Bell Work: Radioactivity What two particles have mass and are found in the nucleus? The ( proton / neutron / electron ) is the atomic number. _____ rays are given off in nuclear reactions. In fission, the atom(s) ( is split / are combined ). Elements are arranged on the _____ table.

RADIOACTIVITY!! N

Atomic #: number protons Mass #(Atomic Mass): protons + neutrons

Atomic Mass: protons + neutrons Atomic #: protons Average Atomic Mass averages all the isotopes of an element Atomic #: protons

GAMMA What is Radioactivity? Spontaneous emission of rays and particles from the nucleus of an unstable nucleus. Elements with atomic numbers greater than 82 are all radioactive. Radioactivity is the result of nuclear reactions: can also emit particles (alpha and beta) GAMMA

Nuclear Symbols Mass number (p+ + no) Element symbol Atomic number (number of p+)

Types of Radioactive Decay 4 alpha production (a): helium nucleus beta production (b): a neutron becomes a proton and an electron is emitted 2+ He 2 Notice how the mass on both sides of the  is equal Notice how the proton number on both sides of the  is equal - 1 e Notice how the mass on both sides of the  is equal Notice how the proton number on both sides of the  is equal

What happens to the atomic nucleus? An atom of one element becomes an atom of another - TRANSMUTATION Why? An element’s identity is defined by the particles in the nucleus – change the nucleus, change the element No other reaction causes transmutation

Alpha Radiation Limited to VERY large nucleii. Notice how the mass before and after is equal Notice how the proton number before and after is equal

Beta Radiation Converts a neutron into a proton. Notice how the mass before and after is equal Notice how the proton number before and after is equal Beta Radiation Converts a neutron into a proton. The atomic number increases by 1.

Energy and Mass Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein’s equation: DE = Dmc2 Dm = mass defect DE = change in energy c = speed of light Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.

Types of Radioactive Decay gamma ray production (g):

Types of Radiation

A radioactive nucleus reaches a stable state by a series of steps A Decay Series

Half Life Each radioactive element undergoes radioactive decay emitting particles and/or energy. The time it takes for this decay to occur is half-life.

Half-life Time it takes for ½ the radioactive substance to decay Arsenic-74 has a half-life of 17.9 days. If you start with 100 grams of As-74, how much will be left after 53.7 days? Number half lives Time (days) Amount left (g) 100 Number half lives Time (days) Amount left (g) Number half lives Time (days) Amount left (g) 100 1 17.9 50 2 35.8 25 3 53.7 12.5 Number half lives Time (days) Amount left (g) 100 1 17.9 50 2 35.8 25 Number half lives Time (days) Amount left (g) 100 1 17.9 50

Fission and Fusion alternative energy sources.

Nuclear Fission and Fusion Fusion: Combining two light nuclei to form a heavier, more stable nucleus. Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers.

Fission

A Fission Reactor

Fusion

Fusion- The energy of tomorrow?