Oh man, you make me want to replay the Orange Box right now.
For those who don't know, Half-Life is a computer game series centered around a cataclysmic event at a secret underground high-energy physics laboratory dubbed Black Mesa.
The protons become hydrogen, and have to go somewhere - does it bubble off? Or does it react with the carbon and become hydrocarbons - or are there simply so few protons that it doesn't matter?
The article refers to beams of "hundreds of trillions of protons". That's very, very few in chemistry terms. Ten hundred trillion (which is the upper limit of the number which that phrase could be talking about) is 10^15. Avogadro's number is 6 x 10^23. So we're talking about 1.6 billionths of a mole of protons.
Let's assume that all turns into hydrogen -- that's as good a hypothesis as any. While randomly Googling for the value of the ideal gas constant (the R in PV=nRT; I note in passing that Google has rendered my prized copy of the CRC Handbook obsolete in a flash) I found the even handier sentence:
The molar volume of any gas at STP is known to be 22.414 L/mol
Which implies that we'll make about 4x10^(-5) milliliters of hydrogen at STP. About enough to fill a cube 330 microns on a side. And that's if we turn them into a gas, which isn't exactly dense.
The moral of this story is that statistical mechanics deals with very large numbers of particles. The second moral is that it's not the current in the proton beam that will kill you. It's the voltage, aka the energy of the protons. Which is not surprising -- if you want to simulate the Big Bang, you need a lot of bang.
Simply. Amazing.