Muon capture in hydrogen and deuterium

We report on a new generation of muon lifetime experiments at PSI to measure the nuclear muon capture rate in hydrogen and deuterium with ≤1% accuracy. The goals are to determine in μp capture the induced pseudoscalar coupling g P predicted in HBchPT, and in μd capture the axial two-body current term L1A described by modern EFT's. For the μp experiment a hydrogen TPC was developed as active muon stop detector, surrounded by cylindrical wire chambers and a plastic hodoscope as electron detector. Ultra-high purity of the hydrogen isotope $^1H_1$ at levels below 10 − 8 was achieved with a specially developed gas circulation and purification system, and with a novel isotope separation column. About 2 ·1010 events were collected which are now in final analysis. Data from the first production run result in g P = 7.3 ± 1.1 in good agreement with theory. The μd experiment is in development. It requires measurements in ultra-pure, cold deuterium gas at ∼30K. For this we are constructing a new Cryo-TP

THz QCL - Based active imaging applied to composite materials diagnostic

This paper is a presentation of the recently developed researches at OLIMPES laboratory in the field of active imaging using THz Quantum Cascade Laser applied to composite materials diagnostic

THz QCL - Based active imaging applied to composite materials diagnostic

This paper presents a CW raster-scanning THz imaging setup, used to perform Non-Destructive Testing of Kevlar and carbon fibre samples. The setup uses a 2.5 THz Quantum Cascade Laser as a source. Delamination defect in a Kevlar sample was detected showing a sensitivity to laser polarization orientation. Detection of a break in a carbon/epoxy sample was also performed

Dynamic modeling of Terahertz Quantum cascade lasers

In this paper, the influence of the simplifications made in the four-equation-based set of rate equations describing the dynamic behavior of a Quantum Cascade Laser (QCL) is studied. Numerical simulations based on the set of four rate equations has been developed, enabling the theoretical study of the influence of different parameters on the direct modulation response of the laser. These equations have been then linearized in order to deduce a set of state system equations, which was written in a matrix formalism. Finally, an approximate second order transfer function has been derived with the linearized dependence of its times constant

THz absolute power measurement: A simple and reliable method

Achieving absolute power measurement is not so easy in the THz range. In this paper, we describe a simple method to perform power measurement no more expressed in a.u. but in Watt. For a 3.8 THz single-plasmon Quantum Cascade Laser, 28.8 mW peak power was measured with 12:1% relative uncertainty. The operating method described is not really a metrologic one but one that can be easily performed in every laboratory

THz QCL-based active imaging dedicated to non-destructive testing of composite materials used in aeronautics

This paper presents a CW raster-scanning THz imaging setup, used to perform Non-Destructive Testing of KevlarTMand carbon fibre samples. The setup uses a 2.5 THz Quantum Cascade Laser as a source. Delamination defect in a Kevlar sample was detected showing a sensitivity to laser polarization orientation. Detection of a break in a carbon/epoxy sample was also performed

Imagerie Terahertz Temps réel de petits objets

Dans cette étude, on utilise la faculté des ondes THz à traverser certains matériaux pour détecter des objets cachés de faibles dimensions. Notre application est ici orientée imagerie temps réel et présente l'avantage d’une détection directe à l'aide d’un montage relativement simple, basé sur un laser à cascade quantique et une caméra infrarouge

Observation of Long-Lived Muonic Hydrogen in the 2S State

The kinetic energy distribution of ground state muonic hydrogen atoms mu-p(1S) is determined from time-of-flight spectra measured at 4, 16, and 64 hPa H2 room-temperature gas. A 0.9 keV-component is discovered and attributed to radiationless deexcitation of long-lived mu-p(2S) atoms in collisions with H2 molecules. The analysis reveals a relative population of about 1%, and a pressure-dependent lifetime (e.g. (30.4 +21.4 -9.7) ns at 64 hPa) of the long-lived mu-p(2S) population, equivalent to a 2S-quench rate in mu-p(2S) + H2 collisions of (4.4 +2.1 -1.8) 10^11 s^-1 at liquid hydrogen density.Comment: 4 pages, 2 figures, accepted for publication in Physical Review Letter

Mid- and Far-Infrared Marker Bands of the Metal Coordination Sites of the Histidine Side Chains in the Protein Cu,Zn-Superoxide Dismutase

International audienceVibrational spectroscopy gives important information on the properties of ligand and metal–ligand bonds in metalloenzymes. Infrared spectroscopy is appealing for the study of metal active sites that are not amenable to Raman spectroscopy. We present a combined experimental and theoretical approach to analyze the mid- and far-IR spectra of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) as a probe of the histidine ligands. This metalloenzyme provides a unique model to identify specific IR signatures of metal–histidine coordination and to study their alterations as a function of the metal (copper/zinc), the copper valence state (+I/+II), the histidine coordination mode (Nτ and Nπ) and the histidine protonation state. DFT calculations combined with normal mode descriptions from potential energy distribution calculations were performed on two slightly different cluster models. Differences in the constraints at the side chain of one histidine Cu ligand sensibly modify the geometric parameters and vibrational properties. Electrochemically induced FTIR difference spectroscopy provided mid- and far-IR fingerprint spectra of the Cu protein in aqueous media that are sensitive to the redox state of the Cu centre at the active site. Comparisons of the DFT predictions with the experimental IR modes of the histidine ligands at the Cu,Zn-SOD active site showed that useful mid-IR markers of histidine Nτ and Nπ coordination were predicted with good accuracy. The DFT analysis further demonstrated a link between the ν(C4–C5) mode frequency of His46 and the specific properties of the His46–Cu bond in Cu,Zn-SOD. A combined theoretical and experimental approach on samples in H2O and 2H2O or 15N-labelled samples identified the contributions from the histidine side chain modes in the 669–629 cm–1 region