Showing papers in "Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment in 1990"

The construction of the L3 experiment

Abstract: The L3 experiment is one of the six large detectors designed for the new generation of electron-positron accelerators. It is the only detector that concentrates its efforts on limited goals of measuring electrons, muons and photons. By not attempting to identify hadrons, L3 has been able to provide an order of magnitude better resolution for electrons, muons and photons. Vertices and hadron jets are also studied. The construction of L3 has involved much state of the art technology in new principles of vertex detection and in new crystals for large scale electromagnetic shower detection and ultraprecise muon detection. This paper presents a summary of the construction of L3.

Aleph: a detector for electron-positron annihilations at Lep

Abstract: Process-centred Software Engineering Environments (PSEE) are the most recent generation of environments supporting software development activities. Most of PSEE are based on mechanisms promoting enforcement and automation of process activities. In this kind of mechanisms the process models are prescribed in a detailed and complete way. But the experience shows that supporting processes is more concerned with the flexibility of guidance offered during the process performance than with enforcement of a collection of predefined process models. In this paper, we present a solution to support strategic processes in a PSEE by providing a flexible guidance during process enactment.

The VIRGO Project: A wide band antenna for gravitational wave detection

Abstract: The status of advancement of the VIRGO Project is presented: the first-generation results from the Pisa seismic noise super attenuator give an upper limit to the noise transfer function of 2 × 10 −8 at 10 Hz. The upper limit to the absolute noise of the 400 kg test mass at 10 Hz has been measured to be 1.5 × 10 −13 m/√Hz. The scheme and the related problems of the VIRGO interferometer, which is supposed to work down to 10 Hz, are also presented. At the 3rd Pisa Meeting in 1986 we presented the idea of what could be a very efficient seismic noise reduction system able to give a sensitivity h ∼ 10 −25 at 10 Hz, in a 3 km interferometer for 1 year integration time. Now we have two new facts to present: the first is that the attenuation has been built, is working in Pisa, and shows remarkable characteristics. The second is the Italian-French interferometer VIRGO [1,2], a 3 km long antenna for low and high frequency (10–1000 Hz) gravitational wave (GW) detection. These two items will be presented in this article.

Problems in obtaining γγ and γe colliding beams at linear colliders

Abstract: Physical principles of colliding γγ and γe beams are described briefly. Beam-beam effects restricting luminosity are considered. A possible scheme of collision and beam ejection is discussed, together with associated problems. Requirements for accelerator and laser parameters are formulated. Estimations of attainable luminosities and examples of physical processes are given.

Extended maximum likelihood

Abstract: An account is given of the method of extended maximum likelihood. This differs from the standard method of maximum likelihood in that the normalisation of the probability distribution function is allowed to vary. It is thus applicable to problems in which the number of samples obtained is itself a relevant measurement. If the function is such that its size and shape can be independently varied, then the estimates given by the extended method are identical to the standard maximum likelihood estimators, though the errors require care of interpretation. If the function does not have this property, then extended maximum likelihood can give better results.

Suboptimal filtering of 1/ƒ-noise in detector charge measurements

Abstract: Processing of 1 tf - noise by suboptimal filters in detector charge measurements is considered. The achievable values of equivalent noise charge are compared to those provided by the optimum filter. Some aspects of filters processing 1 tf - noise , like the degradation in the accuracy of charge measurements due to a bipolar or to a unipolar, flat-topped weighting function are described. Several conclusions are expected to be useful in the design of analog processors for radiation detectors when the front-end 1 tf - noise is not negligible.

Reflective UV photocathodes with gas-phase electron extraction: solid, liquid, and adsorbed thin films

Abstract: The photoemission quantum efficiency of reflective photocathodes in methane gas has been investigated in the spectral range between 140 and 250 nm. The spectral response of solid metals and CsI, as well as of liquid and solid TMAE film, have been measured. The high quantum efficiency of CsI (35% at 170 nm) makes it attractive for BaF 2 or xenon scintillation detection. A BaF 2 crystal coupled to an ionization chamber with a reflective CsI photocathode has been successfully tested. Adsorbed TMAE films can significantly increase the quantum yields of metal and CsI (to 46% at 170 nm), making them suitable for fast RICH and other applications.

