Thanks, interesting story!
The technology is fascinating and not widely known. The RTGs are multi-hundred Watt electrical power generators using thermocouples heated by plutonium at 1,800 degrees F. They had a four year life; initial power rating at launch of 146 W per RTG; end of mission power rating of 108 W. First craft was launched in 1977 and the RTGs are still generating power almost 40 years later! They exceeded the design lifetime just a bit. ;>)
More info at :
http://www.osti.gov/accomplishments/documents/fullText/ACC0165.pdf#page29