Nature of Atoms Study of the Atom began with study of Radiation 1895 German, W K Roentgen studies Fluorescence – emission of light when struck with radiant E (ultraviolet) Accidentally discovered mysterious source of radiation, soon called X-rays

Nature of Atoms 1896 French physicist Henri Becquerel discovered radiation more powerful than X-rays when U-containing mineral (Pitchblende) exposed photographic plates Radiation is stronger than X-rays 1903 French scientist Marie Curie & husband Pierre isolated Polonium and Radium from Pitchblende ore

Nuclear Radiation Nonionizing radiation- low E Visible, infrared, microwave, radio Transfers all its E to matter, causing atoms to vibrate or move e- to higher energy levels (light) Excessive exposure can be dangerous (sunburn) Ionizing radiation- high E Alpha, beta, & gamma radiation, X-rays, U-V) Can ionize atoms/molecules, making them highly reactive, very dangerous to living cells/tissues

Nuclear Radiation Nuclear radiation- form of ionizing radiation that results from nuclear changes Radioactive atoms have unstable nuclei, emitting subatomic particles and E Radioactive atoms may change to other elements if atomic # changes Alpha rays- positively charged particles, helium nuclei Beta rays- negatively charged particles, high speed e- Gamma rays- high speed electromagnetic radiation, no charge

Ernest Rutherford Rutherford- English physicist developed a more modern model of the atom Performed the “gold foil experiment” with Hans Geiger and Ernest Marsden

Gold Foil Experiment

Rutherford's Nuclear Model  1. The atom contains a tiny dense center called the nucleus the volume is about 1/10 trillionth the volume of the atom 2. The nucleus is essentially the entire mass of the atom 3. The nucleus is positively charged the amount of positive charge of the nucleus balances the negative charge of the electrons 4. The electrons move around in the empty space of the atom surrounding the nucleus

Nuclear Radiation Exposure to ionizing radiation: Radioisotopes are natural Different ones emit different types and amounts of radiation Everyone receives background radiation All life forms contain radioisotopes Units for measuring radioactivity: Gray (Gy) – SI unit measures the quantity of ionizing radiation delivered to a sample, 1 Gy = 1J/kg (how much radiation was absorbed by body tissue)

Nuclear Radiation Sievert (Sv) – measures the ability of radiation, regardless of type, to cause ionization of tissue 1 Sv = same effects as one Gy of gamma radiation Sv can be used to compare one type of radiation with another Radiation Absorbed Dose (rad)- U.S. unit, 1 rad = 1/100 Gy Roentgen Equivalent Man (rem)- U.S. unit, 1 rem = 1/100 Sv

Nuclear Energy Nuclear fission – splitting an atom into two or more smaller atoms Splitting U-235 releases about one million times more E than any chemical reaction Strong force is broken in the nucleus resulting in the loss of some of the atom’s mass E = m c2 (Einstein) 1g of matter = 700,000 gallons of gasoline