Energy and our Universe - Pearson Schools

52
BTEC’s own resources
2.8 Understanding radiation
In this section:
Key terms
P4
M2
Nucleus – the inner part of the atom,
where protons and neutrons are found.
Radiation – energy spreading out, as
carried by electromagnetic radiation, or
carried by a particle.
Ionising radiation – radiation that can
remove electrons from atoms, causing
the atom to become positively charged.
Non-ionising radiation – radiation that
does not remove electrons from atoms,
e.g. microwaves or infrared.
When we think of radiation, we
usually think of things like nuclear
bombs and radiation leaks,
which are uncontrolled radiation
and are extremely dangerous.
However, medical physicists can
use controlled radiation to kill
cancer cells in tumours.
D2
A stable nucleus has the right number of protons and neutrons so it
does not break apart. If the number of protons and neutrons changes,
the nucleus becomes unstable and emits ionising radiation. This
radiation has three types: alpha, beta and gamma. They differ in how
ionising and how penetrating they are, and how they react to magnetic
or electrical fi elds.
Non-ionising radiation is radiation from the low frequency end of the
electromagnetic spectrum: radio, microwave, infrared and visible light.
Alpha () radiation
Alpha radiation consists of particles. These are helium nuclei, each
having two protons and two neutrons, and a charge of +2. When
particles hit another substance, e.g. air, they knock electrons off the
particles they hit. This leaves the particles with a positive charge; the
particles have been ionised. Alpha radiation is highly ionising. (If you
swallow particles, they cause serious damage because they ionise
DNA.)
particles are large compared with electrons and protons so they
cannot penetrate far into a material. For example, a few centimetres
of air or a sheet of paper will stop particles. particles are weakly
penetrating. This means there is little chance of particles getting
into the human body through the skin.
Because particles have a positive charge, they will be attracted to a
negatively charged plate.
Activity A
Describe alpha radiation.
Beta () radiation
Beta radiation consists of fast-moving electrons that have been given off
(emitted) by unstable nuclei. If they collide with an atom, they can knock
off an electron and ionise the atom. Because particles are small, they
don’t ionise as much as particles. They are moderately ionising.
Because they are less strongly ionising, particles can travel
further than particles. They can travel through a few millimetres
of aluminium before they are stopped. They are moderately
penetrating. This makes them dangerous if they come into contact
with living things.
Because particles are electrons, which have a negative charge,
they will be attracted to a positively charged metal plate. They are
defl ected more than particles because they are lighter.