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Register a new userA liquid xenon ionization chamber in an all-fluoropolymer vessel
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A novel technique has been developed to build vessels for liquid xenon ionization detectors entirely out of ultra-clean fluoropolymer. We describe the advantages in terms of low radioactivity contamination, provide some details of the construction techniques, and show the energy resolution achieved with a prototype all-fluoropolymer ionization detector.
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Scintillation light produced in liquid xenon (LXe) by alpha particles, electrons and gamma-rays was detected with a large area avalanche photodiode (LAAPD) immersed in the liquid. The alpha scintillation yield was measured as a function of applied electric field. We estimate the quantum efficiency of the LAAPD to be 45%. The best energy resolution from the light measurement at zero electric field is 7.5%(sigma) for 976 keV internal conversion electrons from Bi-207 and 2.6%(sigma) for 5.5 MeV alpha particles from Am-241. The detector used for these measurements was also operated as a gridded ionization chamber to measure the charge yield. We confirm that using a LAAPD in LXe does not introduce impurities which inhibit the drifting of free electrons.
nEXO is a proposed tonne-scale neutrinoless double beta decay ($0 ubetabeta$) experiment using liquid ${}^{136}Xe$ (LXe) in a Time Projection Chamber (TPC) to read out ionization and scintillation signals. Between the field cage and the LXe vessel, a layer of LXe (skin LXe) is present, where no ionization signal is collected. Only scintillation photons are detected, owing to the lack of optical barrier around the field cage. In this work, we show that the light originating in the skin LXe region can be used to improve background discrimination by 5% over previous published estimates. This improvement comes from two elements. First, a fraction of the $gamma$-ray background is removed by identifying light from interactions with an energy deposition in the skin LXe. Second, background from ${}^{222}Rn$ dissolved in the skin LXe can be efficiently rejected by tagging the $alpha$ decay in the ${}^{214}Bi-{}^{214}Po$ chain in the skin LXe.
We present a detector apparatus, DireXeno (DIRectinal Xenon), designed to measure the spatial and temporal properties of scintillation in liquid xenon to very high accuracy. The properties of scintillation are of primary importance for dark matter and neutrinoless double beta decay experiments, however the complicated microphysics involved limits theoretical predictions. We will explore the possibility that scintillation emission exhibits correlation in light emission such as super-radiance, which depends on the type of interaction. Such properties of scintillation light may open a new window for background rejection as well as directionality measurements. We present the technical design and the concepts driving it, and demonstrate that statistical treatment will enable detecting anisotropy of as little as 10% of the photons. We show results from commissioning runs in which the detector operated for over 44 days in stable conditions. The time resolution for individual photons in different PMTs was measured to be $lesssim1.3$ ns FWHM, corresponding to $lesssim0.55$ ns (1 $sigma$).
Measurements of electron drift properties in liquid and gaseous xenon are reported. The electrons are generated by the photoelectric effect in a semi-transparent gold photocathode driven in transmission mode with a pulsed ultraviolet laser. The charges drift and diffuse in a small chamber at various electric fields and a fixed drift distance of 2.0 cm. At an electric field of 0.5 kV/cm, the measured drift velocities and corresponding temperature coefficients respectively are $1.97 pm 0.04$ mm/$mu$s and $(-0.69pm0.05)$%/K for liquid xenon, and $1.42 pm 0.03$ mm/$mu$s and $(+0.11pm0.01)$%/K for gaseous xenon at 1.5 bar. In addition, we measure longitudinal diffusion coefficients of $25.7 pm 4.6$ cm$^2$/s and $149 pm 23$ cm$^2$/s, for liquid and gas, respectively. The quantum efficiency of the gold photocathode is studied at the photon energy of 4.73 eV in liquid and gaseous xenon, and vacuum. These charge transport properties and the behavior of photocathodes in a xenon environment are important in designing and calibrating future large scale noble liquid detectors.
The design, construction and performance characteristics of a simple axial-field ionization chamber suitable for identifying ions in a radioactive beam are presented. Optimized for use with low-energy radioactive beams (< 5 MeV/A) the detector presents only three 0.5 $mu$m/cm$^2$ foils to the beam in addition to the detector gas. A fast charge sensitive amplifier (CSA) integrated into the detector design is also described. Coupling this fast CSA to the axial field ionization chamber produces an output pulse with a risetime of 60-70 ns and a fall time of 100 ns, making the detector capable of sustaining a relatively high rate. Tests with an $alpha$ source establish the detector energy resolution as $sim$8 $%$ for an energy deposit of $sim$3.5 MeV. The energy resolution with beams of 2.5 and 4.0 MeV/A $^{39}$K ions and the dependence of the energy resolution on beam intensity is measured. At an instantaneous rate of 3 x 10$^5$ ions/s the energy resolution has degraded to 14% with a pileup of 12%. The good energy resolution of this detector at rates up to 3 x 10$^5$ ions/s makes it an effective tool in the characterization of low-energy radioactive beams.
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