Nuclear clock

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Nuclear Clock
Nuclear clock concept.png
Concept of a thorium-229 based nuclear optical clock.

A nuclear clock or nuclear optical clock is a notional clock that would use the frequency of a nuclear transition as its reference frequency, [1] in the same manner as an atomic clock uses the frequency of an electronic transition in an atom's shell. Such a clock is expected to be more accurate than the best current atomic clocks by a factor of about 10, with an achievable accuracy approaching the 10−19 level. [2] The only nuclear state suitable for the development of a nuclear clock using existing technology is thorium-229m, a nuclear isomer of thorium-229 and the lowest-energy nuclear isomer known. With an energy of 8.35574(3)  eV , [3] [4] this corresponds to a wavelength of 148.3821(5) nm in the vacuum ultraviolet region, making it accessible to laser excitation. A comprehensive review can be found in reference. [5]

Contents

Principle of operation

Modern optical atomic clocks are today the most accurate time-keeping devices. Their underlying principle of operation is based on the fact that the energy of an atomic transition (the energy difference between two atomic states) is independent of space and time. The atomic transition energy corresponds (via the Planck constant) to a particular frequency of a light wave which is required to drive the transition. Therefore, an atomic transition can be excited with laser light, if the light's frequency exactly corresponds to the energy of the atomic transition. A laser's frequency can be stabilized to match the corresponding atomic transition energy by continuous verification of a successful laser excitation of the atomic transition. Once thus stabilized, the frequency of the laser light will always be the same (independent of space and time).

It is technologically possible to measure the frequency of laser light to extraordinarily high accuracy by counting the oscillations of the light wave with the help of a frequency comb. This allows time to be measured by counting the number of oscillations of the laser light, which has been stabilized to a particular atomic transition. Such a device is known as an optical atomic clock. [6] One prominent example for an optical atomic clock is the ytterbium (Yb) lattice clock, where a particular transition in the ytterbium-171 isotope is used for laser stabilization. [7] In this case, one second has elapsed after 518295836590863.63±0.1 oscillations of the laser light stabilized to the corresponding transition. [8] Other examples for optical atomic clocks of the highest accuracy are the ytterbium(Yb)-171 single-ion clock, [9] the strontium(Sr)-87 optical lattice clock [10] and the aluminum(Al)-27 single-ion clock. [11] The achieved accuracies of these clocks vary around 10−18, corresponding to about 1 second of inaccuracy in 30 billion years, significantly longer than the age of the universe.

A nuclear optical clock would use the same principle of operation, with the important difference that a nuclear transition instead of an atomic shell transition is used for laser stabilization. [1] The expected advantage of a nuclear clock compared to an atomic clock is that the atomic nucleus is smaller than the atomic shell by up to five orders of magnitude, with correspondingly smaller magnetic dipole and electric quadrupole moments, and is therefore significantly less affected by external magnetic and electric fields. Such external perturbations are the limiting factor for the achieved accuracies of atomic-shell based clocks. Due to this conceptual advantage, a nuclear optical clock is expected to achieve a time accuracy approaching 10−19, a ten-fold improvement over atomic-shell based clocks. [2]

Ionization

An excited atomic nucleus can shed its excess energy by two alternative paths:

For most nuclear isomers, the available energy is sufficient to eject any electron, and the inner-shell electrons are the most frequently ejected. In the special case of 229m
Th
, the energy is sufficient only to eject an outer electron (thorium's first ionization energy is 6.3 eV), and once the atom is ionized, there is not enough energy remaining to eject a second (thorium's second ionization energy is 11.5 eV).

The two decay paths have different half-lives. Neutral 229m
Th
 decays almost exclusively by internal conversion, with a half-life of 7±1 μs. [12] In thorium cations, internal conversion is energetically prohibited, and 229m
Th+
 is forced to take the slower path, decaying radiatively with a half-life of around 1740 s. [4]

Thus, in the typical case that the clock is designed to measure radiated photons, it is necessary to hold the thorium in an ionized state. This can be done in an ion trap, or by embedding it in an ionic crystal. In the latter case, the atoms are not 100% ionized, and a small amount of internal conversion is possible (reducing the half-life to approximately 630 s) [4] , but the loss is tolerable.

Different nuclear clock concepts

Two different concepts for nuclear optical clocks have been discussed in the literature: trap-based nuclear clocks and solid-state nuclear clocks.

Trap-based nuclear clocks

For a trap-based nuclear clock either a single 229Th3+ ion is trapped in a Paul trap, known as the single-ion nuclear clock, [1] [2] or a chain of multiple ions is trapped, considered as the multiple-ion nuclear clock. [5] Such clocks are expected to achieve the highest time accuracy, as the ions are to a large extent isolated from their environment. A multiple-ion nuclear clock could have a significant advantage over the single-ion nuclear clock in terms of stability performance.

