Reexamining the temperature and neutron density conditions forr-process nucleosynthesis with augmented nuclear mass models

Abstract

We explore the effects of nuclear masses on the temperature and neutron density conditions required for r-process nucleosynthesis using four nuclear mass models augmented by the latest atomic mass evaluation. For each model we derive the conditions for producing the observed abundance peaks at mass numbers A ∼ 80, 130, and 195 under the waiting-point approximation and further determine the sets of conditions that can best reproduce the r-process abundance patterns (r-patterns) inferred for the solar system and observed in metal-poor stars of the Milky Way halo. In broad agreement with previous studies, we find that (1) the conditions for producing abundance peaks at A ∼ 80 and 195 tend to be very different, which suggests that at least for some nuclear mass models, these two peaks are not produced simultaneously; (2) the typical conditions required by the critical waiting-point (CWP) nuclei with the N = 126 closed neutron shell overlap significantly with those required by the N = 82 CWP nuclei, which enables coproduction of abundance peaks at A ∼ 130 and 195 in accordance with observations of many metal-poor stars; and (3) the typical conditions required by the N = 82 CWP nuclei can reproduce the r-pattern observed in the metal-poor star HD 122563, which differs greatly from the solar r-pattern. We also examine how nuclear mass uncertainties affect the conditions required for the r-process and identify some key nuclei including 76 Ni to 78 Ni, 82 Zn, 131 Cd, and 132 Cd for precise mass measurements at rare-isotope beam facilities.

Diverse, massive-star-associated sources for elements heavier than Fe and the roles of neutrinos

“…Without detailed knowledge of the astrophysical conditions, many parametric studies (e.g., [93]) calculated nucleosynthesis at a constant T and a constant n n for a neutron irradiation time t irr , and compared superpositions of results obtained for different sets of T , n n , and t irr with the solar r-process abundance pattern derived from meteoritic data and s-process studies (e.g., [7]). These calaulations provided a good guide to our understanding of the nuclear physics associated with the r process (e.g., [93,94]). Their adopted sets of T , n n , and t irr may be compatible with some astrophysical sites, but are not the result of self-consistent stellar models.…”

Toward precision mass measurements of neutron-rich nuclei relevant to r-process nucleosynthesis

“…2, clearly demonstrate the importance of precise mass measurements for 76 Ni to 78 Ni. Using this approach, one can identify the key nuclei, including 76 Ni to 78 Ni, 82 Zn, 131 Cd, and 132 Cd [14]. These nuclei at neutron shells N=50 and 82 have the largest impact and are important candidates with high priority for precise mass measurements at rare-isotope beam (RIB) facilities.…”

“…In the waiting-point approach [4,[12][13][14], the abundance ratio between two neighboring isotopes is given by the Saha equation: …”

“…(1) makes it possible to deduce the required T 9 -n n conditions for the r-process, as the required conditions are determined mainly by the neutron separation energies of some crucial waiting points (CWPs) around neutron magic numbers 50, 82, and 126, and of those nuclei around them [4,14]. As an example, we show the importance of knowing the mass of nuclei at and beyond N = 50 along the r-process path, as these nuclei represent the few cases that experiments may be able to access in the near future.…”

Influence of binding energies of electrons on nuclear mass predictions

“…In nuclear physics, it has been widely used to extract the nuclear effective interactions of the mean-field model since it contains a wealth of nuclear structure information, such as the Skyrme effective interactions [3][4][5] and those for the relativistic mean-field (RMF) model [6][7][8][9]. In astrophysics, nuclear mass determines the path of the rapid neuron-capture process (r process), so it is crucial to understand the origin of heavy elements in our universe [2,[10][11][12][13][14][15].…”