Muonic X-ray Research Articles

Absolute nuclear charge radius by Na-like spectral line separation in high-Z elements

Abstract We describe a novel technique to determine absolute nuclear radii of high-Z nuclides. Utilizing accurate theoretical atomic structure calculations together with precise measurements of extreme ultraviolet transitions in highly charged ions this method allows for precise determinations of absolute nuclear charge radii based upon the well-known nuclear radii of their neighboring elements. This method can work for elements without stable isotopes, and its accuracy may be competitive with current methods (electron scattering and muonic x-ray spectroscopy).

High-Frequency Electrochemical Impedance Spectroscopy for Detecting Li Deposition Toward Assessing Thermal Stability in LiBs

Li-deposition is a critical factor in one of the degradation modes of lithium-ion batteries (LiB). The Li-deposition increases the risk of internal short circuits and lowers thermal runaway onset temperature, compromising safety1. Detecting the Li-deposition is possible through disassembly or analysis using large-scale equipment such as muonic X-ray visualization 2. On the other hand, a non-destructive and convenient evaluation technique is required to assess batteries’ safety in commercial use.A novel inspection technique using high-frequency electrochemical impedance spectroscopy (HF-IS) has been developed to detect the presence of Li-deposition3. Electrochemical impedance spectroscopy (EIS), which nondestructively observes ionic diffusion, reaction, and charge transfer in 10 mHz to 10 kHz response, is commonly used for diagnosing the state of battery degradation4. Compared to the conventional EIS, the HF-EIS uses the real part of battery impedance Re(Zbat ) above 100 kHz, allowing observation of only the electronic behavior of the battery in high-frequency regions where ion behavior cannot be tracked. It utilizes the phenomenon of current concentration at interfaces of materials with different conductivities, known as the "skin effect," which is caused by a high-frequency electromagnetic field. Since the Li-deposition occurs at the interface between the negative electrode and the electrolyte, the interface within the high-frequency current path changes from the negative electrode to the Li-metal. This change induces alterations in the electromagnetic field and the high-frequency current path, subsequently resulting in a variation in Re(Zbat ).Figure 1 displays a representative result illustrating the relationship between the thermal runaway onset temperature and the change in Re(Zbat )| freq =1MHz. We conducted a degradation test to deposit Li-metal and a thermal runaway test using two types of 18650 cylindrical cells (NCA-3400 mAh, NCM-2650 mAh). Two batteries subjected to excessive charging C-rates demonstrated the proportional relationship between the decrease in thermal runaway onset temperature and the reduction in Re(Z bat)| freq =1MHz in individual cases. The results indicate that different battery types have different thermal stability of LiB against the Li-deposition.The HF-EIS is not only a safety diagnostic tool but can also contribute to developing battery materials by reducing destructive testing costs. This method of on-the-spot safety quantification diagnosis is expected to contribute to the safer proliferation of the LiBs.Reference1 Li, Y. L. et al. Thermal Runaway Triggered by Plated Lithium on the Anode after Fast Charging. Acs Applied Materials & Interfaces 11, 46839-46850 (2019). https://doi.org/10.1021/acsami.9b165892 Umegaki, I. et al. Nondestructive High-Sensitivity Detections of Metallic Lithium Deposited on a Battery Anode Using Muonic X-rays. Analytical Chemistry 92, 8194-8200 (2020). https://doi.org/10.1021/acs.analchem.0c003703 Ishigaki, M. et al. Operando Li metal plating diagnostics via MHz band electromagnetics. Nature Communications 14, 7275 (2023). https://doi.org/10.1038/s41467-023-43138-w4 Barsoukov, E. Impedance Spectroscopy Theory, Experiment, and Applications Second Edition Preface. Impedance Spectroscopy: Theory, Experiment, and Applications, 2nd Edition, XII-+ (2005). Figure 1

MMC Array to Study X-Ray Transitions in Muonic Atoms

The QUARTET collaboration aims to significantly improve the precision of the absolute nuclear charge radii of light nuclei from Li to Ne by using an array of metallic magnetic calorimeters to perform high-precision X-ray spectroscopy of low-lying states in muonic atoms. A proof-of-principle measurement with lithium, beryllium and boron is planned for fall 2023 at the Paul Scherrer Institute. We discuss the performance achieved with the maXs-30 detector module to be used. To place the detector close to the target chamber where the muon beam will impact the material under study, we have developed a new dilution refrigerator sidearm. We further discuss the expected efficiency given the transparency of the X-ray windows and the quantum efficiency of the detector. The expected muonic X-ray rate combined with the high resolving power and detection efficiency of the detector suggest that QUARTET will be able to study the de-excitation of light muonic atoms at an unprecedented level, increasing the relative energy resolution by up to a factor of 20 compared to conventional detector techniques.

