Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes

Four long-lived neutron-deficient Th isotopes with atomic mass numbers 211 to 218 and abundances of (1-10)x10(-11) relative to Th-232 have been found in a study of naturally-occurring Th using inductively coupled plasma-sector field mass spectrometry. It is deduced that long-lived isomeric states exist in these isotopes. The hypothesis that they might belong to a new class of long-lived high spin super- and hyperdeformed isomeric states is discussed.