Spin Transistor and Quantum Spin Hall Effects in CdBxF2-x - p-CdF2 - CdBxF2-x Sandwich Nanostructures

Planar CdBxF2-x - p-CdF2 - CdBxF2-x sandwich nanostructures prepared on the surface of the n-type CdF2 bulk crystal are studied to register the spin transistor and quantum spin Hall effects. The current-voltage characteristics of the ultra-shallow p+-n junctions verify the CdF2 gap, 7.8 eV, and the quantum subbands of the 2D holes in the p-type CdF2 quantum well confined by the CdBxF2-x delta-barriers. The temperature and magnetic field dependencies of the resistance, specific heat and magnetic susceptibility demonstrate the high temperature superconductor properties for the CdBxF2-x delta-barriers. The value of the superconductor energy gap, 102.06 meV, determined by the tunneling spectroscopy method appears to be in a good agreement with the relationship between the zero-resistance supercurrent in superconductor state and the conductance in normal state at the energies of the 2D hole subbands. The results obtained are evidence of the important role of the multiple Andreev reflections in the creation of the high spin polarization of the 2D holes in the edged channels of the sandwich device. The high spin hole polarization in the edged channels is shown to identify the mechanism of the spin transistor and quantum spin Hall effects induced by varying the top gate voltage, which is revealed by the first observation of the Hall quantum conductance staircase.Comment: 5 pages, 9 figure

SARS-CoV-2 Catalonia contact tracing program : evaluation of key performance indicators

Background: Guidance on SARS-CoV-2 contact tracing indicators have been recently revised by international public health agencies. The aim of the study is to describe and analyse contact tracing indicators based on Catalonia's (Spain) real data and proposing to update them according to recommendations. Methods: Retrospective cohort analysis including Catalonia's contact tracing dataset from 20 May until 31 December 2020. Descriptive statistics are performed including sociodemographic stratification by age, and differences are assessed over the study period. Results: We analysed 923,072 contacts from 301,522 SARS-CoV-2 cases with identified contacts (67.1% contact tracing coverage). The average number of contacts per case was 4.6 (median 3, range 1-243). A total of 403,377 contacts accepted follow-up through three phone calls over a 14-day quarantine period (84.5% of contacts requiring follow-up). The percentage of new cases declared as contacts 14 days prior to diagnosis evolved from 33.9% in May to 57.9% in November. All indicators significantly improved towards the target over time (p < 0.05 for all four indicators). Conclusions: Catalonia's SARS-CoV-2 contact tracing indicators improved over time despite challenging context. The critical revision of the indicator's framework aims to provide essential information in control policies, new indicators proposed will improve system delay's follow-up. The study provides information on COVID-19 indicators framework experience from country's real data, allowing to improve monitoring tools in 2021-2022. With the SARS-CoV-2 pandemic being so harmful to health systems and globally, is important to analyse and share contact tracing data with the scientific community

Boosting background suppression in the NEXT experiment through Richardson-Lucy deconvolution

Next-generation neutrinoless double beta decay experiments aim for half-life sensitivities of ~ 1027 yr, requiring suppressing backgrounds to &lt; 1 count/tonne/yr. For this, any extra background rejection handle, beyond excellent energy resolution and the use of extremely radiopure materials, is of utmost importance. The NEXT experiment exploits differences in the spatial ionization patterns of double beta decay and single-electron events to discriminate signal from background. While the former display two Bragg peak dense ionization regions at the opposite ends of the track, the latter typically have only one such feature. Thus, comparing the energies at the track extremes provides an additional rejection tool. The unique combination of the topology-based background discrimination and excellent energy resolution (1% FWHM at the Q-value of the decay) is the distinguishing feature of NEXT. Previous studies demonstrated a topological background rejection factor of ~ 5 when reconstructing electron-positron pairs in the 208Tl 1.6 MeV double escape peak (with Compton events as background), recorded in the NEXT-White demonstrator at the Laboratorio Subterráneo de Canfranc, with 72% signal efficiency. This was recently improved through the use of a deep convolutional neural network to yield a background rejection factor of ~ 10 with 65% signal efficiency. Here, we present a new reconstruction method, based on the Richardson-Lucy deconvolution algorithm, which allows reversing the blurring induced by electron diffusion and electroluminescence light production in the NEXT TPC. The new method yields highly refined 3D images of reconstructed events, and, as a result, significantly improves the topological background discrimination. When applied to real-data 1.6 MeV e-e+ pairs, it leads to a background rejection factor of 27 at 57% signal efficiency. [Figure not available: see fulltext.]. © 2021, The Author(s)

