https://doi.org/10.1140/epjc/s10052-020-8281-3
Regular Article - Experimental Physics
First limits on double beta decays in 
Th
1
INFN-Laboratori Nazionali del Gran Sasso, 67100, Assergi, AQ, Italy
2
Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
3
Physics Department, Queen’s University, Kingston, ON, K7L 3N6, Canada
* e-mail: bjoernlehnert@lbl.gov
** e-mail: sn65@queensu.ca
Received:
9
April
2020
Accepted:
23
July
2020
Published online:
19
August
2020
As one of the primordial radioactive isotopes, 
mainly undergoes 
-decay with a half-life of 
years. However, it is also one of 35 double beta decay candidates in which the single 
-decay is forbidden or strongly suppressed. 181 mg of thorium contained in a gas mantle were measured in a HPGe well-detector at the Gran Sasso Underground Laboratory with a total exposure of 3.25 g
d.
We obtain half-life limits on all double beta decay modes of to excited states of 
on the order of 
years. For the most likely transition into the 0
state we find a lower half-life limit of 
years (90% C.I.). These are the first constraints on double beta decay excited state transition in .
© The Author(s), 2020
