Universe Colloquium: Why make such a fuss about the doubly magic nucleus Sn-100?

by Thomas Faestermann (TUM)

Wednesday 11 Jul 2012, 16:30 → 18:00 Europe/Berlin

seminar room (Universe Cluster, Garching)

The tin isotope Sn-100 is the heaviest doubly magic nucleus with N=Z. And it is the only such nucleus for which the beta-decay energy is large enough that essentially a single state in the daughter nucleus In-100 should be populated with a ‘Super Gamow-Teller’ transition. Although Sn-100 lies close to the proton drip line and has a very low production yield, we succeeded to produce a sufficient number of these exotic nuclei at the GSI synchrotron to identify them in-flight and to deposit them in a stack of position sensitive Si detectors. From the time delay between implantations and beta-decays we obtained the half-life. From the total energy deposited by the positrons in Si we obtained the endpoint of the continuous beta-spectrum. With these two quantities we can calculate the strength of the beta-transition. And it turned out that this Gamow-Teller strength is the largest one in any nuclear beta-decay as predicted in modern shell model calculations. This is an additional proof that there is a pronounced shell gap at N=Z=50. The understanding of Gamow-Teller transitions is essential e.g. for the modelling of the core collapse of a star in a Supernova.
The experimental details will be described and the results will be discussed. But the main task of the talk will be to explain the expressions used in the jargon of nuclear physics.