What happens to the mass number and the atomic number of an element when it emits \(\gamma\text{-}\)radiation?

1.	mass number decreases by four and atomic number decreases by two.
2.	mass number and atomic number remain unchanged.
3.	mass number remains unchanged while the atomic number decreases by one.
4.	mass number increases by four and the atomic number increases by two.

The half-life of a radioactive sample undergoing \(\alpha- \text{decay}\) is $1.4\times {10}^{17}$ $\sec$. If the number of nuclei in the sample is $2.0$ $\times$ ${10}^{21}$, the activity of the sample is nearly equal to:

1.  ${10}^4$ $Bq$

2.  ${10}^5$ $Bq$

3.  ${10}^6$ $Bq$

4.  ${10}^3$ $Bq$

${}_{n}X_m$ emitted one $\alpha and\mathrm{2 }\beta$ particles, then it will become: 

1. ${}_{n}X_{m-4}$

2. ${}_{n-1}X_{m-1}$

3. ${}_{n}Z_{m-4}$

4. None of these

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 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)

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)

In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. The moderator used have light nuclei. The heavy nuclei will not serve the purpose, because:

Heavy stable nuclei haveVc2 more neutrons than protons. This is because of the fact that

1. neutrons are heavier than protons

2. electrostatic force between protons is repulsive

3. neutrons decay into protons through beta decay

4. nuclear forces between neutrons are weaker than that between protons