Effect Of Detector Geometry Research Articles

Effect of detector geometry and surface finish on Cerenkov based time estimation in monolithic BGO detectors

Objective. Time-of-flight positron emission tomography based on bismuth germanate (BGO) detectors is made possible due to fast emission of Cerenkov light. Only around 17 Cerenkov photons are produced per 511 keV photoelectric event, making high photon collection efficiency crucial for obtaining good time-of-flight capabilities. In this study, we investigate how different lateral and back surface finishes affect the photon collection efficiency and Cerenkov based timing performance in monolithic BGO. Approach. The study is performed using GATE for gamma and optical photon modeling, with surface reflections of photons simulated by the LUT Davis model. We compare for different detector configurations (regarding size and surface finishes) the photon collection efficiency, detection delays of the first few optical photons and coincidence time resolution estimations obtained by modeling the SiPM signals and performing leading edge discrimination. An additional comparison is made to LYSO scintillators and pixelated detectors. Main results. Although Cerenkov photon emission is directional, many high incidence angle Cerenkov photons are emitted due to electron scattering in the crystal. Substituting a polished back (photodetector side) surface for a rough surface increases the collection efficiency of these high angle of incidence photons. Results show that for a monolithic 50 × 50 × 12 mm3 BGO detector with reflective side surfaces, this leads to an overall increase in photon collection efficiency of 34%. Cerenkov photon collection efficiency is also improved, resulting in a reduction of the photon detection delays (and the variation therein) of the first few optical photons. This leads to a better coincidence time resolution, primarily achieved by a shortening of the tails in the time-of-flight kernel, with an 18% reduction in full width at tenth maximum. Significance. This study shows the importance of the photon collection efficiency for timing performance in Cerenkov based monolithic detectors, and how it can be improved with different surface finishes.

Numerical Investigation on Electron and Ion Transmission of GEM-based Detectors

ALICE at the LHC is planning a major upgrade of its detector systems, including the TPC, to cope with an increase of the LHC luminosity after 2018. Different R&D activities are currently concentrated on the adoption of the Gas Electron Multiplier (GEM) as the gas amplification stage of the ALICE-TPC upgrade version. The major challenge is to have low ion feedback in the drift volume as well as to ensure a collection of good percentage of primary electrons in the signal generation process. In the present work, Garfield simulation framework has been adopted to numerically estimate the electron transparency and ion backflow fraction of GEM-based detectors. In this process, extensive simulations have been carried out to enrich our understanding of the complex physical processes occurring within single, triple and quadruple GEM detectors. A detailed study has been performed to observe the effect of detector geometry, field configuration and magnetic field on the above mentioned characteristics.

Simulation of light output from narrow sodium iodide detectors

The use of narrow scintillators in imaging devices raises the question of whether there is enough light output that can yield reasonable energy and spatial resolutions. Compared to scintillation within large-area detectors (such as those used in conventional gamma cameras), scintillation photons within narrow detectors are expected to undergo more reflections because of the proximity of the detector surfaces. In this study, we use simulation methods to estimate the light output from long, narrow sodium iodide crystals, and to investigate the effects of detector geometry and detector surface reflection properties on the fraction of scintillation photons that are able to leave the crystal through the exit window (on one of the long, narrow sides). Our simulations show that the light output from a 3.5-mm wide by 10-mm high by 300-mm long detector can result in reasonable energy resolutions. Our simulations also suggest that, in conjunction with the use of external reflectors, a crystal that has its sides polished to a smooth finish results in better light output than one with sides grounded to a rough finish.

Effects of detector geometry on measured lineshapes and intensities in surface scattering

Effects of detector geometry on measured lineshapes and intensities in surface scattering

Effects of detector geometry on measured lineshapes and intensities in surface scattering

A general expression for the detector response to a given beam flux distribution is given. Illustrative examples are worked out for some simple idealized cases and it is shown that both the measured lineshape and the measured intensity depend on the details of incident beam and detector geometry.

Light collection from a one square metre scintillator for cosmic ray work

Large area scintillation detectors for cosmic ray work are required to have a good spatial uniformity of response, preferably combined with a high photon collection efficiency. The effect of detector geometry and internal surface coating on these characteristics has been investigated with the aim of improving our own detector design while reducing the cost of construction.

Effect of detector geometry on angular number distribution measurements

Effect of detector geometry on angular number distribution measurements

An application of slowing down kernels to thermal neutron density fluctuations in nuclear reactors

The backward equation for the space and energy-dependent probability generating function of the density fluctuations in a nuclear reactor, has been reduced to a more tractable form by the application of a slowing down kernel technique. Simple working expressions have been obtained for the variance, the correlation function and the power spectral density (P.S.D.) in terms of the infinite medium slowing down kernel. The method includes the effects of detectors, delayed neutrons and slowing down time. In addition, the frequency characteristics of the detection apparatus have been accounted for. It is shown that the dominant break frequency, of the fundamental mode component in the power spectral density, is markedly dependent on the slowing down lengths of the delayed neutrons, a result that can lead to appreciable corrections to the experimentally calculated neutron lifetime in certain systems. A general formalism accounting for slowing down, delayed neutrons and detector geometry is developed, and is applied to detectors of various shapes. Marked differences in the P.S.D. are noted for the different detectors in an infinite medium; however, for the finite medium, the effect of detector geometry is not so important and it is shown that, in certain circumstances, experiments can be analysed according to the simple, infinite medium-infinite detector formula.