When were US half dollars made of silver?

All US half dollars dated 1964 and prior are 90% silver (worth about $11 in scrap silver)

All US half dollars dated 1965-1970 are 40% silver (worth about $5 in scrap silver)

All US half dollars dated 1971-present that are circulating contain no silver and are only worth 50 cents. (The US does strike commemorative half dollars and proof silver half dollars for collectors but these are almost always found in mint packaging, not as a loose half dollar).