The reduced cluster widths Ag.s. + aB are found to be comparable for the various levels of the nucleus B. The number of shell model levels and the number of thresholds in a certain energy interval increase with increasing (but not too high) excitation energy. Therefore, in the framework of the shell model, frequently, one may observe an accidental correlation between a maximum in the spectrum of reduced cluster widths and the position of thresholds.

With regard to this one shall not consider a large reduced cluster width in the neighbourhood of the corresponding cluster threshold as an indication of a threshold effect. The existence of threshold effects will be seen in systematic deviations from the reduced widths and energies calculated without account of threshold effects.

By means of lithium induced reactions one may investigate effects of such a kind. In generally, they have large Q-values and allow to draw conclusions about the cluster structure of nuclei. The reduced cluster widths calculated in the framework of the shell model are given for some nuclei of the 1 p-shell.