Solid-state nuclear clocks

As the nucleus is largely unaffected by the atomic shell, it is also intriguing to embed many nuclei into a crystal lattice environment. This concept is known as the crystal-lattice nuclear clock. [1] Due to the high density of embedded nuclei of up to 1018 per cm3, this concept would allow irradiating a huge number of nuclei in parallel, thereby drastically increasing the achievable signal-to-noise ratio, [13] but at the cost of potentially higher external perturbations. [14] It has also been proposed to irradiate a metallic 229Th surface and to probe the isomer’s excitation in the internal conversion channel, which is known as the internal-conversion nuclear clock. [15] Both types of solid-state nuclear clocks were shown to offer the potential for comparable performance.

Transition requirements

From the principle of operation of a nuclear optical clock, it is evident that direct laser excitation of a nuclear state is a central requirement for the development of such a clock. This is impossible for most nuclear transitions, as the typical energy range of nuclear transitions (keV to MeV) is orders of magnitude above the maximum energy which is accessible with significant intensity by today's narrow-bandwidth laser technology (a few eV). There are only two nuclear excited states known which possess a sufficiently low excitation energy (below 100 eV). These are

However, 235m1
U
 has such an extraordinarily long radiative half-life (on the order of 1022 s, 20,000 times the age of the universe, and far longer than its internal conversion half-life of 26 minutes) that it is not practical to use for a clock. [19] [20] This leaves only 229mTh with a realistic chance of direct nuclear laser excitation.

Further requirements for the development of a nuclear clock are that

Fortunately, with 229m
Th+
 having a radiative half-life (time to decay to 229
Th+
) of around 103 s, [4] [21] [22] and 229
Th
 having a half-life (time to decay to 225
Ra
) of 7917±48 years, [23] both conditions are fulfilled for 229m
Th+
, making it an ideal candidate for the development of a nuclear clock.

History

The history of the nuclear clock

As early as 1996 it was proposed by Eugene V. Tkalya to use the nuclear excitation as a "highly stable source of light for metrology". [24]

With the development (around 2000) of the frequency comb for measuring optical frequencies exactly, a nuclear optical clock based on 229m
Th
 was first proposed in 2003 by Ekkehard Peik and Christian Tamm, who developed an idea of Uwe Sterr. [1] The paper contains both concepts, the single-ion nuclear clock, as well as the solid-state nuclear clock.

In their pioneering work, Peik and Tamm proposed to use individual laser-cooled 229
Th3+
 ions in a Paul trap to perform nuclear laser spectroscopy. [1] Here the 3+ charge state is advantageous, as it possesses a shell structure suitable for direct laser cooling. It was further proposed to excite an electronic shell state, to achieve 'good' quantum numbers of the total system of the shell plus nucleus that will lead to a reduction of the influence induced by external perturbing fields. A central idea is to probe the successful laser excitation of the nuclear state via the hyperfine-structure shift induced into the electronic shell due to the different nuclear spins of ground- and excited state. This method is known as the double-resonance method.

The expected performance of a single-ion nuclear clock was further investigated in 2012 by Corey Campbell et al. with the result that a systematic frequency uncertainty (accuracy) of the clock of 1.5×10−19 could be achieved, which would be by about an order of magnitude better than the accuracy achieved by the best optical atomic clocks today. [2] The nuclear clock approach proposed by Campbell et al. slightly differs from the original one proposed by Peik and Tamm. Instead of exciting an electronic shell state in order to obtain the highest insensitivity against external perturbing fields, the nuclear clock proposed by Campbell et al. uses a stretched pair of nuclear hyperfine states in the electronic ground-state configuration, which appears to be advantageous in terms of the achievable quality factor and an improved suppression of the quadratic Zeeman shift.

In 2010, Eugene V. Tkalya showed that it was theoretically possible to use 229m
Th
 as a lasing medium to generate an ultraviolet laser. [25] [26] [27]

The solid-state nuclear clock approach was further developed in 2010 by W.G. Rellergert et al. [14] with the result of an expected long-term accuracy of about 2×10−16. Although expected to be less accurate than the single-ion nuclear clock approach due to line-broadening effects and temperature shifts in the crystal lattice environment, this approach may have advantages in terms of compactness, robustness and power consumption. The expected stability performance was investigated by G. Kazakov et al. in 2012. [13] In 2020, the development of an internal conversion nuclear clock was proposed. [15]

Important steps on the road towards a nuclear clock the successful direct laser cooling of 229
Th3+
 ions in a Paul trap achieved in 2011, [28] and a first detection of the isomer-induced hyperfine-structure shift, enabling the double-resonance method to probe a successful nuclear excitation in 2018. [29]

The history of 229mTh

Since 1976, the 229Th nucleus has been known to possess a low energy excited state, [30] the excitation energy of which was shown to be less than 10 eV in 1990. [31]

This was, however, too broad an energy range to apply high-resolution spectroscopy techniques; the transition energy had to be narrowed down first. Initial efforts used the fact that, after the alpha decay of 233
U
, the resultant 229
Th
 nucleus is in an excited state and promptly emits a gamma ray to decay to either the base state or the metastable state. Measuring the small difference in the gamma-ray energies emitted in these processes allows the metastable state energy to be found by subtraction.

