Internal alignment of the SLD vertex detector using a matrix singular value decomposition technique

The tracking resolution and vertex finding capabilities of the SLD experiment depend upon a precise knowledge of the location and orientation of the 96 elements of the SLD pixel vertex detector (VXD3) in 3D space. At the heart of the deterministic procedure described here to align the 96 CCDs is the matrix inversion technique of singular value decomposition (SVD). This tool is employed to unfold the detector geometry corrections from the track hit residual data in the VXD3. The algorithm is adapted to perform an optimal χ² minimization by careful treatment of the errors and correlations in the residual measurements. The general form of the problems that might be solved with this technique is discussed. The tracking resolution obtained with the aligned geometry is compared with the starting point, based on an optical survey of the CCDs, and is shown to achieve the design performance.     

Vertex reconstruction using a single layer silicon detector

Typical vertex finding algorithms use reconstructed tracks, registered in a multi-layer detector, which directly point to the common point of origin. A detector with a single layer of silicon sensors registers the passage of primary particles only in one place. Nevertheless, the information available from these hits can also be used to estimate the vertex position, when the geometrical properties of silicon sensors and the measured ionization energy losses of the particles are fully exploited. In this paper, the algorithm used for this purpose in the PHOBOS experiment is described. The vertex reconstruction performance is studied using simulations and compared with results obtained from real data. The very large acceptance of a single-layered multiplicity detector permits vertex reconstruction for low multiplicity events where other methods, using small acceptance subdetectors, fail because of insufficient number of registered primary tracks.     

High-speed use of CCD area sensors as high energy particle detectors

A position sensitive detector for minimum ionizing particles is described. It is based on charge coupled devices (CCDs) area image sensors with single pixel sizes of 22 × 22 μm². The operating frequency is 6.75 MHz and the total readout time for 2.3 × 10⁵ pixels is about 40 ms. The devices are operated close to room temperature.     

Large area microchannel plate detector with amorphous silicon pixel array readout for fast neutron radiography

Fast neutron radiography is a non-destructive testing technique with a variety of industrial applications and the capability for element sensitive imaging for contraband and explosives detection.

Commonly used position sensitive detectors for fast neutron radiography are based on charge coupled devices (CCDs) and scintillators. The limited format of CCDs implies that complex optical systems involving lenses and mirrors are required to indirectly image areas that are larger than 8.6 cm×11.05 cm. The use of optics reduces the light collection efficiency of the imaging system, while the efficiency of hydrogen rich scintillators exploiting the proton recoil reaction is limited by the hydrogen concentration and the magnitude of the neutron scattering cross-section.

The light conversion step inevitably involves a tradeoff in scintillator thickness between light yield and spatial resolution.

The development of large area amorphous silicon (a-Si) panel flat panel photodiode arrays and direct neutron-to-charge converters based on microchannel plates, provide an attractive new form of high resolution, large area, fast neutron imaging detector for the non-destructive imaging of large structures. This paper describes some recent results of both Monte Carlo simulations and measurements for such a detector.     

Development of fully depletable CCDs for high energy physics applications

The principles of standard MOS charge coupled devices (CCDs) as position sensitive detectors in high energy physics experiments are described. Improvements for a new generation of CCDs can be realized with a fully depletable three phase pn-CCD for majority carriers. The channel stop concept of these one- and two-dimensional pixel devices is studied in detail with the help of semiconductor device simulations. The basic idea of the fast clear concept is described. Some expected general properties are given in the summary.     

LHCb Vertex Locator prototyping,testing and production

LHCb is the experiment at the Large Hadron Collider (LHC) dedicated to the study of CP violation in the B-system. Its silicon vertex detector, named VELO for VErtex LOcator, will precisely reconstruct the primary pp interaction vertex, the displaced B-decay vertex and tracks originating from them. The use of the VELO in the LHCb trigger together with its operation in a harsh radiation environment puts additional constraints on the design. The project is soon entering the production phase. Recent results on the tests of prototype modules and components are presented with a focus on the sensor and front-end chip performance.     

