Evaluation of turbulent dissipation rate retrievals from Doppler Cloud Radar

Turbulent dissipation rate retrievals from cloud radar Doppler velocity measurements are evaluated using independent, in situ observations in Arctic stratocumulus clouds. In situ validation data sets of dissipation rate are derived using sonic anemometer measurements from a tethered balloon and high frequency pressure variation observations from a research aircraft, both flown in proximity to stationary, ground-based radars. Modest biases are found among the data sets in particularly low- or high-turbulence regimes, but in general the radar-retrieved values correspond well with the in situ measurements. Root mean square differences are typically a factor of 4-6 relative to any given magnitude of dissipation rate. These differences are no larger than those found when comparing dissipation rates computed from tetheredballoon and meteorological tower-mounted sonic anemometer measurements made at spatial distances of a few hundred meters. Temporal lag analyses suggest that approximately half of the observed differences are due to spatial sampling considerations, such that the anticipated radar-based retrieval uncertainty is on the order of a factor of 2-3. Moreover, radar retrievals are clearly able to capture the vertical dissipation rate structure observed by the in situ sensors, while offering substantially more information on the time variability of turbulence profiles. Together these evaluations indicate that radar-based retrievals can, at a minimum, be used to determine the vertical structure of turbulence in Arctic stratocumulus clouds

Results of the material screening program of the NEXT experiment

[EN] The Neutrino Experiment with a Xenon TPC (NEXT), intended to investigate neutrinoless double beta decay, requires extremely low background levels. An extensive material screening and selection process to assess the radioactivity of components is underway combining several techniques, including germanium γ-ray spectrometry performed at the Canfranc Underground Laboratory; recent results of this material screening program are presented here.Dafni, T.; Álvarez-Puerta, V.; Bandac, I.; Bettini, A.; Borges, FIGM.; Camargo, M.; Carcel, S.... (2016). Results of the material screening program of the NEXT experiment. Nuclear and Particle Physics Proceedings. 273-275:2666-2668. https://doi.org/10.1016/j.nuclphysbps.2015.10.024S26662668273-27

An improved measurement of electron-ion recombination in high-pressure xenon gas

We report on results obtained with the NEXT-DEMO prototype of the NEXT-100 high-pressure xenon gas time projection chamber (TPC), exposed to an alpha decay calibration source. Compared to our previous measurements with alpha particles, an upgraded detector and improved analysis techniques have been used. We measure event-by-event correlated fluctuations between ionization and scintillation due to electron-ion recombination in the gas, with correlation coeffcients between -0.80 and -0.56 depending on the drift field conditions. By combining the two signals, we obtain a 2.8% FWHM energy resolution for 5.49 MeV alpha particles and a measurement of the optical gain of the electroluminescent TPC. The improved energy resolution also allows us to measure the specific activity of the radon in the gas due to natural impurities. Finally, we measure the average ratio of excited to ionized atoms produced in the xenon gas by alpha particles to be 0:561 0:045, translating into an average energy to produce a primary scintillation photon ofWex = (39:2 3:2) eV.This work was supported by the following agencies and institutions: the European Research Council under the Advanced Grant 339787-NEXT; the Ministerio de Economia y Competitividad of Spain under grants CONSOLIDER-Ingenio 2010 CSD2008-0037 (CUP), FPA2009-13697-C04 and FIS2012-37947-C04; the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231; and the Portuguese FCT and FEDER through the program COMPETE, project PTDC/FIS/103860/2008.Serra, L.; Sorel, M.; Alvarez, V.; Borges, FIG.; Camargo, M.; Carcel, S.; Cebrian, S.... (2015). An improved measurement of electron-ion recombination in high-pressure xenon gas. Journal of Instrumentation. 10:1-19. https://doi.org/10.1088/1748-0221/10/03/P03025S1191

Near-intrinsic energy resolution for 30-662 keV gamma rays in a high pressure xenon electroluminescent TPC

We present the design, data and results from the NEXT prototype for Double Beta and Dark Matter (NEXT-DBDM) detector, a high-pressure gaseous natural xenon electroluminescent time projection chamber (TPC) that was built at the Lawrence Berkeley National Laboratory. It is a prototype of the planned NEXT-100 136Xe neutrino-less double beta decay (0νββ) experiment with the main objectives of demonstrating near-intrinsic energy resolution at energies up to 662 keV and of optimizing the NEXT-100 detector design and operating parameters. Energy resolutions of ∼1% FWHM for 662 keV gamma rays were obtained at 10 and 15 atm and ∼5% FWHM for 30 keV fluorescence xenon X-rays. These results demonstrate that 0.5% FWHM resolutions for the 2,459 keV hypothetical neutrino-less double beta decay peak are realizable. This energy resolution is a factor 7 to 20 better than that of the current leading 0νββ experiments using liquid xenon and thus represents a significant advancement. We present also first results from a track imaging system consisting of 64 silicon photo-multipliers recently installed in NEXT-DBDM that, along with the excellent energy resolution, demonstrates the key functionalities required for the NEXT-100 0νββ search

