## Physics Questions People Ask Fermilab

Length of Particle Accelerators

I have six questions.

1. How long is a particle accelerator?

2. Is it true that there are weapons 40 times stronger than the fatman and little boy atomic bombs used in World War II?

3. What does E=mc2 mean?

4. Does electricity in general move at the speed of light? How was fusion discovered?

5. Is it true that the sun is a ball of hydrogen that is in a fusion chain reaction?

6. How can you become a scientific worker at Fermilab?

Dear Mr. Bond,

1. The length of particle accelerators vary in size depending on the type of particle being accelerated and how high in energy it is to be accelerated to. Here at Fermilab, the second-highest-energy accelerator in the world, the Tevatron, accelerates protons (and antiprotons) around a 4 mile circular ring thousands of times until they are at almost the speed of light. Other large accelerators exist at different facilities all over the world. The largest man-made one is at CERN in Switzerland and is 27 kilometers around. There are many small accelerators such as cyclotrons which are the size of one's living room. Most particle accelerators are round (or oval) but some are linear so the particles only go through once.

2. There are weapons that are more than 40 times more powerful then Fatman or Little Boy. In fact, they are atomic weapons or nuclear fission bombs. In the 1950's (after the war, and 1945 bomb drop on Japan), the USA developed the hydrogen bomb (thermonuclear or nuclear fusion) bombs. These actually have conventional explosives which push the critical mass of fissionable fuel (plutonium) together and start fission. The nuclear chain reaction heats up some light material such as lithium (or hydrogen) to superhot temperatures which cause a plasma to be formed and eventually a fusion reaction starts. This is how megaton (one million tons of TNT explosive) explosions were concocted. These are much more powerful than Fatman and Little Boy.

3. E = mc^2 is an equation which comes from the special theory of relativity pioneered by Albert Einstein in the early 20th century. It means that an amount of matter (m) can be converted into energy (E). The equivalent amount of energy is calculated from this formula. c is the speed of light (3 x 10^8 meters/second). In a nuclear fission explosion, some of the mass of the nucleus which breaks up (the binding energy) goes into pure energy which can be given as kinetic energy to a neutron. The neutron then starts another nuclear break up (chain reaction).

4. Electricity is slightly different than electromagnetic radiation. The electrons which carry the charge in electric cables do not move at the speed of light even for that material. The speed of light usually quoted is the speed of light in vacuum (in space for example). Radio waves propagate through space at the speed of light (through the atmosphere at almost the speed of light). The speed of the electricity is very fast though. It is maybe some large fraction of the speed of light. In fact for electric cables carrying electric waves or signals (like the ones that deliver the signal to your web TV for ex), the signal travels at I think 2/3 of the speed of light.

5. The sun is a ball of hydrogen (and helium) that is continually fusioning hydrogen nuclei into helium nuclei at hundreds of thousands if not, millions of degrees. I don't recall how fusion was discovered although its probably in an encyclopedia.

6. To become a scientific worker at Fermilab, it depends on what kind of work you want to do. To do the heart of physics and science research (high energy particle physics) you need to take physics (preferably but chemistry or engineering) as a major in college. While in school or right after, you can try to get an internship at a laboratory like this one or another. The Department of Energy and the National Science Foundation have various student programs. Then you must attend graduate school for physics and get a masters and PhD degree. Most students who do particle physics at Fermilab have gotten their PhDs while working at Fermilab through a university program. This is the classical way to enter the field as a doctor (an expert). There are other ways to contribute such as as an engineer or computer programmer, etc. You don't get to play with the fun science all day long though.

Cheers,
Glenn Blanford, PhD
Fermilab Public Affairs
blanford@fnal.gov

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