Experimental mean lives for levels in Sn III and Sn IV

We have used a field emission ion source in a 2 MV Van de Graaff to obtain a beam of Sn⁺ ions with energy between 0.7 and 1.4 MeV, or a beam of Sn²⁺ ions with energy 0.7 MeV. By conventional beam-foil spectroscopy we have studied spectra and mean lives for lines and levels in Sn III and IV. Where possible, our results are compared with recent theoretical calculations for levels in the Ag I and Cd I isoelectronic sequences.     

Performance Characteristics of the 30 MeV Three-Stage Tandem Facility at BNL

The 30 MeV 3-stage Van de Graaff facility at Brookhaven National Laboratory achieved the desired operating specifications on July 28, 1970 and has been in operation on various research programs since. The facility consists of two MP Tandem Van de Graaff accelerators arranged in line with a negative ion source installed in the terminal of the first accelerator. The two accelerators can either be used as separate Tandem accelerators or together in a 3-stage configuration. Proton energies as high as 30.5 MeV with currents as high as 4 microamperes have been obtained.     

应用于离子注入的RFQ加速器

射频四极场(Radio frequency quodrupole,RFQ)加速器是一种非常适于用作MeV级能量离子注入的加速器.它具有束流强、体积小、使用方便、离子源处在地电位,还可同时加速正、负两种离子等优点.本文介绍了RFQ加速器在国际上的发展状况及其基本原理、北京大学研制的1 MeV RFQ加速器的具体结构、性能以及一种新型RFQ-SFRFQ组合加速器的特点.     

Chopped ion beams for radiation effects simulation

The heavy ion source located in the terminal of a 5 MV Van de Graaff has been modified to produce chopped ion-beams useful for studying microstructural phenomena in ion irradiated materials.     

A heavy-ion acceleration system using a low energy Van de Graaff

A system has been developed for heavy-ion irradiation using a 4.75 MV single-ended horizontal Van de Graaff. The present paper describes the development of two PIG ion sources, a beam energy analyzing and a transport system. The facility has been utilized for H(¹⁵N, αγ)¹²C hydrogen depth profiling and Ne surface bombardment studies. Examples of experimental results are discussed.     

Modification of an Ion Source for the Production of Microampere 4He- Beams

Several modifications of the ion source of a model EN Tandem Van de Graaff Accelerator have increased the production of 4He- beams by a factor of 100 over that first obtained with the source (~10 nA). While using H2 gas for charge exchange, the replacement of the source drift tube by a screen and the installation of a system for precise adjustment of the button alignment with respect to the extractor electrode increased the output to 150 nA at the ion source. Recently potassium vapor has been used for charge exchange. Since the introduction of this technique, 4He- beam currents of 1. 2 ?A have been regularly produced. The 4He+ ions from a duoplasmatron ion source are accelerated to 20 keV and passed through the standard exchange canal which is modified by the addition of a potassium vapor chamber. Analyzed 4He++ beams of 0.3 to 0.8 ?A have been obtained with terminal voltage between 1.8 and 6 MV. The modified source has been used with K-vapor exchange for continuous periods of up to 120 hours without deterioration of source performance. Normal operation with H2 gas exchange for other beams is possible without the interruption of the source operation.     

厚铍靶9Be(d,n)反应中子产额测量

能量在3MeV以下厚靶D-Be反应的中子产额实验数据至关重要,但较为缺乏。本工作在北京大学4.5MV静电加速器上对氘束轰击厚铍靶的中子产额进行测量。对入射氘核能量在0.35~2MeV之间的若干能量点用长中子计数管进行了0°方向中子产额、中子角分布及中子总产额的测量。与已有的测量结果和经验公式进行了比较,并拟合出氘束轰击厚铍靶中子总产额的经验公式。     

The nuclear microprobe at the University of Arizona

A nuclear microprobe has been operational at the University of Arizona since early 1994. It utilizes a magnetic quadrupole doublet (model QL-300 from Microscope Associates, Inc.) with an 11 mm diameter aperture and lens lengths of 6 cm each. The magnetic pole tips are electrically insulated to enable electric rotational alignment and beam rastering by application of varying voltages to the pole tips. Ion beams are obtained from a 5.5 MV model CN, High Voltage Engineering Corp. Van de Graaff accelerator with a Penning type ion source. Present mininum beam spot size is about 2 μm obtained with a 4 MeV H₂⁺ beam with a current of about 40 pA. To date, the instrument has been successfully used to map concentrations of Hg, Cr, and As in rabbit renal slices using PIXE.     

