Radon is a noble, radioactive gas produced by the radioactive decay of radium from the dissolution of uranium in soil, water, and various rocks in the environment, which leads to harm to humans and living organisms. The CR39 nuclear track detector was used to measure radioactive rates of radon in one hundred and five samples of different building materials (sand - ceramic - granite - marble -cement - gypsum - bricks) were collected from the Jazan region, Saudi Arabia. The average value of radon gas concentration for all samples of buildings used in the Kingdom of Saudi Arabia was 286.84 ± 33.35 Bq/Kg. The results show the highest value of radiation doses in Royal Gold Granite with a value of 10.98 ± 0.87 mSv / year. The value of the quality coefficient was a correlation between the values of radium concentration and exhalation rates of building materials. As a result, it is advised not to use granite inside homes and only place it on the front of the house.
Research Article
Measuring the concentration of radon gas and its progeny in building materials
https://doi.org/10.21203/rs.3.rs-2077209/v1
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Building materials
Radon gas
SSNTDs
Radon concentration
Effective dose
Exhalation rate
Radon gas has three isotopes, 222Rn resulting from the decay of the 238U chain, 220Rn resulting from the decay of the 232Th chain, and 219Rn resulting from the decay of the chain originating with 235U (Entesar, 2021). The concentration of radon gas and its components increases in unventilated places, which increases the risk of lung cancer.
Building materials contain radioactive cores that depend on the clouds from which they are drawn. Soil contains radioactive nuclei of uranium and thorium, and these radionuclides emit gamma rays, which can be an external source of radiation exposure (ICRP , 2007; Maged, 2012). Much of our natural exposure is binary-to-radon, a natural gas, continually generated from 226-Ra by the radioactive decay of 238-U with ionizing radiation. Radon gas disperses quickly making it more harmful when indoors, as it tends to accumulate in the lung (Vanasundari, 2012). The first daughter of Radon 218-Po is highly reactive, a heavy metal that is attracted to fine particles in the air. The radioactive particles from radon particles are inhaled and deposited (as a solid) in the lung (Chen, 2015). This buildup in the lung can damage the bronchial epithelium, leading to cancer.
The radium activity of ceramic tiles is in a high range with values higher than the permissible rate, which gives a dangerous indication for factory workers exposed to work for long periods. Places of tile production must have high ventilation to reduce the gas values emitted from the quantities of ceramics in the place (Abo-Elmagd, 2014; Entesar, 2019).
Building materials are the second most important source of internal radon production, and the first source of gas flow in internal places is groundwater. There is a continuous development of radon measuring devices, and these measurements are often classified as long-term or short-term (Al-Azmi, 2008). The development includes risk indexes for evaluating radioactive values in building materials to determine the values of restrictions to be subjected to or for further investigations. These indexes are mainly based on 226Ra. 40K and 232Th contents (European Commission, 1999). But it was realized that risk indicators should also consider the 222Rn exhalation and exhalation characteristics of the building (van der Greaf, 2001; Tuccimei, 2006).
Radon travels with its daughters in the form of a solid radioactive substance to low ground, these radioactive particles enter fruits and animals, and then enter the human body. Radon decay products enter the air and smoke, and these particles can lead to lung cancer when inhaled and trapped in the lungs (BEIVR, 1999). World Health Organization data has shown that radon is the cause of 3 of 16 percent of lung cancers. Radon gas can cause a serious problem that damages DNA and leads to lung cancer (Vanasundari, 2012). This tells us that it is a health hazard (Archer, 1973; Entesar 2008; UNSCEAR 2000). The range of radon in the soil is at its widest from 10,000 to 50,000 Bq/m3 (Report, 1995).
The exhalation of radon from building materials depends not only on the concentration of radium but also on factors such as:
- The fraction of the resulting radon that is released from the grains of the material into their interstitial space, also known as the fracture emission strength
- The porosity of the material
- The surface preparation and covering of building materials (Shweikani,2009; Entesar, 2013; Moharram,2012).
The aim of the study is to determine the radioactive contamination or the concentration of radon gas in the different materials used in buildings in the Jazan region, KSA, and to compare radiation rates between them. If the concentration is more than normal rates, we can make a recommendation containing a list of multiple species and areas with high radiation rates.
