Physics – P6 Radioactivity
6.1.1 Electron shells
Electron Energy Levels
Electrons can move between energy levels by absorbing or emitting
electromagnetic radiation.
When it moves down an energy level, it emits EM radiation.
Absorption of EM radiation
It moves to a higher energy level, its ‘excited,’ and has absorbed photons
(packets of energy: EM radiation).
Went up two
Went up one
energy levels.
energy level.
Emission of EM radiation
When it has moved up an energy level, it becomes unstable. Eventually, it moves
down an energy level, and emits photons.
Went down
Went down two energy
one energy levels.
level.
All colours from the visible spectrum are made this way; light waves come from
the electrons moving down energy levels and emitting EM radiation.
Ionisation
Forms positive ions: electrons in the outer energy level are knocked out from an
atom.
- Friction removes electrons
- Absorb EM radiation; gain enough energy to leave the atom
- Chemical reactions
Forms negative ions: gains electrons.
- Chemical reactions
Isotopes
Isotopes have the same
protons and number of protons and
neutrons electrons and different
number of neutrons.
protons
1
, Physics – P6 Radioactivity
6.1.2 Radioactive decay
Radioactive Decay
Unstable nuclei
Occurs due to: too many or too few neutrons.
Radiation
Unstable nuclei emit radiation to become stable, in the form of a high energy
particle or wave. As the radiation moves away from the nucleus, it takes energy,
reducing overall energy of the nucleus, making it more stable.
Process of emitting radiation: radioactive decay; it is a random process.
Types of Radioactive Decay
Alpha particle
Symbol: α. Same as a helium nucleus; two protons and two neutrons, with a
charge of +2.
Beta particle
Symbol: β. When a neutron changes into (a proton and) a fast-moving electron. It
can be affected by a magnetic field, with a charge of -1.
Gamma rays
Symbol: γ. They are EM waves and have the highest energy, with no charge.
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6.1.1 Electron shells
Electron Energy Levels
Electrons can move between energy levels by absorbing or emitting
electromagnetic radiation.
When it moves down an energy level, it emits EM radiation.
Absorption of EM radiation
It moves to a higher energy level, its ‘excited,’ and has absorbed photons
(packets of energy: EM radiation).
Went up two
Went up one
energy levels.
energy level.
Emission of EM radiation
When it has moved up an energy level, it becomes unstable. Eventually, it moves
down an energy level, and emits photons.
Went down
Went down two energy
one energy levels.
level.
All colours from the visible spectrum are made this way; light waves come from
the electrons moving down energy levels and emitting EM radiation.
Ionisation
Forms positive ions: electrons in the outer energy level are knocked out from an
atom.
- Friction removes electrons
- Absorb EM radiation; gain enough energy to leave the atom
- Chemical reactions
Forms negative ions: gains electrons.
- Chemical reactions
Isotopes
Isotopes have the same
protons and number of protons and
neutrons electrons and different
number of neutrons.
protons
1
, Physics – P6 Radioactivity
6.1.2 Radioactive decay
Radioactive Decay
Unstable nuclei
Occurs due to: too many or too few neutrons.
Radiation
Unstable nuclei emit radiation to become stable, in the form of a high energy
particle or wave. As the radiation moves away from the nucleus, it takes energy,
reducing overall energy of the nucleus, making it more stable.
Process of emitting radiation: radioactive decay; it is a random process.
Types of Radioactive Decay
Alpha particle
Symbol: α. Same as a helium nucleus; two protons and two neutrons, with a
charge of +2.
Beta particle
Symbol: β. When a neutron changes into (a proton and) a fast-moving electron. It
can be affected by a magnetic field, with a charge of -1.
Gamma rays
Symbol: γ. They are EM waves and have the highest energy, with no charge.
2
