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Radon activity concentrations and effective doses in ancient Egyptian tombs of the Valley of the Kings
Applied Radiation and Isotopes 55 (2001) 355–362
Radon activity concentrations and effective doses in ancient Egyptian tombs of the Valley of the Kings A.F. Hafez*, A.S. Hussein Faculty of Science, Department of Physics, University of Alexandria, 21511 Alexandria, Egypt Received 6 June 2000; received in revised form 8 January 2001; accepted 6 February 2001
Abstract Radon concentrations and equilibrium factors were measured in three pharaonic tombs during the year 1998. The tombs, which are open to the public are located in a limestone wadi on the West Bank of the River Nile at Luxor, 650 km south of Cairo. The radon activity concentration and equilibrium factor were measured monthly by twointegral nuclear track detectors (bare and diffusion detectors). Seasonal variation of radon concentrations, with summer maximum and winter minimum were observed in all tombs investigated. The yearly mean radon activity concentrations inside the tombs ranged from 540 to 3115 Bq m3. The mean equilibrium factor over a year was found to be 0.25 and 0.32 inside and at the entrance, respectively. Estimated annual effective doses to tour guides ranged from 0.33 to 1.90 mSv, visitors receive doses from 0.65 to 3.80 mSv per visit. The effective dose to tomb workers did not exceed the 20 mSv yr1 limit. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Radon; Seasonal variation; Effective dose; Polymeric track detectors; Valley of the Kings; Egypt
1. Introduction In recent years, it had been recognized that increased concentrations of radon and its progeny can present a potential health risk from inhalation of radon gas and its daughters, particularly when concentrated in some enclosures such as workplaces, tight houses, mines, caves and old Egyptian tombs (Hafez et al., 2000,2001; Hakl et al., 1997; Kobal et a1., 1987; Wang et al., 1996). The sources of radon isotopes (222Rn, 220Rn, 219Rn) in underground cavities, e.g., caves or archaeological Egyptian tombs are the bedrock and deposits. Radon levels in caves are primarily influenced by the activity of their parents (226Ra, 224Ra, 223Ra) present in the limestone environment. Because the concentration of 219 Rn is negligible and the 55 s half-life prevents the 220 Rn to move longer distances from its source, the 222 Rn isotope of 3.8 d half-life is the main constituent in different substances, e.g., cave air, soil, tomb and water. The worldwide average of 226Ra (238U) activity in *Corresponding author.
limestone and other sedimentary rocks is about 25 Bq kg1. This minute quantity of 226Ra results in relatively high values of radon in underground cavities. The present article deals with the measurement of radon in three ancient Egyptian tombs in the Valley of the Kings. The Valley of the Kings is a remote limestone wadi on the west bank of the River Nile at Luxor, 650 km south of Cairo. Cut into its walls are the tombs of the Egyptian kings of the New Kingdom (1550–1070 BC) such as Tutankhamen, Merenptah and Thutmes III (Kent, 2000). These tombs are renowned for their beauty and attract thousands of visitors each year. Therefore, a program for estimating radon levels and effective doses to workers, tour guides and visitors has been started in different archaeological places in the country. As a part of this project the radon activity concentration measurements as well as the effective dose estimation is being carried out for the first time inside the above-mentioned three pharaonic tombs. The radon activity concentrations and equilibrium factor were measured by two integral nuclear track detectors (bare and diffusion detectors).
0969-8043/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 0 1 ) 0 0 0 6 5 - 3
356
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2. Materials and methods The radon measuring device is a diffusion cup of aluminum of 7 cm diameter and 11 cm length. The cup is equipped at its bottom with two internal polymeric nuclear track detectors of different sensitivity (LR-115 and CR-39). Moreover, the cup is covered by 50 mm thick PE foil to keep out the thoron and the radon daughters from the internal detectors (Hafez and Somogyi, 1986; Hafez et al., 2000). An external (bare) LR-115 detector was also fixed outside the cup. This device was used for simultaneous estimation of the radon activity concentration and the equilibrium factor (Somogyi et al., 1984). The diffusion cups were calibrated at the National Institute for Measurements and Standards (NIS), Cairo, Egypt. During the calibration process, the cups were placed inside radon chamber with concentration of 17.4 0.5 kBq m3 for different exposure times. Long-term integrated radon measurements were performed in the air of the concerned three tombs as shown in Figs. 1–3. For this purpose, 10 measuring cups
Fig. 1. Plan of Tutankhamen’s tomb showing cup locations.
