Incident Charged Particles Research Articles

A triple-GEM detector for high-rate particle triggering

We show that adding CF 4 to the standard Ar/CO 2 gas mixture allows to substantially improve the time resolution of triple-GEM detectors. In this paper we discuss measurements of time resolution, discharge probability per incident charged particle and pad multiplicity of a triple-GEM detector with pad readout, with new gas mixtures with CF 4 and isobutane. Results for detectors with GEM foil size of both 10×10 cm 2 and 20×24 cm 2 are presented.

New enhanced tunneling in nuclear processes

The small sub-barrier tunneling probability of nuclear processes can be dramatically enhanced by collision with incident charged particles. Semiclassical methods of theory of complex trajectories have been applied to nuclear tunneling, and conditions for the effects have been obtained. We demonstrate the enhancement of $\ensuremath{\alpha}$ particle decay by incident proton with energy of about $0.25\phantom{\rule{0.3em}{0ex}}\text{MeV}$. We show that the general features of this process are common for other sub-barrier nuclear processes and can be applied to nuclear fission.

Elementary Aharonov-Bohm system in three space dimensions: Quantum attraction with no classical force

As a consequence of the Aharonov-Bohm effect, there is a quantum-induced attraction between a charged particle and a rigid, impenetrable hoop made from an arbitrarily thin tube containing a superconductor quantum of magnetic flux. This is remarkable because in classical physics there is no force between the two objects, and quantum-mechanical effects (associated with uncertainty-principle energy) generally are repulsive rather than attractive. For an incident spinless charged particle in a P wave (in a configuration with total angular momentum zero) we verify a resonance just above threshold using the Kohn variational principle in its S-matrix form. Even if optimistic choices of parameters describing a model system with these properties were feasible, the temperature required to observe the resonance would be far lower than has yet been attained in the laboratory.

The AGILE silicon tracker: testbeam results of the prototype silicon detector

AGILE (Light Imager for Gamma-ray Astrophysics) is a small scientific satellite for the detection of cosmic γ-ray sources in the energy range 30 MeV – 50 GeV with a very large field of view (1/4 of the sky). It is planned to be operational in the years 2003–2006, a period in which no other γ-ray mission in the same energy range is foreseen. The heart of the AGILE scientific instrument is a silicon–tungsten tracker made of 14 planes of single sided silicon detectors for a total of 43 000 readout channels. Each detector has a dimension of 9.5×9.5 cm 2 and a thickness of 410 μm . We present here a detailed description of the performance of the detector prototype during a testbeam period at the CERN PS in May 2000. The Tracker performance is described in terms of position resolution and signal-to-noise ratio for on and off-axis incident charged particles. The measured 40 μm resolution for a large range of incident angles will provide an excellent angular resolution for cosmic γ-ray imaging.

Nonlinear Compton scattering of strong laser radiation on channeled particles in a crystal

A version for intense γ-ray radiation based on the multiphoton scattering of strong laser radiation on relativistic particle beam channeled in a crystal is proposed. The incident laser beam and charged particles beam are counter-propagating and the laser radiation is resonant to the energy levels of transversal motion of channeled particles.

Energy spectra, angular spread, fluence profiles and dose distributions of 6 and 18 MV photon beams: results of Monte Carlo simulations for a Varian 2100EX accelerator

The purpose of this study is to provide detailed characteristics of incident photon beams for different field sizes and beam energies. This information is critical to the future development of accurate treatment planning systems. It also enhances our knowledge of radiotherapy photon beams. The EGS4 Monte Carlo code, BEAM, has been used to simulate 6 and 18 MV photon beams from a Varian Clinac-2100EX accelerator. A simulated realistic beam is stored in a phase space data file, which contains details of each particle's complete history including where it has been and where it has interacted. The phase space files are analysed to obtain energy spectra, angular distribution, fluence profile and mean energy profiles at the phantom surface for particles separated according to their charge and history. The accuracy of a simulated beam is validated by the excellent agreement between the Monte Carlo calculated and measured dose distributions. Measured depth–dose curves are obtained from depth–ionization curves by accounting for newly introduced chamber fluence corrections and the stopping-power ratios for realistic beams. The study presents calculated depth–dose components from different particles as well as calculated surface dose and contribution from different particles to surface dose across the field. It is shown that the increase of surface dose with the increase of the field size is mainly due to the increase of incident contaminant charged particles. At 6 MV, the incident charged particles contribute 7% to 21% of maximum dose at the surface when the field size increases from 10 × 10 to 40 × 40 cm2. At 18 MV, their contributions are up to 11% and 29% of maximum dose at the surface for 10 × 10 cm2 and 40 × 40 cm2 fields respectively. However, the fluence of these incident charged particles is less than 1% of incident photon fluence in all cases.