The NEXT White (NEW) detector

Conceived to host 5 kg of xenon at a pressure of 15 bar in the fiducial volume, the NEXT-White apparatus is currently the largest high pressure xenon gas TPC using electroluminescent amplification in the world. It is also a 1:2 scale model of the NEXT-100 detector for Xe-136 beta beta 0 nu decay searches, scheduled to start operations in 2019. Both detectors measure the energy of the event using a plane of photomultipliers located behind a transparent cathode. They can also reconstruct the trajectories of charged tracks in the dense gas of the TPC with the help of a plane of silicon photomultipliers located behind the anode. A sophisticated gas system, common to both detectors, allows the high gas purity needed to guarantee a long electron lifetime. NEXT-White has been operating since October 2016 at the Laboratorio Subterraneo de Canfranc (LSC), in Spain. This paper describes the detector and associated infrastructures, as well as the main aspects of its initial operation

Measurement of radon-induced backgrounds in the NEXT double beta decay experiment

The measurement of the internal 222Rn activity in the NEXT-White detector during the so-called Run-II period with 136Xe-depleted xenon is discussed in detail, together with its implications for double beta decay searches in NEXT. The activity is measured through the alpha production rate induced in the fiducial volume by 222Rn and its alpha-emitting progeny. The specific activity is measured to be (38.1 ± 2.2 (stat.) ± 5.9 (syst.)) mBq/m3. Radon-induced electrons have also been characterized from the decay of the 214Bi daughter ions plating out on the cathode of the time projection chamber. From our studies, we conclude that radon-induced backgrounds are sufficiently low to enable a successful NEXT-100 physics program, as the projected rate contribution should not exceed 0.1 counts/yr in the neutrinoless double beta decay sample

