Time-domain Simulation of electronic noises

In this paper, a procedure is proposed to computer simulate the electronic noise of ionizing-radiation spectrometers. The viewpoint of the simulator is the output of the preamplifier, with or without an anti-aliasing filter, just in front of the ADC. Examples are given for the case of segmented high purity Germanium detectors (HPGe). The method makes use of the fractional calculus basics. A software procedure provides the noisy waveform as a function of the fundamental electrical-physical parameters of the system, including: detector capacitance, detector leakage current, feedback resistor, 1/f-noise coefficient of the input transistor, temperature of the preamplifier input devices. The ADC quantization noise is also included in the simulation

Optimum Filter Synthesis with DPLMS Method for Energy Reconstruction

Optimum filters are granted increasing recognition as valuable tools for parametric estimation in many scientific and technical fields. The DPLMS method, introduced some twenty years ago, is effective among the synthesis algorithms since it derives the optimum filters directly from the experimental signal and noise waveforms. Two new extensions of the DPLMS method are here presented. The first one speeds up the synthesis phase and improves the energy estimation by synthesizing optimum filters with automatically designed flat-top length. The second one improves the quality of parameter estimation in multi-channel systems by taking advantage of the inter-channel noise correlation properties. The theoretical and functional aspects behind the DPLMS method for optimum filter synthesis are first recalled and illustrated in more detail. The two new DPLMS extensions are subsequently introduced from the theoretical viewpoint and more thoroughly considered from the applicative perspective. The DPLMS optimum filters have been applied first to simulated signals with various amounts and characteristics of superimposed noise and then to the experimental waveforms acquired from a solid-state Ge detector. The results obtained are considered from both the absolute viewpoint and in comparison with those of more traditional, suboptimal filters. The results demonstrate the effectiveness of the two new DPLMS extensions. For single-channel energy estimations, the optimum filters provide comparatively better results than the other filters. The DPLMS multi-channel optimum filters further enhance the quality of the estimations, compared to single-channel optimum filters, with non-negligible inter-channel noise correlation. The effectiveness and robustness of the DPLMS method in synthesizing high-quality filters for energy estimation will be tested soon within leading-edge multi-channel physics experiments.Comment: 15 pages, 13 figure

Characterization of Large Volume 3.5 x 8 inches LaBr3:Ce Detectors

The properties of large volume cylindrical 3.5 x 8 inches (89 mm x 203 mm) LaBr3:Ce scintillation detectors coupled to the Hamamatsu R10233-100SEL photo-multiplier tube were investigated. These crystals are among the largest ones ever produced and still need to be fully characterized to determine how these detectors can be utilized and in which applications. We tested the detectors using monochromatic gamma-ray sources and in-beam reactions producing gamma rays up to 22.6 MeV; we acquired PMT signal pulses and calculated detector energy resolution and response linearity as a function of gamma-ray energy. Two different voltage dividers were coupled to the Hamamatsu R10233-100SEL PMT: the Hamamatsu E1198-26, based on straightforward resistive network design, and the LABRVD, specifically designed for our large volume LaBr3:Ce scintillation detectors, which also includes active semiconductor devices. Because of the extremely high light yield of LaBr3:Ce crystals we observed that, depending on the choice of PMT, voltage divider and applied voltage, some significant deviation from the ideally proportional response of the detector and some pulse shape deformation appear. In addition, crystal non-homogeneities and PMT gain drifts affect the (measured) energy resolution especially in case of high-energy gamma rays. We also measured the time resolution of detectors with different sizes (from 1x1 inches up to 3.5x8 inches), correlating the results with both the intrinsic properties of PMTs and GEANT simulations of the scintillation light collection process. The detector absolute full energy efficiency was measured and simulated up to gamma-rays of 30 Me

A new approach to the front-end readout of cryogenic ionization detectors

We present a novel approach to the readout of ionization detectors. The solution allows to minimize the number of components and the space occupation close to the detector. This way a minimal impact is added on the radioactive background in those experiments where very low signal rates are expected, such as GERDA and MAJORANA. The circuit consists in a JFET transistor and a remote second stage. The DC feedback path is closed using a diode. Two signal cables are only necessary for biasing and readout.Comment: 14 pages, 15 figures and 15 equation

Digital mental health interventions for anxiety and depressive symptoms in university students during the COVID-19 pandemic: A systematic review of randomized controlled trials

