Rate of molecular transfer of allyl alcohol across an AOT surfactant layer using muon spin spectroscopy

The transfer rate of a probe molecule across the interfacial layer of a water-in-oil (w/o) microemulsion was investigated using a combination of Transverse Field muon spin rotation (TF- μSR), Avoided Level Crossing muon spin resonance (ALC-μSR) and Monte Carlo simulations. Reverse microemulsions consist of nanometer sized water droplets dispersed in an apolar solvent separated by a surfactant monolayer. Although the thermodynamic, static model of these systems has been well described, our understanding of their dynamics is currently incomplete. For example, what is the rate of solute transfer between the aqueous and apolar solvents, and how this is influenced by the structure of the interface? With an appropriate choice of system and probe molecule, µSR offers a unique opportunity to directly probe these interfacial transfer dynamics. Here, we have employed a well characterized w/o microemulsion stabilized by bis(2-ethylhexyl) sodium sulphosuccinate (Aerosol OT), with allyl alcohol (CH2=CH-CH2-OH, AA) as the probe. Resonances due to both muoniated radicals, CMuH2-C*H-CH2-OH and C*H2-CHMu-CH2-OH, were observed with the former being the dominant species. All resonances displayed solvent dependence, with those in the microemulsion observed as a single resonance located at intermediate magnetic fields to those present in either of the pure solvents. Observation of a single resonance is strong evidence for interfacial transfer being in the fast exchange limit. Monte-Carlo calculations of the ΔM=0 ALC resonances are consistent with the experimental data, indicating exchange rates greater than 109 s-1, placing the rate of interfacial transfer at the diffusion limit

Characterization of Cryogenic SiPM Down to 6,5 K

SiPM operation at very low temperatures has the potential to improve detector systems for experiments at cryogenic temperatures. We characterized electrical and optical properties of a commercially available cryogenic SiPM over a temperature range of 6.5–286 K, such as breakdown voltage, quenching resistance, gain, pulse waveform, photon detection efficiency and dark count rate. We observed a non-linear temperature dependence of the breakdown voltage and a small change of the pulse waveform at low temperatures. The SiPM gain and maximum allowed overvoltage decrease at low temperatures, however, stable operation down to 6.5 K has been demonstrated. Furthermore, the feasibility of assembling a detector with a plastic scintillator was studied

Molecular Dynamics in the Rod-like Liquid Crystal 4-(trans-4-Pentylcyclohexyl) Benzonitrile (PCH5) Probed by Muon Spin Resonance Spectroscopy

AbstractTwo types of muoniated spin probes were produced by the addition of muonium (Mu) to the phenyl ring of the rod-like liquid crystal 4-(trans-4-pentylcyclohexyl)benzonitrile (PCH5). Avoided level crossing muon spin resonance spec-troscopy was used to characterize the muoniated spin probes and to probe dynamics of PCH5 at the molecular level. The methylene proton hyperfine coupling constant (hfcc) of one of the muoniated spin probes shift in the nematic phase due to the dipolar hyperfine coupling, the ordering of the molecules along the applied magnetic field and fiuctuations about the local director. The amplitude of these fluctuations in PCH5 is determined from the temperature dependence of the methylene proton hfcc

Beam monitoring detectors for High Intensity Muon Beams

We present two novel beam monitors designed for use in current PSI muon beams and upgradable for the High Intensity Muon Beam (HIMB) project beamlines: the scintillating fibre (SciFi) detector, a grid of scintillating fibres coupled to SiPMs, and the MatriX detector, a matrix of plastic scintillators coupled to silicon photomultipliers (SiPMs), both detectors having particle ID capability. The advantage of these highly segmented detectors is the capability to withstand the high beam rate and to perform total beam rate measurements. Furthermore, the use of the SiPM as a photosensor enables operation of these detectors in high magnetic field environments (up to 1.25T). Both detectors have been tested in the beam at PSI and with continuous beam rates up to 108μ+/s. The performance of these detectors as measured on the beamlines are presented.ISSN:0168-9002ISSN:1872-957