Nuclear fission You can split the nucleus of an atom into two smaller fragments with a neutron. This method usually involves isotopes of uranium (uranium-235, uranium-233) or plutonium-239.

Nuclear fusion You can bring two smaller atoms, usually hydrogen or hydrogen isotopes (deuterium, tritium), together to form a larger one (helium or helium isotopes); at high temperatures (millions of degrees) e.g thermonuclear energy from Sun.

Nuclear Energy E = MC 2 Energy from fission of 1 kg of U-235 equal to 20 kilo tons of TNT Energy from fusion is 1000 times more than this.

Energy from fission 1 gram of uranium-235 element is equivalent to 2500 Kg of coal

To build an atomic bomb, you need A source of fissionable or fusionable material of required critical mass A triggering device A way to allow the majority of fuel to fission or fuse before the explosion occur Neutron source

Critical Mass The minimum mass of fissionable material required to sustain a nuclear fission reaction In a fission bomb, the fuel must be kept in separate subcritical masses, which will not support fission, to prevent premature detonationsubcritical

Fission Bombs  To bring the sub critical masses together into a supercritical mass, two techniques are used  Gun-triggered  Implosion

Gun-triggered Fission Bomb A sphere of U-235 is made around the neutron generator and a small bullet of U-235 is removed The bullet is placed at the one end of a long tube with explosives behind it The sphere is placed at the other end

Gun-triggered Fission Bomb A barometric-pressure sensor determines the appropriate altitude for detonation and triggers the following sequence of events

Gun-triggered Fission Bomb The explosives fire and propel the bullet down the barrel. The bullet strikes the sphere and generator, initiating the fission reaction The fission reaction begins The bomb explodes.

TAMPER U-238 SUB-CRITICAL HEMISPHERE U-235 NEUTRON INTIATOR NEUTRON REFLECTOR HE CHARGE DETONATOR FUZE

AS SUB-CRITICAL HEMISPHERES FUSE CRITICAL MASS IS ATTAINED AND WPN DETONATES

GUN TYPE USED AT HIROSHIMA 6 AUG 45. HAS TWO HEMISPHERES OF SUB CRITICAL U235 AT OPP ENDS OF A TUBE. ONE IS FIXED THE OTHER IS MOVABLE. MOVABLE HEMISPHERE IS BACKED BY HE. HE DETONATED. MOVABLE PIECE PROPELS FWD AT HIGH SPEED. HEMISPHERES FUSE ON IMPACT AND ATTAIN CRITICAL MASS.

Comments by a Scientist "If the radiance of a thousand suns were to burst forth at once in the sky, that would be like the splendor of the Mighty One...I am become Death, the shatterer of worlds." Bhagavad Gita, the sacred Hindu epic recalled by J. Robert Oppenheimer while viewing the first nuclear explosion in Alamagordo, New Mexico, July 16, 1945

Implosion type nuclear fission bomb The implosion device consists of a sphere of uranium-235 (tamper) and a plutonium- 239 core surrounded by high explosives. When the bomb is detonated, this is what happens

The explosives fires, creating a shock wave. The shock wave compresses the core. The fission reaction begins. The bomb explodes.

SUB- CRITICAL PLUTONIUM CORE U-238 TAMPER DETONATOR INITIATOR HE LENSES KRYTON SWITCHES FIRING UNIT

KRYTON SWITCHES

ENERGY WAVES DIRECTED INWARD

PU CORE COMPRESSED

CORE COMPRESSED TO CRITICAL MASS

Size of Pu bomb (Nagasaki)

FAT MAN

Stages of fusion Bomb Fission Fusion Fission

Stage 1 Fission: A small fission bomb is exploded to provide high temperature (100 million degrees) for fusion to take place.

Stage 2 Fusion of deuterium and tritium in the central column leading to release of enormous amount of energy.

Stage 3 The extremely powerful neutrons from fusion reaction fissions the fertile isotope U- 238, leading to further release of energy.

DETONATOR HE LENSES TAMPER (U-238) FUSION MTRL FISSION TRIGGER

DETONATOR HE LENSES TAMPER (U-238) FUSION MTRL FISSION TRIGGER HE INITIATED

DETONATOR HE LENSES TAMPER (U-238) FUSION MTRL FISSION TRIGGER FISSION INITIATED

DETONATOR HE LENSES TAMPER (U-238) FUSION MTRL FISSION TRIGGER HIGH TEMP INITIATES FUSION

Fission and fusion bombs Fission bomb – power up to a few thousand kilo tons of TNT. Fusion bomb times more powerful than fission bomb (Practically there is no upper limit)

Cost of making a bomb Each bomb costs $5 billion crores in Indian rupees

CountrySuspected Total Nuclear Weapons China400 Israel200+? Pakistan24-48

CountrySuspected Total Nuclear Weapons France350 Russia~ 10,000 United Kingdom185 United States10,656

Cost of dropping a bomb

Hope for a peaceful tomorrow

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