Radioactive decay
A series of successive disintegration that takes place starting from a radioactive element till the formation of a non-radioactive element till the formation of a non-radioactive end product is called radioactive disintegration series.
The rate of nuclear disintegration is measured by instruments like Geiger-Muller counter or Wilson cloud chamber. It has been experimentally proved that in the radioactive decay the rate of disintegration is directly proportional to the number of atoms present in a sample at that time.
HALF-LIFE PERIOD-The time required for the decay of the radioactive element to one-half of its original amount is called half-life period.
NUCLEAR FISSION-WE know that when a nucleus is bombarded with particles like a particles, protons, and neutrons etc. the nucleus disintegrates ejecting some other sub-atomic particles.
The nuclear reaction in which a heavier nucleus splits up in to lighter nuclei of almost equal size with the release of a huge amount of energy is called nuclear fission.
Otto Hahn and his associates in 1939 bombarded uranium235 with slow moving neutrons and observed that it had broken up to form a pair of stable products barium-141 and kryptum-92 and liberated three neutrons in addition to large amount of energy called fission energy.
USES OF NUCLEAR ENERGY-The tremendous amount of energy released during fission can be used for destructive purposes like atom bomb if it is uncontrolled and if it is controlled it can be used for constructive purposes like nuclear reactors.
ATOMIC BOMB-When the size of uranium-235 nucleus being smaller than a minimum size called critical size. It is said to be in the sub-critical size. In this sub-critical size the secondary neutrons escape in to air and no chain reaction takes place to cause explosion. The size of uranium-235 which is bigger than the critical size is called the super critical size. In this condition a chain reaction takes place to cause explosion. An atomic bomb consists of several pieces of uranium-235 of sub-critical size in its safety position. When it is fired by high explosives like TNT, at the time of explosion all the pieces are driven together rapidly to form one large pieces of super critical size. And a chain reaction results in violent explosion.
NUCLEAR REACTORS-Nuclear reactor is an apparatus in which nuclear fission reaction is carried out in a controlled manner. This can be achieved by using natural Uranium which contains a very large amount of uranium-238 isotope, which reduces the explosive effect. It can also be achieved by using moderators, which slows down the speed of secondary neutrons. Materials like deuterium oxide, graphite etc. have been used as moderators. The essential components are
Core –It consists of aluminum plated uranium rods. In a nuclear power plant fission chain reaction is made to occur is made to occur in this part.
Moderator-When graphite is used as moderator it is called as atomic pile and when deuterium oxide is used, it is called as swimming pool reactor.
Control rods- These rods are made of cadmium or boron. It can be raised or lowered to control the fission process by absorbing neutrons.
Coolant-Coolants are liquids which remove the heat produced in the nuclear reactor. Liquid alloy of sodium and potassium is used as a coolant. The heat in the nuclear reactor is taken by this alloy to the heat exchanger for raising steam that runs that runs a turbine generator to produce electricity. Heavy water, air and carbon dioxide have also been used as coolants.
Shield or protective screen- TO prevent the loss of heat and also to protect the persons operating the reactor from heat and radiation, the entire reactor is enclosed in a 8 feet thick concrete dome.
NUCLEAR FISSION-A nuclear fission reaction in which two lighter nuclei are combined or fused together to form a heavier nucleus is called nuclear fusion. In this respect it is opposite to nuclear fission. However, the similar aspect of both the process is liberation of large amount of energy. The nuclear fusion reactions are temperature dependent reactions and are thermonuclear reactions.
Nuclear fusion explains the stellar energy i.e. the energy of the solar system and the principle of hydrogen bomb.
1) Stellar energy-It is the energy of the sun and other stars. Van and hans decided that stellar energy is due to a series of nuclear reactions which finally indicates the fusion of four H-nuclei in to one helium nucleus and two positrons.
2) Hydrogen bomb-Nuclear fusion reaction needs high temperature. Such a high temperature is obtained from fission of uranium-235. In the preparation of hydrogen bomb a suitable quantity of all the isotopes of hydrogen is combined with an atomic bomb to provide high temperature for nuclear fusion reactions in hydrogen bomb.
APPLICATIONS OF RADIOACTIVITY IN DISEASE
1. Radioactive iodine is used in the treatment of thyroid.
2. In certain blood disorders radioactive phosphorous is used.
3. Radio cobalt and radio gold are used in treatment of cancer.
4. Radio phosphorous also cures certain type of skin disease