Ionization and scintillation of nuclear recoils in gaseous xenon

Abstract Ionization and scintillation produced by nuclear recoils in gaseous xenon at approximately 14 bar have been simultaneously observed in an electroluminescent time projection chamber. Neutrons from radioisotope α-Be neutron sources were used to induce xenon nuclear recoils, and the observed recoil spectra were compared to a detailed Monte Carlo employing estimated ionization and scintillation yields for nuclear recoils. The ability to discriminate between electronic and nuclear recoils using the ratio of ionization to primary scintillation is demonstrated. These results encourage further investigation on the use of xenon in the gas phase as a detector medium in dark matter direct detection experiments.This work was supported by the following agencies and institutions: the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, and the National Energy Research Scientific Computing Center (NERSC), supported by the Office of Science of the U.S. Department of Energy, both under Contract no. DE-AC02-05CH11231; the European Research Council under the Advanced Grant 339787-NEXT; the Ministerio de Economia y Competitividad of Spain under Grants CONSOLIDER-Ingenio 2010 C5D2008-0037 (CUP), FPA2009-13697-004-04, FPA2009-13697-C04-01, FIS2012-37947-C04-01, FIS2012-37947-C04-02, FIS2012-37947-C04-03, and FIS2012-37947-C04-04; and the Portuguese FCT and FEDER through the program COMPETE, Projects PTDC/FIS/103860/2008 and PTDC/FIS/112272/2009. J. Renner acknowledges the support of a Department of Energy National Nuclear Security Administration Stewardship Science Graduate Fellowship, grant number DE-FC52-08NA28752.Renner, J.; Gehman, VM.; Goldschmidt, A.; Matis, HS.; Miller, T.; Nakajima, Y.; Nygren, D.... (2015). Ionization and scintillation of nuclear recoils in gaseous xenon. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 793:62-74. https://doi.org/10.1016/j.nima.2015.04.057S627479

Radiopurity assessment of the tracking readout for the NEXT double beta decay experiment

The Neutrino Experiment with a Xenon Time-Projection Chamber (NEXT) is intended to investigate the neutrinoless double beta decay of 136Xe, which requires a severe suppression of potential backgrounds; therefore, an extensive screening and selection process is underway to control the radio-purity levels of the materials to be used in the experimental set-up of NEXT. The detector design combines the measurement of the topological signature of the event for background discrimination with the energy resolution optimization. Separate energy and tracking readout planes are based on different sensors: photomultiplier tubes for calorimetry and silicon multi-pixel photon counters for tracking. The design of a radio pure tracking plane, in direct contact with the gas detector medium, was a challenge since the needed components have typically activities too large for experiments requiring ultra-low background conditions. Here, the radiopurity assessment of tracking readout components based on gamma-ray spectroscopy using ultra-low background germanium detectors at the Laboratorio Subterráneo de Canfranc (Spain) is described. According to the obtained results, radiopure enough printed circuit boards made of kapton and copper and silicon photomultipliers.We deeply acknowledge John Murphy and Carl Jackson from SensL Technologies Ltd for their efficient collaboration in the analysis of SiPMs. We very much thank also Vicenzo Mancini from SOMACIS company for the care in the development of radiopure kapton PCBs. Special thanks are due to LSC directorate and staff for their strong support for performing the measurements at the LSC Radiopurity Service. The NEXT Collaboration acknowledges funding support from the following agencies and institutions: the European Research Council under the Advanced Grant 339787-NEXT and the T-REX Starting Grant ref. ERC-2009-StG-240054 of the IDEAS program of the 7th EU Framework Program; the Spanish Ministerio de Economia y Competitividad under grants CONSOLIDER-Ingenio 2010 CSD2008-0037 (CUP), FPA2009-13697-C04-04, and FIS2012-37947-C04; the Director, Office of Science, Office of Basic Energy Sciences of the US DoE under Contract no. DE-AC02-05CH11231; and the Portuguese FCT and FEDER through the program COMPETE, Projects PTDC/FIS/103860/2008 and PTDC/FIS/112272/2009.Cebrian, S.; Perez, J.; Bandac, I.; Labarga, L.; Alvarez, V.; Barrado, AI.; Bettini, A.... (2015). Radiopurity assessment of the tracking readout for the NEXT double beta decay experiment. Journal of Instrumentation. 10:1-14. https://doi.org/10.1088/1748-0221/10/05/P05006S1141