 So I hope you understand the general concept of a decay half-life. Let's now look at the systematics of experimental half-lives. We will again look at a nuclear chart to get our bearings. If we look at chains of beta-decays from unstable nuclei back to stability, there is a general trend from shorter half-lives leading to longer half-lives to eventually reach a stable nucleus. Similar behaviour is observed on the other side for chains of beta-plus decays. Note that all forms of radioactive decays, alpha-beta or gamma, have half-lives, and the general rule is that the further the nucleus is from stability, the shorter the half-life is. Let's look at an actual example of the chain of beta-minus decays from unstable potassium-53 down through 53 calcium to 53 scandium, 53 titanium, 53 vanadium, and eventually into 53 chromium, which is stable. The measured half-lives for these decays increase from 30 milliseconds to 90 milliseconds, 2.4 seconds, 32.7 seconds, and 1.4 minutes before reaching chromium-53, which is stable. So far we've been looking at nuclei in mostly qualitative terms. Over the rest of the lectures, we are going to move to be more quantitative and we will show you how to solve nuclear problems and calculate real numbers.