Search

We present a study of the radiation field at various locations in the ATLAS experiment, using compact detector systems based on pixelated silicon sensors assembled with Timepix readout chips. The hodoscope design of the ATLAS-Timepix (TPX) detectors includes neutron converters in between two sensors, allowing the characterization of both neutron and charged particle fields on a track by track basis. Thermal and fast neutrons are discriminated by segmenting the sensor area with dedicated sensitive materials. Using specific pattern recognition algorithms, clusters from electrons and photons above ~10 keV, minimum ionizing particles (MIPs), and highly ionizing particles are classified. A coincidence method using the time-over-threshold mode of the chip is developed to extract stopping power and directional information of energetic charged particles. Thermal neutron fluences are obtained for each ATLAS-TPX unit, illustrating the effect of detector material and shielding in the experimental cavern. Reconstructed trajectories of energetic charged particles point out radiation coming from the interaction point and other hot spots.

The design and performance of a new front-end acquisition system is presented in this paper. It was developed to be used with muon array with resistive plate chamber (RPCs) for tagging air showers (MARTA’s) RPC detectors that measure the muonic component of cosmic ray air showers. The system is hybrid and capable of counting active channels and performing a charge measurement. It is low power (1.43 W per 64 channels), compact ( $21.6 \times 14.4\,\,\mathrm {cm^{2}}$ per 64 channels), stable, and reliable to comply with the strict demands of field operation associated with experiments that measure air showers. The front-end is based on an application-specified integrated circuit [Multi Anode Read-Out Chip (MAROC)] with 64 input channels, which is responsible for the digitization of the RPC signals. While a simple threshold measurement is applied after a fast shaper to count particles, the charge measurement is performed by an analog to digital converter that reads the peak of a slow shaper. An field-programmable gate array is responsible for control of all the digital part which includes storing the MAROC outputs and sending them to a Central Unit [via low voltage differential signal (LVDS)] or PC (via USB). Both the count and charge measurement performance are assessed. The threshold efficiency curve is measured for different temperatures. For all the conditions tested, the efficiency is 100% for charges higher than 52 fC. The overall efficiency to detect muons is studied by placing an RPC between a hodoscope and comparing the efficiency of the front-end with another established data acquisition system. The efficiency results are consistent within the statistical uncertainties of the measurements showing that the MARTA front-end does not introduce unwanted inefficiencies in the setup. The charge measurement is tested in the laboratory using a signal generator. Different shaping conditions and input charges are used to study the waveform of the slow shaper. A linear dependence between input charge and the value measured by the MAROC was found and taken as the calibration curve for the particular channel tested.

We developed a field-programmable gate array (FPGA) TDC module for the tracking devices of Fermilab SeaQuest (E906) experiment, including drift chamber, proportional tube and hodoscope. The requirement of time resolution is better than 4 ns. This 64-channel TDC is made of a 6U VMEbus unit equipped with a Microsemi ProASIC3 Flash based FPGA of low power and high radiation tolerance. The new FPGA firmware (Run2-TDC) is designed to reduce the data volume and data acquisition (DAQ) deadtime. The firmware digitizes multiple input hits of both polarities while allowing users to turn on a multiple-hit elimination logic to remove after-pulses in the wire chambers and proportional tubes. A scaler is fitted into the firmware of each channel to allow for recording the number of hits in its respective channel. The TDC resolution is determined by internal cell delays of 450 ps, and a measurement precision of 200 ps has been achieved. As a demonstration of constructing the Wave Union TDC using an existing multi-hit TDC without modifying its firmware, external wave union launchers are utilized in our test to improve the TDC's measurement precision. Measurement precision is nearly halved (108 ps) in data based on a four-edge wave union. An even larger improvement of measurement precision (69 ps) has been reached by combining the approaches of Wave Union TDC and multiple-channel ganging.

This work compares two possible solutions to achieve a high resolution in a hodoscope based on Plastic Scintillating Fibers (PSF) by obtaining the point of maximum interaction of the radioactive beam with the detector. The two fitting algorithms are the Maximum Likelihood Estimation and a non-linear least-squares fitting with the Levenberg-Marquardt Algorithm. Both approaches have been tested, compared and implemented in Field Programmable Gate Array (FPGA) devices.