were deployed in the air of the tombs. The detectors were changed monthly. In every measuring location, the cups were hung about 2 m above the floor near the route of the guided visitors. The duration of the survey was one year from January to December 1998. Following recovery, the detectors were chemically etched in a freshly prepared NaOH solution; 2.5 M at 608C for 2 h for LR-115 and 6.25 M at 708C for 5 h for CR-39 detectors. The LR-115 and CR-39 a-particle track densities were determined by means of an optical microscope of magnification of 600x. The effective dose of inhaled radon and its progeny can be estimated if the radon activity concentration in the air is known as well as their equilibrium factor and dose conversion factors. If radon and its progeny
Fig. 2. Plan of Merenptah’s tomb showing cup locations.
A.F. Hafez, A.S. Hussein / Applied Radiation and Isotopes 55 (2001) 355–362
357
where k is the attenuation factor for radon transport through the PE foil (Hafez and Somogyi, 1986), Z is the calibration coefficient of the radon measuring device in terms of a- tracks. cm2 day1 per Bq m3 and T is the exposure time, F ¼ aR b;
for 1:25R53;
ð2Þ
where R ¼ k re =ri and a ¼ 0:50; b ¼ 0:53 . The effective dose E of the radon and its progeny can be calculated by means of the following equation (UNSCEAR, 1993): E ¼ C tðer þ ed FÞ;
ð3Þ
where er ¼ 0:17 nSv h1 per Bq m3 and ed ¼ 9 nSv h1 per Bq m3 are the conversion factors for radon dissolved in tissues and radon daughters, respectively, and tðhÞ is the residence time in the tomb.
3. Results and discussion
Fig. 3. Plan of the tomb Thutmes III showing cup locations.
activity concentrations are measured in the air by means of the external and internal LR-115, the respective track densities re and ri are related to the concentration of 222 Rn (C) and the equilibrium factor as follows (Somogyi, 1984; Planinic et al., 1997): C¼
ri ; kZT
ð1Þ
The calibration coefficient Z for LR-115 and CR-39 nuclear track detectors obtained from the calibration experiment are 0.036 and 0.18 a-tracks cm2 day1 per Bq m3 of radon, respectively. These values are in good agreement with that reported by other investigators (Durrani and Ilic0 , 1997; Somogyi, 1990; Mahlobo et al., 1995). The radon activity concentration was calculated using Eq. (1). The yearly mean values of radon activity concentrations, the maximum and the minimum concentrations as measured in the tombs of Tutankhamen, Merenptah and Thutmes III in the Valley of the Kings are summarized in Table 1. The mean radon activity concentration was the highest in the tomb of Thutmes III. The high level of radon may be due to the tomb being cut in the mountain. Generally, tombs, situated in highly fractured rocks (Fig. 4), have numerous openings and fissures leading from the top into the tomb, carrying radon laden air as will be discussed later in this section. In addition, the tomb has a narrow entrance located
Table 1 Summary of Rn-activity concentrations measured in the tombs of Tutankhamen, Merenptah and Thutmes III from January to December 1998 Tomb
Tutankhamen Merenptah Thutmes III
Location
Entrance Inside Entrance Inside Entrance Inside
Radon concentration (Bq m3) Yearly mean SD
Max
Min
86 50 540 420 76 60 760 790 2166 2302 3115 3500
141 1310 218 2303 6596 9298
24 26 21 21 28 28
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Fig. 4. Schematic view of locations of the tombs of Tutankhamen, Merenptah and Thutmes III in the Valley of the Kings.
inside the tunnel leading into the tomb as shown in Figs. 3 and 4. Figs. 5–7 show the monthly variation of radon activity concentrations measured in the air of the tombs. From these data, it is clear that maximum radon levels were detected during summer and minimum values were measured during winter. The results also show that the lowest radon concentration occurs at the entrance area and rise significantly further into the tomb. These findings are similar to the reported data of Szerbin (1996), Hakl et al. (1997), Duenas et al. (1999), Jovanivic (1995) and Lively and Krafthefer (1995). Our results could be explained similarly to the model of air circulation in caves (Atkinson et al., 1983; Hunyadi et al., 1991; Hakl et al., 1995; G!eczy et al., 1989). This model is suitable for describing the air movements in nearly horizontally situated underground ancient Egyptian tombs, embedded in a rock with an advanced fracture system. It is assumed that due to the high thermal capacity of the bedrock the temperature inside the tomb is independent of the seasons. In winter, when the temperature in the tomb and of the fracture system is higher than the outside one, the so-called ‘‘chimney effect’’ takes place, that is: the warm internal air lifts up to the external surface through the fracture system. For the replacement of the left air, the cold low radon concentration atmospheric air flows into the tomb 3 Fig. 5. Seasonal variation of the Rn-activity concentration in the air of Tutankhamen’s tomb.