Developments on muonic X-Ray measurement system for historical-cultural heritage samples in Japan Proton Accelerator Research Complex (J-PARC)

Developments on muonic X-Ray measurement system for historical-cultural heritage samples in Japan Proton Accelerator Research Complex (J-PARC)

Imaging technology based on the interaction between muon and material

Muon imaging technology, as an emerging detection method, is widely used in various fields. Muons can be classified into cosmic ray muons and accelerator muons based on their origins. Cosmic ray muons stand out for wide energy range, strong penetrating power and no artificial radiation. These characteristics make cosmic ray muon imaging technology adept at achieving nondestructive imaging of target objects. Presently, the commonly used imaging methods include scattering and transmission imaging technologies that leverage muon information for imaging. Additionally, muon and muonic secondary particle coincidence imaging technology utilizes information from secondary particles generated during the interaction between muons and target objects for imaging. The accelerator muon, distinguished by its high flux, strong monochromaticity, and adjustable energy, enables rapid and multidimensional imaging of target objects at various depths. Furthermore, it facilitates the analysis of material elements through muonic X-rays. This article provides insights into the production process and physical characteristics of muons, the fundamental principles of muon imaging technology, and its diverse applications across disciplines. It also explores the current development status and emerging trends in fields such as mineral resource exploration, archaeological studies, and nuclear safety.

Towards Precision Muonic X-ray Measurements of Charge Radii of Light Nuclei

We, the QUARTET Collaboration, propose an experiment to measure the nuclear charge radii of light elements with up to 20 times higher accuracy. These are essential both for understanding nuclear physics at low energies, and for experimental and theoretical applications in simple atomic systems. Such comparisons advance the understanding of bound-state quantum electrodynamics and are useful for searching for new physics beyond the Standard Model. The energy levels of muonic atoms are highly susceptible to nuclear structure, especially to the mean square charge radius. The radii of the lightest nuclei (with the atomic number, Z=1,2) have been determined with high accuracy using laser spectroscopy in muonic atoms, while those of medium mass and above were determined using X-ray spectroscopy with semiconductor detectors. In this communication, we present a new experiment, aiming to obtain precision measurements of the radii of light nuclei 3≤Z≤10 using single-photon energy measurements with cryogenic microcalorimeters; a quantum-sensing technology capable of high efficiency with outstanding resolution for low-energy X-rays.

Numerical study of the “two components” model and background effects in muonic hydrogen experiments

In this study, we explore the X-ray time spectra of muonic oxygen in various H 2 + O 2 gaseous mixtures by means of numerical simulations based on a sophisticated kineticrate equations model. Our primary focus is on the “two components” hypothesis, which was put forward to account for the experimentally observed two successive exponential behaviors in the radiation time-distribution. To ensure an accurate representation of the physical processes in the experiments, we incorporate precise transition rate coefficients for the elastic and inelastic scattering between the muonic hydrogen atoms and other gas constituents, in our simulation code. Specifically, a crucial aspect in our approach is the utilization of the energy dependence of the muon transfer rate to oxygen, recently extracted from experimental data by the FAMU collaboration. The accurate knowledge of such muonic oxygen X-ray time spectra is vital for cutting-edge experiments like FAMU, where the hyperfine splitting in muonic hydrogen atoms is to be determined with high accuracy, as this time spectra serves as a significant part of the background for the desired signal.

Status of the detector setup for the FAMU experiment at RIKEN-RAL for a precision measurement of the Zemach radius of the proton in muonic hydrogen

The FAMU experiment at RIKEN-RAL is a muonic atom experiment with the aim to determine the Zemach radius of the proton by measuring the 1s hyperfine splitting in muonic hydrogen. The activity of the FAMU Collaboration in the years 2015–2023 enabled the final optimisation of the detector-target setup as well as the gas working condition in terms of temperature, pressure and gas mixture composition. The experiment has started its data taking in July 2023. The status of the detector setup for the 2023 experimental runs, for the beam characterisation and muonic X-ray detection in the 100–200 keV energy range, is presented and discussed.

