In this paper, we calculate the gravitational acceleration by using simple pendulums within the designated World Pendulum Alliance: a network constituted by fourteen institutions in eight countries, each provided by a pendulum that can be accessed remotely via the Internet. As a pedagogical option for remote laboratory experiences, we show how to access them and measure the pendulum's period for $N$ oscillations. We discuss the role of the repetitions and samples to minimize the experimental uncertainty, and by using the averaged value of the period, we compute the gravitational acceleration locally. Also, we present the corrections due to the moment of inertia of the system. Finally, by taking into account the geographical location of each pendulum, we report gravity's dependence on latitude, longitude, and altitude by discussing the implications on the Earth's shape. We hope this tool will be helpful for introductory and university physics courses due to its remote access features and its relation to fundamental concepts.

The teaching of physics in virtual and distance higher education has always presented challenges due to the high rate of non-approval (>30%) and dropout rates (>10%). Information and communication technologies have allowed the development and creation of digital resources that allow students to be given other types of tools that improve the teaching-learning process. As a consequence, remote and virtual laboratories have gained importance as a complement in the teaching of concepts and skills in experimentation. In the same way, the digital spaces created based on Inquiry Learning have led students to have a greater understanding of concepts. This paper presents the result of the pedagogical implementation and creation path of an inquiry-based learning space (ILS) in Go- Lab. The educational tool was applied in the General Physics course offered to distance in engineering students of the Universidad Nacional Abierta y a Distancia within the framework of the World Pendulum Alliance (WP@ELAB) project. The results show that of the 345 students who made use of the resource, 234 approved the activity, which implies 68% of the sample. In addition, the qualitative analyzes of the students' appreciation of the use of technology in science still show gaps in terms of lack of knowledge in technology and internet coverage.

With the evolution of Information and Communication Technologies (ICT) and the progressive growth of Virtual Learning Environments (VLE), new development needs arise in terms of teaching-learning methodologies in the classroom. On the other hand, the remote education for the COVID-19 health emergency worldwide had a positive impact in the virtual education, increasing the number of online courses through virtual platforms, in which researchers and teachers will be able to develop and implement classroom learning spaces, among which Massive Open Online Courses (MOOC's) and Inquiry-Based Learning Spaces (ILS) stand out. This paper presents the application process of an ILS of differential equations through the free resource GRAASP and published in the Golabz platform during Differential Equations of the Universidad Nacional Abierta y a Distancia. Hake's gain is used for learning assessment, an average gain of 0.37 was found, which implies a medium learning gain.

Este trabajo describe el procedimiento llevado a cabo mediante la técnica de análisis por activación neutrónica para la validación de la determinación de la fracción de masa de lantano (La) en matrices de suelo. En este estudio se muestran los principios del método relativo del análisis por activación neutrónica instrumental y el desarrollo experimental implementado para realizar la evaluación de los parámetros de desempeño: selectividad, linealidad, límite de detección, límite de cuantificación, rango de trabajo, precisión, veracidad e incertidumbre. Los resultados muestran que en el rango de 0,66 a 38,0 mg/kg de La, el método cumple con los criterios de aceptación establecidos en el proceso de validación, y por lo tanto su determinación con la técnica desarrollada ofrece resultados satisfactorios.

El objetivo de este trabajo es presentar los resultados obtenidos al aplicar la técnica de matriz de riesgo, con la aplicación SEVRRA, en braquiterapia, y además las precauciones que se deben tomar en su aplicación y en la interpretación de los resultados. Para este fin se realizó el análisis de riesgo de una instalación de braquiterapia de alta tasa de dosis utilizando el software SEVRRA y con una herramienta desarrollada en base en el método de matriz de riesgo en una hoja de cálculo. Los resultados del segundo cribado mostraron discrepancias entre el perfil de riesgo obtenido con la aplicación SEVRRA y la herramienta propia. El porcentaje de sucesos iniciadores con riesgo alto con la aplicación SEVRRA fue de 6 %, y con la herramienta propia de 14 %. Luego de un análisis de cada suceso se observó que las discrepancias se deben a que la ponderación de la robustez de las barreras de seguridad en SEVRRA es inconsistente con las definidas en la técnica de matriz de riesgo. Estos resultados tienen profundas implicaciones en función de la aceptabilidad del riesgo planteada en la metodología. Adicionalmente, se encontró que la metodología de matriz de riesgo no tiene en cuenta los riesgos inherentes a la práctica. A pesar de las inconsistencias observadas, se reconoce el potencial de la herramienta SEVRRA para la evaluación de riesgo de instalaciones radiactivas, por ser de fácil uso; sin embargo, se recomienda la revisión de la robustez de algunas barreras, con el fin de obtener el perfil de riesgo de acuerdo con la metodología. De esta forma en base a los resultados, se podrán priorizar las medidas que deben adoptarse para garantizar la seguridad radiológica de las instalaciones.

