Level densities inF20: Experimental, shell model, and weak coupling results

Shell-model calculations for ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ in an ${\mathrm{}\left(\mathrm{sd}\right)\mathrm{}}^4$-closed ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ core basis predict significantly fewer than the observed number of levels below any given excitation energy. Calculations in a ${(p_{\frac{1}{2}}-s_{\frac{1}{2}}-d_{\frac{5}{2}})}^8$-closed ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ core basis predict more levels than the observed numbers. A simple weak-coupling extrapolation gives quite good agreement up to at least 7 MeV (75 levels).