Mid-IR narrow bandwidth tuneable laser source for the FAMU experiment

The FAMU (Fisica degli Atomi MUonici) collaboration aims to measure the proton Zemach radius through muonic hydrogen (μp) spectroscopy. The experimental setup relies on a custom-developed pulsed mid-IR laser source that can be tuned over a specific 6780-6790 nm wavelength range needed to ignite the hyperfine transition of the μp ground state 1S (also known as spin-flip transition). The excitation is observed as a distinctive muonic X-rays emission resulting from the oxygen impurity present in the hydrogen target. The mid-IR emission is produced by Difference Frequency Generation (DFG) in a non-linear crystal, pumped with a fixed wavelength 1064 nm Nd-YAG laser and a tuneable Cr:forsterite laser centred on 1262 nm. This setup produces more than 1.2 mJ at 6780 nm with a linewidth smaller than 30 pm. The experiment requires the laser to run continuously 24/7 in a restricted/radiation-controlled area and for this reason a specifically developed control software permits to remotely act on the laser. The characterization of a series of different non-linear crystals was performed during the development of the laser, resulting in the choice of BaGa4Se7.

Muon spectrometers on China Spallation Neutron Source and its application prospects

<sec>The China Spallation Neutron Source Phase-II Project (CSNS-II) includes the construction of a muon source, namely “Muon station for sciEnce technoLOgy and inDustrY” (MELODY). A muon target station and a surface muon beam line will be completed as scheduled in 2029, making MELODY the first Chinese muon facility. This beam line mainly focuses on the application of muon spin relaxation/rotation/resonance (μSR) spectroscopy. The MELODY also reserves the tunnels for building a negative muon beam line and a decay muon beam line in the future, thereby further expanding the research field to muon-induced X-ray emission (MIXE) elemental analysis and μSR measurements in thick cells, respectively. The two types of material characterization technologies keep their uniqueness in multi-disciplinary researches, and also provide complementary insights for other techniques, such as neutron scattering, nuclear magnetic resonance, and X-ray fluorescence analysis.</sec><sec>The μSR spectroscopy is a mature technology for injecting highly spin polarized muon beams into various types of materials. The subsequent precession and relaxation of muon spin in its surrounding atomic environment reflect the static and dynamical properties of the material of interest, which are then measured by detecting the asymmetric emission of positrons from the decay of those muons, with an average lifetime of approximately 2.2 μs. This enables μSR to develop into a powerful quantum magnetic probe for investigating materials related to magnetism, superconductivity, and molecular dynamics. The combination of a positive muon and an electron is known as muonium, which is a unique and sensitive probe in studying semiconductors, new energy materials, free radical chemistry, etc. As the production of muon beams strongly relies on proton accelerator, only five muon facilities in the world are available for μSR experiments. This limits the large-scale application of muon related sciences. Especially, Chinese researchers face fierce competition and can only apply for precious and limited muon beam time from international muon sources to characterize the key properties of their materials.</sec><sec>The construction of the MELODY muon facility at CSNS-II aims to provide intense and pulsed muon beams for Chinese and international users to conduct their μSR measurements with high quality data in a low repetition rate operation mode. To achieve this goal, as shown in <xref ref-type="fig" rid="Figure1">Fig. 1</xref>, the μSR spectrometer is designed with 1) over 3000 detector units to obtain a sufficient counting rate of 80 Million/h to significantly suppress statistical fluctuations in a short measuring time, 2) a high asymmetry of 0.3 to greatly amplify μSR signals so as to further reduce statistical fluctuations, and 3) extendable low temperature devices to cover most μSR applications and also fulfill experiments with extreme condition requirements.</sec><sec>The MIXE elemental analysis is a type of particle induced X-ray emission (PIXE) technology. Due to the heavier mass of negative muon, the energy of muonic X-ray is around 207 higher than that of X-ray or electron induced fluorescence X-ray. Thus, the MIXE technology is more sensitive to materials with low atomic numbers, and thick samples can be effectively studied without scratching their surfaces. Due to these advantages, the MIXE has been successfully applied to the elemental analysis of cultural heritages, meteorites, Li-ion batteries, etc. MELODY reserves tunnels for negative muon extractions and transport to a MIXE terminal. The MELODY research team is developing a new detection technology with high energy resolution and high counting capability to shorten the measuring time to an acceptable amount based on the 1-Hz repetition rate of muon pulses.</sec><sec>The μSR spectroscopy and MIXE are the two most important application fields of accelerator muon beams. The MELODY muon facility aims to develop and promote these technologies in China by constructing dedicated muon beam lines in CSNS-II and in the future. In this overview, we introduce the principles and advantages of the μSR and MIXE technologies, as well as the physical design and application prospects of the μSR and MIXE spectrometers based on the CSNS-II muon source. Finally, discussions and expectations are made regarding the future upgrade of the CSNS-II muon source’s muon beamline and its broader applications.</sec>

