## Physics Questions People Ask Fermilab

Getting particles for the accelerator

Hi I am 11 and my name is Joshua Pevitz. When I grow up I want to work at Fermilab. I was wondering if you could explain to me about how you let only one atom in the accelerator, if everything is made out of atoms?

Dear Joshua,

Thanks for your interesting question! Let me give you the simple answer first, and then I will explain. We do not let only one atom at a time into the accelerator. Instead we have more than 10 trillion protons and close to a trillion antiprotons in the Tevatron accelerator at once.

We get our protons from a bottle of hydrogen gas. Hydrogen is the simplest kind of atom. It has one proton and one electron. We let some of the gas into the first accelerator into our accelerator chain. Not very long after that we take away the electrons so that we are left with only the protons. Since the protons have an electrical charge, we can accelerate them.

It turns out that we accelerate a lot of them all at once to collide with antiprotons that we make by diverting some of the protons onto a target. When we crash the protons into the target antiprotons come streaming out of it, and we make them into a beam. The antiprotons are created in the target following the rules of Einstein's equation [energy equals mass times the speed of light squared].

Once we have a beam of about 10 trillion protons and another beam of about a trillion or so antiprotons, we put them into the Tevatron Collider going in opposite directions. Then we allow them to collide at two places in the large Tevatron ring where there are large detectors to examine what comes out of the collisions. The reason we need to have so many protons and antiprotons in the two beams is that only a few of them actually hit one another each time the beams pass through one another. To make certain we get some collisions to study, we need to begin with lots of protons and antiprotons in each beam. You can think of it like an experiment that you would never want to actually perform, but it illustrates what happens with our beams. Imagine diverting all of the cars in the east bound lane of the interstate into the west bound lane. If there weren't many cars going each way, many of the cars would pass by one another without crashing. But if you had a lot of cars going each way, you would see many collisions.

Anyway, I know that 10 trillion sounds like a lot, but if you weighed all of the protons in our beam you would find that they weigh less than one trillionth of an ounce. In fact, the average flea weighs about 4 billion times more than our beam of protons weighs. We actually let a lot more gas out of the hydrogen bottle than that when we begin the acceleration process, but much of it gets lost as we put it into the accelerator to try to accelerate it.

I hope this answers your question. If it doesn't, don't hesitate to let me know. Meanwhile, good luck with in school, and keep asking those good questions.

Sincerely,

Roger L. Dixon