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Wave Optics

Question
CBSEENPH12038756

Calculate the mass of 1 curie of RaB (Pb2) from its half-life of 26.8 minutes.

Solution

Given, 
Half life of RaB = 26.8 min

Activity of RaB = dNdt = 1 curie = 3.7 × 1010 disintegrations/s

If, λ is the disintegration constant of RaB, we have
                    λ = 0.693T

                       = 0.69326.8 ×60s-1

Let N be the number of atoms of RaB having an activity of 1 curie. Then , 

we have       dNdt = λN

                     N = dNdtλ 

              N = 3.7×1010×26.8×600.693

Further we know that, 

1g of atom = 6.02 × 1023 atoms. 

Mass of 1 curie of atom = 214g = 2146.02 × 1023 

Therefore, the mass of RaB having an activity of 1 curie is, 

         = 214 × 3.7 × 1010 × 26.8 × 606.02 × 1023 × 0.693= 30.52 × 10-9g. 

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