Position Determination of High Energy Photons in Lead Glass

Two 25 element SF5 lead glass Cerenkov counter arrays have been used in the study of photon and ?° production in pN collisions at Fermilab. The method used to identify shower patterns, and the determination of the position of the photon in the lead glass arrays in the energy range 2-32 GeV is presented. The method enables the spatial position of photons in this energy range width to be measured with a resolution of ? = 0.25 inches.     

An Evaluation of Detectors for a Cerenkov Ring-Imaging Chamber

We report results from an ongoing study of single photon detectors for use in a ring-imaging Cerenkov counter. New results on the operation of parallel plate avalanche gaps is presented.     

LHC/ALICE及其光子探测

大型强子对撞机（LHC）上的大型离子对撞机实验（ALICE）将致力于TeV能区重离子碰撞,探测夸克退禁闭的新物质形态——夸克-胶子等离子体（QGP）,探索宇宙诞生之初的物态性质。本文介绍其上的新一代电磁谱仪ALICE光子探测器（PHOS）,它将用于铅-铅碰撞实验中测量直接光子和衰变光子产物,诊断夸克物质的电磁信号。束流测试结果显示,ALICE光子谱仪——PHOS将能够高效探测0.5～100GeV/c的光子。     

A Ring Image Cerenkov Detector for the CERN Omega Spectrometer

A development program has been undertaken to produce a large ring image Cerenkov detector (RICH) for use at the CERN Omega Spectrometer. A prototype Cerenkov counter has been constructed and successfully operated in a high energy particle beam, Cerenkov rings having been observed in an experimental time projection chamber (TPC) using the photoionising agents Triethylamine (TEA) and Tetrakis (dimethylamine) ethylene (TMAE). Systematic measurements have been made of the optical properties of window materials and reflecting surfaces in the vacuum ultraviolet region. Results of these tests are presented, and the design of the large detector based on these experiences together with Monte Carlo simulations of the events expected in the WA69 experiment, is discussed.     

Mathematical feature of photon spectra produced in ultra—relativistic heavy—ion collision

In 1994 the first single-photon spectra from the 200GeV/A S Au collisions at CERN SPS were reported by WA80 group.Based on these data,it can be proved that as long as there is an instantaneous thermal distribution T(r,t) in an expanding fireball at each instant,the basic mathematical feature of various kinds of photon spectra is that photon yield is approximately an exponential function of the transverse momentum PT in some region,which is basically irrelevant to the uncertainties enclosed in the theoretical estimations.     

RF-Tests on Deflecting Cavities for a Superconductinig Particle Separator

A superconducting S-band RF particle separator is under construction which will be used at the CERN 300 GeV proton synchrotron. It is foreseen to separate particles up to at least 30 GeV/c momentum. We give a summary of quality factors-(Q) and peak magnetic field (Hp) measurements on several test-deflectors. A sequence of surface treatments including electropolishing, anodizing and an UHV-annealing around 1850°C allowed us to obtain in a reliable way Q- and Hp-values well above our minimum requirements (5×108 and 310 Oe respectively). The highest values hitherto obtained for the (high-field) Q and Hp are 4.3×109 and 510 Oe corresponding to a mean deflecting field of 3.3 MV/m. The effect of repeated cooling cycles under vacuum and exposure to clean air or methanol was found not to be critical for our range of Q and Hp. The surface resistance depends linearly on an external dcmagnetic field whereas the dependence on the RF field level is much more complicated. With our surface treatment and our deflecting modes multipacting presents no problem. Breakdowns are nearly always caused by magnetic fields. The frequency tuners foreseen are described. Fine and coarse tuning will be done by separated tuners. They have been tested successfully up to Q-values of 109 and peak fields of 390 Oe. Finally a computer program has been written allowing the calculation of multiperiodic deflector modes. An exemple is shown and compared with a ?-mode for uniform periodic structures.     

