Precision mass measurements of indium isotopes allow conclusions on the mass of the doubly-magic atomic nucleus of tin-100


This news is based on a press release of the University of Greifswald

Physicists call the atomic nucleus of tin-100 doubly magic because it simultaneously has two shell closures. Nevertheless, it is very difficult to measure its mass. An international group of scientists at the European research centre CERN (Conseil Européen pour la Recherche Nucléaire) including physicists from GSI Helmholtzzentrum and University of. Greifswald has now succeeded in measuring the precise masses of the indium isotopes 99In, 100In and 101In, thus making it possible to draw conclusions for the mass value of tin-100. 

Similar to electrons in atomic shells, the building blocks of the atomic nuclei, protons and neutrons, quantum mechanically group together in nuclear shells. Full shells correspond to particularly high binding energies and stabilities. Thus, the shell closure numbers 8, 20, 28, 50, 82 and 126 are called “magic” numbers. The doubly-magic nuclei are particularly interesting. For these nuclei, both the proton number Z and the neutron number N indicate shell closures. And, among those doubly-magic nuclei, the nucleus of the tin isotope 100Sn is the most prominent: It is the heaviest nucleus for isotopes that have the same Z and N values, Z = N = 50. But so far, a direct experimental determination of its mass is extremely challenging. This is due to the difficulties in the production of 100Sn as well as in its short half-life of just about a second.

Directly adjacent to the doubly-magic 100Sn, we find the nuclei of the element indium, which have one proton less than the tin nuclei. It was now possible to perform precision mass measurements of the indium isotopes 99In, 100In and 101In with the ISOLTRAP setup at CERN. This was the first direct mass measurement for indium-99; the accuracy of the indium-100 and indium-101 mass values have been improved significantly. Ivan Kulikov, a PhD student at GSI and FAIR, was involved in the experiments and was assigned to CERN for four years.

The new results, published in Nature Physics, confirm values measured at GSI in cooperation with scientists from the Technical University of Munich. “Beta decay of 100Sn has been studied 13 years ago within the RISING gamma-spectroscopy project behind the FRS of GSI and then more recently and with a higher statistics at RIKEN in Japan within EURICA campaign. The observed discrepancy between those two results causes intense discussions in the community,” says Dr. Magdalena Gorska, the co-author of both measurements.
Yuri Litvinov, the principal investigator of the ERC project "ASTRUm", within which the researchers from GSI Atomic Physics division contributed to this experiment, explains:
 “By using the new mass value of 100In and with help of theoretical calculations performed by the group of Prof. Achim Schwenk at the TU Darmstadt, it became possible to draw a clear conclusion on the mass of 100Sn, favoring an older GSI measurement of C. Hinke et al. published in Nature.” 

Among other funding sources, this research was supported by the European Research Council (ERC) through the European Union’s Horizon 2020 research and innovation programme (grant agreement 682841 ‘ASTRUm’).

New possibilities to answer challenging questions in nuclear structure and reactions will be opened up with FAIR. The international accelerator facility, one of the largest research projects worldwide, is currently under construction at GSI. This research at FAIR is pursued by the NUSTAR Collaboration, which builds dedicated state-of-the-art experiments at the future in-flight fragment separator Super-FRS. (LW/Universität Greifswald)

Further information

Original paper: M Mougeot et al. (2021): Mass measurements of 99-101In challenge ab initio nuclear theory of the nuclide 100Sn, Nature Physics.
Press release of University of Greifswald