Modern Physics 3 Question 29

30. The activity of a freshly prepared radioactive sample is 1010 disintegrations per second, whose mean life is 109s. The mass of an atom of this radioisotope is 1025kg. The mass (in mg ) of the radioactive sample is

(2011)

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Solution:

  1. Activity dNdt=λN=1tmean ×N

N=dNdt×tmean = Total number of atoms

Mass of one atom is 1025kg=m (say)

Total mass of radioactive substance

=( number of atoms )×( mass of one atom )=dNdt(tmean )(m)

Substituting the values, we get

Total mass of radioactive substance =1mg

Answer is 1 .



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