natural radioactivity in jordanian soil and building materials and the associated radiation hazards
TRANSCRIPT
J. Enorron. Radioactivity. Vol. 39, No. 1. pp. 9--Z. 1998
(~’ 1998 Elsevier Science Ltd. All rights reserved Prmted in Great Britain
ELSEVIER PII: SO265-931X(97)00046-5 0265-931X/98 $19.00 + 0.00
Natural Radioactivity in Jordanian Soil and Building Materials and the Associated Radiation Hazards
N. Ahmad, Matiullah & A. J. A. Hussein
Centre for Nuclear Studies, P.O. Nilore, Islamabad, Pakistan
(Received 4 March 1997; accepted 22 May 1997)
ABSTRACT
Natural radioactivity in soil and building materials was determined using
gamma spectrometry. Samples were collected from the populated areas of
Jordan. 232Th, 226Ra and 40K activities were determined. Soil samples collected
from the Jordan valley showed high 4oK concentrations which were due to the
presence of a potash factory in the valley. One soil sample ,from southern
sector showed very high 226Ra activity (i.e. 774 Bq kg- ‘). The derived data
were compared with the reported data for other countries in the world.
Radium-equivalent activities were calculated for soil and building mate-
rials to assess the radiation hazards. Only one soil sample showed very high
Ra,, activities (i.e. 979 Bq kg- ‘). All the other soil samples showed Ra,,
activities within the limit set by OECD countries (i.e. 370 Bq kg- t). A few
marble chips samples also showed Ra,, activities greater than the OECD
limit. Most of the materials examined are acceptable for use as building
materials in accord with the OECD criterion. 0 1998 Elsevier Science Ltd.
All rights reserved
INTRODUCTION
The specific radioactivities of soil and building materials are required in setting the standards and guidelines for their safe usage and in assessing the radiation hazard associated with them. In this context, 238U, 232Th and 40K activities have been measured by many groups and the data are available in open literature for many countries (see e.g. UNSECAR, 1988, 1993 and references quoted therein). Sometimes, 226Ra is determined instead of 238U as these may not be in equilibrium. For Jordanian soil and building materials such data were not available. Therefore, systematic studies were performed and the activities of radium and thorium series and 40K nuclide in the
9
10 N. Ahmad et al.
Jordanian soil and building materials were determined. The radium-equiva- lent activities and the external hazard indices were calculated in order to decide whether they are acceptable according to the OECD (1979) criterion.
MATERIALS AND METHODS
Sampie collection
In order to determine the activities in soil and building materials, samples were collected throughout Jordan. For the sake of convenience, the country was divided into three sectors as shown in Fig. 1 and are as follows:
ahaba - \
SECTOR ‘\ \
\ \ \
\ \
----------__-_---
Fig. 1. The map of Jordan.
Natural radioactivity in Jordanian soil 11
(1) The northern sector: This includes the governates of Irbid, Ajloun, Jerash and Mafraq. These governates used to be one governate in the past and was called the governate of Irbid. The people of this sector make up 28.7% of the Jordanian population.
(2) The central sector: This sector includes the governates of the capital Amman, Zaraqa, and Balqa. The population of this sector accounts for 59.06% of the Jordanian population.
(3) The southern sector: This includes the governates of Karak, Tafilah, and Madaba. The population of this sector constitutes 8.5% of the Jordanian population.
The population of the above three sector makes up 96.2% of the total Jordanian population. The remaining population is in the governates of Maan and Aqaba. The area of these two governates is very large and population density is very low.
The materials investigated in this work were soil, gravel aggregate, marble chips, sand, hard rock, cement and ceramics. The samples for this work were collected from the above-mentioned sectors of Jordan. The details are as follows:
Soil samples were collected at depths of -30 cm below the surface from different locations along the roads, Gravel aggregate samples were collected from the quarries and construction sites.
The sand used in northern sector is quarried from sites located between the cities of Zarqa and Jerash. For central sector, sand is quarried from sites around the town of Adasiah, on the road between Amman and the Jordan valley, locally known as the Swaileh sand. In southern sector, sand is quarried from Ghor Al-Safi in the Jordan valley in the governate of Karak.
