 ° C ± 0.1 ° C for nine hours. An optical microscope with a magnification of 150x was used to count the number of tracks per cm 2 in each detector. To relate the density of recorded tracks to radon concentration the dosimeters were previously calibrated in the School of Physics and Space Research at Birmingham University, U. K. During the calibration process, the dosimeters were placed inside radon chamber with concentration of 90 kBq.m "3 and an exposure time of 48 hours. Each dosimeter contained two pieces of CR-39 detectors fixed at its bottom.
Cr-39
h Sponge
LI Figure 1. Configuration of the sealed-can technique used in the experiment.
RESULTS AND DISCUSSION For the purpose of calculating 222Rn concentration levels in natural waters, the radon activity density Ca in the can air above the water sample was determined by measuring the tracks density on the detector according to the following relation:
CotoP
Co - - -
Pot
(1)
where Co is the radon activity concentration of the calibration chamber, to is the calibration exposure time, Po is the surface density of tracks on the calibrated dete~ors, p is the measured surface density of tracks on the exposed detectors and t is the exposure time (2160 h) of our samples. The radon activity density in water C~ was calculated by using a model proposed by Somogyi (Somogyi et el., 1986). According to this model, the number of radon atoms exhaled from the sample surface is equal to the number of radon atoms in the cart air above the water sample multiplied by the probability of decay. In short,
C~ = A Cah t L
(2)
PROCEEDINGS
O F T H E 18TH I N T E R N A T I O N A L
CONFERENCE
593
where ~ is the decay constant of 222Rn , h is the distance from the surface of water in the sample cup to the detector, t is the exposure time of the sample and L is the depth of sample. Table 1 shows the results of radon concentration levels for different water samples. For cold spring water (CSW), the concentration levels range from 3.3 to 10.7 Bq/l with an average of 5.4 + 0.8 Bq/l. In most of these samples the radon concentration was below this average value. One of these samples (CSWS) obtained from Madaba basin, 30 km south of Amman, has a relatively low radon concentration. The main aquifer in this area is the Kurnub sandstone (Lower Cretaceous) partially interconnected with the underlying sandstone of Triassic and Cambrian age. This aquifer contains plant remains and black shale combined with relatively high concentrations of uranium and thorium, which may be dissolved by water flowing through these beds. The rest of cold water samples were originated from lrbid basin in the north part of Jordan. This basin belongs to Wadi es Sir-Amman Formation. These formations are mainly composed of limestone, chert, phosphate and oil shale. They are hydraulically interconnected forming one aquifer. This is either exposed at the surface or confined by the overlying marly Muwaqqar Formation. The samples CSW1 and CSW2 have relatively high radon concentrations. This may be attributed to the presence of oil shale beds in the Muwaqqar Formation. In hot water samples (HSW), the radon concentration levels range from 3.2 to 5.5 Bq/l with an average of 3.8 + 0.5 Bq/l. There is no significant difference in the radon levels between samples from different basins. All samples have relatively low radon concentration. This may be due to the decrease of radon solubility as temperature increases and/or due to the high sulphate content of hot water which cause precipitation of radium before emerging into these hot springs. Moreover, the north part of lrbid basin has been affected by volcanic activity in the Pliocene and Pleistocene eras, causing changes in the physical and chemical properties of the ground water in this area. Samples collected from wells (WW) have radon concentration levels ranged between 3.1 and 5.7 Bq/l with an average of 4.5 _+ 0.8 Bq/l. The sample WW3 which was obtained from a depth of 257m has radon concentration higher than the average by about 25%. This may be due to a thick phosphate beds which are almost located at the bottom of the well, while the sample WW4 obtained from a deeper part of the aquifer at a depth of 750 m shows a lower radon concentration than the average. For sea water samples (SW), the Dead Sea water (SW2) has a noticeable high radon level. This may be due to high salinity and elevated chlorine concentrations which help in retaining radium in water. Furthermore, drinking tap water samples (DTW) have almost similar radon levels even though they were collected from different basins. CONCLUSION In this study, radon levels in different natural water samples from various basins in Jordan are reported. There are no significant variations in radon levels among the different areas. The cold spring water is characterized by the highest average of radon levels (5.4 Bq/l), while the drinking tap water is characterized by the lowest one (3.7 Bq/l). The overall average of radon levels in Jordanian natural waters is 4.5 + 0.9 Bq/l, which is about 25% of the internationally acceptable radon level in water.
Acknowledgement-Theauthors wish to express their gratitude to Dr. S. Durrani for helpful discussions and to his laboratory in Birmingham University for providing calibration facilities.
594
PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE Table I. Radon concentration in diffc~ont types ofnatural water in Jordan.
