liquid drop model|

1. LIQUID DROP MODEL
SUBMITTED BY:
SHRADDHA M.
MADGHE
GUIDED BY:
DR. A.S. BURGHATE MAM

2. CONTENTS
 INTRODUCTION
 POSTULATES OF LIQUID DROP MODEL
 BOHR-WHEELER THEORY OF NUCLEAR FISSION
 ADVANTAGE OF LIQUID DROP MODEL
 LIMITATIONS OF LIQUID DROP MODEL

3. INTRODUCTION
 The liquid drop model was first proposed by George Gamow and further
developed by Niels Bohr and John Wheeler.
George Gamow
Niels Bohr John Wheeler

4. POSTULATES OF LIQUID DROP MODEL
 Nucleus is a homogeneous entity consisting of certain number of protons and neutrons.
 Each nucleon interacts strongly with all its neighbours.
 Considers the collective motion of all the nucleons.
 The interaction force {nuclear force} is assumed to be a short range one tending to saturation. Thus ,
nuclear force is similar to that of intermolecular force of attraction in a liquid drop.
 Nuclear force is independent of charge and spin of the nucleons.
 Behavior of nucleus is comparable to that of a liquid drop.

5. BOHR-WHEELER THEORY OF NUCLEAR
FISSION
The liquid drop model can explain the phenomenon of nuclear fission. A liquid drop has a spherical
shape due to internal molecular forces responsible for surface tension. On applying a large external
force, the sphere may change into on ellipsoid. If the external force is sufficiently large, ellipsoid
may change into a dumb-bell shape and may even break at the narrow end into two portions.
According to Bohr-wheeler theory, the nucleus behaves like a liquid drop. When the nucleus
captures a neutron falling on it, it forms a compound nucleus which is highly energetic. The extra
energy may set up a series of rapid oscillations in the spherical compound nucleus labelled as 'A' in
Fig below. As a result of these oscillations, the shape of the nucleus may change at time form
spherical to ellipsoidal, labelled as 'B' in the same Fig.

6. If the extra energy is large, oscillations may be so violent that stage 'C' and ultimately stage
'D' may be approached. The nucleus is now dumb-bell shaped and both parts of the
dumb-bell which are not necessarily of equal size carry positive charge. The energy
required to change the nucleus from stage 'A' to stage 'D' is called as fission barrier. The
nucleus is now in critical state because once stage D' s reached, the final fission in to
fragments (stage 'E') is inevitable on account of repulsion between the two fragments.

7. ADVANTAGE OF LIQUID DROP MODEL
I) IT PROVIDES BASIS FOR THE EQUATION OF WEIZSACKER FOR CALCULATING THE
ACCURATE BINDING ENERGIES OF NUCLEI AND HENCE THEIR ATOMIC MASSES.
II) RADIOACTIVE DECAY COULD BE PREDICTED, CORRECTLY.
III) IT COULD EXPLAIN NUCLEAR FISSION REACTION.
IV) IT EXPLAINS THE MECHANISM OF LOW ENERGY NUCLEAR REACTIONS.
V) IT PREDICTS A- AND B-EMISSION PROPERTIES.
VI) CAPABLE OF EXPLAINING NUCLEAR PROPERTIES IN EXCITED STATE.

8. LIMITATIONS OF LIQUID DROP MODEL
I)THE PERIODICITY IN NUCLEAR PROPERTIES AT MAGIC NUMBERS OF PROTONS AND
NEUTRONS DOSE NOT FIND ANY SATISFACTORY EXPLANATION IN THIS MODEL I.E.
FAILS TO EXPLAIN MAGIC NUMBERS.
II) IT FAILS TO EXPLAIN THE STABILITY OF HEAVY NUCLIDES.
III) THIS MODEL IS NOT CONSISTENT WITH THE P-P AND N-N PAIRING EFFECTS
WHICH ARE PROMINENTLY OBSERVED IN STABLE NUCLEI.
IV) THE MODEL IGNORES INDEPENDENT MOTIONS OF NUCLEONS, MAGNETIC
MOMENT EFFECTS

9. Thank you!!