Simulation of radiation-induced defects

Mainly due to their outstanding performance the position sensitive silicon detectors are widely used in the tracking systems of High Energy Physics experiments such as the ALICE, ATLAS, CMS and LHCb at LHC, the world's largest particle physics accelerator at CERN, Geneva. The foreseen upgrade of the LHC to its high luminosity (HL) phase (HL-LHC scheduled for 2023), will enable the use of maximal physics potential of the facility. After 10 years of operation the expected fluence will expose the tracking systems at HL-LHC to a radiation environment that is beyond the capacity of the present system design. Thus, for the required upgrade of the all-silicon central trackers extensive measurements and simulation studies for silicon sensors of different designs and materials with sufficient radiation tolerance have been initiated within the RD50 Collaboration. Supplementing measurements, simulations are in vital role for e.g. device structure optimization or predicting the electric fields and trapping in the silicon sensors. The main objective of the device simulations in the RD50 Collaboration is to develop an approach to model and predict the performance of the irradiated silicon detectors using professional software. The first successfully developed quantitative models for radiation damage, based on two effective midgap levels, are able to reproduce the experimentally observed detector characteristics like leakage current, full depletion voltage and charge collection efficiency (CCE). Recent implementations of additional traps at the SiO$_2$/Si interface or close to it have expanded the scope of the experimentally agreeing simulations to such surface properties as the interstrip resistance and capacitance, and the position dependency of CCE for strip sensors irradiated up to $\sim$$1.5\times10^{15}$ n$_{\textrm{eq}}\textrm{cm}^{-2}$.Comment: 13 pages, 11 figures, 6 tables, 24th International Workshop on Vertex Detectors, 1-5 June 2015, Santa Fe, New Mexico, US

Silicon Sensors for Trackers at High-Luminosity Environment

The planned upgrade of the LHC accelerator at CERN, namely the high luminosity (HL) phase of the LHC (HL-LHC foreseen for 2023), will result in a more intense radiation environment than the present tracking system was designed for. The required upgrade of the all-silicon central trackers at the ALICE, ATLAS, CMS and LHCb experiments will include higher granularity and radiation hard sensors. The radiation hardness of the new sensors must be roughly an order of magnitude higher than the one of LHC detectors. To address this, a massive R&D program is underway within the CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" to develop silicon sensors with sufficient radiation tolerance. Research topics include the improvement of the intrinsic radiation tolerance of the sensor material and novel detector designs with benefits like reduced trapping probability (thinned and 3D sensors), maximized sensitive area (active edge sensors) and enhanced charge carrier generation (sensors with intrinsic gain). A review of the recent results from both measurements and TCAD simulations of several detector technologies and silicon materials at radiation levels expected for HL-LHC will be presented.Comment: 7 pages, 9 figures, 10th International Conference on Radiation Effects on Semiconductor Materials, Detectors and Devices (RESMDD14), 8-10 October, Firenze, Ital

Experimental and simulation study of irradiated silicon pad detectors for the CMS High Granularity Calorimeter

The foreseen upgrade of the LHC to its high luminosity phase (HL-LHC), will maximize the physics potential of the facility. The upgrade is expected to increase the instantaneous luminosity by a factor of 5 and deliver an integrated luminosity of 3000 fb-1 after 10 years of operation. As a result of the corresponding increase in radiation and pileup, the electromagnetic calorimetry in the CMS endcaps will sustain maximum integrated doses of 1.5 MGy and neutron fluences above 1e16 neq/cm2, necessitating their replacement for HL-LHC operation. The CMS collaboration has decided to replace the existing endcap electromagnetic and hadronic calorimeters by a High Granularity Calorimeter (HGCAL) that will provide unprecedented information on electromagnetic and hadronic showers in the very high pileup of the HL-LHC. In order to employ Si detectors in HGCAL and to address the challenges brought by the intense radiation environment, an extensive R&D program has been initiated, comprising production of prototype sensors of various types, sizes and thicknesses, their qualification before and after irradiation to the expected levels, and accompanying simulation studies. The ongoing investigation presented here includes measurements of current-voltage and capacitance-voltage characteristics, along with predicted charge collection efficiences of the sensors irradiated to levels expected for the HGCAL at HL-LHC. The status of the study and the first results of the performance of neutron irradiated Si detectors, as well as their comparison with numerical simulations, are presented.Comment: 3 pages, 3 figures, 1 table, 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC

Analysis of fluctuations in velocities, voidage and gas concentration in cfb conditions

