Vanadium-based neutron-beam monitor

A prototype invasive (quasi-parasitic) thermal-neutron beam monitor based on isotropic neutron scattering from a thin natural Vanadium foil and standard $^3$He proportional counters has been conceptualized, designed, simulated, calibrated, and commissioned. As the beam monitor is invasive, very low neutron-beam attenuation is a necessary characteristic. Further, response linearity over as wide a range of rates as possible is highly desirable. The prototype was first calibrated using radioactive neutron sources at the Source-Testing Facility at the Division of Nuclear Physics in Lund, Sweden. Subsequently, the prototype was commissioned with beams of neutrons at the V17 and V20 beamlines of the Helmholtz Zentrum in Berlin, Germany. Both low attenuation and response linearity have been successfully demonstrated, indicating the concept is viable and worth continued development efforts. In this thesis, a monographic overview of the development of the prototype is presented.I am sure you all got to use microscope at some point in your life. And you were able to see the things that would not be possible to see otherwise, didn’t you? Well scientists need microscope all the time. Genetics need to see a structure of the genom and DNA, archeologists need to know what material they dug in the ground and in medicine the doctors will be interested what kind of tumor is in patients body. All of these require a very special microscope: a microscope that needs to be able to identify the placing of Hydrogen atoms. Such microscope can be build using neutrons. And ideally there has to be certain amount of these neutrons and they need to have certain speed at which they are flying. The European Spallation Source (ESS) is going to create such neutrons: it will be the biggest microscope for hydrogen-rich material in the world! We can imagine the ESS target (a place when the neutrons are created) as a geyser. Instead of water the geyser is producing sweets (neutrons) and these sweets are flying in all directions. And over 20 children (20 different scientific stations) are standing around the geyser, wanting to consume the sweets at different rates (some of them need 2 chocolate bars per hour, some of them 10 dried bananas per hour just as our biologist and archeologist each want a different number of neutrons with different properties). In order to ensure that every child has a correct number of sweets, the entire geyser is enclosed in a bunker, leaving tunnels to each child. Along the tunnels, a policemen (choppers) are standing, not allowing bananas to the chocolate-lovers and regulating the rate. And finally, next to the policements, there are student workers (beam monitors) who sit with their notebooks and write down the number of bananas and chocolates flying around, checking that the policemen do their jobs. This thesis is introducing a very devoted student worker (beam monitor), that does not give up even if the the number of sweets is insane and he works all the time, never has a break. In real life, of course the beam monitor is not a student, but rather a piece of equipment placed in order to verify, that the choppers allow for the correct energies and rates of neutrons. Also, for little particles the monitor (student) cannot just observe the neutrons, it has to interact with them (absorb them=eat them or scattered them= hit them with the baseball bat). This beam monitor for this thesis consists of a thin Vanadium foil from which only tiny part of the neutrons (sweets) are scattered (hitted with the baseball bat), and these are then stored in the detectors (boxes) placed around this foil. This scattered part is so tiny, that the kids standing around the bunker will not even notice, the change in rate of sweets. What is stored in the detectors around the foil is then analyzed and therefore the correct functionality of choppers can be verified. Thanks to the policemen choppers and the working-hard students that control the work of the policemen, the neutrons are delivered correctly to the biologist and archeologist and now they can fully use them as a best microscope in the world

Parallel-Coupled Quantum Dots in InAs Nanowires

We use crystal-phase tuning during epitaxial growth of InAs nanowires to create quantum dots with very strong confinement. A set of gate electrodes are used to reproducibly split the quantum dots into even smaller pairs for which we can control the populations down to the last electron. The double quantum dots, which are parallel-coupled to source and drain, show clear and stable odd-even level pairing due to spin degeneracy and the strong confinement. The combination of hard-wall barriers to source and drain, shallow interdot tunnel barriers, and very high single-particle excitation energies allow an order of magnitude tuning of the strength for the first intramolecular bond. We show examples for nanowires with different facet orientations, and suggest possible mechanisms behind the reproducible double-dot formation

Defect characterization studies on 60Co gamma-irradiated p-type Si diodes

Trabajo presentado al 40th RD50 Workshop on Radiation hard semiconductor devices for very high luminosity colliders, celebrado del 21 al 24 de junio de 2022 en el CERN (Zurich).Boron-doped silicon devices used in high radiation environment like the HL-LHC show a degradation in device performance due to the radiation induced deactivation of the active boron dopant. This effect is known as the so-called Acceptor Removal Effect and depends on particle type, energy and radiation dose. Here we present defect characterization studies using TSC (thermally stimulated current technique) and DLTS (Deep Level Transient Spectroscopy) to correlate radiation induced changes in the macroscopic device properties with the formation of microscopic defects. The defect spectroscopy techniques provide us information about defect characteristics such as activation energy, capture cross section and defect concentrations, and were performed on 60Co gamma-irradiated B-doped silicon EPI-diodes of different resistivity.Peer reviewe

GEANT4-based calibration of an organic liquid scintillator

A light-yield calibration of an NE 213A organic liquid scintillator detector has been performed using bothmonoenergetic and polyenergetic gamma-ray sources. Scintillation light was detected in a photomultipliertube, and the corresponding pulses were subjected to waveform digitization on an event-by-event basis. Theresulting Compton edges have been analyzed using a GEANT4 simulation of the detector which models boththe interactions of the ionizing radiation as well as the transport of scintillation photons. The simulation is calibrated and also compared to well-established prescriptions used to determine the Compton edges,resulting ultimately in light-yield calibration functions. In the process, the simulation-based method produced information on the gain and intrinsic pulse-height resolution of the detector. It also facilitated a previously inaccessible understanding of the systematic uncertainties associated with the calibration of the scintillation-light yield. The simulation-based method was also compared to well-established numerical prescriptions for locating the Compton edges. Ultimately, the simulation predicted as much as 17% lower light-yield calibrations than the prescriptions. These calibrations indicate that approximately 35% of the scintillation light associated with a given gamma-ray reaches the photocathode. It is remarkable how well two 50 year old prescriptions for calibrating scintillation-light yield in organic scintillators have stood the test of time