Development of wide range photon detection system for muonic X-ray spectroscopy

We have developed a photon detection system for muonic X-ray spectroscopy. The detector system consists of high-purity germanium detectors with BGO Compton suppressors. The signals from the detectors are readout with a digital acquisition system. The absolute energy accuracy, energy and timing resolutions, photo-peak efficiency, the performance of the Compton suppressor, and high count rate durability are studied with standard γ-ray sources and in-beam experiment using 27Al(p,γ)28Si resonance reaction. The detection system was demonstrated at Paul Scherrer Institute. A calibration method for a photon detector at a muon facility using muonic X-rays of 197Au and 209Bi is proposed.

Feasibility study of a coded aperture imaging technique for position-sensitive muonic X-ray atomic ratio reconstruction

A position-sensitive multi-compound inspection methodology using Muonic X-ray Emission Spectroscopic (μ-XES) element analysis is proposed due to the ability of the coded aperture imaging technique to maintain the relative intensity of X-rays. This methodology can simultaneously obtain the atomic ratio of different regions of the sample under study. Therefore, the mis-judgements of material compositions caused by averaging results can be reduced. The atomic ratio reconstruction quality is mainly related to X-ray counts (Nx ), atomic ratios of materials (AT ), size and placement of sample blocks. In this work, several different sample blocks made of light elements were designed by GEANT4 Monte Carlo (MC) simulations to study the influences of Nx , AT , size and placement of sample on atomic ratio reconstruction quality. In the inspection of multiple sample blocks, this methodology successfully distinguished the material compositions from different regions by reconstructing the atomic ratios of C/N and O/N. Moreover, this methodology can clearly image element blocks larger than 2 × 2 mm2.

The Implementation of MuDirac in Geant4: A Preliminary Approach to the Improvement of the Simulation of the Muonic Atom Cascade Process

Muonic Atom X-ray Emission spectroscopy (µ-XES) is a novel elemental technique that exploits the high-energy X-rays emitted from the muonic atom cascade process to characterize materials. At the ISIS Neutron and Muon Source, the technique is performed at Port4 of the RIKEN-RAL facility, with a user demand that is increasing every year. To cope with this demand, it is necessary to continue to improve the method, either for the hardware (detectors, acquisition, etc.) or software (data analysis and interpretation). In both cases, Monte Carlo codes play an important role: with a simulation, it is possible to reproduce the experimental setup and provide a reliable quantitative analysis. In this work, we investigate the capabilities of GEANT4 for such applications. From the results, we observed that the generation of X-rays, especially the kα and kβ transition for high Z atoms, are not in agreement with the experimental ones. A solution to this issue, other than an attempt with a small modification of the GEANT4 cascade class, could be provided by a database of transition energy calculated by a Dirac equation software called MuDirac. The software, developed by the UKRI scientific computing department and the ISIS muon group, can compute all the transition energy for a given nuclide. Here, preliminary results of the implementation of the MuDirac database in GEANT4 are reported.