An early mis-step was the (incorrect) measurement of the energy value as 3.5±1.0 eV in 1994. [32] In particular, this energy was comfortably below the 6.3 eV ionization energy of thorium (implying that decay by internal conversion was impossible even in neutral thorium, see § Ionization) and the 6.2 eV limit of ultraviolet transmission through molecular oxygen (air). Thus, direct detection experiments were attempted which had no hope of detecting the ultraviolet light at the true, higher, energy. [5]

The energy value remained elusive until 2003, when the nuclear clock proposal triggered a multitude of experimental efforts to pin down the excited state's parameters like energy and half-life. The detection of light emitted in the direct decay of 229m
Th
 would significantly help to determine its energy to higher precision, but all efforts to observe the light emitted in the decay of 229m
Th
 were failing. [5] The energy level was corrected to 7.6±0.5 eV in 2007 [33] (slightly revised to 7.8±0.5 eV in 2009 [34] ). Subsequent experiments continued to fail to observe any signal of light emitted in the direct decay, leading people to suspect the existence of a strong non-radiative decay channel. [35] [36] [37] [38] The detection of light emitted by the decay of 229mTh was reported in 2012, [39] and again in 2018, [40] but the observed signals were the subject of controversy within the community. [41]

A direct detection of electrons emitted by the isomer's internal conversion decay channel was achieved in 2016. [42] This detection laid the foundation for the determination of the 229mTh half-life in neutral, surface-bound atoms in 2017 [12] and a first laser-spectroscopic characterization in 2018. [29]

In 2019, the isomer’s energy was measured via the detection of internal conversion electrons emitted in its direct ground-state decay to 8.28±0.17 eV. [16] Also a first successful excitation of the 29 keV nuclear excited state of 229
Th
 via synchrotron radiation was reported, [43] enabling a clock transition energy measurement of 8.30±0.92 eV. [44] In 2020, an energy of 8.10±0.17 eV was obtained from precision gamma-ray spectroscopy. [17]

Finally, precise measurements were achieved in 2023 by unambiguous detection of the emitted photons (8.338(24) eV) [45] [46] and in April 2024 by two reports of excitation with a tunable laser at 8.355733(10) eV [47] and 8.35574(3)  eV . [3] [4] [48] The light frequency (2020407.6±2.8 GHz) is now known with sufficient accuracy to enable future construction of a prototype clock, [49] and determine the transition's exact frequency and its stability.

Applications

When operational, a nuclear optical clock is expected to be applicable in various fields. Obviously, it may be used wherever today's atomic clocks are in operation, such as satellite-based navigation or data transfer. Its high precision would allow new applications inaccessible to other atomic clocks, such as relativistic geodesy, the search for topological dark matter, [50] or the determination of time variations of fundamental constants. [51]

A nuclear clock has the potential to be highly sensitive to possible time variations of the fine-structure constant. [52] The central idea is that a nuclear transition couples differently to the fine-structure constant than an atomic shell transition does. [19] For this reason a comparison of the frequency of a nuclear clock with an atomic clock could lead to an extraordinary high sensitivity for potential time variations of the fine structure constant. The achievable factor of sensitivity, however, remains subject to speculation. A recent measurement is consistent with enhancement factors between 1 (no enhancement) and 104. [29]

Related Research Articles

<span class="mw-page-title-main">Thorium</span> Chemical element, symbol Th and atomic number 90

Thorium is a chemical element. It has the symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive gray when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.

<span class="mw-page-title-main">Laser cooling</span> Class of methods for cooling atoms to very low temperatures

Laser cooling includes several techniques where atoms, molecules, and small mechanical systems are cooled with laser light. The directed energy of lasers is often associated with heating materials, e.g. laser cutting, so it can be counterintuitive that laser cooling often results in sample temperatures approaching absolute zero. It is a routine step in many atomic physics experiments where the laser-cooled atoms are then subsequently manipulated and measured, or in technologies, such as atom-based quantum computing architectures. Laser cooling relies on the change in momentum when an object, such as an atom, absorbs and re-emits a photon. For example, if laser light illuminates a warm cloud of atoms from all directions and the laser's frequency is tuned below an atomic resonance, the atoms will be cooled. This common type of laser cooling relies on the Doppler effect where individual atoms will preferentially absorb laser light from the direction opposite to the atom's motion. The absorbed light is re-emitted by the atom in a random direction. After repeated emission and absorption of light the net effect on the cloud of atoms is that they will expand more slowly. The slower expansion reflects a decrease in the velocity distribution of the atoms, which corresponds to a lower temperature and therefore the atoms have been cooled. For an ensemble of particles, their thermodynamic temperature is proportional to the variance in their velocity, therefore the lower the distribution of velocities, the lower temperature of the particles.

