• laminar flow: non-turbulent, smooth flow of a fluid.
• LET (linear energy transfer): average amount of energy lost per unit of particle spur-track length.
  1. low LET : radiation characteristic of electrons, x-rays, and gamma rays.
  2. high LET: radiation characteristic of protons and fast neutrons.
• linearity hypothesis: assumption that the biological damage from radiation is linearly proportional to the radiation dose.
• NAS: National Academy of Science.
• NCRP: The National Council on Radiation Protection and Measurements.
• noble gas: a gaseous element with a full octet and therefore unreactive nature.
• NIH: National Institute of Health.
• NRC: The Nuclear Regulatory Commission, or the National Research Council.
• precursor: a precursor of a radioactive isotope is a radioactive chain member which occurs earlier in the decay chain.
• NURE: National Uranium Resource Evaluation.