Sample Code
Location
Ground water basin
Radon conc. (Bq/l)
CSWI
Rahtx',b
Irbid
10.7
26
CSW2
Suk~
Irbid
7.7
23
CSW3
Shdaa
Irbid
4.9
CSW4
Abdda
Irbid
3.6
CSW5
Altrab
Irbid
4.4
24
CSW6
Hobras
Irbid
4.4
22
CSW7
Gweelba
Irbid
3.9
23
CSW8
Hhcanara
Madaba
3.3
21
Al-hima
Irbid
3.3
40
Irbid
3.5
42 45
HSWI HSW2
Al-,,Jaoneh
Average radon conc. (Bq/l)
Temperature oC
22 5.4 + 0.8
21
HSW3
Ma'm..daalal
Madaba
3.2
HSW4
Ma'in-magara
Madaba
3.7
HSW5
Ma'm-pool
Madaba
4.1
48
HSW6
Zarah 1
Dead Sea a~a
3.5
30
HSW7
Zarah 2
Dead Sea area
5.5
31
WWI
Arab valley
Irbid
4.7
30
WW2
Arab valley
lrbid
4.8
32
WW3
Arab valley
Irbid
5.7
WW4
Arab valley.
Lrbid
3.1
40
WW5
Arab valley
Irbid
4.0
26
SW1
Arab Dam
Irbid
4.7
23
SW2
Dead Sea
Dead Sea
6.3
SW3
Aqaba G'ulf
Aqaba
4.3
33
DTWI
Arab Valley
Irbid
4.7
25
DTW2
Yarmtxtk Univ.
Ixbid
2.5
20
DTW3
Zarqa Ma'in
Madaba
2.9
DTW4
Sarah
Al-kcrak
4.1
22
DTW5
Al-hasa
T.,tt",flah
4.4
22
3.8 + 0.5
4.5:1:0.8
5.1 ± 0.9
3.7 ± 0.8
44
28
28
22
REFERENCES
Cross F. T., Harley N. H. and Hofmann W. (1985) Health effects and risks from Rn-222 in drinking water. Health Phys. 48, 649-670. Kenshuh Michihiro, Hirokazu Sugiyama, Toshio Kataoka, Mitsuo Simizu, Eiji Yunoki and Tadashiga Mori (1991) Direct measurement of Rn-222 in natural water by a gamma ray spectrometer with a G¢ detector. Radioisotopes 40, 38-41. Somog~i G., Hafez A., Hunyadi I. and Toth - Szilag~i M. (1986) Measurement of exhalation and diffusion parameters of radon in solids by plastic track detectors. Nucl. Tracks Radiat. Meas. 12, 1-6, 701-704. Tanuer A. B. (1964) Radon migration in the ground: environment, University of Chic,ago, 161-190.
A
review.
The natural radiation
Radiation Measurements, Vol. 28, Not I-6, pp. 591-594, 1997 O 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 1350-4487/97 $17.00 + 0.00 PII: S 1350-4487(97)00146-7
R A D O N M E A S U R E M E N T S IN D I F F E R E N T T Y P E S O F N A T U R A L W A T E R S IN J O R D A N
B. A. AL-BATAINA, A.M. ISMAIL, M.K. KULLAB, K.M. ABUMURAD AND H. MUSTAFA* Physics Department, *Earth Sciences Department, Yarmouk University, Irbid-Jordan ABSTRACT Results on radon (~Rn) conomtration for different natural water resources in Jordan, using CR-39 plastic detectors are presented. The activity density of 222Rn ranges from 3.3-10.7 Bq/l (cold spring water), 3.2-5.5 Bq/1 (hot spring water), 3.1-5.7 Bq/l (well water), 2.5-4.7 Bq/l (drinking water) and 4.3-6.3 Bq/1 (sea water). Thus, no unusual radon levels in Jordanian water were observed.