Recent Results from the Cleo dE/dx System

The installation of the CLEO dE/dx particle identification system was completed last summer. DE/dx measurements are made with a pressurized gas proportional wire chamber system capable of making 117 ionization measurements. We report on measurements of relativistic rise and resolution from data taken on the T resonances and the nearby continuum. We describe the proven capabilities of the device in identifying hadrons in both the low and high momentum regions and electrons above 1 GeV/c.     

Ion-luminescence properties of GaN films being developed for IPEM

Radiation effects microscopy (REM) for the next generation integrated circuits (ICs) will require GeV ions both to provide high ionization and to penetrate the thick overlayers in present day ICs. These ion beams can be provided by only a few cyclotrons in the world. Since it is extremely hard to focus these higher-energy ions, we have proposed the ion photon emission microscope (IPEM) that allows the determination of the ion hits by focusing the emitted photons to a position sensitive detector. The IPEM needs a thin luminescent foil that has high brightness, good spatial resolution and does not change the incident ion’s energy and direction significantly. Available organic-phosphor foils require a large thickness to produce enough photons, which results in poor spatial resolution. To solve this problem, we have developed thin, lightly doped n-type GaN films that are extremely bright. We have grown high quality GaN films on sapphire using metal organic chemical vapor deposition (MOCVD), detached the films from the substrate using laser ablation, and made them self-supporting. The smallest foils have 1 mm² area and 1 μm thickness. The optical properties, such as light yield, spectrum and decay times were measured and compared to those of conventional phosphors, by using both alpha particles from a radioactive source and 250 keV ions from an implanter. We found that the GaN performance strongly depends on composition and doping levels. The conclusion is that 1-2 μm GaN film of a 1 mm² area may become an ideal ion position detector.     

Influence of α-clustering nuclear structure on the rotating collision system

In recent years, the collective motion properties of global rotation of the symmetric colliding system in relativistic energies have been investigated. In addition, the initial geometrical shape effects on the collective flows have been explored using a hydrodynamical model, a transport model, etc. In this work, we study the asymmetric ~(12)C+~(197)Au collision at 200 GeV/c and the effect of the exotic nuclear structure on the global rotation using a multi-phase transport model. The global angular momentum and averaged angular speed were calculated and discussed for the collision system at different evolution stages.     

Evaluation of Counting Efficiency of a Whole-body Counter using the EGS4 Code

Counting efficiencies of a whole-body counter installed in the Japan Atomic Energy Research Institute were evaluated using Monte Carlo simulation and measurement to validate the calculation method of the counting efficiency curves of the whole-body counter for the water-filled block-shape phantoms containing radionuclides. Consequently, the counting efficiency curves in the photon energy range of 300–1,461 keV were obtained using the Monte Carlo simulation. The calculations are in fairly good agreement with the measurements in the photon energy range of 662–1,461 keV. It was also found that the self-scattering effect of photons in the phantoms accounts for about 7% of the counting efficiency for 662 keV photons.     

Results from the SIFTER (Scintillating Fiber Telescope forEnergetic Radiation) beam test apparatus

The Scintillating Fiber Telescope for Energetic Radiation (SIFTER) is a large-area instrument concept for high-energy (E>10 MeV) gamma-ray astronomy. It takes advantage of the technology of fine (~1 mm ²) plastic scintillating fibers in the context of a pair tracker/calorimeter telescope. In our on-going SIFTER research, we have developed a small test apparatus, consisting of 12 fiber planes, each with a potential active area of 10 cm×10 cm covered with a thin tantalum foil converter. This apparatus was tested in July, 1998 with high-energy photons (~0.5-1.6 GeV) at the Thomas Jefferson National Accelerator Laboratory Hall B tagged gamma-ray facility. We report on results of the beam test, concentrating on comparisons with detailed Monte Carlo simulations of the instrument performance, including track reconstruction, angular resolution and detection efficiency     

Calculations of Effective Dose and Ambient Dose Equivalent Conversion Coefficients for High Energy Photons

The conversion coefficients from photon fluence to ambient dose equivalent, H* (10) and effective doses were calculated for photons up to 10 GeV. A Monte Carlo code EGS4 was used for these calculations and secondary particle transports were considered. The calculated ambient dose equivalents were compared to the calculated effective doses. The comparison shows that the ambient dose equivalents at 1 cm depth, H* (10) underestimate the effective doses at the energy above 5MeV. H* (10) is not suitable operational quantity since it does not provide reasonable estimation of effective dose. It is difficult to define the operational quantity which can be consistently used for photons from low energy to high energy above 10 MeV. Instead of operational quantities, the maximum effective dose in various irradiation geometries can be used for shielding design calculations.     

