Agenda
Nuclear Chemistry lesson (nuclear
reactions and half-life)…sorry for the
long lesson today!
**HW: Nuclear reaction practice, “My
Favorite Memory” page MUST be
colored!

There are two types of reactions:
Chemical reaction – involves an exchange of
electrons
Nuclear reaction – involves a change in
the atom’s nucleus,
resulting in
Nuclear Reactions
Unlike chemical reactions, nuclear
reactions are unaffected by
• temperature,
• chemical catalysts or
• pressure
You cannot speed up, slow down,
or STOP radioactive decay!
What is Radioactivity?
Radioactivity – is the spontaneous
emission of radiation caused by:

an unstable atomic nuclei, or

a man-made nuclear reaction
Radioisotopes
Radioisotopes – have unstable nuclei

they gain stability by undergoing
nuclear changes

LARGE amounts of energy
are released (i.e. radioactive emissions)
Radioisotopes cont’d



Most nuclei found in nature are stable,
and remain intact (i.e. they do not emit
radiation)
However, all nuclei with 84 or more
protons are radioactive. (i.e. atomic
numbers of 84 or more)
For example, all isotopes of uranium
(atomic number 92) are radioactive.
3 Types of Radiation

Alpha – positive particle
α

Beta – negative particle
β

Gamma – pure energy
γ
Radiation Strength
Which materials will block the radiation?
Alpha rays






Beta rays





Gamma rays




Another example…
Mass # =
+
p
+
o
n
A closer look at…
The Alpha Particle
Alpha Particle, α, is a positive particle
containing 2 protons and 2 neutrons.
 Helium atom stripped of its electrons
(i.e. a Helium nucleus)
 Symbolized in reaction equations as:
mass number
charge
4
2
He
Alpha Decay
Example Reaction:
238
92
U
4
2
He +
234
90
Th
A closer look at…
The Beta Particle
Beta Particle, β – is a negative particle.
 Formed by the breakdown of a neutron
into a proton and a very high energy
electron!
 Symbolized in reaction equations as:
1
0
n
+1 p +
1
0
-1
e
 Beta Particle
Beta Decay
Example Reaction:
14
6
C
0
-1
e +
14
7
N
A closer look at…
The Gamma Ray
Gamma Ray, γ – is VERY high energy
electromagnetic radiation.
 Emitted by disintegrating nuclei
 Contains no mass, no charge
 Very penetrating and
very dangerous!
Nuclear Reaction Practice
Ex. 1: Write the equation for the beta
decay of Thorium-234.
234
90
Th
0
-1
e
+
234
91
Pa
Ex. 2: Write the equation for the alpha
decay of Radium-230.
230
88
Ra
4
2 He
+
226
86
Rn
Radioisotope Half-Life
Half-Life – time necessary for exactly onehalf of a radioactive material to decay.
 The half-life
for a radioisotope
NEVER changes!
How to read a Half-Life graph
Half-Life example



Strontium-90 has a half-life of approx.
28 years
If I have a 10 gram sample of Strontium90, then, after 28 years I will have 5
grams remaining of my sample.
After another 28 years, I will have 2.5
grams remaining…and so on.