Accelerated electrons

During many years in Scientific Research Institutes of Nuclear Physics and Introscopy at Tomsk Polytechnical University (TPU) researches into induction electron accelerators and their uses for non-destructive radiation quality control of materials and articles have been conducted. Control sensitivity and efficiency detection experimental researches have been conducted with the high-current stereo-betatron modifications [1], and KBC-25 M and BC-50 high-current betatrons [2,3] in range of 11 MeV and 25-50 MeV radiation energy. 

Induction electron accelerators - betatrons- are widely used as radiation sources in industrial flaw detection of materials and articles of high thickness. However, relatively low radiation intensity has become the barrier for the most wider betatron use in this area. For the efficiencyincrease of radiation control method of articles, as well as for the possibility to control materials and articles of the most thickness the significant increase of betatron radiation intensity has been required. 

Standard El spectra are obtained with an electron energy of 70 eV (electrons accelerated through 70 V). For most compounds, it is easier to produce positive ions than negative ones, and most El mass spectrometry is concerned with positive ions. 

Show that the wavelength X associated with a beam of electrons accelerated by a potential dilference Fis given by 1 = h(2eVmgy. Calculate the wavelength of such a beam for an accelerating potential difference of 36.20 kY... 

Irradiation. Although no irradiation systems for pasteurization have been approved by the U.S. Food and Dmg Administration, milk can be pasteurized or sterilized by P tays produced by an electron accelerator or y-rays produced by cobalt-60. Bacteria and enzymes in milk are more resistant to irradiation than higher life forms. For pasteurization, 5000—7500 Gy (500,000—750,000 tad) are requited, and for inactivating enzymes at least 20,000 Gy (2,000,000 rad). Much lower radiation, about 70 Gy (7000 tad), causes an off-flavor. A combination of heat treatment and irradiation may prove to be the most acceptable approach. 

Over the years there have been several studies examining electron-curable adhesives [9-12]. Off-the-shelf acrylate adhesives were the primary focus of the studies. These adhesives, that have potential use for the repair of advanced composites using high-energy electron accelerators, offer several advantages over conventional repair systems, including [6] ... 

All of the types of repairs described can be accomplished using electron/X-ray curing and suitable electron-curable adhesive systems. The advantages ol using an electron accelerator are faster curing cycles, short turn-around time, and higher-temperature-resistant bonds, cured at ambient temperatures. 

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). 

There are several suppliers of electron accelerators suitable for remote repair of composites, including Varian, Siemans, and Schonberg. At present, the only manufacturer of suitable portable electron accelerators is Schonberg Radiation Corporation of Santa Clara, California. Field repair of damaged aircraft components can be accomplished with a remotely controlled, truck-mounted accelerator. Table 13 gives the characteristics for several electron accelerators, all portable, supplied by Schonberg. Fig. 5 shows a schematic layout of a 10-MeV accelerator... 

X-ray and electron beam characteristics of a typical S-band electron accelerator [401... 

Fig. 7. Portable electron accelerator setup for on-aircraft repair.

The facility costs are based on the concept of a mobile remote repair facility. The advantages of this concept are low-cost, minimal shielding requirements, and flexible use of the overall repair facility. The main components for a remote repair are the electron accelerator, the power supply, and the robotic control system including the remote video system. Table 14 shows the estimated costs for these main components. 

The cost of the vehicle to move the accelerator, and temporary shielding, if needed, have not been included in Table 14. The vehicle houses the control console, video system, and robotic controls. A trailer would carry the main robotic system, the electronic accelerator, magnetron, and the supplies. The cost for such a vehicle and trailer is estimated at 100,000. 

Alternatively, the same coatings can be cured by electrons from an electron accelerator without the use of photoinitiators. Electrons from a 150-600 kV accelerator are energetic enough to create free radicals on impact with the polymer molecules and curing ensues. Clear and pigmented coatings can be cured. Electron accelerators are extremely expensive, but are cheap to run. 

Pulse radiolysis requires access to an electron accelerator or similar device. This requirement usually restricts work to specialized laboratories. Thorough descriptions of the experimental apparatus and protocols have been given.23,24... 

More common in the liquid phase is pulse radiolysis6. In this technique, electron accelerators which can deliver intense pulses of electrons lasting a very short time (ns up to /is) are used. Each single pulse can produce concentrations of intermediates which are high enough to be studied by methods such as light absorption spectroscopy or electrical conductivity. 

Compared to a °Co-7 source, the electron accelerator yields an accurately focusable and constant radiation. The °Co-7 source always creates a diffuse radiation, the energy of which decreases with time according to the half-life of the material [40]. 

Absorbed dose rate This is the absorbed dose per unit time expressed in grays per unit time (kGy/s or kGy/min). Dose rate (Dr) for an electron accelerator [48] can be written in terms of beam current (I) and irradiation field area (A) as follows ... 

Depth of EB penetration The depth of penetration of energetic electrons into a material at normal angle of incidence is directly proportional to the energy of the electrons and inversely proportional to the density of the material [49,50]. The depth is expressed as a product of penetration distance and the density of the material (i.e., 1 g/cm = 1 cm X 1 g/cm ). The radiation energy and thus the type of electron accelerator to be used are dependent on the required penetration depth, the density of the irradiated material, and the chosen irradiation system. If one measures the density (d) in gram per cubic centimeter (g/cm ) and the layer thickness (T) in millimeter (mm), one can determine the radiation energy ( ) necessary for optimal homogeneity from [40] ... 

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