There are several isotopes of weapons-grade plutonium. The most commonly used variety, Pu-239 (mentioned by Collins), has a half-life of 24,000 years; others have half-lives as short as fourteen years. Based on 1970s nuclear technology, Collins' 50 kilograms is enough to make seven or eight Hiroshima-sized bombs, but could pose a lethal risk to anyone handling it.
The featured location representing a bombed-out military facility, used to convince the villain that he was living in a war-ravaged America in the year 2000, was actually the former Olive View Medical Center in Sylmar, California. Built in 1970, it was irreparably damaged by an earthquake on February 9, 1971, approximately a year and a half before this episode was filmed.