Neutrons don’t change into protons. Except, sometimes, they do. Radioactivity is the process under which the nucleus can change spontaneously from one element to another. Steve Weatherell suggests that we acknowledge both the usefulness and danger inherent in harvesting radioactivity.
The Voyager spacecraft uses radioactive elements for power. Research where it presently is, how the batteries work, and when they will probably run out. http://voyager.jpl.nasa.gov/
What happened at Fukushima in March 2011? http://www.bbc.co.uk/news/world-asia-pacific-12726591
Listen to this AstronomyCast podcast: http://www.astronomycast.com/2012/06/ep-263-radioactive-decay/
On YouTube, there are many related videos from excellent channels: