N UCLEAR & T HERMAL

R EVIEW 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

R ADIOACTIVITY Radioactivity- is the process in which an unstable atomic nucleus emits charged particles and energy Radioisotope- atom containing unstable nucleus Radioactive isotope

N UCLEAR D ECAY 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

N UCLEAR R ADIATION Nuclear Radiation- charged particles and energy emitted from the nuclei of radioisotopes Three types of nuclear radiation Alpha particles Beta particles Gamma rays

A LPHA D ECAY 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

A LPHA D ECAY

B ETA D ECAY Beta Particle- an electron emitted by an unstable nucleus Has a -1 charge Common symbol for beta particle

B ETA D ECAY Problem? How can a nucleus composed of positive protons and neutral neutrons release a negatively charged electron?

B ETA D ECAY 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

B ETA D ECAY

G AMMA D ECAY 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

G AMMA D ECAY Gamma decay often accompanies alpha or beta decay

F ISSION & F USION

N UCLEAR F ORCES 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

S TRONG N UCLEAR F ORCE VS. E LECTRIC F ORCE 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 atomProton of large atom

U NSTABLE N UCLEI 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

F ISSION 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

F ISSION 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

F USION 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