The usage of muonic x-rays to study elemental properties like nuclear radii ranges back to the seventies. This triggered the pioneering work at the Paul Scherrer Institute (PSI), during the eighties on the Muon-induced x-ray emission (MIXE) technique for a non-destructive assessment of elemental compositions. In recent years, this method has seen a rebirth, improvement, and adoption at most muon facilities around the world. Hereby, the PSI offers unique capabilities with its high-rate continuous muon beam at the Swiss Muon Source (SμS). We report here the decision-making, construction, and commissioning of a dedicated MIXE spectrometer at PSI, the GermanIum Array for Non-destructive Testing (GIANT) setup. Multiple campaigns highlighted the outstanding capabilities of MIXE at PSI, e.g., resolving down to 1 at. % elemental concentrations with as little as 1 h data taking, measuring isotopic ratios for elements from iron to lead, and characterizing gamma rays induced by muon nuclear capture. On-target beam spots were characterized with a dedicated charged particle tracker to be symmetric to 5% with an average σ = 22.80(25) and 14.41(8) mm for 25 and 45 MeV/c, respectively. Advanced analysis of the high-purity germanium signals further allows us to improve energy and timing resolutions to ∼1 keV and 20 ns at 1 MeV, respectively. Within the GIANT setup, an average detector has a photopeak efficiency of $\overline{{ϵ}_E}=0.11$ % and an energy resolution of $\overline{{\sigma }_E}=0.8\text{keV}$ at E = 1000 keV. The overall performance of the GIANT setup at SμS allowed us to start a rich user program with archaeological samples, Li-ion battery research, and collaboration with the industry. Future improvements will include a simulation-based analysis and a higher degree of automation, e.g., automatic scans of a series of muon momenta and automatic sample changing.

Novel emitters of muonium ($\mathrm{Mu}={\mu }^{+}+e^{-}$) with high conversion efficiencies can enhance the precision of muonium spectroscopy experiments and enable next-generation searches for new physics. At the Paul Scherrer Institute (PSI), we investigate muonium production at room-temperature as well as in cryogenic environment using a superfluid helium converter. In this paper, we describe the development of compact detection schemes which resulted in the background-suppressed observation of atomic muonium in vacuum, and can be adapted for cryogenic measurements. Using these setups, we compared the emission characteristics of various muonium production targets at room temperature using low momentum ($p_{\mu }=11–13\mathrm{MeV}/c$) muons, and observed muonium emission from zeolite targets into vacuum. For a specific laser-ablated aerogel target, we determined a muon-to-vacuum-muonium conversion efficiency of $7.23\pm 0.05{\text{(stat)}}_{-0.76}^{+1.06}\text{(sys)}\%$, assuming thermal emission of muonium. Moreover, we investigated muonium-helium collisions and from it we determined an upper temperature limit of 0.3 K for the superfluid helium converter.

Battery research often encounters the challenge of determining chemical information, such as composition and elemental oxidation state, of a layer buried within a cell stack in a non-destructive manner. Spectroscopic techniques based on X-ray emission or absorption are well-suited and commonly employed to reveal this information. However, the attenuation of X-rays as they travel through matter creates a challenge when trying to analyze layers buried at depths exceeding hundred micrometers from the sample's surface. In the context of battery research, the limited escape depth of X-rays often imposes to design experiment-specific cells with thinner inner layers, despite the risk that these tailored cells may not exactly replicate the cycling behavior of larger commercial cells. Muon-induced X-ray emission (MIXE) is a non-destructive spectroscopic technique that involves implanting negative muons into a sample and detecting the highly energetic muonic X-rays generated when these muons are captured by the sample's atoms. By virtue of the high energy of muonic X-rays, the depth of analysis of MIXE greatly exceeds other X-ray based techniques. In this article, we introduce the technique and lay the groundwork for employing MIXE in future in-situ/operando analyses of batteries. We demonstrate that MIXE can detect nearly all elements, including low atomic number ones such as Li. Additionally, we establish the quantitative nature of MIXE through the precise determination of LiNi_xMn_yCo_1-x-yO₂ (NMC) electrode stoichiometries. Finally, we demonstrate that MIXE enables the acquisition of depth-resolved chemical information from 100-1,000 μm thick cells, in good agreement with simulation results.

We report on the realisation of a cyclotron trap assisted positron tungsten moderator for the conversion of positrons with a broad keV–few MeV energy spectrum to a mono-energetic eV beam with an efficiency of 1.8(2)% defined as the ratio of the slow positrons divided by the ${\beta }^{+}$ activity of the radioactive source. This is an improvement of almost two orders of magnitude compared to the state of the art of tungsten moderators. The simulation validated with this measurement suggests that, using an optimised setup, even higher efficiencies are achievable. A novel method for the production of ${}^{48}$V high-activity thin foil positron sources based on a solid target station at a medical cyclotron was developed. This is an improvement of more than one order of magnitude with respect to standard methods.