The ALEPH minivertex detector

Vertex detectors allow high precision reconstruction of particle tracks and therefore make possible the investigation of the decay topology of short-lived particles in collider experiments.In the ALEPH experiment at LEP a minivertex detector will be installed. It consists of silicon microstrip detectors arranged on two concentric “cylindrical” surfaces around the interaction point. With this geometry it will be possible to measure the r − ϕ − z coordinates of particles traversing the detector. The expected position resolution is 10 μm in r − ϕ and 20 μm in r − z.For optimum signal processing monolithic CMOS readout electronics are under development. Each chip consists of 60 charge sensitive preamplifiers, multiplexed into one output channel. Fast power switching will reduce heat dissipation.Details about construction and expected device performance will be described.     

Noise characteristics of stacked CMOS active pixel sensor for charged particles

The noise characteristics of a stacked CMOS active pixel sensor (SCAPS) for incident charged particles have been analyzed under 4.5 keV Si⁺ ion irradiation. The source of SCAPS dark current was found to change from thermal to electron leakage with decreasing device temperature. Leakage current at charge integration part in a pixel has been reduced to 0.1 electrons s⁻¹ at 77 K. The incident ion signals are computed by subtracting reset frame values from each frame using a non-destructive readout operation. With increase of irradiated ions, the dominant noise source changed from read noise, and shot noise from the incident ions, to signal frame fixed-pattern noise from variations in sensitivity between pixels. Pixel read noise is equivalent to ten incident ions. The charge of an incident ion is converted to 1.5 electrons in the pixel capacitor. Shot noise corresponds to the statistical fluctuation of incident ions. Signal frame fixed-pattern noise is 0.7% of the signal. By comparing full well conditions to noise floor, a dynamic range of 80 dB is achieved. SCPAS is useful as a two-dimensional detector for microanalyses such as stigmatic secondary ion mass spectrometry.     

Calibration and X-ray spectroscopy with silicon CCDs

It is shown that the novel mode of operation of charge coupled devices (CCDs) allows a new method of measuring the X-ray energy-to-charge conversion factor, without requiring externally calibrated circuits etc., thereby reducing possible contributions to systematic uncertainties in this measurement. In addition, the low noise operation of CCDs is shown to lead to possibilities for measuring the Fano factor in silicon with improved precision. Advances in CCD X-ray detection performance are described, including energy resolutions of 80 eV FWHM at a temperature of 180 K, and detection efficiencies of greater than 90%. Such improvements are shown to have potential benefit for various X-ray spectroscopic applications.     

CHICSi—a compact ultra-high vacuum compatible detector system for nuclear reaction experiments at storage rings. I. General structure, mechanics and UHV compatibility

CELSIUS Heavy-Ion Collision Silicon detector system (CHICSi) is a large solid angle, barrel-shaped detector system, housing up to 600 detector telescopes arranged in rotational symmetry around the beam axis. CHICSi measures charged particles and fragments from nuclear reactions. It operates at internal targets of storage rings. In order to optimize space and momentum-space coverage and minimize the low-energy detection limits, CHICSi is designed for use in ultra-high vacuum (UHV, 10⁻⁸ Pa) inside a cluster-jet target chamber. This calls for materials in mechanical support, detectors, Very Large Scale Integrated (VLSI) electronics, connectors, cables and other signal transport devices with very low outgassing. Two auxiliary detector systems, which will operate in coincidence with CHICSi, a heavy-recoil, time-of-flight system (HR-TOF) also placed inside the target chamber and a projectile fragmentation wall (PF-WALL) located outside the chamber, have also been constructed. In total, this combined system registers more than 80% of all charged particles and fragments from typical heavy-ion reactions at energies of a few hundreds of MeV per nucleon.     

