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About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 11 March, 2004 Next Week's Question
High-energy neutrons or protons can split atoms
Question
How do you split atoms?

Question
Atoms have a central core, called the nucleus. The nucleus consists of protons and neutrons. The number of protons is called the "atomic number". The sum of the protons and neutrons is the "atomic weight". Nuclei with the same atomic number but different atomic weights are called isotopes of an element. The elements we find on the earth have atomic numbers from 1 to 92 and atomic weights from 1 to 238.

When you hit a nucleus with a particle such as a neutron or proton several things can happen. The particle can bounce off. The particle can be absorbed. There will then usually be a relatively small nuclear change such as transforming a neutron to a proton by emitting an electron or a larger one in which the nucleus emits two protons and two neutrons. Both of these nuclear reactions change the nucleus from one element into another. But the new element is not very different in atomic number or weight from the original one.

In 1938 a German chemist, Otto Hahn, hit uranium, atomic number 92, with neutrons. He created some much lighter elements with atomic numbers between 30 and 60 and weights between 90 and 150. He was astonished by this and sent his results to a former colleague, Lise Meitner. She provided the explanation. The neutrons had split the uranium nucleus into two large fragments. They named the splitting "fission". If each split creates about two new neutrons to do more splitting, a "chain reaction" can result. Fission can only occur in very heavy elements and is likely only in some isotopes.

The phenomenon that atoms can be split this way led to nuclear power plants and the atomic bomb. In a bomb the chain reaction occurs very rapidly which leads to a very quick release of a lot of energy. In a nuclear power plant the speed of the chain reaction is controlled, and so is the rate of release of energy.

Hans A. Bethe

Hans Bethe is professor emeritus of physics at Cornell University. He has been at Cornell since 1935. He won the Nobel Prize for physics in 1967 for explaining how stars make energy. He worked on the atomic bomb during World War II and on the design of nuclear power plants after the war. He has been one of the leading advocates for the peaceful use of atomic energy and for reductions in atomic weapons.

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