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,

${}_{92}{}^{236}U\to {}_{117}X+{}_{117}Y+n+n$

the binding energy per nucleon of X and Y is 8.5 MeV whereas of ${}_{236}U$ is 7.6 MeV. The total energy liberated will be about [1997]

(1) 2000 MeV          (2) 200 MeV               (3) 2 MeV            (4) 1 keV

A nuclear decay is expressed as 

${}_{6}C_{11}\to {}_{5}B_{11}+{\beta }^{+}+X$

Then the unknown particle X is:

(1) Neutron          (2) antineutrino             (3) proton               (4) neutrino

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 energy released by the fission of one  uranium atom is 200 MeV. The number of fission per second required to produce 3.2 W of power is (Take, 1 eV = 1.6$\times$${10}^{-19} J$) [WB JEE 2010]

(1) ${10}^7$           (2) ${10}^{10}$         (3) ${10}^{15}$          (4) ${10}^{11}$

Half-life of a radioactive substance is 12.5 h and its mass is 256 g. After what time, the amount of remaining substance is 1 g? [2001]

(1) 75 h          (2) 100 h            (3) 125 h          (4) 150 h

A radioactive nucleus undergoes a series of decay according to the scheme 

$A\stackrel{\alpha }{\to }{A}_1\stackrel{\beta }{\to }{A}_2\stackrel{\alpha }{\to }{A}_3\stackrel{\gamma }{\to }{A}_4$

If the mass number and atomic number of A are 180 and 72 respectively, then what are these number for $A_4$?

(1) 172 and 69                         (2) 174 and 70

(3) 176 and 69                         (4) 176 and 70

The radioactivity of an element becomes $\frac{1}{64}th$ of its original value in 60 seconds. Then the half value period is

(1) 5 sec              (2) 10 sec            (3) 20 sec            (4) 30 sec

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