There are three main types of radioactive decay: alpha, beta, and gamma decay. Alpha decay occurs when the nucleus ejects an alpha particle (helium nucleus) to reduce proton repulsion. Beta decay occurs when the nucleus emits an electron or positron to balance the neutron to proton ratio. Gamma decay happens when the nucleus releases a high energy photon to fall to a lower energy state. Natural radioactivity involves unstable isotopes decaying through alpha and beta emission until becoming stable lead isotopes, while artificial radioactivity is inducing nuclear reactions through bombardment.

1. Radioactive decay is the process by which an atomic nucleus of an unstable
atom loses energy by emitting ionizing particles (ionizing radiation). There
are many different types of radioactive decay table. A decay, or loss of
energy, results when an atom with one type of nucleus, called the parent
radionuclide, transforms to an atom with a nucleus in a different state, or
to a different nucleus containing different numbers of nucleons. Either of
these products is named the daughter nuclide. In some decays the parent
and daughter are different chemical elements, and thus the decay
process results in nuclear transmutation (creation of an atom of a new
element).
The first decay processes to be discovered were alpha decay, beta decay,
and gamma decay. Alpha decay occurs when the nucleus ejects an alpha
particle (helium nucleus). This is the most common process of
emitting nucleons, but in rarer types of decays, nuclei can eject protons,
or specific nuclei of other elements (in the process called cluster
decay). Beta decay occurs when the nucleus emits
an electron or positron and a type of neutrino, in a process that changes a
proton to a neutron or vice versa. The nucleus may capture an orbiting
electron, converting a proton into an neutron (electron capture). All of
these processes result in nuclear transmutation.
By contrast, there exist radioactive decay processes that do not result in
transmutation. The energy of an excited nucleus may be emitted as a
gamma ray in gamma decay, or used to eject an orbital electron by
interaction with the excited nucleus in a process called internal
conversion. Radioisotopes occasionally emit neutrons, and this results in a
change in an element from one isotope to another.

2. Radioactivity was discovered in 1896 by the French scientist Henri
Becquerel, while working on phosphorescent materials. These materials
glow in the dark after exposure to light, and he suspected that the glow
produced in cathode ray tubes by X-rays might be associated with
phosphorescence. He wrapped a photographic plate in black paper and
placed various phosphorescent salts on it. All results were negative until
he used uranium salts. The result with these compounds was a blackening
of the plate. These radiations were called Becquerel Rays.
At first it seemed that the new radiation was similar to the then
recently-discovered X-rays. Further research by Becquerel, Ernest
Rutherford, Paul Villard, Pierre Curie, Marie Curie, and others discovered
that this form of radioactivity was significantly more complicated.
Different types of decay can occur, producing very different types of
radiation. Rutherford was the first to realize that they all occur with the
same mathematical exponential formula (see below), and Rutherford and
his student Frederick Soddy were first to realize that many decay
processes resulted in the transmutation of one element to another.
Subsequently, the radioactive displacement law of Fajans and Soddy was
formulated to describe the products of alpha and beta decay.
The early researchers also discovered that many other chemical
elements besides uranium have radioactive isotopes. A systematic search
for the total radioactivity in uranium ores also guided Marie Curie to
isolate a new element polonium and to separate a new
element radium from barium. The two elements' chemical similarity would
otherwise have made them difficult to distinguish.
There are three types of radioactivity:
Alpha Decay
The reason alpha decay occurs is because the nucleus has too many protons which
cause excessive repulsion. In an attempt to reduce the repulsion, a Helium nucleus is
emitted.

3. Beta Decay
Beta decay occurs when the neutron to proton ratio is too great
in the nucleus and causes instability. In basic beta decay, a neutron is
turned into a proton and an electron. The electron is then emitted. Here's
a diagram of beta decay with hydrogen-3.
Gamma decay
Gamma decay occurs because the nucleus is at too high an energy. The
nucleus falls down to a lower energy state and, in the process, emits a high
energy photon known as a gamma particle. Here's a diagram of gamma
decay with helium-3.
The differences between artificial
radioactivity and natural radioactivity are:
Natural radioactivity:
Nuclear reactions which occur spontaneously are said to be an example of
natural radioactivity. There are three naturally occurring radioactive
series among the elements in the periodic table. These are known as the
uranium series, the actinium series and the thorium series, each named
after the element at which the series start (except the actinium series
which starts with a different uranium isotope). Each series decays
through a number of unstable nuclei by means of alpha and beta
emmission, until each series end on a different stable istope of lead.
Artificial radioactivity:
Not all nuclear reactions are spontaneous. These reactions occur when
stable isotopes are bombarded with particles such as neutrons. This

4. method of inducing a nuclear reaction to proceed is termed artificial
radioactivity. This meant new nuclear reactions, which wouldn't have been
viewed spontaneously, could now be observed. Since about 1940, a set of
new elements with atomic numbers over 92 (the atomic number of the
heaviest naturally occurring element, Uranium) have been artificially
made. They are called the transuranium elements.
Uses of radioactivity:
1.preservation of food grains and seeds
2. some of the isotopes are used in the treatment of cancer.
3. some of the isotopes are used to study the proper functioning of
internal organs.
4. Gamma radiations are used to sterilize the surgical instruments.
5. radio phosphorous is used for studying the rate of phosphorous
assimilation by the plant.
6.it is used for finding out the faults in metal structures.
7.it is used for preparing synthetic elements (artificial
transmutation)
8. isotopes are used in elucidation of reaction mechanism by using
isotopic effects.
9.in breeder reactors radiations are used to prepare the fuel /
fissile material.
10.trace concentrations of metals can be estimated by isotopic
dilution analysis or neutron activation analysis.
Bibliography
http://www.chm.bris.ac.uk/webprojects2002/sidell/NAT&ART.htm
http://library.thinkquest.org/3471/radiation_types_body.html
http://en.wikipedia.org/wiki/Radioactive_decay
http://in.answers.yahoo.com/question/index?qid=20081020071956AAVPdJD