Discovery of Radiation Roentgen (1895) 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 Studied fluorescent materials that glowed when hit with a beam of electrons.

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.

Thought radioactivity was a property of heavy elements. Pierre and Marie Curie 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=mc 2.

Studied radioactivity and named types of nuclear radiation. Rutherford 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 − 82 Mixture of stable and unstable isotopes Naturally occurring and man made Atomic #s 83 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 (  ) – helium nucleus Beta particle (  -) –electron Positron (  +) –positron Gamma (  ) –high-energy photon

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

Alpha Emission Ex. Plutonium-239 undergoes alpha decay Atomic Mass: = Atomic #: = Masses must be equal = Conservation of mass

Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide. Solve for + Alpha Emission Atomic Mass: 210 = A4 + Atomic #: 84 = Z = A4 - = = Z2 - = 82 =

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

Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide + Beta Emission Atomic Mass: 210 = A0 + Atomic #: 84 = Z = A0 - = 84 = Z1 + = 85 =

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

Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide + Positron Emission Atomic Mass: 210 = A0 + Atomic #: 84 = Z = A0 - = 84 = Z1 - = 83 =

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

Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide + Gamma Emission Atomic Mass: 210 = A0 + Atomic #: 84 = Z 0 + A = 210 Z = 84 =

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

Ex. Polonium-210 captures an electron to produce this daughter nuclide + Electron Capture Atomic Mass: 210 = A0 + Atomic #: 84 = Z + A = 210 Z = 83 =