1. NOTES #7C
Radioactivity

2. Radioactivity
Radioactivity – when energy and particles are spontaneously emitted by an unstable nuclei
Radioisotopes or radioactive nuclei – unstable nuclei
All isotopes of elements beyond Bismuth as well as Technetium and promethium
Radiation – energy (rays) and/or particles emitted
3 kinds (discussed later)

3. Radioactivity
Radioactive Decay – spontaneous process (does not require energy) where unstable nuclei lose energy by emitting radiation
Decay until form a stable (nonradioactive) element
Sometimes form different elements – natural transmutation
Recall Dalton’s Theory

4. Radioactivity Discovered by:
1896, Henri Becquerel found that uranium ores exposed to photographic film formed X-rays
Inspired Marie & Pierre Curie – found radioactivity working with uranium and radium

5. Radioactivity
Geiger counter: gas-filled metal tube used for detecting and counting individual particles of radiation
Invented by: Hans Geiger (worked w/ Rutherford)
Emits tick sounds – closer the ticks are, more radiation

6. Radioactivity
Nuclear Equations – used to show atomic number and mass number of particles
Nuclear Stability: Why are some atoms stable, while others are not?
Primary factor: ratio of # of n to # of p
Unstable if have too few or too many neutrons
Decay in order to form stable composition of neutrons and protons
Explains why there are few radioactive atoms in nature – most have decayed into stable nuclei

7. Radioactivity
Half-life: time needed for half of mass of the radioactive sample to decay into more stable substance
Symbol: t1/2
Handout: Half-life Equations and Example Problems

8. Radioactivity Types of Radiation (hand-out Radiation Types)
Alpha Particle: +2 particle, helium nucleus
Represented by: α or He
Largest – stopped by paper, skin
Nuclear equation – on handout

9. Radioactivity Beta Particle – high speed negatively charged particle
Represented by β or e
2nd largest – stopped by wood
Nuclear equation – on handout

10. Radioactivity Gamma rays – high energy neutral rays Represented by: γ
Not a particle, it’s a ray – stopped by 1ft of concrete or inches of lead, can penetrate skin
Nuclear equation – on handout

11. Radioactivity Types of Nuclear Reactions Fission – atom division
Atoms split when nuclei struck by neutron which then promotes more neutrons to be formed and then hit other nuclei
Continues spontaneously – called chain reaction
Manhattan Project – in 1942 produced first man-made nuclear chain reaction
1945, in New Mexico first nuclear bomb explosion took place (incorrect to say “atomic bomb”)

12. Radioactivity Fusion – nuclei are fused together
Happens only on sun – at very high temperatures
Advantages: no weapons produced, more energy released, no pollution or radioactive wastes produced, fuel (deuterium) extracted from water