Showing papers in "Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment in 2005"

SPlot: A Statistical tool to unfold data distributions

Abstract: The paper advocates the use of a statistical tool dedicated to the exploration of data samples populated by several sources of events. This new technique, called P lot s , is able to unfold the contributions of the different sources to the distribution of a data sample in a given variable. The P lot s tool applies in the context of a likelihood fit which is performed on the data sample to determine the yields of the various sources.

Limits and confidence intervals in the presence of nuisance parameters

Abstract: We study the frequentist properties of confidence intervals computed by the method known to statisticians as the Profile Likelihood. It is seen that the coverage of these intervals is surprisingly good over a wide range of possible parameter values for important classes of problems, in particular whenever there are additional nuisance parameters with statistical or systematic errors. Programs are available for calculating these intervals.

Boosted decision trees as an alternative to artificial neural networks for particle identification

Abstract: The efficacy of particle identification is compared using artificial neutral networks and boosted decision trees. The comparison is performed in the context of the MiniBooNE, an experiment at Fermilab searching for neutrino oscillations. Based on studies of Monte Carlo samples of simulated data, particle identification with boosting algorithms has better performance than that with artificial neural networks for the MiniBooNE experiment. Although the tests in this paper were for one experiment, it is expected that boosting algorithms will find wide application in physics.

Decay chain fitting with a Kalman filter

Abstract: We present a method to perform a least-squares fit of a decay chain involving multiple decay vertices. Our technique allows for the simultaneous extraction of decay time, position and momentum parameters and their uncertainties and correlations for all particles in a decay chain.

Study of water distribution and transport in a polymer electrolyte fuel cell using neutron imaging

Abstract: A procedure to utilize neutron imaging for the visualization of two-phase flow within an operating polymer electrolyte fuel cell has been developed at the Penn State Breazeale Nuclear Reactor. Neutron images allow us to visualize the liquid water inside the flow channel (∼0.5 mm deep) and gas diffusion media (∼200 μm thick) in real operating conditions. The current temporal and spatial resolution for radioscopy is approximately 30 frames/s and 129 μm/pixel in a 50 cm2 image area. Continuous digital radioscopy can be recorded for 45 min. The determination of water volume within the cell has been enabled by referencing a calibration look-up table that correlates neutron attenuation to an equivalent liquid water thickness. It was found that liquid water tends to accumulate at specific locations within the fuel cell, depending on operating conditions. Anode flow channel blockage was observed to occur at low power, while higher power conditions resulted in more dispersed distribution of liquid droplets. Under high-power conditions, liquid water tended to accumulate along or under the channel walls at 180° turns, and radioscopy revealed that individual liquid droplet velocities were several orders of magnitude less than that of the reactant flow, indicating a slug-flow regime up to at least 1 A/cm2.

Results on disordered materials from the GEneral Materials diffractometer, GEM, at ISIS

Abstract: The GEneral Materials diffractometer, GEM, at the ISIS Facility pulsed neutron source is the most advanced materials neutron diffractometer in the world A full description of GEM is given from the point of view of structural studies of disordered materials The key component for these studies is the highly stable detector array, which covers a very wide range in scattering angles and a very large solid angle, leading to a wide dynamic range and a high count rate The high real-space resolution of GEM, due to a high maximum momentum transfer of 55 A ˚ � 1 , is illustrated by data on bioactive phosphate glasses, where bonds from phosphorus to bridging and non-bridging oxygens (which differ in length by approximately 012 A ˚ ) are clearly resolved The low momentum transfer ability of GEM is demonstrated by a measurement on amorphous Si77D23, which yields reliable data down to 01 A ˚ � 1 The first successful isotopic substitution experiment on sol–gel materials has been performed on GEM in a study of amorphous titanium silicates, showing the suitability of the instrument for both isotopic substitution, and for studies of complex materials, even in the presence of hydrogen Studies of the structures of disordered group 11 cyanide crystals show the power of GEM to reveal the nature of disorder in crystalline systems as well as glassy materials The crystal structure of high temperature CuCN has been solved for the first time The disorder in AuCN, AgCN and high temperature CuCN arises from random displacements of the linear –M–(CRN)– chains relative to each other, and the one-dimensional negative thermal expansion is due to long wavelength cooperative motions of the chains

The DIRC particle identification system for the BaBar experiment

Abstract: A new type of ring-imaging Cherenkov detector is being used for hadronic particle identification in the B a B ar experiment at the SLAC B Factory (PEP-II). This detector is called DIRC, an acronym for Detection of Internally Reflected Cherenkov (Light). This paper will discuss the construction, operation and performance of the B a B ar DIRC in detail.

