학술논문
High-resolution, accurate MR-TOF-MS for short-lived, exotic nuclei of few events in their ground and low-lying isomeric states
Document Type
Working Paper
Author
Ayet, S.; Hornung, C.; Ebert, J.; Plaß, W. R.; Dickel, T.; Geissel, H.; Scheidenberger, C.; Bergmann, J.; Greiner, F.; Haettner, E.; Jesch, C.; Lippert, W.; Mardor, I.; Miskun, I.; Patyk, Z.; Pietri, S.; Pihktelev, A.; Purushothaman, S.; Reiter, M. P.; Rink, A. -K.; Weick, H.; Yavor, M. I.; Bagchi, S.; Charviakova, V.; Constantin, P.; Diwisch, M.; Finlay, A.; Kaur, S.; Knöbel, R.; Lang, J.; Mei, B.; Moore, I. D.; Otto, J. -H.; Pohjalainen, I.; Prochazka, A.; Rappold, C.; Takechi, M.; Tanaka, Y. K.; Winfield, J. S.; Xu, X.
Source
Phys. Rev. C 99, 064313 (2019)
Subject
Language
Abstract
Mass measurements of fission and projectile fragments, produced via $^{238}$U and $^{124}$Xe primary beams, have been performed with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher with a mass resolving powers (FWHM) up to 410,000 and an uncertainty of $6\cdot 10^{-8}$. The nuclides were produced and separated in-flight with the fragment separator FRS at 300 to 1000 MeV/u and thermalized in a cryogenic stopping cell. The data-analysis procedure was developed to determine with highest accuracy the mass values and the corresponding uncertainties for the most challenging conditions: down to a few events in a spectrum and overlapping distributions, characterized only by a broader common peak shape. With this procedure, the resolution of low-lying isomers is increased by a factor of up to three compared to standard data analysis. The ground-state masses of 31 short-lived nuclides of 15 different elements with half-lives down to 17.9~ms and count rates as low as 11 events per nuclide were determined. This is the first direct mass measurement for seven nuclides. The excitation energies and the isomer-to-ground state ratios of six isomeric states with excitation energies down to about 280~keV were measured. For nuclides with known mass values, the average relative deviation from the literature values is $(2.9 \pm 6.2) \cdot 10^{-8}$. The measured two-neutron separation energies and their slopes near and at the N=126 and Z=82 shell closures indicate a strong element-dependent binding energy of the first neutron above the closed proton shell Z=82. The experimental results deviate strongly from the theoretical predictions, especially for N=126 and N=127.