Radioactive Decay

 Yesterday we learned that all elements have different isotopes.  Example:  1 H (1 proton, 0 neutrons)  2 H (1 proton, 1 neutron)  3 H (1 proton, 2 neutrons)  Some isotopes are stable and will last essentially forever.  Some aren’t stable.

A Lesson on Pronunciation  Nuclear = NU – clear  Nuclear  NUK-you-lar

Radioactive 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 Decay  Carbon-12 and carbon-13 are stable, but carbon- 14 is radioactive. 6 p + and 6 n 0 6 p + and 7 n 0 6 p + and 8 n 0

What makes a radioisotope unstable?  An isotope can be unstable if:  it is too heavy (more than 83 protons).  its n 0 to p + ratio is too high.  its n 0 to p + ratio is too low.

Band of Stability

Types of Radiation  Alpha radiation  Composition: Alpha particle (helium nucleus)  Symbol:  or 4 He  Charge: +2  Mass: 4 amu  Penetrating power: Low (0.05 mm body tissue)  Shielding: Paper, clothing  Effect on nucleus: Z – 2, A – 4

Alpha Decay alpha

Types of Radiation  Beta radiation  Composition: Beta particle (electron)  Symbol:  or e -  Charge: -1  Mass: 1/1837 amu  Penetrating Power: Moderate (4 mm body tissue)  Shielding: Metal foil  Effect on nucleus: Z + 1; A unchanged.

Beta Decay e-e-

Types of Radiation  Gamma radiation  Composition: High-energy EM radiation  Symbol:   Charge: 0  Mass: 0  Penetrating power: Very high  Shielding: Lead, concrete  Effect on nucleus: decreases energy

Ionizing Radiation Warning Symbol

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 Exposure  Measured in milliSieverts (mSv).  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 NRC  500 to 1000 mSv = victims of Hiroshima and Nagasaki nuclear bombs  500 to 1000 mSv = dose that will cause most people to get sick from short-term exposure  4500 to 5000 mSv = dose that will kill 50% of people after brief exposure

Uses of Radiation  Radioisotopic labelling – can be used to track the movement of a particular substance through a living organism.  Radiometric dating – used to determine the age of ancient objects.  Many uses in medicine, from imaging to cancer therapy.