EFFTRAN : A Monte Carlo efficiency transfer code for gamma-ray spectrometry

Abstract: An implementation of the efficiency transfer method for cylindrical samples in gamma-ray spectrometry is presented, based on a Monte Carlo integration of the interaction probabilities of gamma rays over the detector and sample volumes. This approach makes it possible for the computer code to be relatively straightforward to write and the speed of the calculation to be adequate for routine on-line analysis of gamma-ray spectra. Virtual components of the detector system are introduced to prevent any erroneous or double counting of gamma-ray paths, which simplifies the tracking algorithm.

Modeling of ionization produced by fast charged particles in gases

Abstract: A computer modeling of ionization is necessary for the simulation of gaseous detectors of fast charged particles. The interactions of the incident particle with matter are well described by the photoabsorption ionization (PAI) model, which is based on the relation between the energy deposited by the fast charged particle in a medium and the photoabsorption cross-section of this medium. Some modification of the PAI model energy-transfer cross-section allows to distinguish the interactions with different atomic shells and to determine the energy of the primary photoelectrons and possible atomic relaxation cascades. Further simulation of paths and absorption of secondary particles results in a realistic reproduction of the space distributions and amount of initial ionization.

A test of silicon photomultipliers as readout for PET

Abstract: The silicon photomultiplier (SiPM) is a novel photon detector based on Geiger mode operating avalanche photodiodes. In this paper, we present results from a test, demonstrating the feasibility of SiPM as readout elements in scintillator-based positron emission tomography (PET). As scintillator we use the newly developed LYSO crystals having similar characteristics as LSO. With our setup we measure an energy resolution of about 22% and a time resolution of a single crystal element of ( 1.51 ± 0.07 ) ns , both full-width at half-maximum. A significant improvement in time resolution could be achieved by triggering on the first photoelectron in the signal. We also present the coincidence rate of two detector channels vs. the position of a small point-like 22Na positron source.

Design and performance of the ABCD3TA ASIC for readout of silicon strip detectors in the ATLAS semiconductor tracker

Abstract: The ABCD3TA is a 128-channel ASIC with binary architecture for the readout of silicon strip particle detectors in the Semiconductor Tracker of the ATLAS experiment at the Large Hadron Collider (LHC). The chip comprises fast front-end and amplitude discriminator circuits using bipolar devices, a binary pipeline for first level trigger latency, a second level derandomising buffer and data compression circuitry based on CMOS devices. It has been designed and fabricated in a BiCMOS radiation resistant process. Extensive testing of the ABCD3TA chips assembled into detector modules show that the design meets the specifications and maintains the required performance after irradiation up to a total ionising dose of 10 Mrad and a 1-MeV neutron equivalent fluence of 2×1014 n/cm2, corresponding to 10 years of operation of the LHC at its design luminosity. Wafer screening and quality assurance procedures have been developed and implemented in large volume production to ensure that the chips assembled into modules meet the rigorous acceptance criteria.

The ClearPET™ project: development of a 2nd generation high-performance small animal PET scanner

Abstract: Second generation high-performance PET scanners, called ClearPET$^{TM}$, have been developed by working groups of the Crystal Clear Collaboration (CCC). High sensitivity and high spatial resolution for the ClearPET camera is achieved by using a phoswich arrangement combining two different types of lutetium-based scintillator materials: LSO from CTI and LuYAP:Ce from the CCC (ISTC project). In a first ClearPET prototype, phoswich arrangements of 8$\times$8 crystals of 2$\times$2$\times$10 mm$^3$ are coupled to multi-channel photomultiplier tubes (Hamamatsu R7600). A unit of four PMTs arranged in-line represents one of 20 sectors of the ring design. The opening diameter of the ring is 120 mm, the axial detector length is 110 mm. The PMT pulses are digitized by free-running ADCs and digital data processing determines the gamma energy, the phoswich layer and even the exact pulse starting time, which is subsequently used for coincidence detection. The gantry allows rotation of the detector modules around the field of view. Preliminary data shows a correct identification of the crystal layer about (98$\pm$1)%. Typically the energy resolution is (23.3$\pm$0.5)% for the luyap layer and (15.4$\pm$0.4)% for the lso layer. Early studies showed the timing resolution of 2 ns FWHM and 4.8 ns FWTM. the intrinsic spatial resolution ranges from 1.37 mm to 1.61 mm full-width of half-maximum (FWHM) with a mean of 1.48 mm FWHM. further improvements in image and energy resolution are expected when the system geometry is fully modeled.

