Radioactive DecayRadioactive Decay
Yesterday we learned that all elements have different isotopes.
Example:1H (1 proton, 0 neutrons)2H (1 proton, 1 neutron)3H (1 proton, 2 neutrons)
Some isotopes are stable and will last essentially forever.
Some aren’t stable.
Radioactive DecayRadioactive Decay
An unstable isotope is said to be radioactive.Radioactive (unstable) isotopes = radioisotopes
Radioisotopes eventually decay into more stable forms.
A radioisotope releases energy by emitting radiation during the process of radioactive decay.
Radioactive DecayRadioactive Decay
Carbon-12 and carbon-13 are stable, but carbon-14 is radioactive.
6 p+ and 6 n0 6 p+ and 7 n0 6 p+ and 8 n0
What makes a radioisotope unstable?
What makes a radioisotope unstable?
An isotope can be unstable if:it is too heavy (more than 83 protons).its n0 to p+ ratio is too high.its n0 to p+ ratio is too low.
Types of RadiationTypes of Radiation
Alpha radiationComposition: Alpha particle (helium nucleus)Symbol: or 4HeCharge: +2Mass: 4 amuPenetrating power: Low (0.05 mm body tissue)Shielding: Paper, clothingEffect on nucleus: Z – 2, A – 4
Types of RadiationTypes of Radiation
Beta radiationComposition: Beta particle (electron)Symbol: or e-
Charge: -1Mass: 1/1837 amuPenetrating Power: Moderate (4 mm body tissue)Shielding: Metal foilEffect on nucleus: Z + 1; A unchanged.
Types of RadiationTypes of Radiation
Gamma radiationComposition: High-energy EM radiationSymbol: Charge: 0Mass: 0Penetrating power: Very highShielding: Lead, concreteEffect on nucleus: decreases energy
Hazards of Ionizing Radiation
Hazards of Ionizing Radiation
At low levels of exposure, radiation danger is minimal.Radiation may damage cells, but cells can repair themselves.Severely damaged cells can self-destruct and limit damage to
tissue.Serious trouble happens when radiation causes a non-
lethal (to the cell) mutation that is passed to daughter cells.
If the mutation happens in a gene that controls cell division, the cell could give rise to cancer.
Large radiation exposures can cause death much more quickly from severe tissue damage.
Radiation ExposureRadiation ExposureMeasured in milliSieverts (mSv).
0.001 to 0.01 mSv = hourly dose from cosmic rays on a commercial airliner.
0.27 mSv = average yearly exposure to cosmic radiation in USA (slightly higher at high altitudes)
0.66 mSv = average yearly exposure to radiation from manmade sources in USA
50 mSv = yearly limit for adults set by NRC500 to 1000 mSv = victims of Hiroshima and Nagasaki nuclear bombs500 to 1000 mSv = dose that will cause most people to get sick from
short-term exposure4500 to 5000 mSv = dose that will kill 50% of people after brief
exposure