The use of stone (hard rock) as a building material was limited due to the high cost of cutting and carving by hand. However, since the last few decades, it has become compulsory to use stone in the construction of buildings in most areas in Amman and a few areas in other cities. Almost the entire western sector of Amman is now built from this material. These rocks are mined from two main areas: Maan and Ajloun. In the past, most of these rocks came from Jameen, a small village in the district of Nabluss in the West Bank of Jordan. However, the supply from this site was reduced after the occupation of the west bank in 1967.
Samples of marble chips were collected from Ajloun, Dabaah and Al- Azraq quarries located in different parts of Jordan, whereas the cement samples were collected from all the factories in Jordan.
Ceramics is relatively a new building material in Jordan. In the past, only the privileged part of the society could afford it, because it had to be imported from Spain and Italy. During the last 3-4 decades, its use has
12 N. Ahmad et al.
considerably increased due to the establishment of the ceramic industry in the country.
Sample preparation
Samples of different materials were collected and crushed to make fine powder. The crushed samples were passed through a sieve about 1 mm mesh size to remove the larger-size grains. The powder was then dried in a microprocessor-controlled furnace for 20 h at 100°C. The dried powder and the reference material (Soil-6 from IAEA) were packed in radon impermeable plastic containers having 77 cm diameter and 62.5 cm height. The samples and the reference material were stored for more than 60 days to attain equilibrium amongst 226Ra and its short-lived decay products.
Activity measurement
The activity measurements were performed with an HPGe gamma ray spectrometer. The resolution of this spectrometer was 2.23 keV at 1332 keV gamma rays of 6oCo. A PC based MCA, using APETC (Canada) software, was used to collect and analyze the gamma ray spectra. The samples were counted for 20 h. Background measurements were also taken for 20 h at the weekends and were applied to the data taken during those weeks.
The absolute efficiency of the detection system was determined with the Soil-6 standard provided by IAEA and the reliability of the spectrometer was tested by measuring the activity of an IAEA provided reference mater- ial known as IAEA-312 (soil). The 226Ra activity determination was based on 295.1 (19.2%) and 351.9 (37.1%) keV gamma rays from 2’4Pb and 609.3 (46.1%), 1120.3 (15.0%) and 1764.5 (15.9%) keV gamma rays from 214Bi. The activity of 232Th was determined by the 2386 (43.6%) keV gamma rays from 212Pb, 338.4 (12%), 911.2 (29%) and 969.0 (17.4%) keV gamma rays from 228A~ and 583.0 (86%) keV gamma rays from 208Tl. The activity of 40K was determined through 1460-8 (10.7%) keV gamma ray. The 238U concentration was determined through the 63 keV gamma ray of 234Th. The quoted and measured values of the activities are presented in Table 1. This table shows that the difference in the measured and the quoted average specific activities is extremely small. The good agreement between the measured and the reported activities of the IAEA reference material (Soil- 312) shows that the spectrometer could be relied upon to measure the natural radioactivity in soil and building materials.
Natural radioactivity in Jordunian soil 13
TABLE 1 Quoted and Measured Activities of IAEA-312 Reference Materials
Element Quoted value and confidence interval
Measured values using Soil-6 as standard
22bRa
232Th 338U
269 (Bq kg-‘) (250-287) 91.04 pgg-’ (81.3-101.5)
165pgg-’ (15.7-17.4)
271 (Bq kg-‘)
91 pgg-’ 17lJgg-’
Note: Values in parantheses represent range.
RESULTS AND DISCUSSION
The activities of 226Ra, 232Th and 40K radionuclides have been determined in all the collected samples. The measured minimum, maximum and aver- age activity values of 226Ra, 232Th and 40K are presented in Table 2. The uncertainties in the average values are also given in this table. These were determined using the error propagation formula. As can be seen in this table, the measured minimum vaIue of z32Th activity is 2.1 Bq kg- 1 in a sample of gravel aggregate, whereas the maximum activity is 50.3 Bq kg- ’
in a soil sample collected from southern sector. The minimum observed 226Ra activity is 12.2 Bq kg- ’ in a marble chips sample and the maximum is 774 Bq kg-’ in a soil sample. 40K activity varies from 52.0 Bq kg- ’ in a sample of marble chips to 1729 Bq kg- 1 in a soil sample.
