Nuclear Chemistry

Radioactive Decay  The last unit, 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)  Many isotopes are stable  will last forever  Some are not stable.

Radioactive Decay  Unstable isotopes are radioactive- able to emit particles or gamma rays  Radioactive (unstable) isotopes = radioisotopes  Radioisotopes decay into more stable forms.  Radioisotopes release energy by emitting radiation during the process of radioactive decay.

Radioactive Decay  Carbon-12 and carbon-13 are stable  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 neutron(n 0 ) to proton(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: α or He  Charge: +2  Mass: 4 amu  Penetrating power: Low (0.05 mm body tissue)  Shielding: Paper, clothing 4 2

Alpha Decay  Nuclear equation: +

Types of Radiation  Beta radiation  Composition: Beta particle (electron)  Symbol: β or e  Charge: -1  Mass: 1/1836 amu  Penetrating Power: Moderate (4 mm body tissue)  Shielding: Metal foil 0

Beta Decay  Nuclear equation: +

Types of Radiation  Gamma radiation  Composition: High-energy EM radiation  Symbol: γ or  Charge: 0  Mass: 0  Penetrating power: Very high  Shielding: Lead, concrete  Decreases energy on nucleus +

Radioactivity  Radioactive decay is known as natural transmutation – the spontaneous nuclear decay of a radioisotope.  Occurs naturally – no outside influence needed  other types: artificial transmutation, fission, fusion

Hazards of Ionizing Radiation  Low level exposure  Radiation danger is minimal.  Cell damage, but cells recover and repair  Severely damaged cells self-destruct, limit damage  Non-lethal radiation exposure can still cause genetic mutation  If the mutation occurs 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.