Robust, low-cost micro-linac as a replacement for Ir-192 radiography sources

To improve public security and prevent the diversion of radioactive material for Radiation Dispersion Devices (or so-called dirty bombs) DOE is planning to dramatically reduce the amount of radioactive material in use. Ir-192 is the most common isotope used for radiography and poses a higher risk of being diverted since it must constantly be replenished, and is found in small, portable devices that nevertheless contain dangerous amounts of material. The existing technology of RF linacs based on sophisticated multi-cup copper structures is too complicated and expensive to be compatible with massive replacement.RadiaBeam is developing an inexpensive, energy-tunable, portable linac based on easy-to-manufacture, structure to allow effective capture of tens of keV electron beam injected from an inexpensive electron gun and acceleration to a final energy up to 1 MeV. The structure design significantly simplifies brazing, eliminates time consuming tuning due to the high group velocity in common tube housing. The bremsstrahlung X-rays produced by the ~1 MeV electron beam on a high-Z converter at the end of the linac will match the penetration and dose rate of a typical 200 Ci Ir-192 source.A two-section, hybrid Alumina-Copper, easy-to-fabricate, disk-and-ring-type structure has been designed. The novel design eliminates multi-cell brazing and expensive RF windows as combines them with the couplers. Assembling of the structure is as simple as stuffing of a pipe with the CNC-milled disks and ring. The simulations indicate attaining of a 1.2 MeV energy for a more than 10 mA current with low power ~100 kW X-band magnetron. Seven cells (~1/6th) of the structure have been fabricated at the cost of $180 per cell. Test mockup with the 7 cells driven by a 14 keV electron gun from L3 have been built with novel designs of vacuum port and alternating periodic permanent focusing. Up to 30 mA have been transported through the 7 cells at 50% transmission up to 30 Hz rep rate at better than 0.1 nbar pressure without indications of damage. In Phase II project we are going to design, fabricate and commission the X-ray source based on the novel type structure to match the penetration and dose rate of a typical 200 Ci Ir-192 source. In Phase II we demonstrate suitability of the system for mass production and feasibility of attaining 40 lbs weight of the system.