The maximum observed value of 226Ra in soil was found in a sample collected from the southern sector near the road joining Hasa and Qatrana. This area is rich in phosphate rocks and radium bearing marbles. There- fore, this particular value cannot be a true representative of the region nor the other seven samples collected from the same area which have 226Ra content ranging from 1505 to 203.5 Bq kg-‘. If we ignore the samples collected from this high activity zone, then the maximum 226Ra activity will drop from 774 to 370 Bq kg-’ in marble chips.
The highest observed values of 40K concentrations were observed in the soil samples collected from an area near the potash factory in the Jordan Valley. Other material which showed relatively higher 40K concentration is ceramics.
(i) Soil: The minimum, average and maximum measured values of 232Th, 226Ra and 40K activities for all the sectors are presented in Table 2. As already stated, there are eight samples from the Hasa-Qatrana area in the southern sector which have specific activities of 226Ra greater than 150 Bq kg-‘. If these samples are excluded, then the observed 2Z6Ra activ- ities should be in the range 31.5-95.0 Bq kg-‘. The average value of 226Ra
TA
BL
E
2 Sp
ecif
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in
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Min
232 T
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ean
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(B
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Sw
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h Je
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G
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Al-
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jloun
M
ann
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Mar
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s A
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.5
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57.3
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.9
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8.0
Natural radioactivity in Jordanian soil 15
concentration in all the soil samples examined in this work was 73.4 Bq kg- ‘. When the samples from high 226Ra area are excluded, the mean value drops to 53.6 Bq kg-‘.
Considering the high activity area itself, the average 226Ra concentration should be -248 Bq kg-‘. Since soil is always present as a substructure for all buildings, the contribution of this material to the overall activity is considerable. Also, since soil with high radium content can be the main source of indoor radon, the dwellings in this region are expected to have high indoor radon levels. This region is situated between Hasa and Qatrana on both sides of the desert highway and is very thinly populated. Neverthe- less, further investigation of this area is needed to pin point the exact locations of high levels of radioactivity.
For all the soil samples, as may be seen in Table 2, the observed thorium activity is always less than radium activity. The observed values of thorium activity in the samples ranged from 6.3 to 50.3 Bq kg-‘. The observed 40K specific activities ranged from 182 to 1729 Bq kg- I. If the samples collected from the Jordan valley are excluded, where a potash factory is located, then the activity of 40K in the remaining samples ranged from 182 to 483 Bq kg- i. The fact that some of the samples collected from th Jordan valley region near the potash factory had high 40K concentrations, even though the samples were collected at a depth of N 30 cm below the surface, is not surprising since the land is agricultural and frequently ploughed. Table 3 compares the reported values of natural radioactivity due to 226Ra, 232Th and “OK, taken from the literature, with those determined in this work.
TABLE 3 Specific y-ray Activities of Soil in Jordan and Some Countries in the World
Country No. of “‘Ra “‘Th 4°K Reference
samples (Bq kg-‘) (Bq kg- ‘) (Bq kg- ‘)
Australia
Bangladesh China Ireland
Italy Malaysia Pakistan Taiwan
USA
12 62.9 162.8 403.3 5 88.1 68.2 256.2
1476 44.0 47.0 593.1 60.0 26.0 350.6
5 45.0 49.0 687.0 4 159.1 140.6 851.0
57 46.5 60.8 6986 - 27” - 387.8
327 41.0 36.0 -
Beretka and Mathew (1985)
Mollah et al. (1986) Ziqiang et al. (1988)
McAulay et al. (1988)
Scioccheti et al. (1977) Chong and Ahmad (1982)
Tufail er al. (1992)
Chang et al. (1974) Nazaroff and Nero (1988)
Jordan 75 53-Q 24.2 487.9
u Uranium concentration. *Samples from high 226Ra concentration area were excluded.
