Search for long-lived isomeric states in neutron-deficient thorium isotopes

TL;DR

This study reexamines claims of long-lived isomeric states in neutron-deficient thorium isotopes using highly sensitive accelerator mass spectrometry, but finds no evidence supporting their existence.

Contribution

It provides a more sensitive analysis that challenges previous claims of naturally occurring long-lived thorium isomers.

Findings

No confirmation of previously claimed thorium isomers.

Established upper limits for isotope abundances.

Demonstrated AMS sensitivity in detecting rare isotopes.

Abstract

The discovery of naturally occurring long-lived isomeric states (t_1/2 > 10^8 yr) in the neutron-deficient isotopes 211,213,217,218Th [A. Marinov et al., Phys. Rev. C 76, 021303(R) (2007)] was reexamined using accelerator mass spectrometry (AMS). Because AMS does not suffer from molecular isobaric background in the detection system, it is an extremely sensitive technique. Despite our up to two orders of magnitude higher sensitivity we cannot confirm the discoveries of neutron-deficient thorium isotopes and provide upper limits for their abundances.