Tandem Electrostatic Accelerator Research Articles

An Investigation of CR-39 Nuclear Track Detector Material as a Fast Neutron Microdosemeter

Abstract This work describes the evaluation of CR-39 for use as a fast neutron microdosemeter, and provides some insight as to the feasibility of such use. The material was calibrated by irradiation with protons and alpha particles accelerated by a tandem electrostatic accelerator. Proton energies of 10, 6, and 3 MeV and alpha particle energies of 15, 10, and 7 MeV were used, at angles of incidence from 0 to 85 deg. The critical angle, normal incidence diameter, and track etching rates versus linear energy transfer (LET) were obtained from these measurements. A method for extracting a LET spectrum from CR-39 irradiated in-phantom with the fast neutron beam was developed and these results are compared with LET spectra measured by a 1.27 cm diameter Rossi chamber.

Design of a tandem accelerator free electron laser

The motivation for using a tandem electrostatic accelerator as an electron accelerator for a free electron laser (FEL) is presented. The adaptation of the HVEC EN tandem at the Weizmann Institute for this purpose, electron beam optics and nonlinear FEL computation relevant for this FEL realization are described. In the tandem configuration the terminal is held at a positive potential. The electron beam is accelerated from ground potential to the terminal in one beam tube and then decelerated down the other beam tube. The FEL wiggler and cavity are at the terminal. Due to the beam energy recovery this scheme produces a high power beam at the terminal with a small investment in electrical power.

The critical angle dependence of CR-39 nuclear track detectors for 3–10 MeV protons and 7–15 MeV alpha particles

With the advent of routine clinical usage of fast neutrons as a radiation therapy modality, interest in the solid state nuclear track detector CR-39 as a possible in vivo neutron dosimeter has increased. One facet of the problems associated with this application is the calibration relationship of the linear energy transfer (LET) of a charged particle and the normal incidencediameter of ther etch pits found in CR-39 after exposure and subsequent etching. This study, performed on a tandem electrostatic accelerator at the University of Wisconsin, Madison, provides such a calibration for both critical angle and normal incidence diameter versus linear energy transfer for several incident energies of proton and alpha particles. Plots of detection efficiency versus angle of incidence for 3, 6, and 10 MeV protons, and 7, 10, and 15 MeV alpha particles are used to determine the critical angle of each particle and energy. The bulk etch and track etch rates were determined by a chi-squared minimization calculation based upon published relationships and the measured major and minor axis dimensions obtained at each angle of incidence, particle and energy. Results of normal incidence diameter versus LET measurements show a smooth monotonically increasing curve with LET. A bulk etch rate of 1.32 μm/h for a 16 h etch in 6.25 N NaOH was measured.

Hydrogen depth profiling using the 6.46 MeV 1H( 19F, αγ) 16O resonance by detection of alpha particles

We have utilized the detection of α-particles from the 6.46 MeV 19F resonance nuclear reaction 1H( 19F, αγ) 16O instead of measuring the γ-yield to profile the hydrogen concentration versus depth in hydrogen containing materials. A special particle filter was prepared to make the α-particle energy monoenergetic and to eliminate the recoiled particles and the scattered particles. The depth resolution and sensitivity were evaluated from the analyses of a polyester film and H-implanted silicon. Advantages of this method include: (1) the small space required for the detector arrangement, (2) easy utilization of a satisfactory current of highly-charged 19F ions from a small electrostatic tandem accelerator, (3) a good sensitivity useful for hydrogen depth profiling, even though this cross section is one-fifth that of the 19F 16.5 MeV resonance for 1H( 19F, αγ) 16O and one-third that of the 15N 6.44 MeV resonance for 1H( 15N, αγ) 12C, and (4) a maximum probing depth deep enough to be useful.

A proposal for a tandem accelerator FEL experiment

A proposal for an FEL experiment, based on a tandem electrostatic accelerator, is presented. The proposed FEL is designed to operate at harmonic frequencies in a quasi-cw mode. An internal wiggler scheme is planned to be used, based upon a strong planar wiggler ( a w > 1), positioned in the high voltage terminal of a HVEC model EN tandem accelerator. The electron beam enters the wiggler at the natural injection angle ( a w/ γ). This approach provides a relatively simple and compact FEL system that will be used as a research tool for studying harmonic operation of FELs and investigating post-saturation laser dynamics and efficiency enhancement. The exceptional electron beam quality and long pulse characteristics of electrostatic accelerators give a special advantage to such an experimental scheme as a means for exploring the ultimate performance parameters of FELs.

A system for measuring the energy spread of an accelerated beam

A system has been implemented to monitor directly the energy spread of analyzed beams from a tandem electrostatic accelerator. The dispersion of a deflection magnet in the beam handling system is used to transform the energy distribution into a spatial distribution, which then is measured by electrostatically sweeping the spatially extended beam across a narrow slit.

