The Hoyle state and other resonances in the continuum above the 3 alpha
threshold in 12C are studied in a microscopic cluster model. Whereas the Hoyle
state is a very sharp resonance and can be treated reasonably well in bound
state approximation, the other higher lying states require a proper treatment
of the continuum. The model space consists of an internal region with 3 alpha
particles on a triangular grid and an external region consisting of the 8Be
ground state and excited (pseudo)-states of 8Be with an additional alpha. The
microscopic R-matrix method is used to match the many-body wave function to the
asymptotic Coulomb behavior of bound states, Gamow states and scattering
states. 8Be-alpha phase shifts are analyzed and resonance properties like radii
and transition strengths are investigated.Comment: 7 pages, Talk given at SOTANCP3, 3rd International Workshop on State
of the Art in Nuclear Cluster Physics, Yokohama, Japan, May 26-30, 201
