Download 3 main types of particle

Types of Nuclear Decay
Topic 7.2
The ABC’s of Radioactivity
Nuclear Decay Review
 Describe the nuclear decay process.
 Name the 2 key items involved
 What is the relationship between the rate of
decay and the number nuclei in the sample?
 Describe the term half-life
 Why is the nuclear activity is more meaningful
than the number of particles in the nuclei?
During the decay process…
 the nucleus is ‘broken up’ into smaller pieces
 How does this happen?
 Where does the initial energy come from?
 How would the masses compare before and after
a decay?
 Are there certain types of particles that come out
of a decay or is it random?
Binding energy
This is the work required to completely separate
the nucleons of the nucleus.
Note: Binding Energy is NOT the energy
contained by the nucleus that holds the nucleons
together.
Binding energy
This is the work required to completely separate
the nucleons of the nucleus.
What happens if the nucleus is unstable?
Binding energy per nucleon
This is the work required to completely separate
the nucleons of the nucleus divided by the
number of nucleons.
It is a measure of how stable the nucleus is.
This is an
important graph
for this topic
The Binding Energy curve
Types of Nuclear Decay
They are defined by the 3 main types of particles
that can be ejected from an unstable nuclei.
Types of Nuclear Decay
What is the main reason that make unstable isotopes
‘decay’?
Alpha particles
α
Alpha particles
 2 protons and 2 neutrons joined together
 The same as the nucleus of a helium atom
 Stopped by paper or a few cm of air
 Highly ionising
 Deflected by electric and strong magnetic fields
4
2
2+
He
Alpha Decay
Alpha Decay
Atomic mass goes down by 4
235
231
4
92
90
2
U
2+
He
+
Th
Atomic number goes down by 2
Ionization by alpha particles
Ionization by alpha particles
Beta particles
β
Beta particles
 Fast moving electrons
 Effectively massless
 Stopped by about 3 mm of aluminium
 Weakly ionising
 Deflected by electric and magnetic fields
0
e
-1
Beta Decay
Beta Decay
 In the nucleus a neutron changes into an electron
(the beta particle which is ejected) and a proton
(which stays in the nucleus)
 During beta decay the mass number stays the
same but the proton number goes up by 1.
Remember the electron comes from the nucleus!
231
Th
90
231
0
91
-1
Pa + e
Beta Decay – Mono energetic?
 Unlike alpha particles, beta particles can be
emitted with different energies
 How do we conserve the energy with each
reaction?
231
Th
90
antimatter
antineutrino
Pa + e + ‫ע‬e
231
91
0
-1
0
0
Antiparticles
 Produced naturally  symmetry in the universe!
 Particle + Antiparticle = ENERGY (photons)
 How did matter dominate in our universe?
antimatter
231
Th
90
positron
neutrino
Pa + e + ‫ע‬e
231
91
0
+1
0
0
Gamma rays
Gamma rays
 High frequency electromagnetic radiation
 Stopped by several cm of lead
 Very weakly ionising
 NOT affected by electric or magnetic fields
Gamma rays
Associated with daughter
nucleus of alpha decay
235
231
92
90
U
Th +
α
Types of Nuclear Decay
Particles in a Magnetic Field
If the magnetic
field is coming
out of the page,
name the three
types of radiation
that’s present in
this diagram
Particles in a Magnetic Field
Use the right
hand rule for
alpha particle!
α
Particles in a Magnetic Field
Use the left hand
rule for beta
particle!
β
α
Particles in a Magnetic Field
Gamma rays have
no charge!
β
ϒ
α
Cloud Chamber
 Utilizes ionization properties of alpha & beta
particles
 Vapour condenses around small particles of ‘dust’ 
cloud
 Similar to vapour trails left by airplanes
PhET Simulations
 Alpha Decay
 Beta Decay