(a) Draw the plot of binding energy per nucleon (BE/A) as a function of mass number A. Write two important conclusions that can be drawn regarding the nature of nuclear force.
(b) Use this graph to explain the release of energy in both the processes of nuclear fusion and fission.
(c) Write the basic nuclear process of neutron undergoing `beta`-decay. Why is the detection of neutrinos found very difficult ?

Explanation

(a) The plot of binding energy per nucleon (BE/A) as a function of mass number (A) is shown in Fig. 13.04. Two important conclusions which can be drawn regarding the nature of nuclear force are :
(i) From the constancy of the binding energy per nucleon in the range `30 lt A lt 170` we conclude that the nuclear force is short ranged one. A particular nucleon will be under the influence of only some of the neighbouring nucleons which come within the range of the nuclear force.
(ii) As binding energy is always positive, it suggests that nuclear force is, in general, attractive in nature and much stronger than electrostatic repulsion between the protons.
(c) Beta-particles (or electrons) as such are not present inside a nucleus. However, at the time of `beta^(-)`-decay a neutron decays into a proton, an electron and an antineutrino as per equation :
`" "_(0)^(1)n to " "_(+1)^(1)p+ " "_(-1)^(0)e+ bar(nu) +Q`
where mass and charge of antineutrino particle is zero. Out of the particles formed, the proton remains within the nucleus itself but electron along with anti-neutrino comes out of nucleus. It is this electron which is being emitted as beta-particle.
It is very difficult to detect neutrino (v) and anti-neutrino (`bar(nu)`) particles because these are massless and chargeless.