Thanks for the puzzle; I did not like 5A. TURNT is a slang term that I am totally unfamiliar with; is it US slang? As the word is not in Chambers I was at a loss!
I'm in the US, but I hadn't heard of it either. A web search tells me it's slang, and the Oxford English Dictionary's earliest known use is from 2005. From the OED's Meaning and Use section:
"Stimulated or intoxicated by alcohol or drugs. Also: extremely energized or excited; highly charged. Also with up.
Frequently in the language of rap and hip-hop."
Thank you! Letters are alphabet, but they don't gamble, so you remove bet and get alpha. Alpha particles are also Helium Nuclei (2 protons and 2 neutrons)
I think a helium nucleus is an ALPHA particle (pluralisation is wrong in the clue, I guess). "Letters" are the ALPHABET, removing BET by "don't gamble".
"Stimulated or intoxicated by alcohol or drugs. Also: extremely energized or excited; highly charged. Also with up. Frequently in the language of rap and hip-hop."