Structure of near surface layers of GaAs and Si crystals irradiated by powerful ion beams

We have studied the effect of hydrogen powerful ion beams (PIB) on the structures of GaAs and Si crystals. A “conversion” zone of a high defect concentration was formed in the near surface region. This “conversion” zone is the region where defects induced by stationary beams are escaping to the surface or annihilating at sinks. We used two direct methods of analysis: positron annihilation (PA) and Rutherford back scattering of channeled Ions (RBS/CI). Si and GaAs crystals were irradiated with 300 keV and 500 to 4800 keV beams from the modified “TONUS” and “VERA” accelerators.     

The limits of volume reflection in bent crystals

We show that theory predictions for volume reflection in bent crystals agree with recent experimental data. This makes possible to predict the volume reflection angle and efficiency in a broad range of energy for various crystals. A simple formula is proposed for volume reflection efficiency. We derive the physical limits for application of crystal reflection at high-energy accelerators where it may help beam collimation.     

Gap application results for adjacent electron beams treatment

Nowadays, electron beams from high-energy linear accelerators (LINAC) are widely used in a variety of radiotherapy treatments being suitable especially for superficial tumors. Since this sort of ionizing radiation has stopping power higher than photons, deeper and healthier tissues can be preserved. On the other hand, when applying adjacent electron beams, “hot” spots can be observed, due to penumbra and/or scattering, contributing to the increase of the absorbed dose in the target volume. In this sense, the objective of this work was to investigate the effects of parallel adjacent electron beams using the chemical dosimeter Fricke Xylenol Gel (FXG) and compare the experimental results with ones acquired using Monte Carlo simulation. Thus, 10 × 10, 15 × 15 and 20 × 20 cm² fields were irradiated with 5, 8 and 10 MeV electron beams applying different gap widths. The experimental results and the simulations indicated overdose values up to 40% from the prescribed one for the specific tumor. This demonstrates that specific gaps are necessary in the case of treatments with parallel adjacent electron beams in order to prevent overdoses in the depth of interest.     

Phase space analysis of planar channeled MeV protons

A phase space analysis framework is used for Monte Carlo channeling simulations of the passage of 3 MeV protons through thin silicon layers. The results show the relationship between the spatial location of the protons across the channeling planes, their emergent angle and their energy loss. It is shown how the energy spread of the transmitted beam depends on the ratio of the layer thickness to the channeling oscillation wavelength. For a layer thickness of half a wavelength, or a multiple thereof, the energy spread of the transmitted beam is smallest. By collimating the emergent angle it can be reduced to a value of the same order as that obtained in beams from van de Graaff accelerators. This is important in understanding the limitations on the subsequent transport and focusing of MeV ion beams after passing through thin crystals.     

High energy particles from the six-meter synchrocyclotron and their utilization (review article)

The problem of increasing the efficiency of utilization of the six-meter synchrocyclotron at the Institute of Nuclear Problems, Academy of Sciences USSR is reviewed. The method by which a large number of particle beams is obtained and collimated is described; using these beams it is possible to carry on several simultaneous experiments. Characteristic beam data are presented.Presented at the CERN symposium on high energy accelerators and meson physics (Geneva, June 1956).Deceased.     

A new generation of single-ended Van de Graaff accelerators for ion implantation and ion beam analysis

High voltage Engineering Europa B.V., The Netherlands developed a new generation of single-ended Van de Graaff accelerators for ion implantation and ion beam analysis. The new HVEE Van de Graaff accelerators are equipped with a unique (patented) ion source exchange system capable of handling four lands of ion sources, mass separation at high voltage level and an X-ray intensity suppression system. The accelerators are able to produce a large variety of continuously, homogeneous and highly collimated mass-analyzed ion beams of several hundred μA in the energy range from 50 keV up to l MeV (l MV model) or from 100 keV up to 2 MeV (2 MV model), using singly charged ions, whereby the maximum energy can be easily reached and maintained without conditioning and virtually no X-rays are produced. Combined with two dedicated end stations (one for ion beam analysis using RBS, channeling, NRA and PIXE, and one with an automatic wafer-handling system for both single-wafer implantation and batch processing), these systems are very suitable for research as well as industrial applications.     

