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Description
Gaseous detectors present advantages over solid-state competitors in applications where room temperature operation, large detection areas or volumes and low-cost are important assets. On the other hand, optical gaseous detectors based on electroluminescence (EL) amplification of the primary ionisation signal are highly competitive alternatives to those based on charge avalanche amplification, presenting much better energy resolution and much larger amplitude signal output, due to the additional amplification in the photosensor used for the EL readout. The electrons produced by the radiation interaction are driven towards a region where the electric field is large enough to promote signal amplification. The applied electric field in the scintillation region is only high enough to excite but not ionise the noble gas atoms by electron impact, producing a scintillation-pulse through atom de-excitation, the so-called electroluminescence, which is proportional to the number of electrons produced in the foremost interaction. The statistical fluctuations inherent to the EL processes are much less than those associated to the avalanche ionisation processes, and even fewer than those associated to the charge produced by the radiation interaction. In addition, EL readout through a photosensor has the advantage of electrically decoupling the amplification region from the photosensor, rendering more immunity to electronic noise, radio-frequency pickup and high voltage discharges. For instance, high-pressure or dual-phase time projection chambers (TPCs) based on electroluminescence have gained increasing importance during the last decade due to their application to rare-event detection such as dark matter, double-beta decay and double-electron capture, being xenon and argon the most studied detection media.
Krypton has a radioactive isotope, which disfavours its use in rare-event applications. Nevertheless, Kr is much less expensive, is denser than Ar, and presents even the highest absorption cross section for x-rays in the 14–34 keV energy range, when compared to Xe. These are advantages when large detection volumes and/or high-pressure are requirements and in specific applications where its natural radioactive background will not seriously affect its operation due to the high intensity of incident radiation, like in some x- and gamma-ray spectrometry applications, or the possibility of efficient background discrimination in rare-event detection. Kr detectors have been already proposed for double-beta decay and double electron-capture detection.
The El yield of Xe and Ar have been determined both experimentally and by simulation while for Kr only simulation results are present in the literature. In this work, we present absolute measurements for the EL yield in Kr, using the same methodology as used for Xe and Ar. The simulation results are in agreement with the obtained experimental results.