Noise characteristics of stacked CMOS active pixel sensor for charged particles

The noise characteristics of a stacked CMOS active pixel sensor (SCAPS) for incident charged particles have been analyzed under 4.5 keV Si + ion irradiation. The source of SCAPS dark current was found to change from thermal to electron leakage with decreasing device temperature. Leakage current at charge integration part in a pixel has been reduced to 0.1 electrons s −1 at 77 K. The incident ion signals are computed by subtracting reset frame values from each frame using a non-destructive readout operation. With increase of irradiated ions, the dominant noise source changed from read noise, and shot noise from the incident ions, to signal frame fixed-pattern noise from variations in sensitivity between pixels. Pixel read noise is equivalent to ten incident ions. The charge of an incident ion is converted to 1.5 electrons in the pixel capacitor. Shot noise corresponds to the statistical fluctuation of incident ions. Signal frame fixed-pattern noise is 0.7% of the signal. By comparing full well conditions to noise floor, a dynamic range of 80 dB is achieved. SCPAS is useful as a two-dimensional detector for microanalyses such as stigmatic secondary ion mass spectrometry.

The effect of topographical local charging on the etching of deep-submicron structures in SiO2 as a function of aspect ratio

Physical and electrical influences on plasma etching on the inside of a microtrench in SiO2 were numerically investigated using Monte Carlo simulation of ions and electrons with the aid of surface charge continuity and Poisson’s equation. When the aspect ratio is greater than seven, the bottom is charged up to a potential sufficient to prevent the influence of all the incident ions, with a realistic initial energy of 300 eV for SiO2 etching within the period required for monolayer stripping, resulting in etch stop. The cause of etch stop is purely the result of the electrical local charging due to the topography of the trench, and of the initial conditions for incident charged particles. The etch stop caused by a cw plasma will be disorganized or prevented within a short time by the aid of ion–ion plasma in an afterglow phase.

Output characteristics of stacked CMOS‐type active pixel sensor for charged particles

AbstractA stacked CMOS‐type active pixel sensor (SCAPS) for charged particles has been developed. The SCAPS is an integral‐type detector that has several advantages over conventional systems, including two‐dimensional detection, wide dynamic range, no insensitive time, direct detection of charged particles and a high degree of robustness. The output characteristics of the SCAPS for incident charged particles has been analysed both theoretically and experimentally. The relationships between the output voltage of the SCAPS and the number of incident charged particles were formulated by including corrections for the non‐ideal characteristics of transistors in a pixel. The fluctuation of output characteristics of the SCAPS was evaluated experimentally by irradiation of secondary 4.5 keV Si+ ions generated by SIMS. The function was used to determine the number of incident ions into each SCAPS pixel within twice the statistical error. The SCAPS is useful as a two‐dimensional detector for microanalysis, such as stigmatic SIMS. Copyright © 2001 John Wiley & Sons, Ltd.

Columnar cesium iodide (CsI) and micro-hole arrays for use in gas avalanche detectors

The characteristics of a columnar CsI layer with gas multiplication was investigated by using beta rays from a /sup 90/Sr source. This layer is intended for use as the primary electron source in any gas avalanche microdetector to avoid severe performance loss by the oblique angle of the incident charged particle. It was initially thought that the columnar structure might provide a larger detection efficiency than a planar CsI layer, because of the many surface crossings of incident particle for the columnar geometry. The columnar CsI study was performed in a thin parallel-plane structure, which has a 50-500 /spl mu/m gas gap between a columnar CsI cathode and metal anode. We discuss the secondary emission and electric fields in the columnar structure, and explain why, based upon field simulation and experimental results, this approach does not succeed in this case. New ideas are presented for driftless gas avalanche detectors insensitive to the angle of incidence.