A.F. Hafez, A.S. Hussein / Applied Radiation and Isotopes 55 (2001) 355–362
Fig. 6. Seasonal variation of the Rn-activity concentration in the air of Merenptah’s tomb.
through the entrance resulting in winter minimum. In summer, when the external temperature exceeds the internal one, the direction of the airflow changes to the opposite. The colder air in the tomb and in the fracture system is denser than the external air, thus the air flows out of the tomb through the entrance ‘‘inverse chimney effect’’. The air balance is recovered through the radon rich fracture system giving account for the summer maximum. In both cases, the speed of such air motions is proportional to a first approximation to dT=f , where dT is the temperature difference between the tomb and outside and f is a friction factor. Fig. 8 shows the correlation between the seasonal variation of the mean radon activity concentration measured in the air of the tombs and the mean external temperature. This observation agrees with the previously . observed data in Szemlohegy cave, Buda Mountain in Hungary (Hunyadi et al., 1991; Hakl et al., 1992) and strongly supports the air circulation model.
359
Fig. 7. Seasonal variation of the Rn-activity concentration in the air of the tomb of Thutmes III.
The equilibrium factor F between radon and its daughters in the atmosphere of the three concerned tombs was estimated by the method described by Somogyi et al. (1984) and developed by Planinic et al. (1997). To carry out this method a graph was obtained between the internal track density (ri )and external one (re) measured from January to December 1998 for the inside of the three tombs and another one for the entrances as shown in Figs. 9 and 10. Consequently using Eq. (2), the yearly mean equilibrium factor was 0.32 and 0.25 for the entrance and the inside of the tombs studied, respectively. These values depend on the air exchange rate, the aerosol concentration in the air, size and structure of the tombs. According to literature, values of the equilibrium factor within limestone caves or tombs vary between 0.04 and 0.95 (Hyland and Gunn, 1994; Duffy et al., 1996; Szerbin, 1996; Hafez et al., 1997).
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The mean time spent in a tomb by the workers, the tour guides and the tourists was assessed on the personal communication with those persons and the management. The annual residence time in a tomb was given as 2400 h and 250 h for the workers and the tour guides, respectively. A mean visiting time of 0.5 h was assumed for the visitors. In Egypt, no legislated action level has been adopted for radon in the workplace. The International Commission for Radiological Protection (ICRP, 1993) approach to radon in the workplace is based on the philosophy that workers who are not regarded as occupationally exposed workers are usually treated as members of the public. In this case, members of the public means residents in domestic dwellings. Therefore, the acceptable level of the effective dose to a worker should be the same as the acceptable effective dose to a resident in his own home. Using Eq. (3), the effective dose values to workers, tour guides and visitors were calculated based on the yearly mean value of both radon activity concentration and equilibrium factor for the inside and the entrance of each tomb as summarized in Table 2. The annual effective doses to workers ranged from 0.56 to 18.10 mSv for the tombs of Tutankhamen, Merenptah and Thutmes III. The annual effective doses to tour guides varied from 0.33 to 1.90 mSv. Also, the 3 Fig. 8. The correlation between the seasonal variation of the mean Rn-activity concentration in the air of the tombs and the mean external temperature.
Fig. 9. The correlation between the internal ri and external re track densities measured from January to December, 1998 inside the three tombs.
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Fig. 10. The correlation between the internal ri and external re track densities measured from January to December, 1998 at the entrances of the tombs.