<span class="mw-page-title-main">Nuclear isomer</span> Metastable excited state of a nuclide

A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state (higher energy) levels. "Metastable" describes nuclei whose excited states have half-lives 100 to 1000 times longer than the half-lives of the excited nuclear states that decay with a "prompt" half life (ordinarily on the order of 10−12 seconds). The term "metastable" is usually restricted to isomers with half-lives of 10−9 seconds or longer. Some references recommend 5 × 10−9 seconds to distinguish the metastable half life from the normal "prompt" gamma-emission half-life. Occasionally the half-lives are far longer than this and can last minutes, hours, or years. For example, the 180m
73Ta
 nuclear isomer survives so long (at least 1015 years) that it has never been observed to decay spontaneously. The half-life of a nuclear isomer can even exceed that of the ground state of the same nuclide, as shown by 180m
73Ta
 as well as 186m
75Re
, 192m2
77Ir
, 210m
83Bi
, 212m
84Po
, 242m
95Am
 and multiple holmium isomers.

<span class="mw-page-title-main">Electromagnetically induced transparency</span>

Electromagnetically induced transparency (EIT) is a coherent optical nonlinearity which renders a medium transparent within a narrow spectral range around an absorption line. Extreme dispersion is also created within this transparency "window" which leads to "slow light", described below. It is in essence a quantum interference effect that permits the propagation of light through an otherwise opaque atomic medium.

<span class="mw-page-title-main">Rydberg atom</span> Excited atomic quantum state with high principal quantum number (n)

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Darmstadtium (110Ds) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 269Ds in 1994. There are 11 known radioisotopes from 267Ds to 281Ds and 2 or 3 known isomers. The longest-lived isotope is 281Ds with a half-life of 14 seconds.

Flerovium (114Fl) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 289Fl in 1999. Flerovium has six known isotopes, along with the unconfirmed 290Fl, and possibly two nuclear isomers. The longest-lived isotope is 289Fl with a half-life of 1.9 seconds, but 290Fl may have a longer half-life of 19 seconds.

Moscovium (115Mc) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no known stable isotopes. The first isotope to be synthesized was 288Mc in 2004. There are five known radioisotopes from 286Mc to 290Mc. The longest-lived isotope is 290Mc with a half-life of 0.65 seconds.

Livermorium (116Lv) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 293Lv in 2000. There are five known radioisotopes, with mass numbers 288 and 290–293, as well as a few suggestive indications of a possible heavier isotope 294Lv. The longest-lived known isotope is 293Lv with a half-life of 70 ms.

In spectroscopy, a forbidden mechanism is a spectral line associated with absorption or emission of photons by atomic nuclei, atoms, or molecules which undergo a transition that is not allowed by a particular selection rule but is allowed if the approximation associated with that rule is not made. For example, in a situation where, according to usual approximations, the process cannot happen, but at a higher level of approximation the process is allowed but at a low rate.

In condensed matter physics, an ultracold atom is an atom with a temperature near absolute zero. At such temperatures, an atom's quantum-mechanical properties become important.

<span class="mw-page-title-main">Nitrogen-vacancy center</span> Point defect in diamonds

The nitrogen-vacancy center is one of numerous photoluminescent point defects in diamond. Its most explored and useful properties include its spin-dependent photoluminescence, and its relatively long (millisecond) spin coherence at room temperature. The NV center energy levels are modified by magnetic fields, electric fields, temperature, and strain, which allow it to serve as a sensor of a variety of physical phenomena. Its atomic size and spin properties can form the basis for useful quantum sensors. It has also been explored for applications in quantum computing, quantum simulation, and spintronics.

<span class="mw-page-title-main">Atomic clock</span> Extremely accurate clock

An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions between such states they interact with a very specific frequency of electromagnetic radiation. This phenomenon serves as the basis for the International System of Units' (SI) definition of a second:

The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, , the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1.

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<span class="mw-page-title-main">Patrick Gill (scientist)</span> British physicist

Patrick Gill is a Senior NPL Fellow in Time & Frequency at the National Physical Laboratory (NPL) in the UK.