2.1 Sampling
The radioactivity in building materials varies, it depends not only on the type of samples but also on the sampling areas. Therefore, different types of building materials were randomly collected from different areas in Jazan to measure radiation levels see table 1. One hundred and five samples of different building materials (sand - ceramic - granite – marble -cement - gypsum - bricks) were collected from Jazan region, Saudi Arabia. The samples were ground and analyzed to measure any radiological variation or radiological anomaly that might be present due to the difference in location.
Table 1: The different types of building materials.
|
Building material |
The types of brick |
||||
|
Red brick |
Cement bricks |
White insulating bricks |
Thermal bricks |
||
|
No |
S1 |
S2 |
S3 |
S4 |
|
|
Building material |
The types of Ceramic |
||||
|
Spanish ceramics |
Italian ceramics |
Saudi ceramics |
Egyptian ceramics |
Indian ceramics |
|
|
No |
S5 |
S6 |
S7 |
S8 |
S9 |
|
Building material |
The types of Send |
The types of gypsum |
|||
|
White sand |
Yellow sand |
gypsum 1 |
gypsum 2 |
||
|
No |
S10 |
S11 |
S12 |
S13 |
|
|
Building material |
The types of marble |
||||
|
Omani marble |
Turkish marble |
Italian yellow marble |
Spanish brown marble |
||
|
No |
S14 |
S15 |
S16 |
S17 |
|
|
Building material |
The types of Granite |
The cement |
|||
|
Najran granite |
Royal Rose Granite |
Royal Gold Granite |
|||
|
No |
S18 |
S19 |
S20 |
S21 |
|
2.3- Sample Preparation:
Various samples of building materials that are used in construction were collected in Jizan region. Table 1 shows the samples, where a number of samples of the same type were collected in order to take the average of the types used in construction. The radiation ratios may vary in the same type of building materials according to the withdrawal areas from which the raw materials are collected. Samples were ground, 200 grams of each type were taken and placed in clean containers. Each sample was placed in a glass chamber with the SSNTDs CR-39 reagent featuring optical transparency and high sensitivity as showen in figure 1. These cans are sealed and stored for 30 days, then the exposed detectors (CR-39) are collected and chemically etched with NaOH at 70 °C for 6 h. The etched reagents were washed with flushing water for 20 min. Path density (path/cm) was calculated on a CR-39 detector using optical microscopy (Zarrag, 2012; Rahaf, 2018).
2.4-Measurements and analysis:
The effective exposure time te in hours which measured by the relation:
where is the constant decay of radon and t is the exposure time
The equilibrium concentration of radon Ceq (Bq/m3) is determined from the track density by using the following relation:
Where K is the calibration factor of the CR39 detector which is determined by Rn-chamber (Entesar, 2021;Entesar, 2013).
Exhalation rates for radon are determined using the following relationships.
The mass exhalation rate (Em) (Bq/Kg.h) by:
Em =Ceq Vl / M ------------------3
and the surface exhalation rate (Ea)( Bq/m.h) by:
Ea= Ceq Vl/ A ------------------4
Where M is the mass of the sample (kg), A is the cross-section area of the cup (m2), and V is the effective volume of the cup in m3.
The radium activity (Rac) (Bq/Kg) can be determined by using mass exhalation as:
Rac = Em /λ --------------------------5
Alpha indexes are a basic indicator for evaluating the levels of excess radiation resulting from inhaling radon gas. The following relationship is used to determine the values of the alpha indexes.
The internationally recommended limit for the activity concentration of 226Ra in building materials, recommended by the European Commission, 1999, is 100 to 200 Becquerels per kilogram. This means that if the permissible values if they exceed 200, it is possible that the exhaled rates of radon gas could cause a cancer risk to the public. Therefore, calculating the values of radium and alpha indicators is very necessary for building materials, and this value gives the alpha indicator 1, which is the upper limit of the recommended values and must be adhered to preserve the health of the public.
The annual effective dose H (mSv/yr) was calculated from the following relation:
where F is the indoor equilibrium factor between radon and its progeny (F=0.4), C (B /qm3 ) is the mean radon concentration in air, D is the dose conversion factor (D=9 nSv/h per Bq/m3), and T is time (T=7000 hy−1) (EC, 1999; EC, 2012).
