The external detector method (EDM) is a widely used technique in fission track thermochronology (FTT) in which two different minerals are concomitantly employed: spontaneous tracks are observed in apatite and induced ones in the muscovite external detector. They show intrinsic differences in detection and etching properties that should be taken into account. In this work, new geometry factor values, g, in apatite, were obtained by directly measuring the r ed /r is ratios and independently determined [GQR] ed/is values through the measurement of projected lengths. Five mounts, two of which were large area prismatic sections and three samples composed of random-orientation pieces have been used to determine the g-values. A side effect of applying EDM is that the value of the initial confined induced fission track, L 0 , is not measured in routine analyses. The L 0 -value is an important parameter to quantify with good confidence the degree of annealing of the spontaneous fission tracks in unknown-age samples, and is essential for accurate thermal history modeling. The impact of using arbitrary L 0 -values on the inference of sample thermal history is investigated and discussed. The measurement of the L 0 -value for each sample to be dated using an extra irradiated apatite mount is proposed. This extra mount can be also used for determining the g value as an extension of the r ed / r is ratio method. Eight apatite samples from crystalline basement, with grains at random orientation, were used to determine the g-values. The results found are statistically in agreement with the values found for apatite samples (from Durango, Mexico) measured in prismatic section and also measured at random orientation. There was no observable variation in efficiency regarding crystal orientation, showing that it is relatively safe using non-prismatic grains, especially in samples with paucity of grains, as it is the case of most basin samples. Implications for the z-calibration and for the calibration of the direct (spectrometer-based) fission-track dating are also discussed.
The ARAPUCA is a novel concept for liquid argon scintillation light detection which has been proposed for the photon detection system of the Deep Underground Neutrino Experiment. The test in liquid argon of one of the first ARAPUCA prototypes is presented in this work, where the working principle is experimentally demonstrated. The prototype has an acceptance window of 9 cm 2 and is read-out by a single SiPM with active area of 0.36 cm 2 . Its global detection efficiency was estimated by exposing it to a 238 U α source and to cosmic rays and was found to be 1.15% ± 0.15%, in good agreement with the prediction of a detailed Monte Carlo simulation of the device. Several other ARAPUCA prototypes of bigger dimensions and read-out by arrays of SiPMs have been built and are actually under test. In particular 32 ARAPUCA cells have been installed inside the protoDUNE detector, which is being assembled at CERN and will be operated in the second half of 2018.
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