Electron drift properties in high pressure gaseous xenon

[EN] Gaseous time projection chambers (TPC) are a very attractive detector technology for particle tracking. Characterization of both drift velocity and di¿usion is of great importance to correctly assess their tracking capabilities. NEXT-White is a High Pressure Xenon gas TPC with electroluminescent ampli¿cation, a 1:2 scale model of the future NEXT-100detector, which will be dedicated to neutrinoless double beta decay searches. NEXT-White has been operating at Canfranc Underground Laboratory (LSC) since December2016. The drift parameters have been measured using 83mKr for a range of reduced drift ¿elds at two di¿erent pressure regimes, namely 7.2 bar and 9.1 bar. Theresults have been compared with Magboltz simulations. Agreement at the 5% level or better has been found for drift velocity, longitudinal di¿usion and transverse di¿usion.The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Sklodowska-Curie Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04, the Severo Ochoa Program SEV-2014-0398 and the Maria de Maetzu Program MDM-2016-0692; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT and FEDER through the program COMPETE, projects PTDC/FIS-NUC/2525/2014 and UID/FIS/04559/2013; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M) and de-sc0017721 (University of Texas at Arlington); and the University of Texas at Arlington. We also warmly acknowledge the Laboratorio Nazionale di Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coating of various parts of the NEXT-White TPC. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and supporting the NEXT experiment.Simon, A.; Felkai, R.; Martinez-Lema, G.; Monrabal, F.; Gonzalez-Diaz, D.; Sorel, M.; Hernando Morata, JA.... (2018). Electron drift properties in high pressure gaseous xenon. Journal of Instrumentation. 13. https://doi.org/10.1088/1748-0221/13/07/P07013S13Nygren, D. (2009). High-pressure xenon gas electroluminescent TPC for 0-ν ββ-decay search. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 603(3), 337-348. doi:10.1016/j.nima.2009.01.222Gómez Cadenas, J. J., Álvarez, V., Borges, F. I. G., Cárcel, S., Castel, J., Cebrián, S., … Dias, T. H. V. T. (2014). Present Status and Future Perspectives of the NEXT Experiment. Advances in High Energy Physics, 2014, 1-22. doi:10.1155/2014/907067Martín-Albo, J., Muñoz Vidal, J., Ferrario, P., Nebot-Guinot, M., Gómez-Cadenas, J. J., … Cárcel, S. (2016). Sensitivity of NEXT-100 to neutrinoless double beta decay. Journal of High Energy Physics, 2016(5). doi:10.1007/jhep05(2016)159Álvarez, V., Borges, F. I. G., Cárcel, S., Castel, J., Cebrián, S., Cervera, A., … Díaz, J. (2013). Initial results of NEXT-DEMO, a large-scale prototype of the NEXT-100 experiment. Journal of Instrumentation, 8(04), P04002-P04002. doi:10.1088/1748-0221/8/04/p04002Álvarez, V., Borges, F. I. G., Cárcel, S., Castel, J., Cebrián, S., Cervera, A., … Díaz, J. (2013). Operation and first results of the NEXT-DEMO prototype using a silicon photomultiplier tracking array. Journal of Instrumentation, 8(09), P09011-P09011. doi:10.1088/1748-0221/8/09/p09011Álvarez, V., Borges, F. I. G. M., Cárcel, S., Castel, J., Cebrián, S., Cervera, A., … Díaz, J. (2013). Near-intrinsic energy resolution for 30–662keV gamma rays in a high pressure xenon electroluminescent TPC. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 708, 101-114. doi:10.1016/j.nima.2012.12.123Ferrario, P., Laing, A., López-March, N., Gómez-Cadenas, J. J., Álvarez, V., … Cebrián, S. (2016). First proof of topological signature in the high pressure xenon gas TPC with electroluminescence amplification for the NEXT experiment. Journal of High Energy Physics, 2016(1). doi:10.1007/jhep01(2016)104Pack, J. L., Voshall, R. E., & Phelps, A. V. (1962). Drift Velocities of Slow Electrons in Krypton, Xenon, Deuterium, Carbon Monoxide, Carbon Dioxide, Water Vapor, Nitrous Oxide, and Ammonia. Physical Review, 127(6), 2084-2089. doi:10.1103/physrev.127.2084Pack, J. L., Voshall, R. E., Phelps, A. V., & Kline, L. E. (1992). Longitudinal electron diffusion coefficients in gases: Noble gases. Journal of Applied Physics, 71(11), 5363-5371. doi:10.1063/1.350555Bowe, J. C. (1960). Drift Velocity of Electrons in Nitrogen, Helium, Neon, Argon, Krypton, and Xenon. Physical Review, 117(6), 1411-1415. doi:10.1103/physrev.117.1411Patrick, E. L., Andrews, M. L., & Garscadden, A. (1991). Electron drift velocities in xenon and xenon‐nitrogen gas mixtures. Applied Physics Letters, 59(25), 3239-3240. doi:10.1063/1.105744English, W. N., & Hanna, G. C. (1953). GRID IONIZATION CHAMBER MEASUREMENTS OF ELECTRON DRIFT VELOCITIES IN GAS MIXTURES. Canadian Journal of Physics, 31(5), 768-797. doi:10.1139/p53-070Hunter, S. R., Carter, J. G., & Christophorou, L. G. (1988). Low-energy electron drift and scattering in krypton and xenon. Physical Review A, 38(11), 5539-5551. doi:10.1103/physreva.38.5539Kobayashi, S., Hasebe, N., Hosojima, T., Ishizaki, T., Iwamatsu, K., Mimura, M., … Ishizuka, A. (2006). Ratio of Transverse Diffusion Coefficient to Mobility of Electrons in High-Pressure Xenon and Xenon Doped with Hydrogen. Japanese Journal of Applied Physics, 45(10A), 7894-7900. doi:10.1143/jjap.45.7894Álvarez, V., Borges, F. I. G., Cárcel, S., Cebrián, S., Cervera, A., Conde, C. A. N., … Esteve, R. (2013). Ionization and scintillation response of high-pressure xenon gas to alpha particles. Journal of Instrumentation, 8(05), P05025-P05025. doi:10.1088/1748-0221/8/05/p05025Lorca, D., Martín-Albo, J., Laing, A., Ferrario, P., Gómez-Cadenas, J. J., Álvarez, V., … Cebrián, S. (2014). Characterisation of NEXT-DEMO using xenon KαX-rays. Journal of Instrumentation, 9(10), P10007-P10007. doi:10.1088/1748-0221/9/10/p10007Kusano, H., Lopes, J. A. M., Miyajima, M., & Hasebe, N. (2013). Longitudinal and transverse diffusion of electrons in high-pressure xenon. Journal of Instrumentation, 8(01), C01028-C01028. doi:10.1088/1748-0221/8/01/c01028Henriques, C. A. O., Freitas, E. D. C., Azevedo, C. D. R., González-Díaz, D., Mano, R. D. P., Jorge, M. R., … Álvarez, V. (2017). Secondary scintillation yield of xenon with sub-percent levels of CO2 additive for rare-event detection. Physics Letters B, 773, 663-671. doi:10.1016/j.physletb.2017.09.017Obert, E. F. (1948). Compressibility Chart and the Ideal Reduced Volume. Industrial & Engineering Chemistry, 40(11), 2185-2186. doi:10.1021/ie50467a036Agostinelli, S., Allison, J., Amako, K., Apostolakis, J., Araujo, H., Arce, P., … Barrand, G. (2003). Geant4—a simulation toolkit. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 506(3), 250-303. doi:10.1016/s0168-9002(03)01368-8González-Díaz, D., Monrabal, F., & Murphy, S. (2018). Gaseous and dual-phase time projection chambers for imaging rare processes. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 878, 200-255. doi:10.1016/j.nima.2017.09.024Álvarez, V., Borges, F. I. G. M., Cárcel, S., Castel, J., Cebrián, S., Cervera, A., … Díaz, J. (2014). Characterization of a medium size Xe/TMA TPC instrumented with microbulk Micromegas, using low-energy γ-rays. Journal of Instrumentation, 9(04), C04015-C04015. doi:10.1088/1748-0221/9/04/c0401

