Elastic alpha-particle resonances as evidence of clustering at high excitation in 40 Ca

The elastic-scattering reaction 36 Ar + α was studied using the Thick Target Inverse Kinematics technique. Data were taken at a beam energy of 150 MeV in a reaction chamber filled with 4 He gas, corresponding to the excitation region of 12–20 MeV in 40 Ca. Using a simplified R -matrix method of analysis energies, widths and spin assignments were obtained for 137 resonances. The structure is discussed within the concept of α -cluster structure in the quasi-continuum of 40 Ca and is compared to other nuclei in the same mass region.