It is pointed out that new developments in hodoscope radiation detection technology offer a wide range of capabilities for arms control treaty verification (ACTV) applications. This concept uses an array of radiation detectors to image or detect objects inside opaque containments. Hodoscope systems can detect neutrons and/or gamma-rays. The systems can be based on transmission of radiation through the objects, can detect radiation stimulated in the objects, or can detect intrinsic object radiation. Laboratory measurements to demonstrate a range of potential applications have been performed. Gamma-ray transmission hodoscopes can be used to inspect canisters, rail cars, etc. to monitor objects such as rocket motors. The use of relatively weak isotopic radiation sources makes it unnecessary to employ expensive and high-intensity accelerators. The heavy metal of nuclear warheads is characterized by strong gamma-ray absorption, and these materials could be counted by low-resolution tomography. Absorbers located in line with objects will themselves be detected, and sources located in the object region will be subtracted out as background. Intrinsic gamma-ray radiation from warheads can also be detected in a passive-instrument mode. >

A fine-grain hodoscope to measure the position of showers in the outer (>52 cm) region of the E-705 electromagnetic calorimeter is described. The hodoscope is constructed with two layers of vertical conducting plastic tubes for the X position measurement of showers. Y position measurement of showers was accomplished by cathode-induced horizontal strips. A 50/50-ethane mixture bubbled through isopropyl alcohol at 0 degrees C was circulated through the tubes in parallel. The tubes were operated at +1.925 kV on the wire (below the region of saturated avalanche) in the limited proportionality mode. The hodoscope is described, and results are presented for the position resolution, shower width, and charge detected as a function of calibration electron energy. >

As part of an ongoing program to improve the fuel-motion capability of the fast-neutron hodoscope, a response model has been developed for the Hornyakbutton detector. The model provides a description of the efficiency and gamma sensitivity of a Hornyak button in terms of detector parameters such as scintillator concentration, grain size, length, and transparency. It is possible using this model to quantitatively choose detector parameters for the Hornyak button.

The multichannel hodoscope at TREAT is capable of detecting motion of fuel resulting from intentional meltdown of fuel pins contained within a test capsule. The system has been in operation in its present form since 1969, having participated in over 50 transients. Operational experience and evolutionary improvements are the subject matter of this report. The rather complex hodoscope system, which is supported by an involved series of steps before results can be achieved, has worked well within design prediction. Computer-aided reconstruction of the data has been provided to obtain displays, plots, and movies of fuel motion events.

The design and performance of a 4.2-radiation-length, lead-sandwich, gas tube hodoscope are discussed. The device, measuring 1*2 m/sup 2/ in area and 12 cm in depth, was used in Fermi National Accelerator Laboratory experiment 705. Multiple samplings of anode wires situated within three-walled aluminum tubes were used to generate an X coordinate; similarly, capacitively coupled copper-clad strips were ganged together to yield a Y coordinate. The results reviewed of an analysis of electron calibration data taken during a recent six-month running period are reviewed. The position resolution (in millimeters) is seen to be 0.8+3.3/ square root E+31/E for the 9.92 mm-spaced wires and 0.6+3.2/ square root E+32 for the 12.5-mm strips, where E represents the electron beam energy in GeV. The correlation between energy as measured by the wires and energy as measured by the strips is fairly tight, with an asymmetry RMS (root mean square) for 30-GeV electrons of about 4%. >

The fast-neutron hodoscope at the Transient Reactor Test Facility detects fuel motion in thick opaque capsules during in-core destructive transient tests. Counts from several hundred detectors, each with rates up to a megahertz, are collected at intervals as short as a millisecond for up to tens of seconds. The large amount of data must be decoded, normalized, represented in suitable forms, and analyzed. A computer-controlled magnetic disk data acquisition system has been installed which provides shorter data collection intervals, simplifies decoding, and permits immediate data analysis. Data normalizations and representations have been developed which significantly increase the dynamic range, yield sensitive quantitative indications of fuel mass motion, and render the data intuitively comprehensible. The improved hodoscope system performance level is demonstrated by results from a recent transient test, Pinex-2, which show the quantitative evolution of fuel mass motion from 1515 MW peak reactor power through a 1 MW post-scram radiation level.

