Showing papers in "Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment in 1988"

Position-sensitive detector with microstrip anode for electron multiplication with gases☆

Abstract: A position-sensitive detector of a new type has been developed. A microstrip anode replaces the wires generally used for electron multiplication with gases. The microstrips which are fixed on a glass substrate are produced by means of photolithography. The applied electric potential alternates between each strip. With a position-sensitive neutron detector equipped with this new type of anode a counting rate of 2.3 MHz/cm 2 has been measured. The microstrip anode combines the improved qualities of a proportional counter with certain properties of a photomultiplier tube.

How to combine correlated estimates of a single physical quantity

Abstract: Experiments to measure a single physical quantity often produce several estimates based on the same data, and which are hence correlated. We describe how to combine these correlated estimates in order to provide the best single answer, and also how to check whether the correlated estimates are mutually consistent. We discuss the properties of our technique, and illustrate its application by using it for a specific experiment which measured the lifetime of charmed particles.

The CDF Detector: An Overview

Abstract: The Collider Detector at Fermilab (CDF) is a 5000 t magnetic detector built to study 2 TeV p p collisions at the Fermilab Tevatron. Event analysis is based on charged particle tracking, magnetic momentum analysis and fine-grained calorimetry. The combined electromagnetic and hadron calorimetry has approximately uniform granularity in rapidity-azimuthal angle and extends down to 2° from the beam direction. Various tracking chambers cover the calorimeter acceptance and extend charged particle tracking down to 2 mrad from the beam direction. Charged particle momenta are analyzed in a 1.5 T solenoidal magnetic field, generated by a superconducting coil which is 3 m in diameter and 5 m in length. The central tracking chamber measures particle momenta with a resolution better then δpT/pT2 = 2 × 10−3 (GeV/c)−1 in the region 40°

A 13-element Ge detector for fluorescence EXAFS

Abstract: At low concentrations, recording X-ray absorption spectra in fluorescence excitation mode is more sensitive than transmission mode. For dilute samples, the fluorescence signal is often obscured by scattered X-rays, and matrix and filter fluorescence. To discriminate against this background, while maintaining a large angular acceptance and high count rate capability, we have constructed a new detection system based on an array of intrinsic Ge detectors. The device uses 13 individual 11 mm diameter Ge detectors, clustered in a 1:3:5:3:1 pattern on a common cryostat, combined with Soller slits and filters to reduce the background signals. Pulsed optical feedback preamplifiers are followed by Gaussian-shaping amplifiers having fast discriminators to register the incoming count rate (ICR). Correction for dead time using the ICR signal allowed operation in the vicinity of 75 kHz per channel, with a 1 μs shaping time at 6 keV. For lower count rate applications, an average resolution of 160 eV at 5.9 keV was obtained with 8 μs shaping. Recent experience with this detector at the Stanford Synchrotron Radiation Laboratory is presented. The performance is illustrated using spectra obtained from phosphorus compounds and a thin iridium foil. The performance of this device is compared with previous fluorescence detection schemes, such as those using filter/slit combinations or barrel monochromators.

Data acquisition systems for linear and area X-ray detectors using delay line readout

Abstract: Digital systems for fast readout of linear and area position sensitive detectors based on commercially available CAMAC modules are described. The first version of the system has been used extensively for synchrotron radiation work carried out at the EMBL outstation in Hamburg during the last five years. A second system allowing measurements at count rates up to 600 kHz on a continuous source has been recently installed. An overview of the complete acquisition and information processing system is also given.

Progress in resistive plate counters

Abstract: Results of experimental tests on resistive plate counters of 6 × 0.5 m2 area are reported. The results show that this technique is suitable for time of flight measurements over large areas with a resolution of the order of 1 ns.

Design and performance of an imaging plate system for X-ray diffraction study

Abstract: A new readout system for a BaFBr: Eu2+ photostimulable phosphor screen (imaging plate) was constructed by modifying a drum scanner, with a design optimized for X-ray diffraction and scattering applications. An effort was made to achieve a high detective quantum efficiency below 20 keV, a small pixel size (25 μm × 25 μm), a low quantization noise (0.22%) using 12-bit A/D converters, and the capability to cover an inherent dynamic range (1:105) of the photostimulated luminescence by using two photomultiplier tubes. This system is being used in several synchrotron radiation experiments: Laue diffraction of protein crystals, small angle diffraction from a single muscle fiber, powder diffraction from crystals in a diamond anvil cell, and time-resolved small-angle X-ray scattering from a synthetic polymer during stretching.

