1965-1970 Kennedy half dollars are 40% silver with a value of about $2.00 for the silver.
It was the Franklin half, before that walking liberty, and before that various portraits of Miss Liberty.
It's just 50 cents, spend it.
The US Mint has not issued a 1964 half dollar depicting Lyndon Johnson.
No U.S. coins were pure silver - it's too soft. 10% copper was added to make them hard enough to resist wear.