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Register a new userStructure of $^{20}$Ne states in the resonance $^{16}$O+$alpha$ elastic scattering
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Background The nuclear structure of the cluster bands in $^{20}$Ne presents a challenge for different theoretical approaches. It is especially difficult to explain the broad 0$^+$, 2$^+$ states at 9 MeV excitation energy. Simultaneously, it is important to obtain more reliable experimental data for these levels in order to quantitatively assess the theoretical framework. Purpose To obtain new data on $^{20}$Ne $alpha$ cluster structure. Method Thick target inverse kinematics technique was used to study the $^{16}$O+$alpha$ resonance elastic scattering and the data were analyzed using an textit{R} matrix approach. The $^{20}$Ne spectrum, the cluster and nucleon spectroscopic factors were calculated using cluster-nucleon configuration interaction model (CNCIM). Results We determined the parameters of the broad resonances in textsuperscript{20}Ne: 0$^+$ level at 8.77 $pm$ 0.150 MeV with a width of 750 (+500/-220) keV; 2$^+$ level at 8.75 $pm$ 0.100 MeV with the width of 695 $pm$ 120 keV; the width of 9.48 MeV level of 65 $pm$ 20 keV and showed that 9.19 MeV, 2$^+$ level (if exists) should have width $leq$ 10 keV. The detailed comparison of the theoretical CNCIM predictions with the experimental data on cluster states was made. Conclusions Our experimental results by the TTIK method generally confirm the adopted data on $alpha$ cluster levels in $^{20}$Ne. The CNCIM gives a good description of the $^{20}$Ne positive parity states up to an excitation energy of $sim$ 7 MeV, predicting reasonably well the excitation energy of the states and their cluster and single particle properties. At higher excitations, the qualitative disagreement with the experimentally observed structure is evident, especially for broad resonances.
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The first study of resonances in $^{17}$O+$alpha$ elastic scattering was carried out using the Thick Target Inverse Kinematics (TTIK) method. The data were analyzed in the framework of an $textit{R}$-matrix approach. Many $alpha$-cluster states were found in the $^{21}$Ne excitation region of the 9-13 MeV excitation energy including the first observation of a broad $textit{l}$=0 state in an odd-even nucleus, which is likely the analog of the broad 0$^+$ at 8 MeV in $^{20}$Ne. The observed structure in $^{21}$Ne appeared to be strikingly similar to that in $^{20}$Ne populated in the resonance $^{16}$O+$alpha$ scattering. The results are also useful for refinement of data on an $^{17}$O($alpha$,$textit{n}$) reaction important for astrophysics.
The elastic scattering $^{16}$O$+^{12}$C angular distributions at $^{16}$O bombarding energies of 100.0, 115.9 and 124.0 MeV and their optical model description including the $alpha$-particle exchange contribution calculated in the Coupled Reaction Channel approach are presented. The angular distributions show not only the usual diffraction pattern but also, at larger angles, intermediate structure of refractive origin on which finer oscillations are superimposed. The large angle features can be consistently described including explicitly the elastic $alpha$-transfer process and using a refractive optical potential with a deep real part and a weakly absorptive imaginary part.
The elastic resonance scattering protons decayed from $^{11}$B to the ground state of $^{10}$Be were measured using the thick-target technique in inverse kinematics at the Heavy Ion Research Facility in Lanzhou (HIRFL). The obtained excitation functions were well described by a multichannel R-matrix procedure under the kinematics process assumption of resonant elastic scattering. The excitation energy of the resonant states ranges from 13.0 to 17.0 MeV, and their resonant parameters such as the resonant energy E$_{x}$, the spin-parity J$^pi$, and the proton-decay partial width $Gamma_p$ were determined from R-matrix fits to the data. Two of these states around E$_{x}$ = 14.55 MeV [J$^pi$ = (3/2$^+$, 5/2$^+$), $Gamma_p$ = 475 $pm$ 80 keV] and E$_{x}$ = 14.74 MeV [J$^pi$ = 3/2$^-$, $Gamma_p$ = 830 $pm$ 145 keV], and a probably populated state at E$_x$ = 16.18 MeV [J$^pi$ =(1/2$^-$, 3/2$^-$), $Gamma_p$ $<$ 60 keV], are respectively assigned to the well-known states in $^{11}$B at 14.34 MeV, 15.29 MeV, and 16.43 MeV. The isospin of these three states were previously determined to be T = 3/2, but discrepancies exist in widths and energies due to the current counting statistics and energy resolution. We have compared these states with previous measurements, and the observation of the possibly populated resonance is discussed.
The elastic scattering angular distribution of the $^{16}$O$+^{60}$Ni system at $260$ MeV was measured in the range of the Rutherford cross section down to $7$ orders of magnitude below. The cross sections of the lowest $2^{+}$ and $3^{-}$ inelastic states of the target were also measured over a several orders of magnitude range. Coupled channel (CC) calculations were performed and are shown to be compatible with the whole set of data only when including the excitation of the projectile and when the deformations of the imaginary part of the nuclear optical potential are taken into account. Similar results were obtained when the procedure is applied to the existing data on $^{16}$O$+^{27}$Al elastic and inelastic scattering at $100$ and $280$ MeV. An analysis in terms of Dynamical Polarization Potentials (DPP) indicate the major role of coupled channel effects in the overlapping surface region of the colliding nuclei.
The proton-induced $alpha$ knockout reaction has been utilized for decades to investigate the $alpha$ cluster states of nuclei, of the ground state in particular. However, even in recent years, it is reported that the deduced $alpha$ spectroscopic factors from $alpha$ knockout experiments and reaction analyses with a phenomenological $alpha$ cluster wave function diverge depending on the kinematical condition of the reaction. In the present study we examine the theoretical description of the $^{20}$Ne($p$,$palpha$)$^{16}$O cross section based on the antisymmetrized molecular dynamics and the distorted wave impulse approximation by comparing with existing experimental data. We also investigate the correspondence between the $alpha$ cluster wave function and the $alpha$ knockout cross section. The existing $^{20}$Ne($p$,$palpha$)$^{16}$O data at 101.5 MeV is well reproduced by the present framework. Due to the peripherality of the reaction, the surface region of the cluster wave function is selectively reflected to the knockout cross section. A quantitatively reliable $alpha$ cluster wave function, $p$-$alpha$ cross section, and distorting potentials between scattering particles, $alpha$-$^{16}$O in particular, are crucial for the quantitative description of the ($p$,$palpha$) cross section. Due to the peripherality of the reaction, the ($p$,$palpha$) cross section is a good probe for the surface $alpha$ amplitude.
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