Radon activity concentrations and effective doses in ancient Egyptian tombs of the Valley of the Kings

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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 two-integral 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 m−3. 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 μSv per visit. The effective dose to tomb workers did not exceed the 20 mSv yr−1 limit.

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), Hafez et al (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 219Rn is negligible and the 55 s half-life prevents the 220Rn to move longer distances from its source, the 222Rn 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 limestone and other sedimentary rocks is about 25 Bq kg−1. 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).

Section snippets

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 μm 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

Results and discussion

The calibration coefficient η for LR-115 and CR-39 nuclear track detectors obtained from the calibration experiment are 0.036 and 0.18 α-tracks cm−2 day−1 per Bq m−3 of radon, respectively. These values are in good agreement with that reported by other investigators (Durrani and Ilic′, 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

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 yr−1 recommend by ICRP (1993), whereas for the tomb workers of

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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