Analysis of positron annihilation lifetime data by numerical laplace inversion with the program CONTIN

Abstract: The performance of the program CONTIN [Stephen W. Provencher, Comput. Phys. Commun. 27 (1982) 229], modified to solve Fredholm integral equations with convoluted kernels of the type that occur in the deconvolution and analysis of positron annihilation lifetime data, is investigated with computer-simulated test data. The method avoids direct determination of the instrument resolution function by employing the decay curve of a reference material with a well-known single lifetime. CONTIN employs a constrained, regularized least-squares analysis to calculate a continuous annihilation-rate probability density function (pdf) which is the most parsimonious solution that is consistent with the experimental data and prior knowledge. The performance of the algorithm for extracting positron annihilation lifetime information was evaluated by using several measures of the information content of the data described by Schrader and Usmar [in: Positron Annihilation Studies of Fluids, ed. S. Sharma (World Scientific, Singapore, 1988) p. 215]. The quality of the CONTIN reconstruction of the annihilation-rate pdf is strongly dependent on the information content of the data and is greatly improved as the total number of counts in the data set is increased. Nevertheless, the method provides excellent estimates of the intensities and mean lifetimes of peaks in the annihilation-rate pdf, even when the total counts in the data set are relatively low (105–106). The sensitivity of the algorithm to systematic errors in the data, including errors in the instrument resolution function, shifts in the positron of the zero-time channel of the sample and reference data and contamination of the reference decay by additional lifetime components was also evaluated. Errors in the FWHM of the instrument resolution function and shifts in the zero time channel as small as 1 10 to 1 5 of the channel width of the instrument generate additional spurious peaks in the annihilation-rate pdf and introduce errors in the lifetime parameters of the short-lived components.

Amplex, a low-noise, low-power analog CMOS signal processor for multi-element silicon particle detectors

Abstract: AMPLEX is a monolithic analog signal processor fabricated in 3 μm n-well CMOS and originally designed for the inner silicon detector of the UA2 Experiment at the CERN SPS Collider. However, it is suitable for various other types of detectors, and results are also given for a multiwire proportional chamber (MWPC). The chip contains 16 channels, each consisting of a charge amplifier, a shaper amplifier and a track-and-hold stage. The channel outputs are connected to an analog multiplexer which is controlled by digital circuitry. For a power consumption of 1 mW per channel and an adjustable peaking time of 600 to 800 ns, the equivalent noise charge is 400 rms electrons plus 33 rms electrons per pF of input capacitance. The DC stabilisation of the charge amplifier is obtained using a non-linear feedback resistor. This novel MOS element is a key feature of the design and enables low noise as well as DC stability of the charge amplifier, even for increased detector leakage current up to several hundred nA. Such operating conditions can occur following radiation damage of silicon pad detectors.

A versatile double-axis multicounter neutron powder diffractometer

Abstract: The double-axis multicounter diffractometer (DMC) installed at the 10-MW reactor SAPHIR (PSI) has been designed as a good-flux, good-resolution (presently Δd/d ⩾ 4×10−3) neutron powder diffractometer. The detector bank is based on a commercial position-sensitive linear BF3 detector which may be automatically and precisely positioned on air cushions (standard epoxy floor). Vertically variable focusing germanium or pyrolythic graphite monochromators are used. Special efforts were made to optimize the sample environment, e.g. by developing an oscillating radial collimator system. Although the monochromator shielding is not yet in a final state, the diffractometer is successfully operating since several years. Design properties and operational experience are discussed. Online data analysis based on LSI and VAX computers is facilitated by user-friendly software.

