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."
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".
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)
"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."