Mass measurements of neutron-deficient Y, Zr, and Nb isotopes and their impact on rp and νp nucleosynthesis processes

Y M Xing ,Q Wang,J.H Liu,A Ozawa,T Bao,M Si,M Wang,R.J Chen,H.F Li,C Fröhlich,K.A Li,T Rauscher,P Zhang,X.C Chen,T Uesaka,S Kubono,S Litvinov,Y.H Zhang,G Audi,Q Zeng,B H Sun ,Yoshitaka Yamaguchi ,Xueli Ma ,W J Huang ,H S Xu ,G Martı́nez-Pinedo ,Klaus Blaum ,Y H Lam ,Ruishi Mao ,Mingze Sun ,Xiaodong Tang ,X L Tu ,Jiajia He ,Zhan Wenlong ,Shinya Wanajo ,Friedrich‐Karl Thielemann ,Bo Gao ,Changbo Fu ,Yang Sun ,Takayuki Yamaguchi ,Shuai Peng ,Xing Xu ,Y J Yuan ,A C Dai ,André Sieverding ,Yu A Litvinov ,Xianming Zhou ,Xiao-Bo Yan ,Yang Jiang ,Xu Fang

doi:10.1016/j.physletb.2018.04.009

Abstract

Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of 82Zr and 84Nb were measured for the first time with an uncertainty of ∼10 keV, and the masses of 79Y, 81Zr, and 83Nb were re-determined with a higher precision. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low α separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr–Nb cycle in the rp-process unlikely. The new proton separation energy of 83Nb was determined to be 490(400) keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the p-nucleus 84Sr relative to the neutron-deficient molybdenum isotopes in the previous νp-process simulations.

Highlights

Stellar nucleosynthesis, especially of heavy nuclei, is of great interest in nuclear astrophysics [1, 2]
There is a third class of stable nuclei categorized as p-nuclei [2, 5] which amount to less than one percent of the elemental abundances above Z≥34
In this Letter, we report on precision mass measurements of five nuclei around A∼79−84

Summary

Introduction

Especially of heavy nuclei, is of great interest in nuclear astrophysics [1, 2]. The astrophysical rp- [7] and ν p- [8,9,10] processes have been suggested [14, 15] to describe the production of light pnuclei The former is related to type I X-ray bursts which occur on the surface of neutron stars accreting H- and He-rich matter from a companion star in a stellar binary system. Rp-process model calculations based on the finite range droplet mass model 1992 (FRDM′92) [22] predicted the formation of a Zr-Nb cycle [14] The latter has been emphasized recently based on the previous experimental mass values because it would impose an upper temperature limit for the synthesis of elements beyond Nb [23]. We discuss the overproduction of 84Sr in the νp-process

Experiment

Data analysis and results

Summary