Plumped up carbon fatter than expected

[n2doc]

New experimental results find that a neutron-rich isotope of carbon is far larger than it should be. The explanation: a pair of neutrons that act as a nuclear halo.

By Matt Ford | Last updated January 15, 2010 11:55 AM

Check the periodic table you have hanging on your wall—I know I'm not the only one who has one—and you'll see a weight for each element. This is the element's accepted atomic weight, but it only represents a weighted average of the masses of all the isotopes present in nature. Past experimental research has shown that a pretty consistent trend exists: the size of an atom's nucleus correlates with its mass number (the total number of neutrons and protons in the nucleus). Generally, the size of the nucleus is proportional to the cube root of the mass number.

Every now and then, however, we find an isotope where this relationship does not hold. Recently, it was discovered that 22C (Carbon-22, a carbon atom with six protons and 16 neutrons instead of the normal six and six) has a nucleus that is bigger than 208Pb! Going by the cube root rule of thumb, one would expect it to only be about 20 percent larger than 12C. The reason for this, according to a paper in an upcoming edition of Physical Review Letters, is that 22C represents the largest known "halo" nucleus to date.

Calculating the physical shape of an atomic nucleus can be carried out like any other physics problem: it's a balance of forces acting on the particles—the strong force, centrifugal forces, and the electrostatic force. Most of the time, the nucleus will form a compact and slightly ellipsoidal shape, but recent research has shown that even simple elements can have a much more complicated structure. Scattering experiments that measured the cross section of the neutron-rich 22C have found that it has two "halo" neutrons. These neutrons have a significant probability of tunneling beyond the area in which the nucleus is normally confined.

http://arstechnica.com/science/news/2010/01/plumped-up-carbon-fatter-than-expected.ars

[phantom power]

1. A carbon nucleus with 16 neutrons!

Bet that doesn't last a long time.

[NNadir]

2. t 1/2 = 22 ns. It's the heaviest known isotope of carbon.

I'm going to have to look up how it's made.

[ProfessorGAC]

3. This Is Very Cool

Thanks for the link, too. That was a good article.
GAC