Transcript document

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.
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
Usually involve atoms with large nucleii
such as the Lathanides and Actinides
 They produce ,  and  emissions.
 Involve a nucleus collapsing to form a
smaller nucleus

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



Is emitted from a
nucleus during radio
active decay due to
too many protons
Consists of 2 protons
and 2 neutrons (a
helium nucleus)
Decreases mass by 4
and atomic # by 2
 237Np93 + 4He2
 4.0 cm of air
 Low penetration -protected by skin
 Is the most destructive radiation
because it ionizes atoms it bumps into
 Relative danger is low unless
ingested
 Used in smoke detectors
 241Am95
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. Due to neutron to proton ratio being too
great.
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 while leaving the overall mass unchanged.
231
Th 90
0
 -1
231
+
Pa 91
Notice how  particle emission raises the atomic number by 1
 Particle emissions
Can penetrate 6-300 cm of air
 Blocked by clothing and paper
 Moderate danger
 Excessive exposure can be harmful
 Used in many medical diagnostic tests
and treatments

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
– may accompany  and/or  emissions
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
Sterilization of equipment & foods
Electron Capture
Sometimes a nucleus will capture an
electron and a proton converts to a
neutron.
 This decreases the atomic number but
does not change the mass

 201Hg80
+
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.

 22Na11

0 e
+1
+
22Ne
10
Decay Series
When a radioactive nucleus such as 238U92
decays it often produces another radioactive
isotope which goes on to decay further.
You are going to construct a decay series
on graph paper for the element 238U92 to
show how it eventually forms a stable
isotope of lead 206Pb82
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
* 238U92
Mass
200
78
Atomic 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
* 238U92
234Th
90
Mass
*
200
78
Atomic 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
Atomic 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.






