The science of sterilization has come a long way in the last century, with multiple evolved methods still in use today. However, electron beam (E-Beam) processing has emerged as one of the most efficient and effective methods. Here, we take a closer look at the technology behind this sterilization method.
Using a high-energy electron beam accelerator (also known as a linear accelerator or linac for short), the velocity of ions or subatomic particles is increased by using a sequence of oscillating electric field potentials along a linear beamline. In doing so, electron emission takes place, when electrons are accelerated via a high voltage emitter, and then ejected from the surface.
The negatively charged electrons are targeted using either a heated tantalum or tungsten filament, and guided by a high voltage source inside the chamber of the vacuum. When the electron beam accelerator is on, the energized electrons maintain a strong vacuum by passing through a thin metal foil that allows for electron transmission.
Regardless of proprietary technologies and designs, every linear accelerator has the same basic features: a source of electrons, an evacuated accelerating chamber, and a method of extraction and distribution of particles. The majority of linacs have a filament source, called an electron gun, which produces the necessary heat to achieve sterilization by electron beam processing.
By passing heated electrons through a vacuum with an applied electric field, electrons are energized.
In many cases, direct current (DC) accelerators are used to establish the electric field.
• E-Beam is most effective on materials no more than 3 cm thick.
• The lower the density, the higher the penetration.
The advantage of using DC is that it maintains continuous accelerating voltage between electrodes. However, once the voltage increases to a magnitude of millions, a problem arises: electrical insulation. Enter the next generation of linacs.
The newer particle accelerators solve the issue of electrical insulation by using radio frequency (RF) to generate power. Utilizing high-frequency electromagnetic radio waves, powerful electrical and magnetic fields are created. The RF field is set to oscillate, or change direction, at the appropriate frequency in which charged particles are injected. The RF fields energize the particles without the need to develop the final potential at a specific instant. The immediate benefit is that RF particle accelerators do not need the extreme electrical insulation that DC units do. And an added bonus: The RF accelerators are typically smaller in stature, and therefore, more user-friendly.
Once the energized electrons are freed from the surface, they mix with air molecules and disperse, and create atmospheric-pressure plasma. This process distributes energy to a product’s surface. Typically, E-Beam is considered a cold sterilization process, though it can be used in high temperature and/or nitrogen-heavy environments.
Another advantage of using the electron beam sterilization process is the ability to penetrate through thin packaging. As each electron collides with the packaging, a secondary electron develops under the surface, creating a shower effect. The peak dose of radiation remains just below the surface.
Energy is absorbed by the surface proportionally to the strength of the E-Beam and the rate that the product goes through the treatment area. For optimum sterilization, it’s important to determine the proper dose to be applied. A conveyor system keeps products moving through the irradiation area at a predetermined speed, depending on the density, weight and overall dimension of the product being treated.
For electron beam processing, the required energy level is usually between 3 MeV and 12 MeV (million electron volts), operating at a single energy level. Additional guidelines include:
• >3 MeV for surface treatment or thin film irradiation.
• 5-10 MeV for thicker products like corrugated shippers loaded with pre-packaged products.
• 10 MeV will penetrate approximately 3-5 cm of product.
• 10 MeV is typically the limit for drug sterilization. This is because higher levels can create short half-life radionuclides, and therefore damage the product.
• Penetration in water is at a depth of approximately 3mm for every MeV of accelerating potential.
• E-beam is most effective on materials no more than 3 cm thick.
• The lower the density, the higher the penetration.
A key measurement of proper E-Beam usage is the irradiation dose, or amount of electron energy that is absorbed. A dose of 1 Kilogray (kGy) equals 1 joule of radiation energy per kilogram of material sterilized. For a practical example, to sterilize drugs, a dose of roughly 25 kGy is necessary.
MediZap is an industry leader in sterilization that can help develop custom protocols for proper processes to meet or exceed sterilization standards. Our linac equipment features a unique 2x 10 MeV configuration that guarantees a 99.9% uptime.