Evidence for tetrahedral structure of Calcium-40

More than 100 excited states of the Calcium-40 nucleus, with isospin 0, are classified into rotational–vibrational bands of an intrinsic tetrahedral structure. Almost all observed states below 8[Formula: see text]MeV can be accommodated, as well as many high-spin states above 8[Formula: see text]MeV. The bands have some similarity to those classifying states of Oxygen-16, but the A-mode vibrational frequency is lower relative to the E-mode and F-mode frequencies than in Oxygen-16. Previously identified rotational bands up to spin 16 and energy above 20[Formula: see text]MeV are unified here into a smaller number of tetrahedral bands.