A large acceptance, multisegmented detector system capable of the simultaneous detection of heavy ions and light ions (HILI) has been constructed. The heavy ions are detected with a segmented gas-ionization chamber and a multiwire proportional counter, while the light ions are detected with a 192-element plastic 'phoswich' hodoscope. Processing the large number of signals is accomplished through a combination of CAMAC and FASTBUS modules and preprocessors and a host minicomputer. Details of the data acquisition system and the reasons for adopting a dual-standard system are discussed. A technique for processing signals from an individual hodoscope detector is presented. >

Joint LASL/ANL studies of the fuel motion performance capability of a fast-neutron hodoscope have been performed on a 91-pin fuel bundle. Optimization of the neutron detectors used in the hodoscope was also investigated. The neutron detectors tested were a Hornyak button and a stilbene detector with pulse shape discrimination. These studies show that a hodoscope can provide useful fuel motion detection capability for large bundles and that the amount of information provided is greatly increased by the use of neutron detectors with high neutron thresholds and high detection efficiency. These measurements indicate that the TREAT hodoscope can be upgraded to meet most of the fuel motion diagnostic requirements of new safety facilities.

A multi-chamber fission array has been designed, fabricated, and tested with integrated and condensed electronic circuitry. The intention was to develop an array of over 100 channels of detectors able to cover the high power range of TREAT transients in conjunction with the fast neutron hodoscope. The array has been developed through a prototype stage consisting of 31 possible channels. A wide variety of operating conditions have been tested, including choice of fissile isotope, coating thickness, gas filling, plate spacing, high voltage, and electronic circuitry. The configuration tested at TREAT consisted of ten active channels incorporated in a doubly contained system. Miniaturized electronic circuits are appended almost directly to the parallel plates of the fission counters. Cost and space limitations were major factors in the design.

The fuel-motion measurement capability of the fast-neutron hodoscope has been upgraded by the addition of a 360-detector proton-recoil proportional-counter array, which detects high-energy fission neutrons. The current sensitive amplifier/discriminator module for each detector fits into a 12.7- by 12.7- by 102-mm package and costs less than $100 per module. It has a 50-ns rise time, a noise level of 100 nA, and a deadtime per event of 200 ns. Provision has been provided for the independent adjustment of the input current versus discriminator voltage for each module. The new proportional-counters cost approximately $400 each. Each detector has been tested to have the same gain versus voltage response. A space-charge model relating count-rate changes to space-charge effects has also been developed. The new detector array has been operational for approximately two years and has become the main detector system in fuel-motion analysis. It has significantly improved the linearity, stability, count-rate capability, and setup ease of the hodoscope.

The fast neutron hodoscope at TREAT can be modified for high resolution radiography. Time-resolved radiography normally performed by the hodoscope with coarse spatial resolution may be traded for good space definition at the expense of time resolution, allowing the hodoscope to become a dual purpose instrument. The modifications require remote motorized scanning of the collimator and simultaneous 334-channel data collection over extended intervals of time. By doing so, it becomes possible to generate digital radiographs without the necessity for mechanical disturbance of the object being viewed. Furthermore, separate and distinct images of fuel and steel may be produced.

This report describes a system of electronics to be used with a proportional wire chamber hodoscope. The system, which uses CAMAC packaging and data handling philosophy, consists of octo (8 channel) wire signal amplifiers, octo 4-bit per wire latch modules, gate fanout modules, crate controllers, and two types of data processor-interface units to the SDS 9300 computer. System operation is explained, and each component is described.