Table 2 Effective dose from radon ‘‘222Rn’’ and its decay products to worker, tour guide and tourist in the tombs of Tutankhamen, Merenptah and Thutmes III Tomb
Tutankhamen Merenptah Thutmes III
Location
Entrance Inside Entrance Inside Entrance Inside
Effective dose Worker mSv yr1
Tour guide mSv yr1
Tourist mSv per visit
0.63 3.12 0.56 4.41 15.90 18.10
} 0.33 } 0.46 } 1.90
} 0.65 } 0.92 } 3.80
effective dose to a tourist inside a tomb was found to range from 0.65 to 3.80 mSv per visit as shown in Table 2. These values are comparable to those observed by Szerbin (1996), Duffy et al. (1996), Hyland and Gunn (1994) and Solomon et al. (1995). As it can be seen from Table 2, the calculated effective doses to tour guides and visitors are less than the lower bound of the action levels 3–10 mSv yr1, whereas the effective doses to the tomb workers of Tutankhamen and Merenptah are within the action levels (ICRP, 1993). The effective doses to the tomb workers of Thutmes III varied from 15.90 to 18.10 mSv yr1. This suggests that some workers may be receiving effective doses in excess of 10 mSv yr1, the upper bound of the action levels 310 mSv yr1.
4. Conclusions The results of this study showed that higher radon levels were detected inside three ancient Egyptian tombs during summer when the direction of air flux was from the tombs to the outer atmosphere, and conversely, lower radon concentrations were measured while air moving into the tombs during winter. All the estimated effective doses to tour guides and visitors were found to be less than the lower bound of the action levels 3–10 mSv yr1 recommend by ICRP (1993), whereas for the tomb workers of Tutankhamen and Merenptah the effective doses were within the action levels. In addition, the highest mean radon activity concentration was present inside the tomb of Thutmes III, and it was over the action levels 500–1500 Bq m3,
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giving rise to elevated occupational exposures. This has implication for tomb workers, because of the increased potential health risk associated with exposure to elevated radon levels.
Acknowledgements The authors wish to thank Supreme Council of Antiquities, Ministry of Culture for giving the permission to measure radon concentration in the tombs of the Valley of the Kings, Luxor. The authors are also thankful to Prof. Dr. M.A. El-Fiki, Prof. Dr. H.M. Eissa and Dr. A.R. El-Sersy for providing calibration facilities at National Institute for Standards (NIS).
References Atkinson, T.C., Smart, P.L., Wigley, T.M.L., 1983. Climate and natural radon levels in Castlegurad cave, Columbia Icefields, Alberta, Canada. Ac. Alp. Res. 15, 487. Duenas, C., Fernandez, M.C., Canete, S., Carletero, J., Ligher, E., 1999. 222Rn concentrations, natural flow rate and the radiation exposure levels in the Nerja cave. Atmos. Environ. 33, 510. Duffy, J.T., Madden, J.S., Macking, G.M., McGarry, A.T., 1996. A reconnaissance survey of radon in show caves in Ireland. Environ. Inter. 22, S415. Durrani, S.A., Ilic0 , R., (Eds.), 1997. Radon Measurements by Etched Track Detectors, World Scientific, Singapore. G!eczy, G., Csige, I., Somogyi, G., 1988. Air circulation in caves traced by natural radon. In: Kosa, A. (Ed.), Proceedings of the 10th International Congress of Speleology, Vol. 2. Hungarian Spelological Socity, Budapest, p. 615. Hafez, A.F., Kotb, M.A., Khalil, G.I., 1997. Indoor radon and its progeny concentrations in archaeological places in Alexandria, Egypt. Radiat. Meas. 28, 671. Hafez, A.F., Hussein, A.S., Rasheed, N.M., 2000. Radon measurements in underground metro stations in Cairo city, Seventh Conference of Nuclear Science and Applications, Cairo, Egypt, 6–10 February, 2000. Hafez, A.F., Hussein, A.S., Rasheed, N.M., 2001. A study of radon and thoron release from Egyptian building materials using polymeric nuclear track detectors. Appl. Radiat. Isot. 54, 291. Hafez, A.F., Somogyi, G., 1986. Determinations of radon and thoron permeability through some plastic by track technique. Nucl. Tracks 12, 697. . ocsik, . Hakl, J., Hunyadi, I., Csige, I., G!eczy, L!en!art, L., Tor I., 1992. Outline of natural radon occurrences on karstic terrains of Hungary. Radiat. Prot. Dosim. 45, 183.
