Transcript nuclear powperpoint

Nuclear Chemistry
Nuclear
• Radioactivity – the process by which materials
give off rays and particles.
• Radiation – penetrating rays and particles
emitted by a radioactive substance.
• Radioisotopes – unstable nuclei
Nuclear
Radioactive substances emit radiant energy
because they are unstable
They are unstable because of the protonneutron ratio.
*Neutrons act as “insulation” or “glue” to help keep the
nucleus from breaking apart
*When there are too few neutrons, or too many neutrons, the
nucleus will want to give off energy
Reactions
Chemical reactions vs. Nuclear Reactions
*Chemical reaction- atoms gain or lose electrons, change their
electron configuration
*Nuclear reaction- atoms gain or lose protons, neutrons, or energy;
cannot be sped up, slowed down or stopped.
Dalton was wrong- atoms are divisible
An unstable nucleus releases energy by emitting
radiation during radioactive decay.
Definitions
• Parent nuclei- nucleus that breaks apart.
• Daughter nuclei- nucleus that is formed.
*The total mass and charge should be conserved in a nuclear reaction (law of
conservation of mass)
Types of decay cont.
Alpha Radiation (α)
*emit a particle that has 2 protons, 2 neutrons
*resembles a Helium atom
238
*
4 He + 234 Th
U

92
2
90
the sum of the mass numbers (superscripts) on the
right MUST equal the sum on the left
* the sum of the atomic numbers (subscripts) on the
right MUST equal the sum on the left
Types of Rxns cont.
Beta radiation (β)
*emit an electron
*How? A neutron breaks apart into a proton and
electron.
*The electron is ejected, the proton stays inside
1 neutron  1 proton + 0 electron
0
1
-1
*the nucleus loses a neutron and electron, but gains a
proton
14 C  14 N + 0 e
6
7
-1
*the sum of mass and atomic numbers MUST be equal
on the left and right
Types of Rxns cont.
Gamma radiation (γ)
*Release high-energy photon (called a gamma
ray)
230 Th  230 Th + 0 γ
90
90
0
*Emitting a gamma ray does not change the
mass or atomic numbers
Radiation Graph
Particle
Symbol
Notation
Penetration
Damage
alpha
α
4 He
2
least
most
beta
β
0 e
-1
medium
medium
gamma
γ
0
0γ
most
least
Bombardment rxns
A high energy particle is fired at an unstable
isotope, resulting in a nuclear reaction
Can bombard with alpha particles, neutrons, or
protons
Use this type of reaction to create artificial
elements (Plutonium, Neptunium, etc.)
238 U
92
+ 10n  23993 Np + 0-1e
fission
*The splitting of a nucleus into smaller fragments
When nuclei of certain isotopes are bombarded
with a neutron, they undergo fission
Uranium-235 and Plutonium-239 are the only
nuclei that can undergo fission
235 U + 1 n  91 Kr + 142 Ba +1 n
92
0
36
56
0
Fission cont.
Chain Reaction: some of the neutrons released
react with other fissionable atoms, producing
more neutrons which produces more fission
reaction
Atom Bombs
Devices that start uncontrolled nuclear chain
reactions
When the US dropped them in Japan-120,000
people died instantly
Need enough uranium or plutonium to reach
supercritical mass
Once you have supercritical mass, you can
start the chain reaction
Atom Bombs cont.
Manhattan project-name of the project
that developed the A-bomb
*Dr. Oppenheimer led the project
Who has tested A-bombs? USA, Soviet
Union, United Kingdom, France, China, India,
Pakistan and North Korea
Nuclear Reactors
*use controlled fission reactions to produce energy
Nuclear Reactors cont.
Nuclear Waste
*Fuel rods from nuclear power plants are one
source of nuclear waste.
*Fuel rods contain some Uranium-235 or
Plutonium-239
*takes a long time (more than a decade) for
any remaining radioactive fuel to decay
*the fuel rods must be stored in water cooling
tanks or stored off-site
Fusion
*when nuclei combine to produce a nucleus of
greater mass.
The energy released by the sun is a result of fusion
*Hydrogen nuclei fuse to make Helium nuclei
Releases much more energy that fission reactions
They can only occur at extremely high temperatures
(excess of 40,000,000°C)and are difficult to
control
Fusion cont.
Scientists are interested in fusion because the
fuel is cheap and available.
2 H
1
+ 31H  42He + 10n + energy
Hydrogen Bomb
Based on fusion reactions
10 times more powerful than the atomic bomb
USA, Russia, United Kingdom, France and China
have tested H-bombs
Contains an atomic core: once fission occurs, the
temperature becomes high enough to allow for
the fusion rxn.
Fusion rxn produces a shock wave (extremely
high pressure gas) that causes damage
Radiation Uses
Radiation cannot be seen, heard, felt, or smelled
Radiation detector machines to detect radiation
(Geiger counter, Scintillation counter, film
badge)
Radiation can be harmful because it causes
damage to body tissue
It can also be used to trace, diagnose diseases
and treat cancer