Artículos (Centro Nacional de Aceleradores)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/10939

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8B Reaction Dynamics Researched at HIE-ISOLDE
(Editrice Compositori s.r.l., 2024) Spartà, R.; DiPietro, A.; Figuera, P.; Tengblad, O.; Moro Muñoz, Antonio Matías; Lei, J.; Martel, I.; Fernández García, Juan Pablo; Acosta, L.; Borge, M. J.G.; Onses, S. Viñal; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; European Union (UE). H2020
For the first time a measurement of 8B + 64Zn reaction has been performed at HIE-ISOLDE at CERN at energies around the Coulomb barrier, to understand how the debated halo structure of the light nucleus can affect reaction dynamics.
A Compact Model to Evaluate the Effects of High Level C++ Code Hardening in Radiation Environments
(MDPI, 2019) Reyneri, Leonardo Maria; Serrano Cases, Alejandro; Morilla García, Yolanda; Cuenca Asensi, Sergio; Martínez Álvarez, Antonio; Universidad de Sevilla. Centro Nacional de Aceleradores
A high-level C++ hardening library is designed for the protection of critical software against the harmful effects of radiation environments that can damage systems. A mathematical and empirical model to predict system behavior in the presence of radiation induced faults is also presented. This model generates a quick evaluation and adjustment of several reliability vs. performance trade-offs, to optimize radiation hardening based on the proposed C++ hardening library. Several simulations and irradiation campaigns with protons and neutrons are used to build the model and to tune it. Finally, the effects of our hardening approach are compared with other hardened and non-hardened approaches.
A rotary and reciprocating scintillator based fast-ion loss detector for the MAST-U tokamak
(American Institute of Physics, 2018) Rivero Rodríguez, Juan Francisco; García Muñoz, Manuel; Martin, R.; Galdón Quiroga, Joaquín; Ayllón Guerola, Juan Manuel; Akers, R. J.; García Vallejo, Daniel; González Martín, Javier; Rodríguez Ramos, Mauricio; Sanchis Sánchez, Lucía; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; European Commission (EC); Universidad de Sevilla
The design and unique feature of the first fast-ion loss detector (FILD) for the Mega Amp Spherical Tokamak - Upgrade (MAST-U) is presented here. The MAST-U FILD head is mounted on an axially and angularly actuated mechanism that makes it possible to independently adapt the orientation [0◦ , 90◦ ] and radial position [1.40 m, 1.60 m] of the FILD head, i.e., its collimator, thus maximizing the detector velocity-space coverage in a broad range of plasma scenarios with different q95. The 3D geometry of the detector has been optimized to detect fast-ion losses from the neutral beam injectors. Orbit simulations are used to calculate the strike map and predict the expected signals. The results show a velocity-space range of [4 cm, 13 cm] in gyroradius and [30◦ , 85◦ ] in pitch angle, covering the entire neutral beam ion energy range. The optical system will provide direct sight of the scintillator and simultaneous detection with two cameras, giving high spatial and temporal resolution. The MAST-U FILD will shed light on the dominant fast-ion transport mechanisms in one of the world’s two largest spherical tokamaks through absolute measurements of fast-ion losses.
A view of the implanted SiC damage by Rutherford backscattering spectroscopy, spectroscopic ellipsometry, and transmission electron microscopy
(AIP Publishing, 2006) Battistig, G.; Khánh, N. Q.; Petrik, P.; Lohner, T.; Dobos, L.; Pécz, B.; García López, Francisco Javier; Morilla García, Yolanda; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear
4H-SiC single crystalline substrates were implanted at room temperature with 150 keV Al+ ions using fluences of 4 1014, 1 1015, and 2 1015 cm−2 with current density of 2.5 A cm−2. The samples were subsequently annealed at 1100 °C in N2 for 1 h in order to analyze their structural recovery. The disorder induced in both sublattices by the Al+ ions was studied by backscattering spectrometry in channeling geometry with a 3.5 MeV He2+ beam. The results were compared with the optical properties of the samples measured by spectroscopic ellipsometry. In a previous work, we concluded that during the postimplantation annealing of a highly damaged SiC crystalline material the short distance order can be recovered, while the long distance disorder remains. We also presented the possibility to have grains of different polytypes oriented faraway from the original direction. Now, this alternative is confirmed by the cross-sectional transmission and high resolution electron microscopy studies, carried out to obtain information about the crystal structure.
