Inquiring Minds

Physics Questions People Ask Fermilab

You Wrote:
In my physical science class we watched a video about how they make quarks. Our teacher told us that for extra credit we could write to you and fund the answer to these two questions:

1. How do they make the protons and antiprotons that are used in quarks?

2. How do they make the electron scanning needle?

If you could e-mail me back as soon as possible with the answers I would greatly appreciate it. This extra credit could help my grade a lot.

Thank you

Jackie Ousnamer

Hi Jackie,

Protons along with electrons and neutrons are the building blocks of atoms. One can obtain a proton by stripping an electron from a hydrogen atom because hydrogen consists of one proton and one electron. This is known as ionization. At Fermilab, we take hydrogen and add an extra electron. This results in negative hydrogen ions. A positive voltage is then used to accelerate these ions because a positive voltage will attract the negative ions. The electrons are accelerated to an energy of 75,000 electron volts. This is about the energy of the electron beam found in a television picture tube. This done at Fermilab in a machine known as a Cockcroft-Walton. The negative ions then enter the Linac or linear accelerator and are accelerated to an energy of 400 million electron volts. The ions then pass through a carbon foil that strips off the extra electrons and permits the protons to pass through. Now the protons continue to be accelerated by passing through the booster, main injector and the Tevatron. They reach a final energy of 0.9 to 1 trillion electron volts before they are collided with the antiprotons.

The antiprotons are a lot harder to make. They do not exist freely in nature like normal matter. To make the antiprotons Fermilab uses a 120 giga electron volt beam of protons taken from the main injector. This beam is incident through the side of a drum shaped target made of nickel. The drum is rotated quickly to prevent the beam from hitting the same spot over and over. This prevents the distruction of the target.

This collision with the target produces many particles a very small portion of which are antiprotons. The particles fly off a many angles and have to be focused to fit into the relatively small beam pipe. This focusing cannot be done with conventional quadrapole magnets. Fermilab uses what is known as a lithium lens. The lower atomic mass of lithium prevents scatter in of the antiprotons. After passing though the lens the the positive particles are separated from the negative particle containing the antiprotons with a pulsed magnet. The negative particles are sent down the beam pipe. The negatively charged particles consist of antiprotons, pions and other particles. After sometime the pions and other particles decay away and the antiprotons are left.

After this step there is a lot of work to be done to focus the antiprotons, see http://www.fnal.gov/directorate/public_affairs/ferminews/ferminews99-03-05/ fmi.html. The antiprotons are eventually accelerated to 0.9 to 1 trillion electron volts. They circle in the tevatron in the opposite direction as the protons because they have opposite charge. The antiprotons are eventually collided with the protons.

I do not know exactly what you are referring to when you say, "How do they make the electron scanning needle." Think you mean the electron scanning microscope, here is a good reference that explains the electron scanning microscope, http://www.mos.org/sln/SEM/works.html

If this is not what you are talking about maybe you can give me some more information and I will try to figure it out.

I hope this helped you.

Sincerely,

Christina L. Hebert Graduate Student at Fermilab

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