http://en.wikipedia.org/wiki/Radioi...ctric_generator

Most RTGs use 238Pu, which decays with a half-life of 87.7 years.

at the beginning of 2001, the power generated by the Voyager RTGs had dropped to 315 W for Voyager 1 and to 319 W for Voyager 2. Therefore in early 2001, the RTGs were working at about 67% of their original capacity instead of the expected 83.4%[13].

半衰期 87.7 年。