NUCLEAR & THERMAL
REVIEW

Atoms

Electrons
Negative Charge
 Found in electron cloud
 Orbiting nucleus


Protons
Positive Charge
 Found in nucleus
 The number of protons determines what element the atom is


Neutrons
Neutral Charge
 Found in nucleus

RADIOACTIVITY


Radioactivity- is the process in which an unstable
atomic nucleus emits charged particles and
energy
Radioisotope- atom containing unstable nucleus

Radioactive isotope
NUCLEAR DECAY

Radioisotopes spontaneously change into other
isotopes over time


That process is called Nuclear Decay
Nuclear Decay:

Atoms of one element can change into a different
element


Example: Uranium-238 decays into Thorium-234
Nuclear decay can result in the new element being a
stable isotope or a radioisotope
NUCLEAR RADIATION


Nuclear Radiation- charged particles and energy
emitted from the nuclei of radioisotopes
Three types of nuclear radiation
Alpha particles
 Beta particles
 Gamma rays

ALPHA DECAY

Alpha particle- a positively charged particle
made up of two protons and two neutrons
Same as a helium nucleus
 It has a +2 charge



Each proton +1 (no negative electrons)
Common symbol for an alpha particle
ALPHA DECAY
BETA DECAY

Beta Particle- an electron emitted by an unstable
nucleus
Has a -1 charge
 Common symbol for beta particle

BETA DECAY

Problem?
 How
can a nucleus composed of
positive protons and neutral
neutrons release a negatively
charged electron?
BETA DECAY

In Beta Decay:



A neutron breaks down into a proton and an electron
The electron is emitted from the nucleus
The proton stays trapped in the nucleus turning it
into a new element
BETA DECAY
GAMMA DECAY

Gamma Ray- ray of energy emitted from an
unstable nucleus
No Mass
 No Charge
 Energy wave that travel at speed of light
 Atomic number and mass number stay the same


Common symbol
GAMMA DECAY

Gamma decay often accompanies alpha or beta
decay
FISSION & FUSION
NUCLEAR FORCES

Strong Nuclear Force – the attractive force that
binds the particles of a nucleus together

Does not depend on charge


Active pp, nn, pn
Over short distances strong nuclear force is much
stronger than the electric forces among protons
Protons have a positive electrical charge that repel each other
 Strong Nuclear Force 100x stronger than electrical force at
distance the width of a proton

STRONG NUCLEAR FORCE VS. ELECTRIC FORCE

Electric force depends on number of protons


Larger atoms (more protons) have a greater electric
force repelling protons
Strong Nuclear force is the same on individual
protons in both large and small atoms
Proton of small atom
Proton of large atom
UNSTABLE NUCLEI

When:
Strong Nuclear Force < Electric Force
The atom becomes unstable - Radioactive

Since strong nuclear force doesn’t increase with
size but electric force does all elements with more
than 83 protons are radioactive
FISSION


Fission- the splitting of an atomic nucleus into
two smaller parts
Otto Hahn & Fritz Strassman discovered by
accident
Bombarding uranium-235 with neutrons trying to
make larger elements
 Instead of finding larger elements they found the
smaller element barium
 Lise Meitner helped them figure out what happened
and theorized the u-235 nuclei had broken down into
smaller fragments demonstrating nuclear fission

FISSION

In nuclear fission:

A lot of energy is released from a very small mass
1 kg uranium-235 fission = burning 17,000 kg coal
 First nuclear bombs contained 5-6 kg plutonium


Chain reaction- neutrons released during
splitting initial nucleus trigger a series of nuclear
fissions
FUSION


Fusion- process where nuclei of atoms combine to
form a larger nucleus
Stars are powered by fusion
600 million tons H undergo fusion into He every
second
 Requires extremely high temperatures

10,000,000 degrees Celsius
 Matter exists as plasma at these temperatures


Not achievable on Earth with present technology