Technical design and performance of the NEMO 3 detector

Abstract: The development of the NEMO3 detector, which is now running in the Frejus Underground Laboratory (L.S.M. Laboratoire Souterrain de Modane), was begun more than ten years ago. The NEMO3 detector uses a tracking-calorimeter technique in order to investigate double beta decay processes for several isotopes. The technical description of the detector is followed by the presentation of its performance.

The asset of ultra-fast digitizers for positron-lifetime spectroscopy

Abstract: A spectrometer for positron-lifetime measurements assembled from two BaF2 scintillation detectors and two 8-bit, 4 GS s - 1 digitizes in a master–slave configuration is described in detail. We report the results of comparative testing measurements of the lifetime of positrons annihilating in α -Fe using this setup and a setup formed by the same pair of detectors working in conjunction with analog electronics modules. The data from these measurements demonstrate for the first time that replacing the analog electronics chain by fast digitizers leads to a substantial improvement of the precision in positron-lifetime measurements. A record timing resolution of 131–136 ps has been achieved with the described spectrometer at coincidence counting rate comparable or virtually equal to that obtained with the fast–fast setup.

Radio-Detection Signature of High Energy Cosmic Rays by the CODALEMA Experiment

Abstract: Taking advantage of recent technical progress which has overcome some of the difficulties encountered in the 1960s in the radio detection of extensive air showers induced by ultra-high-energy cosmic rays (UHECR), a new experimental apparatus (CODALEMA) has been built and operated. We will present the characteristics of this device and the analysis techniques that have been developed for observing electrical transients associated with cosmic rays. We find a collection of events for which both time and arrival direction coincidences between particle and radio signals are observed. The counting rate corresponds to shower energies ⩾ 5 × 10 16 eV . The performance level which has been reached considerably enlarges the perspectives for studying UHECR events using radio detection.

High-speed particle tracking in nuclear emulsion by last-generation automatic microscopes

Abstract: The technique of nuclear emulsions for high-energy physics experiments is being revived, thanks to the remarkable progress in measurement automation achieved in the past years. The present paper describes the features and performances of the European Scanning System, a last-generation automatic microscope working at a scanning speed of 20 cm 2 / h . The system has been developed in the framework of the OPERA experiment, designed to unambigously detect ν μ → ν τ oscillations in nuclear emulsions.

Methods of scattering corrections for quantitative neutron radiography

Abstract: From neutron radiography experiments, often statements like “how many grams of water are in my sample?” are expected. Such statements are delicate, because contributions of scattered neutrons in the image signal disturb the radiographies for a simple quantitative evaluation. The idea is to consider the scattered neutrons in a computational procedure. The obtained corrected image data set can then be evaluated according to the exponential attenuation law or reference values obtained by simulations or experiments. The correction is based on the iterative reconstruction of the measured image by overlapping point scattered functions (PScF). The PScFs are determined by Monte-Carlo simulations using the MCNPX software. Important parameters beside the material are the dimensions of the sample, the distance between sample and detector, the detector properties and the energy spectrum of the initial neutron beam. Evaluations of measurements with different detectors result in differing effective attenuation cross-sections of the samples. This can be explained by the different detector sensitivity on the epithermic domain of the energy spectrum. If the sample is inside an enclosing material (e.g. water in a container), this can affect the evaluation of the samples cross-section. Also this effect is understood with the PScF and can be taken into account. For known simple geometries the reconstructions are in good agreement with the measurements and allow a more exact evaluation of the involved cross-sections.

