Page 316 - General Knowledge
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GENERAL KNOWLEDGE 2019
ranges from zero to infinity. The mean life of a radioactive substance is defined as the ratio
of total life time of all the radioactive atoms to the total number of atoms in it.
Geiger Muller Counter
A Geiger counter (Geiger-Muller tube) is a device used for the detection and measurement
of all types of radiation: alpha, beta and gamma radiation.
Basically, it consists of a pair of electrodes surrounded by a gas. The electrodes have a high
voltage across them.
The gas used is usually Helium or Argon. When radiation enters the tube it can ionize the gas.
The ions (and electrons) are attracted to the electrodes and an electric current is produced.
A scalar counts the current pulses, and one obtains‖count‖ whenever radiation ionizes the gas.
Nuclear Fusion
Nuclear fusion is a process in which two or more lighter nuclei combine to form a heavier
nucleus.
The mass of the product nucleus is always less than the sum of the masses of the individual
lighter nuclei.
The difference in mass is converted into energy.
The fusion process can be carried out only at an extremely high temperature of the order of
107K because; only at these very high temperatures the nuclei are able to overcome their
mutual repulsion.
Therefore, before fusion, the lighter nuclei must have their temperature raised by several
million degrees. The nuclear fusion reactions are known as thermo-nuclear reactions.
Cosmic Rays
Cosmic rays are atom fragments that rain down on the Earth from outside of the solar
system.
They blaze at the speed of light and have been blamed for electronics problems in satellites
and other machinery.
The ionising radiation many times stronger than γ-rays entering the earth from all the
directions from cosmic or interstellar space is known as cosmic rays.
The cosmic rays can be broadly classified into primary and secondary cosmic rays. The
primary cosmic rays are those coming from outer space and enter the outer boundary of the
earth‘s atmosphere.
The primary cosmic rays consist of 90% protons, 9% helium nuclei and remaining heavy nuclei.
The energy of the primary cosmic rays is of the order 108 MeV.
The secondary cosmic rays are produced when primary cosmic rays interact with gases in
the upper layers of the atmosphere.
They are made up of particles like α-particles, protons, electrons, positrons, mesons,
photons, etc. in different proportions.
11. NANOTECHNOLOGY
Nano science and nanotechnology are the study and application of extremely small things
and can be used across all the other scientific fields, such as chemistry, biology, physics,
materials science, and engineering.
The ability of growing the nano scale materials and structures.
The ability of detecting and manipulating on the nano scale.
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