There has never been a pure silver half dollar, or any other circulating U.S. coin for that matter. All contain at least 10% copper. Halves made from 1965 to 1969 are 60% copper, and halves from 1971 to today have no silver at all - just nickel and copper.
Your coin's value depends on its date, condition, and mint mark. Please post a new question with those details.