A fast parallel logic system employing MECL II integrated circuits with a total analysis time of about 100 nsec was used to preselect elastic scattering events in a K-p scattering experiment. A ninety counter scintillation hodoscope arranged in banks of ten counters each allowed the selection of events on the basis of a) The presence of exactly two outgoing particles b) Coplanarity of outgoing particles with respect to the incoming beam c) Approximate agreement of outgoing angles with calculated kinematic requirements. About 3% of candidate events satisfied this set of restrictions and initiated spark chamber pulsing and data transfer to a computer.

A hodoscope sensitive to penetrating fast fission neutrons has been designed for the test reactor TREAT. Discrete portions of an imaginary 15 × 23 matrix centered on the fuel plane are scanned by individual fast neutron detector channels. Located outside the reactor core, 13 ft from the test pin, this hodoscope is able to record the movement of fuel with a 0.15-in. horizontal resolution and close to 1-msec time resolution. Instrumentation was optimized with regard to cost. Each neutron signal is translated to a digital positive pulse, several microseconds duration, which gates a 6977 fluorescent vacuum tube into conduction. An array of 334 lamps is photographed by a fast framing camera at 1000 frames/sec, making the readout system, in effect, an inexpensive two-parameter analyzer with a capability approaching 107 cps.

Dual Zone Spatial Analysis (ZSA2 or ZSA-ZSA) performs spatial (position) analysis of detector data, applying techniques familiar in two-parameter pulse-height analysis. ZSA-ZSA is designed to police multiple-detector (hodoscope) nuclear experiments during initial setup and throughout data accumulation and readout. Interconnection, timing, and operational errors, equipment failure, detector misalignment, and noise pulses are detected, annunciated, localized, and tallied. Programmed test routines simulate the experiment. Data logging further assures integrity. Simultaneous studies are readily performed by steering data to different memory locations. The current version handles two 32 detector arrays plus control detectors. Capacity is limited by the 1024 word (17 bit words) ferrite core memory.

A 16-channel discriminator-gated latch CAMAC module using MECL II has been designed and built for use in a phototube trigger hodoscope array. The module includes individual discriminator outputs, analog summing outputs, and high speed digital multiplicity outputs which are processed by an "analyzer" in order to decide if the particle multiplicity is suitable for streamer chamber firing. Latch data are transmitted to a PDP-9 for recording and further processing.

The fast neutron hodoscope used at TREAT reactor for fuel meltdown studies has been improved to permit count rates above 106/sec in each channel. Also a digital readout system, based on integrated circuit scalers, has been introduced. Peak instantaneous data rate capability, now about 107/sec, can be expanded to 109/sec.

The Vela-4 satellite energetic-particle experiment consists of (a) a pair of diffused-junction semiconductor detectors for electrons in the energy range 30-600 keV, and (b) a garded, four-element, solar particle telescope for detecting protons from 0.5-100 MeV and alpha particles from 3.6-380 MeV, in 13 dfferentially-counted channels. Separation of protons from alpha particles is accomplished by an in-flight particle identifier. Two additional simplified telescopes are used to extend the angular coverage of the primary telescope, and a wide angle, high sensitivity scintillation detector is employed to monitor low intensity solar particle events. The design and operation of these instruments will be described.

At energies of 10 Bev and higher, it is not easy to obtain physically separated beams of ? and ? mesons. We have constructed a hodoscope system which will register the identity of each of 20 particles entering a bubble chamber over a 100 microsecond time interval. Particles are localized by a scintillator hodoscope with matrix elements 1 cm square. Particle identity is determined with Cerenkov counters. The combined information is displayed on an oscilloscope and photographed at each bubble chamber expansion.

The wires of wire spark chambers or hodoscope planes are individually threaded through magnetic memory cores, which are "set" by the spark currents. Only a small fraction of the wires are struck by the sparks of one event, so that it is practical to generate addresses for those cores which have been "set." Circuits are described which scan the cores sequentially, 32 at a time, generating addresses and transmitting them to a buffer store or to a computer. A certain minimum time, in our case determined by the transit time of signals in cables, is required to scan the cores. A small additional time is required to generate and store each address. Any number of sparks may be handled in one event, and checking features have been incorporated in the system.