Importance of the Plasmon Damping for the Dynamical Image Forces

In the framework of the semiclassical approach the image force energy W(z) for incident or emitted charged particles moving in vacuum normal to the metal surface is calculated taking into account the finite lifetime of plasmons in the metal. It is shown that the deep oscillations of W(z) induced by the creation of real plasmons are heavily damped by the dissipation factor, so that they may be not taken into account in the asymptotic region where the electrostatic dependence for W(z) is restored.

Utilization of a thin columnar cesium iodide (CsI) layer in gas avalanche microdetector

A thin (200–300 μm) layer of columnar cesium iodide (CsI) crystals has been coupled to a conventional microstrip gas chamber. This layer provides the dominant source of electron production by incident charged particles in gas avalanche microdetectors, and is expected to make a significant improvement in spatial and time resolution, and detection efficiency, with respect to particle's angle of incidence. The CsI layer also makes the chamber useful for X- or γ-ray detection with good position accuracy. In this paper, measurements are presented of signal enhancement due to the columnar CsI layer, and the efficiency versus angle.

A proton dose calculation algorithm for conformal therapy simulations based on Molière's theory of lateral deflections.

An algorithm is developed for computing proton dose distributions in the therapeutic energy range (100-250 MeV). The goal is to provide accurate pencil beam dose distributions for two-dimensional or three-dimensional simulations of possible intensity-modulated proton therapy delivery schemes. The algorithm is based on Molière's theory of lateral deflections, which accurately describes the distribution of lateral deflections suffered by incident charged particles. The theory is applied to nonuniform targets through the usual pencil beam approximation which assumes that all protons from a given pencil beam pass through the same material at each depth. Fluence-to-dose conversion is made via Monte Carlo calculated broad-field central-axis depth-dose curves, which accounts for attenuation due to nuclear collisions and range straggling. Calculation speed is enhanced by using a best-fit Gaussian approximation of the radial distribution function at depth. Representative pencil beam and spread-out Bragg-peak computations are presented at 250 MeV and 160 MeV in water. Computed lateral full-widths-at-half-maximum's in water, at the Bragg peak, agree with the expected theoretical lateral values to within 1% at 160 MeV and to within 3% at 250 MeV. This algorithm differs from convolution methods in that the effect of the depth of any inhomogeneities in density or atomic composition are accounted for in a rigorous fashion. The algorithm differs from Fermi-Eyges based methods by accounting in a rigorous way for the effect of nonsmall-angle scattering and screening due to atomic electrons. The computational burden is only slightly greater than that expected using the less-rigorous Fermi-Eyges theory.

Injection and acceleration of thermal protons at quasi‐parallel shocks: A hybrid simulation parameter survey

Collisionless shocks that propagate along the mean magnetic field are known to accelerate some fraction of the incident charged particles directly from the thermal pool to energies that are considerably higher than the energy at which the plasma rams into the shock. Using hybrid simulations, we address two issues: (1) the dependence of the injection/acceleration of thermal protons to energies much higher than the plasma ram energy on various shock parameters such as Mach number, plasma beta, etc., and (2) the effect of the high‐energy particles, accelerated directly from the thermal population by the shock, on the macroscopic properties of the shock, most notably, on the density compression. We find that for supercritical Mach numbers the acceleration of the thermal plasma is efficient enough that the back pressure due to the energetic particles can significantly increase the density compression across the shock, above the value expected from the simple Rankine‐Hugoniot prediction. Additionally, at low Alfvén Mach number, where the acceleration of the thermal plasma is inefficient, the density compression is smaller than the simple Rankine‐Hugoniot prediction owing to the nonresonant fire hose instability. The acceleration efficiency increases with Mach number except at very high Alfvén Mach numbers, where it begins to decrease for Mach numbers greater than ∼ 10. This is due to the presence of a fixed, free‐escape boundary that limits the size of the foreshock region measured in units of the mean‐free paths of the accelerated particles. Additionally, we find that regardless of the upstream plasma parameters, the acceleration efficiency increases with both the density compression ratio across the shock and the distance to the free‐escape boundary measured in units of the mean‐free path of the energetic particles. Both of these are consistent with analytic theory and numerical models that use a phenomenological scattering law.

