The first video lesson on radioactivity summarises the reasons why some atoms are unstable and undergo decay and why some do not. The effect on the parent atom of the three types of radioactivity, namely alpha, beta and gamma is described and explained.
The second video is an description the range of each type of radiation in air of the relative penetration / absorption of alpha, beta and gamma radiation with different materials.
A more detailed explanation of beta plus and beta minus decay follows in the third tutorial and the final video lesson explains how some of the processes of change can be tracked and illustrated using Feynman diagrams.
Illustrated notes on radioactivity which you are free to copy are available here.
Details of further video lessons on radioactivity and atomic structure are part of the tutorials available to buy on flash drive, details are available here.