Irradiation and dosimetry of each organ of rats

Details of irradiation using ⁵⁶Mn and the corresponding internal dose estimation have been described in Stepanenko et al. 2016a and Stepanenko et al. 2016b. In brief, ⁵⁶MnO₂ was obtained by neutron activation of 100 mg of MnO₂ powder using the Baikal-1 nuclear reactor at Kurchatov, Kazakhstan. A thermal neutron fluence of 4 × 10¹⁴ n/cm² was applied to produce 2.74 × 10⁸ Bq of radioactivity of ⁵⁶Mn. The activated MnO₂ powder was sprayed into sealed boxes containing six rats per box (one box was used for Experiment 1, and two boxes were used for Experiment 2). In Experiment 1, the exposure box was equipped with air filters only, while an additional forced ventilation system was installed to improve animal welfare in the boxes in Experiment 2. The same total activity of ⁵⁶Mn equal to 2.74 × 10⁸ Bq was used for irradiation in both experiments. The specific activity of ⁵⁶Mn powder was the same (2.74 × 10⁹ Bq/g) as well. After 1 h, rats were removed from the exposure box(es) into fresh cages, cooled down for 2.5–3 h. Then, three of the animals were killed by intraperitoneal injection of an excessive dose of pentobarbital. A piece of each organ was dissected, weighted and put into a vial. The radioactivity of ⁵⁶Mn in samples of each organ was measured with a gamma spectrometer. The absorbed fractions from beta and gamma irradiation of each organ as well as the whole body were calculated based on the Monte Carlo code (version MCNP-4C) and the mathematical phantom of a rat. Assessment of internal radiation doses was performed by measuring of ⁵⁶Mn activity in each organ and calculating the absorbed fractions of internal exposure to photons and electrons. Details of the dosimetry are described in an accompanying paper (Stepanenko et al. 2016a).

Whole body γ-ray irradiation of 2 Gy was performed at a dose rate of 2.6 Gy/min using a Teragam K-2 unit (UJP Praha, Praha-Zbraslav, Czech Republic).