arXiv subjects

Magnus Schlösser

Publications and source records attributed to Magnus Schlösser.

9 recordsLinked to original sources

arXiv2026

Cryogenic source of atomic tritium for neutrino-mass measurements and precision spectroscopy

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.

physics.atom-ph↗

arXiv2026

Following the Long-Term Evolution of sp$^3$-type Defects in Tritiated Graphene using Raman Spectroscopy

We report on the evolution of tritium-induced sp$^3$-defects in monolayer graphene on a Si/SiO$_2$ substrate, by comparing large-area Raman maps of the same two samples, acquired just after fabrication and twice thereafter, about 9-12 months apart. Inbetween measurements the samples were kept under standard laboratory conditions. Using a conservative classification of sp$^3$-type spectra, based on the D/D' peak intensity ratio, we observed almost complete depletion of sp$^3$-type defects over the investigation period of about two years. This by far exceeds the ~5.5% annual reduction expected from tritium decay alone (~3x larger). This change in the defect composition is accompanied by a recovery of the 2D-band of graphene and an overall decrease in defect-density, as determined via the D/G intensity ratio. Hydogenated graphene is reported to be reasonably stable over several months, when kept under vacuum, but suffers substantial hydrogen loss under laboratory air conditions. While the results shown here for tritiated graphene exhibit similarities with hydrogenated graphene, however, some distinct differences are observed.

cond-mat.mtrl-sci↗

arXiv2025

Comparison of the detector response and calibration function of metallic microcalorimeters for X-ray photons and external electrons

Metallic microcalorimeters (MMCs) are cryogenic single-particle detectors that rely on a calorimetric detection principle. Due to their excellent energy resolution, close-to-ideal linear detector response, fast signal rise time and the potential for \SI{100}{\%} quantum efficiency, MMCs outperform conventional detectors by several orders of magnitude in resolution. These attributes make them particularly interesting for a broad spectrum of applications, including a next-generation neutrino mass experiment based on the measurement of the tritium beta-decay spectrum, with an objective of achieving a sensitivity surpassing that of the pioneering KATRIN experiment. However, although MMCs have been used in measurements of photons and heavy ions with great success, no information is currently available on the interaction between MMCs and external light charged particles such as electrons. This work aims to provide such missing information and to demonstrate that MMC-based detectors are suitable for high-resolution spectroscopy of external electron sources. Particularly, we present the first-ever measurements of external electrons using a metallic microcalorimeter, comprehensively discuss the characteristics of the signal shape and the calibration function and give a direct comparison between well-defined conversion electron and X-ray photon signals from the same $^{83}$Rb/$^{83m}$Kr source.

physics.ins-det↗

arXiv2025

Graphene structure modification under tritium exposure: 3H chemisorption dominates over defect formation by \b{eta}-radiation

Potential structural modifications of graphene exposed to gaseous tritium are important for membrane-based hydrogen isotope separation. Such modifications cannot be explained by electron irradiation alone. Instead, tritiation, caused by the tritium radicals remaining after the decay, is the primary effect causing the modification of the graphene surface, as confirmed by confocal Raman spectroscopy. The effect of the interaction of tritium atoms with the graphene surface exceeds that of electron irradiation at the average energy of the beta particles (5.7 keV). Compared to previously investigated high electron doses in the absence of tritium, remarkably low concentrations of tritium already induce a significant amount of sp3- and vacancy-type defects at short exposure times. Our findings are supported by molecular dynamics simulations of graphene bombardment with tritium atoms. As a consequence, tritium saturation of graphene may alter its permeability for hydrogen isotopes, thus affecting potential applications.

cond-mat.mtrl-sci↗

arXiv2025

Sterile-neutrino search based on 259 days of KATRIN data

Neutrinos are the most abundant fundamental matter particles in the Universe and play a crucial role in particle physics and cosmology. Neutrino oscillation, discovered about 25 years ago, reveals that the three known species mix with each other. Anomalous results from reactor and radioactive-source experiments suggest a possible fourth neutrino state, the sterile neutrino, which does not interact via the weak force. The KATRIN experiment, primarily designed to measure the neutrino mass via tritium $β$-decay, also searches for sterile neutrinos suggested by these anomalies. A sterile-neutrino signal would appear as a distortion in the $β$-decay energy spectrum, characterized by a discontinuity in curvature (kink) related to the sterile-neutrino mass. This signature, which depends only on the shape of the spectrum rather than its absolute normalization, offers a robust, complementary approach to reactor experiments. KATRIN examined the energy spectrum of 36 million tritium $β$-decay electrons recorded in 259 measurement days within the last 40 electronvolt below the endpoint. The results exclude a substantial part of the parameter space suggested by the gallium anomaly and challenge the Neutrino-4 claim. Together with other neutrino-disappearance experiments, KATRIN probes sterile-to-active mass splittings from a fraction of an electron-volt squared to several hundred electron-volts squared, excluding light sterile neutrinos with mixing angles above a few percent.

