Astrophysical production of 146Sm in nuclear p - processes

Cristiana Oprea,Alexandru Ioan Oprea,Alexandru Mihul,Mihai Potlog,Alina Neagu,Sorin Zgura

doi:10.1088/1742-6596/1668/1/012031

Abstract

The large time of life of 146Sm suggests the possibility to use this p - nuclide as astrophysical chronometer to study the geochemical galactic evolution. Due to the high temperature and large densities of gamma quanta, neutrons and protons in stellar environment 146Sm nucleus can be obtained in (γ,n), (n,2n), (p,2n) processes on 147Sm.The knowledge of corresponding cross sections of gamma rays, neutrons and alpha induced processes is of a great importance for the explanation of (146Sm/144Sm) ratio uncertainties observed on the Earth, meteorites, Moon and other celestial bodies.Cross sections of (γ,n), (n,2n), (α,γ) processes induced by fast gamma rays, neutrons and alphas on 147Sm and 142Nd, from threshold up to 25 MeV were evaluated and predicted in the frame of Hauser-Feshbach statistical model by using Talys software and the own computer programs. For each nuclear reaction contribution of direct, compound and pre-equilibrium mechanisms were determined. Theoretical evaluations are compared with existing experimental data. Parameters of optical potential in the incident and emergent channels and of nuclear densities were extracted. Calculated cross sections together with corresponding nuclear data were used in the evaluation of astrophysical rates necessary in the determination of elemental abundances as needed by nuclear astrophysical networks.

Highlights

Astrophysical motivation and previous dataDuring the core He-burning and shell C-burning evolutionary stages of massive stars (M>8M ), a large amount of neutrons are released via the 22Ne(α, n) reaction [1]
The n time of flight (TOF) experimental weighted count rate as a function of the neutron energy is shown in Fig. 2 with an arbitrary scale
Ratios between count rates of C6D6 detectors and the silicon monitor were calculated. These ratios have to remain constant along the experiment, and any variation in the number of counts registered by the silicon monitor must occur in the C6D6 detectors keeping the ratio between them constant

Summary

Astrophysical motivation and previous data

During the core He-burning and shell C-burning evolutionary stages of massive stars (M>8M ), a large amount of neutrons are released via the 22Ne(α, n) reaction [1]. Long-lived radioactive nuclei (T1/2 > 10 y) may produce a split in the nucleosysnthesis path, producing a local isotopic abundance pattern that can be used to probe the physical conditions along different evolutionary stages, mainly during the ∼30 keV characteristic of He-burning and the ∼90 keV regime in C-burning [2] In this contribution we focus on the s-process branching nucleus 79Se(T1/2 = 3.27(8)×105 y) [3], which has the peculiarity that it has a few quantum states at low excitation energy that are thermally populated in the stellar environment. Cross section data was obtained only beyond neutron energies of ∼3 keV This prevented the measurement of one large s-wave resonance in the keV-region. An assessment of possible neutron-sensitivity deviations in our or previous experiments will be made in future stages of the data analysis

Methodology

Preliminary Results

Summary and outlook