preparing-an-isotopically-pure-229th-ion-beam-for-studies-of-229mth

Preparing an Isotopically Pure <sup>229</sup>Th Ion Beam for Studies of <sup>229m</sup>Th

A methodology is described to generate an isotopically pure 229Th ion beam in the 2+ and 3+ charge states. This ion beam enables one to investigate the ...

Ludwig-Maximilians-Universität München

The first excited isomeric state of ^{229}Th possesses the lowest energy among all known excited nuclear states. The expected energy is accessible with today's laser technology and in principle allows for a direct optical laser excitation of the nucleus. The isomer decays via three channels to its ground state (internal conversion, γ decay, and bound internal conversion), whose strengths depend on the charge state of ^{229m}Th. We report on the measurement of the internal-conversion decay half-life of neutral ^{229m}Th. A half-life of 7±1  μs has been measured, which is in the range of theoretical predictions and, based on the theoretically expected lifetime of ≈10^{4}  s of the photonic decay channel, gives further support for an internal conversion coefficient of ≈10^{9}, thus constraining the strength of a radiative branch in the presence of internal conversion.

Lifetime Measurement of the ^{229}Th Nuclear Isomer.

Direct laser excitation of the lowest known nuclear excited state in ^{229}Th has been a long-standing objective. It is generally assumed that reaching this goal would require a considerably reduced uncertainty of the isomer's excitation energy compared to the presently adopted value of (7.8±0.5)  eV. Here we present a direct laser excitation scheme for ^{229m}Th, which circumvents this requirement. The proposed excitation scheme makes use of already existing laser technology and therefore paves the way for nuclear laser spectroscopy. In this concept, the recently experimentally observed internal-conversion decay channel of the isomeric state is used for probing the isomeric population. A signal-to-background ratio of better than 10^{4} and a total measurement time of less than three days for laser scanning appear to be achievable.

A Laser Excitation Scheme for ^{229m}Th.

The isotope Th is the only nucleus known to possess an excited state Th in the energy range of a few electronvolts-a transition energy typical for electrons in the valence shell of atoms, but about four orders of magnitude lower than typical nuclear excitation energies. Of the many applications that have been proposed for this nuclear system, which is accessible by optical methods, the most promising is a highly precise nuclear clock that outperforms existing atomic timekeepers. Here we present the laser spectroscopic investigation of the hyperfine structure of the doubly charged Th ion and the determination of the fundamental nuclear properties of the isomer, namely, its magnetic dipole and electric quadrupole moments, as well as its nuclear charge radius. Following the recent direct detection of this long-sought isomer, we provide detailed insight into its nuclear structure and present a method for its non-destructive optical detection.

Article	Year
Lifetime Measurement of the ^{229}Th Nuclear Isomer. Physical review letters\| PubMed ID: 28186791	2017
A Laser Excitation Scheme for ^{229m}Th. Physical review letters\| PubMed ID: 29341722	2017
Laser spectroscopic characterization of the nuclear-clock isomer Th. Nature\| PubMed ID: 29670266	2018

Lars von der Wense

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