Accelerator Mass Spectrometry (AMS) in Radioecology
(Elsevier, 2018) García León, Manuel; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Ministerio de Economía y Competitividad (MINECO). España
Accelerator Mass Spectrometry (AMS) provides with an excellent sensitivity for the determination of radionuclides in the environment. In fact, conventional radiometric techniques can hardly compete with AMS in the solution of many problems involving the measurement of very low levels of radioactivity in Nature. For that reason, during the last years AMS has become a powerful tool for Radioecology studies. In this paper a review is done on the evolution of AMS applications to the measurement of environmental radioactivity and, therefore, its contribution to the understanding of radionuclide behavior in Nature.For that, the advantages of using AMS to determine key nuclides as 129I, 14C, Pu-isotopes and others in different natural compartments will be discussed. The content of the paper is illustrated with the contributions to these studies of the Spanish National Center for Accelerators (CNA) AMS systems.
Accurate,robust and harmonized implementation of morpho-functional imaging in treatment planning for personalized radiotherapy
(Public Library of Science, 2019-01-09) Jiménez Ortega, Elisa Eugenia; Ureba Sánchez, Ana María; Baeza, José Antonio; Pereira Barbeiro, Ana Rita; Balcerzyk, Marcin; Parrado-Gallego, Ángel; Wals-Zurita, Amadeo; García-Gómez, Francisco Javier; Leal Plaza, Antonio; Universidad de Sevilla. Departamento de Fisiología Médica y Biofísica; Junta de Andalucía; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
In this work we present a methodology able to use harmonized PET/CT imaging in dose painting by number (DPBN) approach by means of a robust and accurate treatment planning system. Image processing and treatment planning were performed by using a Matlab-based platform, called CARMEN, in which a full Monte Carlo simulation is included. Linear programming formulation was developed for a voxel-by-voxel robust optimization and a specific direct aperture optimization was designed for an efficient adaptive radiotherapy implementation. DPBN approach with our methodology was tested to reduce the uncertainties associated with both, the absolute value and the relative value of the information in the functional image. For the same H&N case, a single robust treatment was planned for dose prescription maps corresponding to standardized uptake value distributions from two different image reconstruction protocols: One to fulfill EARL accreditation for harmonization of [18F]FDG PET/CT image, and the other one to use the highest available spatial resolution. Also, a robust treatment was planned to fulfill dose prescription maps corresponding to both approaches, the dose painting by contour based on volumes and our voxel-by-voxel DPBN. Adaptive planning was also carried out to check the suitability of our proposal. Different plans showed robustness to cover a range of scenarios for implementation of harmonizing strategies by using the highest available resolution. Also, robustness associated to discretization level of dose prescription according to the use of contours or numbers was achieved. All plans showed excellent quality index histogram and quality factors below 2%. Efficient solution for adaptive radiotherapy based directly on changes in functional image was obtained. We proved that by using voxel-by-voxel DPBN approach it is possible to overcome typical drawbacks linked to PET/CT images, providing to the clinical specialist confidence enough for routinely implementation of functional imaging for personalized radiotherapy.
Characterization of New Silicon Carbide Neutron Detectors with Thermal and Fast Neutrons
(Elsevier, 2024) Pérez, Martín; Zamorano, Felipe; Fleta, Celeste; Fernández Martínez, Begoña; Guerrero Sánchez, Carlos; Godignon, Philippe; Pellegrini, Giulio; Pérez Maroto, Pablo; Guardiola, Consuelo; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; European Union (UE). H2022; Ministerio de Ciencia, Innovación y Universidades (MICIU). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
The aim of this work is to present a characterization of a new silicon carbide (SiC) neutron detector fabricated at the Institute of Microelectronics of Barcelona (IMB-CNM-CSIC). The device is based on a 50μm thick p-n diode built in a 4H-SiC wafer. Performance studies were carried out under different neutron energy spectra, including thermal and quasi-monoenergetic fast neutrons at the CNA HiSPANoS facility. We implemented a method for the fabrication of enriched LiF conversion layers to use for the detection of thermal neutrons. The detector was proven to be capable of being used for thermal neutron detection with conversion layers of 10B and LiF. A detection efficiency of 6 ± 1% was achieved with a 25μm thick LiF conversion layer. It was also confirmed that the device can be employed for the detection of recoil nuclei and protons produced by fast neutrons. The spectra obtained experimentally were compared with PHITS simulations. This work represents the first step towards the design and fabrication of new SiC neutron detectors in the IMB-CNM-CSIC clean room with potential applications in various scientific and technological fields.
