Expanded array for giant air shower observation at Akeno

As the first stage of a future huge air shower array, the Akeno array was expanded to about 20 km² by adding 19 scintillation counters of 2.25 m² area outside the present 1 km² array and installing a new data collection system. These detectors are connected successively by two optical fiber cables. The total number of electrons and the arrival direction of extensive air showers of 10¹⁰ GeV can be determined with accuracies of 25% and 3° respectively with this array. The present recording system is applicable to other experiments in which many sensors are connected in sequence.     

A new method to detect gamma ray extensive air showers which directly measures angles and identifies muons

We describe an extensive air shower array (GRAND™) ⁷ which is currently under construction. It is dedicated to recording ultrahigh energy (UHE) gamma rays from stellar point sources by measuring the angle of charged secondaries with proportional wire chamber tracking detectors. This new method is designed to give 0.25° angular resolution for the primary gamma direction with 100 detected secondary electrons. These same tracking detectors make possible a new, inexpensive detector for muons thereby enabling the rejection of muon-rich hadronic shower background.     

Development of low cost liquid scintillator counters for cosmic ray experiments

Large area scintillation counters for use in an extensive air shower array have been developed. These detectors are based on liquid scintillator contained in vacuum-formed acrylic dishes and exhibit good spatial uniformity and timing resolution.     

Specific features of 3-D detection arrays of plastic scintillators

This paper describes the 3-D array of scintillation detectors made of a plastic scintillator. Its operation is based on obtaining simultaneously the signal arrival time, spatial coordinates, and amplitude of scintillation signal produced in detection elements by radiation. Such arrays are capable of identifying and localizing neutron and gamma sources, discriminating signals from these sources, and reducing the background caused by gamma rays, cosmic-ray muons, and neutrons.     

Development of a NaI(Tl) detector with superior photon energy resolution for use above 100 MeV

We have designed and tested a new high resolution NaI(Tl) total absorption scintillation counter. The detector is a cylinder composed of a 26.7 cm diameter by 55.9 cm long NaI core with a concentric 10.8 cm thick NaI annulus that is divided into quadrants. The NaI detector is surrounded by a 12.7 cm thick plastic scintillator to veto both cosmic rays and events with significant shower leakage from the NaI. High uniformity of light production and collection throughout the detector is required for superior resolution. The detector has a measured resolution of 1.3% and 1.7% FWHM for 130 MeV photons and 330 MeV electrons, respectively. Computer simulations to account for loss of resolution due to pileup and energy spread of the beam indicate that the ultimate experimental resolutions at these energies are 1.2±0.1% and 1.3±0.1%. The resolutions at these two energies are at least a factor of 2 better than that of any other total absorption scintillation counter available today. Based on shower simulations, the detector is expected to have a resolution of approximately 1.3% for collimated 130–2000 MeV photons.     

Detector system for the measurement of the muon array density spectrum in cosmic ray showers

A Monte Carlo simulation is performed in order to find the optimum detector configuration for measurements of the array density spectrum of muons (E > 1 GeV) in extensive air showers. Preliminary measurements were done with a pair of thin plastic scintillation detectors.     

Bragg curve spectroscopy in a 4π geometry

Ionization counters employing Bragg curve spectroscopy have been constructed for use in a 4π geometry. These detectors compare very favorably in terms of both energy and charge resolution with small solid angle devices. These detectors have a large dynamic range because they are backed by scintillation detectors, and are thus capable of detecting and identifying particles with energies from 1 MeV/nucleon up to 200 MeV/nucleon.     

Fabrication and characterization of large size LiF/CaF2:Eu eutectic composites with the ordered lamellar structure

As alternative candidates for the ³He neutron detectors, ⁶LiF/CaF₂:Eu eutectic composites were fabricated and their scintillation properties were evaluated. Large size LiF/CaF₂:Eu eutectic composites of 58 mm diameter and 50 mm thickness were produced by Bridgman method. The composites had a finely ordered lamellar structure along the solidification direction. The lamellar structure was controlled by the direction and the rate of solidification, and it was optimized to improve the scintillation properties. Better results were achieved when thinner lamellar layers were aligned along the scintillation light path.     

Extensive air shower experiment at Kolar Gold Fields

An experiment to determine the nature of primary cosmic rays of energy > 10¹⁴ eV by studying high energy (> 220 GeV) muons and their correlations with other parameters of extensive air showers generated by them, was carried out at Kolar Gold Fields, India (atmospheric depth of 920 g cm⁻²). An accurate estimate of shower parameters in showers as small as 10⁴ particles was achieved by means of a closely packed array of large area detectors and by employing special methods of analysis. In this paper, the details of the array, the data recording system, the procedure of data analysis and error estimates are described.     

