119976206
Current progress of nuclear astrophysical reaction and decay study at CIAE
Presented here was current progress of the study of nuclear astrophysical reaction and decay at CIAE. We studied astrophysical 12N(p,γ)13O reaction through the measurement of the 12N(d,n)13O angular distribution in inverse kinematics. Our result is in agreement with that from the 14N(12N,13O)13C reaction and two shell model calculations. We also measured the angular distributions of single neutron transfer reaction of 7Li(6Li,7Li)6Li, and derived the reaction cross section for 6Li(n,γ)7Li by using the present spectroscopic factor. The astrophysical reaction rate is found to be higher by a factor of 1.7 than the value adopted in previous reaction network calculations. In addition, half-life of 147Sm in metal samarium and Sm2O3 was measured. No significant change has been observed within the experimental uncertainty.
119276160
New determination of the 13C(a, n)16O reaction rate and its influence on the s-process nucleosynthesis in AGB stars
We present a new measurement of the $\alpha$-spectroscopic factor ($S_\alpha$) and the asymptotic normalization coefficient (ANC) for the 6.356 MeV 1/2$^+$ subthreshold state of $^{17}$O through the $^{13}$C($^{11}$B, $^{7}$Li)$^{17}$O transfer reaction and we determine the $\alpha$-width of this state. This is believed to have a strong effect on the rate of the $^{13}$C($\alpha$, $n$)$^{16}$O reaction, the main neutron source for {\it slow} neutron captures (the $s$-process) in asymptotic giant branch (AGB) stars. Based on the new width we derive the astrophysical S-factor and the stellar rate of the $^{13}$C($\alpha$, $n$)$^{16}$O reaction. At a temperature of 100 MK our rate is roughly two times larger than that by \citet{cau88} and two times smaller than that recommended by the NACRE compilation. We use the new rate and different rates available in the literature as input in simulations of AGB stars to study their influence on the abundances of selected $s$-process elements and isotopic ratios. There are no changes in the final results using the different rates for the $^{13}$C($\alpha$, $n$)$^{16}$O reaction when the $^{13}$C burns completely in radiative conditions. When the $^{13}$C burns in convective conditions, as in stars of initial mass lower than $\sim$2 $M_\sun$ and in post-AGB stars, some changes are to be expected, e.g., of up to 25% for Pb in our models. These variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available.
119216112
Neutron spectroscopic factors of 7Li and astrophysical 6Li(n,g)7Li reaction rates
Angular distributions of the 7Li(6Li, 6Li)7Li elastic scattering and the 7Li(6Li, 7Lig.s.)6Li, 7Li(6Li, 7Li0.48)6Li transfer reactions at Ec.m. = 23.7 MeV are measured with the Q3D magnetic spectrograph. The optical potential of 6Li + 7Li is obtained by fitting the elastic scattering differential cross sections. Based on the distorted wave Born approximation (DWBA) analysis, spectroscopic factors of 7Li = 6Li ⊗ n are determined to be 0.73 ± 0.05 and 0.90 ± 0.09 for the ground and first exited states in 7Li, respectively. Using the spectroscopic factors, the cross sections of the 6Li(n, γ0, 1)7Li direct neutron capture reactions and the astrophysical 6Li(n, γ)7Li reaction rates are derived.
121312122
The Daya Bay Experiment and the Discovery of a New Type of Neutrino Oscillation
We know nowadays that the matter world we live in is made of 12 elementary particles, including 6 quarks, 3 charged leptons and 3 neutrinos. Among them, neutrinos are least known since they do not carry the electric charge and interact with others only weakly (often referred as the nuclear weak interactions). In the Standard Model of particle physics before 1998, neutrinos are considered as massless for simplicity and lack of experimental evidence. However, they are so abundant in the universe that their masses, even if tiny, will have significant impact to the particle physics, astrophysics and cosmology.
120221743
Asymmetric Hopf bifurcation for proton beams with electron cooling
We observed maintained longitudinal limiting cycle oscillations, which grew rapidly once a critical threshold in the relative velocity between the proton beam and the cooling electrons was exceeded. The threshold for the bifurcation of a fixed point into a limit cycle, also known as a Hopf bifurcation, was found to be asymmetric with respect to the relative velocity. This asymmetry of Hopf bifurcation was found to be related to the electron beam alignment with respect to the stored proton beam.
17103243
An analytical model probing the internal state of coronal mass ejections based on observations of their expansions and propagations
[1] In this paper, a generic self-similar flux rope model is proposed to probe the internal state of CMEs in order to understand the thermodynamic process and expansion of CMEs in interplanetary space. Using this model, three physical parameters and their variations with heliocentric distance can be inferred based on coronagraph observations of CMEs' propagation and expansion. One is the polytropic index Γ of the CME plasma, and the other two are the average Lorentz force and the thermal pressure force inside CMEs. By applying the model to the 8 October 2007 CME observed by STEREO/SECCHI, we find that (1) the polytropic index of the CME plasma increased from initially 1.24 to more than 1.35 quickly and then slowly decreased to about 1.34; it suggests that there be continuously heat injected/converted into the CME plasma and the value of Γ tends to be , a critical value inferred from the model for a force-free flux rope; (2) the Lorentz force directed inward while the thermal pressure force outward, and both of them decreased rapidly as the CME moved out; the direction of the two forces reveals that the thermal pressure force is the internal driver of the CME expansion, whereas the Lorentz force prevented the CME from expanding. Some limitations of the model and approximations are discussed meanwhile.
2164692
Precise measurement of the pi+-->pi0 e+nu branching ratio.
Using a large acceptance calorimeter and a stopped pion beam we have made a precise measurement of the rare pi(+)-->pi(0)e(+)nu (pi(beta)) decay branching ratio. We have evaluated the branching ratio by normalizing the number of observed pi(beta) decays to the number of observed pi(+)-->e(+)nu (pi(e2)) decays. We find the value of Gamma(pi(+)-->pi(0)e(+)nu)/Gamma(total)=[1.036+/-0.004(stat)+/-0.004(syst)+/-0.003(pi(e2))]x10(-8), where the first uncertainty is statistical, the second systematic, and the third is the pi(e2) branching ratio uncertainty. Our result agrees well with the standard model prediction.