Measurements of low decay energies of beta-processes using Penning traps

Two topics of fundamental physics are considered where nuclides with a low beta-decay energy are of high interest, namely nuclear astrophysics and neutrino physics. A few relevant ground-to-ground beta-transitions were addressed by Penning-trap mass spectrometry (PT-MS), employing the Shiptrap (GSI, Darmstadt) and Isoltrap (CERN, Geneva) facilities. In nuclear astrophysics the decay energy of a nuclide is an important spectroscopic parameter. Thus, in the case of the pure s-process nuclide 123Te, it was shown that when its decay energy is accurately and precisely known, the complete decay scheme in a hot stellar environment can be reliably reconstructed. It is shown that at typical s-process conditions the half-life of 123Te can be by many orders of magnitude shorter than the terrestrial value. This circumstance may be used, for example, for tests of astrophysical models in the A = 123 mass region. In neutrino physics, low-energy beta-transitions can be used for determination of the neutrino rest mass. The decay energies (Q-values) of 131Cs and 202Pb were determined. It turned out that the nuclide 202Pb can hardly be used for the neutrino mass determination due to its too high Q-value, whereas 131Cs can be confidently excluded from the consideration since the examined beta-transition is energetically forbidden. The directly measured Q-value of 187Re has shown that on the level of our present accuracy of 33 eV there are no unexpected systematic effects inherent in cryogenic microcalorimetry (CM), which was used for the beta-spectra acquisition of 187Re. A specific problem in neutrino physics is the existence of sterile neutrinos, especially those which can contribute to the so-called Warm Dark Matter. It is shown that the combined efforts of PT-MS and CM may contribute to the keV sterile neutrino search in electron capture in a variety of nuclides

Observation of a low-lying metastable electronic state in highly charged lead by Penning-trap mass spectrometry

Highly charged ions (HCIs) offer many opportunities for next-generation clock research due to the vast landscape of available electronic transitions in different charge states. The development of XUV frequency combs has enabled the search for clock transitions based on shorter wavelengths in HCIs. However, without initial knowledge of the energy of the clock states, these narrow transitions are difficult to be probed by lasers. In this Letter, we provide experimental observation and theoretical calculation of a long-lived electronic state in Nb-like Pb$^{41+}$ which could be used as a clock state. With the mass spectrometer Pentatrap, the excitation energy of this metastable state is directly determined as a mass difference at an energy of 31.2(8) eV, corresponding to one of the most precise relative mass determinations to date with a fractional uncertainty of $4\times10^{-12}$. This experimental result agrees within 1 $\sigma$ with two partially different \textit{ab initio} multi-configuration Dirac-Hartree-Fock calculations of 31.68(13) eV and 31.76(35) eV, respectively. With a calculated lifetime of 26.5(5.3) days, the transition from this metastable state to the ground state bears a quality factor of $1.1\times10^{23}$ and allows for the construction of a HCI clock with a fractional frequency instability of $<10^{-19}/\sqrt{\tau}$

Detection of metastable electronic states by Penning trap mass spectrometry

State-of-the-art optical clocks achieve fractional precisions of $10^{-18}$ and below using ensembles of atoms in optical lattices or individual ions in radio-frequency traps. Promising candidates for novel clocks are highly charged ions (HCIs) and nuclear transitions, which are largely insensitive to external perturbations and reach wavelengths beyond the optical range, now becoming accessible to frequency combs. However, insufficiently accurate atomic structure calculations still hinder the identification of suitable transitions in HCIs. Here, we report on the discovery of a long-lived metastable electronic state in a HCI by measuring the mass difference of the ground and the excited state in Re, the first non-destructive, direct determination of an electronic excitation energy. This result agrees with our advanced calculations, and we confirmed them with an Os ion with the same electronic configuration. We used the high-precision Penning-trap mass spectrometer PENTATRAP, unique in its synchronous use of five individual traps for simultaneous mass measurements. The cyclotron frequency ratio $R$ of the ion in the ground state to the metastable state could be determined to a precision of $\delta R=1\cdot 10^{-11}$, unprecedented in the heavy atom regime. With a lifetime of about 130 days, the potential soft x-ray frequency reference at $\nu=4.86\cdot 10^{16}\,\text{Hz}$ has a linewidth of only $\Delta \nu\approx 5\cdot 10^{-8}\,\text{Hz}$, and one of the highest electronic quality factor ($Q=\frac{\nu}{\Delta \nu}\approx 10^{24}$) ever seen in an experiment. Our low uncertainty enables searching for more HCI soft x-ray clock transitions, needed for promising precision studies of fundamental physics in a thus far unexplored frontier

The decay energy of the pure s-process nuclide ¹²³ Te

A direct and high-precision measurement of the mass difference of ¹²³Te and ¹²³Sb has been performed with the Penning-trap mass spectrometer SHIPTRAP using the recently introduced phase-imaging ioncyclotron-resonance technique. The obtained mass difference is 51.912(67) keV/c². Using the masses of the neutral ground states and the energy difference between the ionic states an effective half-life of ¹²³Te has been estimated for various astrophysical conditions. A dramatic influence of the electron capture process on the decay properties of ¹²³Te in hot stellar conditions has been discussed

The Electron Capture in 163^{163} Ho Experiment - a Short Update

The definition of the absolute neutrino mass scale is one of the main goals of the Particle Physics today. The study of the end-point regions of the β- and electron capture (EC) spectrum offers a possibility to determine the effective electron (anti-)neutrino mass in a completely model independent way, as it only relies on the energy and momentum conservation. The ECHo (Electron Capture in 163Ho) experiment has been designed in the attempt to measure the effective mass of the electron neutrino by performing high statistics and high energy resolution measurements of the 163 Ho electron capture spectrum. To achieve this goal, large arrays of low temperature metallic magnetic calorimeters (MMCs) implanted with with 163Ho are used. Here we report on the structure and the status of the experiment

Direct decay-energy measurement as a route to the neutrino mass

International audienceA high-precision measurement of the$^{131}$Cs→$^{131}$Xe ground-to-ground-state electron-capture Q$_{EC}$-value was performed using the ISOLTRAP mass spectrometer at ISOLDE/CERN. The novel PI-ICR technique allowed to reach a relative mass precision δm/m of 1.4 ⋅ 10$^{− 9}$. A mass resolving power m/Δm exceeding 1 ⋅ 10$^{7}$ was obtained in only 1s trapping time. Allowed electron-capture transitions with sub-keV or lower decay energies are of high interest for the direct determination of the ν$_{e}$ mass. The new measurement improves the uncertainty on the ground-to-ground-state Q$_{EC}$-value by a factor 25 precluding the$^{131}$Cs→$^{131}$Xe pair as a feasible candidate for the direct determination of the ν$_{e}$ mass

High-precision mass measurement of doubly magic

The absolute atomic mass of $$^{208}$$Pb has been determined with a fractional uncertainty of $$7\times 10^{-11}$$ by measuring the cyclotron-frequency ratio R of $$^{208}$$Pb$$^{41+}$$ to $$^{132}$$Xe$$^{26+}$$ with the high-precision Penning-trap mass spectrometer Pentatra