On the thermoionization in hot cavities

Abstract: Thermally equilibrated gases of low pressure are characterized by a high degree of ionization at temperatures easily reached with laboratory devices. This property is generally believed to be the principle behind ion sources of the hot-cavity-type. The necessary condition of thermal equilibrium for the cavity plasma is, however, often very unlikely, though in general tacitly assumed. It is shown that especially in the most widespread application - low pressure operation for isotope separation on-line - the cavity plasma is far off thermal equilibrium. The consequence is that the influence of the cavity parameters (work function, temperature, plasma density and pressure of the neutral particles) on the ionization efficiency is decisively different from what is expected for a thermalized system.

An extended range neutron rem counter

Abstract: Extensive Monte Carlo calculations have been carried out to assess the possibility of extending the sensitivity of a neutron rem counter of the Andersson-Braun type up to several hundred MeV. The validity of the model adopted has first been checked by comparing with experimental data the calculated response curve and the angular dependence of the sensitivity for a well known commercial rem counter. Next, a number of modifications to the configuration of the moderator-attenuator have been investigated. The response functions and angular distributions produced by two simple solutions yielding an instrument with a sensitivity extended up to 400 MeV are presented. The response of the original rem counter and of its two modified versions to nine test spectra has also been calculated. The resulting instrument is transportable rather than portable, but the availability of an extended range neutron survey meter would be of great advantage at medium and high energy particle accelerator facilities.

Large harmonic bunching in a high-gain free-electron laser

Abstract: Properly taking into account the coupling between different harmonics in a high-gain free-electron laser (FEL), we demonstrate that the exponential gain of the fundamental radiation wavelength drives the third-harmonic bunching at a rate which is three times that of the fundamental. This leads to almost equal saturation bunching parameters on the fundamental and the harmonic wavelength. This is the underlying mechanism of the resonant-frequency tripling method in a two-wiggler FEL.

Estimation of absolute photon yields in liquid argon and xenon for relativistic (1 MeV) electrons

Abstract: Using recent scintillation data of liquid argon and xenon, the numbers of photons emitted in both liquids have been estimated. The ideal photon yields are 5.1 × 10 4 photons/MeV for liquid argon and 6.8 × 10 4 photons/MeV for liquid xenon. The photon yields due to 1 MeV electrons are 4.0 × 10 4 photons and 4.2 × 10 4 photons for respective liquids. These numbers are almost the same as that of a NaI(Tl) crystal.

The MSU Miniball 4π fragment detection array

Abstract: A compact and highly granular charged particle detection array, covering 89% of 4π in solid angle, is described. In its present configuration, the array consists of 188 fast-plastic CsI(Tl) phoswich detectors arranged in 11 rings coaxial about the beam axis. Each phoswich detector is comprised of a 40 μm thick plastic scintillator foil and a 2 cm thick CsI(Tl) crystal selected for good scintillation uniformity. The detectors are read out by photomultiplier tubes. Elemental identification up to Z ≈ 18 and isotopic identification of H and He nuclei is achieved by exploiting pulse shape discrimination techniques.

The fast simulation of electromagnetic and hadronic showers

Abstract: A program for the fast simulation of electromagnetic and hadronic showers using parameterizations for the longitudinal and lateral profile is described. The fluctuations and correlations of the parameters are taken into account in a consistent way. Comparisons with data over a wide energy range are made.