The purpose of the present study is to evaluate the possibilities to estimate the fluctuation characteristics of gas concentrations in a CFB from the characteristics of velocity and voidage fluctuations. In CFB combustion, the local concentrations of reactant gases strongly fluctuate which affects the reaction rates. In CFD modeling, the effect of turbulent mixing on reaction rates is commonly taken into account by means of mixing descriptions based on fluctuation time scales. For fast reactions the mixing rate can be the rate limiting step. Similar to gas phase reactions, for heterogeneous combustion of solid fuel, fluctuations in gas concentrations should also be taken into account. One estimate for gas species mixing is obtained by analyzing velocity fluctuations on the basis of which mixing time scales can be determined (1). This approach does not account for the actual correlation between velocity and concentration fluctuations. In a combustion chamber, air enters from riser bottom while combustible gases are released in dense suspension from fresh fuel. There are regions of high oxygen concentration and regions with high concentration of volatiles. The paper shows by means of a simplified CFD simulation how the characteristics of the concentration fluctuations are related to the fluctuations in velocities and voidage. In the simulation, air enters from riser bottom and CO that reacts with oxygen is added to dense suspension. The time-averaged fluctuation characteristics show a similarity to velocity fluctuations and that the effect of the uneven distribution of gas components should be accounted for in the modeling. REFERENCES 1. J. Peltola, S. Kallio, Estimation of turbulent diffusion coefficients in a CFB on basis of transient CFD simulations, Proceedings (Vol. 2) of 21st International Conference on Fluidized Bed Combustion, 2012, pp. 595 – 60

Numerical simulations of semiconductor radiation detectors for high-energy physics and spectroscopy applications

The position sensitive silicon particle detectors are widely used in the tracking systems of High Energy Physics experiments such as the CMS at LHC, the world's largest particle accelerator at CERN. The foreseen upgrade of the LHC to its high luminosity (HL) phase, will enable the use of maximal physics potential of the facility. However, after 10 years of operation the expected fluence will result in a radiation environment that is beyond the capacity of the present tracking system design. The required upgrade of the all-silicon central trackers will include higher granularity and radiation hard sensors that can tolerate the increased occupancy and the higher radiation levels. To address this, extensive measurement and simulation studies have been performed to investigate different designs and silicon materials. The work in this thesis has been carried out within the CMS Tracker Upgrade Project and the multi-experiment RD50 Collaboration. Simulations serve a vital role in device structure optimization and predicting the electric fields and trapping in the silicon sensors. The main objective of device simulations is by using professional software to develop an approach to both model and predict the performance of the irradiated silicon detectors. In the course of this thesis, an effective non-uniform defect model is developed using the Sentaurus TCAD simulation framework. The model reproduces both the observed bulk and surface properties and can predict the performance of strip detectors up to HL-LHC fluences. When applied to measurements of the position dependence of Charge Collection Efficiency, the model can provide a means for the parametrization of oxide charge accumulation at the detector s SiO2/Si interface as a function of irradiation dose. TCAD simulations are also applied for a comparative study of a thin p-on-p pixel sensor and a more conventional p-on-n pixel sensor. The simulations are used to provide an explanation to the measured charge collection behavior and for a detailed investigation of the electrical properties of the two sensor types. Finally, the scope of TCAD simulations is extended to GaAs, a compound semiconductor material. By implementing the observed deep donor defect level to the simulation, the resulting electrical properties are in close agreement with the measurements of an epitaxial GaAs radiation detector. Also, the transferred electron effect observed in the transient current measurements is reproduced by the simulation. The combined results of this thesis demonstrate the versatility and power of the TCAD simulations of semiconductor detectors as a tool to bridge the gap from observation to parametrization.Paikkaherkkiä pii-hiukkasilmaisimia käytetään laajalti suurenergia-fysiikan kokeiden jälki-ilmaisin systeemeissä, kuten CMS:ssa LHC:lla, maailman suurimmalla hiukkaskiihdyttimellä CERN:issä. LHC:n edessä oleva päivitys korkean luminositeetin (HL) vaiheeseen tulee mahdollistamaan laitteiston fysiikkapotentiaalin maksimaalisen hyödyntämisen. Kymmenen vuoden toiminnan jälkeen odotettavissa oleva kokonaisannos tulee kuitenkin aiheuttamaan säteily-ympäristön, joka ylittää nykyisen jälki-ilmaisin systeemin kapasiteetin. Kokonaan piistä valmistetuille keskisille jälki-ilmaisimille edellytettyyn päivitykseen tulee kuulumaan suuremman rakeisuuden ja säteilynkestävyyden omaavia ilmaisimia, jotka pystyvät kestämään suurempia hetkellisiä hiukkasannoksia ja korkeampia säteilytasoja. Tämän johdosta on suoritettu laajoja mittaus- ja simulaatiotutkimuksia erilaisilla ilmaisinrakenteilla ja pii-materiaaleilla. Tässä väitöskirjassa esitetetty tutkimus on suoritettu CMS Tracker Upgrade-projektin ja RD50 kollaboraation puitteissa. Simulaatiot ovat oleellisessa osassa ilmaisinrakenteiden optimoinnissa sekä ennakoitaessa sähkökenttiä ja loukkuuntumista pii-ilmaisimissa. Ilmaisinsimulaatioiden pääasiallinen tavoite on kaupallisia ohjelmistoja käyttäen kehittää metodi säteilytettyjen pii-ilmaisimien toiminnan mallintamiseksi ja ennusteiden laatimiseksi. Tässä väitöskirjassa esitellään efektiivisen epäyhtenäisen säteilyvaurio-mallin kehitysprosessi Sentaurus TCAD simulaatio-ohjelmistopakettia käyttäen. Malli toisintaa kokeellisesti havaitut bulkki- ja pintaominaisuudet ja kykenee tuottamaan ennusteita nauhailmaisimille HL-LHC säteilyannoksiin asti. Sovellettuna varauksen keräystehokkuuden paikkariippuvuus mittauksiin, malli voi tarjota keinon oksidivarauksen akkumulaation parametrisointiin annoksen funktiona ilmaisimen pii-oksidi rajapinnalla. TCAD simulaatioita käyttäen on myös suoritettu vertaileva tutkimus ohuen p-on-p pikselisensorin ja tavanomaisemman p-on-n pikselisensorin välillä. Simulaatiot tarjoavat sekä selityksen havaitulle varauksen keräys käyttäytymiselle että yksityiskohtaisen selvityksen kahden sensorityypin sähköisistä ominaisuuksista. Lopuksi TCAD simulaatiot ulotetaan GaAs:iin, seospuolijohteeseen. Lisäämällä kokeellisesti havaittu kidevirhe simulaatioon, tuotetut sähköiset ominaisuudet toisintavat epitaksiaalin GaAs säteilynilmaisimen mittaukset. Lisäksi simulaatio pystyy toisintamaan transienttivirta mittauksissa havaitun vaihdetun elektronin efektin. Tämän väitöskirjan yhdistetyt tulokset osoittavat puolijohdeilmaisimien TCAD simulaatioiden monipuolisuuden ja tehokkuuden työkaluna, jolla siirtyä havainnosta parametrisaatioon