CR-39 detector based thermal neutron flux measurements, in the photo neutron project

PhoNeS (photo neutron source) is a project aimed at the production and moderation of neutrons by exploiting high energy linear accelerators, currently used in radiotherapy. A feasibility study has been carried out with the scope in mind to use the high energy photon beams from these accelerators for the production of neutrons suitable for boron neutron capture therapy (BNCT). Within these investigations, it was necessary to carry out preliminary measurements of the thermal neutron component of neutron spectra, produced by the photo-conversion of X-ray radiotherapy beams supplied by three LinAcs: 15 MV, 18 MV and 23 MV. To this end, a simple passive thermal neutron detector has been used which consists of a CR-39 track detector facing a new type of boron-loaded radiator. Once calibrated, this passive detector has been used for the measurement of both the thermal neutron component and the cadmium ratio of different neutron spectra. In addition, bubble detectors with a response highly sensitive to thermal neutrons have also been used. Both thermal neutron detectors are simple to use, very compact and totally insensitive to low-ionizing radiation such as electrons and X-rays. The resultant thermal neutron flux was above 10⁶ n/cm²s and the cadmium ratio was no greater than 15 for the first attempt of photo-conversion of X-ray radiotherapy beams.     

Feasibility of an epithermal neutron source for BNCT based on RFQ accelerator

The use of boron neutron capture therapy for the treatment of deep-seated tumours, such as glioblastoma multiforme, requires neutron beams of suitable energy and intensity. The analysis of the therapeutic gain shows that a high tumour control probability with sublethal dose at healthy tissues can be achieved, in most cases, by using neutron beams of a few keV energy, with a flux of about 10⁹ neutrons/cm² s. Therapeutic neutron beams with high-spectral purity in this energy range could be produced by accelerator-based neutron sources through a suitable neutron-producing reaction. We investigate the feasibility of a solution based on a small radio frequency quadrupole for a proton beam current of 30 mA and an energy of 2 MeV. An appropriate choice of the function parameters of the RFQ (modulation, efficiency of acceleration, phase shift, etc., …) allows one to design relatively compact accelerators, which could eventually lead to setup hospital-based BNCT facilities.     

大功率、高均匀度电子束扫描仪电路

本文提出了二种结构新型的大功率电子束扫描电路,能够将扫描均匀度提高到90％以上。可用于能量20MeV以下的各种电子束加速器。     

Recent Advances in DC Methods of Particle Acceleration

Four recent developments have contributed significantly to broadening the scope of dc particle-acceleration systems: 1. Tandem principle of utilizing the generated high-voltage several times; 2. Insulating-core transformer for generating high-voltage dc power; 3. Inclined-field acceleration tube that minimizes the "total voltage effect, a previous limitation of dc acceleration systems; 4. Ion-source and beam-optical designs to increase useful ion intensities and to improve efficiency of transporting accelerated dc beams. These developments are currently being incorporated, in various combinations, into several dc accelerator designs, including: a. Sub-Mev electron and positive-ion accelerators with high beam power; b. Tandem Van de Graaff accelerators with at least 10 million-volt potential; c. Powerful Tandem accelerator at moderate voltage and very high current. Typical systems arising out of these advances are described in the light of applications now being exploited in research and industry.     

High Intensity Multi-GeV Proton Accelerators

For performing many high-energy physics experiments, it is necessary to have high-energy particle beams of very high intensity. The intensity of particle beams in circular proton accelerators in the multi-GeV energy range depends, first, on the number of protons accelerated per pulse and, second, on the number of pulses per second. The number of protons which can be accelerated per pulse is limited by the space charge effects, and the number of pulses per second is limited by the design or type of the accelerator. These intensity limitations and methods of pushing back these limits are discussed. It is now feasible both technologically and economically to construct accelerators in the tens of GeV energy range which will accelerate more than 1014 protons per second.     

Characterization and calibration of a SSNTD for heavy-ion detection and strangelet search in cosmic rays

A commercially available grade of polymer was investigated for its suitability as a solid state nuclear track detector (SSNTD) to look for rare events in cosmic rays at very high mountain altitudes. It was identified to be polyethylene terephthalate (PET) and found to have a higher detection threshold compared to many other widely used SSNTDs. Hence it is particularly suited for rare event search in cosmic rays by eliminating the dominant low Z background. Systematic studies were carried out to determine the ideal etching condition. Also the charge response of PET was studied using various ion beams from accelerators. The results of such studies were combined to obtain the calibration curve for PET as SSNTD, by which one can identify and characterize charged particles.     