References

  1. 1 2 3 4 5 6 Peik, Ekkehard; Tamm, Christian (15 January 2003). "Nuclear laser spectroscopy of the 3.5 eV transition in 229Th" (PDF). Europhysics Letters. 61 (2): 181–186. Bibcode:2003EL.....61..181P. doi:10.1209/epl/i2003-00210-x. S2CID   250818523. Archived (PDF) from the original on 2024-04-11. Retrieved 2019-03-17.
  2. 1 2 3 4 C. Campbell; et al. (2012). "A single ion nuclear clock for metrology at the 19th decimal place". Physical Review Letters . 108 (12) 120802. arXiv: 1110.2490 . Bibcode:2012PhRvL.108l0802C. doi:10.1103/PhysRevLett.108.120802. PMID   22540568. S2CID   40863227.
  3. 1 2 Thirolf, Peter (April 29, 2024). "Shedding Light on the Thorium-229 Nuclear Clock Isomer". Physics . Vol. 17. doi:10.1103/Physics.17.71.
  4. 1 2 3 4 5 Tiedau, J.; Okhapkin, M. V.; Zhang, K.; Thielking, J.; Zitzer, G.; Peik, E.; et al. (29 April 2024). "Laser Excitation of the Th-229 Nucleus" (PDF). Physical Review Letters . 132 (18) 182501. Bibcode:2024PhRvL.132r2501T. doi:10.1103/PhysRevLett.132.182501. The nuclear resonance for the Th4+ ions in Th:CaF2 is measured at the wavelength 148.3821(5) nm, frequency 2020.409(7) THz, and the fluorescence lifetime in the crystal is 630(15) s, corresponding to an isomer half-life of 1740(50) s for a nucleus isolated in vacuum.
  5. 1 2 3 4 von der Wense, Lars; Seiferle, Benedict (2 November 2020). "The 229Th isomer: prospects for a nuclear optical clock". Eur. Phys. J. A . 56 (11) 277. arXiv: 2009.13633 . Bibcode:2020EPJA...56..277V. doi:10.1140/epja/s10050-020-00263-0. S2CID   221995928.
  6. ↑ Ludlow, Andrew D.; Boyd, Martin M.; Ye, Jun; Peik, E.; Schmidt, P. O. (26 June 2015). "Optical atomic clocks" (PDF). Reviews of Modern Physics . 87 (2): 637–699. arXiv: 1407.3493 . Bibcode:2015RvMP...87..637L. doi:10.1103/RevModPhys.87.637. S2CID   119116973.
  7. ↑ W.F. McGrew; et al. (2018). "Atomic clock performance enabling geodesy below the centimetre level". Nature. 564 (7734): 87–90. arXiv: 1807.11282 . Bibcode:2018Natur.564...87M. doi:10.1038/s41586-018-0738-2. PMID   30487601. S2CID   53803712.
  8. ↑ H.S. Margolis; G. Panfilo; G. Petit; C. Oates; T. Ido; S. Bize (25 January 2024). "The CIPM list "Recommended values of standard frequencies": 2021 update". Metrologia. 61 (3) 035005. arXiv: 2401.14537 . Bibcode:2024Metro..61c5005M. doi:10.1088/1681-7575/ad3afc.
  9. ↑ N. Huntemann; et al. (2016). "Single-ion atomic clock with 3·10−18 systematic uncertainty". Phys. Rev. Lett. 116 (6) 063001. arXiv: 1602.03908 . Bibcode:2016PhRvL.116f3001H. doi:10.1103/PhysRevLett.116.063001. PMID   26918984. S2CID   19870627.
  10. ↑ T.L. Nicholson; et al. (2015). "Systematic evaluation of an atomic clock at 2·10−18 total uncertainty" (PDF). Nature Communications. 6 6896. arXiv: 1412.8261 . doi:10.1038/ncomms7896. PMC   4411304 . PMID   25898253.
  11. ↑ S.M. Brewer; et al. (2019). "An 27Al+ quantum-logic clock with systematic uncertainty below 10−18". Phys. Rev. Lett. 123 (3) 033201. arXiv: 1902.07694 . doi:10.1103/PhysRevLett.123.033201. PMID   31386450. S2CID   119075546.
  12. 1 2 Seiferle, Benedict; von der Wense, Lars; Thirolf, Peter G. (26 January 2017). "Lifetime measurement of the 229Th nuclear isomer". Phys. Rev. Lett. 118 (4) 042501. arXiv: 1801.05205 . Bibcode:2017PhRvL.118d2501S. doi:10.1103/PhysRevLett.118.042501. PMID   28186791. S2CID   37518294.
  13. 1 2 G.A. Kazakov; et al. (2012). "Performance of a 229Thorium solid-state nuclear clock". New Journal of Physics. 14 (8) 083019. arXiv: 1204.3268 . Bibcode:2012NJPh...14h3019K. doi: 10.1088/1367-2630/14/8/083019 . S2CID   118341064.