Beam tests with large area silicon sandwich calorimeters for electron energies between 1 and 6 GeV

Specially developed large area silicon detectors were used for electromagnetic shower calorimeters. Tests have been performed in the energy range between 1 and 6 GeV. Measurements of shower development, visible energy and energy resolution are presented and compared to those obtained in other experiments.     

Imaging of high-Z material for nuclear contraband detection with a minimal prototype of a muon tomography station based on GEM detectors

Muon Tomography based on the measurement of multiple scattering of atmospheric cosmic ray muons in matter is a promising technique for detecting heavily shielded high-Z radioactive materials (U, Pu) in cargo or vehicles. The technique uses the deflection of cosmic ray muons in matter to perform tomographic imaging of high-Z material inside a probed volume. A Muon Tomography Station (MTS) requires position-sensitive detectors with high spatial resolution for optimal tracking of incoming and outgoing cosmic ray muons. Micro Pattern Gaseous Detector (MPGD) technologies such as Gas Electron Multiplier (GEM) detectors are excellent candidates for this application. We have built and operated a minimal MTS prototype based on 30 cm×30 cm GEM detectors for probing targets with various Z values inside the MTS volume. We report the first successful detection and imaging of medium-Z and high-Z targets of small volumes (∼0.03 L) using GEM-based Muon Tomography.     

Fabrication of excimer laser annealed poly-Si thin film transistor by using an elevated temperature ion shower doping

We have investigated the effect of an ion shower doping of laser annealed poly-Si films at elevated substrate temperatures. The substrate temperature was varied from room temperature to 300°C when the poly-Si film was doped with phosphorus by a non-mass-separated ion shower. Optical, structural, and electrical characterizations have been performed in order to study the effect of the ion shower doping. The sheet resistance of the doped poly-Si films was decreased from 7 × 10⁶ Ω/sq to 700 Ω/sq when the substrate temperature was increased from room temperature to 300°C. This large change in sheet resistance is due to the fact that the doped films do not become amorphous but remain in the polycrystallinephase. The mildly elevated substrate heating appears to contribute mainly to reduction of ion damages incurred in the poly-Si films in addition to the activation of dopants during the ion shower doping. From the fabricated n-channel poly-Si TFTs, the current crowding effect do not occur because of the low contact source-drain resistance and the field effect mobility of 120 cm²/(V s) has been obtained.     

Electromagnetic shower development in uranium and tungsten: A comparison of data from a silicon sampling calorimeter

Longitudinal electromagnetic shower development has been studied in uranium and tungsten using a sandwich calorimeter with silicon as the active medium. Data were taken with incoming electron energies of 2, 4 and 6 GeV. The silicon detectors were operated with depletion layers of both 200 and 70 μm. The energy resolution of the calorimeter was reduced by less than 10–15% when the detectors had depleted layer widths of 70 μm.     

Scintillating and particle discrimination properties of selected crystals for low-temperature bolometers: from LiF to BGO

Selected crystals have been investigated at 20 mK for their properties of scintillation produced under irradiation. A scintillation signal is found in preliminary studies of YAP:Ce, GSO:Ce, CaF₂:Eu and Al₂O₃:Ti crystals thanks to high sensitivity light detectors. The full mixed “light-and-heat” bolometric technique has been applied to further characterize materials already employed in rare event researches: CaWO₄, BGO, undoped Al₂O₃ (sapphire). All these crystals show powerful discrimination properties for /γ or nuclear recoil/γ detection, with a special mention to undoped Al₂O₃, hitherto untested, which revealed an unexpected strong light emission. A weaker light signal has been found on LiF and TeO₂ bolometers too, sufficient to separate alpha from gamma events in these crystals.     

TANGO Array.: 1. The instrument

TANGO Array is an air shower experiment which has been constructed in Buenos Aires, Argentina. It was commissioned during the year 2000 becoming fully operational in September, 2000. The array consists of four water Cherenkov detectors enclosing a geometrical area of $\text{∼30,000}\text{m}{}^2$ and its design has been optimized for the observation of Extended Air Showers produced by cosmic rays near the “knee” energy region $\text{∼4×10}{}^{15}\text{eV}$. Three of the detectors have been constructed using 12,000-l stainless-steel tanks, and the fourth has been mounted in a smaller, 400-l plastic container. The detectors are connected by cables to the data acquisition room, where a very simple system, which takes advantage of the features of a four-channel digital oscilloscope, was set for data collection. This data collection setup allows a fully automatic experiment control which does not require operator intervention. It includes monitoring, data logging, and daily calibration of all detectors. This paper describes the detectors and their associated electronics, and details are given on the data acquisition system, the triggering and calibration procedures, and the operation of the array. Examples of air shower traces, recorded by the array, are presented.     

