In last week’s edition of Nature, NSCL Senior Physicist Daniel Bazin contributes a “News & Views” piece on the progress made towards unlocking the secrets of 100Sn – the heaviest symmetrical doubly magic nucleus on the chart of the nuclides (Nature 486, 330-331 (21 June 2012); doi:10.1038/486330a).
Like electrons orbiting a nucleus, protons and neutrons within the nucleus preferentially fill energy shells as more and more nucleons are added to the structure. And like the noble gasses, when these energy levels are perfectly filled, the nucleus becomes much more stable than its neighboring nuclei.
Light symmetrically doubly magic nuclei – 4He, 16O, and 40Ca – are stable and easy enough to produce for experiments. However, as more protons are added to the mix, more and more neutrons are required to bind the system.
With 50 protons, tin requires more than 50 neutrons to become stable. At 50 neutrons, it is unstable and does not last long, making its production for experimentation rather difficult. But nuclear physics facilities around the world are becoming better at producing this rare isotope for study. As such, more and more is being learned every year from this special isotope.
Recent results from GSI have taken a giant step forward in 100Sn’s study. The measurement of its half-life has been greatly improved, the end point of the energy spectrum of beta-decay has been determined, and gamma-ray transitions have been observed. Of interest and note, 100Sn seems to have the highest known beta-decay strength of all nuclei, and has been classified as a ‘superallowed Gamow-Teller decay’.
As more facilities – including FRIB – begin to tackle the study of 100Sn in more detail, many more questions are hoped to be answered. For example, is it really doubly magic and simple in structure? How is the strength of its β-decay distributed across the energy levels of its daughter nucleus, indium-100? Does it have isomeric (metastable) states? Only the future will tell.