In a radioactive substance at t = 0, the number of atoms is 8, its half-life period is 3 yr. The number of atoms equal to will remain after an interval of:
1. 9 yr
2. 8 yr
3. 6 yr
4. 24 yr
The half-life of radium is 1622 years. How long will it take for seven-eighth of a given amount of radium to decay
1. 3244 years
2. 6488 years
3. 4866 years
4. 811 years
In a radioactive sample the fraction of initial number of radioactive nuclei, which remains undecayed after n mean lives is:
1.
2.
3.
4.
The activity of a radioactive sample is measured as 9750 counts/min at t = 0 and as 975 counts/min at t = 5 min. The decay constant is approximately:
1. 0.922/min
2. 0.691/min
3. 0.461/min
4. 0.230/min
At time t = 0, N1 nuclei of decay constant λ1 and N2 nuclei of decay constant λ2 are mixed. The decay rate of the mixture is:
1.
2.
3.
4.
The half-life period of a radioactive substance is 6 h. If after 24 h, activity is 0.01 Ci, what was the initial activity?
1. 0.04 Ci
2. 0.08 Ci
3. 0.24 Ci
4. 0.16 Ci
The radioactivity of a sample is at a time and at time . If the mean life of the specimen is T, the number of atoms that have disintegrated in the time interval of is:
1.
2.
3.
4.
The relationship between disintegration constant and half-life [T] will be:
1.
2.
3.
4.
Alpha particles are
1. 2 free protons
2. helium atoms
3. singly ionized helium atoms
4. doubly ionised helium atoms
A radioactive sample with a half-life of 1 month has the label: 'Activity = 2 microcurie on 1-8-1991'. What would be its activity two months earlier?
1. 1.0 microcurie
2. 0.5 microcurie
3. 4 microcurie
4. 8 microcurie