Characterization of a continuous muon source for the Muon-Induced X-ray Emission (MIXE) Technique

The toolbox for material characterization has never been richer than today. Great progress with all kinds of particles and interaction methods provide access to nearly all properties of an object under study. However, a tomographic analysis of the subsurface region remains still a challenge today. In this regard, the Muon-Induced X-ray Emission (MIXE) technique has seen rebirth fueled by the availability of high intensity muon beams. We report here a study conducted at the Paul Scherrer Institute (PSI). It demonstrates that the absence of any beam time-structure leads to low pile-up events and a high signal-to-noise ratio (SNR) with less than one hour acquisition time per sample or data point. This performance creates the perspective to open this technique to a wider audience for the routine investigation of non-destructive and depth-sensitive elemental compositions, for example in rare and precious samples. Using a hetero-structured sample of known elements and thicknesses, we successfully detected the characteristic muonic X-rays, emitted during the capture of a negative muon by an atom, and the gamma-rays resulting from the nuclear capture of the muon, characterizing the capabilities of MIXE at PSI. This sample emphasizes the quality of a continuous beam, and the exceptional SNR at high rates. Such sensitivity will enable totally new statistically intense aspects in the field of MIXE, e.g. elemental 3D-tomography and chemical analysis. Therefore, we are currently advancing our proof-of-concept experiments with the goal of creating a full fledged permanently operated user station to make MIXE available to the wider scientific community as well as industry

Studies of muonic 185,187Re, 226Ra, and 248Cm for the extraction of nuclear charge radii

This thesis was conducted in the context of the muX collaboration, which aims to determine for the first time the absolute nuclear charge radius of 226Ra employing the muonic atom spectroscopy method. Radium constitutes a good candidate for measurements of atomic parity violation (APV) which serves as a sensitive probe to search for new physics. The interpretation of such an APV experiment in radium and the extraction of the fundamental underlying parameters requires the knowledge of its nuclear charge radius with a precision of 0.2 %. Having developed the analysis and experimental techniques that enable the measurement of radium, 248Cm was studied in a first step as the heaviest and largest nucleus ever probed with muons. Nuclear charge radii can be precisely measured using muonic atom spectroscopy. With the muons being 207 times heavier than electrons, the low-lying muonic wave functions extensively overlap with the nuclear charge distribution. As a result, the muonic levels exhibit high sensitivity to the nuclear properties, which in turn can be determined by measuring the energies of emitted muonic x rays with High Purity Germanium (HPGe) detectors. The traditional muonic atom spectroscopy method has been heavily used in the past decades to determine the nuclear charge radii of almost all stable and a few unstable atoms. The formation of muonic atoms is traditionally realized by stopping a negative muon beam in macroscopic targets of O(100 mg). However, only microgram quantities are nowadays typically permitted in experimental facilities for open radioactive targets such as radium and curium, for which the direct muon stops cannot be realized. The muX collaboration has developed a technique that employs subsequent transfer reactions of the muon inside a vessel filled with 100 bar of hydrogen and per mill admixtures of deuterium gas, enabling the measurement of radioactive targets with microgram masses. As the last stable element with a yet unmeasured nuclear charge radius, the measurement of isotopically pure 185Re and 187Re was pursued prior to the radioactive targets. First, the spectroscopic quadrupole moments of rhenium are extracted from the analysis of the 5 → 4 muonic transitions as Q(185Re) = 2.07(5) b and Q(187Re) = 1.94(5) b. In a next step, the determination of the nuclear charge radius from the analysis of the 2p → 1s muonic transitions was undertaken. The preliminary charge radii are R(185Re) = 5.297(2)stat(6)sys fm and R(187Re) = 5.288(2)stat(4)sys fm. Improved and more complete theoretical input outside of the scope of this thesis is still needed to conclude the analysis and provide final absolute charge radii for these two isotopes. The measurement of the 226Ra and 248Cm isotopes was conducted in 2019 with a 1.35 μg and 15.46 μg target, respectively. Due to the low efficiency of the HPGe detectors at the 2p → 1s muonic x-ray energies, various methods are employed to improve the signal-to-background ratio. Despite the efforts, no muonic transitions are observed in radium and an additional attempt needs to be undertaken in the near future. On the other hand, the 2p → 1s transitions are clearly observed in curium. The nuclear charge radius and quadrupole moment determined from the analysis of the curium hyperfine transitions are R = 5.9455(1)stat(117)sys fm and Q = 12.003(8)stat(361)sys b. With a further revision of the theory and a combined analysis with higher muonic x-ray transitions, the current dominant sources of systematic effects are expected to be significantly reduced in the future

