Question

What is the difference between atomic and nuclear physics?

Asked by: Kelley D. Burroughs

 Answer

What is the difference between atomic and nuclear physics? Really short and non-informative answer would be that one deals with atoms, while the other deals with nuclei.

Of course, nucleus is a part of the atom. So what is it that separates these two branches of physics? Atomic physics deals with the properties of atoms, which are mainly due to their electron configuration. The nucleus is also involved, but only with its overall properties. As far as atomic physics is concerned, the nucleus is a single massive particle, with spin, mass, and charge. The internal workings of the nucleus are irrelevant.

Nuclear physics, on the other hand, deals only with nuclei. It studies the structure of nuclei, and their reactions and interactions.

The distance scales involved are inherently different - atomic physics deals with distances of the order of nanometers - (10-9 m) while nuclear physics deals with distances of the order of femtometers (10-15 m).

Also, energy scales involved in the two branches are quite different. The energies involved in atomic physics are in the 1 eV (electron volt) to 1 keV range. The energies in nuclear physics are generally 1 MeV to 1 GeV. (Anything higher may be considered elementary particle physics, but it is hard to draw lines.)

These differences in scale and energies are due to differences of the forces under study. Atoms are by and large governed by electromagnetic interactions, where electrons are bound at a typical distance of a fraction of nanometers, with a typical energy of electron volts. Nuclei, however, are bound by nuclear forces, which are shorter ranged, yet much stronger than electromagnetic forces - the typical binding distance is a femtometer, with binding energies of a couple MeV per nucleon in a nucleus.

As a final note, the 'atom bomb' is probably a misnomer - the energy released from the detonation of an atom bomb is not due to an 'atomic reaction', but due to a 'nuclear reaction', where the nuclei are broken up. So, 'nuclear bomb' is the better way of referring to it.

Answered by: Yasar Safkan, Ph.D. M.I.T., Software Engineer, Istanbul, Turkey

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'The strength and weakness of physicists is that we believe in what we can measure. And if we can't measure it, then we say it probably doesn't exist. And that closes us off to an enormous amount of phenomena that we may not be able to measure because they only happened once. For example, the Big Bang. ... That's one reason why they scoffed at higher dimensions for so many years. Now we realize that there's no alternative... '

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