Precision Mass Measurements Of Neutron-deficient Nuclei In Storage Rings

The mass of atomic nucleus, closely related to its binding energy, refects thesum efect of the complicated interplay of the strong, electromagnetic and weakinteractions among its constituting nucleons. In this thesis work we reported onthe precision mass measurements of the neutron-defcient nuclei employing thestorage ring mass spectrometry and on the impact of our new masses on themodelling of astrophysical rp-process.At GSI Helmholtzzentrum fu¨r Schwerionenforschung GmbH in Darmstadt,Germany, direct mass measurements were performed for neutron-defcient152Smprojectile fragments at the FRS-ESR facility by employing the time-resolvedSchottky Mass Spectrometry. Exotic nuclei were produced via fragmentation ofrelativistic152Sm projectiles in a thick beryllium target. The reaction productswere separated in-fight with the fragment separator FRS, and injected into thestorage-cooler ring ESR. In the ESR, the initial velocity spread of the stored ionswas reduced to the level of1.2×107by the electron-cooling process. In thisexperiment,311nuclides were identifed by means of the measured revolutionfrequencies. Mass calibration of the frequency spectra showed that apart fromthe known dependence of the ions’ revolution frequencies on the ions’ mass-over-charge ratio, a subtle additional systematic dependence on the ions’ chargewas also present. Therefore, a new mass evaluation method has been developedto considerably reduce the systematic error in the mass determination. Theachieved relative mass uncertainty was about1.8×107. Masses for9nuclides(114I,122,123La,124,125Ce,127Pr,129Nd,132Pm,134Sm,137Eu) have been determined for the frst time. The study of underlying physics with the new masses is inprogress.At the heavy ion cooler-storage-ring CSRe at IMP in Lanzhou, China, di-rect mass measurements were carried out for neutron-defcient58Ni fragments byemploying the Isochronous Mass Spectrometry. Short-lived nuclei were producedvia projectile fragmentation of58Ni primary beam, separated by the radioactivebeam line RIBLL2and injected into CSRe. The revolution-times of the ionsstored in the ring were measured by a dedicated time-of-fight detector. The in-fuences on the ions’ revolution-times due to instabilities of magnetic felds of theCSRe dipole magnets, have been greatly reduced by a new data analysis method.Masses of series of Tz=3/2short-lived neutron-defcient nuclides, including41Ti,43V,45Cr,47Mn,49Fe and53Ni, were measured with a typical uncertaintyof30keV. One-zone X-ray burst model calculations showed that our new massesturned out to be important for constraining the path of the rp-process in X-raybursts. In particular, a dramatic impact on the burst light curve and the compo-sition of the burst ashes was found to be due to a possible formation of the Ca-Sccycling in X-ray bursts. In this respect, the mass of45Cr was essential for deter-mining the time integrated reaction fow through Ca-Sc cycling. With our newprecise45Cr mass value, the formation of a strong Ca-Sc cycle in X-ray burstscan be excluded, and thus one of the uncertainties in X-ray burst modelling wasremoved.