Radon ( ) and its progeny is the main source of radioactivity in the environment. They enter the respiratory system after inhalation. The investigations indicated that Radon is the second cause for lung cancer. The main source of is (half life years). So its production is continuous despite its short half life. exists in the air, mines, groundwater, oil and natural gas. Also a lot of houses in our country were built on the big bed Granit stones and this Gas can enter the houses by Building materials and all individuals receive the radioactive radiation from Radon and its progeny. So it is necessary the calculation the critical organs' absorbed dose form Radon and its progeny. Using simulation of phantom and Monte Carlo methods, the calculations of absorbed dose from photon and electron decays from Radon and its progeny was presented. Materials and methods Among radon progeny, , only two isotopes: and , decay by emission of beta particles. Since the daughters may be produced at excitation states, there are gamma-rays, X-rays and conversion electrons after beta decay. In this work we used the adult man ORNL phantom. Since the Radon progeny attached to the aerosols in the air, enter the lungs after inhalation and decay in the lungs, so we can define the lungs as the main radiation source for input file of MCNP code. Calculations of organ absorbed doses ( ) were performed for gamma-rays, beta particles, conversion electrons and X-rays. Then the absorbed doses were reported per (Radon concentration measurement unit) in . Results Photon and electron absorbed doses were estimated for 23 organs with an uncertainty less than 2%. Then based on these data, whole body effective dose was obtained according to ICRP103 recommendation. As expected, the results show the lungs receive more absorbed dose than the other organs. Also, this study represents that the organ doses from X-rays can be omitted in comparison with other radiation organ doses; whereas conversion electrons should be considered in dosimetry calculations as well as beta and gamma-rays. Conclusion Some of electron and photon particles emitted by Radon progeny have enough energy to leave the lungs and deposit their energies in different organs. So, the dosimetry of electrons and photons is important, particularly, for situations with high levels of exposure to radon and radon's decay products. Radon-meters measure radon concentration in a good accuracy, and one can evaluate the corresponding organ and effective doses by multiplication of dose values per 1WLM by radon concentration in WLM. Therefore, the useful data sheets per radon concentration (WLM-1) should be estimated in order to increase the accuracy of dose evaluations for people exposed to radon and its progeny.

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