Quick scanning exafs: First experiments

Abstract: By speeding up a conventional X-ray monochromator by a factor of 100 using the quick scanning EXAFS (QEXAFS) mode the data collection time required for a typical EXAFS scan was reduced to a couple of seconds, making XANES scans in a split second possible. Typical absorption spectra of Fe and Cu foils taken in 3.5–10 s covering an energy region of up to 800 ev are shown. It is demonstrated that the normalized Cu-EXAFS and its Fourier transform agree very well with the results of a conventional step by step measurement. The new approach allows the use of fluorescence detection and hereby makes possible the time dependent investigation of the changes in structure or valence state of a wide variety of samples which are inaccessible for transmission spectroscopy.

The CDF central electromagnetic calorimeter

Abstract: The central electromagnetic calorimeter for the Collider Detector at Fermilab uses a hybrid design with scintillator and wavelength shifter for energy measurement and an embedded strip chamber for position determination and longitudinal shower development. Complementary calibration systems are incorporated in the design. Calorimeter characteristics and performance are summarized. An average energy resolution, σ(E) E , of 13.5%√E sin θ (with E in GeV), and a position resolution of ±2 mm at 50 GeV are measured.

A new scintillation material: Pure CsI with 10 ns decay time

Abstract: The properties of pure CsI have been studied with respect to its application as a scintillation material.

Limitations on the use of the pulsed-wire field measuring technique☆

Abstract: As wigglers become longer and the wavelength of the light they produce becomes shorter, the requirements for magnetic field uniformity and precision of wiggler construction become more severe. Techniques used to measure magnetic fields and to estimate the performance of wigglers are now being pushed to their limits in precision and are generally awkward and time consuming in practice. A new field-error measurement technique has been developed that has the usual advantages of a null technique, demonstrates high sensitivity to field errors, and is rapid and simple to employ. With this technique, it appears practical to use computer control to both measure and correct field errors. In a particularly attractive application, these measuring and correcting steps could be carried out on a daily basis for an operational wiggler, which is mounted under vacuum in its optical cavity. In this way, changes in the fields caused by aging or by thermal or radiation-induced deterioration effects could be rapidly identified and corrections could be instituted without significant interruption to normal operations. The principles and limitations of this technique will be described and examples given of various implementations that have been examined experimentally.

15 UD Pelletron of the Nuclear Science Centre — status report

Abstract: An Inter-University research centre is being established in New Delhi with a 15 UD Pelletron accelerator in its first phase. The present status of this project is described.

The Cdf Central and Endwall Hadron Calorimeter

Abstract: The CDF central and endwall hadron calorimeter covers the polar region between 30° and 150° and a full 2π in azimuth. It consists of 48 steel-scintillator central modules with 2.5 cm sampling and 48 steel-scintillator endwall modules with 5.0 cm sampling. A general description of the detector is given. Calibration techniques and performance are discussed. Some results of the test beam studies are shown.

X-ray microprobe using multilayer mirrors

Abstract: Multilayer reflectors for the X-ray region have now progressed beyond the experimental stage to the point where they can be relied upon as optics for experimental systems, in synchrotron radiation research as well as in other fields. This paper reviews the design considerations for an X-ray microprobe, and summarizes experience with prototypes tested at both SSRL and NSLS. The optical systems described employ multilayer-coated spherical mirrors arranged in the Kirkpatrick-Baez configuration to demagnify the X-ray source by a factor of several hundred. By this means a spot of X-rays less than 10 μm square can be produced. The optical aberrations and other factors that limit the performance are detailed, and possible ways to improve the performance are discussed. In the prototypes the spot is directed on the specimen which is carried on a stage that can be translated horizontally and vertically. The characteristic fluorescent X-rays excited by the focused 10 keV photons are analysed by an energy-dispersive Si(Li) detector, so that by scanning the stage an elemental concentration map of the specimen is built up. In a companion paper [A.C. Thompson, J.H. Underwood, Y. Wu, R.D. Giauque, K.W. Jones and M.L. Rivers, these Proceedings, p. 318] some experimental programs are described, and estimates of the elemental sensitivity are provided.

Microsecond mass separation of heavy compound nucleus residues using the Daresbury recoil separator

Abstract: The recoil separator at the Daresbury Laboratory is described. An efficient charged particle beam transport system is combined with Wien filters to select heavy ions within a small velocity range at angles around 0° which have been produced by heavy ion induced reactions. The system separates and refocusses particles with a given mass to charge ( A Q ) ratio. Resolution in A Q is 1 in 300. The time taken to determine the atomic mass A and atomic number Z of an individual nucleus passing through the recoil separator is about 10−6 s. This is fast enough for phenomena associated with the compound nucleus decay to be electronically tagged according to the nuclear species produced. An example using γ-ray detectors around the compound nucleus formation target is given.

