In a radioactive material, the activity at time is and at a later time, is . If the decay constant of the material is , then:
1.
2.
3.
4.
A and B are two radioactive substances whose half-lives are 1 and 2 years respectively. Initially 10 g of A and 1 g of B is taken. The time (approximate) after which they will have the same quantity remaining is:
1. 6.62 yr
2. 5 yr
3. 3.2 yr
4. 7 yr
Two radioactive substances A and B have decay constant 5λ and λ respectively. At t = 0 they have the same number of nuclei. The ratio of the number of nuclei of A to those of B will be (1/e)2 after a time interval of:
1.
2.
3.
4.
The activity of the radioactive element decreases to one-third of the original activity in a period of 7 years. After a further lapse of 7 years, its activity will be:
1.
2.
3.
4.
A radioactive nucleus X decays to a stable nucleus 'y'. The graph of the rate of formation of 'y' against time 't' will be:
1. | 2. | ||
3. | 4. |
What fraction of a radioactive material will get disintegrated in a period of two half-lives?
1. whole
2. half
3. one-fourth
4. three-fourth
Half-lives of two radioactive substances A and B respectively are 20 min and 40 min. Initially, the samples of A and B have an equal number of nuclei. After 80 min the ratio of the remaining number of A and B nuclei is:
1. 1 : 16
2. 4 : 1
3. 1 : 4
4. 1 : 1
The counting rate observed from a radioactive source at t = 0 second was 1600 counts per second and at t = 8 seconds it was 100 counts per second. The counting rate observed, as counts per second, at t = 6 seconds will be:
1. 400
2. 300
3. 200
4. 150
The rate of disintegration of a fixed quantity of a radioactive substance can be increased by:
1. increasing the temperature.
2. increasing the pressure.
3. chemical reaction.
4. it is not possible.
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