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Posted By: dr_rocket Scientists Explore Nuclear Island - 12/26/06 04:57 PM
Physicists in Germany have created the transuranic hassium-270. The hassium atoms were created by firing magnesium-26 ions, at high speed, toward a curium-248 target. Hassium has 108 protons and 162 neutrons and an estimated half-life of 22 seconds!! The story can be found here:

This is an impressive feat on its own, however there are theoretical implications. These have to do with the stability of atoms and nuclei. It has been known for a long time that fully assembled atoms have less mass than their constituant particles. This is known as the "mass defect". For example, helium has two neutrons and two protons. If we add up the masses of these as four free particles, the total is more than the mass of the helium atom. The difference is due to the binding energy between the particles. The binding energy is that which is needed to separate the nucleons into its parts. The greater the binding energy, and thus the mass defect, the more stable the nucleus.

At certain nuclear masses the binding energy is especially high. These high binding energies occur at masses 2, 8, 20, 28, 50, 82 and 126. These are called "magic numbers." It has been speculated on theoretical grounds that there are larger magic numbers numbers, e.g. 184.

As you go through the periodic table the binding energy follows a zig-zag pattern of higher and lower binding energies. This leads to the idea of nuclear shells just as we have electron shells in the outer part of the atom. Just as with electron shells, those that are closed are very stable while unfilled shells are active. Compare helium with lithium. Helium is closed and forms no compounds under normal circumstances. Lithium has one more electron than helium and this electron does not fill the next shell. This gives lithium an "extra" electron to contribute to reactions. Something similar seems to hold for the nucleus.

If you plot the binding energy as height for each element in the periodic table you get a picture like the one shown in this Wiki article:

You will see that the hassium at the "south end" of this island.

Dr. R.
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