Dynamitrons

Schematic of a direct accelerator (Dynamitron) accelerator. (Courtesy of IBA.)...

A radiation dose of 1 kw. could irradiate about 795 pounds per hour of any material to a dose level of 1 Mrad at 100% efficiency. The power efficiency of the different machines varies from a low of 15% for a Van de Graaff accelerator or resonant transformer to 90% for an insulating core transformer. On the other hand, the Van de Graaff accelerator, being a d.c. machine, can be precisely controlled and adjusted, which is important for research and development. The resonant transformer, Dynamitron, and ICT are less precise, but they have lower operating costs and higher output power, making them more suitable for production purposes. 

The use to which the machine will be put has a bearing on its choice. If it is used for sheets, films, or surface treatment, where only modest penetration, is called for, a low voltage machine, such as the ICT, is suitable. If greater penetration is necessary, a higher voltage machine is needed, and the choice is between the resonant transformer and the Dynamitron. For surface treatment, an ultraviolet light might be sufficient. This is created when an electric arc passes between electrodes separated by gas or vapor. There are two main classes of arcs open, such as the carbon arc, and closed as the various vapor lamps. 

Larger 3- and 4-m.e.v. Dynamitron electron beam accelerators are likewise available commercially. Service capabilities increase with the m.e.v. level of the electron beam accelerator. A 3.0-m.e.v. Dynamitron electron beam accelerator furnishes radiation capable of penetrating a maximum 370 mils of a unit density material or 185 mils of 2.0-density material other performance capabilities are doubled as well. The overwhelming majority of polyolefin plastic products now being manufactured have section thicknesses which can be penetrated safely even by a 1.5-m.e.v. electron beam accelerator. Two possible exceptions would be printed circuit board and thick-walled pipe. A 3-m.e.v. accelerator could readily meet such requirements. The performance capabilities of the 3-m.e.v. accelerator (12-ma. power supply) are increased not only with respect to maximum depth of penetration but also processing capability, which amounts to 14,000 megarad-pounds per hour at 50% absorption efficiency. 

Irradiations were carried out using a Dynamitron 1.5 MeV electron accelerator, or EBES. In the former case, samples were placed on a conveyor tray and passed underneath the beam. At a velocity of 5.7 cm/sec and a beam current of 1 mA, an absorbed dose of 0.5 Mrads is delivered in a single pass. The dose is thus built up by multiple passes. Alternatively the sample could be held stationary underneath the beam for the requisite period of time necessary to attain a given dose. It will be shown later that the latter approach causes the temperature of the sample to rise significantly during irradiation. 

The dose rate in EBES is several orders of magnitude greater than that provided by the Dynamitron so that temperature control might be expected to be more of a problem. However, it should be pointed out that the films are very thin and are supported on silicon wafers which facilitate efficient heat dissipation. Further, since the diameter of the beam is typically <1.0 /tm, the corresponding... 

Key , EBES single pass , EBES multiple pass and, O, Dynamitron exposed (calculated from olefin peak absorbance. 

Several industrial irradiation facilities can now provide both X-ray and electron beam processing for a variety of applications. There are three such facilities in Japan. One of these is equipped with a 5.0 MeV, 150 kW Cockcroft Walton accelerator [14], Another one has a 5.0 MeV, 200 kW Dynamitron accelerator [15], and the third facility has a Rhodotron... 

Typical layout of a Dynamitron electron beam processing facility... 

Schematic of a Dynamitron traveling-wave linear electron accelerator... 

The earlier types of electrical accelerating machines such as the Van de Graaff, the Capacitron, the Resonant Transformer, and the Linear Accelerator have been supplemented by two new types, the Insulated Core Transformer and the Dynamitron. 

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