Second flavor of heavy ions

The existence of the Second Flavor of Hydrogen Atoms (SFHA), predicted theoretically in 2001, has been confirmed by four different types of atomic or molecular experiments, and evidenced by two different types of astrophysical observations. The SFHA is based on the second analytical solution of the standard Dirac equation. Despite this solution is singular at small r, it can be matched with the regular solution inside the proton for the S-states, and thus becomes legitimate. The SFHA have only the S-states: so, in accordance to the selection rules of quantum mechanics they do not couple to the electromagnetic radiation (except for the 21 cm spectral line): they remain dark. In the present paper we extended the legitimacy of the second analytical solution of the Dirac equation outside the nucleus to heavy ions. We predicted the existence of the second flavor of heavy ions and thus the flavor symmetry of these ions. These ions have only the S-states, so that they remain dark just as the SFHA. This theoretical result has the fundamental importance in its own right. Also, it could encourage experimentalists to perform experiments for the verification of the existence of the second flavor of heavy ions. The most probable candidates are ions whose nuclei are double-magic and thus spherical. As an application of the above fundamental result, we referred to the comparison between the nuclear charge radius rn,μ, determined experimentally by the muonic x-ray transition energies, and the nuclear charge radius rn,e, determined experimentally from the elastic electron scattering. The comparison was possible for two spherical nuclei: for 40Ca20, as well as for 48Ca20. In each case, rn,e turned out to be by about 1% smaller, than rn,μ, the difference being well beyond the experimental error margin. We showed in both above examples, that a relatively small admixture (∼10%) of the second flavor of heavy ions in the target reconciles the values of the nuclear charge radius, measured by two different methods, in favor of the larger value. Finally, we noted that while the SFHA is one of the leading candidates for dark matter or a part of it, there are still unsuccessful attempts to find Weakly Interactive Massive Particles (WIMP) as a part of dark matter. We suggested that if there are massive dark matter particles, then more realistically they could be the second flavor of heavy ions, described in the present paper: they are really dark.

Investigation of the muonic atoms distribution in materials through muonic x-rays momentum simulation using Geant4

Determining the distribution of muonic atoms is essential for μ-X ray imaging. In this study, the generation and de-excitation of muonic atoms in multi-elemental targets were simulated using the Monte Carlo software toolkit Geant4. An approach that reconstructs the production sites of muonic atoms from the μ-X ray momentum is proposed. The imaging results indicated a high simulated spatial resolution of 0.1 mm and a significant increase in the detection efficiency compared to that achieved by the 3-mm pinhole imaging technique. In addition, an analysis of the image quality index (Q) revealed that a superior image quality can be achieved for elements with high and medium atomic numbers. The proposed method has the potential to be further developed into an accurate and efficient technique for positioning the distribution of elements.

Muonic x-ray spectroscopy on implanted targets

Muonic x-ray spectroscopy uses muons to obtain information about the structure of the atom and the nucleus. In muonic atoms, the energy levels of atomic orbitals are significantly more sensitive to the finite size correction. By probing these orbitals using x-ray spectroscopy, the nuclear size correction can be extracted, providing valuable input for laser spectroscopy in the form of absolute charge radii with a relative precision better than 10−3. Continuing on developments that allowed measurements on target quantities of about 5 μg, we showed the feasibility of using implanted targets. In the future, this will allow the measurement of absolute charge radii of long-lived radioactive isotopes that are not available in sufficient enrichment or large quantities. In this contribution, we shall report on the target preparation, involving high-fluence implantation, and on the preliminary results of the muX experimental campaign.

GermanIum array for non-destructive testing (GIANT) setup for muon-induced x-ray emission (MIXE) at the Paul Scherrer Institute

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 ϵĒ=0.11% and an energy resolution of σĒ=0.8keV 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.

Development of Nondestructive Elemental Analysis System for Hayabusa2 Samples Using Muonic X-rays

The concentrations of carbon and other major elements in asteroid samples provide very important information on the birth of life on the Earth and the solar-system evolution. Elemental analysis using muonic X-rays is one of the best analytical methods to determine the elemental composition of solid materials and, notably, is the only method to determine the concentration of light elements in bulk samples in a nondestructive manner. We developed a new analysis system using muonic X-rays to measure the concentrations of carbon and other major elements in precious and expectedly tiny samples recovered from the asteroid Ryugu by spacecraft Hayabusa2. Here we report the development process of the system in 4 stages and their system configurations, The analysis system is composed of a stainless-steel analysis chamber, an acrylic glovebox for manipulating asteroid samples in a clean environment, and Ge semiconductor detectors arranged to surround the analysis chamber. The performance of the analysis system, including the background level, which is crucial for the measurement, was greatly improved from the first stage to the later ones. Our feasibility study showed that the latest model of our muonic X-ray analysis system is capable of determining the carbon concentration in Hayabusa2’s sample model with an uncertainty of less than 10% in a 6 day measurement.

