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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 13 NUCLEUS

Subatomic particles

Nucleus

Nucleons

Atomic mass unit

Mass energy

Mass defect

Nuclear force

Nuclear binding energy

Binding energy per nucleon

Properties of binding force and binding energy

Relation of nuclear size and atomic mass number

Nuclear density

Isotopes

Isobars

Isotones

Isomers

Radioactivity

α-rays

β-rays

γ-rays

Law of radioactive decay

Rate of decay of nucleus

Half-life of a radioactive element

Average life or mean life of a radioactive element (τ)

Nuclear fission

Structure of nuclear reactor

Nuclear fuel

Moderator

Control rods

Coolant in nuclear reactor

Pressure vessel or pressure tubes in nuclear reactor

Steam generator in nuclear reactor

Nuclear fusion

The proton-proton (p, p) cycle in the sun

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 13 NUCLEUS

Nuclear fusion

When light nuclei fuse into a heavier nucleus it is called fusion. Energy in stars is due to fusion.

H11+H11  H12+e++ν+0.42 MeV 

H12+H12  H23e+n+3.27 MeV 

H12+H12  H13+H11+4.03 MeV

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.

The temperature at which two protons in a proton gas would (on an average) have enough energy to overcome the coulomb barrier:

(3/2)kT = KE ≈ 400 keV, which gives T ~ 3 × 109 K.

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.

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