N. A. Smith

The DELPHI Microvertex detector

The DELPHI Microvertex detector, which has been in operation since the start of the 1990 LEP run, consists of three layers of silicon microstrip detectors at average radii of 6.3, 9.0 and 11.0 cm. The 73728 readout strips, oriented along the beam, have a total active area of 0.42 m2. The strip pitch is 25 μm and every other strip is read out by low power charge amplifiers, giving a signal to noise ratio of 15:1 for minimum ionizing particles. On-line zero suppression results in an average data size of 4 kbyte for Z0 events. After a mechanical survey and an alignment with tracks, the impact parameter uncertainty as determined from hadronic Z0 decays is well described by (69pt)2 + 242 μm, with pt in GeV/c. For the 45 GeV/c tracks from Z0 → μ− decays we find an uncertainty of 21 μm for the impact parameter, which corresponds to a precision of 8 μm per point. The stability during the run is monitored using light spots and capacitive probes. An analysis of tracks through sector overlaps provides an additional check of the stability. The same analysis also results in a value of 6 μm for the intrinsic precision of the detector.

Design and performance of an analog delay and buffer chip for use with silicon strip detectors at LHC

Abstract An analog delay and buffer chip has been designed and built in 1.2 μm CMOS technology to be used in silicon detectors at LHC. Measurements on the performance of the prototype chip are presented. The storage cells variations are smaller than 0.65 rms mV, i.e. 1 100 of the signal in its input for a minimum ionizing particle.

Proton tracking for medical imaging and dosimetry

For many years, silicon micro-strip detectors have been successfully used as tracking detectors for particle and nuclear physics experiments. A new application of this technology is to the field of particle therapy, where radiotherapy is carried out by use of charged particles such as protons or carbon ions. Such a treatment has been shown to have advantages over standard x-ray radiotherapy and as a result of this, many new centres offering particle therapy are currently under construction - including two in the U.K.. The characteristics of a new silicon micro-strip detector based system for this application will be presented. The array uses specifically designed large area sensors in several stations in an x-u-v co-ordinate configuration suitable for very fast proton tracking with minimal ambiguities. The sensors will form a tracker capable of giving information on the path of high energy protons entering and exiting a patient. This will allow proton computed tomography (pCT) to aid the accurate delivery of treatment dose with tuned beam profile and energy. The tracker will also be capable of proton counting and position measurement at the higher fluences and full range of energies used during treatment allowing monitoring of the beam profile and total dose. Results and initial characterisation of sensors will be presented along with details of the proposed readout electronics. Radiation tests and studies with different electronics at the Clatterbridge Cancer Centre and the higher energy proton therapy facility of iThemba LABS in South Africa will also be shown.

A new silicon tracker for proton imaging and dosimetry.

For many years, silicon micro-strip detectors have been successfully used as tracking detectors for particle and nuclear physics experiments. A new application of this technology is to the field of particle therapy where radiotherapy is carried out by use of charged particles such as protons or carbon ions. Such a treatment has been shown to have advantages over standard x-ray radiotherapy and as a result of this, many new centres offering particle therapy are currently under construction around the world today. The Proton Radiotherapy, Verification and Dosimetry Applications (PRaVDA) consortium are developing instrumentation for particle therapy based upon technology from high-energy physics. The characteristics of a new silicon micro-strip tracker for particle therapy will be presented. The array uses specifically designed, large area sensors with technology choices that follow closely those taken for the ATLAS experiment at the HL-LHC. These detectors will be arranged into four units each with three layers in an x–u–v configuration to be suitable for fast proton tracking with minimal ambiguities. The sensors will form a tracker capable of tracing the path of ~200 MeV protons entering and exiting a patient allowing a new mode of imaging known as proton computed tomography (pCT). This will aid the accurate delivery of treatment doses and in addition, the tracker will also be used to monitor the beam profile and total dose delivered during the high fluences used for treatment. We present here details of the design, construction and assembly of one of the four units that will make up the complete tracker along with its characterisation using radiation tests carried out using a 90Sr source in the laboratory and a 60 MeV proton beam at the Clatterbridge Cancer Centre.

Performance, high voltage operation and radiation hardness of full-size ATLAS charge division silicon detectors with LHC electronics

ATLAS silicon detectors designed for charge division read-out were produced during 1995 and have been extensively studied both in the laboratory and test beam at the CERN SPS. Data have been taken with the analogue read-out FELIX-128 chip and studies simulating other read-out architectures under consideration by ATLAS have been performed. To evaluate survival in the harsh environment of the LHC, detectors have been tested to high voltage, both before and after radiation damage by protons exceeding the expected charged hadron dose after 10 years of LHC operation. These tests have all employed analogue read-out to be sensitive to changes in noise and charge collection efficiency as a function of the detector damage.

Silicon detectors for forward tracking in ATLAS

Abstract A 12 cm long silicon microstrip detector module with a fan geometry has been designed and constructed. The performance of the detector has been studied in a test beam at CERN. Results are presented on the hit efficiency and the position resolution as a function of position along the strips. With a hit efficiency of 99.5% and a spatial resolution of typically 35 μm the performance of these detectors exceeds that of other candidate technologies for the precision forward tracker of the ATLAS inner detector.

A thirty-two channel VME scaler

Abstract This article describes a novel programmable scaler design. It is highly adaptable and has 32 possible inputs in one unit making it a convenient and cost effective method of providing scalers for large complicated experiments. Programming and reading of the contents is performed over a VME interface.

Stochastic Trap Analysis and Risking – A Multi-seed Stochastic Approach to Fully 3D (Geocellular-based) Trap Analysis

Trap analysis is inherently a three-dimensional problem involving fault geometry, stratigraphy, and seal integrity. The complex interplay of these elements can make it very difficult to understand and visualize the controls on column height – even for a trap analysis expert. Compounding the issue is the uncertainty associated with reservoir distribution, fault offset and seal thickness. Despite the often equivocal nature of the input, fault seal analysis in the industry has historically been done in a deterministic manner with some attempt at varying the stratigraphic model to give low, medium and high cases. Further, the calculation of fault sealing potential has commonly been done on a per fault basis rather than within the greater context of a trap framework. There are, of course, vendor products and practitioners that address column height prediction in an integrated and perhaps stochastic fashion. However, it could be argued that these practices have created a perception that fault seal analysis is a black box affair, which is often perceived as an ‘art’ rather than a rigorous investigation.

The DELPHI microvertex detector

The main characteristics of the DELPHI Microvertex Detector are presented. The performance in terms of impact parameter resolution, association efficiency, and ambiguity is evaluated after two years of data taking at LEP.

ALIBAVA : A portable readout system for silicon microstrip sensors

A portable readout system for micro-strip silicon sensors has been developed. The system uses an analogue pipelined readout chip, which was developed for the LHC experiments. The system will be used to characterise the properties of both non-irradiated and irradiated micro-strip sensors. Heavily irradiated sensors will be operated at the Super LHC (SLHC). The system hardware has two main parts: a daughter board and a mother board. The daughter board contains two readout chips, analogue data buffering, power supply regulation and chip-to-sensor fan-in structures. The mother board is intended to process the analogue data that comes from the readout chips and from external trigger signals, to control the whole system and to communicate with a PC via USB. There is provision for an external trigger input (e.g. scintillator trigger) and a synchronised trigger output for pulsing an external excitation source (e.g. laser system). A prototype of the system will be presented.