A particular radioactive source produces 100 mrad of 1 MeVgamma rays per hour at

Question

A particular radioactive source produces 100 mrad of 1 MeVgamma rays per hour at a distance of 1.0 m. (a) How long could a person stand at thisdistance before accumulating an intolerable dose of 1 rem?
1 h

(b) Assuming the gamma radiation is emitted uniformly in alldirections, at what distance would a person receive a dose of5 mrad/h from this source?
2 m (a) How long could a person stand at thisdistance before accumulating an intolerable dose of 1 rem?
1 h

(b) Assuming the gamma radiation is emitted uniformly in alldirections, at what distance would a person receive a dose of5 mrad/h from this source?
2 m

Explanation / Answer

For x- ray or -rays = 1.0 Relative biologicaleffectiveness a)1 rem = 100 x 10-3 rad/hr x 1RBE x t = 10 hr b)We know that            I= P / 4r2          I 1 / r2    Therefore              I1 / I2 = r22 /r12    Therefore              I1 / I2 = r22 /r12               Given that I1 = 100 mrad / h                  I2 = 5 mrad/h                  r1 = 1.0 m                  r2 = ?                                     r12 * I1 / I2 =r22                                                  r2 = 4.47 m

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