Computational aspects of optics design and simulation: COSY INFINITY

Abstract: The new differential algebraic (DA) techniques allow very efficient treatment and understanding of nonlinear motion in optical systems as well as circular accelerators. To utilize these techniques in their most general way, a powerful software environment is essential. A language with structure elements similar to Pascal was developed. It has object oriented features to allow for a direct utilization of the elementary operations of the DA package. The compiler of the language is written in Fortran 77 to guarantee wide portability. The language was used to write a very general beam optics code, COSY INFINITY. At its lowest level, it allows the computation of the maps of standard beam line elements including fringe fields and system parameters to arbitrary order. The power of the DA approach coupled with an adequate language environment reveals itself in the very limited length of COSY INFINITY of only a few hundred lines. Grouping of elements as well as structures for optimization and study are readily available through the features of the language. Because of the openness of the approach, it offers a lot of power for more advanced purposes. For example, it is very easy to construct new particle optical elements. There are also many ways to efficiently manipulate and analyze the maps.

Generation of XUV light by resonant frequency tripling in a two-wiggler FEL amplifier☆

Abstract: FEL operation at short wavelengths is limited by electron-beam quality, by the availability of mirrors for oscillators and by the availability of input sources for FEL amplifiers. It is possible to use an FEL amplifier as a resonant-frequency tripling device, generating light and strong bunching at the third harmonic of a conventional input source in an initial wiggler section, then using a second wiggler section resonant at the tripled frequency to amplify the short-wavelength light. Neither mirrors nor a short-wavelength input source are required, and some relaxation of the electron-beam quality appears to be possible. We illustrate the scheme with a one-dimensional model and then with NUTMEG simulations of an 80 nm FEL amplifier initiated by a 240 nm input signal, in which an efficiency of the electron-beam power conversion to 80 nm light of nearly 10−4 was obtained.

Coincidence summing in gamma-ray spectroscopy

Abstract: A new technique has been developed to calculate coincidence-summing corrections in γ-ray spectroscopy. In this technique the general coincidence-summing equations were derived in matrix notation, which allowed extracting either the first-order correction (combinations of only two coincident γ-rays) or a full correction (all possible combinations of emitted γ-rays). Subsequently, it is shown how the technique can be applied to the determination of the source disintegration rate, γ-ray emission rates or peak efficiencies in the presence of coincidence summing. In particular, the technique has been applied to the determination of peak efficiencies of a germanium detector. The peak efficiencies were iterated self-consistently using the coincidence-summing equations. The above calculation showed that, in general, the full correction is necessary for complicated decay schemes. In addition, a method has been developed to determine the peak-to-total ratio for a germanium detector in the presence of an interfering γ-ray.

The Karlsruhe 4π barium fluoride detector

Abstract: A new experimental approach has been implemented for accurate measurements of neutron capture cross sections in the energy range from 5 to 200 keV. The Karlsruhe 4π barium fluoride detector consists of 42 crystals shaped as hexagonal and pentagonal truncated pyramids forming a spherical shell with 10 cm inner radius and 15 cm thickness. All crystals are supplied with reflector and photomultiplier, thus representing independent gamma-ray detectors. The energy resolution of the 4π detector is 14% at 662 keV and 7% at 2.5 MeV gamma-ray energy, the overall time resolution is 500 ps and the peak efficiency 90% at 1 MeV. The detector allows to register capture cascades with 95% probability above a threshold energy of 2.5 MeV. Neutrons are produced via the 7Li(p, n)7Be reaction using the pulsed proton beam of a Van de Graaff accelerator. A collimated neutron beam is passing through the detector and hits the sample in the centre. The energy of captured neutrons is determined via time of flight, the primary flight path being 77 cm. The combination of short primary flight path, a 10 cm inner radius of the spherical BaF2 shell, and the low capture cross section of barium allows to discriminate background due to capture of sample-scattered neutrons in the scintillator by time of flight, leaving part of the neutron energy range completely undisturbed. This feature, together with the high efficiency and good energy resolution for capture gamma-rays, allows to separate the various background components reliably enough, that the capture cross section ratio of two isotopes can be determined with an accuracy of ≤ 1.0%. The detector will be used for nuclear astrophysics to investigate the origin of the heavy elements in the slow neutron capture process.