CDF Central Muon Detector

Abstract: Design, construction and performance characteristics of the streamer chambers for the central muon detector at CDF are described. A single hit TDC is used for measurements in the drift (azimuth) direction while charge division is used for measurements along the sense wire (pseudorapidity). The chambers operate in the limited streamer mode with a 50%/50% ratio of argon/ethane bubbled through ethanol. Measurements in a cosmic ray test stand, pion test beam and as part of the CDF detector indicate that an rms resolution of 250 μm in the drift direction and an rms resolution of 1.2 mm along the sense wire are attainable.

Speed and noise limits in ionization chamber calorimeters

Abstract: Relations among the speed of response, the signal-to-noise ratio and the charge collection time in ionization chamber calorimeters are analyzed. A dominant limiting factor to the speed of response is the charge transfer time from the electrodes to the amplifier determined by the electrode capacitance CD and the inductance of connections Ls. The time parameter L s C D sol1 2 has to be at least an order of magnitude smaller than the required length of the overall calorimeter response. The charge collection time plays a secondary role in determining the speed of response, while together with the charge yield it affects the signal-to-noise ratio.

SHADOW: New developments

Abstract: We describe the new extensions that we have implemented in our synchrotron radiation ray tracing code, SHADOW. The most important are the new wiggler source, the extension of 100 keV of the optical constant database, the novel power density calculations capabilities and the inclusion of the full crystal and multilayer optics cases. Current work and future prospects will also be discussed.

Sassy, a gas-filled magnetic separator for the study of fusion reaction products

Abstract: A gas-filled on-line recoil separator at the Berkeley SuperHILAC is described. The separator consists of a magnetic dipole and a quadrupole doublet. The system is filled with He at a pressure of about 1 Torr (∼ 130 Pa). It separates particles according to their average magnetic rigidity. This allows a separation of evaporation residues, scattered target atoms and beam projectiles in a nuclear reaction. The separation time is in the order of 10 −6 s; the transmission is about 50% for evaporation residues, less than 10 −3 for scattered target-like recoil ions and transfer products, and about 10 −15 for full energy beam projectiles. Experimental data over a wide range of reactions are given and it is shown that the average charge of the recoils is determined by the atomic shell structure of the moving ionized atom in the gas.

Particle identification via pulse-shape discrimination with a charge-integrating ADC

Abstract: A charge-integrating ADC has been used to sample the intensity in two different time regions of a pulse and thus to sense the shape of the pulse. This idea has been applied to produce neutron/γ-ray discrimination from pulses in a liquid scintillation detector. Optimization of available parameters yields good pulse-shape discrimination for pulses greater than those produced by 100 keV electrons. The method uses only general purpose electronics.

Performance of a scintillating fibre detector for the UA2 upgrade

Abstract: A large scintillating fibre detector for the UA2 experiment at the CERN p p Collider is under construction. It will be used for tracking and electron identification. The performance of a full scale test module containing 960 fibres of 2.1 m length and 1 mm diameter is described.

The magnicon — An advanced version of the gyrocon

Abstract: A new VHF generator with circular deflection of a high power relativistic electron beam is described as an outgrowing of the gyrocon proposed by Budker in 1967. The output resonator of the device is placed in a static magnetic field providing synchronous interaction of electrons with the electromagnetic field. An accompanying magnetic field and prolonged time of interaction enable one to achieve higher power within the decimeter and centimeter wave range compared to that of the gyrocon and klystron due to the higher electrical strength of the output resonator, a decreased heat generation and an easier beam guidance. In order to get higher gain and efficiency the magnicon deflection resonator is also placed in a magnetic field (of double magnitude). Test results for a magnicon of 30 cm wave range built at the INP are given. The power obtained is 2.6 MW for a pulse duration of 30 μs with a repetition rate of 1 Hz and an electron efficiency of 85%.

Progress toward a soft X-ray FEL☆

Abstract: We review the FEL physics and obtain scaling laws for the extension of its operation to the soft X-ray region. We also discuss the properties of an electron beam needed to drive such an FEL, and the present state of the art for the beam production.

