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 pp, nn, pn

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 ForceThe 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