https://doi.org/10.1140/epja/s10050-020-00263-0
Review
The 
Th isomer: prospects for a nuclear optical clock
Ludwig-Maximilians-Universität München, 85748, Garching, Germany
a
L.Wense@physik.uni-muenchen.de
Received:
9
March
2020
Accepted:
19
September
2020
Published online:
2
November
2020
The proposal for the development of a nuclear optical clock has triggered a multitude of experimental and theoretical studies. In particular the prediction of an unprecedented systematic frequency uncertainty of about 
has rendered a nuclear clock an interesting tool for many applications, potentially even for a re-definition of the second. The focus of the corresponding research is a nuclear transition of the Th nucleus, which possesses a uniquely low nuclear excitation energy of only 
eV (
nm). This energy is sufficiently low to allow for nuclear laser spectroscopy, an inherent requirement for a nuclear clock. Recently, some significant progress toward the development of a nuclear frequency standard has been made and by today there is no doubt that a nuclear clock will become reality, most likely not even in the too far future. Here we present a comprehensive review of the current status of nuclear clock development with the objective of providing a rather complete list of literature related to the topic, which could serve as a reference for future investigations.
© The Author(s) 2020
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