Shanghai Yingwu Institute made progress in key reactions of stellar thorium combustion

The Institute of Nuclear Physics of the Shanghai Institute of Applied Physics, Chinese Academy of Sciences cooperates with the Department of Physics of Tsinghua University to iteratively fit almost all the 16O nuclear systems based on their newly developed multi-channel, multi-level reduced R-matrix theory for low-energy nuclear reactions. Available experimental data were extrapolated to the internal self-consistent 12C (α, γ) 16O response astrophysical S-factor and its response rate. This is the first time that the physical response rate of 12C (α, γ) 16O is met theoretically to meet the accuracy requirements of stellar evolution and elemental nuclear synthesis model (less than 10% uncertainty). Research papers have recently been published online on Astrophysical Journal Letters (ApJ, 817, L5 (2016)) and Physical Review C (PRC92, 045802 (2015)).

In the combustion phase of the star helium, the 3α and 12C (α, γ) 16O reactions compete with each other, and the reaction rates of the two determine the abundance ratios of 12C and 16O after the enthalpy burning. This value is the subsequent evolution of the massive star and its concomitant Elemental nuclear synthesis process initial conditions. These processes are extremely sensitive to the reaction rate of 12C (α,γ)16O in the stellar environment at a temperature of T9=0.2 (unit 109 K, mass center system energy 0.3 MeV). The 1983 Nobel laureate William Fowler clearly stated that determining the 12C/16O abundance ratio and the solar neutrino problem are two fundamental problems that need to be solved in nuclear astrophysics, and that the 12C (alpha, gamma) 16O reaction is called The "Holy Grail" for nuclear astrophysics. At present, the most direct and reliable way to obtain the response rate of 12C (α,γ)16O is to measure its astrophysical S factor as far as possible in the low energy region and extrapolate it to the interesting energy region through theory to calculate the astrophysical response. rate.

PhD student An Zhendong of Shanghai Yingshi Research Institute under the guidance of the researcher Ma Yugang and the partner Tsinghua University professor Chen Zhenpeng developed a multi-channel, multi-level reduced R-matrix for low-energy nuclear reactions based on the classical R-matrix method. theory. Using covariance statistics and error propagation theory, it fits iteratively to more than 40 experimental data available for the 16O system, and extrapolates the total S factor of the enthalpy of combustion at 0.3 MeV to 162.7±7.3 keVb. At the same time, based on the R-matrix analysis given the S factor of the omnipotent region, the physical response rate of 12C (α, γ) 16O at 0.04 ≤ T9 ≤ 10 was calculated. At T9=0.2, the recommended response rate is (7.83±0.35)×1015 cm3mol−1s−1 with a relative error of 4.5%. This reaction rate helps scientists to understand the synthesis of medium-mass nuclear species up to the iron region, the reaction mechanism of the heavy-nuclear synthesis of s, r, and p in the iron region, and the subsequent evolution of the massive stars ( Cooling of white dwarfs, supernova explosions, formation of neutron stars, and large masses of X-ray black hole binary stars).

At present, the nuclear physics research office is planning to establish the Shanghai Laser Electronic Gamma Source (SLEGS) line station, one of the Phase II of Shanghai Light Source Line Station Project. After completion, it is expected that the integral cross section of the inverse reaction 16O(γ,α)12C corresponding to the center of mass energy near 0.3 MeV will help to directly solve the 12C (α,γ)16O reaction rate in this experiment. This is a holy grail of nuclear astrophysics. "problem.

The project was jointly funded by the National Natural Science Foundation of China, the Innovation Committee of the Foundation Committee, and the "973" project.

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