A low-speed modification of the chronotron has been adapted to recording data from an array of 144 photomultiplier tubes. By noting the kinds of co. nbinations of signals expected for the various physical events of interest a relatively simple pulse position code is devised to display the data. This display gives addresses and amplitudes of signals for a composite event and in addition permits us to determine whether the waveforms are bona fide in nature or spurious. Some degree of redundancy may also be incorporated into the system.

A large area time-of-flight telescope has been studied for future application in space-borne cosmic ray experiments. A new compensation technique for propagation delays inside the scintillators has been applied, which is operative in two perpendicular directions. This technique, superior to conventional one-dimensional compensations, allows high rejection probability for upward moving single particles at very short counter distances. Besides mechanical advantages a short counter distance is desirable because it permits a large field of view for the detector. A measurement of light transit times in scintillators is presented and based on it, directionality for shower events is discussed.

In order to exploit the high event rates at ISABELLE, it will be necessary to have fast detection with fine spatial resolution. The authors are currently constructing a prototype fine-grained hodoscope, the elements of which are scintillating optical fibers. The fibers have been drawn from commercially available plastic scintillator which has been clad with a thin layer of silicone. So far it has been demonstrated with one mm diameter fibers, that with a photodetector at each end, the fibers are more than 99% efficient for lengths of about 60 cm. The readout will be accomplished either with small diameter photomultiplier tubes or avalanche photodiodes used either in the linear or Geiger mode. The program of fiber development and evaluation will be described. In addition an account of the progress on the prototype hodoscope will be given.

Starting with 1 inch diameter PVT scintillator as a preform, the authors have drawn fibers of several diameters ranging from 1 to 4 mm. These fibers have been coated in line with the draw to form optical fibers. Several cladding materials whose index of refraction ranges from 1.35 to 1.55 have been used. The most successful fiber has been obtained with an extra thick (200 micron) cladding of silicone in combination with a linear draw, as opposed to a spool draw. This fiber is acceptable, but it is extremely fragile and its quality is difficult to control. The authors are currently constructing a 12 channel hodoscope with 1 mm spatial resolution using 4 mm diameter fibers. An account is also given of the progress made in using the Avalanche Photo Diode (APD) operated in the Geiger mode as the photo detector.

We have measured the centroids of high energy electromagnetic showers initiated by positrons in the energy range 2 to 17.5 GeV with a fine grained scintillation hodoscope composed of seven 1 cm wide elements placed behind a 3.6 radiation length (15 cm) converter composed of SCG1-C scintillation glass. A simple first moment calculation using the ionization observed in each element of this hodoscope yields a shower position resolution as a function of energy of: ?(mm) ? 0.7 ± 5.6/?E(GeV). We present results on the energy dependence of the shower profiles and the ionization measured by this hodoscope.

A short analysis of a hodoscope system and digital arithmetic devices for selection a defined scattering angle is made. Some construction and experimental results are presented.

For interactions of the type M1 + M2 ? M3 + M4 the kinematics of both initial particles and one secondary particle determine the reaction completely. Given a fixed initial state and any missing mass M4, the momentum-angle correlation for particle M3 is determined uniquely. In the spectrometer described, this correlation is preserved as a line image in the focal plane of a double focusing magnetic lens. Dispersions both in the plane of production and at right angles to it separate the images corresponding to different values of M4, for which the spectrum is obtained directly by means of a 28-counter hodoscope in the focal plane. Each hodoscope counter is gated with a scintillation and Cerenkov counter telescope to identify particle M3. During each beam pulse the outputs from the hodoscope counters are recorded on 10 Mc/sec scalers. Between accelerator pulses the contents of these scalers are read onto magnetic tape and into a PDP-5 computer, which accumulates, corrects, and displays the data continuously to provide an on-line monitor.

A scintillation counter hodoscope with 1 mm granularity using fiber optic light guides was designed for use in a 200-GeV secondary hadron beam. Special care was taken to position the scintillators withhigh accuracy. The efficiency in a beam of 2.5? 106 particles/sec is 98%.