Does expanding wood use in construction and textile markets contribute to climate change mitigation?

Wood use is expanding to new markets, driven by the need to substitute fossil-intensive products and energy. Wood products can contribute to climate change mitigation, if they have a lower fossil footprint than alternative products serving the same function. However, the climate change mitigation potential is contingent on the net fossil and biogenic emissions over time, as well as the realism of the counterfactual scenario and market assumptions. This study aims to improve the consistency of assessing the avoided fossil emissions attributed to changes in wood use, and to estimate the additional mitigation potential of increased wood use in construction and textile markets based on wood harvested in Finland. The results show that, compared to baseline, an increase in the market share of wood leads to an increase in atmospheric CO2 concentration by 2050. Thus, the substitution impacts of wood use are not large enough to compensate for the reduction in forest carbon sinks in the short and medium term. This outcome is further aggravated, considering the decarbonization of the energy sector driven by the Paris Agreement, which lowers the fossil emissions of competing sectors more than those of the forest sector. The expected decarbonization is a highly desirable trend, but it will further lengthen the carbon parity period associated with an increase in wood harvest. This creates a strong motive to pursue shifts in wood uses instead of merely expanding all wood uses.Peer reviewe

A novel digital patient-reported outcome platform (noona) for clinical use in patients with cancer : Pilot study assessing suitability

Publisher Copyright: © 2021 JMIR Formative Research. All rights reserved.Background: As the incidence of cancer is on the rise, there is a need to develop modern communication tools between patients and the medical personnel. Electronic patient-reported outcome (ePRO) measures increase the safety of cancer treatments and may have an impact on treatment outcome as well. ePRO may also provide a cost-efficient way to organize follow-up for patients with cancer. Noona is an internet-based system for patients to self-report symptoms and adverse events of cancer treatments from home via a computer or a smart device (eg, smartphone, tablet). Objective: In this pilot study, we assessed the suitability of a novel ePRO application (Noona) for patients with cancer, nurses, and doctors at the Helsinki University Hospital, Finland. Methods: The study included 44 patients with cancer (different solid tumor types) and 17 health care professionals (nurses or medical doctors). Patients were either operated or received systemic treatment or radiotherapy. Patients reported their symptoms to the medical staff via Noona. In addition, patients and clinicians answered a questionnaire, based on which Noona's suitability for clinical use was evaluated in terms of usability (ease of use, operability, and learnability), reliability (subjective opinion of the participant), and incidence of harmful events reported by the participants. Results: A total of 41/44 (93%) patients and 15/17 (88%) professionals reported that the program was easy or quite easy to use; 38/44 (86%) patients and 11/17 (65%) professionals found Noona reliable, and 38/44 (86%) patients and 10/17 (59%) professionals would recommend Noona to other patients or their colleagues. No harmful incidences caused by the use of Noona were reported by the patients; however, 1 harmful incidence was reported by one of the professionals. Conclusions: The majority of the participants felt that Noona appeared reliable and it was easy to use. Noona seems to be a useful tool for monitoring patient's symptoms during cancer therapy. Future studies will determine the impact of this ePRO platform in routine clinical practice.Peer reviewe