Measurement of 238 U, 232 Th, 222 Rn and 220 Rn Contents in Optical Contact Lenses: Resulting Alpha and Beta Equivalent Doses to the Eye Tissues of Adult Patients.

ABSTRACT: To estimate equivalent doses received by eye tissues of patients, contents of uranium ( 238 U), thorium ( 232 Th), radon ( 222 Rn), and thoron ( 220 Rn) were determined inside various optical contact lenses used for vision correction. 238 U, 232 Th, 222 Rn, and 220 Rn contents varied between (3.44 ± 0.24) mBq kg -1 and (18.3 ± 1.28) mBq kg -1 , (0.57 ± 0.04) mBq kg -1 and (3.53 ± 0.25) mBq kg -1 , (3.44 ± 0.24) mBq kg -1 and (18.3 ± 1.28) mBq kg -1 , and (0.57 ± 0.04) mBq kg -1 and (3.53 ± 0.25) mBq kg -1 , respectively. New external dosimetric models, depending on the cornea eye surface of patients, 238 U, 232 Th, and 222 Rn concentrations inside optical contact lenses, half-life of the emitting radionuclides, and exposure time of patients, have been developed. It has been shown that alpha-particles emitted by the 238 U and 232 Th series inside the studied optical lenses transfer their energies essentially to the cornea tissues whereas the emitted beta-particles may reach and lose their energies in the crystalline lens of eyes of patients. Alpha-equivalent doses received by eye tissues of patients due to the diffusion of 222 Rn and 220 Rn gases present in the considered optical lenses were determined. The higher value of the total (alpha plus beta) equivalent dose to the left and right eyes of adult patients wearing optical contact lenses (14 hours per day) has been found equal to 1.32 mSv y -1 cm - 2 . It is recommended for patients to reduce the wearing period of optical contact lenses to reduce eye disease risks such as cataract.

222Rn, 220Rn and Their Progenies Measured in the Air of Different Dwellings and Workplaces and Resulting Alpha Radiation Doses to the Eyes of Individuals.

In order to assess radiation doses to the eyes of individuals, concentrations of Rn, Rn and their decay products were measured in different dwelling rooms, café rooms and vehicle repair shops by using two different types of solid state nuclear track detectors (SSNTDs). The influence of building materials, pollution and ventilation rate on radon and thoron alpha-activities inside the studied locations has been investigated. A new dosimetric model was developed for evaluating radiation doses to the eyes of individuals due to alpha particles emitted by the radon and thoron series in the air of the studied dwelling rooms, café rooms, and vehicle repair shops. The influence of the radon and thoron activities in the air of the studied locations, as well as exposure time on committed equivalent dose to the eyes of individuals, was investigated. A maximum value of the committed equivalent dose to the eyes of individuals due to alpha particles emitted by the radon and thoron series was found equal to 0.1 mSv y cm. Committed equivalent dose to the eyes of individuals due to the diffusion of the Rn and Rn gases present in ambient air of the studied locations has been evaluated.