Radiation damage in silicon microstrip detectors

Abstract: A radiation damage effect on silicon strip detectors of pn-junction type is investigated using a high energy proton beam. In order to clarify the cause of leakage current increase, several variations of strip detectors with different surface structures were made and tested. No appreciable differences in leakage current increase are observed among these samples. A strong temperature dependence on leakage current is observed. This can be explained by a formation of radiation induced trap energy levels in the bulk silicon. A moderate room temperature annealing is seen. A pulse height degradation of about 10–20% is observed at a few Mrad of radiation. Some implications of the present results are discussed for possible application of silicon semiconductor detectors in future high energy hadron colliders.

The Beam and Detector for a High Precision Measurement of {CP} Violation in Neutral Kaon Decays

Abstract: The K0 beam and detector used for a high-precision measurement of the CP-violation parameter ϵ′ at the CERN Super Proton Synchrotron (SPS) are described. The beam provides KL and KS alternately through a common decay region. The detection of the decays is based on wire chambers and calorimeters without employing a magnet. The trigger and readout system achieve a high selectively for the suppressed, CP-violating, two-pion decays of the KL by incorporation of hard-wired processors. The readout is based on Fastbus for maximum data rates.

Performance of a uranium/tetramethylpentane electromagnetic calorimeter

Abstract: A calorimeter, consisting of uranium plates and thin liquid ionization chambers filled with tetramethylpentane (TMP) at room temperature, has been tested using electrons between 10 and 70 GeV. The essential characteristics of the liquid are discussed, including measurements of the free electron lifetime. Results on uniformity, linearity and energy resolution are described and some information on the response to hadrons has been obtained. A single TMP box containing four electrodes and a TMP position detector for electromagnetic showers have also been tested.

New structures for position sensitive semiconductor detectors

Abstract: Some recent developments in “standard” detectors such as silicon strip detectors are described and a proposal for further improvement is made In view of future applications in high rate environments we propose completely new detector-amplification structures for two dimensional measurement with gating and fast clearing possibilities One of them allows local storage of several charge images in sequence and delayed selective readout

High resolution hadron calorimetry

Abstract: The components that contribute to the signal of a hadron calorimeter and the factors that affect its performance are discussed, concentrating on two aspects: energy resolution and signal linearity. Both are decisively dependent on the relative response to the electromagnetic and the nonelectromagnetic shower components, the e/h signal ratio, which should be equal to 1.0 for optimal performance. The factors that determine the value of this ratio are examined. The calorimeter performance is crucially determined by its response to the abundantly present soft neutrons in the shower. The presence of a considerable fraction of hydrogen atoms in the active medium is essential for achieving the best possible results. Firstly, this allows one to tune e/h to the desired value by choosing the appropriate sampling fraction. And secondly, the efficient neutron detection via recoil protons in the readout medium itself reduces considerably the effect of fluctuations in binding energy losses at the nuclear level, which dominate the intrinsic energy resolution. Signal equalization, or compensation (e/h = 1.0) does not seem to be a property unique to 238U, but can also be achieved with lead and probably even iron absorbers.

The los alamos photoinjector program

Abstract: Free electron lasers (FELs) require electron beams of high peak brightness. In this presentation, we describe the design of a compact high-brightness electron source for driving short-wavelength FELs. The experiment uses a laser-illuminated Cs 3 Sb photoemitter located in the first rf cavity of an injector linac. The photocathode source and associated hardware are described. The doubled YAG laser (532 nm), which is used to drive the photocathode, produces 75 ps micropulses at 108 MHz repetition rate and peak powers of approximately 300 kW. Diagnostics include a pepper-pot emittance analyzer, a magnetic spectrometer, and a 4 ps resolution streak camera. Present experiments give the following results: micropulse current amplitudes of 100 mA to 400 A, beam emittances ranging from 10 π mm mrad to 40 π mm mrad, an energy spread of ± 3%, and peak current densities of 600 A/cm 2 The design of experiment has now been changed to include a separately phased rf cavity immediately following the first cavity. This modification enables us to study the effects of phasing with the possibility of improving the injector performance. Also, this change will improve the vacuum conditions in the photoelectron source with a consequent improvement in lifetime performance. A brief discussion on the possible applications of this very bright and compact electron source is presented.

Superpositional many-detector systems and neutron diffraction of microsamples

Abstract: The superposition method for recording neutron diffraction patterns by means of multidetector movable systems is described. Luminosity and resolution characteritics of “small” systems (with 10–16 detectors) and the annular diffractometer DISK (with 224 detectors) are shown. Applications of the diffractometer DISK to structural research using microquantities of matter (of about 1 mg or less) are proposed and results of such experiments are demonstrated.