Modular Addressable Research Irradiators using Flat Panel X-ray Sources
- Stellarray, Inc., Austin, TX (United States)
This SBIR fast-track project developed and qualified novel flat panel x-ray sources (FPXS) and designed research irradiator systems based on them to replace the Cs-137 isotope irradiators still used in a wide range of radiobiology and radiochemistry research, e.g. cellular or small animal studies of radiotherapy. Three irradiators were designed based on a detailed analysis of why Cs-137 is still preferred by the research community for certain applications. The high power research irradiator (HP-RI) was designed for high dose rate studies, especially those concerned with DNA repair, which is modulated or prevented by sustained high radiation doses. The high voltage irradiator (HV-RI) is for high-energy radiation studies, to approximate the energies of isotope sources and provide more uniform doses. In the digitally addressable irradiator (DA-RI), individual x-ray flux columns irradiate the contents of individual wells in the micro-well plates ubiquitous in biology and biochemistry research, for a massive increase in research throughput. Each irradiator requires a different FPXS design, i.e. HP-XS, HV-XS and DA-XS. Most project work was on the sources, since they are the main innovation, the core of the irradiators and the biggest challenge. Three types of modeling informed panel and system design. The first, using COMSOL for panel electrostatics, showed how design changes could reduce arcing incidence at high voltages, which was a major factor in getting the HP-XS anode voltage above its target of 160kV. Geometric models were made for DA-XS that showed how to avoid cross-talk between the wells in the micro-well plate. The third type of modeling used Stellarray’s XssT Monte-Carlo tool to estimate x-ray flux dose rates and uniformity given by panel operating parameters and system designs. This led to designs for the three systems with dose rates and uniformity exceeding the best performance of Cs-137 irradiators. Considerable work was done on panel fabrication process development and testing as the designs were improved. A number of HP-XS and HP-XS, using filament cathode arrays, were designed, built and tested. Over 240 separate process steps were required for each panel and separate process development experiments were conducted for a number of these steps. Ion back bombardment of the filaments caused the first panels to be short-lived. This problem was resolved by the use of shielding strips under the filaments. HP-XS panels were tested to the target 160 kV and to over 20 mA at lower voltages. In HV-XS, it was not possible to get beyond 177 kV and reach the first target level of 225 kV due primarily to external arcing on the panels. This source was redesigned for better arc mitigation. The DA-XS panels have a fundamentally different architecture and required the development of annular cold cathode arrays to supply the separate electron beams for the 96 “x-ray pixels” (xels) used to illuminate the separate wells. Several cold cathodes were designed and tested. The one chosen uses a multi-layer, “triple point” film deposited on Mo strips and emitting from the edges of holes in the strip. A matrix-addressing extraction gate structure is formed on ceramic plates that sandwich the Mo strips. The cathodes were tested to well beyond their 2 mA target. Processes were developed for alignment of the resulting emitter structure and the 96 window openings at panel flux exit end. The first panel was completed. All three irradiators were designed to have the high voltage amplifiers (HVA) connected directly to the broad anode plate of the source so as to reduce cabling, enhance safety and make the irradiators very compact in comparison to Cs-137 and x-ray tube models. The HV amplifiers and controls were designed for all three and bread-boarded for HP-RI and DA-RI. Electrical insulation/thermal transfer solutions were developed for the grounded casing enclosing the panels and integrated HVA. The casing will also hold a voltage measurement circuit and an anode current measurement to provide precise control of x-ray flux. Modeling results for dose rate and uniformity were used in the design of all three irradiators. HP-RI requires four HP-XS, each operating to 160 kV and over 20 mA, to exceed the dose and uniformity performance of the best available Cs-137 irradiator. HV-RI will require two panels and much more insulation. DA-RI was designed as a compact, desktop model to deliver up to 2 mA per xel at 100 kV, providing up to 10m Gy/min/well, well beyond research needs for cell and other radiobiology studies.
- Research Organization:
- Stellarray, Inc., Austin, TX (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- SC0013867
- OSTI ID:
- 1474298
- Type / Phase:
- SBIR (Phase IIA)
- Report Number(s):
- DOE-SRAY-SC0013867
- Country of Publication:
- United States
- Language:
- English
Similar Records
Sterile Insect X-ray Irradiator, Phase II Final Report
Response of LiF:Mg,Ti thermoluminescent dosimeters at photon energies relevant to the dosimetry of brachytherapy (<1 MeV)