Conceptual Design of a Scintillator-Based Fast-Ion Loss Detector for the Wendelstein 7-X Stellarator
(IEEE, 2022) Van Vuuren, Anton Jansen; Lazerson, S. A.; Leviness, A.; García Muñoz, Manuel; Gates, D.; Galdón Quiroga, Joaquín; Hidalgo Salaverri, Javier; Rueda Rueda, José; García Domínguez, Javier; Ayllón Guerola, Juan Manuel; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; European Union (UE); Ministerio de Ciencia e Innovación (MICIN). España
A conceptual design of a scintillator-based fast-ion loss detector (FILD) has been developed for the Wendelstein 7-X stellarator (W7-X). Simulations using the Monte Carlo codes ASCOT5 and BEAMS3D have been performed to calculate the expected flux of neutral beam injection (NBI)-generated fast hydrogen ions onto the conceptual detector probe head. These fast-ion loss fluxes have been calculated for several magnetic field configurations as well as probe insertion positions. At the maximum insertion position, both co- and counter-going losses with high incident pitch angles are observed; however, at retracted positions, only co-going fast ions reach the probe head. The FILDSIM code has been used to optimize the geometry of the detector entrance and collimating elements to achieve a wide velocity space coverage as well as a high velocity–space resolution. A synthetic FILD signal is calculated for the expected loss distribution via forward modeling using the instrument response function. The synthetic signal is found to largely retain the velocity space features of the loss distribution.
Correlation between Mn oxidation state and magnetic behavior in Mn/ZnO multilayers prepared by sputtering
(AIP Publishing, 2007) Céspedes, E.; García López, Francisco Javier; García Hernández, M.; Andrés, A. de; Prieto, C.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear
Compositional, microstructural, and magnetic characterization of ZnO 30 Å/Mn x n multilayers prepared by sputtering is presented to study the observed ferromagnetism in the Mn-ZnO system. The nominal Mn layer thickness, x, is varied from 3 to 60 Å, while the number of bilayers, n, is increased to maintain the total amount of Mn constant. Microstructure information was deduced from x-ray reflectivity, Mn oxidation state was determined by x-ray absorption spectroscopy, and magnetic properties were measured over a temperature range of 5–400 K. Magnetic behavior of these samples is found to be related to the Mn layer thickness x. Multilayers with x 30 Å exhibit ferromagnetism with a Curie temperature above 400 K, while mostly paramagnetic behavior is obtained for x15 Å. Magnetic behavior is discussed in terms of electronic and structural parameters of samples. Mn-ZnO interface effect is related to the ferromagnetic order of the samples, but it is not a sufficient condition. The essential role of the Mn oxidation state in the magnetic behavior of this system is pointed out. It is shown a correlation between the obtained ferromagnetism and a Mn oxidation state close to 2+.
COSMONAUT: A COmpact Spectrometer for Measurements of Neutrons at the ASDEX Upgrade Tokamak
(American Institute of Physics, 2024) Nocente, M.; Molin, A. D.; D Rigamonti, D.; Rosa, M. D.; Fernández Martínez, Begoña; Fugazza, S.; Guerrero Sánchez, Carlos; Gorini, G.; Kazakov, Y. O.; Tardini, G.; Tardocchi, M.; ASDEX Upgrade Team; Eurofus Tokamak Exploitat Team; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; European Union (UE); European Union (UE). H2020
A COmpact Spectrometer for Measurements Of Neutrons at the ASDEX Upgrade Tokamak (COSMONAUT) has been developed for spectroscopy measurements of the 2.45 MeV neutron emission from deuterium plasmas at the ASDEX Upgrade. The instrument is based on a CLYC-7 inorganic scintillator, whereby the detection of fusion neutrons occurs via their interaction with 35Cl nuclei in the detector crystal, leading to a peak in the detector response function and providing excellent neutron/gamma-ray discrimination capabilities. The diagnostics is installed along a radial line of sight and makes use of a digital system to record time resolved data for the whole duration of the discharge. Measurements in ASDEX Upgrade plasmas with neutral beam injection have been carried out and are successfully interpreted using state-of-the-art modeling codes. Next step applications of the diagnostics are in experiments aimed at generating energetic particles by ion cyclotron resonance heating schemes. In these scenarios, COSMONAUT will provide unique information on the acceleration of deuterons beyond the beam injection energy and on their confinement, for comparison with modeling.
