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Register a new userStatistical theory of light nucleus reaction and application to $^9$Be(p, xn) reaction
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A statistical theory of light nucleus reaction (STLN) is proposed to describe both neutron and light charged particle induced nuclear reactions with 1p-shell light nuclei involved. The dynamic of STLN is described by the unified Hauser-Feshbach and exciton model, of which the angular momentum and parity conservations are considered in equilibrium and pre-equilibrium processes. The Coulomb barriers of the incident and outgoing charged particles, which seriously influence the open reaction channels, could be reasonably considered in the incident channel and the different outgoing channels. In kinematics, the recoiling effects in various emission processes are taken strictly into account. Taking $^9$Be(p, xn) reaction as an example, we calculate the double-differential cross sections of outgoing neutrons and charged particles using PUNF code in the frame of STLN. The calculated results agree very well with the existing experimental neutron double-differential cross sections at $E_p=18$ MeV, and indicate that PUNF code is a powerful tool to set up file-6 in the reaction data library for the light charged particle induced nuclear reactions with 1p-shell light nuclei involved.
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We propose a new approach to probe the spatial extension of the valence neutron orbital in the $^{9}$Be nucleus via the ${}^{9}$Be($p,pn$)${}^{8}$Be knockout reaction. This property of the nuclear molecular orbital has not been established in previous experimental studies and divergence exists between the theoretical descriptions of ${}^{9}$Be from different perspectives, textit{i.e.}, the antisymmetrized molecular dynamics and the container pictures of cluster dynamics. These pictures are represented by two different well-proven microscopic models, the antisymmetrized molecular dynamics (AMD) and Tohsaki-Horiuchi-Schuck-R{o}pke (THSR) wave functions. The corresponding reduced width amplitudes (RWAs) in the $^{8}$Be$+n$ channel are extracted from both the AMD and THSR wave functions, and they are found to describe drastically different valence-nucleon motion, which shows the theoretical ambiguity in describing the $pi$-orbitals in $^{9}$Be. Using the RWAs as input, the physical observables of the ${}^{9}$Be($p,pn$)${}^{8}$Be knockout reaction are predicted by the distorted-wave impulse approximation (DWIA) framework. The magnitudes of the triple-differential cross sections (TDX) are found to be highly sensitive to the RWA input. It is concluded that the ${}^{9}$Be($p,pn$)${}^{8}$Be knockout reaction could provide a feasible probing for the subtle differences between several structure models manifesting through the spatial extension of the $pi$-orbital in the $^{9}$Be nucleus.
The study of inelastic scattering and multi-nucleon transfer reactions was performed by bombarding a $^{9}$Be target with a $^3$He beam at an incident energy of 30 MeV. Angular distributions for $^9$Be($^3$He,$^3$He)$^{9}$Be, $^9$Be($^3$He,$^4$He)$^{8}$Be, $^9$Be($^3$He,$^5$He)$^{7}$Be, $^9$Be($^3$He,$^6$Li)$^6$Li and $^9$Be($^3$He,$^5$Li)$^7$Li reaction channels were measured. Experimental angular distributions for the corresponding ground states (g.s.) were analysed within the framework of the optical model, the coupled-channel approach and the distorted-wave Born approximation. Cross sections for channels leading to unbound $^5$He$_{g.s.}$, $^5$Li$_{g.s.}$ and $^8$Be systems were obtained from singles measurements where the relationship between the energy and the scattering angle of the observed stable ejectile is constrained by two-body kinematics. Information on the cluster structure of $^{9}$Be was obtained from the transfer channels. It was concluded that cluster transfer is an important mechanism in the investigated nuclear reactions. In the present work an attempt was made to estimate the relative strengths of the interesting $^8$Be+$n$ and $^5$He+$alpha$ cluster configurations in $^9$Be. The branching ratios have been determined confirming that the $^5$He+$alpha$ configuration plays an important role. The configuration of $^9$Be consisting of two bound helium clusters $^3$He+$^6$He is significantly suppressed, whereas the two-body configurations ${}^{8}$Be+$n$ and ${}^{5}$He+$alpha$ including unbound $^8$Be and $^5$He are found more probable.
The structure of the Borromean nucleus $^9$Be ($alpha+alpha+n$) is addressed within a three-body approach using the analytical transformed harmonic oscillator method. The three-body formalism provides an accurate description of the radiative capture reaction rate for the entire temperature range relevant in Astrophysics. At high temperatures, results match the calculations based on two-step sequential processes. At low temperatures, where the particles have no access to intermediate two-body resonances, the three-body direct capture leads to reaction rates larger than the sequential processes. These results support the reliability of the method for systems with several charged particles.
The low-lying states of the $^{9}$Li nucleus are investigated with a unified framework of microscopic structure and reaction models. In the structure model, the wave function is fully antisymmetrized and the $^{9}$Li nucleus is described as an $alpha$ + $t$ + $n$ + $n$ four-body system, and low-lying 1/2$^{-}$, 3/2$^{-}$, 5/2$^{-}$, and 7/2$^{-}$ states are obtained by the stochastic multi-configuration mixing method. Using these wave functions, the quasi-elastic cross section at $E/A$ = 60 MeV and the elastic and inelastic cross sections at $E/A$ = 50 MeV on the $^{12}$C target are calculated in the framework of the microscopic coupled channel (MCC) method. The characteristic inelastic angular distribution is seen in the 3/2$_{2}^{-}$ state, whose $alpha+t$ cluster structure and valence neutron configurations are discussed in detail. We find the possibility of triaxial deformation and mixing of di-neutron components in the $^{9}$Li nucleus.
We present calculations of the invariant mass spectra of the $Lambda$p system for the exclusive $p p to K^+ Lambda p$ reaction with the aim of studying the final state interaction between the $Lambda$-hyperon and the proton. The reaction is described within a meson exchange framework and the final state $Lambda p$ interaction is incorporated through an off-shell t-matrix for the $Lambda p to Lambda p$ scattering, constructed using the available hyperon-nucleon (YN) potentials. The cross sections are found to be sensitive to the type of YN potential used especially at the $Lambda$ and $Sigma$ production thresholds. Hence, data on this exclusive reaction, which can be used to constrain the YN potentials are desirable.
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