The ORNL 25 MV tandem accelerator control system

The CAMAC-based control system for the 25 MV tandem electrostatic accelerator of the Holifield Heavy Ion Research Facility at Oak Ridge National Laboratory (ORNL) was specified by ORNL and built by the National Electrostatics Corporation. Two Perkin-Elmer 32-bit minicomputers are used in the system: a message switching computer and a supervisory computer. The message switching computer transmits and receives control information on six serial highways. This computer shares memory with the supervisory computer. Operator consoles are located on a serial highway; control is by means of a console CRT, trackball, and assignable shaft encoders and meters. Two identical consoles operate simultaneously: one is located in the tandem control room; the other is located in the cyclotron control room to facilitate operation during injection of tandem beams into the cyclotron or when beam lines under control of the cyclotron control system are used. The supervisory computer is used for accelerator parameter setup calculations, actual accelerator setup for new beams based on scaled, recorded parameters from previously run beams, and various other functions. The experience of nearly seven years of control system operation and improvements is discussed.

Superconducting linacs — some recent developments

The paper is a review of superconducting linacs that are of interest for heavy-ion acceleration. Most of the paper is concerned with energy boosters for projectiles from tandem electrostatic accelerators, the only application for which superconducting linacs are now used for heavy-ion acceleration. There is also a brief discussion of the concept of a superconducting injector linac being developed as a replacement of the tandem in a multi-stage acceleration system. Throughout, the emphasis is on the technology of the superconducting linac, including some attention to the relationships between resonator design parameters and accelerator performance characteristics.

Initial performance of a 2 MeV single ended ion implanter

The first system for production implantation of B, P, and As at MeV energies has been operational since mid-1983. It uses a tandem electrostatic accelerator. NEC has also built an in-house implanter, which uses a 2 MV single-ended accelerator, for wafer implants and development tests. Both systems have automatic, serial wafer handling, microcomputer implant controls, and crystal-locked electrostatic beam scanning. We compare the systems and describe developments toward eliminating the need for toxic gases in the positive ion source.

An electrostatic beam line for accelerator mass spectroscopy of exotic particles

An all-electrostatic charged particle spectrometer has been constructed to perform high sensitivity searches for exotic states of matter. This spectrometer consists of an electrostatic beam line capable of mass independent charged particle transport and selection together with time-of-flight, energy loss and total energy detectors. This system has been used in conjunction with the tandem electrostatic accelerator at the Nuclear Structure Research Laboratory of the University of Rochester to search for fractionally charged or anomalously heavy particles.

An accelerator facility within a mineral research establishment

The importance of the minerals industry in Australia is evident from its share of about 40% of the country's export earnings. Its economic success is due in no small measure to the industry's ability to keep abreast with technological innovations and scientific developments, often through collaborations with federal Governments research laboratories such as the CSIRO. In this context, the CSIRO Division of Mineral Physics recently commissioned a Laboratory, known as HIAF — the Heavy Ion Analytical Facility — based on a General Ionex 3 MV Tandetron. a tandem electrostatic accelerator. The Laboratory was designed to facilitate the development of the applications of a host of ion-beam techniques to problems in the geosciences, extending or complementing established methods. Flow-on to the minerals industry is anticipated, with varying degrees of immediacy dependent on the particular technique. The first stage operational at the commissioning provides RBS (Rutherford backscattering spectrometry), PIXE (particle induced X-ray emission) and NRA (nuclear reaction analysis) measurements, and includes the development of a beam microprobe. An ultra-sensitive accelerator mass spectrometry (AMS) system is planned for the second stage, to permit studies of chronology based on radio cosmogenic isotopes and ultra-traces in mineral samples.

On the production of the KrF − and XeF − Ion beams for the tandem electrostatic accelerators

Negative ion formation of KrF 2 and XeF 2 was studied by using a Penning ion source with radial extraction, and the extraction of KrF − and XeF − from the ion source was confirmed by observing the mass fragmentation patterns. Improving the gas feeding system, we could have negative ion currents one order of magnitude larger than the currents reported previously. Typical yields for KrF − and XeF − were 100 nA and 50 nA, and maxima of 320 nA and 150 nA.

PIXE detection limits for some aerosol collection substrates by excitation with protons and 4He 2+ ions from a 3 MV tandem accelerator

Comparisons of PIXE detection limits for K α X rays using 2–5 MeV protons and 7–8 MeV 4He 2+ ions as projectiles have been performed. The comparisons have been made for common aerosol backings. According to simple theoretical considerations regarding X-ray production cross sections and the production of background radiation, detection limits for 4He 2+ should be two to four times lower than for protons for equal velocity projectiles of equal numbers. However, the background in X-ray spectra arising from γ quanta being Compton scattered in the Si(Li) detector can strongly affect the detection limits. The detection limits using protons and 4He 2+ ions from a 3 MV electrostatic tandem accelerator are determined and discussed.

