Nuclei- 2

Question 1

NUCLEAR FORCE

Answer 1

(i) The nuclear force is much stronger than the Coulomb force
acting between charges or the gravitational forces between
masses.

(ii) The nuclear force between two nucleons falls rapidly to zero as their distance is more than a few femtometres. This leads to saturation of forces in a medium or a large-sized
nucleus, which is the reason for the constancy of the binding energy per nucleon.

iii) This means that the force is attractive for distances larger than 0.8 fm ( till about 2-3 fm) and repulsive if they are separated by distances less than 0.8 fm.

iv) The nuclear force between neutron-neutron, proton-neutron and proton-proton is approximately the same. The nuclear force does not depend on the electric charge.

v) it does not follow inverse square law. They are noncentral force

vi) Nuclear force is dependent on the spin or angular momentum of the nucleons.

Question 2

what is radioactive decay

Answer 2

a nuclear phenomenon in which an unstable nucleus undergoes a decay.

This is referred to as radioactive decay. Three types of radioactive decay
occur in nature :

(i) a-decay in which a helium nucleus 4
2 He is emitted;

(ii) b-decay in which electrons or positrons (particles with the same mass
as electrons, but with a charge exactly opposite to that of electron)
are emitted;

(iii) g-decay in which high energy (hundreds of keV or more) photons are
emitted.

Question 3

what is nuclar fission

Answer 3

It is the phenomenon of splitting of a heavy nucleus (usually A> 230) into 2 or more smaller components.

• The fragment products are radioactive nuclei; they emit b particles in
  succession to achieve stable end products.
• The energy released (the Q value ) in the fission reaction of nuclei like uranium is of the order of 200 MeV per fissioning nucleus./ per atom
• The disintegration energy in fission events first appears as the kinetic energy of the fragments and neutrons. ( 93% as ke of pdts and 7% as neutrons/ gamma rays)

-Eventually it is transferred to the
surrounding matter appearing as heat.

Question 4

nuclear fusion

Answer 4

it is the process of fusion of 2 or more lighter nuclei to form a heavier more stable nucleus.

For fusion to take place, the two nuclei must come close enough so that
attractive short-range nuclear force is able to affect them. However,
since they are both positively charged particles, they experience coulomb
repulsion. They, therefore, must have enough energy to overcome this
coulomb barrier. The height of the barrier depends on the charges and
radii of the two interacting nuclei.

Question 5

thermonuclear fusion

Answer 5

When fusion is achieved by raising the temperature of the system so
that particles have enough kinetic energy to overcome the coulomb
repulsive behaviour, it is called thermonuclear fusion.

Question 6

conditions of nuclear fusion

Answer 6

(a) High Temperature
Which provide kinetic energy to nuclei to overcome the repulsive electrostatic force between them.

(b) High Pressure (or density)
Which ensure frequent collision and increases the probability of fusion.
These condition exist in the sun and in many other stars. The source of energy in the sun is nuclear fusion, where
hydrogen is in plasma state and protons fuse to form helium nuclei.