Efficiency of Gas Filled Detector for the Detection of Beta and Gamma Radiations
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Date
2006-07
Authors
Kare, Anno
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Publisher
Addis Ababa University
Abstract
There are many forms of radiation –heat, light, radar, radio waves etc. differ from
one another in frequency but not in kind. The so called “kinds” of radiation are
characterized by the techniques used to produce and detect them; The classical theory of
Maxwell applies to all these radiations and all are ultimately due to the acceleration of
electrical charges. Except for differences of frequency, and observation made on
one’Kind “of radiation must also be true of all other kinds.
Radiation is energy in the form of waves or particles. The great majority of it
occurs naturally and we are all exposed to it all of the time .It is all around us-in
atmosphere, the earth, our food our bodies and from cosmic rays, from outer space and
medical X-rays. Radiation can be produced from a variety of sources. There are two
broad types - ionizing and non-ionizing radiation - classified in terms of their effects on
matter. Non-ionizing radiation includes some ultra violet light, visible and infrared light,
microwaves, radar and radio waves. Ionizing radiation is that which has enough energy to
remove an electron from an atom, thereby producing an ion - an electrically charged atom
or grouping of atoms. Cosmic rays, x-rays and the radiation emitted by the decay of
radioactive substances are examples of ionizing radiation. Although they are types of
radiation, alpha and beta particles and neutrons are not parts of the electro-magnetic
spectrum because they are particles not waves. We are most affected by ionizing
radiation, which deposits some of its energy as a result of electrical interactions when it
passes through matter. It can be harmful to the human body in excessive doses because it
can damage individual cells, possibly resulting in damage to organs, or other long-term
effects.
Radiologist discovered that repeated exposure of their hands to X-rays resulted in skin
burns. This discovery led to the wide spread use of X-rays in the treatment of cancer.
Also it was realized that excessive exposure of the body to radiation could result in
radiation different in their biological effect on tissues even when the absorbed dose is the
same. This basically depends on ionizing power of radiation. The relative biological
effectiveness of electrons and positions are the same. Whereas, heavy ionizing particles
such as alpha particles and fission fragments produce much greeter biological effect.
However, containing it, shielding against it, moving away from it, or removing the source
can gain effective protection from radiation. Radiation has the same effect, whether from
natural or man-made sources. Most people receive their greatest exposure to radiation
from the naturally occurring radioactive gas radon. It is produced as a result of the decay
of uranium - which is present in all rocks and soils. We all breathe it every day and it
accounts for about 50 per cent of our total radiation dose. In fact, about 85 per cent of our
total dose is the result of naturally occurring radiation. Medical sources, such as x-rays,
account for a further 14 per cent. The fall-out from past nuclear weapons tests and
incidents such as Chernobyl amount to 0.2 per cent and discharges from the nuclear
industry total much less than 0.1 per cent
It may be wondered why it is, if the surfaces of all bodies are continually emitting
radiant energy, that all bodies do not eventually radiate away all their internal energy and
cool down to a temperature of absolute zero. The answer is that they would do so if
energy were not supplied to them in some way. In the case of filament of an eclectic
lamp, energy is supplied electrically to make up for the energy radiated. As soon as the
energy supply is cut off, bodies do, infact, cool down very quickly to room temperature.
The reason that they don not cool further is that their surroundings (the walls, and other
objects in the room) are also radiating and some of this radiant energy is intercepted,
absorbed and converted into internal energy. The same thing is true of all other objects in
the room –each is both emitting and absorbing radiant energy simultaneously
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Efficiency of Gas Filled Detector