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by: Joe Lovin

Electron beam equipment and technology have matured from a little known technology in the mid 1950's to a mature, reliable process system of choice for many processes today. Not only is the process’ chemistry better understood, E- beam initiated chemistry or sterilization offers a more economical and controllable processing tool. Also, the equipment penetration range and throughput can more readily be tailored to individual applications needs. The equipment is also much improved in reliability and maintainability as a result of maturity in the base equipment design itself as well as the utilization of computer based control systems to manage the system to provide rapid self diagnostics for trouble shooting of system problems even while the system is operational.

Historical Perspective

Commercial exploitation of the radiation for the purpose of sterilization of medical products began in the late 40's and early 50's; whereas, the use of radiation for cross-linking of commercial products was not seriously investigated and exploited until the mid 50's.

Johnson & Johnson is generally recognized as the pioneers of the use of machine generated radiation on a routine basis for sterilization of sutures. In or about the mid 50's both the Cryovac Division of W. R. Grace

and The Raychem Corporation began serious efforts to exploit machine generated radiation for the purpose of cross-linking plastics to obtain improved properties.

These early efforts utilized primitive Cockcroft-Walton, van der Graff generators or resonant transformer type devices. Needless to say control problems, poor machine reliability as well as the lack of machine predictability caused a great deal of grief in the beginning. This resulted in the medical industry’s turning to the more reliable isotope radiation as a source for sterilization, but isotope throughput capability was too slow to be commercially feasible for cross linking so that industry elected to push for improved machine reliability and maintainability to achieve their goals.

Fortunately for the industry the efforts of these early pioneers and others that came later were successful not only in realizing dramatic equipment improvements, but also the understanding and breadth of radiation chemistry has been enhanced.

Equipment Today

Penetration and machine production capacity for a given application tends to be very industry specific. Terminal energy available and type of equipment is generally segregated as follows:

150 kev to 300 kev, single gap, non scanned beams. These units are available in widths from less than one meter to more than three meters. Beam currents can vary from a few milliamperes to more 2000 milliamperes.

Typical applications for this type of equipment are: curing of coatings on such substrates as wood panels, floor coverings, magnetic media, printing inks, etc... This equipment has also been extensively applied to cross- linking small single strand wire as well as to cross-link relatively thin plastic sheeting or plastic laminates or co-extrusions.

This equipment can be procured with oil filled or gas filled power supplies.

All of the systems today are supplied with a PLC based control system with the specific type or manufacturer of the PLC specified by the buyer.

450 kev to 750 kev scanned beam systems are the next general decrement of equipment in use today. This type of equipment is available in widths from approximately 0.5 meters up to approximately 1.8 meters in width. Beam currents are generally available from 25 milliamperes to approximately 250 milliamperes. Typical applications include curing of coating, cross-linking of plastic sheeting and tubing, and polymerization of liquid and semi-liquid emulsions. This range of equipment has been extensively applied in the tire and rubber and plastics industry.

This equipment is typically supplied with gas filled power supplies but has also been supplied with oil-filled power supplies. These units are more often supplied with PLC based controls but have in some recent instances been supplied with P. C. Based control in combination with PLC's.

1 Mev to 4.4 Mev, scanned beam systems are the next general decrement of equipment in use today. This type of equipment is available in widths from 0.5 meters to 1.8 meters in width. These units are characterized by beam power rather than beam current available. Beam powers of these units run from as little as 25 kw to 150 kw. These units have a broad range of application from cross-linking of thicker cross sections of materials to polymer rheology modification and sterilization of medical products in the higher penetration ranges.

The equipment is always supplied with gas filled power supplies and all of the more modern equipment is supplied with PLC based control systems. These systems can be difficult to bring back on line when a power supply has failed or a vacuum failure has occurred. This is due to conditioning time required to reestablish the high voltage and the vacuum system. This is particularly true above 3 Mev. Another recently emerging issue is the cost of gas with sulfur hexafloride gas filled power supplies, especially for the larger power supply vessels. The price of this gas has more than doubled in the last four years and is seeing more and more pressure from state and federal regulatory agencies in a similar manner as Freon 12.


