Nuclear Stability
The stability of an atom’s nucleus depends on the ratio of
protons and neutrons
- too many or too few neutrons can lead to instability
- many isotopes are radioactive (unstable nucleus)
 Any nucleus with more than 82 protons is unstable and
therefore radioactive
 A nucleus can become stable by releasing energy
- the more unstable the nucleus, the more energy it will release
Examples:

Nuclear Force- one of the four fundamental forces in our universe
- incredibly powerful, holds nucleus of atom together
- releasing this force results in a nuclear reaction
4
2
206
82
He
Pb
The process by which an unstable nucleus becomes stable
Radiation: the penetrating rays and particles emitted by an unstable nucleus
-similar to x-rays
Radioisotopes: isotopes with unstable nuclei
Ex. Carbon-14, Uranium 235, Thorium– 230, Thorium– 234
Radioactive decay:when an unstable nucleus loses energy by emitting radiation
-it becomes smaller more stable nucleus
Radiation
How was radiation discovered and what scientist
worked to understand it?
1)
Alpha radiation
~Radiation that occurs when a helium nucleus (alpha particle) is emitted from an unstable nucleus
Uranium-238
Alpha particle (α)
Atomic mass
Thorium– 234
Atomic #
 helium nucleus
 2 protons, 2 neutrons
2) Beta radiation
~Radiation that occurs when a fast moving electrons emitted from a radioactive source
- neutron decomposes into an
0
electron and a proton
-1
- electron is released (β particle)
e
3) Gamma radiation
~ Radiation that occurs when high energy electromagnetic radiation is given off by a radioisotope
- visible light is also electromagnetic radiation, but of a much
lower energy
 no mass (not matter like the others)
0
 gamma rays are always accompanied by a beta or alpha particle
0
γ
Used to represent the type of radiation
occurring from a nuclear reaction
1)
238
92
U
2)
14
6
C
3)
230
90
4)
234
90
Th
Th
234
90
14
7
N
Th
+
Use these symbols to
complete the equations
+
226
88
Ra
+
234
Pa
+
91
0
-1
e


the splitting of a nucleus into smaller fragments
fission occurs when the nuclei of certain radioisotopes are bombarded
with neutrons
Nuclear fission can unleash enormous amounts of energy
- each time a nucleus splits energy is released
- the more atoms, the bigger the boom
 In an uncontrolled fission reaction the total energy released is nearly instantaneous
- all nuclei split at roughly the same time
 1 kg of uranium-235 = 20,000 tons of dynamite

Fission is a chain reaction
 uranium-235 or plutonium-239 is typically used
in nuclear power plants.
 nuclear power plants create electricity by producing heat
- How does heat = electricity?
 fission is controlled by the use of cadmium
control rods
- the control rods absorb neutrons to slow
down reaction
- if the reaction goes uncontrolled the reactor
core will melt down.
What about the nuclear waste?
Nuclear Reactor



2
1
3
1
fusion occurs when two light nuclei combine to produce
a nucleus of greater mass
the energy released by the sun is a result of fusion
a fusion reaction requires a starting temperature in excess of 40,000,000 K.
H
Deuterium
H
Tritium
4
2
He
At present why aren’t we able to use nuclear fusion as a way to generate electricity?
Half life- time required for one-half of the nuclei of a radioisotope sample to
decay.

After one half-life, half of the original radioisotope decays into stable atoms of a new element.
Carbon Dating
 It takes 5730 years for half of a carbon-14 sample to decay.
 by comparing how much carbon-14 and nitrogen-14 is in a
fossil scientists can estimate the age.
The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams would be
left after 7.2 minutes has elapsed?
After 24.0 days, 2.00 milligrams of an original 128.0 milligram sample remain. What is the half-life of
the sample?