基于Cerenkov效应水下放射源搜寻技术的可行性分析研究

本文采用Geant4对水下放射源致Cerenkov光及Cerenkov光在水中的输运过程进行计算研究,获得Cerenkov光强及光子数在水平面上的分布规律,进而对该技术手段进行了理论验证和可行性分析。研究结果表明:当放射源出射粒子能量满足产生Cerenkov光的条件时,其在水面形成的Cerenkov光斑及Cerenkov光子数在水面的分布具有规律性,可以此来确定放射源的位置和深度。本工作为基于Cerenkov效应水下放射源搜寻技术的发展提供了理论依据和科学基础。     

Photon and positron production by ultrahigh-intensity laser interaction with various plasma foils

The generation of γ photons and positrons using an ultrahigh-intensity laser pulse interacting with various plasma solid foils is investigated with a series of quantum electrodynamic particlein-cell(PIC) simulations. When ultrahigh-intensity lasers interact with plasma foils, a large amount of the laser energy is converted into γ photon energy. The simulation results indicate that for a fixed laser intensity with different foil densities, the conversion efficiency of the laser to γphotons and the number of produced photons are highly related to the foil density. We determine the optimal foil density by PIC simulations for high conversion efficiencies as approximately 250 times the critical plasma density, and this result agrees very well with our theoretical assumptions. Four different foil thicknesses are simulated and the effects of foil thickness on γ photon emission and positron production are discussed. The results indicate that optimal foil thickness plays an important role in obtaining the desired γ photon and positron production according to the foil density and laser intensity. Further, a relation between the laser intensity and conversion efficiency is present for the optimal foil density and thickness.     

A Risetime Discriminator for Low Level Tritium Counting

This paper describes the design of a risetime discriminator circuit (RTD), with associated anticoincidence/coincidence (AC/C) logic and its application to the counting of low-activity tritium samples in gas proportional counter systems. The circuitry, packaged in a double-width NIM, extracts signal risetime information which is used in conjunction with the output of an annular guard counter to electronically reject background counts due to high energy charged particles (?-mesons), and gamma-ray photons. The use of the guard and AC/C logic without RTD is effective in reducing the background due to charged particles because of the high probability of coincidental detection by the guard and proportional counters. However, the reduction of backgromd related to gamma-ray photons by simple AC/C techniques is ineffective because of the small probability of a coincidence event occurring in the two counters. The RTD circuit utilizes the property that gamma photons and high energy pmesons produce ionization tracks in the proportional counter that are typically longer and have lower specific charge density than those tracks produced by low-energy (tritium) beta particles. Thus, these events have longer charge collection times and result in slower signal risetimes at the output of a charge-sensitive (integrating) preamplifier. The RTD circuit differentiates the wide-band preamplifier signal which produces a pulse with amplitude proportional to the signal risetime. The derivative is then peak-detected, stretched, delayed and inverted. An amplitude comparison is then made between the stretched derivative and the linear input signal using a linear summation amplifier.     

Development of Silica Aerogel Cerenkov Detectors

Recently silica aerogel has been employed as a Cerenkov radiator. This solid material can be produced with a refractive index of 1.01-1.10, thus complementing the refractive indices easily obtained with gases and liquids. It is very well suited for identification of particles having momenta of about one or a few GeV/c. Examples of efficient detectors with active surfaces of about 0.1 m2 using light collection system constructed from mirrors and diffusing walls are given. With a refractive index of 1.03 and an aerogel thickness of 9 cm, signals of about 6 photoelectrons have been obtained for ? = 1 particles.     

