1. 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

2. 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

3. 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

4. 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

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

6. Gold Foil Experiment

7. 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

8. 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)

9. 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

10. 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