Theory of Fission and Spontaneous Fission

1. Theory of Fission and Spontaneous Fission
Submitted To:
Dr. Naveed Ahmad
Submitted By:
Usama Yousaf
BS Physics (VIII)Eve
BSF1800372
University of Education , Township Lahore

2. Introduction
⇨Nuclear fission is a reaction in which the nucleus of a heavy
nuclide splits into smaller nuclides, a few new neutrons are
created and a significant amount of energy is released.
⇨ Spontaneous fission is a type of radioactive decay in which
certain unstable nuclei of heavier elements split into two
nearly equal fragments and liberate a large amount of energy.
⇨ In nuclear physics, nuclear fission is either a nuclear
reaction or a radioactive decay process. The case of decay
process is called spontaneous fission and it is very rare
process.

3. THEORY OF FISSION
 Here we will discuss about Bohr Wheeler theory of Fission.
 Bohr and wheeler in 1939 gave a successful explanation of
fission phenomenon.
⇨The short range nuclear attractive forces produce surface
tension and maintain the spherical shape of the nucleus by
overcoming the coloumb force of repulsion between protons.
⇨When a heavy nucleus is imparted with some energy by
thermal neutrons , it forms a compound nucleus and surface
oscillations are set up in the nucleus and distorting it spherical
shape to ellipsoidal .

5. ⇨The strong nuclear forces want to return the nucleus in the
spherical shape whereas the repulsive force wants to distort its
shape.
⇨If the excitation energy is high then the coloumb force
overcome the nuclear forces and compound nucleus is now like
a dumb-bell shape.
⇨Excitation energy produces oscillations which splits two parts
of dum-bell because of p-p repulsion
And consequently , two fission fragments , some neutrons and
high amount of energy is obtained.

6. Spontaneous Fission
⇨ In 1940, Flarov and Petrzhak explained that without external
bombardment of nuclear particles on uranium and heavy nucleus, nuclei
itself undergo fission which is called spontaneous fission.

7. SYMMETRIC FISSION:
⇨The fission reaction which spontaneously splits into two
equal mass fragments having mass no. A/2 and Z/2 , this type of
fission is called symmetric fission.
ENERGY RELEASED IN SYMMETRIC FISSION:
𝐸𝑓 = 𝑀 𝑍, 𝐴 − 2𝑀(
𝑍
2
,
𝐴
2
)

8. ⇨ 𝑀 𝑍, 𝐴 is exact mass of nuclei
⇨ 𝑀(
𝑍
2
,
𝐴
2
) is exact mass of fission product.
By putting these values in equation we will get energy release
equation
Where
 𝑎𝑠 = 13𝑀𝑒𝑣 , 𝑎𝑐=0.595𝑀𝑒𝑣

9. Applications