This work
16 N. Ahmad et al.
(ii) Gravel aggregate: The measured minimum average and maximum values of 232Th, 226Ra and 40K are presented in Table 2. The observed thorium content was very low as compared with the radium content. The maximum observed radium activity was 73.2 Bq kg-’ while the mean values for the three sectors varied from 33 to 46.3 Bq kg- ‘.
(iii) Sand: The measured minimum, maximum and the average specific activities due to 232Th, 226Ra and 40K in the sand samples are presented in Table 2. In all the samples, 232Th concentration was smaller than 226Ra concentration. The average values of 226Ra activities ranged from 20 to 28 Bq kg- ‘. On the other hand, 232Th and 40K activities in sand samples, collected from Ghor Al-Safi area, were greater than those found in the samples collected from Jerash area whilst corresponding activities in sand samples collected from Adasiah area were smaller than those found in sand samples from Jerash area. The values of natural radioactivity in sand samples, reported in the literature (UNSCEAR, 1988, 1993; Tufail et al., 1992), and compared with the present results in Table 4.
(iv) Stone (hard rock): The measured minimum, average and maximum 232Th, 226Ra and 40K activities are presented in Table 2. The average value of 232Th activity in the hard rock samples, collected from Jameen and Ajloun, was higher than that found in hard rock samples from Maan. The average values of 226Ra and 40K activities in all the samples were approx- imately equal.
(v) iWarble chips: The measured values of activity of 226Ra in marble stones mined from Dabaah quarries, varied from 264.9 to 369.5 Bq kg- ‘.
These values were greater than those observed in other materials by a factor of 6-16, except in a few soil and ceramics samples studied in this work, as
TABLE 4 Specific y-ray Activities of Sand in Jordan and Some Countries in the World
Country No. of Z6Ra 2.11 T/i 4°K Rt$erence samples (Bq kg ‘) (Bq kg - ‘) (Bq kg I)
Australia 3 3.1 40.1 44.1 Bangladesh 5 248.2 219 389.2 China - 32 32 634 Germany 15.5 17.8 395 Italy 14 24 21 528 Mexico 22.2 22.8 - Malaysia 5 IO.3 33.3 425.5 The Netherlands 4 8.1 10.6 200 Pakistan 30 21 40.63 566.9
Beretka and Mathew (1985) Mollah et al. (1986) Ziqiang et al. (1988) UNSCEAR (1971)
Sciocchetti et a/. (1977) Espinosa et al. (1986)
Chong and Ahmad (1982) Ackers et al. (1985) Tufail et al. (1992)
Jordan 73 25.1 14.6 188-l This work
Natural radioactivity in Jordanian soil 17
well as, those reported in the literature (Tufail et cd., 1992; Papastefanou et al., 1984; Chang et al., 1974) and presented in Table 5. The average concentration of 226Ra in marble chips from Dabaah was 308.9 Bq kg- ’
This value is 15 times greater than that found in chips samples, the 40K and 232Th activities were very low as compared with the 226 Ra activities found in the Dabaah chips. The desert around the Al-Azraq quarries is full of volcanic rocks, therefore, one would expect larger amount of 226Ra in the samples collected from this area. However, the results obtained in this work do not support this expectation.
(vi) Cement: The measured minimum, average and maximum activities of 232Th, 226Ra and 40K in cement samples are presented in Table 2. It may be seen from this table that 226Ra and 232Th activities in all the collected cement samples do not vary greatly. The concentration of 40K in white cement was half of that found in other cements. The reported values of natural radio- activity in cement samples are compared with the present data in Table 6.
(vii) Ceramics: This building material showed the highest 232Th concen- tration. The concentration of 232Th ranged from 94.7 to 108.1 Bq kg- ‘. The ‘OK concentration in ceramics was also the highest when the soil samples collected from the Jordan Valley region were excluded.
