First Observations of Short-lived Pear-shaped Atomic Nuclei

An anonymous reader sends this quote from a press release at CERN: "An international team at the ISOLDE radioactive-beam facility at CERN has shown that some atomic nuclei can assume asymmetric, 'pear' shapes (abstract). The observations contradict some existing nuclear theories and will require others to be amended. ... Most nuclei have the shape of a rugby ball. While state-of-the-art theories are able to predict this behaviour, the same theories have predicted that for some particular combinations of protons and neutrons, nuclei can also assume asymmetric shapes, like a pear. In this case there is more mass at one end of the nucleus than the other."

Comments

Reference to Island of Stablility

[Anonymous Coward]

For those interested: Nuclei with shapes like this or barbells are significant in solving the problem of filling that range of elements on the Periodic table that were skipped. Ideas were proposed that nuclei would need to have these shapes in order to be stable if the nucleus followed a shell model similar to electron shells. You can read more by researching "Island of Stability"

http://en.wikipedia.org/wiki/Island_of_stability

Re:Reference to Island of Stablility

[DontLickJesus]

For those interested: Nuclei with shapes like this or barbells are significant in solving the problem of filling that range of elements on the Periodic table that were skipped. Ideas were proposed that nuclei would need to have these shapes in order to be stable if the nucleus followed a shell model similar to electron shells. You can read more by researching "Island of Stability"

http://en.wikipedia.org/wiki/Island_of_stability

Eh, fark. This is mine. Stupid login.

Re:Reference to Island of Stablility

[kyrsjo]

The problem is that the strong force (QCD) is behaving really weirdly - in effect a proton is composed of an infinite amount of particles: Two up quarks an a down, together carrying most of the momentum (as measured in deep inelastic scattering experiments), a bunch of gluons which, well, glues everything together, and an infinite amount of quark-antiquark pairs.

Re:Reference to Island of Stablility

[kyrsjo]

This means we can to a certain degree simulate simpler systems, such as pions (composed as an up and an anti-up OR down+anti-down pluss all the gluons and "sea" quarks) using lattice QCD numerical simulations. But for a whole proton, the theory and our computers just aren't up to scratch. For a whole nuclei (which is simplified by "grouping" the quarks into protons and nucleons) it quickly gets VERY hairy as you move up the mass scale. Many-particle quantum dynamics is tough stuff, especially when the interactions get powerfull - and QCD is as powerfull as it gets...

Re:have you considered

[Anonymous Coward]

The acceleration referred to in the title does not have an effect on that, as it refers to the beam being accelerated before measurements are made (a long time before on the nuclear reaction time scales). The method of smacking nuclei together to excite them then measure the gamma rays produced by the relaxation of the excited nuclei is pretty standard. Although typically it used to be beam of accelerated stable isotopes hitting a radioactive target, and now they are instead accelerating the radioactive isotopes and hitting a stable stationary target. This doesn't have an effect on the reaction/excitation, but instead allows them to use less of the radioactive isotopes for the same amount of reactions, compared to having a large radioactive target most of which is not hit by nuclei in the beam. And obviously the collisions have an effect on the nuclei as that excitation is exactly what they are studying, although in ways that will average over nuclei to prevent random single nuclei effects from affecting the result.