Nuclear Astrophysics Experiments in Collaboration with Ruhr University

This paper reports on two nuclear astrophysics experiments performed in collabora- tion with Ruhr University. In a 12C＋2C fusion reaction, the 12C（12C, a）20e and 12C（12C, p）23Na reactions were studied in the energy range of E = 2.10 MeV to 4.75 MeV using -y-ray spectroscopy. The deduced astrophysical S（E）＊ factor exhibited a new, strong resonance at E -= 2.14 MeV, which lay at the high-energy tail of the Gamow peak. The resonance increased the reaction rate of the ^-channel by a factor of five near T = 8 ~ l0s K. The electron screening in d（d, p）t was stud- ied for a series of deuterated metal, insulator and semiconductor targets. Compared with the measurements performed with a gaseous D2 target, a large effect was observed in most metals, while a comparatively small effect was found in the insulators and semiconductors. Subsequently the temperature dependence of the electron screening in the d（d, p）t reaction was studied for the deuterated metals Pt and Co. Enhanced electron screening decreased with increasing tempera- ture. These data represent the first observations of the temperature dependence of a nuclear cross section.

First result from the Jinping Underground Nuclear Astrophysics experiment JUNA:precise measurement of the 92 keV ^(25)Mg(p,γ)^(26)Al resonance

The ^(25)Mg(p,γ)^(26)Al reaction plays an important role in the study of cosmic 1.809 MeV γ-ray as a signature of ongoing nucleosynthesis in the Galaxy.At astrophysical temperature around 0.1 GK,the ^(25)Mg(p,γ)^(26)Al reaction rates are dominated by the 92 keV resonance capture process.We report a precise measurement of the 92 keV ^(25)Mg(p,γ)^(26)Al resonance in the day-one experiment at Jinping Underground Nuclear Astrophysics experiment(JUNA)facility in the China Jinping Underground Laboratory(CJPL).The resonance strength and ground state feeding factor are determined to be 3.8±0.3×10^(-10) eV and 0:660:04,respectively.The results are in agreement with those reported in the previous direct underground measurement within uncertainty,but with significantly reduced uncertainties.Consequently,we recommend new ^(25)Mg(p,γ)^(26)Al reaction rates which are by a factor of 2.4 larger than those adopted in REACLIB database at the temperature around 0.1 GK.The new results indicate higher production rates of ^(26g)Al and the cosmic 1.809 MeV γ-ray.The implication of the new rates for the understanding of other astrophysical situations is also discussed.

Direct measurement of the break-out ^(19)F(p,γ)^(20)Ne reaction in the China Jinping underground laboratory(CJPL)

Calcium production and the stellar evolution of first-generation stars remain fascinating mysteries in astrophysics.As one possible nucleosynthesis scenario,break-out from the hot carbon–nitrogen–oxygen(HCNO)cycle was thought to be the source of the calcium observed in these oldest stars.However,according to the stellar modeling,a nearly tenfold increase in the thermonuclear rate ratio of the break-out ^(19)F(p,γ)^(20) Ne reaction with respect to the competing ^(19)F(p,α)^(16) O back-processing reaction is required to reproduce the observed calcium abundance.We performed a direct measurement of this break-out reaction at the China Jinping underground laboratory.The measurement was performed down to the low-energy limit of E_(c.m.)=186 keV in the center-of-mass frame.The key resonance was observed at 225.2 keV for the first time.At a temperature of approximately 0.1 GK,this new resonance enhanced the thermonuclear ^(19)F(p,γ)^(20) Ne rate by up to a factor of≈7.4,compared with the previously recommended NACRE rate.This is of particular interest to the study of the evolution of the first stars and implies a stronger breakdown in their“warm”CNO cycle through the ^(19)F(p,γ)^(20) Ne reaction than previously envisioned.This break-out resulted in the production of the calcium observed in the oldest stars,enhancing our understanding of the evolution of the first stars.

The SLEGS beamline of SSRF

The Shanghai Laser Electron Gamma Source(SLEGS, located in BL03SSID) beamline at the Shanghai Synchrotron Radiation Facility(SSRF) is a Laser Compton Scattering(LCS) gamma source used for the investigation of nuclear structure, which is in extensive demand in fields such as nuclear astrophysics, nuclear cluster structure, polarization physics, and nuclear energy. The beamline is based on the inverse Compton scattering of 10640 nm photons on 3.5 GeV electrons and a gamma source with variable energy by changing the scattering angle from 20° to 160°. γ rays of 0.25-21.1 MeV can be extracted by the scheme consisting of the interaction chamber, coarse collimator, fine collimator, and attenuator. The maximum photon flux for 180° is approximately 10~7 photons/s at the target at 21.7 MeV, with a 3-mm-diameter beam. The beamline was equipped with four types of spectrometers for experiments in( γ,γ'),( γ,n),( γ,p), and( γ,α). At present, Nuclear Resonance Fluorescence(NRF) spectrometry, Flat-Efficiency neutron Detector(FED) spectrometry, neutron Time-Of-Flight(TOF) spectrometry, and Light-Charged Particle(LCP) spectrometry methods have been developed.