Read-noise characterization of focal plane array detectors via mean-variance analysis

Mean-variance analysis is described as a method for characterization of the read-noise and gain of focal plane array (FPA) detectors, including charge-coupled devices (CCDs), charge-injection devices (CIDs), and complementary metal-oxide-semiconductor (CMOS) multiplexers (infrared arrays). Practical FPA detector characterization is outlined. The nondestructive readout capability available in some CIDs and FPA devices is discussed as a means for signal-to-noise ratio improvement. Derivations of the equations are fully presented to unify understanding of this method by the spectroscopic community.     

Requirements for relative intensity correction of Raman spectra obtained by column-summing charge-coupled device data

The relative intensity correction of Raman spectra requires the measurement of a source of known relative irradiance. Raman spectrometers that employ two-dimensional charge-coupled device (CCD) array detectors may be operated in two distinct modes. One mode directly measures the counts in each CCD pixel, but more commonly for the collection of spectra, the counts in the CCD row pixels are summed for a given column. If distortions in the corrected spectral shapes are to be avoided, operation in the mode where rows are summed places restrictions on the spatial intensity profile of the source of known irradiance that is used for the relative intensity correction procedure and, in some cases, also on the spatial intensity profile of the measured Raman light. Numerical expressions are given from which these restrictions can be derived. Magnitudes of distortions that can arise when intensity-correcting spectra obtained with CCD data where rows in a column are summed are estimated by modeling different cases. Data are given showing the inherent pixel quantum efficiency variation that exists in CCDs. Spectra are given showing the effects of a local area of significant change in pixel quantum efficiency that was found to be present on one CCD detector.     

Applications of silicon detectors in high energy physics and astrophysics

Silicon detectors are being increasingly used in high energy physics and in astronomy. In the former case they are used for precisely locating the trajectories of particles which traverse the detectors, while in the latter case they are used for very low level light imaging. In both applications, the use of silicon is preferred because of the low energy needed to liberate an electron-hole pair in the medium and because of the highly developed planar technology which allows sophisticated devices with excellent spatial precision to be fabricated.The specific devices discussed are microstrip detectors and 2-dimensional imaging CCDs, including a summary of radiation damage since this is of importance in both the astronomical and particle physics applications.     

A comparative review of charged particle microbeam facilities

At the low doses (and low dose rates) relevant to environmental and occupational radiation exposure (0-50 mSv), which are of practical concern for radiation protection, very few cells in the human organism experience more than one traversal by densely ionising particles in their lifetime, the intervals between the tracks, if any, typically being months or years. The biological effects of exactly one particle are not well known and cannot be simulated in vitro by conventional broad-beam exposures, due to the random Poisson distribution of tracks. Charged particle microbeam facilities are a unique tool that allows targeting of single cells and analysis of the induced damage on a cell-by-cell basis. In the past few years, many charged particle microbeam facilities for radiobiology have come into operation or are under development worldwide. Different experimental designs have been adopted at various laboratories regarding the achievement of micrometre (or sub-micrometre) ion beam size, by mechanical collimation or focusing, particle detection, and cell recognition and positioning systems. The different approaches are reviewed and discussed in this paper.     

Track fitting in the OPAL vertex detector with stereo wires

The geometry of the vertex chamber for the OPAL detector at LEP is reviewed and expressions for the coordinates of the hits are given in terms of the measured drift distance and z-coordinate. The tracks are fitted by a procedure based on the Lagrange multipliers method. The increase in the accuracy of the fit due to the use of the stereo wires is discussed.     

Recent developments in detector research

Recently developed methods of cryogenic particle detection and potential applications will be introduced. The main part of this article focuses on our experimental results on two different approaches of detecting nuclear radiation with superconducting tunnel junctions. The best energy resolution is obtained when the junction itself serves as absorber. Using Sn/SnO_x/Sn tunnel junctions we obtained an energy resolution of about 90 eV for 6 keV X-rays up to now. The processes limiting the resolution of the present devices will be discussed. Larger absorber masses and position resolution are realized by an entirely new type of particle detector based on the detection of nonthermal phonons which are generated by the absorption of radiation within a single-crystalline absorber of dielectric material. We report on experimental tests of a detector composed of a silicon single crystal (size: 10 × 20 × 3 mm³) and of an array of superconducting Al/Al₂O₃/Al tunnel junctions evaporated onto the surface of the crystal, serving as phonon detectors. Pulse height analysis and the investigation of time differences between pulse onsets in different junctions are shown to yield information about the absorption point of -particles.     