Ion beam characterization of advanced luminescent materials for application in radiation effects microscopy

The ion photon emission microscope (IPEM) is a technique developed at Sandia National Laboratories (SNL) to study radiation effects in integrated circuits with high energy, heavy ions, such as those produced by the 88” cyclotron at Lawrence Berkeley National Laboratory (LBNL). In this method, an ion-luminescent film is used to produce photons from the point of ion impact. The photons emitted due to an ion impact are imaged on a position-sensitive detector to determine the location of a single event effect (SEE). Due to stringent resolution, intensity, wavelength, decay time, and radiation tolerance demands, an engineered material with very specific properties is required to act as the luminescent film. The requirements for this material are extensive. It must produce a high enough induced luminescent intensity so at least one photon is detected per ion hit. The emission wavelength must match the sensitivity of the detector used, and the luminescent decay time must be short enough to limit accidental coincidences. In addition, the material must be easy to handle and its luminescent properties must be tolerant to radiation damage. Materials studied for this application include plastic scintillators, GaN and GaN/InGaN quantum well structures, and lanthanide-activated ceramic phosphors. Results from characterization studies on these materials will be presented; including photoluminescence, cathodoluminescence, ion beam induced luminescence, luminescent decay times, and radiation damage. Results indicate that the ceramic phosphors are currently proving to be the ideal material for IPEM investigations.     

X-ray fluorescent computer tomography with synchrotron radiation

This paper describes the possibility of a quantitative calculation of the distribution of a nonradioactive element within a selected cross section with nondestructive methods with the help of X-ray fluorescent tomography (XFCT). In order to increase measurement sensitivity, the use of a lamellar collimator was avoided. One of the main problems for the quantitative determination of concentration was absorption of the stimulating synchrotron ray as well as re-absorption of the emitted fluorescent light. The absorption coefficients required for a consideration of the absorption processes have been determined with two absorption tomograms. The algebraic reconstruction technique (ART) and the maximum likelihood method with expectation maximization (MLEM) were used for the reconstruction of the chemical element to be classified, with close consideration of the absorption phenomenon. The experiments were undertaken at the bending-magnet beamline, CEMO, at the laboratory for synchrotron radiation in Hamburg, HASYLAB (4.5 GeV) (100 mA). The photon intensity flux was approximately 10/sup 9/ photons/mm/sup 2//s. The concentration of iodine was calculated with phantoms and an untreated, dissected human thyroid gland with the help of a calibration curve. The total error related to the reconstructed mean value amounts to 20%. One can find at least an iodide concentration of 0.6 mmol/l in this experimental setup.     

The ionoluminescence apparatus at the LABEC external microbeam facility

In this paper, we describe the main features of the ionoluminescence (IL) apparatus recently installed at the external scanning microbeam facility of the 3 MV Tandetron accelerator of the INFN LABEC Laboratory in Firenze. The peculiarity of this IL set-up resides in the fact that the light produced by the ion irradiation of the specimen is collected by a bifurcated optical fiber, so that photons are shunted both to a CCD spectrometer, working in the 200-900 nm wavelength range, and to a photomultiplier (PMT). The accurate focusing of the optical system allows high photon collection efficiency and this results in rapid acquisition of luminescence spectra with low ion currents on luminescent materials; simultaneously, luminescence maps with a spatial resolution of 10 μm can be acquired through the synchronization of PMT photon detection with the position of the scanning focused ion beam. An optical filter with a narrow passband facing the photomultiplier allows chromatic selectivity of the luminescence centres.The IL apparatus is synergistically integrated into the existing set-up for ion beam analyses (IBA). The upgraded system permits simultaneous IL and PIXE/PIGE/BS measurements. With our integrated system, we have been studying raw lapis lazuli samples of different known origins and precious lapis lazuli artworks of the Collezione Medicea of Museum of Natural History, University of Firenze, aiming at characterising their composition and provenance.