Marshall R. Cleland

Accelerator requirements for electron beam processing

Abstract This paper discusses the physical aspects of electron beam processing and presents practical methods for estimating the required specifications of the electron accelerator. The accelerator voltage (electron energy) is determined by the thickness and density of the irradiated material. The electron beam current is calculated from the area thruput rate and the surface dose. The electron beam power is calculated from the mass thruput rate and the average dose. Useful formulas, data tables and graphs showing these relationship are presented for electron energies between 0.30 and 10.0 MeV. The influence of the atomic composition of the irradiated material is also considered. To illustrate the utility of these procedures, the beam power, mass thruput formula is applied to the irradiation of bulk materials and thin plastic film. The beam current, area thruput relationship is applied to the treatment of cable, pipe, wire and tubing. These examples show how the accelerator requirements for typical electron beam processes can be predicted.

X-ray treatment at 5 MeV and above

Abstract There is agreement in the scientific community that X-ray treatment of food at 7.5 MeV can be safe. Possible process improvements for treating at higher than 5 MeV X-rays have been re-visited. Monte Carlo methods have been applied to simulate the X-ray conversion process and to calculate dose distributions in homogeneous phantoms. Experimental data obtained using X-rays produced with a Rhodotron TT200 at 5 and 10 MeV verifies a representative set of data which is calculated with the presented method. With this qualified Monte Carlo tool, calculations at 7.5 MeV incident electron energy were performed. The analysis gives special attention to higher photon yield, improved product penetration, as well as surface and edge effects.

Medium and high-energy electron beam radiation processing equipment for commercial applications

Abstract Electron beam processing of materials was introduced during the 1950s, and this technology has been continually evolving since then. A variety of industrial electron accelerators can now provide electron energies from 0.3 MeV to more than 10 MeV with average beam power capabilities up to 300 kW. The most important types are described briefly in this paper. Several types of material handling systems are used to present products to the electron beam. The objectives are to utilize the beam power efficiently and to obtain acceptable dose uniformity. The main methods for material handling are described. Simplified equations are provided for relating the electron energy and beam power ratings to the material thickness, area throughput and mass throughput rates. The basic requirements for personnel safety are also reviewed.

Industrial applications of electron accelerators

This paper addresses the industrial applications of electron accelerators for modifying the physical, chemical or biological properties of materials and commercial products by treatment with ionizing radiation. Many beneficial effects can be obtained with these methods, which are known as radiation processing. The earliest practical applications occurred during the 1950s, and the business of radiation processing has been expanding since that time. The most prevalent applications are the modification of many different plastic and rubber products and the sterilization of single-use medical devices. Emerging applications are the pasteurization and preservation of foods and the treatment of toxic industrial wastes. Industrial accelerators can now provide electron energies greater than 10 MeV and average beam powers as high as 700 kW. The availability of high-energy, high-power electron beams is stimulating interest in the use of X-rays (bremsstrahlung) as an alternative to gamma rays from radioactive nuclides.

Radiation pretreatments for optimizing the sugar yield in the acid hydrolysis of waste cellulose

Abstract Cellulosic wastes are now recognized as an underutilized renewable resource for both materials and energy recovery rather than a solid waste disposal problem. Acid hydrolysis offers a potentially attractive route for upgrading the value of cellulosic wastes by converting them to glucose. The glucose can then be used as an alternate feedstock to petrochemicals for fuels, intermediates and the synthesis of single cell protein. A key step in this developing technology is a cost effective cellulose waste pretreatment for optimizing the sugar yield. Various experimental approaches for achieving this objective are described. A combination waste cellulose waste feedstock followed by a short time dilute sulfuric acid hydrolysis has been found to be particularly effective. Data are also given on the employment of various organic acids in place of sulfuric acid for the hydrolysis reaction.

