NOTES #7C Radioactivity

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)

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

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

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

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

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

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

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

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

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”)

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