Radioactivity
Radioactivity is
the spontaneous/induced disintegration
or decay of unstable atomic nuclide
resulting in the emission of particles or radiation such as alpha
particles, beta particles and gamma rays.
Factors that contribute to radioactivity. All nuclei except
H (hydrogen) contains two kids of fundamental particles called protons and
neutrons. Some nuclei are unstable. The stability of a nucleus depends on the
protons and neutron ratio. When the nucleus becomes unstable it undergoes spontaneous
decay or disintegration to emit particles and radiation. All elements which have atomic number greater
than 83 are radioactive. A radioactive substance is one that’s capable of
undergoing spontaneous decay to emit particles and radiation. When a nuclide is
bombarded with a proton(s) and neutron(s) they undergo a change in
neutralization or process called nuclear
transmutation.
| 14 7 |
N + | 4 2 |
He → | 17 8 |
O + | 1 1 |
H |
Nuclear Stability. The stability of any nucleus is
determined by the difference between the force of repulsion and short range
attraction. If the nucleus disintegrates emitting particles and radiations. If
attraction prevails the nucleus will be stable. The main factor for determining
whether a nucleus is stable in the proton-neutron ratio. For stable atoms of elements
of low z n: p value is closer to 1. The presence of large excess neutrons over
protons also distracts the stability of the nucleus.
The half-life of the nucleus. The half-life of a radioactive
isotope provides a quantitative measure of its relative stability and remains
constant and unique for each radioactive decay process. The shorter the
half-life the faster and the more unstable it is. On the other hand the longer
the half –life the slower the decay process and the more stable the isotope.
Types
of Radioactivity
Natural radioactivity: It is the spontaneous disintegration or
decay of unstable atomic nuclei resulting in the emission of particles or
radiation such as Alpha, Beta and Gamma rays
Artificial radioactivity: It is the decay of atomic nuclei
which have been rendered unstable by bombarding them with subatomic particles resulting
in the emission of particles and radiation such as alpha, beta gamma rays.
Particles emitted by radioactivity
Alpha particle. They consist of two protons and two neutrons
that act as a single particle. It is identical to the nucleus of helium atom.
It has a mass of 4amu and a charge of 2+. It is represented as 
Alpha decay. It is the emission of an alpha particle during
radioactivity. When an alpha particle is emitted from unstable radioactive
nucleus the atom is transmitted into different elements. Any nucleus which
emits an alpha particle has its Z reduced by 2 and A reduced by 4.
Beta Particles. Beta particles are fast moving electrons.
Each beta particle carries a charge of -1 and has a mass of 1/2000amu. It is
represented as
Beta decay. Emission of beta particles during radioactivity
can occur in two ways. A neutron turns into protons by emitting 2 negatively
charged particles and other particles called anti-neutrino.
Proton can also turn into neutron by emitting two (2) neutrino
and a positron. After the decay the nucleus of the atom contains either one
less or one more proton. Beta decay transmutes the atom into new elements that
is represented by different atomic number.
Gamma rays. Mass-less and changeless radiation with high
energy. They are emitted from the nucleus of an atom when it under goes
radioactive decay. The energy of a gamma ray account for the difference in
energy between the nucleus and the decayed products. Typically they have about
the same energy as a high energy X it represented by the symbol 
Penetration Power of Sub Atomic Particles
Gamma rays. They are the most energetic and have the highest
penetration power. This makes them injurious than any radioactive emission. It
can penetrate a card few millimeters thickness of aluminum and can only be
stopped by a concrete wall or shield of lead metal.
Beta Particle. They are less energetic and have less
penetration power than gamma rays. This makes them less injurious than the
gamma rays. The however have a greater penetration power and more injurious
than alpha particles. It can penetrate a card but can be stopped by few millimeters thickness of aluminum.
Alpha particle. They are the least energetic with the lowest
penetration power and as such the least injurious. It can be stopped by a card.
Behavior of
radioactive emissions in magnetic and electric fields
Gamma rays are
neither deflected by electric or magnetic field. They therefore move in a
straight path when passing through an electric or magnetic field. Beta particles
are attracted to a positive plate
repelled by the negative plate of an electric field.
Alpha particles are attracted to the negative plate but repelled by the positive plate of an electric field. Since alpha particles are more massive than beta particle, they are deflected to a lesser extent than the latter in a magnetic and electric field.
Alpha particles are attracted to the negative plate but repelled by the positive plate of an electric field. Since alpha particles are more massive than beta particle, they are deflected to a lesser extent than the latter in a magnetic and electric field.
The Nature of radioactive particle in tabulated form
Uses of Radioactivity
Sterilization of surgical equipment.
| Type of Radiation | Alpha particle | Beta particle | Gamma ray |
| Symbol |
or  or
|
or  |
|
| Mass (amu) | 4 | 1/2000 | 0 |
| Charge | +2 | -1 | 0 |
| Speed | slow | fast | very fast (speed of light) |
| Ionising ability | high | medium | 0 |
| Penetrating power | low | medium | high |
| Stopped by: | paper | aluminium | lead |
Uses of Radioactivity
Sterilization of surgical equipment.
Carbon dating
Sterilization of pests
Irradiation
Determining of molecular size
Cure cancer
Harmful effect of
radioactivity
Leukemia
Environmental pollution
Mutation
Harmful radiations (bombs)
Cancer