(viii) Concrete: Concrete was not analyzed as an independent material. Its activities were determined from the weighted average concentrations of its constituents. Concrete in Jordan is made by mixing gravel aggregate, sand, cement and water. The mass fractions of aggregate, sand, and cement are 80%, 10.5% and 9.5%, respectively. Based on these ratios, the activity values in the concrete manufactured in Jordan were determined and are compared in Table 7 with those reported in the literature for other coun- tries in the world.
TABLE 5 Specific y-ray Activities of Marble Chips in Jordan and Some Countries in the World
Countr?, ““Ra 232Th 40K RGference
(Bq kg :, (Bq kg :, 0% kg - ‘l
Greece” 80.8 33.7 483.1 Papastefanou et al. (1984) Pakistan 16.0 20 248 Tafail et al. (1992) Taiwan 1643 63.9 Chang et al. (1974)
Jordanb This work Dahaah 308.9 6-6 59.2 Ajloun 19.3 11.9 93.3 Azraq 20.1 11.4 850
“Average in 5 locations. ‘Average value for each area.
18 N. Ahmad et al.
TABLE 6 Specific y-ray Activities of Cement in Jordan and Some Countries in the World
Country No. of 226& 2q.h 4”,K Reference
samples (Bg kg ‘) (Bq kg- ‘) (Bq kg ‘)
Australia Austria Bangladesh Belgium China Finland Germany Greece Italy Malaysia Mexico The Netherlands Norway Pakistan Taiwan
Jordan Fuhais South White
1 18 3 2
11
4 6 5
6
38 -
25 43.21 1 l-23 265.12 25 45.07 1 l-42 226.4 23 49.1 13.47 111.91
51.8 48.1 114.7 Beretka and Mathew (1985) 26.7 14.2 210 Sorantin and Steger (1984)
120.2 132.4 505.7 Mollah et al. (1986) 62 76 - Proffijin et al. (1984) 56 33 - Ziqiang et a/. (1988) 40.2 19.9 251 Mustonen (1984) 15.1 22.9 325 UNSCEAR (1977) 64 14.62 447.3 Papastefanou et al. (1984) 46 42 316 Sciocchetti et al. (1977) 81.4 59.2 303.5 Chong and Ahmad (1982) 26 52.6 - Espinosa et ul. (1986) 21 19 230 Ackers et ul. (1985) 29.6 18.5 259 Straden and Berteig (1980) 36.5 28.1 214.9 Tufail et al. (1992) 33 279.9 Chang et ul. (1974)
This work
TABLE 7 Specific y-ray Activities of Concretes in Jordan and Some Countries in the World
Country 2”Ra 232Tll 4’,K Reference
(Bq kg - :, (Bq kg - ‘J 0% kg - :,
Austria 15 Bangladesh 16 Finland 53 Germany 67 Greece 46 Italy 19 Malaysia 85 The Netherlands 14 Norway 28 Pakistan 27 Sweden 47 Taiwan 43 UK 22 USA 21
Jordan 38
41 171 38 63
7 24 52 16 36 21 80
42 11
6
200 294 838 550 250 451 322 130 650 240 577 358
350
138
Sorantin and Steger (1984) Mollah et al. (1986)
Mustonen (1984) UNSCEAR (1977)
Papastefanou et al. (1984) Sciocchetti et al. (1977)
Chong and Ahmad (1982) Ackers et al. (1985)
Straden and Berteig (1980) Tufail et al. (1992) UNSCEAR (1977) Chang et al. (1974) UNSCEAR (1977) IJNSCEAR (1977)
This work
Natural radioactivity in Jordanian soil 19
RADIATION HAZARDS
To assess the radiation hazards associated with the materials used in the construction of dwellings, the following two quantities have been defined (OECD, 1979; Beretka and Mathew, 1985):
(i) Radium-equivalent activity. (ii) External hazards index.
Since these two quantities provide the same information in a slightly different way, therefore, only radium-equivalent activity was considered.
