Apparatus for measuring electron-impact excitation cross sections using fast metastable atoms produced via charge exchange

Boffard, John B.; Lagus, Mark E.; Anderson, L. W.; Lin, Chun C.

doi:10.1063/1.1147102

Cited by 17 publications

(9 citation statements)

References 20 publications

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“…2.5 1s 3 ,1.28 0.28 6 0.19 8.54 6 3.38 13.63 6 5.63 · · · · · · · · · · · · 10 1s 3 ,0.85 ,0.14 10.76 6 4.26 18.79 6 7.76 · · · · · · · · · · · · 2.5 1s 5 0. 15 different from the results presented in this work. In general, their measured cross sections are about an order of magnitude larger than ours at 10 eV.…”

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Measurement of Cross Sections for Electron Excitation out of the Metastable Levels of Argon

et al. 1998

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We have measured electron excitation cross sections out of the 1s 3 and 1s 5 metastable levels of Ar into eight levels of the 3p 5 4p manifold. We use the optical method to determine the cross sections by measuring the radiation of the excited atoms. By optically pumping the 1s 5 metastable atoms with a laser, we separate the contributions that each metastable level makes to our observed signal, and thus we can determine the excitation cross sections out of the individual metastable levels. We also interpret the trends in both magnitude and energy dependence observed for the cross sections.[S0031-9007(98)06582-X]

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“…To study excitation at energies above ground state excitation onset we have a different apparatus that utilizes a fast beam of metastable atoms [14,15]. A radiofrequency ion source produces a 2.1 keV Ar ion beam, which passes through a cesium vapor target.…”

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Measurement of Cross Sections for Electron Excitation out of the Metastable Levels of Argon

et al. 1998

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“…To measure the lifetime of neutral isolated 229m Th, the ions need to be neutralized without getting into contact with any surface, e.g. by charge exchange with caesium vapor in a charge transfer cell as for example described in [39].…”

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Lifetime Measurement of the Th229 nuclear isomer

2017

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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 IC.229 Th is the only known nucleus providing an excited isomeric state of sufficiently low energy to allow for direct nuclear optical laser excitation [1]. The possibility to drive the transition with laser technology has led to the proposal of a multitude of interesting applications. The predicted spectroscopic properties of the 229m Th ground-state transition make it a promising candidate for a nuclear optical clock that may outperform today's existing atomic clock technology [2][3][4]. As other ultra-precise optical clocks, a nuclear clock could be a tool in the search for dark matter [5], gravitational waves [6] as well as for geodesy [7]. Such a nuclear clock promises ultra-high sensitivity for potential time variations of fundamental constants [8]. There exist also proposals towards a nuclear γ-ray laser [9] based on the 229m Th ground-state transition and a nuclear qubit for quantum computing [10]. However, to enable laser excitation, precise knowledge on the spectroscopic properties of the transition, such as the lifetime and the excitation energy, is required. Since the first proposal of the existence of a low-energy isomeric state of 229 Th in 1976 [11] several indirect energy measurements [12][13][14] have been performed. With steadily improved detector energy resolution, these measurements pinned down the energy to 7.8 ± 0.5 eV [15] (λ ≈ 159 ± 10 nm). A direct half-life measurement of a photonic decay channel [16] has been controversially discussed [17].Several different experimental approaches have been pursued, aiming for a measurement of the isomer's properties or for an optical laser excitation of the nucleus [18][19][20][21][22][23][24][25][26][27]. However, despite significant experimental effort, no conclusive measurement of the isomeric half-life has been reported so far.As a result of the low excitation energy, the isomer can decay via three decay channels to its ground state, whose occurrence depends on the electronic surrounding of the nucleus [28][29][30][31]: when the binding energy of an electron E B in the surrounding of the nucleus is lower than the excitation energy of the isomer E I , the isomer decays preferably via internal conversion (IC) by emit...

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“…They are also contaminated by ground state species, with typically only one in 10 5 of the atoms in the excited state. Perhaps the most successful and cleanest sources to date have been the charge-transfer devices [10,11], which have been used for measurements of total ionization cross sections for neon metastables [10] and total cross sections for electronic excitation of He metastables [11].…”

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Electron Collisions with Laser Cooled and Trapped Metastable Helium Atoms: Total Scattering Cross Sections

et al. 2005

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Absolute measurements of total scattering cross sections for low energy (5-70 eV) electrons by metastable helium (2(3)S) atoms are presented. The measurements are performed using a magneto-optical trap which is loaded from a laser-cooled, bright beam of slow He(2(3)S) atoms. The data are compared with predictions from convergent close coupling and R matrix with pseudostate calculations, and we find good agreement between experiment and theory.

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Apparatus for measuring electron-impact excitation cross sections using fast metastable atoms produced via charge exchange

Cited by 17 publications

References 20 publications

Measurement of Cross Sections for Electron Excitation out of the Metastable Levels of Argon

Measurement of Cross Sections for Electron Excitation out of the Metastable Levels of Argon

Lifetime Measurement of the Th229 nuclear isomer

Electron Collisions with Laser Cooled and Trapped Metastable Helium Atoms: Total Scattering Cross Sections

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