  14. 1 2 W.G. Rellergert; et al. (2010). "Constraining the evolution of the fundamental constants with a solid-state optical frequency reference based on the 229Th nucleus" (PDF). Phys. Rev. Lett. 104 (20) 200802. doi:10.1103/PhysRevLett.104.200802. PMID   20867019.
  15. 1 2 L. von der Wense; C. Zhang (2020). "Concepts for direct frequency-comb spectroscopy of 229mTh and an internal-conversion-based solid-state nuclear clock". Eur. Phys. J. D . 74 (7): 146. arXiv: 1905.08060 . Bibcode:2020EPJD...74..146V. doi:10.1140/epjd/e2020-100582-5. S2CID   209322360.
  16. 1 2 B. Seiferle; et al. (2019). "Energy of the 229Th nuclear clock transition". Nature . 573 (7773): 243–246. arXiv: 1905.06308 . Bibcode:2019Natur.573..243S. doi:10.1038/s41586-019-1533-4. PMID   31511684. S2CID   155090121.
  17. 1 2 T. Sikorsky; et al. (2020). "Measurement of the 229Th isomer energy with a magnetic micro-calorimeter". Phys. Rev. Lett. 125 (14) 142503. arXiv: 2005.13340 . Bibcode:2020PhRvL.125n2503S. doi:10.1103/PhysRevLett.125.142503. PMID   33064540. S2CID   218900580.
  18. ↑ F. Ponce; et al. (2018). "Accurate measurement of the first excited nuclear state in 235U". Phys. Rev. C . 97 (5) 054310. Bibcode:2018PhRvC..97e4310P. doi: 10.1103/PhysRevC.97.054310 .
  19. 1 2 Thirolf, Peter; Seiferle, Benedict; von der Wense, Lars (2022-09-05). "From atomic to nuclear clocks". CERN Courier . Retrieved 2024-04-30.
  20. ↑ E. Peik; T. Schumm; M.S. Safronova; A. Pálffy; J. Weitenberg; P.G. Thirolf (15 April 2021). "Nuclear clocks for testing fundamental physics". Quantum Science and Technology. 6 (3) 034002. arXiv: 2012.09304 . Bibcode:2021QS&T....6c4002P. doi: 10.1088/2058-9565/abe9c2 . Due to the extremely small transition strength in 235mU (radiative lifetime ∼ 1022 s), only 229mTh qualifies for a direct laser excitation and thus for the development of a nuclear clock.
  21. ↑ E.V. Tkalya; et al. (2015). "Radiative lifetime and energy of the low-energy isomeric level in 229Th". Phys. Rev. C. 92 (5): 054324. arXiv: 1509.09101 . Bibcode:2015PhRvC..92e4324T. doi:10.1103/PhysRevC.92.054324. S2CID   118374372.
  22. ↑ N. Minkov; A. Pálffy (2017). "Reduced transition probabilities for the gamma decay of the 7.8 eV isomer in 229mTh". Phys. Rev. Lett. 118 (21): 212501. arXiv: 1704.07919 . Bibcode:2017PhRvL.118u2501M. doi:10.1103/PhysRevLett.118.212501. PMID   28598657. S2CID   40694257.
  23. ↑ Z. Varga; A. Nicholl; K. Mayer (2014). "Determination of the 229Th half-life". Phys. Rev. C . 89 064310. doi: 10.1103/PhysRevC.89.064310 .
  24. ↑ Tkalya, Eugene V.; et al. (March 1996). "Processes of the nuclear isomer 229mTh(3/2+, 3.5±1.0 eV) Resonant excitation by optical photons". Physica Scripta. 53 (3): 296–299. Bibcode:1996PhyS...53..296T. doi:10.1088/0031-8949/53/3/003. S2CID   250744766.
  25. ↑ Tkayla, Eugene V. (3 November 2010). "Proposal for a nuclear gamma-ray laser of optical range". Physical Review Letters . 106 (16) 162501. arXiv: 1011.0858 . doi:10.1103/PhysRevLett.106.162501. PMID   21599361. A possibility of the amplification of the 7.6 eV γ radiation by the stimulated γ emission of the ensemble of the (229m)Th isomeric nuclei in a host dielectric crystal is proved theoretically.
  26. ↑ Zyga, Lisa (May 2, 2011). "Proposed gamma-ray laser could emit 'nuclear light'". Phys.org.
  27. ↑ Harris, David (April 22, 2011). "Laser from Atomic Nuclei". Physical Review Focus. Vol. 27. A laser that emits visible light using atomic nuclei, rather than electrons, could be made from a thorium alloy. It could be a first step toward a gamma-ray laser.