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

[EN] The "Neutrino Experiment with a Xenon Time-Projection Chamber" (NEXT) experiment intends to investigate the neutrinoless double beta decay of 136Xe, and therefore requires a severe suppression of potential backgrounds. An extensive material screening and selection process was undertaken to quantify the radioactivity of the materials used in the experiment. Separate energy and tracking readout planes using different sensors allow us to combine the measurement of the topological signature of the event for background discrimination with the energy resolution optimization. The design of radiopure readout planes, in direct contact with the gas detector medium, was especially challenging since the required components typically have activities too large for experiments demanding ultra-low background conditions. After studying the tracking plane, here the radiopurity control of the energy plane is presented, mainly based on gamma-ray spectroscopy using ultra-low background germanium detectors at the Laboratorio Subterráneo de Canfranc (Spain). All the available units of the selected model of photomultiplier have been screened together with most of the components for the bases, enclosures and windows. According to these results for the activity of the relevant radioisotopes, the selected components of the energy plane would give a contribution to the overall background level in the region of interest of at most 2.4 × 10¿4 counts per keV, kg and year, satisfying the sensitivity requirements of the NEXT experiment.Special thanks are due to LSC directorate and staff for their strong support for performing the measurements at the LSC Radiopurity Service. We are really grateful to Grzegorz Zuzel for the radon emanation measurements. The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04 and the Severo Ochoa Program SEV-2014-0398; the GVA of Spain under grant PROMETEO/2016/120; the Portuguese FCT and FEDER through the program COMPETE, project PTDC/FIS/103860/2008; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory) and DE-FG02-13ER42020 (Texas A & and the University of Texas at Arlington.Cebrian, S.; Perez, J.; Bandac, I.; Labarga, L.; Álvarez-Puerta, V.; Azevedo, CDR.; Benlloch-Rodriguez, JM.... (2017). Radiopurity assessment of the energy readout for the NEXT double beta decay experiment. Journal of Instrumentation. 12. https://doi.org/10.1088/1748-0221/12/08/T08003S12Avignone, F. T., Elliott, S. R., & Engel, J. (2008). Double beta decay, Majorana neutrinos, and neutrino mass. Reviews of Modern Physics, 80(2), 481-516. doi:10.1103/revmodphys.80.481Martín-Albo, J., Muñoz Vidal, J., Ferrario, P., Nebot-Guinot, M., Gómez-Cadenas, J. J., … Cárcel, S. (2016). Sensitivity of NEXT-100 to neutrinoless double beta decay. Journal of High Energy Physics, 2016(5). doi:10.1007/jhep05(2016)159Renner, J., Farbin, A., Vidal, J. M., Benlloch-Rodríguez, J. M., Botas, A., Ferrario, P., … Borges, F. I. G. (2017). Background rejection in NEXT using deep neural networks. Journal of Instrumentation, 12(01), T01004-T01004. doi:10.1088/1748-0221/12/01/t01004Dafni, T., Álvarez, V., Bandac, I., Bettini, A., Borges, F. I. G. M., Camargo, M., … Conde, C. A. N. (2016). Results of the material screening program of the NEXT experiment. Nuclear and Particle Physics Proceedings, 273-275, 2666-2668. doi:10.1016/j.nuclphysbps.2015.10.024Cebrián, S., Pérez, J., Bandac, I., Labarga, L., Álvarez, V., Barrado, A. I., … Cárcel, S. (2015). Radiopurity assessment of the tracking readout for the NEXT double beta decay experiment. Journal of Instrumentation, 10(05), P05006-P05006. doi:10.1088/1748-0221/10/05/p05006Wang, X., Chen, X., Fu, C., Ji, X., Liu, X., Mao, Y., … Zhang, T. (2016). Material screening with HPGe counting station for PandaX experiment. Journal of Instrumentation, 11(12), T12002-T12002. doi:10.1088/1748-0221/11/12/t12002Barrow, P., Baudis, L., Cichon, D., Danisch, M., Franco, D., Kaether, F., … Wulf, J. (2017). Qualification tests of the R11410-21 photomultiplier tubes for the XENON1T detector. Journal of Instrumentation, 12(01), P01024-P01024. doi:10.1088/1748-0221/12/01/p01024Busto, J., Gonin, Y., Hubert, F., Hubert, P., & Vuilleumier, J.-M. (2002). Radioactivity measurements of a large number of adhesives. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 492(1-2), 35-42. doi:10.1016/s0168-9002(02)01280-9Nisi, S., Di Vacri, A., Di Vacri, M. L., Stramenga, A., & Laubenstein, M. (2009). Comparison of inductively coupled mass spectrometry and ultra low-level gamma-ray spectroscopy for ultra low background material selection. Applied Radiation and Isotopes, 67(5), 828-832. doi:10.1016/j.apradiso.2009.01.02