Defect characterization studies on neutron irradiated boron-doped silicon pad diodes and Low Gain Avalanche Detectors

High-energy physics detectors with internal charge multiplication, like Low Gain Avalanche Detectors (LGADs), that will be used for fast timing in the High Luminosity LHC experiments, have to exhibit a significant radiation tolerance. In this context, the impact of radiation on the highly boron-doped gain layer is of particular interest, since due to the so-called Acceptor Removal Effect (ARE) a radiation-induced deactivation of active boron dopants takes place, that is causing a progressive loss in the gain with increasing irradiation level. In this paper we present defect-spectroscopy measurements (Deep-Level Transient Spectroscopy and Thermally Stimulated Current technique) on neutron, proton and electron irradiated p-type silicon pad diodes of different resistivity as well as LGADs neutron irradiated at fluences up to 1×1015 neq/cm2. We show that compared to silicon pad diodes the determination of LGAD defect introduction rates is less straightforward as they are strongly influenced by the impact of the gain layer. The measured gain layer capacitance has a strong frequency and temperature dependence which makes DLTS measurements challenging to perform with results difficult to interpret. With the TSC technique the defects formed in the LGADs are nicely observed and can be compared to the defects formed in the silicon pad diodes. However, the exact assignment of defects to the gain layer or bulk region remains challenging and the charge amplification effect of the LGADs impacts the exact determination of defect concentrations. We also demonstrate that, depending on the TSC measurement conditions, defect induced internal electric fields are built up in the irradiated LGADs which impact the signal current. •Presentation of defect spectroscopy studies (DLTS, TSC) on irradiated LGADs•Significant impact of the highly doped gain layer on the defect spectroscopy results•Measured gain layer capacitance shows strong frequency and temperature dependence•Defect induced internal electrical fields can be built up in irradiated LGADs•BiOi introduction rates for neutron, electron and proton irradiated diodes are givenHigh-energy physics detectors, like Low Gain Avalanche Detectors (LGADs) that will be used as fast timing detectors in the High Luminosity LHC experiments, have to exhibit a significant radiation tolerance. Thereby the impact of radiation on the highly boron-doped gain layer that enables the internal charge multiplication, is of special interest, since due to the so-called Acceptor Removal Effect (ARE) a radiation-induced deactivation of active boron dopants takes place. In this paper we present defect-spectroscopy measurements (Deep-Level Transient Spectroscopy and Thermally Stimulated Current technique) on neutron irradiated p-type silicon pad diodes of different resistivity as well as LGADs irradiated at fluences up to 1 x 10^15 neq/cm2. Thereby we show that while for the silicon pad diodes irradiated with electrons, neutrons or protons the determination of defect electronic properties and defect introduction rates is straightforward, DLTS and TSC measurements on LGADs are strongly influenced by the impact of the gain layer. It is shown that the measurability of the capacitance of the gain layer shows a strong frequency and temperature dependence leading to a capacitance drop in DLTS and non-reliable measurement results. With TSC defects formed in the LGADs can be very nicely observed and compared to the defects formed in the silicon pad diodes. However the exact assignment of defects to the gain layer or bulk region remains challenging and the charge amplification effect of the LGADs impacts the exact determination of defect concentrations. Additionally, we will demonstrate that depending on the TSC measurement conditions defect induced residual internal electric fields are built up in the irradiated LGADs that are influencing the current signal of carriers emitted from the defect states

Strategic R&D Programme on Technologies for Future Experiments - Annual Report 2020

This report summarises the activities and achievements of the strategic R&D programme on technologies for future experiments in the year 2020

Strategic R&D Programme on Technologies for Future Experiments - Annual Report 2021

This report summarises the activities and main achievements of the CERN strategic R&D programme on technologies for future experiments during the year 2021

Extension of the R&D Programme on Technologies for Future Experiments

we have conceived an extension of the R&D programme covering the period 2024 to 2028, i.e. again a 5-year period, however with 2024 as overlap year. This step was encouraged by the success of the current programme but also by the Europe-wide efforts to launch new Detector R&D collaborations in the framework of the ECFA Detector R&D Roadmap. We propose to continue our R&D programme with the main activities in essentially the same areas. All activities are fully aligned with the ECFA Roadmap and in most cases will be carried out under the umbrella of one of the new DRD collaborations. The program is a mix of natural continuations of the current activities and a couple of very innovative new developments, such as a radiation hard embedded FPGA implemented in an ASIC based on System-on-Chip technology. A special and urgent topic is the fabrication of Al-reinforced super-conducting cables. Such cables are a core ingredient of any new superconducting magnet such as BabyIAXO, PANDA, EIC, ALICE-3 etc. Production volumes are small and demands come in irregular intervals. Industry (world-wide) is no longer able and willing to fabricate such cables. The most effective approach (technically and financially) may be to re-invent the process at CERN, together with interested partners, and offer this service to the community

Annual Report 2022

This report summarises the activities and main achievements of the CERN strategic R&D programme on technologies for future experiments during the year 202