Comparison of PVT and NaI(Tl) scintillators for vehicle portal monitor applications

Abstract: The demand for radiation portal monitor (RPM) systems has increased, and their capabilities are being further scrutinized as they are being applied to the task of detecting nuclear weapons, special nuclear material, and radiation dispersal device materials that could appear at borders. The requirements and constraints on RPM systems deployed at high-volume border crossings are significantly different from those at weapons facilities or steel recycling plants, where RPMs have been historically employed. In this new homeland security application, RPM systems must rapidly detect localized sources of radiation with a very high detection probability and low false-alarm rate, while screening all of the traffic without impeding the flow of commerce. In light of this new Department of Homeland Security application, the capabilities of two popular gamma-ray-detector materials as applied to these needs are re-examined. Both experimental data and computer simulations, together with practical deployment experience, are used to assess currently available polyvinyltoluene and NaI(Tl) gamma-ray detectors for border applications.

Perspectives on the future development of new scintillators

Abstract: The search for new scintillators has become increasingly sophisticated and increasingly successful in recent years, driven to a large degree by the rapidly growing needs of medical imaging and high energy physics. Better understanding of the various scintillation mechanisms has led to innovative new materials for both gamma-ray and neutron detection, and the concept of scintillator design and engineering has emerged, whereby materials are optimized according to the scintillation properties needed by specific applications. Numerous promising candidates have been identified during the last few years, and several are currently being actively developed for commercial production. Economical crystal growth often represents a significant challenge in the practical application of new scintillation materials.

Rare Isotopes INvestigation at GSI (RISING) using Gamma-ray Spectroscopy at Relativistic Energies

Abstract: The Rare ISotopes INvestigation at GSI project combines the former EUROBALL Ge-Cluster detectors, the MINIBALL Ge detectors, BaF2--HECTOR detectors, and the fragment separator at GSI for high-resolution in-beam gamma-ray spectroscopy measurements with radioactive beams. These secondary beams produced at relativistic energies are used for Coulomb excitation or secondary fragmentation experiments in order to explore the nuclear structure of the projectiles or projectile like nuclei by measuring de-excitation photons. The newly designed detector array is described and the performance characteristics are given. Moreover, particularities of the experimental technique are discussed.

Thin films of HfO2 and ZrO2 as potential scintillators

Abstract: Emission, excitation and absorption spectra of HfO2 and ZrO2 thin films grown by atomic layer deposition were investigated in the temperature range of 10-300 K. Time-resolved luminescence spectra were excited with a pulsed ArF laser and tuneable synchrotron radiation in UV–VUV. The strong emission with the peak position at 4.2–4.4 eV and with the decay time in μs range was revealed at 10 K in both materials. The emission was ascribed to the radiative decay of self-trapped excitons (STE). the features observed in the absorption and excitation spectra at 5.8 and 5.4 eV were most probably due to the formation of excitons; While the interband transitions started to dominate at 6.15 and 5.85 ev in HfO2 and ZrO2, respectively.

A novel type of proximity focusing RICH counter with multiple refractive index aerogel radiator

Abstract: A proximity focusing ring imaging Cherenkov detector, with the radiator consisting of two or more aerogel layers of different refractive indices, has been tested in 1 – 4 GeV / c pion beams at KEK. Essentially, a multiple refractive index aerogel radiator allows for an increase in Cherenkov photon yield on account of the increase in overall radiator thickness, while avoiding the simultaneous degradation in single photon angular resolution associated with the increased uncertainty of the emission point. With the refractive index of consecutive layers suitably increasing in the downstream direction, one may achieve overlapping of the Cherenkov rings from a single charged particle. The impact of the observed improvement on the π / K separation at the upgraded Belle detector is discussed.

Hadron and jet detection with a dual-readout calorimeter

Abstract: Hadronic shower development in a copper-based fiber calorimeter is studied by simultaneously measuring the scintillation light and the Cherenkov light generated in this process. By comparing these two signals, the electromagnetic shower fraction can be measured event by event. Fluctuations in this fraction are the dominant contribution to the hadronic energy resolution. They are also responsible for the signal non-linearity and the non-Gaussian response function typical for hadron calorimeters. The dual-readout technique makes it possible to eliminate the effects of these fluctuations.

POLAR, a compact detector for gamma-ray bursts photon polarization measurements

Abstract: The design and the simulated performances of a compact detector dedicated to the measurement of GRB photon polarization is presented. Such a detector would permit to answer the question “are most of the GRB strongly polarized?” in a mission of one year in space.

