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arXiv:2609.22186

Design of a Lamb-Shift Polarimeter for $^3$He Ions and Atoms

N. Faatz, R. Engels, C. Kannis, S. J. Pütz, J. Steinhage

physics.ins-detphysics.atom-phquant-phSubmitted Aug 28, 2026• Announced Aug 31, 2026• Revised Sep 24, 2026 (v2)
v1 · Aug 28, 2026v2 · Sep 24, 2026v3 · Sep 28, 2026
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Abstract

In high energy physics experiments $^3$He$^{2+}$ nucleons are suitable to test the internal structure of neutrons, which makes them the perfect substitute. Moreover, it is one of the atomic species for which high polarization values are achievable through the use of optical pumping methods. Therefore, nuclear polarized sources for $^3$He$^{2+}$ ions are currently in development. Consequently, detector systems validating their nuclear polarization value need to be established. Such a detector system, based on the Lamb-shift polarimeter, is introduced in this work. Its advantage is that it can operate at low energies in the range of 10 to 100 keV, which makes preacceleration unnecessary. In addition, a fast evaluation of the nuclear polarization within seconds leads to shorter disruptions for beam times.

Comments
In the introduction and the conclusion we mixed up the Q-value of the tritium decay and the kinetic energy of the 3He atom after the bound-beta decay. Therefore, we must modify the method how the Lamb-shift polarimeter can be used to measure the nuclear polarization of these atoms

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We show that a measurement of the anisotropy in the angular distribution of the quenching radiation emitted by metastable hydrogen and deuterium atoms in an electric field can be used to determine the Lamb shift to an accuracy of at least \ifmmode\pm\else\textpm\fi{}0.1%. The method can be extended to the hydrogenic ions, where it offers several advantages over the quench-rate technique used in earlier measurements. The experiment is interpreted by means of a nonperturbative theory of the quenching process, which includes hyperfine structure and time-dependent effects. In the limit of zero field strength, the anisotropies of H and D are measured to be 0.139 01 \ifmmode\pm\else\textpm\fi{} 0.000 12 and 0.141 21 \ifmmode\pm\else\textpm\fi{} 0.000 14, while the theoretical values are 0.139 078 and 0.141 30, respectively. The corresponding Lamb shifts are 1057.3 \ifmmode\pm\else\textpm\fi{} 0.9 MHz and 1058.7 \ifmmode\pm\else\textpm\fi{} 1.1 MHz.
Polarized atomic beam sources have been in operation for many years to produce either nuclear polarized atomic hydrogen or deuterium beams. In recent experiments, such a source was used to polarize both isotopes independently at the same time. By recombination of the atoms, hydrogen-deuterium molecules with all possible nuclear spin combinations can be created. Those spin isomers are useful for further applications, like precision spectroscopy, as polarized targets for laser-particle acceleration, polarized fuel for fusion reactors, or as an option for future measurements of electric dipole moments.
A beam of unpolarized metastable He('+) 2s(, 1/2) ions, quenched by a static electric field, (')E has an anisotropy in the emitted radiation that can be used to determine the He('+) 2('2)s(, 1/2)-2('2)p(, 1/2) Lamb shift. A high precision measurement of this anisotropy for a field strength of (VBAR)(')E(VBAR) = (370.97 (+OR-) 0.06) V/cm has been made. The value of the field-free anisotropy, A('(0)), adjusted by small corrections is (0.1178082 (+OR-) 0.0000086), where the uncertainty is the statistical one standard deviation. Using much improved apparatus over Drake, Goldman and van Wijngaarden, our values for both the anisotropy A('(0)) and the Lamb shift, S = (14022.67 (+OR-) 1.06) MHz lie lower by 17 standard deviations from theirs. The great discrepancy is not understood, and may be attributed to the inherent difficulties of measuring light intensities by photon counting techniques. Source: Dissertation Abstracts International, Volume: 47-09, Section: B, page: 3817. Thesis (Ph.D.)--University of Windsor (Canada), 1986.
We propose a concept for a cryogenic source of atomic tritium at sub-Kelvin temperatures and energies suitable for magnetic trapping. The source is based on the dissociation of solid molecular T2 films below 1 K by electrons from a pulsed RF discharge, a technique recently demonstrated for atomic hydrogen, combined with buffer-gas cooling and magnetic confinement. We analyze the key processes limiting the source performance, adsorption, spin exchange and recombination, and show that atomic tritium fluxes exceeding 1e15 1/s at kinetic energies of 100 mK can be achieved at the entrance to the magnetic trap. Such a source would enable Doppler-free two-photon 1S-2S spectroscopy in atomic tritium for high-precision measurements of the triton charge radius, providing a crucial benchmark for bound-state QED and improving the comparison between electronic, muonic, and scattering determinations of nuclear sizes in light systems. Beyond spectroscopy, an atomic tritium source avoids molecular final state broadening in the beta decay and is therefore necessary for next generation neutrino mass measurements; combined with detector technologies such as sub-eV resolution quantum sensors or cyclotron radiation emission spectroscopy, it enables an order of magnitude improvement compared to the current best experimental limit. Additionally, the source can be used to generate a beam of low field seeking deuterium atoms for loading magnetic traps, an important benchmark before trapping tritium atoms, which is useful for precision spectroscopy.