Two radioactive substances A and B have decay constants 5 λ and λ respectively. At t = 0, they have the same number of nuclei. The ratio of number of nuclei of A to that of B will be (1/e)2 after a time interval of
The half-life of a radioactive isotope X is 20 yr. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio 1 : 7 in a sample of a given rock. The age of the rock is estimated to be
40 yr
60 yr
80 yr
100 yr
B.
60 yr
A certain mass of hydrogen is changed to helium by the process of fusion. The mass defect in fusion reaction is 0.02866 u. The energy liberated per u is (given 1 u = 931 MeV)
2.67 MeV
26.7 MeV
6.675 MeV
13.35 MeV
For the radioactive nuclei that undergo either α or β decay, which one of the following cannot occur ?
Isobar of original nucleus is produced
Isotope of the original nucleus is produced
Nuclei with higher atomic number than that of the original nucleus is produced
Nuclei with lower atomic number than that of the original nucleus is produced