New results from isochronous mass measurements of neutron-rich uranium fission fragments with the FRS-ESR-facility at GSI

Abstract.Masses of uranium fission fragments have been measured with the FRagment Separator (FRS) combined with the Experimental Storage Ring (ESR) at GSI. A 410-415 MeV/u 238U projectile beam was fast extracted from the synchrotron SIS-18 with an average intensity of 109/spill. The projectiles were focused on a 1g/cm2 beryllium target at the entrance of the FRS to create neutron-rich isotopes via abrasion-fission. The fission fragments were spatially separated with the FRS and injected into the isochronous storage ring ESR for fast mass measurements without applying cooling. The Isochronous Mass Spectrometry (IMS) was performed under two different experimental conditions, with and without B$\rho$-tagging at the high-resolution dispersive central focal plane of the FRS. The evaluation has been done for the combined data sets from both experiments with a new method of data analysis. The use of a correlation matrix has provided experimental mass values for 23 different neutron-rich isotopes for the first time and 6 masses with improved values. The new masses were obtained for nuclides in the element range from Se to Ce. The applied analysis has given access even to rare isotopes detected with an intensity of a few atoms per week. The novel data analysis and systematic error determination are described and the results are compared with extrapolations of experimental values and theoretical models.

[1]  H. Geissel,et al.  New features of the Monte-Carlo code MOCADI , 2011 .

[2]  O. Klepper,et al.  First isochronous mass spectrometry at the experimental storage ring ESR , 2000 .

[3]  Krzysztof Piotr Rykaczewski,et al.  The GSI projectile fragment separator (FRS): A Versatile magnetic system for relativistic heavy ions , 1992 .

[4]  S. Goriely,et al.  Nuclear mass formula with Bogolyubov-enhanced shell-quenching: application to r-process , 1996 .

[5]  Wei Zhang,et al.  A data analysis method for isochronous mass spectrometry using two time-of-flight detectors at CSRe , 2015, 1603.07169.

[6]  J. Pearson,et al.  Nuclear mass formula via an approximation to the hartree-fock method , 1995 .

[7]  A. H. Wapstra,et al.  The AME2012 atomic mass evaluation (II). Tables, graphs and references , 2012 .

[8]  T. Dickel,et al.  Design of a new time-of-flight detector for isochronous mass spectrometry in the collector ring at FAIR , 2015 .

[9]  F. Thielemann,et al.  Nuclear Physics: A Key Ingredient in Astrophysical Modeling , 2005 .

[10]  B. Franzke.  The heavy ion storage and cooler ring project ESR at GSI , 1987 .

[11]  Suzuki,et al.  New magic number, N = 16, near the neutron drip line , 2000, Physical review letters.

[12]  G. Münzenberg,et al.  Mass measurements of exotic nuclei at the ESR , 1992 .

[13]  A. Musumarra,et al.  Nuclear structure studies of short-lived neutron-rich nuclei with the novel large-scale isochronous mass spectrometry at the FRS-ESR facility , 2008 .

[14]  W. Myers,et al.  Nuclear ground state masses and deformations , 1995 .

[15]  E. GWYNNE JONES,et al.  Nuclear Structure , 1932, Nature.

[16]  G. Breit,et al.  Nuclear Structure, Vol. 1 , 1970 .

[17]  B. A. Brown,et al.  Magic numbers in exotic nuclei and spin-isospin properties of the NN interaction. , 2001, Physical review letters.

[18]  K. Blaum,et al.  100 years of Mass Spectrometry , 2013 .

[19]  C. Kozhuharov,et al.  First direct mass measurements of stored neutron-rich 129,130,131Cd isotopes with FRS-ESR , 2016 .

[20]  K. Beckert,et al.  A new experimental approach for isochronous mass measurements of short-lived exotic nuclei with the FRS-ESR facility , 2006 .

[21]  K. Blaum,et al.  Precision Penning trap mass measurements on exotic ions: status and perspectives , 2009 .

[22]  A. Saiani,et al.  Microscopy and Microanalysis , 2017, Microscopy Today.

[23]  S. Goriely,et al.  Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XIII. The 2012 atomic mass evaluation and the symmetry coefficient , 2013 .

[24]  Sheikh,et al.  Nuclear shell structure at particle drip lines. , 1994, Physical review letters.

[25]  M. Winkler,et al.  The Challenge of High-Resolution Spectrometer Experiments with Exotic Nuclei , 2015, Microscopy and Microanalysis.

[26]  R. Kanungo.  A new view of nuclear shells , 2013 .

[27]  Wolfgang R. Plaß,et al.  Multiple-reflection time-of-flight mass spectrometry , 2013 .

[28]  A. Poskanzer,et al.  Direct measurement of the masses of Li 11 and Na 2 6 − 3 2 with an on-line mass spectrometer , 1975 .

[29]  O. Klepper,et al.  Schottky mass measurements of stored and cooled neutron-deficient projectile fragments in the element range of 57≤Z≤84 , 2000 .

[30]  Zuker,et al.  Microscopic mass formulas. , 1995, Physical review. C, Nuclear physics.

[31]  G. Münzenberg,et al.  Mass and lifetime measurements of exotic nuclei in storage rings. , 2008, Mass spectrometry reviews.

[32]  H. Wollnik,et al.  Opportunistic mass measurements at the Holifield Radioactive Ion Beam Facility , 2006 .

[34]  D. Lascar,et al.  First results from the CARIBU facility: mass measurements on the r-process path. , 2013, Physical review letters.