Decay period by counting a-particles

To determine the decay constant of radium from the rate of emission of a-particles. 

The number of a-particles emitted per second by 1 g of radium was counted by Rutherford and Geiger (see Problem 167) and was found to be 3.4 X 10 . 

From the number of a-particles emitted per gram, we calculate the number emitted in 1 second per atom and this is the decay constant. 

Taking the atomic weight of radium as 226 g mole and Avogadro s number as 0.602 x 10 mole we obtain for the decay constant 

We have used the original measurements from which the calculation weis first performed. The most recent value (see Mattauch, Nuclear physics tables , Interscience, 1946) is 

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