Particle beams, bubbles and beer.

Particle beams, bubbles and beer

The story goes that physicist Donald A. Glaser, while developing the bubble chamber for detecting subatomic particles at the University of Michigan back in the 1950s, used to sit for hors in the student union staring into a glass of beer, looking for tracks of bubbles left by mu mesons -- energetic particles created in violent encounters between cosmic rays and particles in the atmosphere.

The story itself is apocryphal. Nonetheless, physicist Frank S. Crawford of the University of California, Berkeley, felt compelled to tackle the question: Do ionizing particles actually produce bubbles in fresh beer?

He tried holding a small, cobalt-60 source of gamma rays against a glass of freshly poured beer. He saw no extra bubbles. He tried more intense gamma-ray sources. Still no bubbles.

The quest escalated to stronger and stronger particle interactions, with each experiment requiring increasingly sophisticated equipment. Crawford tried alpha particles, then iron nuclei, and finally looked at the effect of firing bare uranium nuclei into beer. He and an assortment of onlookers monitored the uranium experiment, performed last spring at the Bevatron accelerator in Berkeley, byremote television.

"Stare as we migh, we saw no bubbles," Crawford reports in the November AMERICAN JOURNAL OF PHYSICS. "After turning off the beam, we sprinkled a teaspoon of salt into the beer. It foamed as strongly as usual."

The observation that ionizing particles don't generate bubbles in beer but produce them in copious quantities in a liquid-hydrogen bubble chamber isn't a complete surprise. The superheated liquid in a bubble chamber is physically quite different from a supersaturated liquid -- in this case, beer saturated with carbon dioxide.

Perhaps it would be wroth trying the experiments on champagne -- just to check.