Radiometric and simulation analysis with MCNP 6.3 of products that expose the skin by absorption

This study focuses on the evaluation of the natural radioactivity levels of ²²⁶Ra, ²³²Th, and ⁴⁰K in 51 samples of various types of cleaning materials, cosmetics, and daily care products that are available in the markets of the State of Rio de Janeiro (Brazil). The specific activities, the radium equivalent concentration, and the annual effective doses to the skin were determined using the gamma spectroscopy method and a High Purity Germanium detector. Using the Monte Carlo method (MCNP 6.3), the cosmetic Henna radioactive products were simulated with the reference phantom, and the organ doses were calculated with the usage scenario. The mean values of activity concentrations were 4.49 ± 1.25, 3.82 ± 0.44, 38.75 ± 8.70, and 12.94 ± 2.56 Bq kg⁻¹ for ²²⁶Ra, ²³²Th, ⁴⁰K, and Ra_eq, respectively. Meanwhile, the effective skin dose ranged from (0.74 ± 0.16 to 94.2 ± 24.9) μSv y⁻¹, with an average value of 7.49 ± 1.39 μSv y⁻¹, below the limit value of 1 mSv y⁻¹. The average annual effective skin dose values simulated by MCNP 6.3 for the arm and head regions exposed to the Henna cosmetic were 1.1 ± 0.1 and 1.9 ± 0.2 μSv y⁻¹, respectively. However, the value found in this present work was 2.0 ± 0.1 μSv y⁻¹, a percentage difference of 5.26 %. According to the regulation in CNEN 3.01 NN of 2024, the results indicated that the products studied do not significantly harm consumers' health in a radiological sense.