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• Historical outline of radioactivity: work of
Becquerel (discovery of radiation from
uranium salts); Marie and Pierre Curie
(discovery of polonium and radium).
• Widespread occurrence of radioactivity.
Antoine Henri Becquerel
• In 1896, while investigating
uranium salts, Becquerel
radioactivity . Becquerel
found that the photographic
plates were fully exposed
when in contact with
• developed a theory of
for isolating radioactive
isotopes, and discovered
two new elements,
Polonium and Radium
Natural Radiation comes from
Sources in the earth that contain
Sources from space in the form of
Sources in the atmosphere,
particularly from Radon gas that is
released from the Earth's crust.
About 15% of background radiation
comes from medical X-rays and
About 3% of background radiation
comes from other man-made sources
such as: nuclear testing, power plants,
and smoke detectors.
• Pierre discovered nuclear
energy, by identifying the
continuous emission of heat
from Radium particles. He
also investigated the radiation
emissions of radioactive
substances, which lead to the
discovery of Alpha, Beta and
• Alpha, beta and gamma radiation (nature and
penetrating ability).One example each of:
• an α-emitter, e.g. 241Am
• a β-emitter, e.g. 14C
• a γ-emitter, e.g. 60Co.
• Is the spontaneous
breaking up of
unstable nuclei with
the emission of one or
more types of
• There are three types
alpha, beta and gamma
Made of 2 protons + 2 neutrons
From unstable nuclei
Low penetration; stopped by a sheet of
• Americum-241 [used in smoke detectors]
emits alpha particles
• Formed when a neutron decays into a
proton and an electron
• Penetrate 5mm of aluminum
• Carbon-14 used in carbon-dating emits beta
• Uses of radioisotopes (three examples).
• 14C age determination (calculations not
• 60Co for cancer treatment.
• Food irradiation.
The animation below shows the decay of a
radioactive sample of Carbon-14 to stable
Nitrogen by the emission of beta particles.
Carbon-14 decays to nitrogen-14
Take in Carbon-14
• The percentage of
carbon-14 in all of
these living things is
the same as the
percentage of carbon14 in the atmosphere.
• The carbon-14 within
thing will someday
turn back into
High energy electromagnetic radiation
Not deflected by magnetic or electric fields
Only stopped by several cms of lead.
Cobalt-60 [used to treat cancer] emits
• Demonstration of properties –detection and
• Distinction between chemical reaction and
• (simple equations required –confine
examples to alpha and beta emissions).
• Emission of radioactive radiation
• In a nuclear reaction the nucleus forms a
Loss of an alpha particle
• Radium-226 Radon-222 + alpha particle
226 Ra222 Rn
• Mass decreases by 4 
• Atomic number decreases by 2 
• Carbon-14 nitrogen-14 + beta
• 146C 147N + 0-1e
• Mass number stays the same
• Atomic number increases by 1
• A Radioisotope (radionuclide) is an atom
with an unstable nucleus.
• Change of one element into another
• Rutherford confirmed the artificial
transmutation of nitrogen. Alpha particles
were allowed to pass through nitrogen gas;
when one struck a nitrogen nucleus, a
hydrogen nucleus was ejected, and an
oxygen nucleus formed.
• Time taken for
half of the nuclei
in any given
sample to decay
• Medical—.gamma rays kill cancerous cells
and sterilises equipment
• Archaeological—after a living thing dies
the amount of C-14 decreases. Used to
determine the age of a plant/animal
• Food—gamma rays kill disease causing