Law of the radioactive decay
Equal amounts of different radioactive materials do not give off radiation at the same rate
measure of radiation: activity (number of decays /unit time)
unit for activity: 1 curie (Ci) = 3.7 x 1010 decays/second
activity of a sample determined by two factors
- number of radioactive atoms in the sample
basic law: the probability P that a radioactive nucleus will decay is the same at each time moment (until the nucleus decays)
result: The amount of radioactive nucleus which are
in the sample, decays exponentially in time (activity
decays exponentially in time)
analogy: throwing a given number of dice, and removing the 1 results (activity proportional with the number of remained dice)
notion of half-life (the time it takes the activity to drop to one-half its original value) - constant during the evolution!
half-lifes inversely proportional with the probability P
different type of nucleus have different half-lifes, or
different P values! - like throwing dice with other
number of faces, and taking out again those showing: 1