Study of nuclear properties with muonic atoms

Muons are a fascinating probe to study nuclear properties. Muonic atoms can easily be formed by stopping negative muons inside a material. The muon is subsequently captured by the nucleus and, due to its much higher mass compared to the electron, orbits the nucleus at very small distances. During this atomic capture process, the muon emits characteristic X-rays during its cascade down to the ground state. The energies of these X-rays reveal the muonic energy level scheme, from which properties like the nuclear charge radius or its quadrupole moment can be extracted. While almost all stable elements have been examined using muons, probing highly radioactive atoms has so far not been possible. The muX experiment has developed a technique based on transfer reaction inside a high-pressure hydrogen/deuterium gas cell to examine targets available only in microgram quantities.ISSN:2190-544

Proton Direct Ionization in Sub-Micron Technologies : Test Methodologies and Modelling

Two different low energy proton (LEP) test methods, one with quasi-monoenergetic and the other with very wide proton beam energy spectra, have been studied. The two test methodologies have been applied to devices that were suggested from prior heavy-ion tests to be sensitive to proton direct ionization (PDI). The advantages and disadvantages of the two test methods are discussed. The test method using quasi-monoenergetic beams requires device preparation and high energy resolution beams, but delivers results that can be interpreted directly and can be used in various soft error rate (SER) calculation methods. The other method, using a heavily degraded high energy proton beam, requires little to no device preparation but more efforts on the beam characterization, and is confined to a specific SER method. While both methods deliver comparable estimates on the SER, the relatively complex determination of the beam characteristics in the degraded beam method makes it less straightforward to use. This work furthers presents a method to extract PDI sensitive volume parameters from degraded high energy proton beam cross-section data. This method extends the use of a previously published method to the degraded high energy beam LEP testing method.peerReviewe

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 ϵE=0.11% and an energy resolution of σE =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.ISSN:0034-6748ISSN:1089-762

Room-temperature emission of muonium from aerogel and zeolite targets

Novel emitters of muonium (Mu = μ+ + 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 (pμ = 11–13 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 ± 0.05(stat)+1.06 −0.76(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 converte.ISSN:1094-1622ISSN:0556-2791ISSN:1050-294

The non-destructive investigation of a late antique knob bow fibula (Bügelknopffibel) from Kaiseraugst/CH using Muon Induced X-ray Emission (MIXE)

A knob bow fibula (Bügelknopffibel) of the Leutkirch type, which typologically belongs to the second half of the 4th and early 5th century CE, was excavated in 2018 in the Roman city of Augusta Raurica, present-day Kaiseraugst (AG, Switzerland). This was analyzed for the first time for its elemental composition by using the non-destructive technique of Muon Induced X-ray Emission (MIXE) in the continuous muon beam facility at the Paul Scherrer Institute (PSI). In the present work, the detection limit is 0.4 wt% with ∼ 1.5 hours of measurement time. The fibula was measured at six different positions, at a depth of 0.3–0.4 mm inside the material. The experimental results show that the fibula is made of bronze, containing the main elements copper (Cu), zinc (Zn), tin (Sn) and lead (Pb). The compositional similarities/differences between different parts of the fibula reveal that it was manufactured as two “workpieces”. One workpiece consists of the knob (13.0±0.6 wt% Pb), bow (11.9±0.4 wt% Pb) and foot (12.5 ± 0.9 wt% Pb). These show a higher Pb content, suggesting a cast bronze. The spiral (3.2 ± 0.2 wt% Pb), which is part of the other workpiece, has a comparatively lower Pb content, suggesting a forged bronze.ISSN:2050-744

