by
Lisa Chamoff, Contributing Reporter | November 12, 2014
From the September 2014 issue of HealthCare Business News magazine
Depending on the type of part being outgassed and/or brazed, temperatures can range from 475 to 1,800 degrees Celsius. This outgassing and brazing, or high-temperature soldering, which on average takes about six hours, creates a complete and airtight envelope for X-rays to be produced.
Next comes the plasma coating to create surfaces that either absorb or reflect the incredible amount of heat that builds up in the tubes — a target can get as hot as a 2,700 degrees centigrade. The tube produces 99 percent heat and 1 percent X-rays, Jonaitis says. Much of the technology and design of the tubes is for heat management. Cleaning, while it sounds simple, is an important step, and requires an investment in ultrasonic waterand solvent-based cleaning systems, which can be as tall as 15 feet.
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Cleaning helps to prevent arcing, which occurs when there is a short circuit within the tube, usually caused by residual gas or an improper electrical path, and stops the X-ray output — not something you want to happen mid-scan. Warming up your tube before use can also prevent arcing.
Tube outgassing
Photo courtesy of Dunlee
After degassing and cleaning, the parts, which can absorb gases from the atmosphere, must be stored in cabinets filled with nitrogen which boils away from liquid air at a lower temperature than oxygen, to prevent reabsorption. Varian partnered with their supplier to build a 100-foot by 100-foot on-site nitrogen plant, Dunlee buys large quantities of liquid nitrogen, and then lets it evaporate and collects the gas, creating ultra-pure nitrogen used during many of the operation steps.
Clean room
Photo courtesy of Dunlee
2. Assembly
The two major parts of the X-ray tube — the negatively charged cathode, which contains the filament wire, usually made of tungsten, that generates the electrons used to produce X-rays, and the positively charged anode, which contains the target that the electrons collide into — are assembled in a clean, HEPA-filtered space similar to a sterile operating room, where workers don gowns, gloves, and headcovers. There must be a strong connection between the target and its stem, otherwise the anode assembly can become unbalanced and the tube will not function correctly.