  • 5 Mev to 10 Mev scanned beam linacs offer the highest level of penetration in the machine produced business. Most of these systems are offered in scan widths from 0.5 meters to 1.8 meters and most are pulsed output devices. Even though linacs have been around for a number of years, there have been significant improvements in power output and reliability in approximately the last 5 years. Beam power levels are available from 25 Kw up to 350 Kw, and continuous wave machines are available that operate at significantly lower frequency than previously available S and L band microwave sourced machines. This design feature offers greater power density capability, reduced susceptibly to temperature drift, and in addition the newer design eliminates the need for SF6 gas insulation. More over, the R. F. components are cheaper and more readily available than their microwave counterparts.

This range of penetration is commonly used for medical product

sterilization, cross-linking of thick section products , food disinfestation,

waste water remediation, Polymer rheology modification, gem stone

enhancement, and shelf life extension for food and fruits.

Successful Proven Applications

Cross-linking is by far the most successful application of electron beam technology, due in part to the early intense pioneering effort in this applications arena, plus the obvious economic benefits to be achieved by the use of this technology.

In addition, cross-linking applications tend to be in line operations or high volume batch operations that demand high reliability, controllability, and predictability of all system components.

The usual high volume cross-linking operation is a physically large, multistep, multi-machine operation that is usually manned by not more than one operator and in some cases an assistant. Therefore, all line components must be capable of producing high volumes of product with demonstrable consistent properties 24 hours a day, seven days per week, year round with minimal attention from operating personnel and maintenance personnel.

All these requirements play to the advantage of the modern electron beam, and in particular to the more recently engineered systems that have had intense scrutiny of reliability and are more user friendly.

More sophisticated industrial operations require that production lines be statistically evaluated on start up to demonstrate first, statistical stability and second, that they are in demonstrable statistical control. It is generally the E-Beam component of these types of operations that is the first line component to be qualified as stable and in control. This is a result of many years of intense scrutiny of the system reliability, and more recently, the application of high speed computers to monitor the operation of E-Beam systems.

Cross-linking as a broad category covers the entire range of penetration with beam current requirements (beam power) varying from a few mA to as much as 2000mA. The product categories range from printing inks to floor coverings to thick wire insulation and plastic pipe and tire applications.

The second most successful application of E-Beam technology as measured by volume of use is medical sterilization. E-Beam sterilization of medical products has gained a solid foothold in medical product sterilization as a high throughput, environmentally friendly alternative to gamma and ETO sterilization. It should be emphasized, however, that all of these sterilization technologies have an appropriate niche depending on end use needs and regulatory pressures.

The sleeping giants in the application of radiation technology are food irradiation and pasteurization, decontamination of waste water and sewage sludge. The treatment of contaminated effluent from industrial stack emissions, such as sulfur and nitrogen compounds as well as hydrocarbon contaminated effluent offer tremendous opportunity for remediation through the use of E-Beam technology.

Applications Information

Critical information needed to develop the process specifications for a new application are the process target speed (throughput), dose, depth of penetration into the product required, and finally the dose uniformity needed to insure that the desired product or process parameters are achieved.

Figure 1 and Figure 2 are examples of the energy distribution for a range of different terminal energies. The penetration range in unit density material varies from less than one millimeter at 300kV to slightly over 5 cm at 10 Mev.

Low penetration is generally sufficient for the curing of coatings, printing inks, and the cross-linking of thin plastic sheet or thin wire insulation. The dose uniformity needed to cure coating and inks through the thickness of the product is easily achieved with very low penetration equipment. The dose uniformity across the width of the product will generally vary as much as plus or minus 5% with a typical low energy single gap accelerator. This kind of dose uniformity is very adequate for the end use, however.

As the material thickness and/ or density or both increase, higher penetration equipment is needed to accomplish the desired end results. Radiating the product from both sides may also be necessary to achieve the desire dose uniformity. Figure 3 shows an example of this type of dose distribution when a product has been irradiated from both sides

with a 10 Mev beam. Typically two sided irradiation is used when cross-linking relative thick products that need a reasonably high degree of dose uniformity. It is fairly common to use two sided irradiation for boxed, bulk products that are processed in the medical sterilization business. More than 50 cm of product of a density of 0.15g/cc can be radiated to reasonably uniform dose levels using a 10 Mev beam and double sided irradiation. (see Fig 3)

To achieve the maximum uniformity utilizing two sided irradiation, the product density thickness would need to equal to the density thickness at the 50% point on the depth-dose curve. For single sided irradiation the most uniform dose would be achieved when the product density thickness results in the dose at the beam exit side of the product is equal to the surface dose at the beam entry point.

