Polarization transfer to a bound proton in polarized electron knock-out reactions, A(e→,e′p→), is a powerful tool to look for an in-medium modification of the bound proton. It requires comparison to ...calculations that consider the many-body effects accompanying the quasi-free process. We report here measured components Px′, Pz′, and their ratio Px′/Pz′, of polarization transfer to protons bound in Ca40, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations that cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio GE/GM. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, (Px′/Pz′)A/(Px′/Pz′)H, and its dependence on the bound-proton virtuality.
A cryogenic supersonic gas jet target was developed for the MAGIX experiment at the high-intensity electron accelerator MESA. It will be operated as an internal, windowless target in the ...energy-recovering recirculation arc of the accelerator with different target gases, e.g., hydrogen, deuterium, helium, oxygen, argon, or xenon. Detailed studies have been carried out at the existing A1 multi-spectrometer facility at the electron accelerator MAMI. This paper focuses on the developed handling procedures and diagnostic tools, and on the performance of the gas jet target under beam conditions. Considering the special features of this type of target, it proves to be well suited for a new generation of high-precision electron scattering experiments at high-intensity electron accelerators.
A highly segmented neutron polarimeter for A1 Spreckels, R.; Hoek, M.; Müller, U. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2024, Volume:
1062
Journal Article
Peer reviewed
Open access
A new neutron polarimeter for measuring the neutron’s electric form factor was designed and constructed to complement the A1 spectrometer setup at the Mainz Microtron (MAMI). The design is based on a ...previous polarimeter with significant improvements to halve the error of the extracted form factor. A higher granularity of the polarimeter sections and a deeper first section on the one hand, and a faster readout employing Time-over-Threshold methods to measure the signal amplitudes combined with a high-precision FPGA-based TDC on the other hand will allow to achieve this goal. The performance of the new polarimeter during a first measurement campaign in 2019 using liquid hydrogen and deuterium targets will be discussed.
The MAGIX experiment is a versatile system optimized for low-energy nuclear and particle physics measurements. The setup is currently under development and will be installed at the MESA electron ...accelerator, at the Institute for Nuclear Physics of the University of Mainz. The main detectors of that experiment are a couple of high-precision magnetic spectrometers, each of them equipped with a GEM-based TPC at the focal plane to achieve a momentum resolution and angular resolution at the scattering vertex respectively of ≈δPP<10−4and≈1 1 mrad on scattered electron momenta between 1 MeV/c and 105 MeV/c. The limiting factor to achieve those results is the amount and uniformity of the material before the focal plane and even the presence of the TPC field cage can be relevant. Therefore we developed, and hereby introduce, an open field-cage TPC to fulfil those challenging requirements.
Using Fourier transform electron paramagnetic resonance (FT EPR), the radicals generated by the oxidation of 1-methylthymine were detected in the nanosecond time scale. The radicals were generated ...via triplet-sensitized electron transfer to anthraquinone-2,6-disulfonic acid in aqueous solution with laser photolysis at 308 nm. Both radicals show strong chemically induced dynamic electron polarization (CIDEP) by the triplet mechanism. This strong enhancement of the FT EPR intensity enabled the radical cation of 1-methylthymine to be detected in the nanosecond time scale at a low pH. The transformation of the radical cation to the N3-deprotonated successor radical was directly observed in the microsecond time scale. After a few microseconds, additional successor radicals of the primary radical cation were measured depending on the pH, and the radicals formed by the addition of OH- and/or PO4 3- at C6 of the radical cation were detected.
The light collection of several fiber configurations embedded in a box-shaped plastic scintillating counter was studied by scanning with minimum ionizing electrons. The light was read out by silicon ...photomultipliers at both ends. The light yield produced by the 855-MeV beam of the Mainz Microtron showed a strong dependence on the transverse distance from the beam position to the fibers. The observations were modeled by attributing the collection of indirect light inside of the counter and of direct light reaching a fiber to the total light yield. The light collection with fibers was compared to that of a scintillating counter without fibers. These studies were carried out within the development of plastic scintillating detectors as an active veto system for the DarkMESA electron beam-dump experiment that will search for light dark matter particles in the MeV mass range.
Using laser photolysis at 308 nm and FT–EPR, the triplet sensitized electron transfer from thymine to 9,10-anthraquinone-2,6-disulfonate in aqueous solution was studied. The anthraquinone radical ...anion and the deprotonated thymine-1-yl radical are spin-polarized by the CIDEP triplet mechanism and radical pair mechanism. The structure of the anthraquinone radical anion is strongly influenced by the pH of the solution. In weak acidic solution the radical anion dominates whereas the p
K of the radical protonation was determined to be 3.2. The deprotonated thymine-1-yl radical shows two different radical pair polarization patterns which are distinguished by the phase of the polarization. This unusual behavior can be attributed to two different states in the primary radical pair.
Using nanosecond laser photolysis with 308 nm and Fourier transform EPR spectroscopy, the pyrimidine radicals (thymine, uracil and 6-methyluracil) generated by electron transfer from the pyrimidine ...ground state to spin-polarized anthraquinone-2,6-disulfonate (2,6-AQDS) triplets were studied. The pyrimidine radical cations decay by deprotonation at the N(1) position to the neutral pyrimidine-1-yl radical. No other reaction channel could be found. The rate constant of the electron transfer could be estimated from the triplet spin-polarization (CIDEP) of the 2,6-AQDS radical anions to:
k
et(thymine) = 4.1 × 10
9 M
−1 s
−1,
k
et(uracil) = 2.4 × 10
9 M
−1 s
−1 and
k
et(6-methyluracil) = 4.5 × 10
9 M
−1 s
−1.
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