II. Natural radioactivity and cosmic radiation

The history is briefly described of the discovery of radioactivity. Alpha, beta and gamma radioactive element decays and laws of radioactive decay are described. The characteristic of the decay constant, half-life and lifetime of radioactive atoms is given. On the example of the decay of 226Ra to 222Rn the equilibrium is described between mother and daughter elements. Graphically shown are natural radioactive series, i.e., the uranium, the actinium and the thorium series. The use is described of sealed radium preparations most frequently in form of radium needles or the use of emanation for therapeutical purposes. Cosmic radiation is also described as part of natural radioactivity and the absorption curve of cosmic radiation in lead is represented. (E.S.)