The calculation of the working level (WL) is based on the concentration of radon and its descendants in the air, which largely depends on the level of ventilation in the premises. The work level calculation also helps determine if the buildings comply with internationally permissible values. The level of work can be calculated by using the following equation:
The effective dose was calculated for members of the building users due to external irradiation caused by radon. The DFEXT code which concerned itself with the calculation of dose
The equilibrium concentrations of radon gas in collected samples are measured by the CR-39 detector. Figure 2 summarized the concentration of radon in different samples. The results showed that the highest value of the concentration of radioactivity in different building materials was 560.68 ± 44.24 Bq/kg in royal gold granite while the lowest concentrations of rad Omani marble with a value of 112.88 ± 39.20 Bq/kg. The average value of radon gas concentration for all samples of buildings used in the Kingdom of Saudi Arabia was 286.84 ± 33.35 Bq/Kg. The large variations in obtained values can be attributed to the variation in the radium concentration of soil and the presence of faults in the samples. The health and environmental protection agencies have recommended a safe limit of radon in soil for human beings. EC, (European Commission) has proposed a maximum contaminant level from 25 Bq/m3 in the sand to 500 Bq/m3 in stones for radon concentration (EC, 1999). These levels are set to represent a concentration that does not result in any significant risk to health over the lifetime of soil. Results reveal that 19% is higher than the recommended safe limit.
Figure 3 summarizes the annual effective dose in the different building samples. The results show a significant change between the values of radiation doses in the studied samples, ranging from 2.39±0.99 mSv / year in Omani marble to 11.85±1.11 mSv / year in Royal Gold Granite with an average value of 6.07±0.84 mSv / year. The change in values is attributed to the difference in the number of uranium atoms in the samples, which depends on the amount of uranium in the soil from which the samples were drawn. The International Commission on Radiological Protection (Entesar, 2021) reported that the dose limits for radon are (3-10 mSv/year). The results show approximately 19 % of the effective abrogation dose is above the recommended safe limit for ICRP.
The results in table 2 showed that the values of exhalation rates in the samples change due to the different places of production of the aggregated building materials. The difference in the country of production means the difference in the concentration of radium atoms in the samples. The values of mass exhalation rates in the samples ranged from 10.23 ± 0.04 in Omani marble to 50.76 ± 0.04 in Royal Gold Granite Bq/ kg.h, with an average of 25.99 ± 0.05 Bq/ kg. h. From the results, we find that the values of the mass exhalation rates of all building materials samples are less than the values recommended by the Organization for Economic Cooperation and Development (OECD, 2009), which is (370 Bq kg 1). The average values of surface exhalation rate were 547.94±0.64 Bq/m.h in bricks, 342.16±0.46 Bq/m.h in ceramics, 546.01±0.68 Bq/m.h in sand, 344.09±0.45 Bq/m.h in gypsum, 381.58±0.81Bq/m.h in marble, 841.10±0.69 Bq/m.h in granite, 186.91±0.25 Bq/m.h in cement.
Alpha index values determine the extent of the hazard affecting the public, so calculating alpha indexes is very necessary for building materials. The values of alpha indexes range from 0.2822 ± 0.0010 to 1.4007 ± 0.0011, and this value gives alpha index 1 higher than the upper limit of the recommended values. Values above the recommended limit were recorded in granite and red bricks, and the highest value was recorded in Royal Gold Granite. Therefore, it is preferable not to use granite in the interior finishes of buildings, and it is used only in the exterior facades. The results show that the average values for working levels ranged from 8.27 to 10.19 with a mean value of 5.87.
Figures 4&5 show the relationship between radium concentration, surface exhalation rate, and mass exhalation rate. The correlation of radium concentration with the quantity of radon can be confirmed by the quality factor R2, which is obtained from the correlation between radium concentration and surface exhalation rate, and mass exhalation rate of building materials. The results showed a linear agreement between radium concentration and expiratory rates. The value of the quality factor was very good R2 = 1 showing the correlation between the values. The value of the quality coefficient was a correlation between the values of radium concentration and exhalation rates.