KEYWORDS Radon; water resources; closed can technique; SSNTD's; dosimeter; aquifer; activity density. INTRODUCTION Due to its long half-life time relative to other isotopes, radon ( 222Rn, Tt/2 = 3.82 d) which is a descendent of 23SU is considered to be the most significant isotope of radon problem in the environmental studies. Trace particles of 238Uare found in most natural rocks. The acidic magmatic rocks such as granite contain, in general, more radioactive elements than sedimentary rocks, and the latter contain more than basic magmatic rocks such as basalt. Uranium has affinity to some materials such as phosphates, coal, oil shale etc. Jordan has rich phosphate deposits and thus it is likely to have high values of uranium and radon. Once radon is formed, a proportion of it will escape from its immediate environment into air or water-filled pore-spaces via the process of alpha recoil from its parent, 226Ra, (Tanuer, 1964). Water which is percolating and flowing through pores of the soil and rocks dissolves radioactive elements, especially radium and radon out of these rocks. Radon is subsequently diffused or transported with water, which becomes radioactive. Radon in water presents a dual pathway for exposure of individuals: by ingestion from direct water consumption, and by inhalation exposure when radon emanates from water. The dose to the respiratory system outweighs the dose to the digestion system (Cross et al., 1985). Activities of Z~2Rn in natural water are usually measured by different techniques such as liquid scintillation counter, ionization chamber and gamma ray spectrometry. However, the results obtained by these methods are not always accurate (Kenshuh et al., 1991). This study of radon activity in natural waters is being carried out for the first time in Jordan by using super grade quality of CR=39 solid state nuclear track detectors (SSNTD's), which has proved to be a very economical and reliable method. These detectors have a unique registration sensitivity for alpha particles with energies of ~100 keV. EXPERIMENTAL TECHNIQUE In this work, a variety of water samples from different locations of Jordan were collected and analyzed by using closed can technique; details about sites' locations are shown in Table 1. Water samples were taken in clean plastic bottles from a depth of 0.5 m under the surface of the water whenever possible. In order to prevent radon leakage, the bottles were closed tightly at the site and
591
592
PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE
carried gently to minimize degassing. 50 g samples of water from each bottle were poured into plastic cups. Each sample cup was covered and glued tightly by an inverted passive radon dosimeter cup, see Figure I. A circular hole was made in the dosimeter lid, and covered by a piece of sponge with dimensions 5 cm x 5 cm x 0.5 cm glued onto the interior surface of the lid. This configuration was necessary to maintain the same calibration conditions, also to make sure that thoron (22°Rn, Ttr2 = 55.6 s) cannot reach the detector and to minimize the evaporation from water samples. Atter an exposure time of 90 days, the dosimeter cups were separated from the sample cups. Fortunately no water droplets were formed on the surface of the detectors. The detectors were removed and chemically etched, using a 30% solution of KOH at a temperature of 70 ° C ± 0.1 ° C for nine hours. An optical microscope with a magnification of 150x was used to count the number of tracks per cm 2 in each detector. To relate the density of recorded tracks to radon concentration the dosimeters were previously calibrated in the School of Physics and Space Research at Birmingham University, U. K. During the calibration process, the dosimeters were placed inside radon chamber with concentration of 90 kBq.m "3 and an exposure time of 48 hours. Each dosimeter contained two pieces of CR-39 detectors fixed at its bottom.
Cr-39
h Sponge
LI Figure 1. Configuration of the sealed-can technique used in the experiment.
RESULTS AND DISCUSSION For the purpose of calculating 222Rn concentration levels in natural waters, the radon activity density Ca in the can air above the water sample was determined by measuring the tracks density on the detector according to the following relation:
CotoP
Co - - -
Pot
(1)
where Co is the radon activity concentration of the calibration chamber, to is the calibration exposure time, Po is the surface density of tracks on the calibrated dete~ors, p is the measured surface density of tracks on the exposed detectors and t is the exposure time (2160 h) of our samples. The radon activity density in water C~ was calculated by using a model proposed by Somogyi (Somogyi et el., 1986). According to this model, the number of radon atoms exhaled from the sample surface is equal to the number of radon atoms in the cart air above the water sample multiplied by the probability of decay. In short,
C~ = A Cah t L
(2)
PROCEEDINGS
O F T H E 18TH I N T E R N A T I O N A L
CONFERENCE
593