En este trabajo se miden los parámetros de relación de flujo neutrónico térmico a epitérmico (f) y flujo neutrónico térmico (Φth) (asumiendo α = 0), para la posición de irradiación (G3-G4) en la periferia del núcleo del Reactor Nuclear de Investigación IAN-R1 del Servicio Geológico Colombiano. Esta medición se realizó a partir de las actividades inducidas por reacciones de captura neutrónica (n, γ), en 4 réplicas de dos suelos de referencia, las cuales fueron irradiadas en conjunto con monitores de Al-Au. Para los suelos de referencia, se consideraron cuatro reacciones de captura para isótopos de elementos de fracción de masa certificada y con comportamiento 1/ν para la variación de la sección ecaz en el rango de energía correspondiente a neutrones térmicos. Se encontró un valor promedio de 33 para el parámetro f, en las 8 posiciones del contenedor en donde se ubicaron los suelos de referencia (CV = 9%), valor que es comparable con mediciones realizadas en canales de irradiación en la periferia de reactores tipo TRIGA. El flujo neutrónico térmico promedio determinado para las 8 posiciones del contenedor fue de 1,5×1011 n cm-2 s-1 (CV = 4 %).

The Neutron Activation Analysis (NAA) laboratory at the Colombian Geological Survey has developed a technique for multi elemental analysis of soil and plant matrices, based on Instrumental Neutron Activation Analysis (INAA) using the comparator method. In order to evaluate the analytical capabilities of the technique, the laboratory has been participating in inter-comparison tests organized by Wepal (Wageningen Evaluating Programs for Analytical Laboratories). In this work, the experimental procedure and results for the multi-elemental analysis of four soil and four plant samples during participation in the first round on 2015 of Wepal proficiency test are presented. Only elements with radioactive isotopes with medium and long half-lives have been evaluated, 15 elements for soils (As, Ce, Co, Cr, Cs, Fe, K, La, Na, Rb, Sb, Sc, Th, U and Zn) and 7 elements for plants (Br, Co, Cr, Fe, K, Na and Zn). The performance assessment by Wepal based on Z-score distributions showed that most results obtained vertical bar Z-score vertical bar <= 3.

This paper presents the progress made by the Neutron Activation Analysis (NAA) laboratory at the Colombian Geological Survey (SGC in its Spanish acronym), towards the characterization of its gamma spectrometric systems for Instrumental Neutron Activation Analysis (INAA), with the aim of introducing corrections to the measurements by variations in sample geometry. Characterization includes the empirical determination of the interaction point of gamma radiation inside the Germanium crystal, through the application of a linear model and the use of a fast Monte Carlo N-Particle (MCNP) software to estimate correction factors for differences in counting efficiency that arise from variations in sample density between samples and standards.