A Compact Dication Source for Ba2+^{2+} Tagging and Heavy Metal Ion Sensor Development

We present a tunable metal ion beam that delivers controllable ion currents in the picoamp range for testing of dry-phase ion sensors. Ion beams are formed by sequential atomic evaporation and single or multiple electron impact ionization, followed by acceleration into a sensing region. Controllability of the ionic charge state is achieved through tuning of electrode potentials that influence the retention time in the ionization region. Barium, lead, and cobalt samples have been used to test the system, with ion currents identified and quantified using a quadrupole mass analyzer. Realization of a clean $\mathrm{Ba^{2+}}$ ion beam within a bench-top system represents an important technical advance toward the development and characterization of barium tagging systems for neutrinoless double beta decay searches in xenon gas. This system also provides a testbed for investigation of novel ion sensing methodologies for environmental assay applications, with dication beams of Pb$^{2+}$ and Cd$^{2+}$ also demonstrated for this purpose

Microscopic simulation of xenon-based optical TPCs in the presence of molecular additives

[EN] We introduce a simulation framework for the transport of high and low energy electrons in xenon-based optical time projection chambers (OTPCs). The simulation relies on elementary cross sections (electron-atom and electron-molecule) and incorporates, in order to compute the gas scintillation, the reaction/quenching rates (atom-atom and atom-molecule) of the first 41 excited states of xenon and the relevant associated excimers, together with their radiative cascade. The results compare positively with observations made in pure xenon and its mixtures with CO2 and CF4 in a range of pressures from 0.1 to 10 bar. This work sheds some light on the elementary processes responsible for the primary and secondary xenon-scintillation mechanisms in the presence of additives, that are of interest to the OTPC technology.DGD is supported by the Ramon y Cajal program (Spain) under contract number RYC-2015-18820. The authors want to acknowledge the RD51 collaboration for encouragement and support during the elaboration of this work, and in particular discussions with F. Resnati, A. Milov, V. Peskov, M. Suzuki and A. F. Borghesani. The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04 and the Severo Ochoa Program SEV-2014-0398; the GVA of Spain under grant PROM-ETEO/2016/120; the Portuguese FCT and FEDER through the program COMPETE, project PTDC/FIS-NUC/2525/2014 and UID/FIS/04559/2013; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory) and DE-FG02-13ER42020 (Texas A& and the University of Texas at Arlington.Azevedo, C.; Gonzalez-Diaz, D.; Biagi, SF.; Oliveira, CAB.; Henriques, CAO.; Escada, J.; Monrabal, F.... (2018). Microscopic simulation of xenon-based optical TPCs in the presence of molecular additives. Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment. 877:157-172. https://doi.org/10.1016/j.nima.2017.08.049S15717287