University students are particularly vulnerable to mental health issues, with anxiety and depression identified as the most common conditions. During the COVID-19 pandemic, social distancing, self-isolation, and difficulties linked to online teaching and learning have increased their burden of anxiety and depressive symptoms. Thus, the urgent need to intervene in favour of these vulnerable subjects, together with the difficulties in delivering in-person interventions because of lockdowns and restrictions, has led to prioritize digital mental health strategies. This study aimed at systematically reviewing the existing literature on digital mental health interventions targeting anxiety and depressive symptoms in university students during the COVID-19 emergency. Systematic searches of Medline, Embase, and PsycInfo databases identified eight randomized controlled trials. Regarding anxiety symptoms, digitally delivered cognitive behavioural therapy, dialectical behaviour therapy, and mind-body practice techniques emerged as valid strategies, while digital positive psychology and mindfulness-based interventions showed mixed results. On the other hand, digitally delivered dialectical behaviour therapy and positive psychology interventions have shown some efficacy in reducing depressive symptoms. Overall, the available literature, albeit of low quality, seems to support the role of digital interventions in promoting the mental health of university students during the COVID-19 pandemic

Identification and rejection of scattered neutrons in AGATA

Gamma rays and neutrons, emitted following spontaneous fission of 252Cf, were measured in an AGATA experiment performed at INFN Laboratori Nazionali di Legnaro in Italy. The setup consisted of four AGATA triple cluster detectors (12 36-fold segmented high-purity germanium crystals), placed at a distance of 50 cm from the source, and 16 HELENA BaF2 detectors. The aim of the experiment was to study the interaction of neutrons in the segmented high-purity germanium detectors of AGATA and to investigate the possibility to discriminate neutrons and gamma rays with the gamma-ray tracking technique. The BaF2 detectors were used for a time-of-flight measurement, which gave an independent discrimination of neutrons and gamma rays and which was used to optimise the gamma-ray tracking-based neutron rejection methods. It was found that standard gamma-ray tracking, without any additional neutron rejection features, eliminates effectively most of the interaction points due to recoiling Ge nuclei after elastic scattering of neutrons. Standard tracking rejects also a significant amount of the events due to inelastic scattering of neutrons in the germanium crystals. Further enhancements of the neutron rejection was obtained by setting conditions on the following quantities, which were evaluated for each event by the tracking algorithm: energy of the first and second interaction point, difference in the calculated incoming direction of the gamma ray, figure-of-merit value. The experimental results of tracking with neutron rejection agree rather well with Geant4 simulations

Optimization and first electronic implementation of the Constant-Fraction Time-Over-Threshold pulse shape discrimination method

In this contribution we report on further investigations of the recently-evaluated Constant-Fraction Time-over-Threshold (CF-ToT) method for neutron/gamma-ray pulse shape discrimination (PSD). The superiority of the CF-ToT PSD method over the constant-threshold (CT-ToT) method was previously demonstrated, down to low neutron energy thresholds of 100 keVee. Here, we report on a quantitative comparison between the traditionally used Charge Comparison (CC) method and the CF-ToT method using a stilbene scintillator coupled to a silicon photomultiplier, implementing an offline analysis of recorded fast-neutron and gamma-ray waveforms. An optimization of the constant fraction value indicates that a 20%-fraction yields the optimum figure-of-merit (FOM) and gamma-ray peak-to-valley (P/V) ratio. The results obtained for a particle energy threshold of 100 keVee show that the FOM and P/V values achieved with the CF-ToT method are superior to those obtained using the standard CC method. In addition, a first electronic implementation of the CF-ToT method was performed using simple circuitry suitable for multichannel architecture. Initial results obtained with this circuit prototype are presented.Comment: 10 pages, 8 figures. To be submitted to JINS

Mental Health and COVID-19 in University Students: Findings from a Qualitative, Comparative Study in Italy and the UK

Introduction: COVID-19 restrictions introduced several changes in university academic and social experience. Self-isolation and online teaching have amplified students’ mental health vulnerability. Thus, we aimed to explore feelings and perspectives about the impact of the pandemic on mental health, comparing students from Italy and the UK. Methods: Data were collected from the qualitative portion of “the CAMPUS study”, longitudinally assessing mental health of students at the University of Milano-Bicocca (Italy) and the University of Surrey (UK). We conducted in-depth interviews and thematically analysed the transcripts. Results: The explanatory model was developed from four themes identified across 33 interviews: anxiety exacerbated by COVID-19; putative mechanisms leading to poor mental health; the most vulnerable subgroups; and coping strategies. Generalised and social anxiety resulted from COVID-19 restrictions by being associated with loneliness, excessive time online, unhealthy management of time and space and poor communication with the university. Freshers, international students, and people on the extremes of the introversion/extroversion spectrum, were identified as vulnerable, while effective coping strategies included taking advantage of free time, connection with family and mental health support. The impact of COVID-19 was mostly related to academic issues by students from Italy, whereas to the drastic loss of social connectedness by the UK sample. Conclusions: Mental health support for students has an essential role, and measures that encourage communication and social connectedness are likely to be beneficial