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

International audiencePrecision studies of the properties of nuclei are essential both for understanding nuclear physics at low energy, and for confronting experiment and theory in simple atomic systems. Such comparisons advance our 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 RMS charge radius. The radii of the lightest nuclei ($Z=1,2$) have been determined with high accuracy via laser spectroscopy in muonic atoms, while those of medium mass and above, from X-ray spectroscopy with semiconductor detectors. In this communication we present a new experiment aiming at precision measurements of the radii of light nuclei $3 \leq Z \leq 10$ via single-photon energy measurements with cryogenic microcalorimeters; a quantum sensing technology capable of high efficiency and outstanding resolution for low-energy X-rays

Characterization of a Continuous Muon Source for the Non-Destructive and Depth-Selective Elemental Composition Analysis by Muon Induced X-and Gamma-rays

The toolbox for material characterization has never been richer than today. Great progress with all kinds of particles and interaction methods provide access to nearly all properties of an object under study. However, a tomographic analysis of the subsurface region remains still a challenge today. In this regard, the Muon Induced X-ray Emission (MIXE) technique has seen rebirth fueled by the availability of high intensity muon beams. We report here a study conducted at the Paul Scherrer Institute (PSI). It demonstrates that the absence of any beam time-structure leads to low pile-up events and a high signal-to-noise ratio (SNR) with less than one hour acquisition time per sample or data point. This performance creates the perspective to open this technique to a wider audience for the routine investigation of non-destructive and depth-sensitive elemental compositions, for example in rare and precious samples. Using a hetero-structured sample of known elements and thicknesses, we successfully detected the characteristic muonic X-rays, emitted during the capture of a negative muon by an atom, and the gamma-rays resulting from the nuclear capture of the muon, characterizing the capabilities of MIXE at PSI. This sample emphasizes the quality of a continuous beam, and the exceptional SNR at high rates. Such sensitivity will enable totally new statistically intense aspects in the field of MIXE, e.g., elemental 3D-tomography and chemical analysis. Therefore, we are currently advancing our proof-of-concept experiments with the goal of creating a full fledged permanently operated user station to make MIXE available to the wider scientific community as well as industry.</p

Characterization of a continuous muon source for the Muon-Induced X-ray Emission (MIXE) Technique

The toolbox for material characterization has never been richer than today. Great progress with all kinds of particles and interaction methods provide access to nearly all properties of an object under study. However, a tomographic analysis of the subsurface region remains still a challenge today. In this regard, the Muon-Induced X-ray Emission (MIXE) technique has seen rebirth fueled by the availability of high intensity muon beams. We report here a study conducted at the Paul Scherrer Institute (PSI). It demonstrates that the absence of any beam time-structure leads to low pile-up events and a high signal-to-noise ratio (SNR) with less than one hour acquisition time per sample or data point. This performance creates the perspective to open this technique to a wider audience for the routine investigation of non-destructive and depth-sensitive elemental compositions, for example in rare and precious samples. Using a hetero-structured sample of known elements and thicknesses, we successfully detected the characteristic muonic X-rays, emitted during the capture of a negative muon by an atom, and the gamma-rays resulting from the nuclear capture of the muon, characterizing the capabilities of MIXE at PSI. This sample emphasizes the quality of a continuous beam, and the exceptional SNR at high rates. Such sensitivity will enable totally new statistically intense aspects in the field of MIXE, e.g. elemental 3D-tomography and chemical analysis. Therefore, we are currently advancing our proof-of-concept experiments with the goal of creating a full fledged permanently operated user station to make MIXE available to the wider scientific community as well as industry