hep-ex↗

arXiv2024

Demonstration of tritium adsorption on graphene

In this work, we report on studies of graphene exposed to tritium gas in a controlled environment. The single layer graphene on a $\textrm{SiO}_2$/Si substrate was exposed to 400 mbar of $\textrm{T}_2$ for a total time of $\approx$ 55 h. The resistivity of the graphene sample was measured $\textit{in situ}$ during tritium exposure using the Van der Pauw method. We found that the sheet resistance increases by three orders of magnitude during the exposure, suggesting significant chemisorption of tritium. After exposure, the samples were characterised $\textit{ex situ}$ via spatio-chemical mapping with a confocal Raman microscope, to study the effect of tritium on the graphene structure (tritiation yielding T-graphene), as well as the homogeneity of modifications across the whole area of the graphene film. The Raman spectra after tritium exposure were comparable to previously observed results in hydrogen-loading experiments, carried out by other groups. By thermal annealing we also could demonstrate, using Raman spectral analysis, that the structural changes were largely reversible. Considering all observations, we conclude that the graphene film was at least partially tritiated during the tritium exposure, and that the graphene film by and large withstands the bombardment by electrons from the $β$-decay of tritium, as well as by energetic primary and secondary ions.

cond-mat.mes-hall↗

arXiv2023

The Generation and Analysis of Tritium-substituted Methane

An unavoidable category of molecular species in large-scale tritium applications, such as nuclear fusion, are tritium-substituted hydrocarbons; these form by radiochemical reactions in the presence of (circulating) tritium and carbon (mainly from the steel of vessels and tubing). Tritiumsubstituted methane species, CQ$_4$ (with Q = H , D , T), are often the precursor for higher-order reaction chains, and thus are of particular interest. Here we describe the controlled production of CQ$_4$ carried out in the CAPER facility of the Tritium Laboratory Karlsruhe (TLK), exploiting catalytic reactions and species-enrichment via the CAPER-integral permeator. CQ4 was generated in substantial quantity (>1000 cm$^3$ at ~850 mbar, with CQ$_4$ - content of up to ~20 %). These samples were analyzed using laser Raman and mass spectrometry, to determine the relative isotopologue composition and to trace the generation of tritiated chain-hydrocarbons.

physics.chem-ph↗

arXiv2022

Operation Modes of the KATRIN Experiment Tritium Loop System using $^{83\mathrm{m}}$Kr

The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to search for the effective electron antineutrino mass with a sensitivity of 0.2 eV (90 % C.L.). In order to achieve this goal, KATRIN measurement phases focusing on the neutrino mass search are alternated with phases of investigations of systematic effects. During these phases, metastable $^{83\mathrm{m}}$Kr is used as a calibration source. The monoenergetic conversion electrons emitted accompanying the decay of $^{83\mathrm{m}}$Kr allow a direct access to the starting conditions of $β$-electrons produced inside the windowless gaseous tritium source (WGTS) of KATRIN. To make use of $^{83\mathrm{m}}$Kr in the WGTS, the Tritium Loop System, which provides a stable flow of tritium to the WGTS, needs to be operated in special modes. This paper focuses on the technical implementation of these modes and their performance with regard to the achievable $^{83\mathrm{m}}$Kr-rates, gas densities, and gas compositions inside the WGTS.

physics.ins-det↗

arXiv2012

Monitoring of tritium purity during long-term circulation in the KATRIN test experiment LOOPINO using laser Raman spectroscopy

The gas circulation loop LOOPINO has been set up and commissioned at Tritium Laboratory Karlsruhe (TLK) to perform Raman measurements of circulating tritium mixtures under conditions similar to the inner loop system of the neutrino-mass experiment KATRIN, which is currently under construction. A custom-made interface is used to connect the tritium containing measurement cell, located inside a glove box, with the Raman setup standing on the outside. A tritium sample (purity > 95%, 20 kPa total pressure) was circulated in LOOPINO for more than three weeks with a total throughput of 770 g of tritium. Compositional changes in the sample and the formation of tritiated and deuterated methanes CT_(4-n)X_n (X=H,D; n=0,1) were observed. Both effects are caused by hydrogen isotope exchange reactions and gas-wall interactions, due to tritium β decay. A precision of 0.1% was achieved for the monitoring of the T_2 Q_1-branch, which fulfills the requirements for the KATRIN experiment and demonstrates the feasibility of high-precision Raman measurements with tritium inside a glove box.

physics.ins-det↗