An alpha-particle beam enters a charge collector and is measured to carry 2.0 × 10⁻¹⁴ C of charge into the collector each second. The beam has a cross-sectional area of 150 mm², and it penetrates human skin to a depth of 0.14 mm. Each particle has an initial energy of 4.0 MeV. The Q for such particles is about 15. What effective dose, in Sv and in rem, does a person’s skin receive when exposed to this beam for 20 s? Take ρ = 900 kg/m³ for skin.