X-ray Plant Design

The layout of the plant and manufacturing process is designed to fulfill international standards, including the quality management system standard for medical devices ISO 13485, ISO 11137: Sterilization of Healthcare Products – Radiation, cGMP and Food and Drug Administration guidelines.

As X-ray processing utilizes Electron Beam technology, an electron accelerator is a vital component. STERIS AST uses the Rhodotron, a high energy and highly powered machine which operates on the basic principle that electrons gain energy when they cross a region where an axial electric field exists.

The originality of the Rhodotron lies in the fact, that this radial electric field is generated through a single accelerating cavity, which is crossed over several times by the electrons: the Rhodotron is a recirculating accelerator. This feature makes it possible to operate the machine in a continuous mode.

The electrons are generated in a vacuum environment by the source (or electron gun), located at the outer wall of the cavity. The electrons are then drawn away and accelerated by the radial electric field, which transmits energy to them. The electrons undergo a first acceleration toward the inner wall of the cavity. They then pass through openings in the centre conductor.

Since the electric field is reversed when they emerge in the second part of the cavity, they are accelerated a second time, completing a crossing of the diameter. The accelerated beam is then bent by an external magnet, which sends it back into the cavity for a second accelerating cycle. The electron beam therefore travels along a rose‑shaped path, which explains why the name Rhodotron was chosen (“Rhodos”, in Greek, means rose).

At the exit of the accelerator, the cylindrical shaped beam of high‑energy electrons is transported or guided through beam lines from the accelerator to the radiation vault.

Conveyor Design

Conveyance mechanism is required to facilitate moving of pallets in front of X-Ray beam. Pallets are moved through a maze built from re-enforced concrete. The maze prevents X-rays, which move in a straight line, from escaping the radiation room.

The product conveyor system is synchronized with the accelerator, assuring that the beam is only operational when the conveyor system is moving at the defined speed. A production factor is used assuring that the conveyor speed is proportional to the beam power, so even for different power settings of the beam the amount of dose per cycle remains as defined.

All key parameters are continuously monitored for being within the predefined limits.

The design of conveyor system gives a great flexibility as the dose is a function of the increments. Pallets with different increments specification (or dose requirements) can be treated in the same time.

The conveyance mechanism meets the following pallet requirements:

• Pallet weight range: 50 – 1000 kg
• Pallet size: 80×120 (Euro) or 100×120 (industrial)
• Process load height (product + pallet): 195cm