Efficiency optimization of microchannel plate (MCP) neutron imaging detectors. I. Square channels with 10B doping

Abstract: Microchannel plate (MCP) event-counting imaging detectors with very high spatial resolution ( ∼ 10 μ m ) and timing accuracy ( ∼ 100 ps ) are widely employed for the detection and imaging applications of electrons and ions, as well as UV and X-ray photons. Recently, it was demonstrated that the many advantages of MCPs are also applicable to neutron detection with high two-dimensional spatial resolution. Boron, enriched in the isotope 10B, was added to the MCP glass structure to enhance the neutron interaction within the MCP through the B 10 ( n , α ) 7 Li reaction. The energetic charged particle reaction products release secondary electrons directly into MCP channels, initiating an electron avalanche and a subsequent strong output pulse. In this paper we present a detailed model for calculating the quantum detection efficiency of MCP neutron detectors incorporating 10B, for the specific case of square channel MCP geometry. This model predicts that for thermal neutrons (0.025 eV), MCP detection efficiencies of up to 78% are possible using square channels. We also show theoretically that square channel MCPs should have a very sharp ( ∼ 17 mrad ) angular drop in sensitivity for detection of normal incidence neutrons, opening up new possibilities for angle-sensitive neutron imaging as well as collimation. The calculations can be used to optimize MCP neutron detection efficiency for a variety of applications. In a subsequent companion paper, the model will be extended to the case of hexagonally packed circular channels.

The photon-scattering facility at the superconducting electron accelerator ELBE

Abstract: A new facility for the production of polarised bremsstrahlung has been built at the superconducting electron accelerator ELBE of the Forschungszentrum Rossendorf. The bremsstrahlung facility and the setup for photon-scattering experiments are designed such that the background radiation caused by the scattering of photons and the production of neutrons is minimised. The sensitive setup in connection with electron energies up to 20 MeV and average currents up to 1 mA delivered by the ELBE accelerator enables novel experiments using photon-induced reactions. First results of photon-scattering experiments are presented.

Proposal for an absolute luminosity determination in colliding beam experiments using vertex detection of beam-gas interactions

Abstract: We propose a method for determining the absolute luminosity in a colliding-beam experiment at circular accelerators by measuring vertices of beam–gas interaction to determine the beam shapes and overlap. This method can be applied (for example) at all Large Hadron Collider experiments without modification of their detectors.

Thick GEM-like multipliers—a simple solution for large area UV-RICH detectors

Abstract: We report on the properties of thick GEM-like (THGEM) electron multipliers made of 0.4 mm thick double-sided Cu-clad G-10 plates, perforated with a dense hexagonal array of 0.3 mm diameter drilled holes. Photon detectors comprising THGEMs coupled to semi-transparent CsI photocathodes or reflective ones deposited on the THGEM surface were studied with Ar / CO 2 (70:30), Ar / CH 4 (95:5), CH 4 and CF 4 . Gains of ∼ 10 5 or exceeding 10 6 were reached with single- or double-THGEM, respectively; the signals have 5–10 ns rise times. The electric field configurations at the THGEM electrodes result in an efficient extraction of photoelectrons and their focusing into the holes; this occurs already at rather low gains, below 100. These detectors, with single-photon sensitivity and with expected sub-millimeter localization, can operate at MHz / mm 2 rates. We discuss their prospects for large-area UV-photon imaging for RICH.

Studies of boosted decision trees for MiniBooNE particle identification

Abstract: Boosted decision trees are applied to particle identification in the MiniBooNE experiment operated at Fermi National Accelerator Laboratory (Fermilab) for neutrino oscillations. Numerous attempts are made to tune the boosted decision trees, to compare performance of various boosting algorithms, and to select input variables for optimal performance.

Absorption of scintillation light in a 100 l liquid xenon γ-ray detector and expected detector performance

Abstract: An 800 l liquid xenon scintillation γ -ray detector is being developed for the MEG experiment which will search for μ + → e + γ decay at the Paul Scherrer Institut Absorption of scintillation light of xenon by impurities might possibly limit the performance of such a detector We used a 100 l prototype with an active volume of 372 × 372 × 496 mm 3 to study the scintillation light absorption We have developed a method to evaluate the light absorption, separately from elastic scattering of light, by measuring cosmic rays and α sources By using a suitable purification technique, an absorption length longer than 100 cm has been achieved The effects of the light absorption on the energy resolution are estimated by Monte Carlo simulation