The variation of the decay rate of two radioactive samples A and B with time is shown in the figure.

Which of the following statements are true?
 

1. (a, b)

2. (a, c)

3. (b, d)

4. (c, d)

From a newly formed radioactive substance (Half-life 2 hours), the intensity of radiation is 64 times the permissible safe level. The minimum time after which work can be done safely from this source is:
1. 6 hours           
2. 12 hours
3. 24 hours         
4. 128 hours

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 half-life of ${}_{38}{}^{90}Sr$ is 28 years. What is the disintegration rate of 15 mg of this isotope?
1. \(9.64 \times 10^{10}~\mathrm{atoms} / \mathrm{s}\)
2. \(11.12 \times 10^{11}~\mathrm{atoms} / \mathrm{s}\)
3. \(7.87 \times 10^{10}~\mathrm{atoms}/ \mathrm{s}\)
4. \(10.04 \times 10^{11}~\mathrm{atoms}/ \mathrm{s}\)

In one average-life,

1.  half the active nuclei decay

2.  less than half the active nuclei decay

3.  more than half the active nuclei decay

4.  all the nuclei decay

In a radioactive decay, neither the atomic number nor the mass number changes. Which of the following particles is emitted in the decay?

1.  proton

2.  neutron

3.  electron

4.  photon

Samples of two radioactive nuclides A and B are taken. ${\mathrm{\lambda }}_{\mathrm{A}}$ and ${\mathrm{\lambda }}_{\mathrm{B}}$ are the disintegration constants of A and B respectively. In which of the following cases, the two samples can simultaneously have the same decay rate at any time?

(a) Initial rate of decay of A is twice the initial rate of decay of B and ${\mathrm{\lambda }}_{\mathrm{A}}$ = ${\mathrm{\lambda }}_{\mathrm{B}}$
(b) Initial rate of decay of A is twice the initial rate of decay of B and ${\mathrm{\lambda }}_{\mathrm{A}}$ > ${\mathrm{\lambda }}_{\mathrm{B}}$
(c) Initial rate of decay of B is twice the initial rate of decay of A and ${\mathrm{\lambda }}_{\mathrm{A}}$ > ${\mathrm{\lambda }}_{\mathrm{B}}$
(d) Initial rate of decay of B is same as the rate of decay of A at t = 2 h and ${\mathrm{\lambda }}_{\mathrm{A}}$ < ${\mathrm{\lambda }}_{\mathrm{B}}$

1. (a, b)

2. (a, c)

3. (b, d)

4. (c, d)

A human body required the 0.01 Curie activity of radioactive substance after 24 hours. The half-life of radioactive is 6 hours. The maximum activity of a radioactive substance that can be injected will be: 
1.  0.08
2.  0.04
3.  0.16
4.  0.32

The half-life of ${}_{92}{}^{238}\mathrm{U}$ undergoing $\mathrm{\alpha }$-decay is $4.5\times {10}^9$ years. What is the activity of the 1g sample of ${}_{92}{}^{238}\mathrm{U}$?

1. $2.11\times {10}^4<mspace\; width="1em"></mspace>Bq$

2. $3.12\times {10}^3<mspace\; width="1em"></mspace>Bq$

3. $1.23\times {10}^4<mspace\; width="1em"></mspace>Bq$

4. $2.38\times {10}^3<mspace\; width="1em"></mspace>Bq$