Introduction The potential hazards posed by exposure to radiation from radon have been of great concern worldwide, since it is especially associated with increased risk of lung cancer. Some radioisotopes of radon progeny deposited in the human lungs emit β particles followed by the γ rays. While γ rays are comparatively less damaging to the respiratory system than α and β particles, it is the principal deposited energy in other organs. Materials and Methods In order to establish a quantitative estimate of hazards caused by the radiation, this paper studies the photon absorbed doses from radon progeny in all major organs of the human body through a simulation of the Oak Ridge National Laboratory (ORNL) adult phantom using MCNPX2.4.0 Monte Carlo code and calculations which were performed in photon/electron mode. Results Effective dose due to photons from radon progeny deposited in the human lungs was about 1.69 μSvWLM-1. Based on UNSCEAR2006 reports, the effective dose of these photons per year is about 5.7610-1mSv in for radon concentration of 31000 Bq/m3 (the maximum concentration of radon in Iran). Therefore, this value is comparable with 1mSv (The annual allowable effective dose). Conclusion The dosimetry of photons particularly in areas with high levels of exposure to radon and radon\'s decay products is important because all organs receive the photon absorbed dose from radon progeny

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