nuclear fission

Nuclear fission : 

Nuclear fission

DEFINITION : 

DEFINITION In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts, often producing free neutrons and lighter nuclei, which may eventually produce photons (in the form of gamma rays). Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place).

THEORY : 

THEORY Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom. Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Both uses are made possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.

conditions : 

conditions The fission process is possible only if the nucleus is excited to the sufficient energy and attains the stage of dumbbell. The excitation energy required to split the nucleus is called the CRITICAL ENERGY. It should be more than the neutrons binding energy

Requirements : 

Requirements To sustain the fission process the following requirements must be fulfilled. The neutrons emitted in fission must have adequate energy to cause fission of other nuclei. The no of neutrons produced must be able not only to sustain the fission process but also to increase the rate of fission. The fission process must liberate the energy It must be possible to control the rate of energy liberation

CHAIN REACTION : 

CHAIN REACTION

DEFINITION : 

DEFINITION It is a process in which the number of neutrons keeps on multiplying rapidly during the fission till whole of the fissionable material is disintegrated. The chain reaction will become self sustaining or self propagating.

CONDITIONS : 

CONDITIONS This condition can be conveniently expressed in the form of MULTIPLICATION FACTOR or REPRODUCTION FACTOR. K= no of neutrons in any particular generations no of neutrons in the preceding generations For sustaining chain reaction, k should be >1 and if k<1, chain reaction cannot be maintained.

CONSTRAINTS : 

CONSTRAINTS There are 2 reasons why not all the fission neutrons cause further fission. absorption of some neutrons causes further fission products, non fissionable nuclei in the fuel, structural material, moderator and so on. leakage of neutrons escaping from the core.

EXAMPLE : 

EXAMPLE About 2.5 neutrons are released in fission of each nuclei of U235. out of these 1 neutron is used to sustain the chain reaction. 0.9 neutrons are absorbed by U 238 and become fissionable material pu 239. the remaining 0.6 neutrons are partly absorbed by control rod material, coolant, moderator and partly escape from the reactor.

Fission bombs : 

Fission bombs One class of nuclear weapon, a fission bomb (not to be confused with the fusion bomb), otherwise known as an atomic bomb or atom bomb, is a fission reactor designed to liberate as much energy as possible as rapidly as possible, before the released energy causes the reactor to explode (and the chain reaction to stop). Development of nuclear weapons was the motivation behind early research into nuclear fission: the Manhattan Project of the U.S. military during World War II carried out most of the early scientific work on fission chain reactions, culminating in the Trinity test bomb and the Little Boy and Fat Man bombs that were exploded over the cities Hiroshima, and Nagasaki, Japan in August 1945.

Slide 15: 

Say YES to nuclear energy... Say NO to nuclear weapons..