High energy and high brightness laser compton backscattering gamma-ray source at IHEP

Based on the LINAC of BEPCII, a high-polarized, high bightness, energy-tunable, monoenergetic laser compton backscattering (LCS)gamma-ray source is under construction at IHEP. The gamma-ray energy range is from 1 MeV to 111 MeV. It is a powerful and hopeful researchplatform to reveal the underlying physics of the nuclear, the basic particles and the vacuum or to check the exist basic physical models, quantumelectrodynamic (QED) theories. In the platform, a 1.064 mm Nd:YAG laser system and a 10.6 mm CO_(2) laser system are employed. All the triggersignals to the laser system and the electron control system are from the only reference clock at the very beginning of the LINAC to make sure thetemporal synchronization. Two optical transition radiation (OTR) targets and two charged-couple devices (CCD) are used to monitor and to alignthe electron beam and the laser beam. With the LCS gamma-ray source, it is proposed to experimentally check the gamma-ray calibrations, thephoton-nuclear physics, nuclear astrophysics and some basic QED phenomena.

Exotic Beam for Direct Measurement of the 22^Mg＋a

The scattering and resonance reactions of ^22Mg＋p and ^22Mg＋α play crucial roles for studying deeply not only in the structure of proton-rich nuclei of ^23A1 and ^26Si but also for the interest of astrophysics. It is believed that ^22Mg nucleus is a waiting point in the αp-process of nucleosynthesis in novae. We supposed to perform direct measurement the ^22Mg＋α system in invert kinematics using radioactive ion （RI） beam. The ^22Mg beam of 3.73 MeV/u was produced at CRIB facility of the University of Tokyo located at RIKEN, Japan in 2011. In this paper, we report the results the scattering and resonance reactions with the alpha target. of the ^22Mg beam production used for the direct measurement of

Excited States in ^18Ne Studied via ^17F＋p

The elastic resonance scattering of ^17F＋p is studied in inverse kinematics via a thick-target method. The excitation function for ^17F＋p elastic scattering is obtained within the energy interval of Ec.m ≈ 0.4-1.7 MeV. The experimental excitation function is analyzed with a multilevel R-matrix code MULTI7, and the proton widths are deduced. The α decay from 6.15 MeV 1- state in 18Ne is observed, which is critical to the 14O（α, p）17F reaction as the main breakout route from CNO cycle to rp-process in supernovae and x-ray bursts.

Laser-driven plasma collider for nuclear studies

A novel method of initiating nuclear fusion reactions in a full plasma environment was suggested, and a proof-of-concept experiment was carried out with the D ＋D → n＋3He reaction. In this new approach, two plasma jets generated by high-intensity lasers collide headon-head. The center-of-mass energy of the nuclei increases accordingly, and therefore, reaction products can be significantly enhanced, especially in the sub-Coulomb barrier ranges. As a result of the fusion reaction, up to - 7.6 ×105 neutrons had been observed. This new type of ＂plasma collider＂ could provide an innovative tool to study nuclear reactions under astrophysical conditions.

Novel thick-target inverse kinematics method for the astrophysical ^(12)C+^(12)C fusion reaction

The ^(12)C+^(12)C fusion is one of the most important reactions in modern nuclear astrophysics.The trend and magnitude of the reaction rate within the Gamow window strongly influence various astrophysical processes.However,direct measurement of this reaction is extremely difficult,which makes it necessary to develop indirect methods.In this study,the ^(23)Na+p reaction system was used to study the compound nucleus ^(24)Mg.We employed a thick-target inverse kinematics method combined with the -charged-particle coincidence technique to measure the proton and exit channels of ^(24)Mg.Technical details of the ^(23)Na+p thick-target inverse kinematics experiment and analysis are presented herein.