Hakl, J., Hunyadi, I., V!arhegyi, A., 1995. The study of subsurface transport dynamics based on monitoring in caves. In: Dubois, C. (Ed.), Gas Geochemistry Science Reviews. Nortwoody, pp. 391–398. Hakl, J., Hunyadi, I., Csige, I., G!eczy, G., L!en!art, L., V!arhegyi, A., 1997. Radon transport phenomena studied in karst caves, International experiences on radon levels and exposures. Radiat. Meas. 28, 675. Hunyadi, I., Hakl, J., L!en!art, L., G!eczy, G., Csige, I., 1991. Regular subsurface radon measurements in Hungarian karstic regions. Nucl. Tracks Radiat. Meas. 19, 321. Hyland, R., Gunn, J., 1994. International comparison of cave radon concentration identifying the potential alpha radiation risks to British cave users. Health Phys. 67, 176. ICRP 65-International Commission on Radiological Protection, 1993. Protection Against Radon-222 at Home and at Work. Pergamon Press, Oxford. Jovanivic, P., 1995. Radon measurements in karst cave in Slovenia. Presented at: Sixth. International Symposium on the Nature Radiation Environment, Montreal, Quebec, Canada, 5–9 June. Kent, R.W., 2000. Atlas of the Valley of the Kings. American University, Cario, Egypt. Kobal, I., Smodies, B., Burger, J., Skofjancec, M., 1987. Atmospheric 222Rn in tourist caves of Slovenia, Yogoslavia. Health Phys. 52, 473. Lively, R.S., Krafthefer, B.C., 1995. 222Rn variations in mystery cave, Minnesota. Health Phys. 68, 590. Mahlobo, M., Nsibande, M., Farid, S.M., 1995. Indoor 222Rn measurements in Swaziland with solid state nuclear track detector. J. Environ. Radioact. 27, 261. Planinic, J., Radolic, V., Fai, Z., Surveljak, B., 1997. Radon equilibrium factor and aerosols. Nucl. Inst. and Meth. A 396, 414. Solomon, S.B., Langroo, R. Lyons, R. G., James, J.M., 1995. Radon exposure to tour guides in Australian show caves.Presented at: Sixth International Symposium on the Natural Radiation Environment, Montreal, Quebec, Canada, 5–9 June. Somogyi, G., 1990. The environmental behavior of radium, Technical Reports Series No. 310, Vol. 1. IAEA, Vienna (Chapters 3–8). Somogyi, G., Paripas, B., Varga, Zs., 1984. Measurement of radon, radon daughters and thoron concentration by multidetector devices. Nucl. Tracks 8, 423. Szerbin, P., 1996. Radon concentrations and exposure levels in Hungarian caves. Health Phys. 71, 362. UNSCEAR-United Nations Scientific Committee on the Effects of Atomic Radiation, 1993. Sources and Effects of Ionizing Radiation. United Nations, New York. Wang, Z-Y., Lubin, J.H., Wang, L-D., Conrath, S., Zhang, S-Z., Kleinerman, R., Shang, B., Bao, S-X., Cao, P-Y., Lei, S-W., Bioce Jr., J.D., 1996. Radon measurements in underground dwellings from two prefectures in China. Health Phys. 70, 192.
Radon activity concentrations and effective doses in ancient Egyptian tombs of the Valley of the Kings A.F. Hafez*, A.S. Hussein Faculty of Science, Department of Physics, University of Alexandria, 21511 Alexandria, Egypt Received 6 June 2000; received in revised form 8 January 2001; accepted 6 February 2001
Abstract Radon concentrations and equilibrium factors were measured in three pharaonic tombs during the year 1998. The tombs, which are open to the public are located in a limestone wadi on the West Bank of the River Nile at Luxor, 650 km south of Cairo. The radon activity concentration and equilibrium factor were measured monthly by twointegral nuclear track detectors (bare and diffusion detectors). Seasonal variation of radon concentrations, with summer maximum and winter minimum were observed in all tombs investigated. The yearly mean radon activity concentrations inside the tombs ranged from 540 to 3115 Bq m3. The mean equilibrium factor over a year was found to be 0.25 and 0.32 inside and at the entrance, respectively. Estimated annual effective doses to tour guides ranged from 0.33 to 1.90 mSv, visitors receive doses from 0.65 to 3.80 mSv per visit. The effective dose to tomb workers did not exceed the 20 mSv yr1 limit. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Radon; Seasonal variation; Effective dose; Polymeric track detectors; Valley of the Kings; Egypt
1. Introduction In recent years, it had been recognized that increased concentrations of radon and its progeny can present a potential health risk from inhalation of radon gas and its daughters, particularly when concentrated in some enclosures such as workplaces, tight houses, mines, caves and old Egyptian tombs (Hafez et al., 2000,2001; Hakl et al., 1997; Kobal et a1., 1987; Wang et al., 1996). The sources of radon isotopes (222Rn, 220Rn, 219Rn) in underground cavities, e.g., caves or archaeological Egyptian tombs are the bedrock and deposits. Radon levels in caves are primarily influenced by the activity of their parents (226Ra, 224Ra, 223Ra) present in the limestone environment. Because the concentration of 219 Rn is negligible and the 55 s half-life prevents the 220 Rn to move longer distances from its source, the 222 Rn isotope of 3.8 d half-life is the main constituent in different substances, e.g., cave air, soil, tomb and water. The worldwide average of 226Ra (238U) activity in *Corresponding author.
