3. 50 MBq of 24NaCl solution spilled over a circular area 50 cm in diameter. What is the gamma-ray dose- equivalent rate at a height of (a) 30 cm? (b) 1 m? Note that a surface concentration Ca MBq/m2 of a gamma emitter I' Sv (air kerma) per hour per MBq at 1 m, then, mSv . m 4.74 x 10 MBq . h the dose-equivalent rate at a point p. at a distance / along the central axis, is given by rith Gy H I . C .+ In h