Optimum filters for detector charge measurements in presence of {1}/{f} noise

Abstract: The optimum shape of the weighting function for detector charge measurements, in the presence of series 1 f noise superimposed on parallel and series white noises, is investigated. The corresponding theoretical limits in charge resolution for finite or infinite processing times have been calculated, and compared with the values obtained using traditional cusplike weighting functions optimum for white noises only.

Simultaneous pattern recognition and track fitting by the Kalman filtering method

Abstract: A progressive pattern recognition algorithm based on the Kalman filtering method has been tested. The algorithm starts from a small track segment or from a fitted track of a neighbouring detector, then extends the candidate tracks by adding measured points one by one. The fitted parameters and weight matrix of the candidate track are updated when adding a point, and give an increasing precision on prediction of the next point. Thus, pattern recognition and track fitting can be accomplished simultaneously. The method has been implemented and tested for track reconstruction for the vertex detector of the ZEUS experiment at DESY. Detailed procedures of the method and its performance are presented. Its flexibility is described as well.

Experimental confirmation of a new semiconductor detector principle

Abstract: A new detector-amplification principle proposed by Kemmer and Lutz in 1986 has been experimentally verified. Outstanding features of this device are the built-in amplification, the signal charge storage capability and the possibility of repeated non-destructive readout. The device was used for detection of X-rays from a 241 Am and from Am and from an 55 Fe source. Very low noise figures ( σ =30 electrons corresponding to an energy resolution of FWHM = 250 eV at 6 keV energy) have been obtained at room temperature. Various applications of the structure either as detector or as purely electronic element are possible. One of the most intriguing is the use as a pixel detector with random access non-destructive readout. This device may be operated at very low power, as only reading (of one single pixel at a time), not storing, consumes power. Further options of the device are fast clearing, gating and variation of the pixel size during readout. The latter property can be used to drastically increase the readout speed compared to more standard two dimensional devices as e.g. CCD detectors, as one may restrict the high density readout to regions of interest determined beforehand by a coarse scan of the whole detector. An alternative use of the device is as an analog or digital memory, or as a simple transistor with drastically reduced parasitic capacitances. Possible further developments are the combination with a novel three dimensional analog storage device which may either be used as a detector with built-in storage of several charge images or as a three dimensional analog memory.

Lead fluoride: An ultra-compact Cherenkov radiator for em calorimetry

Abstract: We have tested the material PbF2 and found that it is a Cherenkov radiator suitable for electromagnetic calorimetry. It has a density of 7.77 g/cm3, a radiation length of 0.93 cm, a refractive index of 1.8, and an optical cutoff at about 280 nm. An electromagnetic shower is 15% shorter longitudinally, and its apparent lateral extent has a 13 smaller radius in PbF2 than in BGO. We have measured 1300 photoelectrons per GeV of deposited energy and have set an upper limit on the energy resolution of 5.1%/√E. The first measurements show PbF2 to be much more radiation resistant than lead glass; also, when damaged, it almost fully recovers after a short exposure to UV light.

Coulomb interactions in particle beams

Abstract: The physical aspects of an analytical model for the different manifestations of Coulomb interactions between charged particles in low and medium density beams, e.g. as found in electron beam lithography instruments and scanning electron microscopes, are reviewed. The theory is found to be in close agreement with the results of numerical Monte Carlo simulations. A comparison is given with other existing theories on the subject.

Dwarf Ball and Dwarf Wall: Design, instrumentation, and response characteristics of a 4π CsI(Tl) plastic phoswich multidetector system for light charged particle and intermediate mass fragment spectrometry

