Achievements of Liquid Drop Model

Achievements of liquid drop model

(i) Stable nucleus

We can explain the stability of nuclei on the basis of liquid drop model .The stability of liquid drop is due to cohesion between the molecules ,similarly, the stability of the nucleus is due to the binding energy of each nucleon .Just as to remove a molecule from liquid drop energy has to supply to it in the form of heat ,energy will have to be supplied to the nucleon equal to or greater than its binding energy removes it .Hence the stability of nucleons is explained .

(ii) Radioactive nucleus

Radioactivephenomenon can be explained by the liquid drop model as follows ,

In a liquid , with the increase in temperature,thermal agitation of its molecules becomes more and more rapid and at a particular stage,evaporation takes place .A molecule in a liquid drop evaporates gaining energy from its neighboring molecules during the process of collision,thus exhibiting the phenomenon of radioactivity .

(iii) Artificial radioactivity

The liquid drop model explains the phenomenon of artificial radioactivity .It is supposed that when a nucleus is bombarded by fast moving the particle, an incoming particle enters the target nucleus forming a compounds nucleus. It quickly shares its energy with the nucleons which already present so that no single particles has sufficient energy for escape. The decay or disintegration of the compounds nucleus occur when the energy is again accidentally concentrated on someone particles which escape giving rise to the phenomenon of artificial radioactivity, Or energy may be lost by the emission of a \(\gamma\)-rays.

(iv) This model agrees with experimental graph f B.E. except for the lighter nuclei .This model also explains the nuclear stability against \(\alpha\) decay \(\beta\)- decay or disintegration .

(V) Nuclear fission

The nuclear fission can be explained force subjected to liquid drop model .

According to this mode, when the external force is subjected to liquid drop model ,its shape is deformed from spherical to ellipsoid. If we further increase the external force ,It turns into dumbells shape and finally splits into two drops of the same size . Similarly, if the nucleus is bombarded by the projectile ,the capture reaction occurs and compounds nucleus is formed. In this process,energy is imparted to the nucleus so that, oscillation of nucleus occur. If excitation energy exceeds the nuclear force binding the nucleus. The ellipsoid nucleus turns into dumbbell shapes and finally split into the two daughter nuclei .The representation is as shown in below

Failure/ Limitation of LDM

(i) The model fails to explain the high stability of nuclei with the magic number.i.e discontinuities of B/A curve can't be explained on the basis of this model .

(ii) This model fails to explain the concept of the pairing energy.

(iii) Naturally abundant even An isobar are not explained by this model

(v) This model cannot explain discontinuities in B/E nucleon.

(vi) The breaking of nuclei in lighter elements is not successfully interpreted by this model .

Analogy between nucleus and Liquid drop model

Just as the molecules of a liquid are held together by short range intermolecular forces of cohesion ,the nucleons in a nucleus are held together by extremely short-range nuclear forces.

A liquid drop is spherical in shape due to surface tension, a nucleon is also almost spherical in shape due to the short-range nuclear forces.

In a liquid, with the increase of temperature, the thermal agitation of its molecules becomes more and more rapid and at a particular stage, evaporation may take place.A molecule in a liquid drop evaporates by gaining energy from its neighboring molecules during the process of collision. Similarly, a nucleon or a group of nucleons may leave the nucleus by gaining energy from the neighboring nucleons during the process of collision, thus exhibiting the phenomenon of radioactivity with the emission of \(\alpha\) and \(\beta\)-particles .