  28. ↑ C.J. Campbell; A.G. Radnaev; A. Kuzmich (2 June 2011). "Wigner crystals of 229Th for optical excitation of the nuclear isomer". Phys. Rev. Lett. 106 (22) 223001. arXiv: 1110.2339 . doi:10.1103/PhysRevLett.106.223001. PMID   21702597. S2CID   20801170.
  29. 1 2 3 Thielking, Johannes; et al. (2018). "Laser spectroscopic characterization of the nuclear-clock isomer 229mTh". Nature . 556 (7701): 321–325. arXiv: 1709.05325 . Bibcode:2018Natur.556..321T. doi:10.1038/s41586-018-0011-8. PMID   29670266. S2CID   4990345.
  30. ↑ L.A. Kroger; C.W. Reich (1976). "Features of the low energy level scheme of 229Th as observed in the α decay of 233U". Nucl. Phys. A . 259 (1): 29–60. Bibcode:1976NuPhA.259...29K. doi:10.1016/0375-9474(76)90494-2.
  31. ↑ C.W. Reich; R.G. Helmer (15 January 1990). "Energy separation of the doublet of intrinsic states at the ground state of 229Th". Phys. Rev. Lett. 64 (3). American Physical Society: 271–273. Bibcode:1990PhRvL..64..271R. doi:10.1103/PhysRevLett.64.271. PMID   10041937. It has been known for some time that the intrinsic state labeled by the asymptotic quantum numbers 3/2+[631] lies quite close (< 0.1 keV) to the 5/2+[633] ground state of 229Th. Using the energies of selected γ rays emitted following the α decay of 233U, we have obtained a value of 1±4 eV for the energy separation of these two intrinsic states.
  32. ↑ R.G. Helmer; C.W. Reich (1994). "An Excited State of 229Th at 3.5 eV". Phys. Rev. C . 49 (4): 1845–1858. Bibcode:1994PhRvC..49.1845H. doi:10.1103/PhysRevC.49.1845. PMID   9969412.
  33. ↑ B.R. Beck; et al. (2007). "Energy splitting in the ground state doublet in the nucleus 229Th". Phys. Rev. Lett. 98 (14) 142501. Bibcode:2007PhRvL..98n2501B. doi:10.1103/PhysRevLett.98.142501. PMID   17501268.
  34. ↑ B.R. Beck; et al. (2009). Improved value for the energy splitting of the ground-state doublet in the nucleus 229Th (PDF). 12th Int. Conf. on Nuclear Reaction Mechanisms. Varenna, Italy. LLNL-PROC-415170. Archived from the original (PDF) on 2017-01-27. Retrieved 2019-03-17.
  35. ↑ Jeet, Justin; et al. (23 June 2015). "Results of a Direct Search Using Synchrotron Radiation for the Low-Energy 229Th Nuclear Isomeric Transition". Physical Review Letters . 114 (25) 253001. arXiv: 1502.02189 . Bibcode:2015PhRvL.114y3001J. doi: 10.1103/physrevlett.114.253001 . PMID   26197124. S2CID   1322253.
  36. ↑ A. Yamaguchi; et al. (28 May 2015). "Experimental search for the low-energy nuclear transition in 229Th with undulator radiation". New Journal of Physics. 17 (5) 053053. Bibcode:2015NJPh...17e3053Y. doi: 10.1088/1367-2630/17/5/053053 . ISSN   1367-2630.
  37. ↑ von der Wense, Lars (2016). On the direct detection of 229mTh (PDF) (PhD thesis). Ludwig Maximilian University of Munich. ISBN   978-3-319-70461-6.
  38. ↑ Stellmer, Simon; Kazakov, Georgy; Schreitl, Matthias; Kaser, Hendrik; Kolbe, Michael; Schumm, Thorsten (18 June 2018). "Attempt to optically excite the nuclear isomer in 229Th". Phys. Rev. A . 97 (6) 062506. arXiv: 1803.09294 . Bibcode:2018PhRvA..97f2506S. doi:10.1103/PhysRevA.97.062506. S2CID   4946329.
  39. ↑ X. Zhao; et al. (2012). "Observation of the Deexcitation of the 229mTh Nuclear Isomer". Physical Review Letters . 109 (16) 160801. Bibcode:2012PhRvL.109p0801Z. doi: 10.1103/PhysRevLett.109.160801 . ISSN   0031-9007. PMID   23215066.
  40. ↑ P.V. Borisyuk; et al. (2018). "Excitation of 229Th nuclei in laser plasma: the energy and half-life of the low-lying isomeric state". arXiv: 1804.00299 [nucl-th].
  41. ↑ E. Peik; K. Zimmermann (2013). "Comment on "Observation of the Deexcitation of the 229mTh Nuclear Isomer"". Physical Review Letters . 111 (1) 018901. Bibcode:2013PhRvL.111a8901P. doi:10.1103/PhysRevLett.111.018901. PMID   23863029.