Design and characterization of ion-implanted tracks for 16 Mbit/cm2storage density bubble memory devices

The ion-implanted propagation tracks with contiguous disk patterns (CD tracks) have been confirmed to be better for high density propagation tracks (≥ 16 Mbit/cm²) than those with snake patterns (snake tracks), because of less interactions between bubbles on the other side in the same track. The CD tracks with 1.8 µm × 2.0 µm cell size for 0.5 µm bubbles have been evaluated. The large operating bias field margin of 12.4 percent is obtained at the quasi-static operation with rotating field HRof 60 Oe. The minimum rotating field is 40 Oe. Interdigital folded minor loops are proposed and operated. The proposed minor loops are composed of straight propagation tracks connected alternately to relax the in-side turns. The overall operating margin of 8.4 percent (46 Oe) is obtained at HR= 60 Oe. The feasibility of 16 Mbit/cm²storage density bubble memory devices is confirmed.     

Multiplexed Readout of MMC Detector Arrays Using Non-hysteretic rf-SQUIDs

Metallic magnetic calorimeters (MMCs) are widely used for various experiments in fields ranging from atomic and nuclear physics to X-ray spectroscopy, laboratory astrophysics or material science. Whereas in previous experiments single pixel detectors or small arrays have been used, for future applications large arrays are needed. Therefore, suitable multiplexing techniques for MMC arrays are currently under development. A promising approach for the readout of large arrays is the microwave SQUID multiplexer that employs non-hysteretic rf-SQUIDs to create a frequency shift of high \(Q\) resonators that is in accordance with the detector signal and that can be monitored by using standard microwave measurement techniques. In this paper we discuss the design of a recently developed and fabricated 64 pixel detector array with integrated microwave SQUID multiplexer that was produced to test the suitability of this readout technique. The characterization of dc-SQUIDs with virtually identical washer design compared to the rf-SQUIDs of the SQUID multiplexer revealed that the crucial SQUID parameters such as the critical current of the Josephson junctions or the washer inductance are close to the design values and anticipates a successful operation of the SQUID multiplexer.     

HIGH CONCENTRATION DUST MASS MONITOR

The development and testing of a portable, rugged, self-contained monitoring prototype instrument capable of detecting and measuring airborne, potentially explosive, dust levels at concentrations in the range of 20 to 500 g/m³, has been completed. The output signal provided by this monitor is designed to be essentially independent of particle size and composition. Direct mass concentration readout as well as internal memory capabilities for unattended operation have been incorporated in this device. The design emphasizes rugged-ness, versatility of operation, and adherence to intrinsic safety requirements.

The sensing method incorporated in this monitoring instrument is based on direct air-path beta attenuation detection across a gap of the order of 2 centimeters using a very low energy beta-emitting isotope (Ni-63). The measurement system includes automatic periodic clean-air referencing in order to compensate for any air density fluctuations and/or detector drifts. Measurements, directly indicated in g/m³, are updated automatically every 10 seconds.

Operating at a beta count rate of approximately 6000 to 7000 sec _-1, over the 10-second count period, the observed standard deviation of the measurements was of the order of 2.5 g/m³, around the zero-concentration level.     

Low-temperature tracking detectors

RD39 collaboration develops new detector techniques for particle trackers, which have to withstand fluences up to 10¹⁶ cm⁻² of high-energy particles. The work focuses on the optimization of silicon detectors and their readout electronics while keeping the temperature as a free parameter. Our results so far suggest that the best operating temperature is around 130 K. We shall also describe in this paper how the current-injected mode of operation reduces the polarization of the bulk silicon at low temperatures, and how the engineering and materials problems related with vacuum and low temperature can be solved.