Table 2: The values aerie exhalation rate EA (Bq/m.h), mass exhalation rate Em ( Bq/Kg.h), alpha index Iα (mBq/Kg), and working-level WL for building material.
|
No. |
EA (Bq/m.h) |
Em (Bq/Kg.h) |
Iα(mBq/Kg) |
WL |
|
|
S1 |
739.26±0.83 |
41.07±0.04 |
1.1333±0.0011 |
4.97 |
|
|
S2 |
489.63±0.24 |
27.20±0.01 |
0.7506±0.0003 |
1.44 |
|
|
S3 |
421.19±0.66 |
23.40±0.03 |
0.6457±0.0009 |
3.91 |
|
|
S4 |
541.67±0.82 |
30.09±0.04 |
0.8304±0.0011 |
4.88 |
|
|
S5 |
350.83±0.60 |
19.49±0.03 |
0.5378±0.0008 |
3.57 |
|
|
S6 |
377.82±0.54 |
20.99±0.03 |
0.5792±0.0007 |
3.19 |
|
|
S7 |
312.28±0.28 |
17.35±0.01 |
0.4787±0.0004 |
1.67 |
|
|
S8 |
293.00±0.59 |
16.28±0.03 |
0.4492±0.0008 |
3.54 |
|
|
S9 |
376.86±0.28 |
20.94±0.01 |
0.5777±0.0004 |
1.69 |
|
|
S10 |
519.50±0.91 |
28.86±0.05 |
0.7964±0.0012 |
16.21 |
|
|
S11 |
572.51±0.46 |
31.81±0.02 |
0.8777±0.0006 |
2.74 |
|
|
S12 |
311.32±0.62 |
17.30±0.03 |
0.4772±0.0009 |
8.04 |
|
|
S13 |
376.86±0.28 |
20.94±0.01 |
0.5777±0.0004 |
1.69 |
|
|
S14 |
184.09±0.71 |
10.23±0.04 |
0.2822±0.0010 |
8.57 |
|
|
S15 |
519.50±0.91 |
28.86±0.05 |
0.7964±0.0012 |
16.21 |
|
|
S16 |
510.83±0.86 |
28.38±0.04 |
0.7831±0.0012 |
7.30 |
|
|
S 17 |
215.90±0.76 |
11.99±0.04 |
0.3310±0.0009 |
8.88 |
|
|
S 18 |
767.21±0.66 |
42.62±0.03 |
1.1761±0.0009 |
7.17 |
|
|
S 19 |
842.39±0.63 |
46.80±0.03 |
1.2914±0.0009 |
5.90 |
|
|
S 20 |
913.71±0.80 |
50.76±0.04 |
1.4007±0.0011 |
10.19 |
|
|
S 21 |
186.98±0.25 |
10.39±0.01 |
0.2866±0.0004 |
1.52 |
|
|
average |
467.78±0.98 |
25.99±0.05 |
0.7171±0.0014 |
5.87 |
|
The CR-39 detector is useful in determining the radiation rates of radon gas and radium content in building materials collected from the Jazan region, Saudi Arabia. Based on the results obtained, it was found that the highest value of radon gas rates was in granite, the highest activity of radon gas was found in Royal Gold Granite, and the lowest value was in Omani marble. Radon values were variable in the building samples due to the different compositions of the samples and the number of raw materials withdrawn from the soil. The ascending order of the radiation rates in the samples was cement ˂ceramic ˂ gypsum ˂ marble ˂ sand ˂ brick ˂ granite and this corresponds to the variation in radium values found in common rock units. All values of radon gas fall within the internationally permissible limits recommended by the International Committee for Radiological Protection (200-600), except for granite, which recorded values higher than the permissible with an average of 841.10 ± 0.18Bq/Kg. The results showed that 19% of the radiation dose values were higher than the internationally permissible values. There was a good correlation between radium values and exhaled rates of radon. As a result, it is advised not to use granite inside homes and only place it on the front of the house.
No funding was obtained for this study
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Authorship statement
Entesar. H. EL-Araby: Conceptualization, Visualization, Methodology, Writing – review & editing, Validation, Software, Formal analysis. Doaa H. Shabaan: Conceptualization, Data curation, , Investigation, – Resources, original draft, Writing – review & editing.
- Ethical statement-Not Applicable
- Consent statement -Not Applicable
Data Availability Statement: Not Applicable
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No competing interests reported.