Neutron and Alpha Structure in Neutron Deficient Nuclei in Astrophysics

The paper includes discussions on the important role of neutron and alpha configurations in proton-rich nuclei in nuclear astrophysics in terms of nucleosynthesis under extremely high-temperature hydrogenburning conditions. The νp-process, which is supposed to take place at the very early epoch of type II supernovae, has considerable neutrons and alphas together with protons. The alpha-induced reactions on proton-rich unstable nuclei in the light mass regions is expected to play a crucial role, but very few of them were investigated well yet because of the experimental difficulties. Specifically, I report our recent experimental effort for the breakout process from the pp-chain region,~7Be(α, γ)^(11)C(α,p)^(14)N under the νp-process. The neutron-induced reactions on proton-rich nuclei, which is even more a challenging subject, were investigated previously for very few nuclei. One possible experimental method is the Trojan Horse Method(THM). We successfully have applied THM to the ^(18)F(n,α)^(14)N reaction study with an unstable beam of ^(18)F.

Radiative^(9)Be(n,γ0+1+2+3+4+5)^(10)Be reaction rate in the potential cluster model

Within the framework of the modified potential cluster model with forbidden states,the total cross-sections of radiative n^(9)Be capture to the ground and five low-lying excited states are calculated at energies from 10^(-2)eV up to 5 MeV.The thermal cross-section σ_(th)=8.35mb is in good agreement with experimental data.We considered five resonances at the excitation energies E_(x)from 7.371 MeV up to 10.570 MeV corresponding to the following states with J^(π)(E_(x),MeV):3^(-)(7.371),2^(+)(7.542),3^(+)(9.4),2^(+)(9.56),and 3^(-)(10.570).The partial and total ^(9)Be(n,γ0+1+2+3+4+5)^(10)Be reaction rates are calculated at temperatures from 0.001 to 10 T_(9).Contrary to the available data,we propose that the rise in the reaction rate near factor five at T_(9)>1 is mainly due to the first 3^(-)(E_(R)=0.559 MeV)resonance.We foresee this contrast as arising from different model approaches.

A proposed direct measurement of cross section at Gamow window for key reaction 19F(p,α) 16O in Asymptotic Giant Branch stars with a planned accelerator in CJPL

In 2014, the National Natural Science Foundation of China （NSFC） approved the Jinping Underground Nuclear Astrophysics laboratory （JUNA） project, which aims at direct cross-section measurements of four key stellar nuclear reactions right down to the Gamow windows. In order to solve the observed fluorine overabundances in Asymptotic Giant Branch （AGB） stars, measuring the key 19F（p,a）16O reaction at effective burning energies （i.e., at Gamow window） is established as one of the scientific research sub-projects. The present paper describes this sub-project in details, including motivation, status, experimental setup, yield and background estimation, aboveground test, as well as other relevant reactions.

Observatory science with eXTP

In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

Effects of relativistic parameter sets on tidal deformabilities and f-mode oscillations of neutron stars

The implications of relativistic parameter sets established at saturation density on the tidal deformabilities and f-mode oscillations of neutron stars(NSs)are examined using constraints from the gravitational wave(GW)event GW170817 and NICER.According to our findings,the isovector saturation parameters have a greater impact on the radii and tidal deformabilities of NSs than the isoscalar saturation parameters.Our analysis also examines the impact of saturation properties on f-mode frequencies and finds that f-mode frequencies with 1.4 M⊙(solar mass)are roughly between 1.95 and 2.15 kHz.These findings could be confirmed by future advanced GW detectors.A good linear parameter-independent correlation between f-mode frequencies inferred from saturation parameters in the entire region is also observed,and we attempt to fit an updated version of this universal relationship.Furthermore,we used chiral effective theory(χEFT)together with the multi-messenger astronomy constraints to further reinforce the rationality of the conclusions we have reached.

Short-range correlation effects in neutron star's radial and non-radial oscillations

In this study,we determine the influence of the nucleon-nucleon short range correlation(SRC)on static spherically symmetric neutron stars(NSs)from the perspectives of radial and nonradial oscillations for the first time.We revise the equation of state and coupling parameters in the relativistic mean field theory after considering the SRC effect,and select the hyperon coupling parameters as the SU(3)model.For the non-radial oscillations,the SRC effect decreases the f-mode frequency by 0.2~0.3 kHz.For the radial oscillations,it decreases the fundamental radial frequency f_(1) by 0.75~0.85 kHz.Additionally,we refit the linear relationship between the average density and f-mode frequency for SRC.Combining the characteristics of the radial and non-radial frequencies,we provide a view of inferring the maximum mass of NSs.Owing to the characteristics of the SRC influence on the radial frequency,we expect that the SRC can be tested by future observation and can also be used as a probe for the structure inside NSs.