Radiation hardness study of high purity silicon and the development of a radiation damage monitoring system for silicon devices in mixed radiation fields

This thesis describes an experimental study into the radiation hardness of high purity silicon. This material is principally used in the manufacture of silicon based microstrip detectors and other similar devices. Radiation detector test structures which had been fabricated on the base of different types of silicon were exposed to ~1 MeV neutrons. This was done to determine the role of different impurities in the formation of radiation induced crystallographic defects within the silicon lattice. Oxygenated silicon, nitrogenised silicon and silicon containing the standard residual impurities was investigated. The effect of the deep level states associated with the defects on the detector electrical properties was also studied. At the relatively high neutron fluence employed, up to 7.5x10(superscript 13) n.cm(superscript -2), the conventional capacitance based Deep Level Transient Spectroscopy (DLTS) technique is not applicable. In order to detect and measure the properties of the defects a new technique was used known as Optical Deep Level Transient Conductance Spectroscopy (ODLTCS). Spectral features identified in the ODLTCS spectra were attributed to known radiation induced defects in silicon through the comparison of the measured energy levels of the associated deep level states and the measured introduction rates with data contained in the literature. Using ODLTCS the kinetics of the growth and contraction of particular defect concentrations in each of the irradiated detector types was measured as a function of room temperature annealing. Correlation in the evolution of the radiation induced C(subscript i)-O(subscript i) and the short term annealing of the effective impurity concentration (N[subscript eff]) was observed. Based on this finding a microscopic explanation for the improved radiation hardness of oxygenated silicon is described. Other possible mechanisms of defect engineering were also investigated. No deep level defect identified from the ODLTCS spectra could be attributed to the long term reverse anneal of N(subscript eff). This suggested that the responsible defect had a energy state outside the ODLTCS detection limit of less than (0.16 eV) as measured from either the conduction or valence band edge. Significant reduction in the production rate of the V-O defect was observed in nitrogenised silicon. Evidence supporting possible metastability of the V-O defect was also obtained. Another important aspect of this research was the development of technologies for use in the on-line monitoring of radiation damage to silicon devices in mixed radiation fields. It is shown that a PIN Dosimeter diode which has been calibrated in an epithermal neutron beam in terms of (?, see abstract in 01Front file) can be used to measure (?, see abstract in 01Front file) in a fast neutron field. This finding supports the use of a PIN Dosimeter Diode for measuring (?, see abstract in 01Front file) in neutrons fields with any arbitrary energy spectra. The response of the PIN Dosimeter Diode in a high energy electron field in terms of (?, see abstract in 01Front file) is studied. Based on experimental findings it is reasoned that PIN Dosimeter Diode can provide a universal means of measuring dose associated with Non Ionising Energy Loss (NIEL) in silicon when exposed to any mixed radiation field in terms of (?, see abstract in 01Front file). Sensors for measuring does due to Ionising Energy Loss (IEL) in SiO(subscript 2) when exposed to mixed radiation fields were also investigated. It is shown that an IEL sensor based on photodetector is not suitable in a radiation environment containing NIEL type radiations. An alternative sensor in the form of MOSFET is found to suitably radiation hard against dose associated with NIEL and able to measure IEL over a wide range of response. Based on the MOSFET and PIN Dosimeter Diode results a Radiation Damage Monitoring System is designed for the measurement of damage to electronic devices in mixed radiation fields. The system was implemented in the Belle experiment at the KEK B-Factory in Japan, and within the lepton collider at SLAC in the USA

Why the epistemologies of trust researchers matter

In this thought piece we take stock of and evaluate the nature of knowledge production in the field of trust research by examining the epistemologies of 167 leading trust scholars, who responded to a short survey. Following a brief review of major epistemological perspectives we discuss the nature of the prevalent views and their geographical distribution within our field. We call on trust researchers to engage in epistemological reflection, develop their own awareness of alternative epistemologies, and ensure their work draws on and cites relevant research contrary to their preferred epistemological approach. To support this we ask editors of relevant journals to foster pluralism in trust research, publishing work from a range of epistemologies

A Real-time Image Reconstruction System for Particle Treatment Planning Using Proton Computed Tomography (pCT)

Proton computed tomography (pCT) is a novel medical imaging modality for mapping the distribution of proton relative stopping power (RSP) in medical objects of interest. Compared to conventional X-ray computed tomography, where range uncertainty margins are around 3.5%, pCT has the potential to provide more accurate measurements to within 1%. This improved efficiency will be beneficial to proton-therapy planning and pre-treatment verification. A prototype pCT imaging device has recently been developed capable of rapidly acquiring low-dose proton radiographs of head-sized objects. We have also developed an advanced, fast image reconstruction software based on distributed computing that utilizes parallel processors and graphical processing units. The combination of fast data acquisition and fast image reconstruction will enable the availability of RSP images within minutes for use in clinical settings. The performance of our image reconstruction software has been evaluated using data collected by the prototype pCT scanner from several phantoms.Comment: Paper presented at Conference on the Application of Accelerators in Research and Industry, CAARI 2016, 30 October to 4 November 2016, Ft. Worth, TX, US

The farmer, the worker and the MP: The digital divide and territorial paradoxes in Switzerland

The territorial dimension of the digital divide is usually considered as a phenomenon that penalizes the peripheral regions, especially in terms of regional economic development. Taking into account the territorial networking of ICT (Information & Communication Technologies) infrastructures—particularly high-speed networks—provides what is probably the principal reason for such a perception. This is particularly true considering that the most-peripheral regions and those with the smallest population densities are also the poorest in terms of ICT infrastructures. In Western countries, however, the digital divide is no longer the result of network-related problems. Nowadays, the issue of the skills required to adequately exploit the potential of ICT is at the forefront. Yet this evolution is likely to lead to an inversion of the inequalities between the centre and the periphery, as populations without such skills—recent immigrants, the unemployed, the illiterate, people with little education or on low incomes and other socially marginalized people—are generally concentrated in urban centres. Consequently, the priority for reducing inequalities of access to ICT resources is no longer the provision of high-performance ICT infrastructures for peripheral regions, but rather the implementation of continuing education and social action policies within the urban centre

"I am not delusional!" Sensory dysaesthesia secondary to degenerative cervical myelopathy.

