Does a flat piece of contaminated steel plate meet a release

Does a flat piece of contaminated steel plate meet a release criterion of 1000 dpm/100 cm2 if a 15 cm2 probe with an efficiency of 10%, in contact with the surface, gives 200 net counts per minute? Justify your answer.

Solution

number of counts decays per minute is

       N = ( 1000 decays/min)/ (100 cm² ))( 15 cm² )

             = 150 counts/min

since detector has efficiency 10%

        N ⁼15 counts /min