where ~ is the decay constant of 222Rn , h is the distance from the surface of water in the sample cup to the detector, t is the exposure time of the sample and L is the depth of sample. Table 1 shows the results of radon concentration levels for different water samples. For cold spring water (CSW), the concentration levels range from 3.3 to 10.7 Bq/l with an average of 5.4 + 0.8 Bq/l. In most of these samples the radon concentration was below this average value. One of these samples (CSWS) obtained from Madaba basin, 30 km south of Amman, has a relatively low radon concentration. The main aquifer in this area is the Kurnub sandstone (Lower Cretaceous) partially interconnected with the underlying sandstone of Triassic and Cambrian age. This aquifer contains plant remains and black shale combined with relatively high concentrations of uranium and thorium, which may be dissolved by water flowing through these beds. The rest of cold water samples were originated from lrbid basin in the north part of Jordan. This basin belongs to Wadi es Sir-Amman Formation. These formations are mainly composed of limestone, chert, phosphate and oil shale. They are hydraulically interconnected forming one aquifer. This is either exposed at the surface or confined by the overlying marly Muwaqqar Formation. The samples CSW1 and CSW2 have relatively high radon concentrations. This may be attributed to the presence of oil shale beds in the Muwaqqar Formation. In hot water samples (HSW), the radon concentration levels range from 3.2 to 5.5 Bq/l with an average of 3.8 + 0.5 Bq/l. There is no significant difference in the radon levels between samples from different basins. All samples have relatively low radon concentration. This may be due to the decrease of radon solubility as temperature increases and/or due to the high sulphate content of hot water which cause precipitation of radium before emerging into these hot springs. Moreover, the north part of lrbid basin has been affected by volcanic activity in the Pliocene and Pleistocene eras, causing changes in the physical and chemical properties of the ground water in this area. Samples collected from wells (WW) have radon concentration levels ranged between 3.1 and 5.7 Bq/l with an average of 4.5 _+ 0.8 Bq/l. The sample WW3 which was obtained from a depth of 257m has radon concentration higher than the average by about 25%. This may be due to a thick phosphate beds which are almost located at the bottom of the well, while the sample WW4 obtained from a deeper part of the aquifer at a depth of 750 m shows a lower radon concentration than the average. For sea water samples (SW), the Dead Sea water (SW2) has a noticeable high radon level. This may be due to high salinity and elevated chlorine concentrations which help in retaining radium in water. Furthermore, drinking tap water samples (DTW) have almost similar radon levels even though they were collected from different basins. CONCLUSION In this study, radon levels in different natural water samples from various basins in Jordan are reported. There are no significant variations in radon levels among the different areas. The cold spring water is characterized by the highest average of radon levels (5.4 Bq/l), while the drinking tap water is characterized by the lowest one (3.7 Bq/l). The overall average of radon levels in Jordanian natural waters is 4.5 + 0.9 Bq/l, which is about 25% of the internationally acceptable radon level in water.
Acknowledgement-Theauthors wish to express their gratitude to Dr. S. Durrani for helpful discussions and to his laboratory in Birmingham University for providing calibration facilities.
594
PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE Table I. Radon concentration in diffc~ont types ofnatural water in Jordan.
Sample Code
Location
Ground water basin
Radon conc. (Bq/l)
CSWI
Rahtx',b
Irbid
10.7
26
CSW2
Suk~
Irbid
7.7
23
CSW3
Shdaa
Irbid
4.9
CSW4
Abdda
Irbid
3.6
CSW5
Altrab
Irbid
4.4
24
CSW6
Hobras
Irbid
4.4
22
CSW7
Gweelba
Irbid
3.9
23
CSW8
Hhcanara
Madaba
3.3
21
Al-hima
Irbid
3.3
40
Irbid
3.5
42 45
HSWI HSW2
Al-,,Jaoneh
Average radon conc. (Bq/l)
Temperature oC
22 5.4 + 0.8
21
HSW3
Ma'm..daalal
Madaba
3.2
HSW4
Ma'in-magara
Madaba
3.7
HSW5
Ma'm-pool
Madaba
4.1
48
HSW6
Zarah 1
Dead Sea a~a
3.5
30
HSW7
Zarah 2
Dead Sea area
5.5
31
WWI
Arab valley
Irbid
4.7
30
WW2
Arab valley
lrbid
4.8
32
WW3
Arab valley
Irbid
5.7
WW4
Arab valley.
Lrbid
3.1
40
WW5
Arab valley
Irbid
4.0
26
SW1
Arab Dam
Irbid
4.7
23
SW2
Dead Sea
Dead Sea
6.3
SW3
Aqaba G'ulf
Aqaba
4.3
33
DTWI
Arab Valley
Irbid
4.7
25
DTW2
Yarmtxtk Univ.
Ixbid
2.5
20
DTW3
Zarqa Ma'in
Madaba
2.9
DTW4
Sarah
Al-kcrak
4.1
22
DTW5
Al-hasa
T.,tt",flah
4.4
22
3.8 + 0.5
4.5:1:0.8
5.1 ± 0.9
3.7 ± 0.8
44
28
28
22
REFERENCES
Cross F. T., Harley N. H. and Hofmann W. (1985) Health effects and risks from Rn-222 in drinking water. Health Phys. 48, 649-670. Kenshuh Michihiro, Hirokazu Sugiyama, Toshio Kataoka, Mitsuo Simizu, Eiji Yunoki and Tadashiga Mori (1991) Direct measurement of Rn-222 in natural water by a gamma ray spectrometer with a G¢ detector. Radioisotopes 40, 38-41. Somog~i G., Hafez A., Hunyadi I. and Toth - Szilag~i M. (1986) Measurement of exhalation and diffusion parameters of radon in solids by plastic track detectors. Nucl. Tracks Radiat. Meas. 12, 1-6, 701-704. Tanuer A. B. (1964) Radon migration in the ground: environment, University of Chic,ago, 161-190.
A
review.
The natural radiation