As part of the T-REX project, a number of R&D and prototyping activities have been carried out during the last years to explore the applicability of gaseous Time Projection Chambers (TPCs) with Micromesh Gas Structures (Micromegas) in rare event searches like double beta decay, axion research and low-mass WIMP searches. In both this and its companion paper, we compile the main results of the project and give an outlook of application prospects for this detection technique. While in the companion paper we focus on axions and WIMPs, in this paper we focus on the results regarding the measurement of the double beta decay (DBD) of 136Xe in a high pressure Xe (HPXe) TPC. Micromegas of the microbulk type have been extensively studied in high pressure Xe and Xe mixtures. Particularly relevant are the results obtained in Xe + trimethylamine (TMA) mixtures, showing very promising results in terms of gain, stability of operation, and energy resolution at high pressures up to 10 bar. The addition of TMA at levels of ∼ 1% reduces electron diffusion by up to a factor of 10 with respect to pure Xe, improving the quality of the topological pattern, with a positive impact on the discrimination capability. Operation with a medium size prototype of 30 cm diameter and 38 cm of drift (holding about 1 kg of Xe at 10 bar in the fiducial volume, enough to contain high energy electron tracks in the detector volume) has allowed to test the detection concept in realistic experimental conditions. Microbulk Micromegas are able to image the DBD ionization signature with high quality while, at the same time, measuring its energy deposition with a resolution of at least a ∼ 3% FWHM @ Qββ. This value was experimentally demonstrated for high-energy extended tracks at 10 bar, and is probably improvable down to the ∼ 1% FWHM levels as extrapolated from low energy events. In addition, first results on the topological signature information (one straggling track ending in two blobs) show promising background discrimination capabilities out of reach of other experimental implementations. Moreover, microbulk Micromegas have very low levels of intrinsic radioactivity, and offer cost-effective scaling-up options. All these results demonstrate that Micromegas-read HPXe TPC remains a very competitive technique for the next generation DBD experiments.

As part of the T-REX project, a number of R&D and prototyping activities have been carried out during the last years to explore the applicability of gaseous Time Projection Chambers (TPCs) with Micromesh Gas Structures (Micromegas) in rare event searches like double beta decay, axion research and low-mass WIMP searches. While in the companion paper we focus on double beta decay, in this paper we focus on the results regarding the search for dark matter candidates, both axions and WIMPs. Small (few cm wide) ultra-low background Micromegas detectors are used to image the axion-induced x-ray signal expected in axion helioscopes like the CERN Axion Solar Telescope (CAST) experiment. Background levels as low as 0.8 × 10−6 counts keV−1 cm−2 s−1 have already been achieved in CAST while values down to ∼10−7 counts keV−1 cm−2 s−1 have been obtained in a test bench placed underground in the Laboratorio Subterráneo de Canfranc (LSC). Prospects to consolidate and further reduce these values down to ∼10−8 counts keV−1 cm−2 s−1 will be described. Such detectors, placed at the focal point of x-ray telescopes in the future International Axion Observatory (IAXO), would allow for 105 better signal-to-noise ratio than CAST, and search for solar axions with gaγ down to few 1012 GeV−1, well into unexplored axion parameter space. In addition, a scaled-up version of these TPCs, properly shielded and placed underground, can be competitive in the search for low-mass WIMPs. The TREX-DM prototype, with ∼ 0.300 kg of Ar at 10 bar, or alternatively ∼ 0.160 kg of Ne at 10 bar, and energy threshold well below 1 keV, has been built to test this concept. We will describe the main technical solutions developed, as well as the results from the commissioning phase on surface. The anticipated sensitivity of this technique might reach ∼10−44 cm2 for low mass (<10 GeV) WIMPs, well beyond current experimental limits in this mass range.

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 gamma-ray spectrometry performed at the Canfranc Underground Laboratory; recent results of this material screening program are presented here.

We report on results obtained with the NEXT-DEMO prototype of the NEXT-100 high-pressure xenon gas time projection chamber (TPC), filled with pure xenon gas at 10 bar pressure and 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 electronion recombination in the gas, with correlation coefficients 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 of W-ex = (39.2 +/- 3.2) eV.

We model the response of a state of the art micro-hole single-stage charge amplication device (`microbulk' Micromegas) in a gaseous atmosphere consisting of Xenon/trimethylamine at various concentrations and pressures. The amplifying structure, made with photo-lithographic techniques similar to those followed in the fabrication of gas electron multipliers (GEMs), consisted of a 100 um-side equilateral-triangle pattern with 50 um-diameter holes placed at its vertexes. Once the primary electrons are guided into the holes by virtue of an optimized field configuration, avalanches develop along the 50 um-height channels etched out of the original doubly copper-clad polyimide foil. In order to properly account for the strong field gradients at the holes' entrance as well as for the fluctuations of the avalanche process (that ultimately determine the achievable energy resolution), we abandoned the hydrodynamic framework, resorting to a purely microscopic description of the electron trajectories as obtained from elementary cross-sections. We show that achieving a satisfactory description needs additional assumptions about atom-molecule (Penning) transfer reactions and charge recombination to be made.

