Download Nuclear Processes

Nuclear Processes
In chemical reactions, electrons
in atoms are responsible for
bonds forming and being
destroyed.
The identity of the atoms
involved does not change
This is not true for nuclear
processes because;
These reactions involve the
protons and neutrons in the
nucleus – too large or too small
of a ratio between protons and
neutrons
There are two types of nuclear
reaction
Fission and Fusion Reactions
Fission Reactions
• Involve a nucleus collapsing to form a
smaller nucleus
• Usually involve atoms with large nucleii
such as the Lathanides and Actinides
• They produce ,  and  emissions.
Fusion Reactions
• These involve nuclei joining together to
make larger ones.
• These type of reactions are what go on
inside stars and provide the energy that
causes them to shine.
The  particle
• Consists of 2 protons
and 2 neutrons
• Is emitted from a
nucleus during radio
active decay
• Is the most destructive
radiation because it
ionizes atoms it bumps
into
The  particle
• Has a relative mass of 4 amu
• Low penetration ability (stopped by paper
or skin)
• Harmful if ingested or inhaled (can’t get
out)
• Decreases atomic number by 2
• Decreases mass by 4
The  particle
• The particle is the
same as a Helium
atom with the
electrons removed.
• It is often written as
4 He in nuclear
2
equations
An  decay reaction
The Uranium atom U23892 decays by  particle emission
238
U 92
He
What is represented by ?
4
2
+
?
234
90
An  decay reaction
The Uranium atom U23892 decays by  particle emission
238
U 92
He
4
2
234
+
Th 90
Th is thorium – we can work it out by using the periodic table
and looking up the atom with atomic number 90. The mass
number does not matter – it is simply an isotope of Th.
More  decay reactions
The Thorium atom Th22790 decays by  particle emission
227
Th 90
Complete the equation
More  decay reactions
227
Th 90
He
4
2
223
+
Ra 88
More  decay reactions
The Actinium atom Ac22589 decays by 3  particle emissions
225
Ac 89
Complete the equation
More  decay reactions
225
Ac 89
3He
4
2
213
+
Bi 83
 Particle emissions
 Particles are electrons but they do not come from the electron
shells which surround the nucleus – they come from the
nucleus itself.
The electron is emitted when a neutron sheds its negative charge
and becomes a proton. (Bet you didn’t know it could do that!)
1
0N
1
1
p
0
-1
Tritium decay (beta)
 Particle emissions
The effect of  Particle emission is to increase the proton count
by 1 whilst leaving the overall mass unchanged.
231
Th 90
What is ?
0
 -1
+
?
 Particle emissions
The effect of  Particle emission is to increase the proton count
by 1 while leaving the overall mass unchanged.
231
Th 90
231
0
 -1
+
Pa
91
Notice how  particle emission raises the atomic number by 1
Gamma decay occurs because the nucleus is
at too high an energy. The nucleus falls down
to a lower energy state and, in the process,
emits a high energy photon known as a
gamma radiation.
Gamma Ray Emission
• Gamma rays have no mass and no charge
• High energy and very penetrating
• May be stopped with very thick (6 ft. or so
of concrete) or 3-5 cm of lead (think about
the dentist)
• γ00 or 00γ
• Used for medical tests and treatments
Electron Capture
• Some times a nucleus will capture an
electron and a proton converts to a neutron.
• This decreases the atomic number but does
not change the mass
•
201Hg
80
+
0 e
-1
 201Au79 + γ00
Positron Emission
• A positron has the mass of an electron and
the charge of a proton – it’s kind of like a
“positive electron”
• It may be emitted when a proton turns into a
neutron
• Atomic number decreases and mass stays
the same.
•
22Na
11

0
+1e +
22Ne
10
Decay Series
When a radioactive nucleus such as U23892 decays it
often produces another radioactive isotope which
goes on to decay further.
We are going to construct a decay series on
graph paper for the element U23892 to show how
it eventually forms a stable isotope of lead
Pb20682
GET A PIECE OF GRAPH
PAPER
• Draw a vertical axis representing atomic
mass. It will need to run from 200 to 240
• Draw a horizontal axis representing atomic
number. It will need to run from 78 to 93.
• Position the isotope U23892 on your graph
and mark it clearly.
240
* U23892
Mass
200
78
Number
93
Plotting an  decay
• The nucleus gives off an alpha particle first
to form a new nucleus
• Work out what the new nucleus is
• Find the nucleus on your graph and add it in
• Join the points with an arrow
240
* U23892
Th23490 *
Mass
200
78
Number
93
Plotting a beta emission
• The Thorium next loses a Beta particle
• Work out what would be formed
• Add the nucleus onto your chart
240
* U23892
Th23490 * * Pa23491
Mass
200
78
Number
93
Building up the decay series
Continue to build up the series using the following
emissions. Each alpha emission is shown as a
diagonal to the left and each beta emission is a
horizontal line to the right.
If you are successful you should end up with Pb20682
Good Luck !
Emission sequence (including the
first two example emissions)
1.
2.
3.
4.
5.
6.
7.







8.
9.
10.
11.
12.
13.
14.