Defect Engineering of Silicon with Ion Pulses from Laser Acceleration
(Springer Nature, 2023) Redjem, Walid; Amsellem, Ariel J.; Allen, Frances I.; Benndorf, Gabriele; Bin, Jianhui; Bulanov, Stepan; Esarey, Eric; Feldman, Leonard C.; Ferrer Fernández, Francisco Javier; García López, Francisco Javier; Schenkel, Thomas; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Office of Science. EE.UU.
Defect engineering is foundational to classical electronic device development and for emerging quantum devices. Here, we report on defect engineering of silicon with ion pulses from a laser accelerator in the laser intensity range of 1019 W cm−2 and ion flux levels of up to 1022 ions cm−2 s−1, about five orders of magnitude higher than conventional ion implanters. Low energy ions from plasma expansion of the laser-foil target are implanted near the surface and then diffuse into silicon samples locally pre-heated by high energy ions from the same laser-ion pulse. Silicon crystals exfoliate in the areas of highest energy deposition. Color centers, predominantly W and G-centers, form directly in response to ion pulses without a subsequent annealing step. We find that the linewidth of G-centers increases with high ion flux faster than the linewidth of W-centers, consistent with density functional theory calculations of their electronic structure. Intense ion pulses from a laser-accelerator drive materials far from equilibrium and enable direct local defect engineering and high flux doping of semiconductors.
Description of continuum structures in a discrete basis: Three-body resonances and two-nucleon decays
(SciPost, 2020) Casal Berbel, Jesús; Rodríguez Gallardo, Manuela; Arias Carrasco, José Miguel; Gómez Camacho, Joaquín José; Fortunato, Lorenzo; Vitturi, Andrea; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Università degli Studi di Padova. Italia; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; European Union (UE). H2020
Weakly bound and unbound three-body nuclei are studied by using the pseudostate method within the hyperspherical formalism. After introducing the theoretical framework, the method is applied first to the 9Be nucleus, showing a good agreement with the available data for its low-lying dipole response. Then, recent results on the structure and decay of the two-neutron emitters 26O and 16Be are presented. In particular, the role of the n-n correlation in shaping their properties is discussed.
Destruction of the cosmic γ-ray emitter 26 Al in massive stars: Study of the key 26 Al ( n , p ) reaction
(American Physical Society, 2021) Lederer Woods, Claudia; Woods, P. J.; Davinson, T.; Kahl, D.; Lonsdale, S. J.; Aberle, O.; Chiaveri, Enrico; Cortés Giraldo, Miguel Antonio; Ferrer Fernández, Francisco Javier; Guerrero Sánchez, Carlos; Lerendegui Marco, Jorge; Quesada Molina, José Manuel; Sabaté Gilarte, Marta; Žugec, P.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Austrian Science Fund (FWF). Austria; Consejo de Instalaciones Científicas y Tecnológicas (STFC). Reino Unido; Consejo Europeo de Investigación. Unión Europea
The 26 Al (n ,p) 26 Mg reaction is the key reaction impacting on the abundances of the cosmic y-ray emitter 26 Al produced in massive stars and impacts on the potential pollution of the early solar system with 26 Al by asymptotic giant branch stars. We performed a measurement of the 26 Al ( n , p ) 26 Mg cross section at the high-flux beam line EAR-2 at the n_TOF facility (CERN). We report resonance strengths for eleven resonances, nine being measured for the first time, while there is only one previous measurement for the other two. Our resonance strengths are significantly lower than the only previous values available. Our cross-section data range to 150 keV neutron energy, which is sufficient for a reliable determination of astrophysical reactivities up to 0.5 GK stellar temperature.
