Nuclear Physics LATEST EDITION 2024/25 GUARANTEED GRADE A+
Properties of α radiation 2
Alpha particles can only be emitted by nuclei with an atomic number greater than 82.
Typically, alpha particles cannot penetrate through a sheet of paper or a few mm of air.
Rutherford Scattering
In the ear...
Nuclear Physics LATEST EDITION
2024/25 GUARANTEED GRADE A+
Properties of α radiation 2
Alpha particles can only be emitted by nuclei with an atomic number
greater than 82.
Typically, alpha particles cannot penetrate through a sheet of paper
or a few mm of air.
Rutherford Scattering
In the early 20th century Ernest Rutherford conducted an experiment
which completely changed our model of the atom.
The experiment
Rutherford conducted an experiment where he fired alpha particles at
a very thin piece of gold leaf.
The particles mostly passed through the gold leaf, but some were
deflected at large angles.
This was not expected and disproved the 'plum pudding model'.
Explanation of results
The strong deflections were caused by electrostatic repulsion between
the positive nucleus and the positive alpha particles.
Most alpha particles passed through as the atom is mostly free space.
This new theory became our current model of the atom, a positive
nucleus with negative electrons in orbit.
Why did most alpha particles pass through the gold leaf?
Atoms are mainly empty space
Gold has little mass
Alpha particles have no mass
There were holes in the leaf
Atoms are mainly empty space
Democritus
In the 5th century BC, Democritus suggested that matter was made of
lumps called atomos.
All atomos were believed to be identical.
The atomo was considered the smallest possible unit of matter.
Dalton
In the 1800s, Dalton agreed with Democritus.
However, he believed that different types of atom corresponded to
different elements.
Thomson
Thomson discovered that electrons could be removed from atoms.
, This showed that atoms were not the smallest units of matter.
Thomson believed that atoms were clouds of positive charge with
negative electrons suspended inside.This was called the plum-pudding
model.
Rutherford
Rutherford used his famous scattering experiment to show that atoms
consist of a positively charged nucleus with orbiting negatively
charged electrons.
This is the current day model of the atom.
Properties of α radiation
Alpha particles are:
Two protons and two neutrons bound together (the equivalent of a
helium nucleus)
Weakly penetrating
Easily absorbed
Positively charged
Properties of β radiation
Beta particles are:
Electrons (or positrons) that are emitted from an unstable nucleus
Moderately penetrative
Either positively or negatively charged
Beta plus particles emitted by proton rich nuclei
Beta minus particles emitted by neutron rich nuclei.
Applications of beta particles
Typically, beta particles cannot penetrate through about 5 mm of
aluminium or about 30 cm of air.
A beta source is used for gauging the thickness of aluminium sheeting
or foil.
A beta-plus emitter is used in medical PET scanning.
Applications of α radiation
An alpha source is used in fire alarms. Alpha particles cannot
penetrate through smoke. This is detected and sets off the alarm.
Beta particles are:
1
Moderately penetrative
2
Either positively or negatively charged
3
Positrons or electrons
Radioactivity Safety
All institutions that hold radioactive sources need a permit to do so.
The institution will have to follow some local rules about storage
and use of sources. Protective measures should include:
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