Coupled Operation Experience at the Holifield Heavy Ion Research Facility

The 25URC Pelletron tandem electrostatic accelerator and the Oak Ridge Isochronous Cyclotron (ORIC) comprise the accelerators of the Holifield Heavy-Ion Research Facility (HHIRF). The two machines may be operated individually or coupled, with ORIC serving as an energy booster for the tandem. In the coupled dode, the ion beam enters the cyclotron through the dee stem and is directed by the inflection magnet so that it is tangent to an orbit suitable for acceleration at a higher charge state. A thin carbon foil, placed at the point of tangency, strips the ions so that a substantial fraction are in the desired higher charge state. This fraction of the beam is then accelerated and extracted in the normal fashion. Full energy performance (25 MeV/A oxygen) was demonstrated during first coupled operation in January 1981. Routine coupled operation for experiments commenced in July 1982.

A six tesla analyzing magnet for heavy-ion beam transport

A superconducting analyzer magnet for particle beam deflection has been designed and is being fabricated for use at the Argonne Tandem-Linac Accelerator System (ATLAS). This six tesla magnet will provide 45° of deflection for the heavy-ion beams from the ATLAS tandem electrostatic accelerator and together with its twin will replace the existing conventional 90° analyzer magnet which will become inadequate when ATLAS is completed.

The New Large Tandem Electrostatic Accelerators

Of the five large electrostatic tandem accelerators listed in Table 1, four have undergone column voltage tests and three are presently running commissioning teats with full beam capability. None of the machines has yet to achieve the full rated terminal potential with acceleration tubes installed. At this time each of these latter three machines has reached approximately 90% of full rating. The column voltage tests on these machines have given good assurance of the voltage holding capability of the basic generator structure. The ability to reach design voltages now depends on successful performance of the acceleration tubes. Although no clear sign of total voltage effect is indicated at this time, that would lead to degrading the rated tube gradients, the concern remains over the effects of the large amount of stored energy present in these accelerators and the effect of the huge currents generated during voltage breakdown. Although full rated voltages on these new large machines will undoubtedly take time and patience to achieve, we can expect the first of these machines to begin operating for research purposes during the present year. The era of the large tandems has, in fact, begun.

Measurement of 10Be/ 9Be ratios using an electrostatic tandem accelerator

The applicability of direct atom counting using tandem electrostatic accelerators to the determination of reaction cross sections involving long-lived products has been demonstrated by the measurement of the 10Be/ 9Be ratio in beryllium metal samples irradiated with a known flux of thermal neutrons. The 10Be/ 9Be ratios in enriched samples were measured in the range 10 −10 −10 −13. The background ratio in a non-irradiated sample was found to be (7 ± 3) × 10 −15.

Radioisotope detection with tandem electrostatic accelerators

An MP tandem Van de Graaff accelerator at the University of Rochester has been employed since May 1977 to detect 14C in terrestrial samples, 36Cl in terrestrial and extraterrestrial samples and 10Be and 26Al in samples produced by reactor and accelerator irradiation. The sample sizes ranged from about 10 to less than 1 mg and the ratio of the radioisotope to the stable isotopes approached one part in 10 16 for 14C and 36Cl and one part in 10 14 for 10Be and 26Al. 14C has been measured in a number of samples of geological and archaeological interest. 36Cl has been measured in various groundwater samples as well as samples at Antarctic meteorites and ice. Dedicated systems for 14C dating and geological measurements based on the tandem electrostatic accelerator principle are presently under construction for laboratories in the U.S.A., U.K. and Canada.

New techniques for the preparation of long lived carbon strippers under heavy ion bombardment

The behaviour of carbon stripper foils under heavy ion bombardment has become the subject of extensive study. It is well known that for tandem electrostatic accelerators the yield of high energy heavy ions is greater for solid than gas strippers. The disadvantage of stripper foils is that their lifetime can be short. Attention has been given to a study of new methods for producing carbon stripper foils. Such foils have been subjected to lifetime tests using a special clean irradiation facility with a 4.8 MeV argon beam. This arrangement simulates the conditions in a tandem accelerator. Results of measured lifetimes and behaviour under irradiation are given.

Initial Operation of the Argonne Superconducting Heavy-Ion Linac

Initial operation and recent development of the Argonne superconducting heavy-ion linac are discussed. The linac has been developed in order to demonstrate a cost-effective means of extending the performance of electrostatic tandem accelerators. The results of beam acceleration tests which began in June '78 are described. At present 7 of a planned array of 22 resonators are operating on-line, and the linac system provides an effective accelerating potential of 7.5 MV. Although some technical problems remain, the level of performance and reliability is sufficient that appreciable beam time is becoming available to users.