Physics IGCSE – Radioactivity Notes
Specification:
, 7.1 The unit for the activity of a radioactive source is Becquerel, Bq.
7.2, 7.3
235
U92
This is how to represent a Uranium atom, with 235 protons and neutrons, and 92 electrons.
The mass (or nucleon) number = the number of protons and neutrons. The atomic (or
proton) number is the number of electrons in the atom
Isotopes are atoms of the same element, with the same mass number, but different atomic
number.
7.4 Radioactivity - the emitting of ionising radiation from unstable atoms in a
random process.
Why does a nucleus decay?
An unstable nucleus becomes more stable.
The process is spontaneous (has no cause) and random (unpredictable).
7.5, 7.7, 7.8 The four types of radiation (at GCSE level) are alpha
particles, beta particles, gamma rays and nuclear radiation.
Alpha particles are highly ionising.
Beta particles are moderately ionising.
Gamma rays are lowly ionising.
Alpha (α )
These are the least penetrating.
Stopped by paper, 5cm of air, and skin.
An α particle is a helium nucleus He∨ 42¿ 42α .¿
¿226 222 4
88 Ra → 86 Rn + 2α .
In emitting an alpha particle, an atom of one element becomes an atom of
another element, 2 places back in the periodic table.
When something emits alpha particles, it always decreases the mass number by
4, decreases the proton number 2, and decreases the neutron number by 2.
Beta ( β )
They are stopped by aluminium a few mm thick.
They are extremely fast-moving electrons. Note that this is nothing to do
with the atomic electrons.
A β particle is an electron, −10e−¿∨−10 β ¿
14 14 0 −¿
6 C → 7 N +−1e ¿
In emitting a beta particle, a neutron turns into a proton, and emits an electron
(because another electron is needed to balance the charges). This electron
emitted is the beta particle.
When something emits beta particles, it always keeps the mass number the
same, decreases the proton number by 1, and decreases the neutron number by
2.
Gamma γ rays
Specification:
, 7.1 The unit for the activity of a radioactive source is Becquerel, Bq.
7.2, 7.3
235
U92
This is how to represent a Uranium atom, with 235 protons and neutrons, and 92 electrons.
The mass (or nucleon) number = the number of protons and neutrons. The atomic (or
proton) number is the number of electrons in the atom
Isotopes are atoms of the same element, with the same mass number, but different atomic
number.
7.4 Radioactivity - the emitting of ionising radiation from unstable atoms in a
random process.
Why does a nucleus decay?
An unstable nucleus becomes more stable.
The process is spontaneous (has no cause) and random (unpredictable).
7.5, 7.7, 7.8 The four types of radiation (at GCSE level) are alpha
particles, beta particles, gamma rays and nuclear radiation.
Alpha particles are highly ionising.
Beta particles are moderately ionising.
Gamma rays are lowly ionising.
Alpha (α )
These are the least penetrating.
Stopped by paper, 5cm of air, and skin.
An α particle is a helium nucleus He∨ 42¿ 42α .¿
¿226 222 4
88 Ra → 86 Rn + 2α .
In emitting an alpha particle, an atom of one element becomes an atom of
another element, 2 places back in the periodic table.
When something emits alpha particles, it always decreases the mass number by
4, decreases the proton number 2, and decreases the neutron number by 2.
Beta ( β )
They are stopped by aluminium a few mm thick.
They are extremely fast-moving electrons. Note that this is nothing to do
with the atomic electrons.
A β particle is an electron, −10e−¿∨−10 β ¿
14 14 0 −¿
6 C → 7 N +−1e ¿
In emitting a beta particle, a neutron turns into a proton, and emits an electron
(because another electron is needed to balance the charges). This electron
emitted is the beta particle.
When something emits beta particles, it always keeps the mass number the
same, decreases the proton number by 1, and decreases the neutron number by
2.
Gamma γ rays
