10.1
Radioactivity
Nuclear Decay…
• Atoms of one element can change into atoms of a
different element altogether.
• An unstable atom has excess internal energy, with the
result that the nucleus can undergo a spontaneous change
towards a more stable form.
• Radioisotopes are atoms that contain an
unstable nucleus and will change into another
isotope over time.
• Scientists can estimate the age of fossils by
looking at nuclear decay.
Radioactivity…
is the process in which
an unstable atomic
nucleus emits charged
particles and energy.
3 Types of Nuclear
Radiation
1. Alpha Particles
2. Beta Particles
3. Gamma Rays
Nuclear Radiation…
charged particles and energy
that are emitted from the
nuclei of radioisotopes.
• If an element decays and emits an alpha or beta particle, it
becomes a new element.
• Gamma rays are often emitted with alpha or beta radiation
also, as the nucleus decays to a less excited state.
Alpha Particle
• Positively charged
particle made up of two
protons and two
neutrons—the same as a
helium nucleus.
• When a uranium-238
sample decays, it emits
alpha particles.
• An alpha particle has a
2+ charge.
• Symbol for alpha: 
Beta Particle
• negatively charged radiation
• electron emitted by an
unstable nucleus
• A beta particle is assigned an
atomic number of –1.
• Symbol for beta: 
Gamma Ray
• Penetrating ray of energy emitted by an
unstable nucleus.
• Gamma radiation has no mass and no
charge.
• Like X-rays and visible light, gamma rays
are energy waves that travel through space
at the speed of light.
•Symbol for gamma: 
Units of Radioactivity…
• The amount of radioactive material is given in
becquerel (Bq), a measure which enables us
to compare the typical radioactivity of some
natural and other materials.
• A becquerel is one atomic decay per second.
Radioactivity of some natural and other materials
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1 adult human (100 Bq/kg) 7000 Bq
1 kg of coffee 1000 Bq
1 kg superphosphate fertiliser 5000 Bq
The air in a 100 sq metre Australian home (radon) 3000 Bq
The air in many 100 sq metre European homes (radon) up to 30 000 Bq
1 household smoke detector (with americium) 30 000 Bq
Radioisotope for medical diagnosis 70 million Bq
Radioisotope source for medical therapy 100 000 000 million Bq (100
TBq)
1 kg 50-year old vitrified high-level nuclear waste 10 000 000 million Bq
(10 TBq)
1 luminous Exit sign (1970s) 1 000 000 million Bq (1 TBq)
1 kg uranium 25 million Bq
1 kg uranium ore (Canadian, 15%) 25 million Bq
1 kg uranium ore (Australian, 0.3% 500 000 Bq
1 kg low level radioactive waste 1 million Bq
1 kg of coal ash 2000 Bq 1 kg of granite 1000 Bq
Electromagnetic Radiation
• Consist of electromagnetic waves
• Most of these are harmless