limestone and other sedimentary rocks is about 25 Bq kg1. This minute quantity of 226Ra results in relatively high values of radon in underground cavities. The present article deals with the measurement of radon in three ancient Egyptian tombs in the Valley of the Kings. The Valley of the Kings is a remote limestone wadi on the west bank of the River Nile at Luxor, 650 km south of Cairo. Cut into its walls are the tombs of the Egyptian kings of the New Kingdom (1550–1070 BC) such as Tutankhamen, Merenptah and Thutmes III (Kent, 2000). These tombs are renowned for their beauty and attract thousands of visitors each year. Therefore, a program for estimating radon levels and effective doses to workers, tour guides and visitors has been started in different archaeological places in the country. As a part of this project the radon activity concentration measurements as well as the effective dose estimation is being carried out for the first time inside the above-mentioned three pharaonic tombs. The radon activity concentrations and equilibrium factor were measured by two integral nuclear track detectors (bare and diffusion detectors).
0969-8043/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 0 1 ) 0 0 0 6 5 - 3
356
A.F. Hafez, A.S. Hussein / Applied Radiation and Isotopes 55 (2001) 355–362
2. Materials and methods The radon measuring device is a diffusion cup of aluminum of 7 cm diameter and 11 cm length. The cup is equipped at its bottom with two internal polymeric nuclear track detectors of different sensitivity (LR-115 and CR-39). Moreover, the cup is covered by 50 mm thick PE foil to keep out the thoron and the radon daughters from the internal detectors (Hafez and Somogyi, 1986; Hafez et al., 2000). An external (bare) LR-115 detector was also fixed outside the cup. This device was used for simultaneous estimation of the radon activity concentration and the equilibrium factor (Somogyi et al., 1984). The diffusion cups were calibrated at the National Institute for Measurements and Standards (NIS), Cairo, Egypt. During the calibration process, the cups were placed inside radon chamber with concentration of 17.4 0.5 kBq m3 for different exposure times. Long-term integrated radon measurements were performed in the air of the concerned three tombs as shown in Figs. 1–3. For this purpose, 10 measuring cups
Fig. 1. Plan of Tutankhamen’s tomb showing cup locations.
were deployed in the air of the tombs. The detectors were changed monthly. In every measuring location, the cups were hung about 2 m above the floor near the route of the guided visitors. The duration of the survey was one year from January to December 1998. Following recovery, the detectors were chemically etched in a freshly prepared NaOH solution; 2.5 M at 608C for 2 h for LR-115 and 6.25 M at 708C for 5 h for CR-39 detectors. The LR-115 and CR-39 a-particle track densities were determined by means of an optical microscope of magnification of 600x. The effective dose of inhaled radon and its progeny can be estimated if the radon activity concentration in the air is known as well as their equilibrium factor and dose conversion factors. If radon and its progeny
Fig. 2. Plan of Merenptah’s tomb showing cup locations.
A.F. Hafez, A.S. Hussein / Applied Radiation and Isotopes 55 (2001) 355–362
357
where k is the attenuation factor for radon transport through the PE foil (Hafez and Somogyi, 1986), Z is the calibration coefficient of the radon measuring device in terms of a- tracks. cm2 day1 per Bq m3 and T is the exposure time, F ¼ aR b;
for 1:25R53;
ð2Þ
where R ¼ k re =ri and a ¼ 0:50; b ¼ 0:53 . The effective dose E of the radon and its progeny can be calculated by means of the following equation (UNSCEAR, 1993): E ¼ C tðer þ ed FÞ;
ð3Þ
where er ¼ 0:17 nSv h1 per Bq m3 and ed ¼ 9 nSv h1 per Bq m3 are the conversion factors for radon dissolved in tissues and radon daughters, respectively, and tðhÞ is the residence time in the tomb.