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.     

用于2.5MeV质子静电加速器ns脉冲装置的晶体管移相倍频器

本文介绍一个幅-相和相-幅特性均优良、能跟随加速器长期稳定运行的晶体管移相倍频器。它用于我所2.5MeV质子静电加速器ns脉冲装置的电子线路中。调节该器输出电压幅值和相位,能有效地控制频率为2MHz、宽度为10—20ns的脉冲束沿中心轨道横向偏转的张角大小和对称性。     

Determination of tritium using a small Van de Graaff accelerator

Determination of $\text{T}\text{D}$ ratios in heavy water samples were carried out using a small Van de Graaff accelerator. The accelerator mass spectrometry system used is described. For comparison, the $\text{T}\text{D}$ ratios were also determined with beta-ray counting methods. Our result demonstrates that tritium at a concentration of 1 part in 10¹⁴ of deuterium was determined with a small Van de Graaff accelerator, and the potential sensitivity would be 2–3 orders of magnitude higher. A simple and cheap 1–2 MeV small accelerator with a suitable ion source and high intensity ion beam may be a powerful tool for determination of tritium.     

Electron paramagnetic resonance dose response studies for neutron irradiated human teeth

The dosimetric response of neutron irradiated human tooth enamel has been investigated using electron paramagnetic resonance (EPR) dosimetry. Continuous energy fast neutrons of mean energy less than 450 keV were produced from the McMaster University 3 MV K.N. Van de Graaff accelerator employing a thick lithium target via ⁷Li(p,n)⁷Be interaction. Prior to its use for various experiments, the gamma dose contamination of the neutron beams was determined at the selected proton beam energies using the tissue-equivalent proportional counter (TEPC). The neutron sensitivity (/Gy-100 mg) of human tooth enamel remained constant for various mean neutron energies ranging from 167 to 450 keV. Similarly, the EPR signal intensity remained independent of the neutron dose rate variation from 0.5 to 2.4 Gy/h.     

Sub-100 keV ion beam generation with a Van De Graaff accelerator using an external DC voltage supply

We present a method to produce stable proton and helium ion beams with energies of 10-100 keV from a 30-year-old Van De Graaff accelerator using an external stabilized DC voltage supply instead of the belt charging system. Requiring no other modifications, this makes an ideal system for ion irradiation with fluences up to 10¹⁵ ions/cm². Such ion energies and fluences are required in the emerging fields such as silicon micromachining using ion irradiation and we give examples of structures created with sizes as small as 200 nm.     

The Schonland Micro-Scanning Ion Beam Analysis Facility

The Schonland Micro-Scanning Ion Beam Analysis Facility is used for interdisciplinary research, uniting physics and many other disciplines. It has a unique dual accelerator input configuration. A wide range of high energy heavy and light ions is available from an EN Tandem van de Graaff accelerator with 6.0 MV terminal voltage. Light ions at lower energy but with much increased luminosity are available from a 2.5 MV single-ended van de Graaff accelerator. The sample chamber is equipped to image radiation and particles from a wide range of ion-beam interactions with matter. These include the ion beam analytical techniques of RBS, ERDA, PIXE, NRA, SecEM and STIM. Some of these techniques have been performed tomographically or under channeling conditions. Sub- or near-micron spot sizes for many of these techniques are available. The user interface to the sample chamber is highly automated, allowing safe and friendly interaction. The OMDAQ system developed at Oxford University is dedicated to on-line acquisition and preliminary analysis of singles spectra. The Physics Analysis Workstation (PAW + +) system developed for CERN and ported to a CAMAC-PC environment manages the more sophisticated multi-parameter acquisition and post-processing.     

