Download Radioactivity - Garbally Chemistry

Chapter8
Radioactivity
Radioactivity is the emission of alpha, beta or gamma radiation from the nucleus of
unstable atoms.
It was discovered by Becquerel, who found that an uranium salt had affected a
photographic plate. Pierre and Mari Curie found two new radioactive elements- polonium
and radium.
Radioactive radiation can be detected using a Geiger Muller tube.
Alpha radiation consists of a stream of positively charged particles and so are
deflected towards the negatively charged plate, and by a magnetic field.
Alpha particles consists of two protons and two neutrons which is the same as the
nucleus of Helium.
The have low penetrating power and are stopped by a few centimeters of Air or a sheet of
paper.
Examples of elements which emit alpha particles is americium-241(smoke detectors).
Beta particles are simply electrons. A beta particle is formed when a neutron is
changed into a proton and an electron.
They are more penetrating than Alpha particles and can penetrate up to 5mm of
aluminium.
Gamma radiation is high energy electromagnetic radiation of very short wavelength.
It is not deflected in electric or magnetic fields. Gamma rays have high penetrating
ability.
Cobalt-60 gives off Gamma radiation. Used to kill cancerous cells.
Radiation
Alpha
Beta
Their nature
+ particles(Helium)
- particles(electrons)
Gamma
Electromagnetic
Penetrating power
Low-sheet of paper
Medium 5mm
aluminium
High- lead
The Half-life of an element is the time taken for half of the nuclei in any given sample of
decay.
Uses of radioisotopes.
 Medicine Food preservation Industry Archeology-
Cobalt-60 kill cancer cells
Gamma rays kill microbes
Tracers added to find source of leaking pipes
Carbon-14 dating by beta emmission