Study of a [formula omitted] measurement and the gas-gain saturation by a prototype drift chamber for the BELLE-CDC

We studied the performance of a dE dx measurement using an actual real-size prototype of the Central Drift Chamber for the KEK B-Factory. The observed dependences on the track incident angles showed a gas-gain saturation effect due to the space-charge. This gas-gain saturation caused the chamber response to dE dx of the incident particles to be weaker. We measured gas-gain saturation as a function of the line-charge density on a sense wire made by an incident charged particle, and observed that the line-charge density dominantly determined the gas-gain saturation.

A particle energy determination with an imaging plate

It is shown that the stimulation spectra of Eu 2+ luminescence in BaFBr:Eu 2+ based imaging plates are strongly dependent on the energies of the incident charged particles and the ratios of the luminescences stimulated by two different light wave lengths, e.g. of 600 and 500 nm, indicate simply the energies. This additional feature enables us to determine the incident particle energies by the imaging plate itself, keeping all the high performances of the imaging plate intact.

A particle telescope system for nuclear reaction identification

A particle telescope system is described, consisting of a thin (28 μm) dE dx and a thick (300 μm) E silicon detector operating in coincidence mode, with relatively high solid angle of acceptance and very low background characteristics. This apparatus is capable of determining both the energy and identity of incident charged particle species and therefore of identifying nuclear processes. Additional advantages of this system are that it is capable of operating in corrosive environments and of reducing the charged particle background to as low as one count per week. The system calibration was carried out for MeV energy protons, 4He and β particles. Nuclear reactions were produced through high energy (190 keV) deuterium ion implantation of metallic foils and thin films. The particle telescope system was employed to measure the energy and determine the species of charged particles produced by nuclear reactions occurring within the films and foils.

Optical observation of self-quenching streamers by /spl alpha/- and /spl beta/-rays

Optical images of self-quenching streamers (SQSs) in a gas counter have been observed for /spl alpha/- and /spl beta/-rays, incident charged particles. Individual images of the streamers were obtained by using an image-intensifier system with a gating function. The observation was performed from the axial direction of the gas counter used. For /spl alpha/-ray irradiation, streamers develop only in two specific directions orienting tracks formed by /spl alpha/-rays. On the other hand, for /spl beta/-ray, streamers grow in various directions; obtained images are similar to those for X-rays. On the basis of the observation, SQS-formation mechanisms by different sorts of ionizing radiation are discussed. A possible mechanism of primary-ionization track oriented (PRITOR) type SQS induced by /spl alpha/-rays is proposed. >

Populations of highly excited atoms and ions in the optically thin plasma

Treating it as a boundary-value problem, the equations of highly excited state populations of atoms and ions are theoretically studied in case of recombining plasma. Scattering and spontaneous transitions as well as those induced by background radiation, are taken into account in the kinetic equations. The kinetic coefficients for inelastic scattering of incident charged particles on highly excited atoms and ions have been calculated in the asymptotically exact case: 1.6×105 (z/n)2)T e −1 ≪1.

Self-energy of a moving charged particle in the presence of a metal surface.

The general expression for the self-energy of a moving charged particle interacting with a metal surface has been derived for its above-threshold speed. The dispersion of the surface as well as bulk plasmon has been taken into account. Expressions for the energy loss and the effective mass of the incident charged particle have been also derived. Numerical results for the self-energy, energy loss, and the effective mass of the incident charged particle have been presented. It is found that effects of plasmon dispersion are quite significant.