Experimental and Theoretical Studies of Microstructural Instabilities in WS2 Undergoing Electron Irradiation

In this article, we report the study of WS₂ crystals after being irradiated with a high dose of electrons. A 2 MeV Van de Graaff acelerator was used to irradiate the sample at the following conditions: 1.3 MeV voltage, 5μA current, dose rate 25 kGy/min, total dosage 1000 kGy. The samples were examined in a high resolution transmission electron microscope. Three distinct structures were observed: onions layers with fullerene like structure, randomly oriented worm-like structures with their planes rotated with respect of each other by well-defined angles, and nanotube like structures. We present calculations showing that relative rotations of the sulphur layers by 2°, 4°, 5°, 8° and 16° basically have the same average energy and average energy/atom as the unrotated structure. Therefore, rotations of the layers through those angles will be favorable. Instabilities on the structure produced by the irradiation will induce rotations as well as other capricious structures resembling a knot formation.     

Performance of the ATLAS electromagnetic calorimeter barrel module 0

The construction and performance of the barrel pre-series module 0 of the future ATLAS electromagnetic calorimeter at the LHC is described. The signal reconstruction and performance of ATLAS-like electronics has been studied. The signal to noise ratio for muons has been found to be 7.11±0.07. An energy resolution of better than (sampling term) has been obtained with electron beams of up to 245 GeV. The uniformity of the response to electrons in an area of Δη×Δφ=1.2×0.075 has been measured to be better than 0.8%.     

Mechanism of formation of 60° and 90° misfit dislocations in semiconductor heterostructures

A proposal is made and experimental evidence provided for a mechanism of formation of 60° glissile (a/2)101[111] (mixed) and 90° (a/2)110[001] (edge) misfit dislocations in semiconductor heterostructures such as Ge/Si and GaAs/Si. With increasing thickness of the epilayer the nature of dislocations was found to change from being predominantly 60° to mostly 90°. Calculations of atomic structures of dislocations using Stillinger-Weber interatomic potentials were done to show that it is energetically favorable for a 60° core to transform into a 90° core. Thus the strained layer system relaxes its energy by minimizing short-range core distortions as well as long-range elastic displacements. A distinguishing feature of the present mechanism is that the second 60° dislocation is nucleated near the surface in the appropriate glide plane to meet (primarily via a glide process and partly by a climb process) and react with the first 60° dislocation which is already at the interface. High resolution transmission electron microscopy studies have been performed to rationalize and confirm the proposed mechanism.     

Energy determination of cosmic ray showers in surface arrays using signal inference at a single distance from the core

In most high energy cosmic ray surface arrays, the primary energy is currently determined from the value of the lateral distribution function at a fixed distance from the shower core, r₀. The value of r₀ is mainly related to the geometry of the array and is, therefore, considered as fixed independently of the shower energy or direction. We argue, however, that the dependence of r₀ on energy and zenith angle is not negligible. Therefore, in the present work we propose a new characteristic distance, which we call r_opt, specifically determined for each individual shower, with the objective of optimizing the energy reconstruction. This parameter may not only improve the energy determination, but also allow a more reliable reconstruction of the shape and position of rapidly varying spectral features. We show that the use of a specific r_opt determined on a shower-to-shower basis, instead of using a fixed characteristic value, is of particular benefit in dealing with the energy reconstruction of events with saturated detectors, which are in general a large fraction of all the events detected by an array as energy increases. Furthermore, the r_opt approach has the additional advantage of applying the same unified treatment for all detected events, regardless of whether they have saturated detectors or not.     

On the use of tapered bismuth germanate crystals in positron emission tomography

An analytical model of gamma ray transport within the detectors of a positron camera, based on exponential absorption, has been developed and verified experimentally. The model has been used to study the intrinsic resolution obtained with scintillation detectors that have had their front corners removed. It is concluded that for crystals greater than 0.8 cm wide, tapering the face of the detector results in improved uniformity of resolution. Thus it is useful for medium and low resolution scanners. In these cases, it has been found that the loss in sensitivity resulting from the use of tapered crystals is less than that which occurs when septa are placed between crystals to achieve comparable uniformity of resolution. It has also been established that, in some instances, reducing the length of the detectors results in a more uniform resolution than that obtained with tapered crystals, although this leads to a loss in ring sensitivity and an increase in the detected scatter fraction.