A radioactive element has half-life period 800 yr. After 6400 yr, what fraction will remain? [1989]

1. $\frac{1}{2}$

2. $\frac{1}{16}$ 

3. $\frac{1}{8}$ 

4.$\frac{1}{256}$

If a proton and anti-proton come close to each other and annihilate, how much energy will be released:

1. $1.5\times {10}^{-10} J$           

2. $3\times {10}^{-10} J$         

3. $4.5\times {10}^{-10} J$         

4. None of these

The stable nucleus that has a radius half of the radius of $F{e}^{56}$ is:

1. $L{i}^7$ 

2. $N{a}^{21}$

3. $S^{16}$

4. $C{a}^{40}$

The mass density of a nucleus varies with mass number A as [1992]

1. $A^2$

2. A 

3. Constant 

4. $\frac{1}{A}$

Energy released in the fission of a single ${}_{92}U_{235}$ nucleus is 200 MeV. The fission rate of a ${}_{92}U_{235}$ filled reactor operating at a power level of 5 W is 

1. $1.56\times {10}^{-10} s^{-1}$ 

2. $1.56\times {10}^{11} s^{-1}$

3. $1.56\times {10}^{-16} s^{-1}$   

4. $1.56\times {10}^{-17} s^{-1}$

In one \(\alpha-\)$$ and \(2\beta-\)$emissions:$

Which of the following is used as a moderator in nuclear reactors? 

1. Plutonium 

2. Cadmium 

3. Heavy water

4. Uranium 

Heavy water is used as a moderator in a nuclear reactor. The function of the moderator is 

1. to control energy released in the reactor

2. to absorb neutrons and stop the chain reaction

3. to cool the reactor

4. to slow down the neutrons to thermal energies

The binding energy per nucleon of deuterium and helium atom is 1.1 MeV and 7.0 MeV. If two deuterium nuclei fuse to form a helium atom, the energy released is:

1. 19.2 MeV

2. 23.6 MeV

3. 26.9 MeV 

4. 13.9 MeV

In a fission reaction,

$$\(^{236}_{92}U\rightarrow ~^{117}X~+~^{117}Y~+~^1_0n~+~^1_0n,\) the binding energy per nucleon of X and Y is 8.5 MeV whereas that of \(^{236}U\) is 7.6 MeV. The total energy liberated will be about:

1. 2000 MeV

2. 200 MeV

3. 2 MeV 

4. 1 keV