“A neutron walks into a bar…” (bar joke)

A neutron walks into a bar and asks the bartender, “How much for a beer?” The bartender replies, “For you, no charge.”
 
The popular “neutron walks into a bar…” bar joke has been cited in print since at least 1996.  “Two hydrogen atoms walk into a bar…” is another bar joke that is frequently paired with this one.
 
   
Google Groups: alt.comedy.british
Neutron joke
Keith Jenkins  
6/2/96
A little titterer for al you particle physicists out there.
A neutron walks into a bar and orders a beer.  the bartender gives it to him, and the neutron asks, so how much do I owe you?  the bartender says, “for you…no charge” 
aaaahahahahahhahhahahahhahahahahhaahahahahahhaahahahahahhaahhah
 
Citypaper (Philadelphia, PA)
November 21–28, 1996
CITIC PICK
Don McMillan
Don McMillan, the tall, lanky, red-haired guy from the Budweiser commercials, cracks me up. (...) While his comedy derives more from his awkward stature (he’s 6 feet 5 inches tall and has size 15 feet) than from his scientific background, he throws a few curveballs from chemistry class in for good measure: “A neutron walks into a bar and asks the bartender how much a drink costs and the bartender replies, ‘For you, no charge.’”
Nov. 27 & 29-Dec. 1, Catch a Rising Star, 221 South St., 440-4242.
— Brian Howard
 
30 October 1997, Orange (TX) Leader,  “Internet has plenty of pun-gent stories” by Joe Murray, pg. 4A, col. 4:
A neutron goes into a bar and asks the bartender, “How much for a beer?” The bartender replies, “For you, no charge.”
 
A Prairie Home Companion - Jokes 1999
April 6, 1999
Two for the science crowd…
#1: Two atoms walk into a bar. They sit down, order beers, and start talking. One atom says, “Uh-oh.”“What’s wrong?” asks the second atom.The first atom says, “I think I lost an electron.” The second atom says, “That’s terrible! Are you sure?” “Yes,” replys the first atom. “I’m positive!”
 
#2A neutron walks into a bar and orders a beer. He drinks it and gets up to leave. He asks the bartender, “How much to I owe you?” The bartender looks at the neutron and says, “For you? No charge.”
Mike Richards,Age: 17
 
Google Books
The Mammoth Book of Humor
Edited by Geoff Tibballs
New York, NY: Carroll & Graf
2000
Pg. 52:
A neutron walked into a bar and asked the bartender “How much for a beer?” The bartender said: “For you, no charge.”
 
Neatorama
Physics Joke: A Neutron Walked Into a Bar ...
Alex Santoso •  Friday, October 10, 2008 at 12:09 AM
So, a neutron walked into a bar and said “I’d like a beer, please.”
After the bartender gave him one, he said “How much will that be?”
“For you?” said the bartender “No charge.”
 
Google Books
A Neutron Walks into a Bar—
Random Facts and Big Ideas About Our Universe and Everything in It
By Science140
Dublin: Hachette Books Ireland
2012
Pg. ?:
A neutron walks into a bar, orders a beer, and asks, ‘How much?’ Barman says, ‘For you, no charge.’ Boom,boom!