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Register a new userNuclear masses near $N=82$ that influence $r$-process abundances
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Nuclear masses are one of the key ingredients of nuclear physics that go into astrophysical simulations of the $r$ process. Nuclear masses effect $r$-process abundances by entering into calculations of Q-values, neutron capture rates, photo-dissociation rates, beta-decay rates, branching ratios and the properties of fission. Most of the thousands of short-lived neutron-rich nuclei which are believed to participate in the $r$ process lack any experimental verification, thus the identification of the most influential nuclei is of paramount importance. We have conducted mass sensitivity studies near the $N=82$ closed shell in the context of a main $r$-process. Our studies take into account how an uncertainty in a single nuclear mass propagates to influence the relevant quantities of neighboring nuclei and finally to $r$-process abundances. We identify influential nuclei in various astrophysical conditions using the FRDM mass model. We show that our conclusions regarding these key nuclei are still retained when a superposition of astrophysical trajectories is considered.
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We have performed for the first time a complete $r$-process mass sensitivity study in the $N=82$ region. We take into account how an uncertainty in a single nuclear mass propagates to influence important quantities of neighboring nuclei, including Q-values and reaction rates. We demonstrate that nuclear mass uncertainties of $pm0.5$ MeV in the $N=82$ region result in up to an order of magnitude local change in $r$-process abundance predictions. We identify key nuclei in the study whose mass has a substantial impact on final $r$-process abundances and could be measured at future radioactive beam facilities.
The impact of nuclear mass uncertainties on the emph{r}-process abundances has been systematically studied with the classical emph{r}-process model by varying the mass of every individual nucleus in the range of $pm0.1$ to $pm3.0 mathrm{MeV}$ based on six different mass models. A new quantitative relation between the uncertainties of emph{r}-process abundances and those of the nuclear masses is extracted, i.e., a mass uncertainty of $pm0.5 mathrm{MeV}$ would lead to an abundance uncertainty of a factor around 2.5. It is found that this conclusion holds true for various mass models.
The rapid neutron capture process (r-process) is thought to be responsible for the creation of more than half of all elements beyond iron. The scientific challenges to understanding the origin of the heavy elements beyond iron lie in both the uncertainties associated with astrophysical conditions that are needed to allow an r-process to occur and a vast lack of knowledge about the properties of nuclei far from stability. There is great global competition to access and measure the most exotic nuclei that existing facilities can reach, while simultaneously building new, more powerful accelerators to make even more exotic nuclei. This work is an attempt to determine the most crucial nuclear masses to measure using an r-process simulation code and several mass models (FRDM, Duflo-Zuker, and HFB-21). The most important nuclear masses to measure are determined by the changes in the resulting r-process abundances. Nuclei around the closed shells near N=50, 82, and 126 have the largest impact on r-process abundances irrespective of the mass models used.
Motivated by the newly observed $^{39}$Na in experiments, systematic calculations of global nuclear binding energies with seven Skyrme forces are performed. We demonstrate the strong correlation between the two-neutron separation energies ($S_{2n}$) of $^{39}$Na and the total number of bound nuclei of the whole nuclear landscape. Furthermore, with calculated nuclear masses, we perform astrophysical rapid-neutron capture process ($r$-process) simulations by using nuclear reaction code TALYS and nuclear reaction network code SkyNet. $r$-process abundances from ejecta of neutron star mergers and core-collapse supernova are compared. Prominent covariance correlations between nuclear landscape boundaries and neutron-rich $r$-process abundances before the third peak are shown. This study highlights the needs for further experimental studies of drip-line nuclei around $^{39}$Na for better constraints on nuclear landscape boundaries and $r$-process.
Precision mass spectrometry of neutron-rich nuclei is of great relevance for astrophysics. Masses of exotic nuclides impose constraints on models for the nuclear interaction and thus affect the description of the equation of state of nuclear matter, which can be extended to describe neutron-star matter. With knowledge of the masses of nuclides near shell closures, one can also derive the neutron-star crustal composition. The Penning-trap mass spectrometer ISOLTRAP at CERN-ISOLDE has recently achieved a breakthrough measuring the mass of 82Zn, which allowed constraining neutron-star crust composition to deeper layers (Wolf et al., PRL 110, 2013). We perform a more detailed study on the sequence of nuclei in the outer crust of neutron stars with input from different nuclear models to illustrate the sensitivity to masses and the robustness of neutron-star models. The dominant role of the N=50 and N=82 closed neutron shells for the crustal composition is confirmed.
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