Degenerative cervical myelopathy (DCM) is the most common cause of adult spinal cord dysfunction, most classically presenting with a broad-based gait and clumsy hands. Limb sensory loss and paraesthesia are considered common symptoms of DCM. However, we report an unusual case of a patient presenting with prominent and atypical sensory symptoms. The patient repeatedly presented to accident and emergency complaining of her body resembling a wet gel-like substance that she attributed to the use of olive oil moisturising cream. The patient was found to have myelopathic signs on examination and MRI consistent with severe cervical myelopathy. She subsequently underwent successful decompressive anterior cervical discectomy, as recommended by international guidelines. This case serves to remind health professionals of uncommon presentations of common disease and the importance of maintaining a wide initial differential diagnosis

The role of CO2 decline for the onset of Northern Hemisphere glaciation

The Pliocene–Pleistocene Transition (PPT), from around 3.2 to 2.5 million years ago (Ma), represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern Eurasia and North America. Paleo evidence indicates that the PPT was accompanied and possibly caused by a decrease in atmospheric CO2, but the temporal resolution of CO2 reconstructions is low for this period of time and uncertainties remain large. Therefore, instead of applying existent CO2 reconstructions we solved an ‘inverse’ problem by finding a schematic CO2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records. To this end, we performed an ensemble of transient simulations with an Earth system model of intermediate complexity from which we derived a best guess transient CO2 scenario for the interval from 3.2 to 2.4 Ma that gives the best fit between the simulated and reconstructed benthic δ18O and global sea surface temperature evolution. Our data-constrained CO2 scenarios are consistent with recent CO2 reconstructions and suggest a gradual CO2 decline from 375–425 to 275–300 ppm, between 3.2 and 2.4 Ma. In addition to a gradual decline, the best fit to paleoclimate data requires the existence of pronounced CO2 variability coherent with the 41-kyr (1 kyr = 1000 years) obliquity cycle. In our simulations the long-term CO2 decline is accompanied by a relatively abrupt intensification of Northern Hemisphere glaciation at around 2.7 Ma. This is the result of a threshold behaviour of the ice sheets response to gradual CO2 decrease and orbital forcing. The simulated Northern Hemisphere ice sheets during the early Pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m. Both ice volume and benthic δ18O are dominated by 41-kyr cyclicity. Our simulations suggest that before 2.7 Ma Greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation. A fully glaciated Greenland comparable to its present-day ice volume is modelled only during glacial maxima after 2.7 Ma and more continuously after 2.5 Ma

Zielführende Strategien zur Lokalisierung von Störsignalen im Wirkbereich moderner Mobilfunksysteme

Der Schutz des elektromagnetischen Spektrums ist ein Kernelement der EMV. Er wird durch Zuteilung von Frequenzbändern und Vorgabe von Grenzwerten gewährleistet und ermöglicht so den Betrieb von Funksystemen. Trotz dieses Schutzes werden auch moderne Netze wie GSM (2G), UMTS (3G) und LTE (4G) immer wieder durch Störsignale beeinträchtigt. Diese können ihre Ursache in Emissionen von Geräten bzw. Systemen besitzen oder sie werden gar absichtlich erzeugt. Der Fokus dieser Untersuchung liegt nicht auf dem Erklären und Beseitigen von EMV-Störungen, sondern auf der Lokalisierung der Störquelle im Wirkbereich moderner Funknetze. An die Stelle einer EMVLaborUmgebung tritt hier also ein von reflektierenden Objekten geprägtes Umfeld

Zielführende Strategien zur Lokalisierung von Störsignalen im Wirkbereich moderner Mobilfunksysteme

Der Schutz des elektromagnetischen Spektrums ist ein Kernelement der EMV. Er wird durch Zuteilung von Frequenzbändern und Vorgabe von Grenzwerten gewährleistet und ermöglicht so den Betrieb von Funksystemen. Trotz dieses Schutzes werden auch moderne Netze wie GSM (2G), UMTS (3G) und LTE (4G) immer wieder durch Störsignale beeinträchtigt. Diese können ihre Ursache in Emissionen von Geräten bzw. Systemen besitzen oder sie werden gar absichtlich erzeugt. Der Fokus dieser Untersuchung liegt nicht auf dem Erklären und Beseitigen von EMV-Störungen, sondern auf der Lokalisierung der Störquelle im Wirkbereich moderner Funknetze. An die Stelle einer EMVLaborUmgebung tritt hier also ein von reflektierenden Objekten geprägtes Umfeld

Destructive Groups: The Role of Projective Identification in Suicidal Groups of Young People

Group suicidal behaviour by young people has been attracting increasing worldwide attention, but the subject has rarely been studied from a clinical or psychodynamic perspective. Although etiological factors are not well understood, unconscious as well as conscious group processes likely contribute to self-destructive actions. In this article we discuss the role of projective identification in the development of suicidal behavior by individuals who are part of a destructive group. We consider how these factors may operate, illustrated through a case description of a young man involved with a group of high school students that included at least four who made serious suicide attempts. Recognition and understanding of these forms of communication have important implications for clinical practice and suicide prevention