Van de Graaff electron accelerator

Janata E (1992a) Instrumentation of kinetic spectroscopy. 9. Use of a computer for automatic performance of start-up procedures on a 4 MeV Van de Graaff electron accelerator. Radiat Phys Chem 40 217-223... 

Luthjens LH, Vermeulen MJW, Horn ML, Loos MJ, de Geer SB van der. (2005) Revision of (sub)nanosecond pulser for IRl Van de Graaff electron accelerator aided by field propagation calculations. Rev Sci Instrum 76 024702. 

There are seven types of electron accelerator available for industrial uses [41] (1) Van de Graaff generator (2) Cockcroft-Walton generator (3) insulated core transformer (4) parallel coupling, cascading rectifier accelerator (5) resonant beam transformer (6) Rhodetron (7) linear accelerator (LINAC). 

Protons can also be used instead of X-rays or electrons to create the initial vacancies in the inner electron shells, giving rise to a method known as proton induced X-ray emission (PIXE). In these instruments a high intensity, highly focused beam of protons is produced by a van de Graaff accelerator,... 

The first few tests were carried out using an 8-m.e.v. linear electron accelerator at Berkeley, Calif. In subsequent tests, a 3-m.e.v. Van de Graaff generator at MIT was used. 

Van de Graaff Irradiations. The vertically mounted Van de Graaff accelerator (High Voltage Engineering Co.), used for the electron irradiations, was operated at 2 m.e.v. at all times. 

The electron source was a 2-m.e.v. van de Graaff accelerator equipped with a 15-inch beam scanner. Samples of foam, 2 X 3% X 5% inches, were placed on a shuttle and passed 10 times under the electron beam of the machine operating at 60 / a. and 2 m.e.v. Each pass delivered about 1,000,000 rads, so the total dose to the foam was about 10 megarads. All of the irradiations were carried out in air at room temperature. 

That free radicals are produced in the radiolysis of liquid systems was first shown conclusively by the esr experiments of Fessenden and Schuler71. The esr spectra were observed during the continuous irradiation of the liquid samples by an electron beam from a Van de Graaff accelerator. The spectrum obtained... 

It is difficult to span the intervening energy gap between photo- and radiation chemistry, however, high powered pulsed lasers, utilising multiphoton absorption by the medium, do much to remedy this situation. For the most part, the work described falls into two categories, data with steady state irradiation i.e. light sources and Co-y rays, and pulsed experiments as with lasers and pulsed electron accelerators such as Van de Graaffs and Linacs. 

Pulse radiolysis, in contrast to gamma radiolysis, involves the rapid production of radicals via a pulse of electrons deposited into an aqueous solution, usually delivered by a van de Graaff or electron accelerator. The production and distribution of radicals are identical to that described in gamma radiolysis, but here the radicals are generally produced in sub-microsecond pulses with current fast limits of picosecond pulses. This affords the advantage of following reaction kinetics and not just looking at overall yields. 

Almost all the work in pulse radiolysis is based on the use of three types of electron accelerators linear accelerators (linacs). Van de Graaff accelerators, and Febetrons. The first accelerator used by Keene at Manchester was a 4-MeV linac with pulses of 0.2-2 ps duration [47a] this was replaced in 1967 with an 8-12-MeV linac capable of delivering pulses from 5 ns to 5 ps duration [93]. Further improvements made to the Manchester system up to 1989 have been documented [93]. Similarly, the 13-MeV linac used at Argonne in 1960 by Matheson and Dorfman produced pulses of 0.4 to 5 ps duration [46], whereas in 1989 the equipment comprised a 20-MeV linac, capable of producing pulses from 25 ps to 10 ps duration, and a 3-MeV Van de Graaff accelerator, which is dedicated to EPR and magnetic resonance studies (see below) [95, 98]. 

The electron accelerator employed has been an AS 2000 Van de Graaff accelerator manufactured by High Energy Corporation, Burlington, Mass. The electronic control circuit has been modified considerably, and at present, this accelerator is capable of delivering 30 ns to 5 ys electron pulses of 2 - 2.5 MeV energy and v 1.2 A current at a repetition rate of 60Hz or less. The accelerator can also be operated in the continuous beam mode. The focussed beam has a diameter of 0.3 cm at the output window. 

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