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Register a new userDevelopment of the MICROMEGAS Detector for Measuring the Energy Spectrum of Alpha Particles by using a 241-Am Source
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We have developed MICROMEGAS (MICRO MEsh GASeous) detectors for detecting {alpha} particles emitted from an 241-Am standard source. The voltage applied to the ionization region of the detector is optimized for stable operation at room temperature and atmospheric pressure. The energy of {alpha} particles from the 241-Am source can be varied by changing the flight path of the {alpha} particle from the 241 Am source. The channel numbers of the experimentally-measured pulse peak positions for different energies of the {alpha} particles are associated with the energies deposited by the alpha particles in the ionization region of the detector as calculated by using GEANT4 simulations; thus, the energy calibration of the MICROMEGAS detector for {alpha} particles is done. For the energy calibration, the thickness of the ionization region is adjusted so that {alpha} particles may completely stop in the ionization region and their kinetic energies are fully deposited in the region. The efficiency of our MICROMEGAS detector for {alpha} particles under the present conditions is found to be ~ 97.3 %.
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The response of a position-sensitive Li-glass scintillator detector to $alpha$-particles from a collimated $^{241}$Am source scanned across the face of the detector has been measured. Scintillation light was read out by an 8 X 8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector.
Micromegas is a type of micro-pattern gaseous detector currently under R&D for applications in rare event search experiments. Here we report the performance of a Micromegas structure constructed with a micromesh thermo-bonded to a readout plane, motivated by its potential application in two-phase xenon detectors for dark matter and neutrinoless double beta decay experiments. The study is carried out in pure xenon at room temperature. Measurements with alpha particles from the Americium-241 source showed that gas gains larger than 200 can be obtained at xenon pressure up to 3 atm. Gamma rays down to 8 keV were observed with such a device.
The latest Micromesh Gas Amplification Structures (Micromegas) are achieving outstanding energy resolution for low energy photons, with values as low as 11% FWHM for the 5.9 keV line of $^{55}$Fe in argon/isobutane mixtures at atmospheric pressure. At higher energies (MeV scale), these measurements are more complicated due to the difficulty in confining the events in the chamber, although there is no fundamental reason why resolutions of 1% FWHM or below could not be reached. There is much motivation to demonstrate experimentally this fact in Xe mixtures due to the possible application of Micromegas readouts to the Double Beta Decay search of $^{136}$Xe, or in other experiments needing calorimetry and topology in the same detector. In this paper, we report on systematic measurements of energy resolution with state-of-the-art Micromegas using a 5.5 MeV alpha source in high pressure Ar/isobutane mixtures. Values as low as 1.8% FWHM have been obtained, with possible evidence that better resolutions are achievable. Similar measurements in Xe, of which a preliminary result is also shown here, are under progress.
A MICROMEGAS detection amplifier has been incorporated into the design of the TAMU MDM focal plane detector with the purpose of improving the energy resolution and thus, the particle identification. Beam tests showed a factor of 2 improvement over the original design, from 10-12% to 4-6%, for ions with A<40 at E/A around 10-20 MeV.
We have developed a novel detector, referred to as an $alpha$-ToF detector, for correlated measurements of atomic masses and decay properties of low-yield, short-lived radioactive isotopes using a multi-reflection time-of-flight mass spectrograph. By correlating measured time-of-flight signals with decay events, it will be possible to suppress background events and obtain accurate, high-precision mass values even in cases of very low event rates. An offline test of the $alpha$-ToF detector has shown that the time-of-flight detection efficiency for 5.48~MeV $alpha$-rays is more than 90% and yields a time resolution of 251.5(68)~ps and an energy resolution of 141.1(9)~keV. Using a two-dimensional spectrum of the correlated $alpha$-ray energy and time-of-flight, the $alpha$-rays from mixed $alpha$ sources could be fairly well resolved.
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