The use of dose and charge distributions in electron beam processing

Absorbed dose distributions in products treated with energetic electrons are influenced by the electron energy, the atomic composition of the material. the size and shape of the product and its orientation to the electron beam. Dose distributions can be measured by placing small dosimeters at various positions within some products, but more detailed data can be calculated with Monte Carlo codes that are readily available. For high-dose treatment processes, the magnitude and internal distribution of electrostatic charges may be significant. The accumulation of high charges could cause discharges through some materials, which could damage the products. This effect can be avoided by using electrons with sufficiently high energy, so that most of them will pass through the material. Charge distributions are difficult to measure, but they can be calculated with the Monte Carlo method. Dose and charge distributions with a wide range of electron energies in typical materials are presented in this paper. These have been obtained with the Integrated Tiger Series of Coupled Electron/Photon Monte Carlo Transport Codes (ITS). The data illustrate the effects of electron energy and material composition. These quantitative results will enable users to determine the electron energy beam current and beam power requirements for a variety of electron beam treatment processes

X-ray processing a review of the status and prospects

Abstract After many years of investigation, X-ray (bremsstrahlung) processing of products and materials has recently been implemented. Several accelerator manufacturers have developed high-power equipment suitable for this purpose and several electron beam processing facilities can now provide X-ray treatment as well. Guidelines on the proper use of this new technology are being prepared by ASTM and ISO. The penetrating quality and forward concentration of high-energy X-rays are advantageoous for some applications. Information on absorbed dose distributions, processing rates and costs are given in the paper.

Radiological safety of medical devices sterilized with X-rays at 7.5 MeV

The induced radioactivity in medical devices when sterilized with 7.5 MeV X-rays has been investigated theoretically and verified by dedicated experiments. The experimental setup has been chosen to simulate closely the situation in a commercial irradiation facility. The purpose of this study is twofold: compare activation of medical devices with regulatory limits and evaluate corresponding dose exposure of persons in contact with those devices. Samples of medical devices, classified in several test groups, were, located in a stack of low-density material at the position of the highest photoneutron fluence and irradiated to X-ray doses between 25 and 30 kGy. The induced activities were measured with high purity germanium (HPGe) gamma ray spectrometers. The X-rays were generated, in a tantalum target using a 7.3 MeV electron beam with a narrow energy spread during the first experiment and with a broad energy spectrum for a second one. Results have been scaled to 50 kGy and compared with theoretical estimates. In addition, the radiation exposure of four categories of persons (logistics personnel in the irradiation facility, truck drivers, doctors and patients) has been calculated from the measured activities. The measured activities are higher than theoretical expectations but still below governmental regulations. The annual dose received by the person category with the highest exposure is about 1% of the worldwide average environmental exposure, and for other categories it is negligible. The paper concludes that provided some precautions are considered, sterilization with X-rays from 7.5 MeV electrons can be regarded safe from the standpoint of public health and personal safety

The Palletron: A High Dose Uniformity Pallet Irradiator With X-Rays

A new concept of X‐ray irradiator for high‐density products on pallets is proposed. Monte Carlo simulations are applied to predict the performance of this system and compare it to alternative pallet irradiators. The Monte Carlo predictions are in good agreement with experimental data obtained using pallets of different densities.

Treatment of foods with high-energy X rays

The treatment of foods with ionizing energy in the form of gamma rays, accelerated electrons and X rays can produce beneficial effects, such as inhibiting the sprouting in potatoes, onions and garlic, controlling insects in fruits, vegetables and grains, inhibiting the growth of fungi, pasteurizing fresh meat. poultry and seafood and sterilizing spices and food additives. After many years of research, these processes have been approved by regulatory authorities in many countries and commercial applications have been increasing. High-energy X rays are especially useful for treating large packages of food. The most attractive features are product penetration, absorbed dose uniformity, high utilization efficiency and short processing time. The ability to energize the X-ray source only when needed enhances the safety and convenience of this technique. The availability of high-energy, high-power electron accelerators, which can be used as X-ray generators, makes it feasible to process large quantities of food economically. Several industrial accelerator facilities already have X-ray conversion equipment and several more will soon be built with product conveying systems designed to take advantage of the unique characteristics of high-energy X rays. These concepts are reviewed briefly in the paper.