Determination of 25 trace element concentrations in biological reference materials by ICP-MS following different microwave-assisted acid digestion methods based on scaling masses of digested samples
(2013) Abril Hernández, José María; Enamorado Báez, Santiago Miguel; Gómez Guzmán, José Manuel
Determining B(E1) distributions of weakly bound nuclei from breakup cross sections using Continuum Discretized Coupled Channels calculations. Application to 11Be
(Elsevier, 2020) Moro Muñoz, Antonio Matías; Lay Valera, José Antonio; Gómez Camacho, Joaquín José; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); European Union (UE); Ministerio de Ciencia, Innovación y Universidades de España y fondos FEDER FIS2017-88410-P y RTI2018-098117-B-C21; Programa de investigación e innovación Horizonte 2020 de la Unión Europea Subvención No. 654002.
A novel method to extract the B(E1) strength of a weakly bound nucleus from experimental Coulomb dissociation data is proposed. The method makes use of continuum discretized coupled channels (CDCC) calculations, in which both nuclear and Coulomb forces are taken into account to all orders. This is a crucial advantage with respect to the standard procedure based on the Equivalent Photon Method (EPM) which does not properly take into account nuclear distortion, higher order coupling effects, or Coulomb- nuclear interference terms. The systematic and statistical uncertainties of this procedure are evaluated. The procedure is applied to the 11Be nucleus using two sets of available experimental data at different energies, for which seemingly incompatible B(E1) have been reported using the EPM. We show that the present procedure gives consistent B(E1) strengths, thus solving the aforementioned long-standing discrepancy between the two measurements.
Development of Slowed Down Beams at the Fragment Separator for FAIR
(Jagiellonian University, 2011) Naqvi, F.; Boutachkov, P.; Górska, M.; Gerl, J.; Farinon, F.; Gregor, E.T.; González Álvarez, Marcos Aurelio; Wollersheim, H.J.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear
The feasibility studies of the slowed down beam setup involving deceleration of a 64Ni beam at 250 MeV/u to 13 MeV/u in a thick Al degrader was performed at the FRagment Separator (FRS) at GSI. The experimentally measured energy spread and the nuclear reaction yields in the degrader are in good agreement with simulations.
Experimental study of 6He Coulomb breakup as an indirect measurement of 4He(2n,γ)6He reaction rate for the astrophysical r-process
(EDP Sciences, 2024-10-08) Godos, D.; Acosta, L.; Fernández García, Juan Pablo; O'Malley, P.; Sánchez Benítez, A. M.; Casal Berbel, Jesús; Gómez Camacho, Joaquín José; Arias Carrasco, José Miguel; Rodríguez Gallardo, Manuela; von Seeger, W.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; National Science Foundation (NSF). United States; Universidad Autónoma de México (UNAM); Consejo Nacional de Ciencia y Tecnología (CONACYT). México
In this work, we report the measurement of elastic and Coulomb break-up channels in 6He+208Pb collisions at Elab = 19.3 MeV, close to the Coulomb barrier of this system ∼ 19 MeV. In the context of the astrophysical r-process, the reaction 4He(2n,γ)6He has been proposed to be a key reaction in the path of synthesizing seed nuclei for the r-process, as 12C, in an environment composed mainly of alpha particles and neutrons. Based on a theoretical approach for treating three body reactions by means of which its reaction rate can be inferred, our experimental approach aims to obtain an indirect measurement of the reaction rate of 4He(2n,γ)6He by measuring the Coulomb breakup of 6He under the intense electric field produced by a 208Pb target nucleus. The experiment was carried out at the TriSol facility operated in the Nuclear Science Laboratory of the University of Notre Dame, USA, which delivered a 6He beam together with other contaminants. Particular care must be taken for the alpha particles produced in the production reaction.
Experiments and Gyrokinetic Simulations of TCV Plasmas with Negative Triangularity in View of DTT Operations
(Institute of Physics Publishing, 2024) Balestri, A.; Mantica, P.; Mariani, A.; Bagnato, F.; Bolzonella, T.; Ball, J.; Coda, S.; Dunne, M.; Faitsch, M.; Innocente, P.; Viezzer, Eleonora; EUROfusion MST1 Team; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; EUROfusion Consortium
Negative triangularity (NT) scenarios in TCV have been compared to positive triangularity (PT) scenarios using the same plasma shapes foreseen for divertor tokamak test tokamak operations. The experiments provided a NT/PT L-mode pair and a PT H-mode with different heating mixes. Regardless of the heating mix, NT L-modes always reached higher values of plasma pressure with respect to PT L-modes with the same power and recovered the central pressure of PT H-mode scenarios heated with up to twice the injected power. The experimental analysis shows that this enhanced performance in NT is due to larger temperature and density gradients close to the edge ( ρ t o r = [ 0.8 − 1.0 ] ) and higher values of pressure at the separatrix. Local gyrokinetic simulations agree with the experimental results and are able to catch the effect of shaping alone. Integrated modeling performed with ASTRA-TGLF reproduces reasonably well the PT shot but is not able to fully capture the improvements in the NT shot.
