Nuclear resonant scattering experiment with fast time response: Photonuclear excitation of 
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Thorium-229 is a unique case in nuclear physics: it presents a metastable first excited state 229m Th, just a few electronvolts above the nuclear ground state. This so-called isomer is accessible by VUV lasers, which allows transferring the amazing precision of atomic laser spectroscopy to nuclear physics. Being able to manipulate the 229 Th nuclear states at will opens up a multitude of prospects, from studies of the fundamental interactions in physics to applications as a compact and robust nuclear clock. However, direct optical excitation of the isomer or its radiative decay back to the ground state has not yet been observed, and a series of key nuclear structure parameters such as the exact energies and half-lives of the low-lying nuclear levels of 229 Th are yet unknown. Here we present the first active optical pumping into 229m Th. Our scheme employs narrow-band 29 keV synchrotron radiation to resonantly excite the second excited state, which then predominantly decays into the isomer. We determine the resonance energy with 0.07 eV accuracy, measure a half-life of 82.2 ps, an excitation linewidth of 1.70 neV, and extract the branching ratio of the second excited state into the ground and isomeric state respectively. These measurements allow us to re-evaluate gamma spectroscopy data that have been collected over 40 years.

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“…First, the 229m Th production rate is high; it amounts to 25 an activity about 700 times larger than that used in our target.…”

Section: Discussion and Summarymentioning

confidence: 97%

X-ray pumping of the 229Th nuclear clock isomer

Masuda

Yoshimi

Fujieda

et al. 2019

Nature

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“…The apparatus of the NRS measurement was almost identical to that used in previous work (Yoshimi et al, 2018;Masuda et al, 2019b), only the target was different. The 40 K target was a KCl pellet (diameter 3 mm, thickness 0.5 mm) prepared by pressing 5 mg KCl powder with $ 2 MPa.…”

Section: Nrs Measurementmentioning

confidence: 99%

Absolute X-ray energy measurement using a high-accuracy angle encoder

Masuda

Watanabe

Beeks

et al. 2021

J Synchrotron Radiat

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This paper presents an absolute X-ray photon energy measurement method that uses a Bond diffractometer. The proposed system enables the prompt and rapid in situ measurement of photon energies over a wide energy range. The diffractometer uses a reference silicon single-crystal plate and a highly accurate angle encoder called SelfA. The performance of the system is evaluated by repeatedly measuring the energy of the first excited state of the potassium-40 nuclide. The excitation energy is determined as 29829.39 (6) eV, and this is one order of magnitude more accurate than the previous measurement. The estimated uncertainty of the photon energy measurement was 0.7 p.p.m. as a standard deviation and the maximum observed deviation was 2 p.p.m.

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“…In 2019, excitation of the nuclear state at 29 keV via synchrotron radiation was reported [214] (see also [414]). A 229 Th oxide target of 1.8 kBq activity and 0.4 mm diameter was placed in the focus of a 29.19 keV X-ray beam generated via undulators at the high-brilliance X-ray beamline of the SPring-8 synchrotron facility in Japan.…”

Section: Lambda Excitation Of 229m Thmentioning

confidence: 99%

The $$^{229}$$Th isomer: prospects for a nuclear optical clock

Wense

2020

Eur. Phys. J. A

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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 $$10^{-19}$$ 10 - 19 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 $$^{229}$$ 229 Th nucleus, which possesses a uniquely low nuclear excitation energy of only $$8.12\pm 0.11$$ 8.12 ± 0.11 eV ($$152.7\pm 2.1$$ 152.7 ± 2.1 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.

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Nuclear resonant scattering experiment with fast time response: Photonuclear excitation of Hg201

Cited by 14 publications

References 48 publications

X-ray pumping of the 229Th nuclear clock isomer

X-ray pumping of the 229Th nuclear clock isomer

Absolute X-ray energy measurement using a high-accuracy angle encoder

The $$^{229}$$Th isomer: prospects for a nuclear optical clock

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