COMPARISON OF ABSORBED DOSE MEASUREMENTS WITH AN EXTRAPOLATION CHAMBER AND A FARMER CHAMBER IN HIGH ENERGY ELECTRON BEAM

I The extrapolation ehaJ口ber(EC)which was develoPed at the Xinjiang Institute ofPhysics(XIP)was used for the detert苗nation of relative absorbed dose distribution invarious material。认the wo比descri卜刃勿Jin Taol,1.FOllowing this,experimente have加en unde到进ken in a high energy elec物”n beam,the皿印ose ofwhiehwastoeheekthe suitability of the EC for the dete恤ination of absolute absorbed dose byeomparison with a ealibrated Farmer type ionization ehamber.These experiments were洲而rmed …     

High-resolution PIXE instrumentation survey. Part II

High-resolution PIXE facilities (X-ray crystal spectrometers working on ion beams of accelerators) and their applications in chemical analysis and in basic research are surveyed.     

Spark source for multiply-charged ions

Most well-known spark sources for multiply-charged ions make use of weak inductively-coupled sparks which are obtained by means of a Tesla coil [1], [2]. These sources have not been used in charged-particle accelerators because of the small ion current, low charge multiplicity of the ions which are obtained, and general unstable operation. Starting in 1953 the authors have been carrying out an investigation of “hot” vacuum sparks obtained by the discharge of high-voltage condensers in an effort to obtain intense beams of multiply-charged ions with high charge multiplicities. In 1954 a source was constructed and found suitable for use in pulsed accelerators of multiply-charged ions.     

Simulations of volume reflection and capture in bent crystals

Recent experiments at PNPI (Gatchina), IHEP (Protvino) and CERN have measured for the first time the proton volume reflection in bent crystals. We show that these measurements agree with Monte Carlo simulations and predict strong effects for a possible crystal application at the 7 TeV Large Hadron Collider (CERN) and for the ongoing experiment at the Tevatron (FNAL). We suggest a simple formula for volume reflection efficiency. The reflection experiments are essential in validation of the theory that predicts a significant improvement in crystal-based collimation at accelerators.     

Use of Superconducting RF Systems in Low-Energy Accelerators

The basic problems of the development and construction of charged-particle accelerators using superconducting rf accelerating structures are discussed. The characteristics of the modular systems currently used in high-energy superconducting accelerators and their application to accelerators for tens or hundreds of MeV are examined. __________ Translated from Atomnaya Energiya, Vol. 99, No. 4, pp. 289–295, October, 2005.     

Experimental determination of the radiation quality factor near high-energy accelerators

Experimental data characterizing the effective quality factor QF of multicomponent pulse radiation in various parts of a 10-GeV synchrophasotron are presented. The measurements were made by the recombination method. The value of QF varied from 3 to 11. The results of the measurements are compared with values determined for other high-energy accelerators. Values of QF obtained in experiments on particle beams in a 680-MeV synchrocyclotron are also given.Translated from Atomnaya Énergiya, Vol. 20, No. 5, pp. 392–396, May, 1966.     

Electron dumps for ITER HNB and DNB beamlines

The negative ion accelerators that produce the high-energy particle beams for the neutral injection systems for the International Tokamak Experimental Reactor (ITER) also produce unwanted particles such as electrons. These electrons are emitted in a wide angular spectrum that allows some of them to directly intercept sensitive beamline components such as the cryogenic pumps. As the electrons are also subject to backscattering, indirect interception always occurs. In this article the electron spectra produced by the Heating Neutral Beam (HNB) and Diagnostic Neutral Beam (DNB) accelerators are calculated. It is shown that these are very different. It is proposed to install electron dumps in the beamlines to intercept electron power directed towards inconvenient places in the HNB and DNB beamlines.     

On the Generation and Focusing of Intense Ion Beams for Pellet Fusion

The current limits of magnetic focusing systems are examined and approximate formulas for long solenoids and periodic channels with short lenses (solenoids and quadrupole doublets) are derived. The characteristics and limitations of conventional sources, pulsed ion diodes, and collective-field accelerators for the generation of intense, energetic ion beams are compared. Use of a collective-ion accelerator with debuncher is suggested as injector into an induction accelerator.