Question

A does of 5 mc of ³⁰₁₅P is administered intravenously to a patient whose blood volume is 3.5 litre. At the end of one hour it is assumed that the phosphorus is uniformly distributed. Then the count rate after per ml of withdrawn blood after one hour is (assume that the counter had an efficiency of only 10%). Given 1 mc = 3.7×10⁷ dis/s and half life of phosphorous is 14 day.

(1) 5.3×10² dis/s 

(2) 5.0×10³ dis/s 

(3) 5.3×10⁷ dis/s

(4) 530 dis/s

Answer 1

Correct option : (1) 5.3×10² dis/s

Explanation: 

Dose per ml = 5/3500 mc

Number of disintegration 1/700 x 3.7 x 10⁷ per sec. in blood

After one hour we can assume no decay. 

Disintegration counted = 1/10 x 1/700 x 3.7 x 10⁷ 

= 5.3×10² dis/s