Dose is proportional to current density and exposure time. Stated in mathematical form Dose = K x (I/A) x T:

Dose(kGy) = K(kGy-kg/mA-min x I(mA)/kg x T(min). K factor is empirically derived by performing dose tests with the particular beam of interest. The K factor is a figure of merit for the performance of the electron system. A more specific form of the dose equation can be written as follows: Dose = K x mA / 1

kg/min Beam


The equation above predicts bulk or mass throughput which is defined as the dose one can expect through the entire bulk of a product being passed under the beam under the conditions stipulated in the equation. If one wishes to predict surface throughput, you simply have to substitute meters per minute for kilograms per minute in the above equation to do so.

Some useful numbers to remember when dealing with dose predictions are: 1 KW of Beam power will process 360 Mega-Rad- kilograms of material or 800 Mega-Rad pounds of material per hour, assuming 100% efficiency.

Figure 4 shows a plot of surface dose K factor or figure of merit for low penetration equipment. Similar curves can be developed for higher penetration equipment, but would typically be written for predicting bulk throughput rather than surface dose.

Recent developments in electron beam technology, particularly in high penetration equipment like the Rhodotron developed by IBA can provide beam power capabilities in demonstrated terminal energies of 5 Mev and

10 Mev in beam power levels to 350 kw. Terminal energies as low as 500 Kev are possible with this type machine but IBA has elected to concentrate on high end equipment to date.

Other advantages to the IBA design are excellent temperature stability of the machine, the elimination of SF-6 gas, and a very robust system design that has resulted in a very high system reliability.

The unique capabilities of radiation processing can be summarized as follows:

  • Contrary to conventional wisdom, radiation treatment is a very environmentally friendly process. Radiation processing provides a unique tool for the remediation of many forms of environmental contamination. Food treated with radiation for shelf life extension or disinfestation of insects has a lower chemical burden than the same products treated by chemical means.
  • Radiation processing, such as cross-linking, can provide unique product properties not achievable by other means. Where there are alternatives to radiation, radiation almost always provides higher processing speeds with superior properties. Electron beam technology, in particular, is capable of high processing speeds.

The costs of switching to radiation technology are: retooling cost and the learning curve for the new technology (training, etc.) Help in accomplishing these hurdles are abundantly available from both equipment suppliers, suppliers of radiation chemistry, and engineering firms that specialize in radiation technology. Users that might want to utilize radiation technology but who prefer not to invest in the purchase and installation of a radiation system can work with companies that specialize in radiation contracting such as Steris, E-Beam Services, and others.

The future of the Industry

The future of the electron beam processing industry seems to be very bright for both commercial applications as well as medical sterilization applications.

Even though cross-linking has been the most successful commercial application to date, it is reasonable to assume that there are many untapped cross-linking application yet to be exploited. Cross-linking has proven to be a path to creating new niche markets as well providing a tool for the development of new products.

In the food industry, the potential has barely been tapped. This has been largely due to misinformation and smear tactics used by anti-radiation activists, even in the face of overwhelming scientific evidence to the contrary. Fortunately the adverse publicity and smear tactics have been largely discredited today. The future of pasteurization and shelf life extension of foods will be developed on a controlled basis and the potential volume is huge. The pay off is a significant improvement in wholeness of food as well as a large reduction in the loss of available food worldwide.

Even though this sterilization of medical products is a proven, accepted use of radiation , the application of electron beams has been more limited than the application of Cobalt due to the limited penetration of e-beam and in many cases power limitations. New higher power beams controlled by modern high speed computers will open new applications for electron beam sterilization.

Another arena that has been proven technically, but not exploited commercially to any significant degree, is the decontamination of waste streams and the remediation of contaminated ground water. There are competing technologies in some of these arenas, but they are quite often more expensive to implement than electron beam technology and seldom as fast as electon beam treatment.

Rheology modification of plastics is another proven successful application of electron beam technology that is not widely known with the possible exception of the degradation of scrap PTFE.

In summary, the future of radiation processing by means of electron – beam technology is very bright . Modern technological improvements in the electron beam systems, as well as greatly expanded understanding of radiation technology offers vast horizons of opportunity for the industry in the near term as well as the long term.