Revolutionary X-ray Tube Design

The 4 pi Emitter Series

The standard design for an X-ray tube has varied very little from the originals built by Roentgen in 1895. A beam of electrons was focused on a small target and cooling was applied to the back of the target. While this technology has worked well for applications such as medical imaging, which require minimizing radiation for safety purposes, it performs poorly in irradiation applications. The two primary reasons why X-rays have not been used for high radiation level applications are tube geometry and the inability to remove the heat generated during continuous operation.

In conventional X-ray tubes, the target emits a 4 pi field of photons at normal kVp levels (160 kVp). However, this field is limited by the tube geometry which only allows less than 18% of the photons generated to be used. The balance of the photons is absorbed into the shielding. In addition to the shielding that lowers the efficiency of the photon production, the X-ray spectrum itself must be filtered to achieve dose uniformity. To compensate for these two inefficiencies, the amount of current that generates the photons can be increased. Unfortunately, as the current is increased, so is the heat that is generated in the tube. The high current concentrated on a small target area (typically 1-3 kilowatts per square millimeter) is such that conventional X-ray tubes typically result in short tube life.

New patented technology has mitigated these shortcomings. Rad Source’s 4 pi emitter series uses entirely different geometry. A large cylindrical target reduces the heat resulting from the high current by vastly increasing the target area and thereby the power per unit area by a factor 4X10^5 (figure 1).

The same cylindrical target shape allows forward emitted electrons to go directly to the field and rearward projected photons to pass through the cylinder and contribute to the dose on the opposite side (figure 2). This results in a 4 pi field around the tube that utilizes 100% of the photon production as opposed to the less than 20% usage netted by conventional design.

In addition, the significantly reduced heat per unit area allows the use of a more efficient emission target. In conventional tubes a tungsten target is used because of its heat resistance. In this new design, the use of gold provides about a 10-15% increase in production efficiency and an even higher increase in average energy. This results in an X-ray emitter with about 20 times the dose per unit power of the conventional tube design.

The final improvement to the X-ray tube design is the ability to repair the tube. With any filament driven device, the filament will be consumed over time. The ability to replace the filament increases usable tube life many thousands of hours and reduces overall costs for irradiation. Currently the tubes are produced commercially up to 160 kVp. The International Atomic Energy Commission has evaluated equipment configured with Rad Source 4 pi emitter technology for Sterile Insect Technique (SIT) use and has designated it as an alternative to cobalt for SIT programs (IAEA, 2009). Other equipment incorporating this technology is being used by BSL-4 labs to achieve viral inactivation, providing dose rates up to 1 Megarad per hour. This is because the technology is scalable such that higher power, either as current or energy, can be increased with some design accommodation to meet customer’s needs. This technology is especially timely considering the nation’s current concerns regarding the potential use of radioactive materials for malevolent acts (U.S. Nuclear Regulatory Commission, 2006). To protect against such acts, many precautions have been taken and will be taken. Among these are tighter source restrictions, increased security requirements, and reduced disposal options, all of which has increased the cost of owning and using radioactive sources. Rad Source, anticipating these issues, has created alternatives to replace most self-shielded radioactive sources. To learn more about these alternatives please visit us at www.radsource.com or call us at 770-887-8669. About Rad Source Technologies Rad Source Technologies is currently the only company in the world supplying a comprehensive line of commercial X-ray radiation products designed to replace self-shielded gamma sources. The company’s current products are used for the irradiation of small animals, cells, sterile insect technique (SIT) applications, viral inactivation, and various other scientific applications.

###

IAEA. Joint FAO/IAEA Programme Nuclear Techniques in Food and Agriculture. Irradiation. Insect Pest Control Newsletter 72: 20; 2009. U.S. Nuclear Regulatory Commission. The Radiation Source Protection and Security Task Force Report. Report to the President and the U.S. Congress Under Public Law 109-58, The Energy Policy Act of 2005 vii; 2006.