Nuclear Reactions



Many atoms contain nuclei that are unstable, and so easily decay
An unstable nucleus is described as being radioactive, and will decay releasing
radiation
Each nucleus has its own rate of radioactive decay
Symbols of particles common in nuclear equations
Particle
Electron
Symbol
Neutron
Alpha particle
4
2
He
Beta particle
Summary of Alpha particles, Beta Particles and Gamma rays
Property
Nature of radiation
Alpha
4
2 He nuclei
Beta
Beta particle
Charge
Mass
+2
4 amu
-1
0
Gamma
High energy
radiation
0
0
Isotopes
The different isotopes of a given element have the same atomic number but different
mass numbers since they have different numbers of neutrons. The chemical properties
of the different isotopes of an element are identical, but they will often have great
differences in nuclear stability
Nuclear Notation
Sometimes you will see C-14 written. This means the isotopes of carbon with mass
number 14 (instead of normal 12).
Types of Emissions and Balancing Nuclear Reactions



When a nuclide decays, it will form a nuclide of lower energy, and the excess
energy will be emitted as radiation.
This radiation can be emitted in different forms, of which 3 are discussed
below.
When balancing a nuclear reaction, the total A and Z values must remain the
same in reactants and products.
A
Z
Re ac tan ts 
A
Z
Pr oducts
1
Alpha Particles and Decay
 Involves the loss of one alpha particle, which is identical to a Helium nucleus
( 24 He )
Example 1:
Note that the total mass numbers and atomic numbers on both sides are equal
Mass number total
Atomic number total
Left of the equation Right of the equation
234
=
4+ 230
92
=
2 + 90
Beta Particles and Decay
 Occurs when an isotope emits an electron, called a beta particle.
Example 2:
Mass number total
Atomic number total
Left of the equation Right of the equation
233
=
0+ 233
92
=
-1 + 93
Gamma Rays and Emission
 Accompanies alpha or beta emission,
 Gamma rays have neither mass nor charge. Generally, gamma rays are not
shown when writing nuclear reactions.
Artificial Transmutation
In artificial transmutation, the nucleus does not spontaneously decompose but
decomposes when it is bombarded by a neutron or another nucleus. The process of
artificial transmutation can be used to produce atoms with a specific number of protons
and neutrons. The particles used must be travelling at very high speeds in order to
overcome the electrostatic repulsion between them and the target nucleus. The high
speed of the particles is produced in particle accelerators, which use magnetic and
electric fields. You will not be able to predict the products of these reactions because
different particles may be produced in artificial transmutation. You can predict the
unknown if you are given enough information.
Example 4:
What element is produced during bombardment of a chlorine-35 nucleus
with a neutron to produce a proton?
35
17
Unknown:
Element X would be S-35 (mass # 35, atomic #16)
Cl
+ 01 n

Equation:
A
B
X + 11 p
2
Fission
Nuclear fission is a very important process for energy production today. Nuclear fission
occurs when a nucleus absorbs a neutron and splits into two smaller nuclei and several
neutrons. The produced neutrons collide with other fissionable nuclei, causing a chain
reaction. Nuclear fission reactions release a tremendous amount of energy and are used
in nuclear reactors today.
Example 15: Identify the unknown in the equation for the nuclear fission of uranium235 (notice that in this equation there are three neutrons produced so the
total mass of all of the neutrons produced will be 3)
235
92
A
1
U  01 n  87
35 Br  B X  3 0 n
Mass number
235
+1
=
87
+
A
+
3
Atomic number
92
+0
=
35
+
B
+
0
The unknown element is Lanthanum.
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