We have recently reported the development of a new type of high-pressure Xenon time projection chamber operated with an ultra-low diffusion mixture and that simultaneously displays Penning effect and fluorescence in the near-visible region (300 nm). The concept, dubbed ‘Penning-Fluorescent’ TPC, allows the simultaneous reconstruction of primary charge and scintillation with high topological and calorimetric fidelity.

We have studied the calibration of PMTs in scintillation detectors, inducing single electron response on the PMT from primary scintillation produced by x-ray interaction. The results agree with those obtained by the commonly used single electron response (SER) method, which uses LED light pulses to induce the PMT SER. The use of the primary scintillation for PMT calibration will be convenient in situations where the PMT is already in situ, when it becomes difficult or even impossible to apply the SER method, e.g. in commercial sealed scintillator/PMT devices. Furthermore, we have experimentally investigated the possibility of fitting the high-charge tail of the PMT SER pulse-height distribution to an exponential function, inferring the PMT gain from the inverse of the exponent. The results of the exponential fit method agree with those obtained by the SER method for pulse-height distributions resulting from an average number of around 1.0 photoelectrons reaching the first dynode per light/scintillation pulse. The SER method has higher precision and, therefore, is used in a larger number of applications. Nevertheless, the exponential fit method will be useful in situations where the single photoelectron peak is under the background or noise peak and it may present an alternative, simple way, for relative gain calibration of PMT arrays as well as for monitoring the PMT gain variations.

We report the performance of a 10 atm Xenon/trimethylamine time projection chamber (TPC) for the detection of X-rays (30 keV) and gamma-rays (0.511-1.275 MeV) in conjunction with the accurate tracking of the associated electrons. When operated at such a high pressure and in similar to 1%-admixtures, trimethylamine (TMA) endows Xenon with an extremely low electron diffusion (1.3 +/- 0.13 mm-sigma (longitudinal), 0.95 +/- 0.20 mm-sigma (transverse) along 1 m drift) besides forming a convenient Penning-Fluorescent' mixture. The TPC, that houses 1.1 kg of gas in its fiducial volume, operated continuously for 100 live-days in charge amplification mode. The readout was performed through the recently introduced microbulk Micromegas technology and the AFTER chip, providing a 3D voxelization of 8 mm x 8 mm x 1.2 mm for approximately 10 cm/MeV-long electron tracks. Resolution in energy (epsilon) at full width half maximum (R) inside the fiducial volume ranged from R = 14.6% (30 keV) to R = 4.6% (1.275 MeV).This work was developed as part of the R&D program of the NEXT collaboration for future detector upgrades in the search of the neutrino-less double beta decay (beta beta 0 nu) in Xe-136, specifically those based on novel gas mixtures. Therefore we ultimately focus on the calorimetric and topological properties of the reconstructed MeV-electron tracks. In particular, the obtained energy resolution has been decomposed in its various contributions and improvements towards achieving the R =1.4%root MeV/epsilon levels obtained in small sensors are discussed. (C) 2015 Elsevier BY. All rights reserved.

The Neutrino Experiment with a Xenon TPC (NEXT), intended to investigate the neutrinoless double beta decay using a high-pressure xenon gas TPC filled with Xe enriched in 136Xe at the Canfranc Underground Laboratory in Spain, requires ultra-low background conditions demanding an exhaustive control of material radiopurity and environmental radon levels. An extensive material screening process is underway for several years based mainly on gamma-ray spectroscopy using ultra-low background germanium detectors in Canfranc but also on mass spectrometry techniques like GDMS and ICPMS. Components from shielding, pressure vessel, electroluminescence and high voltage elements and energy and tracking readout planes have been analyzed, helping in the final design of the experiment and in the construction of the background model. The latest measurements carried out will be presented and the implication on NEXT of their results will be discussed. The commissioning of the NEW detector, as a first step towards NEXT, has started in Canfranc; in-situ measurements of airborne radon levels were taken there to optimize the system for radon mitigation and will be shown too.