Nuclear Reactions
Nuclear Reactions vs.
Normal Chemical Changes
NUCLEAR REACTIONS involve the NUCLEUS.
PROTONS and NEUTRONS are
REARRANGED in the nucleus, releasing a
tremendous amount of energy.
“Normal” CHEMICAL REACTIONS involve
ELECTRONS, not protons and neutrons.
Why do Nuclear
Reactions happen?
Nuclear Instability
The stability of a nucleus is dependent
on the neutron to proton ratio (N:Z)
For light nuclei (elements 1-20), the N:Z ratio should be 1:1
For heavy nuclei (elements above 20), the N:Z ratio should be 1.5:1
Atoms that lie either above
or below the band of
stability will undergo
nuclear decay to achieve
stability.
Atoms that lie ABOVE
the band of stability have
TOO MANY NEUTRONS.
Atoms that lie BELOW
the band of stability have
TOO MANY PROTONS.
Two Types of Nuclear Reactions
Fission – nucleus splits into smaller nuclei
to become more stable.
Fusion – nuclei fuse into one larger
nucleus to become more stable.
Uses for Nuclear Reactions
Fission:
• atomic bombs (like those dropped on Hiroshima and
Nagasaki).
• Nuclear reactors
Fusion:
• the sun (or any star)
• Creating elements larger than Element 92 Uranium
– Elements 1-92 occur naturally in the universe
Half-Life (Radiocarbon dating):
• Using the known half-life of elements to determine
the age of artifacts
Half-Life
• Radioisotope: an unstable, radioactive
atom that decays over time to become
more stable.
• Half-Life: the amount of time that it
takes half of a radioisotope sample to
decay.
Nuclear Decay
RADIATION: particles & electromagnetic
waves released during nuclear decay.
Most radiation comes from the SUN & COSMIC
RADIATION.
Nuclear Decay Products
4
2
He
or 4
2

ALPHA particle: α
is a Helium-4 nucleus
has POOR PENETRATING ability –
can be stopped by PAPER.
Nuclear Decay Products
BETA particle: β
0
-1

or
e
0
-1
aka. ELECTRON or NEGATRON
has a negative charge
A NEUTRON emits a negatron and then BECOMES a PROTON

0
+1
or
e
0
+1
POSITRON
aka. ANTIELECTRON
has a positive charge
A PROTON emits a positron and then BECOMES a NEUTRON
Penetrate BETTER than ALPHA particles, but can be stopped by an
ALUMINUM sheet.
Nuclear Decay Products
0
0
g
GAMMA ray: γ
is a gamma PHOTON.
has GREAT PENETRATING ability – can ONLY be
stopped by LEAD or CONCRETE.
is very DANGEROUS.
can be released with other forms of decay.
Nuclear Decay Products
Nuclear Equations
Reactants
Yield
Products
Nuclear equations must be BALANCED.
The sum of the MASS NUMBERS and the
sum of the ATOMIC NUMBERS must be
the SAME on both sides of the equation.
Alpha Decay Reaction
238
92
U
234
90
Th +
4
2
Mass # Change: decrease by 4
Atomic # Change: decrease by 2
He
Beta Decay Reaction
14
6
C
14
7
N +
e
0
-1
Mass # Change: no change
Atomic # Change: increase by 1
Electron Capture Reaction
51
24
Cr +
0
-1
e
51
23
V
Mass # Change: no change
Atomic # Change: decrease by 1
Positron Emission Reaction
49
24
Cr
49
23
V +
0
+1
e
Mass # Change: no change
Atomic # Change: decrease by 1
Nuclear Reactions
Radiation
Type
Particle
Involved
He
Alpha
Decay
4
2
Beta
Decay
0
-1
Positron
Emission
Gamma
Radiation
e
0
e
+1
0
0
g
Mass
Charge
Change in Change in
Mass # Atomic #
4
2
Decreases
by 4
Decreases
by 2
0
-1
N/C
Increases
by 1
0
1
N/C
Decreases
by 1
0
0
N/C
N/C