The rad is a deprecated unit of absorbed radiation dose, defined as 1 rad = 0.01 Gy = 0.01 J/kg. It was originally defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by one gram of matter. It has been replaced by the gray in SI but is still used in some countries. A related unit, the roentgen, is used to quantify the number of rad deposited into a target when it is exposed to radiation. The F-factor can be used to convert between rad and roentgens. The material absorbing the radiation can be human tissue or silicon microchips or any other medium (for examp...

Dopamine (or 3,4-dihydroxyphenethylamine) is a neurotransmitter in the catecholamine and phenethylamine families that plays a number of important roles in the brains and bodies of animals. Its name derives from its chemical structure: it is an amine that is formed by removing a carboxyl group from a molecule of L-DOPA. In the brain, dopamine functions as a neurotransmitter—a chemical released by nerve cells to send signals to other nerve cells. The brain includes several distinct dopamine systems, one of which plays a major role in reward-motivated behavior. Every type of reward that...