Q 11 :

A radioactive element X92242 emits two α-particles, one electron and two positrons. The product nucleus is represented by YP234. The value of P is ________.           [2023]



(87)

P=92-2-2+1-1-1

P=92-5

P = 87



Q 12 :

A radioactive nucleus decays by two different process. The half life of the first process is 5 minutes and that of the second process is 30 s. The effective half-life of the nucleus is calculated to be α11 s. The value of α is _________.                  [2023]



(300)

dN1dt=-λ1N

dN2dt=-λ2N

dNdt=-(λ1+λ2)N

 λeq=λ1+λ2

 1t1/2=1300+130=11300

 t1/2=30011



Q 13 :

The decay constant for a radioactive nuclide is 1.5×10-5 s-1. Atomic of the substance is 60 g mole-1, (NA=6×1023). The activity of 1.0 μg of the substance is _________ ×1010 Bq.                   [2023]



(15)

λ=1.5×10-5 s-1

Number of mole=1×10-660=10-76

No. of atoms=no. of moles×NA

                          =10-76×6×1023=1016

A=Nλe-λt

For t=0, A0=N0λ=1.5×10-5×1016=15×1010 Bq