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.     

利用静电加速器质谱技术测定氚

本工作描述基于2.5MV静电加速器建立的加速器质谱计的基本原理、实验装置以及重水样品中氚浓度(T/D)的测定。为了比较,还用放射性法进行了测量。实验结果表明,基于一台能量约1—2MeV加速器测定氚的灵敏度已达到10~(-14),而潜在灵敏度还可能高2—3个量级。本文还讨论了这种技术的前景和问题。     

Symmetric Neutralized Ion Beams for Magnetic Fusion Applications

A symmetric neutralized ion beam (SNIB) is composed of positive and negative ions, and is capable of propagating across a transverse magnetic field due to the polarization of the beam. Such a beam may be of use as an alternative or complement to conventional neutral beam injection (NBI) in magnetic confinement fusion devices. SNIBs of energies from hundreds of keV up to a few MeV can be efficiently produced through a novel application of radio frequency quadrupole (RFQ) accelerators. Because the cross-field propagation ability of the SNIB depends mainly on beam density, SNIBs of significantly lower energy than the 1 MeV envisioned for ITER neutral beams can in principle reach the center of a magnetically confined plasma. Some challenges that need to be overcome for this technique to be viable are identified; nevertheless, the approach is attractive when compared to the bulky, high voltage, conventional neutral beam systems. Distributed injection of many beams is possible due to the relative compactness of a SNIB module.     

Recent developments in ion implantation accelerators

Ion implantation technology plays an important role in different fields of materials modification and has become a well established industrial technique. In semiconductor device fabrication more than 1000 ion implanters operating in the low- and medium-energy range (≤, 400 keV) are working worldwide. There is also an increasing interest in the improvement of the surface properties of metals, ceramics, and polymers by means of ion implantation. For some of the newer applications the required penetration depth is large, up to several μm, corresponding to an ion beam energy of several MeV. Furthermore, certain processes involve implant doses up to 10¹⁸ ions/cm², which implies that high currents are needed as well. Both requirements — high ion current and high energy — are difficult to fulfill simultaneously by the commonly used static machines. Modem rf linacs combine strong radial focusing with efficient acceleration, which allows for high currents and high energy. In this paper recent developments in this field will be discussed.     

Characterization of human fingernail elements using PIXE technique

PIXE technique was employed in the determination of the major, minor and trace elemental concentrations in finger-nails of 62 healthy young adults (30 females and 32 males), aged between 20 and 37 years. The elemental concentrations in the nails of the analyzed population provide good reference data set for further health studies. The PIXE measurements were carried out using 1.8 MeV collimated proton beam from the 2.5 MV AN-2000 Van de Graaff accelerator at INFN, LNL, Legnaro (Padova), Italy. The results show the presence of twenty elements. Their metabolic roles in humans are presented and discussed. The comparison of our results with those of other authors are also presented.     

Investigation into the Liner Stabilizer for the Oxford Injector

A mathematical analysis is presented of a combined liner and spray charge control system for regulating the voltage of the single ended Van de Graaff which forms the injector of the Oxford coupled Electrostatic Generators. The stabilizer design, based on this analysis, incorporates automatic switch-over to an auxiliary generating voltmeter stabilizer loop. An automatic gain control in the slit amplifiers eliminates the necessity for manual gain adjustments in most operating conditions. The voltage stability achieved in operation gave a beam energy stability of ± 7 parts in 105 i.e. 4.447 ± 0.000325 MeV measured using the resonance in the reaction 15N(?, ?)19F. Repeated voltage breakdowns of the HT terminal were prevented by a protection circuit based on the analysis of the breakdown behaviour of the generator. The calculated performance of the circuit has been verified by the observed behaviour after total breakdown.