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Register a new userSchottky mass measurements of heavy neutron-rich nuclides in the element range $70leZ le79$ at the ESR
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Storage-ring mass spectrometry was applied to neutron-rich $^{197}$Au projectile fragments. Masses of $^{181,183}$Lu, $^{185,186}$Hf, $^{187,188}$Ta, $^{191}$W, and $^{192,193}$Re nuclei were measured for the first time. The uncertainty of previously known masses of $^{189,190}$W and $^{195}$Os nuclei was improved. Observed irregularities on the smooth two-neutron separation energies for Hf and W isotopes are linked to the collectivity phenomena in the corresponding nuclei.
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The JYFLTRAP mass spectrometer was used to measure the masses of neutron-rich nuclei in the region between N = 28 to N = 82 with uncertainties better than 10 keV. The impacts on nuclear structure and the r-process paths are reviewed.
The use of chemically selective laser ionization combined with beta-delayed neutron counting at CERN/ISOLDE has permitted identification and half-life measurements for 623-ms Mn-61 up through 14-ms Mn-69. The measured half-lives are found to be significantly longer near N=40 than the values calculated with a QRPA shell model using ground-state deformations from the FRDM and ETFSI models. Gamma-ray singles and coincidence spectroscopy has been performed for Mn-64 and Mn-66 decays to levels of Fe-64 and Fe-66, revealing a significant drop in the energy of the first 2+ state in these nuclides that suggests an unanticipated increase in collectivity near N=40.
With a new detector setup and the high-resolution performance of the fragment separator FRS at GSI we discovered 57 new isotopes in the atomic number range of 60$leq Z leq 78$: uc{159-161}{Nb}, uc{160-163}{Pm}, uc{163-166}Sm, uc{167-168}{Eu}, uc{167-171}{Gd}, uc{169-171}{Tb}, uc{171-174}{Dy}, uc{173-176}{Ho}, uc{176-178}{Er}, uc{178-181}{Tm}, uc{183-185}{Yb}, uc{187-188}{Lu}, uc{191}{Hf}, uc{193-194}{Ta}, uc{196-197}{W}, uc{199-200}{Re}, uc{201-203}{Os}, uc{204-205}{Ir} and uc{206-209}{Pt}. The new isotopes have been unambiguously identified in reactions with a $^{238}$U beam impinging on a Be target at 1 GeV/u. The isotopic production cross-section for the new isotopes have been measured and compared with predictions of different model calculations. In general, the ABRABLA and COFRA models agree better than a factor of two with the new data, whereas the semiempirical EPAX model deviates much more. Projectile fragmentation is the dominant reaction creating the new isotopes, whereas fission contributes significantly only up to about the element holmium.
We report on the mass measurements of several neutron-rich $mathrm{Rb}$ and $mathrm{Sr}$ isotopes in the $A approx 100$ region with the TITAN Penning-trap mass spectrometer. Using highly charged ions in the charge state $q=10+$, the masses of $^{98,99}mathrm{Rb}$ and $^{98-100}mathrm{Sr}$ have been determined with a precision of $6 - 12 mathrm{keV}$, making their uncertainty negligible for r-process nucleosynthesis network calculations. The mass of $^{101}mathrm{Sr}$ has been determined directly for the first time with a precision eight times higher than the previous indirect measurement and a deviation of $3sigma$ when compared to the Atomic Mass Evaluation. We also confirm the mass of $^{100}mathrm{Rb}$ from a previous measurement. Furthermore, our data indicates the existance of a low-lying isomer with $80 mathrm{keV}$ excitation energy in $^{98}mathrm{Rb}$. We show that our updated mass values lead to minor changes in the r-process by calculating fractional abundances in the $Aapprox 100$ region of the nuclear chart.
The region near Z=28, N=40 is a subject of great interest for nuclear structure studies due to spectroscopic signatures in $^{68}$Ni suggesting a subshell closure at N=40. Trends in nuclear masses and their derivatives provide a complementary approach to shell structure investigations via separation energies. Penning trap mass spectrometry has provided precise measurements for a number of nuclei in this region, however a complete picture of the mass surfaces has so far been limited by the large uncertainty remaining for nuclei with N > 40 along the iron and cobalt chains. Here we present the first Penning trap measurements of $^{68,69}$Co, performed at the Low-Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory. In addition, we perform ab initio calculations of ground state and two-neutron separation energies of cobalt isotopes with the valence-space in-medium similarity renormalization group approach based on a particular set of two- and three-nucleon forces which predict saturation in infinite matter. We discuss the importance of these measurements and calculations for understanding the evolution of nuclear structure near $^{68}$Ni.
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