3. Results and discussion
Fig. 3. Plan of the tomb Thutmes III showing cup locations.
activity concentrations are measured in the air by means of the external and internal LR-115, the respective track densities re and ri are related to the concentration of 222 Rn (C) and the equilibrium factor as follows (Somogyi, 1984; Planinic et al., 1997): C¼
ri ; kZT
ð1Þ
The calibration coefficient Z for LR-115 and CR-39 nuclear track detectors obtained from the calibration experiment are 0.036 and 0.18 a-tracks cm2 day1 per Bq m3 of radon, respectively. These values are in good agreement with that reported by other investigators (Durrani and Ilic0 , 1997; Somogyi, 1990; Mahlobo et al., 1995). The radon activity concentration was calculated using Eq. (1). The yearly mean values of radon activity concentrations, the maximum and the minimum concentrations as measured in the tombs of Tutankhamen, Merenptah and Thutmes III in the Valley of the Kings are summarized in Table 1. The mean radon activity concentration was the highest in the tomb of Thutmes III. The high level of radon may be due to the tomb being cut in the mountain. Generally, tombs, situated in highly fractured rocks (Fig. 4), have numerous openings and fissures leading from the top into the tomb, carrying radon laden air as will be discussed later in this section. In addition, the tomb has a narrow entrance located
Table 1 Summary of Rn-activity concentrations measured in the tombs of Tutankhamen, Merenptah and Thutmes III from January to December 1998 Tomb
Tutankhamen Merenptah Thutmes III
Location
Entrance Inside Entrance Inside Entrance Inside
Radon concentration (Bq m3) Yearly mean SD
Max
Min
86 50 540 420 76 60 760 790 2166 2302 3115 3500
141 1310 218 2303 6596 9298
24 26 21 21 28 28
358
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Fig. 4. Schematic view of locations of the tombs of Tutankhamen, Merenptah and Thutmes III in the Valley of the Kings.
inside the tunnel leading into the tomb as shown in Figs. 3 and 4. Figs. 5–7 show the monthly variation of radon activity concentrations measured in the air of the tombs. From these data, it is clear that maximum radon levels were detected during summer and minimum values were measured during winter. The results also show that the lowest radon concentration occurs at the entrance area and rise significantly further into the tomb. These findings are similar to the reported data of Szerbin (1996), Hakl et al. (1997), Duenas et al. (1999), Jovanivic (1995) and Lively and Krafthefer (1995). Our results could be explained similarly to the model of air circulation in caves (Atkinson et al., 1983; Hunyadi et al., 1991; Hakl et al., 1995; G!eczy et al., 1989). This model is suitable for describing the air movements in nearly horizontally situated underground ancient Egyptian tombs, embedded in a rock with an advanced fracture system. It is assumed that due to the high thermal capacity of the bedrock the temperature inside the tomb is independent of the seasons. In winter, when the temperature in the tomb and of the fracture system is higher than the outside one, the so-called ‘‘chimney effect’’ takes place, that is: the warm internal air lifts up to the external surface through the fracture system. For the replacement of the left air, the cold low radon concentration atmospheric air flows into the tomb 3 Fig. 5. Seasonal variation of the Rn-activity concentration in the air of Tutankhamen’s tomb.
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Fig. 6. Seasonal variation of the Rn-activity concentration in the air of Merenptah’s tomb.
through the entrance resulting in winter minimum. In summer, when the external temperature exceeds the internal one, the direction of the airflow changes to the opposite. The colder air in the tomb and in the fracture system is denser than the external air, thus the air flows out of the tomb through the entrance ‘‘inverse chimney effect’’. The air balance is recovered through the radon rich fracture system giving account for the summer maximum. In both cases, the speed of such air motions is proportional to a first approximation to dT=f , where dT is the temperature difference between the tomb and outside and f is a friction factor. Fig. 8 shows the correlation between the seasonal variation of the mean radon activity concentration measured in the air of the tombs and the mean external temperature. This observation agrees with the previously . observed data in Szemlohegy cave, Buda Mountain in Hungary (Hunyadi et al., 1991; Hakl et al., 1992) and strongly supports the air circulation model.
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Fig. 7. Seasonal variation of the Rn-activity concentration in the air of the tomb of Thutmes III.