Abstract: A 4π multidetector intermediate mass fragment and charged particle spectrometer is described. It consists of the Dwarf Ball section with 65 CsI(Tl) plastic scintillator phoswiches closely packed to cover the angular range of 32°–168°, and the Dwarf Wall section, with 40 CsI(Tl) plastic phoswiches covering the angular range of 4°–32°. For each detector that fires, three regions of the photomultiplier anode current are separately integrated; one at early times for the fast plastic ΔE, another at intermediate times for the bulk of the signal from the CsI(Tl), and a third in the tail region of the CsI(Tl) signal. In addition, the times are recorded for each detector that fires. From this information, 1,2,3H, 3,4He and the elements from Li to Mn can be identified and their energies measured over a large dynamic range. The geometry, construction, energy calibration, gain stability, associated electronics, and an approximate light charged particle identification procedure are discussed. Examples of the performance of the spectrometer from heavy-ion induced reaction experiments are given. The capabilities of this device as a channel selecting device in conjunction with the spin spectrometer are also discussed.

Results of prototype studies for a spaghetti calorimeter

Abstract: In the framework of the LAA project, prototypes for a new type of calorimeter, intended for the detection of both electromagnetic (em) and hadronic showers, muons and missing energy (eg neutrinos) at high-luminosity multi-TeV pp colliders, were tested The detector consists of scintillating plastic fibres embedded in a lead matrix at a volume ratio 1:4, such as to achieve compensation The optimization of the construction of the detector modules is described, as well as the performance concerning em shower and muon detection and e/π separation We used electron, pion and muon beams in the energy range 10–150 GeV for this purpose For the energy resolution of electrons we found 13%/trE, with a constant term of 1% The signal uniformity was better than 3% over the total surface of projective modules The signal linearity for em shower detection was better than 1%, and the e/π separation was better than 5 × 10−4 for isolated particles Channeling effects are negligible, provided that the angle between the incoming particles and the fibre axis is larger than 2°

Design of an associated particle imaging system

Abstract: A fast-neutron-capture imaging system is being designed. 14.1 MeV neutrons will be produced with a sealed-tube neutron generator (STNG) via the t(d, n) 4 He reaction. The associated alpha particle will be imaged defining the neutron direction. The timing and energy of a neutron-inelastic-scatter gamma ray will define the source-to-target distance and the target isotope. A special sealed-tube neutron generator (STNG) has been designed. The performance of various components of the system has been measured or calculated, and the results are used to predict the overall performance of the system.

Mosaic crystal X-ray spectrometer to resolve inelastic background from anomalous scattering experiments

Abstract: We describe a mosaic crystal X-ray energy analyzing spectrometer to separate the inelastic scattering enhanced by radiation near an absorption edge from the elastic diffraction of interest for atomic site determinations. An important consideration is to minimize the sensitivity to changing source profile so that diffracted intensities are comparable over large angular ranges. Energy resolution limited mainly by fractional-mm source sizes is comparable to that with nearly perfect crystals. High spectrometer efficiency for the diffusely distributed X-ray scattering associated with amorphous materials and the weak Laue scattering from chemical order in crystalline solid solutions is achieved with a combination of sagittal and parafocusing from a mosaic graphite monochromator. Because of the mosaic nature of the crystal, the parafocusing geometry achieves meridional focusing for a magnification of 1 : 1, and a broad energy range proportional to the mosaic spread is dispersed along a linear position-sensitive detector for simultaneous detection. Energy resolution ΔE/E of 1 500 and lower is achieved in the 6–10-keV energy range tested. Though the sagittal radius is fixed, the spectrometer will operate effectively over an X-ray energy range of E ± 0.5E with fixed focal distances. This mosaic crystal spectrometer offers similar advantages for X-ray spectroscopy experiments.

A gas-filled UV-photon detector with CsI photocathode for the detection of Xe light

Abstract: Xe-scintillation UV photons are detected with a CsI photocathode coupled to a double-stage low-pressure wire chamber. At 20 Torr of Ch4 the quantum efficiency of the photocathode is 9%. The combination of a gas scintillation chamber with the solid photocathode avalanche chamber (SPAC) yields an energy resolution of 4.1% (FWHM) for 60 keV X-rays. The stability of the photocathode is discussed.