Technology

External beam radiotherapy (RT), nuclear physics (NP), high energy physics (HEP), and a number of industrial/commercial applications all have a need for next-generation radiation detectors for ionizing particles and photons. In particular, both FLASH-RT and NP require improved particle and photon beam monitors with faster response time, wider dynamic range, higher particle/beam transmissivity, better spatial resolution and higher radiation damage resistance among other desired improvements. For the U.S. Department of Energy (DOE-NP) and the National Cancer Institute (NIH-NCI), the need for next-generation radiation beam monitors is compelling, especially for FLASH-RT where large-area ionization chambers cannot respond fast enough (with 2D high-resolution beam images) and therefore the UFT beam monitor would be an enabling technology. At DOE national laboratories such as the Facility for Rare Isotope Beams (FRIB), the UFT beam monitor can provide beam tuning capability not possible with conventional beam monitoring technology.

The UFT (ultra-fast transmissive) beam detector technology invented by Integrated Sensors (I-S) for real-time beam monitoring[1] constitutes an extremely versatile detection system that can monitor any type of ionizing radiation, from single particles to high intensity beams, in air or in vacuum. Results show order-of-magnitude advantages over ionization chambers for position resolution, readout time and beam hardening. UFT-beam monitors are also being developed for precision position (≤ 0.01 mm) and time-of-flight (≤ 50 ps) measurements in heavy-ion and rare isotope or exotic particle beam accelerators from Be-7 (+4 charge) to U-238 (+92 charge) nuclei. The largest potential market is for FLASH-RT for particle and photon beam monitoring and patient quality assurance. All UFT beam monitors include an internal self-calibration system that can automatically perform a complete self-calibration in vivo, in approximately 1 minute or less, as frequently as desired.

For both particle and photon therapy, the UFT beam monitors provide exceptional performance for tracking beam position and movement, intensity profile, fluence/external dosimetry, and angular divergence, all in real-time. Real-time high-resolution images at 10 µs to 1 ms have been demonstrated. Radiation damage testing downstream from the nozzle or multileaf collimator has demonstrated that UFT beam monitors can last several years without significant radiation damage in a typical FLASH-RT radiation environment.

The plasma panel sensor (PPS) invented by I-S is a novel micropattern detector inspired by many operational and fabrication principles common to plasma display panels used in television displays. It is comprised of an array of small pixels, either open-cell or closed-cell, each independently capable of detecting free-electrons or ions generated within the cell by incident ionizing radiation, and can operate either with high gain in the Geiger discharge mode, or with lower gain but faster response in the avalanche mode.[2] Both structures and modes of operation provide high granularity and position resolution, are physically robust, intrinsically radiation-hard and hermetically-sealed. PPS detectors are being developed primarily for high-resolution particle beam tracking and imaging. Closed-cell microcavity-PPS devices have demonstrated high efficiencies of 95-100% over a 100 volt plateau, < 1 ns time resolution, submillimeter spatial resolution capability, and high S/N ratios in excess of 1000:1. They are thin, lightweight, size scalable and inexpensive. They have also demonstrated high rate capability and high stability, operating continuously (i.e., 24/7) at rates of 350 kHz/cm² for 6 days with a stability over this period of better than 1%. We have not established an upper rate limit before saturation, but suspect that we should be able to achieve rates on the order of ≥ 1 MHz/cm².

Our most recent microcavity-PPS innovation, jointly developed with the University of Michigan (UM), is the microhexcavity plasma panel (µCPP) tracking detector [1], which was originally motivated towards high energy physics (HEP) applications. However, its low cost, scalability, precision and portability lends it to applications in a wider spectrum of research fields, nuclear medicine, industry, archaeology, homeland security and education. The µCPP tracking detector also lends itself to being configured as a low cost camera, capable of detecting radioactive material remotely, for example at a nuclear spill site. Unlike virtually any other type of gaseous detector, i.e. drift tube chambers, Micromegas, resistive plate chambers (RPCs), thin gap chambers (TGCs), etc., the PPS and µCPP requires no expensive and maintenance-intensive gas system for its operation.

[1] Patents pending.

[2] A. Mulski et al., “Operation and Performance of Microhexcavity Pixel Detector in Gas Discharge and Avalanche Mode,” Nucl. Instrum. Meth., vol. A954 (2020), February 1, 2020 (https://doi.org/10.1016/j.nima.2018.09.066).