Human oocytes and zygotes are ready for ultra-fast vitrification after 2 minutes of exposure to standard CPA solutions
(Nature Research, 2019) Gallardo Molina, Miguel; Sáenz Cuesta, Jaime Luis; Risco, Ramón; Universidad de Sevilla. Departamento de Física Aplicada III
Vitrification of human oocytes and embryos in different stages of development is a key element of daily clinical practice of in vitro fertilization treatments. Despite the cooling and warming of the cells is ultra-fast, the procedure as a whole is time consuming. Most of the duration is employed in a long (8–15 minutes), gradual or direct exposure to a non-vitrifying cryoprotectant solution, which is followed by a short exposure to a more concentrated vitrifying solution. A reduction in the duration of the protocols is desirable to improve the workflow in the IVF setting and reduce the time of exposure to suboptimal temperature and osmolarity, as well as potentially toxic cryoprotectants. In this work it is shown that this reduction is feasible. In silico (MatLab program using two-parameter permeability model) and in vitro observations of the oocytes’ osmotic behaviour indicate that the dehydration upon exposure to standard cryoprotectant solutions occurs very fast: the point of minimum volume of the shrink-swell curve is reached within 60 seconds. At that point, intracellular water ejection is complete, which coupled with the permeation of low molecular weight cryoprotectants results in similar intracellular and extracellular solute concentrations. This shows that prolonging the exposure to the cryoprotectant solutions does not improve the cytosolic glass forming tendency and could be avoided. To test this finding, human oocytes and zygotes that were donated for research were subjected to a shortened, dehydration-based protocol, consisting of two consecutive exposures of one-minute to two standard cryoprotectant solutions, containing ethylene glycol, dimethyl sulfoxide and sucrose. At the end of this two-minute dehydration protocol, the critical intracellular solute concentration necessary for successful vitrification was attained, confirmed by the post-warming survival and ability to resume cytokinesis of the cells. Further studies of the developmental competency of oocytes and embryos would be necessary to determine the suitability of this specific dehydration protocol for clinical practice, but based on our results, short times of exposure to increasingly hypertonic solutions could be a more time-efficient strategy to prepare human oocytes and embryos for vitrification.
Impact of Gamma Radiation on Dynamic RDSON Characteristics in AlGaN/GaN Power HEMTs
(MDPI, 2019) Martínez, Pedro J.; Maset, Enrique; Martín Holgado, Pedro; Morilla García, Yolanda; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear
GaN high-electron-mobility transistors (HEMTs) are promising next-generation devices in the power electronics field which can coexist with silicon semiconductors, mainly in some radiation-intensive environments, such as power space converters, where high frequencies and voltages are also needed. Its wide band gap (WBG), large breakdown electric field, and thermal stability improve actual silicon performances. However, at the moment, GaN HEMT technology suffers from some reliability issues, one of the more relevant of which is the dynamic on-state resistance (RON_dyn) regarding power switching converter applications. In this study, we focused on the drain-to-source on-resistance (RDSON) characteristics under 60Co gamma radiation of two different commercial power GaN HEMT structures. Different bias conditions were applied to both structures during irradiation and some static measurements, such as threshold voltage and leakage currents, were performed. Additionally, dynamic resistance was measured to obtain practical information about device trapping under radiation during switching mode, and how trapping in the device is affected by gamma radiation. The experimental results showed a high dependence on the HEMT structure and the bias condition applied during irradiation. Specifically, a free current collapse structure showed great stability until 3.7 Mrad(Si), unlike the other structure tested, which showed high degradation of the parameters measured. The changes were demonstrated to be due to trapping effects generated or enhanced by gamma radiation. These new results obtained about RON_dyn will help elucidate trap behaviors in switching transistors.

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