  42. ↑ von der Wense, Lars; et al. (5 May 2016). "Direct detection of the 229Th nuclear clock transition". Nature . 533 (7601): 47–51. arXiv: 1710.11398 . Bibcode:2016Natur.533...47V. doi:10.1038/nature17669. PMID   27147026. S2CID   205248786.
  43. ↑ Masuda, Takahiko; Yoshimi, Akihiro; Fujieda, Akira; Fujimoto, Hiroyuki; Haba, Hiromitsu; Hara, Hideaki; et al. (2019). "X-ray pumping of the 229Th nuclear clock isomer". Nature . 573 (7773): 238–242. arXiv: 1902.04823 . Bibcode:2019Natur.573..238M. doi:10.1038/s41586-019-1542-3. PMID   31511686. S2CID   119083861.
  44. ↑ A. Yamaguchi; et al. (2019). "Energy of the 229Th nuclear clock isomer determined by absolute gamma-ray energy difference". Phys. Rev. Lett. 123 (22) 222501. arXiv: 1912.05395 . Bibcode:2019PhRvL.123v2501Y. doi:10.1103/PhysRevLett.123.222501. PMID   31868403. S2CID   209202193.
  45. ↑ Conover, Emily (June 1, 2023). "Measurements of a key radioactive decay nudge a nuclear clock closer to reality". ScienceNews .
  46. ↑ Kraemer, Sandro; et al. (May 25, 2023). "Observation of the radiative decay of the 229Th nuclear clock isomer". Nature . 617 (7962): 706. arXiv: 2209.10276 . Bibcode:2023Natur.617..706K. doi:10.1038/s41586-023-05894-z. PMID   37225880. photons of 8.338(24) eV are measured, in agreement with recent measurements and the uncertainty is decreased by a factor of seven. The half-life of 229mTh embedded in MgF2 is determined to be 670(102) s
  47. ↑ Elwell, R.; Schneider, Christian; Jeet, Justin; Terhune, J. E. S.; Morgan, H. W. T.; Alexandrova, A. N.; Tran Tan, Hoang Bao; Derevianko, Andrei; Hudson, Eric R. (18 April 2024). "Laser excitation of the 229Th nuclear isomeric transition in a solid-state host". arXiv: 2404.12311 [physics.atom-ph]. a narrow, laser-linewidth-limited spectral feature at 148.38219(4)stat(20)sys nm (2020407.3(5)stat(30)sys GHz) that decays with a lifetime of 568(13)stat(20)sys s. This feature is assigned to the excitation of the 229Th nuclear isomeric state, whose energy is found to be 8.355733(2)stat(10)</sys> eV in 229Th:LiSrAlF6.
  48. ↑ Klapetz, Patrick (2024-04-29). "Thorium-229: Erstmals Atomkern mit Laser angeregt" [Thorium-229: First atomic nucleus excited by laser]. Golem.de: IT-News für Profis (in German). Archived from the original on 2024-04-30. Retrieved 2024-04-30.
  49. ↑ Thirolf, Peter G.; et al. (March 2020). 'Phase Transition' in the 'Thorium-Isomer Story'. XXXVI Mazurian Lakes Conference on Physics (1–7 November 2019) (PDF). Acta Physica Polonica B. Vol. 51, no. 3. Piaski, Pisz County, Poland. pp. 561–570. arXiv: 2108.13388 . doi: 10.5506/APhysPolB.51.561 . Originally presented as Characterization of the elusive 229mTh isomer – milestones towards a nuclear clock.
  50. ↑ A. Derevianko; M. Pospelov (2014). "Hunting for topological dark matter with atomic clocks". Nature Physics. 10 (12): 933–936. arXiv: 1311.1244 . Bibcode:2014NatPh..10..933D. doi:10.1038/nphys3137. S2CID   53630878.
  51. ↑ P.G. Thirolf; B. Seiferle; L. von der Wense (2019). "Improving Our Knowledge on the 229mThorium Isomer: Toward a Test Bench for Time Variations of Fundamental Constants". Annalen der Physik. 531 (5): 1800381. Bibcode:2019AnP...53100381T. doi:10.1002/andp.201800381.
  52. ↑ V.V. Flambaum (2006). "Enhanced Effect of Temporal Variation of the Fine Structure Constant and the Strong Interaction in 229mTh". Phys. Rev. Lett. 97 (9) 092502. arXiv: physics/0601034 . doi:10.1103/PhysRevLett.97.092502. PMID   17026357. S2CID   4109230.
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