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Background: Clustering phenomena in N = Z nuclei provide an opportunity to understand the interplay between cluster and nucleon degrees of freedom. Purpose:To study resonances in the 18 O spectrum, populated in 14 C+α elastic scattering.Method: The Thick Target Inverse Kinematics (TTIK) technique was used to measure the excitation function for the 14 C+α elastic scattering. A 42 MeV 14 C beam was used to populate states of excitation energy up to 14.9 MeV in 18 O. The analysis was performed using a multi-level, multi-channel R-Matrix approach.Results: Detailed spectroscopic information, including spin-parities, partial α-and neutron-decay widths and dimensionless reduced widths, was obtained for excited states in 18 O between 8 and 14.9 MeV in excitation energy. Cluster-Nucleon Configuration Interaction Model calculations of the same quantities are performed and compared to the experimental results.Conclusions: Strong fragmentation of large α-cluster strengths is observed in the spectrum of 18 O making the α-cluster structure of 18 O quite different from the pattern of known quasi-rotational bands of alternating parity that are characteristic of N = Z, even-even nuclei like 16 O and 20 Ne.

Nuclear clustering, alpha decays, and multi-particle correlations are important components of nuclear dynamics. In this work we put forward the Cluster-Nucleon Configuration Interaction Model. We use the modern configuration-interaction approach with advanced realistic shell-model Hamiltonians in order to study clustering phenomena; the study is facilitated by the algebraic properties of many-nucleon configurations in the harmonic oscillator basis.Using translationally invariant formalism we built cluster channels that satisfy Pauli exclusion principle as well as orthogonality and normalization conditions. We formally justify the formalism and demonstrate that, within the new method, clustering strengths satisfy sum rules that are consistent with the statistical properties of nuclear reactions with composite particles. Using properly renormalized cluster form factors our approach appears to resolve long-standing problems related to absolute normalization of the alpha clustering spectroscopic factors and their behavior in sd-shell nuclei.Our methods are demonstrated in studies of α spectroscopic factors in sd-shell nuclei and in 16 O treated in p-sd shells. Comparison with experimental data supports validity of the approach.

A convenient method of calculation has been developed to determine the cluster spectroscopic factors for the ejection of excited and complex fragments {'He, Li, 'Li, 'Be, etc. ) from the low-lying levels of the p-shell nuclei followed by transition both to the states of the lowest shell configuration of the daughter nucleus and to its hole states. The method can be used to analyze the cluster knock-out, transfer reactions induced by heavy ions, etc. NUCLEAB STRUCTURE p-shell nuclei; calculated cluster spectroscopic factors. Harmonic oscillator shell model.

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