Radium-equivalent activity
To represent the specific activities of 226Ra, 232Th and 40K by a single quantity, which takes into account the radiation hazards associated with them, a common index has been introduced. It is called the radium equiva- lent activity (Ra,,) and is defined as (OECD, 1979; Beretka and Mathew, 1985)
Ra,, = Aaa + I-43Ar,, + 0077&, (1)
where ARa, ATh, and AK are the specific activities of 226Ra, 232Th and 40K, respectively. It may be noted that 238U has been replaced with its decay product 226Ra, because there may be a disequilibrium between 238U and 226Ra, as stated earlier. While defining Ra,, activity by eqn (1) it has been assumed that 10 Bq kg-’ of 226Ra, 7 Bq kg-’ of 232Th and 130 Bq kg-’ of 40K produce the same gamma doses. The maximum value of Ra,, in building materials must be less than 370 Bq kg- i for safe use, i.e. to keep the external dose below 1.5 mGy per year (OECD, 1979; Beretka and Mathew, 1985). The Ra,, values using eqn (1) have been calculated and are presented in Table 8. It is clear from this table that the Ra,, values in the ceramics are the highest (i.e. 376.4 Bq kg- ‘) followed by chips samples from Dabaah (i.e. 322.9 Bq kg-‘). It was observed that there were four chips samples from Dabaah having Ra,, greater than 370 Bq kg- * which is the recommended limit by OECD. Except one soil sample from the southern sector, for all other materials studied in this work, the average Ra,, values were within the limit set by OECD.
Dabaah tiles are used extensively in Jordan. These are prepared by mixing Ajloun marble chips in powder form, white cement, Dabaah chips, fine crushed limestone and cement in the ratios 5 : 2 : 6 : 8 : 2, respectively. For such proportions of the materials, the estimated radium-equivalent activity of the above tiles was - 122 Bq kg-i. This values is lower than the upper limit of 370 Bq kg- ‘. It is worth noting here that although the Ra,, value of
20 N. Ahmad et al.
TABLE 8 Radium-Equivalent Activity for Jordanian Soil and Building Materials
Material Location in
Jordan
Radium equivalent activity (Bq kg-‘)
Min MaX Mean
Soil
Aggregate
Sand
Stone (hard rock)
Marble chips
Cement
Ceramics
North sector Central sector South sector
North sector Central sector South sector
Swaileh Jerash Al-Safi
Ajloun
Maan Jameen
Ajloun Amman
Azraq
Fuhais Southern
White
58.9 162.4 117.8 68.3 165.6 136.2 58.4 979.1 166.7
36.7 60.4 47.4 41.3 67.8 53.5 37,2 95.9 63.2
32.8 51.7 41.1 24.8 104.2 54.1 71.5 102.0 85.6
84.9 130.3 109.4 72.6 112.0 88.1
101.1 146.1 125.6
26.9 62.6 43.4 275.3 398.3 322.9
34.2 52.89 42.9
68.6 94.3 79.1 70.8 87.0 78.8 66.0 91.5 71.0
292.1 376.4 329.0
Dabaah chips is approaching or is greater than the upper limit recommen- ded by OECD countries (OECD, 1979) its smaller fraction in the tiles has resulted in acceptable Ra,, value for the Dabaah tiles.
CONCLUSIONS
The measured 226Ra activity in some soil samples from the southern sector is high. This high activity area is thinly populated. The marble chips samples collected from Dabaah have also very high radium content. These two areas are very close to each other, and therefore, these areas should be further investigated. The soil samples collected from the Jordan Valley show high 40K concentration. This was mainly due to the presence of a potash factory in that region. The 232Th concentration in each sample was lower than 226Ra concentration.
The estimated average values of radium equivalent activity in the materials (except some soil and marble stone samples) were less than
Natural radioactivity in Jordanian soil 21
370 Bqkg- ‘. Therefore, all the materials (except marble chips from Dabaah, soil from high radium activity zone and ceramics) may be declared safe in accord with the OECD (1979; OECD). For Dabaah tiles,l which were prepared by mixing several materials with marble chips from Dabaah, the radium-equivalent activity was one-third of the recommended limit.
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