Impact of the electron environment on the lifetime of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mi /><mml:mrow><mml:mn>229</mml:mn></mml:mrow></mml:msup><mml:msup><mml:mi mathvariant="normal">Th</mml:mi><mml:mrow><mml:mi>m</mml:mi></mml:mrow></mml:msup></mml:mrow></mml:math>low-lying isomer

Karpeshin, F. F.; Trzhaskovskaya, M. B.

doi:10.1103/physrevc.76.054313

Cited by 72 publications

(106 citation statements)

References 27 publications

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“…In the considered case of neutral 229 Th atoms, the internal conversion decay is allowed due to an isomeric energy exceeding the thorium ionization potential of 6.31 eV [25]. This results in a reduced isomeric lifetime of τ tot = 1/Γ tot ≈ 10 µs [26,27], which was recently experimentally confirmed [20]. From the assumption of a radiative isomeric lifetime of τ γ ≈ 10 4 s, the internal conversion coefficient can thus be inferred to take a value of α ic ≈ 10…”

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confidence: 99%

“…However, it should be explicitly pointed out that the above detection scheme assumes a 100% radiative decay of the isomer, which we consider as unlikely [24]. Any non-radiative decay, e.g., in the form of electronic bridge processes [27], might easily suppress the emission of light during the isomeric decay by several orders of magnitude, thereby preventing the isomer detection.…”

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A Laser Excitation Scheme for Th229m

et al. 2017

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Direct laser excitation of the lowest known nuclear excited state in 229 Th has been a longstanding 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.Direct nuclear laser excitation has come closer into reach within the past years, partly due to the development of free-electron-laser technology. Such ideas are typically dealing with the excitation of nuclear states in the energy range of at least a few keV or above [1,2]. However, there is one exceptional nuclear state known for the last 40 years with a significantly lower energy of presumably below 10 eV [3,4]. An excitation energy of (7.8 ± 0.5) eV, corresponding to (159 ± 11) nm wavelength or ∼ 1900 THz, is by today the most accepted value for the isomeric first excited state of 229 Th [5,6]. This state conceptionally allows for direct nuclear laser excitation using solid-state laser technology and was proposed for the development of a nuclear clock of extremely high stability, due to an expected high resilience against external influences and a radiative lifetime in the range of minutes to hours [7][8][9][10]. It is generally assumed that direct nuclear laser excitation of 229m Th requires a considerably improved knowledge of the isomeric transition energy (see e.g. Ref.[11] and references therein). The reasons are that, first, the present uncertainty in the knowledge of the isomeric energy value is still rather large. The currently best energy value of 7.8±0.5 eV leads to an energy range of at least 1 eV (corresponding to 2.4·1014 Hz) to be scanned when searching for the isomeric excitation. Second, the radiative lifetime of 229m Th was theoretically predicted to be in the range of hours [12][13][14], leading to long required detection times when searching for a radiative decay channel. This has led to the assumption that the required time for laserbased scanning of the large energy range of 1 eV would be prohibitively long. In order to shorten the required scanning times, there are worldwide efforts ongoing to decrease the uncertainty of the transition energy, which would bring the isomeric state into realistic reach of direct laser excitation (see e.g. Refs. [15-18]). A recent review is found in Ref. [11].Here we propose a different approach, which allows for a direct laser excitation of 229m Th without the requirement of an improved knowledge of the transition energy. As the requi...

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A Laser Excitation Scheme for Th229m

et al. 2017

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“…CaF 2 is a promising candidate for such a host crystal3741. Its fairly simple lattice has a band-gap of about 12 eV, which ensures optical transparency down to 120 nm.…”

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Radioluminescence and photoluminescence of Th:CaF2 crystals

Stellmer

Schreitl

Schumm

2015

Sci Rep

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We study thorium-doped CaF2 crystals as a possible platform for optical spectroscopy of the 229Th nuclear isomer transition. We anticipate two major sources of background signal that might cover the nuclear spectroscopy signal: VUV-photoluminescence, caused by the probe light, and radioluminescence, caused by the radioactive decay of 229Th and its daughters. We find a rich photoluminescence spectrum at wavelengths above 260 nm, and radioluminescence emission above 220 nm. This is very promising, as fluorescence originating from the isomer transition, predicted at a wavelength shorter than 200 nm, could be filtered spectrally from the crystal luminescence. Furthermore, we investigate the temperature-dependent decay time of the luminescence, as well as thermoluminescence properties. Our findings allow for an immediate optimization of spectroscopy protocols for both the initial search for the nuclear transition using synchrotron radiation, as well as future optical clock operation with narrow-linewidth lasers.

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“…The predicted value for the half-life significantly depends on the energy of the isomeric transition and the electronic surrounding, as internal conversion (IC) effects and bound internal conversion (BIC) effects are expected to play a significant role. If internal conversion is allowed by the electronic environment, the isomer is expected to predominantly decay via the IC channel (α IC ≈ 10 9 ) and the halflife is predicted to be as short as 10 −5 s [5]. In case that IC is suppressed, but BIC has to be considered, life-times of minutes to hours have been predicted [5,6,7,8].…”

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confidence: 99%

“…If internal conversion is allowed by the electronic environment, the isomer is expected to predominantly decay via the IC channel (α IC ≈ 10 9 ) and the halflife is predicted to be as short as 10 −5 s [5]. In case that IC is suppressed, but BIC has to be considered, life-times of minutes to hours have been predicted [5,6,7,8]. A BIC decay enhancement factor of 400-600 compared to the radiative decay was estimated for a 3.5 eV isomeric transition energy [6].…”

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Determination of the extraction efficiency for 233U source α-recoil ions from the MLL buffer-gas stopping cell

2015

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Abstract. Following the α decay of 233 U, 229 Th recoil ions are shown to be extracted in a significant amount from the MLL buffer-gas stopping cell. The produced recoil ions and subsequent daughter nuclei are mass purified with the help of a customized quadrupole mass spectrometer. The combined extraction and mass-purification efficiency for 229 Th 3+ is determined via MCP-based measurements and via the direct detection of the 229 Th α decay. A large value of (10 ± 2)% for the combined extraction and mass-purification efficiency of 229 Th 3+ is obtained at a mass resolution of about 1 u/e. In addition to 229 Th, also other α-recoil ions of the 233,232 U decay chains are addressed.PACS. 27.90.+b A≥220 -23.60.+e α decay -07.75.+h mass spectrometers -23.35.+g isomer decay

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Impact of the electron environment on the lifetime of the229Thmlow-lying isomer

Cited by 72 publications

References 27 publications

A Laser Excitation Scheme for Th229m

A Laser Excitation Scheme for Th229m

Radioluminescence and photoluminescence of Th:CaF2 crystals

Determination of the extraction efficiency for 233U source α-recoil ions from the MLL buffer-gas stopping cell

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