Discovery of Radiation Roentgen (1895) Studied fluorescent materials that glowed when hit with a beam of electrons. Discovered a mysterious form of radiation was given off even without electron beam. This radiation could pass through paper and other objects but not dense materials (lead, bone). Called them X-rays

Becquerel (1896) Studied fluorescent minerals containing uranium. Discovered radioactivity by accident on a cloudy day: Thought that an external source was needed to produce the mysterious radiation. Found that uranium emits radiation without external source.

Pierre and Marie Curie Thought radioactivity was a property of heavy elements. During study, discovered new radioactive elements: Polonium and Radium. Wondered how small mass can give off large amount of energy: Explained by Einstein with E=mc2.

Rutherford Studied radioactivity and named types of nuclear radiation. Discovered that elements decay into other elements after emitting nuclear radiation. Called it Nuclear Decay. Gold foil experiment revealed that the mass of an atom is concentrated in the nucleus (atom is mostly space)

Stable vs Unstable Isotopes Atomic #s 1 − 19 Stable & unstable, naturally occurring isotopes Atomic #s 20 − 83 Mixture of stable and unstable isotopes Naturally occurring and man made Atomic #s 84 and higher All unstable

Unstable Isotopes Unstable isotopes will automatically change into a more stable form Transmutation ═ the process of one element changing into another element Law of Conservation of Mass Net charge remains unchanged

Nuclear Symbol Mass Number X Atomic Number where Mass Number = Protons + Neutrons X = Symbol of Element Atomic Number = # of Protons (Electrons) **The atomic number tells the symbol to use

Types of Radiation Alpha particle () Beta particle (-) Positron (+) helium nucleus Beta particle (-) electron Positron (+) positron Gamma () high-energy photon

Alpha Emission Numbers must balance!! parent nuclide daughter nuclide occurs when the nucleus has too many protons which cause excessive repulsion. parent nuclide daughter nuclide alpha particle Numbers must balance!!

Alpha Emission Ex. Plutonium-239 undergoes alpha decay + = + 239 235 4 Atomic Mass: = 94 92 + Atomic #: 2 Masses must be equal = Conservation of mass

Alpha Emission + = + = - = = + = - = = 210 A 4 210 A 4 206 84 Z 2 84 Z Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide. Solve for + 210 = A 4 + Atomic Mass: 210 = A 4 - = 206 84 = Z 2 + Atomic #: 84 = Z 2 - = 82 =

Beta Emission electron occurs when the neutron to proton ratio is too great. electron

Beta Emission + = + = - = = + = + = = 210 A 210 A 210 84 Z -1 84 Z 1 Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide + 210 = A + Atomic Mass: 210 = A - = 210 84 = Z -1 + Atomic #: 84 = Z 1 + = 85 =

Positron Emission positron Occurs when the neutron to proton ratio is too small. positron

Positron Emission + = + = - = = + = - = = 210 A 210 A 210 84 Z +1 84 Z Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide + 210 = A + Atomic Mass: 210 = A - = 210 84 = Z +1 + Atomic #: 84 = Z 1 - = 83 =

Gamma Emission Emission of high energy electromagnetic wave. occurs when the nucleus is at too high an energy. Emission of high energy electromagnetic wave.

Gamma Emission + = + = = + = = 210 A A 210 84 Z Z 84 Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide + 210 = A + Atomic Mass: A = 210 84 = Z + Atomic #: Z = 84 =

Electron Capture electron occurs when the neutron to proton ratio in the nucleus is too small. electron

Electron Capture + = + = = + = = 210 A A 210 84 Z -1 Z 83 Ex. Polonium-210 captures an electron to produce this daughter nuclide + 210 = A + Atomic Mass: A = 210 84 = Z -1 + Atomic #: Z = 83 =