Preface

Proceedings of the 15th International Conference on Muon Spin Relaxation, Rotation and Resonance28th August to 2nd September 2022 Parma, ItalyEditors: Giacomo Prando and Francis PrattThe 15th International Conference on Muon Spin Rotation, Relaxation and Resonance, µSR2020, took place at the University of Parma, Italy, from August 28th to September 2nd 2022, after a delay of over two years due to the COVID-19 pandemic. µSR2020 was promoted by the International Society for µSR Spectroscopy (ISMS) and co-organised by the Department of Mathematical, Physical and Computer Sciences of the University of Parma in Italy and the ISIS Muon Group at the STFC Rutherford Appleton Laboratory in the UK.µSR spectroscopy makes use of beams of positive and negative muons that are produced at only a small (but growing) number of accelerator facilities around the world. This conference series, which started in 1978 in Rorschach, Switzerland, and has continued with a triennial cadence until the present day, plays a very important role in fostering the exchanges of a well-established, open community of users, promoting and disseminating new experimental developments, as well as informing on scientific breakthroughs associated with the technique and the theoretical advances that support data interpretation.After the uncertainties of the pandemic years, the organisers welcomed the strong support shown by the community for the meeting, with 183 delegates from 17 different countries attending this 15th edition. Of these, it was good to see over 40 early stage researchers taking part in the conference. At the time of the meeting, delegates from a number of countries were still finding international travel difficult, and therefore hybrid sessions were included in the programme to allow remote participation.The Conference Program was selected with the generous help of an International Advisory Committee of 32 distinguished scientists, chaired by Mauro Riccò, University of Parma, and a Scientific Program Committee, composed of nine distinguished scientists, chaired by Pietro Carretta, University of Pavia. Outreach to the local community was an important aspect of the Conference, which was enhanced by a well-attended public engagement event held on the Thursday evening at the Museo APE Parma.Following a well-established tradition, the conference opened with a Student Day on the Sunday. Starting with a short session of four introductory tutorials, the bulk of the day was given over to the students themselves, to share their research with their peers though 12 selected contributions. The day was very well attended (with up to 70 delegates taking part), with the new format much appreciated by all.The start of the regular event was marked by the award of the Yamazaki Prize to Stephen Blundell, followed by his Yamazaki Prize Lecture on ‘The Quantum Muon’. The program was built around eight plenary keynote talks, covering a diverse range of subjects in condensed matter, materials and molecular sciences, where muon spectroscopy is making a significant contribution. Continuing a tradition started at a previous meeting, these contributions were selected from distinguished scientists who, while friends of µSR, are mostly active in complementary fields. The keynote talks were given by Catia Arbizzani (Bologna, energy materials), Bruce Gaulin (McMaster, spin liquids), Giacomo Ghiringhelli (Milano, strongly correlated electron systems), Reizo Kato (RIKEN, molecular materials), Ioan Pop (Karlsruhe, superconducting quantum circuits), Jorge Quintanilla (Kent, machine learning to analyse muon results), Roberta Sessoli (Florence, single molecule magnets) and Reiner Zorn (Jülich, dynamics of liquids, glasses and polymers).The 49 oral contributions presented during the conference were selected from the submitted abstracts. While many of these were related to the topics of the keynote talks, others extended the discussion to applications of muons in additional areas. Presentations were grouped into sessions covering topical subject areas such as Spin Liquids (seven), Strongly Correlated Electron systems (six), Superconductivity (eight), Energy Materials (five), Semiconductors (five), Molecular Chemistry (six), Site Calculations (five) and New Techniques (three). The conference also introduced a session on Muonic x-rays, with the four presentations covering areas such as cultural heritage and in-operando batteries. A further session was dedicated to six facility reports, testifying to the active developments going on at the established facilities and the progress of future ones. Three poster sessions accommodated 129 further contributions across a similar range of subjects, with an online forum catering for those who could not join us at the meeting. The ISMS awarded two prizes to young scientists for best oral and poster presentations, with three further poster prizes awarded to young scientists by the Conference. The meeting concluded with a Conference Summary talk by Tom Lancaster and a closing ceremony, the latter being led by the Conference Honorary Chair, Cesare Bucci.List of Conference Organisation and Sponsor lists and the confererence photograph are available in the pdf.

Non-destructive operando measurements of muonic x-rays on Li-ion battery

We have developed a non-destructive technique to observe Li in an electrode and metallic Li deposition on an anode using muonic x-rays. With high intent negative muon beam at J-PARC, we have attempted operando measurements of Li and metallic Li deposition in LIBs for the first time. Both increase and decrease of Li in a cathode during charging and discharging processes were observed. We also observed significant increase of muonic x-rays of Li with cycles, which may correspond to the degradation of charge capacity with the cycles.