Short answers, pulled from the story.
ALSEP was a set of scientific instruments placed by astronauts at the landing sites of five Apollo missions: Apollos 12, 14, 15, 16, and 17. The instruments were designed to operate autonomously after the crews left, transmitting data to Earth for years. They were powered by a radioisotope thermoelectric generator using plutonium-238.
The ALSEP stations ran from their deployment until the 30th of September 1977, when support operations were officially terminated for budgetary reasons. After the shutdown, all five stations were still observed transmitting by the Soviet radio telescope RATAN-600 between the 18th of October and the 28th of November 1977.
The Laser Ranging Retroreflectors are the only ALSEP experiments still in use. They reflect laser pulses fired from Earth, and the round-trip travel time gives an accurate measurement of the distance between the Earth and the Moon.
Apollo 11 left a simpler package called the Early Apollo Scientific Experiments Package because geologists persuaded NASA to allow only experiments deployable within ten minutes, due to the risk of an early abort. The mission had only one planned EVA of two hours and forty minutes, which was not enough time for a full ALSEP deployment.
ALSEP was built and tested by Bendix Aerospace in Ann Arbor, Michigan. The experiments were assigned in February 1966 to research institutions including MIT, Columbia University, Rice University, Stanford University, and several NASA centers.
ALSEP used a Radioisotope Thermoelectric Generator that converted heat from the radioactive decay of plutonium-238 into approximately 70 watts of electrical power. The Central Station then distributed this power to each instrument and to the communications equipment that relayed data to Earth.