The equilibrium factor F between radon and its daughters in the atmosphere of the three concerned tombs was estimated by the method described by Somogyi et al. (1984) and developed by Planinic et al. (1997). To carry out this method a graph was obtained between the internal track density (ri )and external one (re) measured from January to December 1998 for the inside of the three tombs and another one for the entrances as shown in Figs. 9 and 10. Consequently using Eq. (2), the yearly mean equilibrium factor was 0.32 and 0.25 for the entrance and the inside of the tombs studied, respectively. These values depend on the air exchange rate, the aerosol concentration in the air, size and structure of the tombs. According to literature, values of the equilibrium factor within limestone caves or tombs vary between 0.04 and 0.95 (Hyland and Gunn, 1994; Duffy et al., 1996; Szerbin, 1996; Hafez et al., 1997).
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The mean time spent in a tomb by the workers, the tour guides and the tourists was assessed on the personal communication with those persons and the management. The annual residence time in a tomb was given as 2400 h and 250 h for the workers and the tour guides, respectively. A mean visiting time of 0.5 h was assumed for the visitors. In Egypt, no legislated action level has been adopted for radon in the workplace. The International Commission for Radiological Protection (ICRP, 1993) approach to radon in the workplace is based on the philosophy that workers who are not regarded as occupationally exposed workers are usually treated as members of the public. In this case, members of the public means residents in domestic dwellings. Therefore, the acceptable level of the effective dose to a worker should be the same as the acceptable effective dose to a resident in his own home. Using Eq. (3), the effective dose values to workers, tour guides and visitors were calculated based on the yearly mean value of both radon activity concentration and equilibrium factor for the inside and the entrance of each tomb as summarized in Table 2. The annual effective doses to workers ranged from 0.56 to 18.10 mSv for the tombs of Tutankhamen, Merenptah and Thutmes III. The annual effective doses to tour guides varied from 0.33 to 1.90 mSv. Also, the 3 Fig. 8. The correlation between the seasonal variation of the mean Rn-activity concentration in the air of the tombs and the mean external temperature.
Fig. 9. The correlation between the internal ri and external re track densities measured from January to December, 1998 inside the three tombs.
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Fig. 10. The correlation between the internal ri and external re track densities measured from January to December, 1998 at the entrances of the tombs.
Table 2 Effective dose from radon ‘‘222Rn’’ and its decay products to worker, tour guide and tourist in the tombs of Tutankhamen, Merenptah and Thutmes III Tomb
Tutankhamen Merenptah Thutmes III
Location
Entrance Inside Entrance Inside Entrance Inside
Effective dose Worker mSv yr1
Tour guide mSv yr1
Tourist mSv per visit
0.63 3.12 0.56 4.41 15.90 18.10
} 0.33 } 0.46 } 1.90
} 0.65 } 0.92 } 3.80
effective dose to a tourist inside a tomb was found to range from 0.65 to 3.80 mSv per visit as shown in Table 2. These values are comparable to those observed by Szerbin (1996), Duffy et al. (1996), Hyland and Gunn (1994) and Solomon et al. (1995). As it can be seen from Table 2, the calculated effective doses to tour guides and visitors are less than the lower bound of the action levels 3–10 mSv yr1, whereas the effective doses to the tomb workers of Tutankhamen and Merenptah are within the action levels (ICRP, 1993). The effective doses to the tomb workers of Thutmes III varied from 15.90 to 18.10 mSv yr1. This suggests that some workers may be receiving effective doses in excess of 10 mSv yr1, the upper bound of the action levels 310 mSv yr1.
4. Conclusions The results of this study showed that higher radon levels were detected inside three ancient Egyptian tombs during summer when the direction of air flux was from the tombs to the outer atmosphere, and conversely, lower radon concentrations were measured while air moving into the tombs during winter. All the estimated effective doses to tour guides and visitors were found to be less than the lower bound of the action levels 3–10 mSv yr1 recommend by ICRP (1993), whereas for the tomb workers of Tutankhamen and Merenptah the effective doses were within the action levels. In addition, the highest mean radon activity concentration was present inside the tomb of Thutmes III, and it was over the action levels 500–1500 Bq m3,
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giving rise to elevated occupational exposures. This has implication for tomb workers, because of the increased potential health risk associated with exposure to elevated radon levels.
Acknowledgements The authors wish to thank Supreme Council of Antiquities, Ministry of Culture for giving the permission to measure radon concentration in the tombs of the Valley of the Kings, Luxor. The authors are also thankful to Prof. Dr. M.A. El-Fiki, Prof. Dr. H.M. Eissa and Dr. A.R. El-Sersy for providing calibration facilities at National Institute for Standards (NIS).
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