Self‐powered nano‐porous aerogel x‐ray sensor employing fast electron current

Abstract

Purpose We developed a new class of aerogel‐based thin‐film self‐powered radiation sensors employing high‐energy electron current (HEC) in periodic multilayer (high‐Z | polyimide aerogel (PA) | low‐Z) electrode microstructures. Materials Low‐Z (Al) and high‐Z (Ta) electrodes were deposited on 50 μm‐thick PA films to obtain sensors with Al‐PA‐Ta‐PA‐Al structures. Sensors were tested with x rays in the 40–120 kVp range and with 2.5 MV, 6 MV, and 6 MV‐FFF linac beams (TrueBeam, Varian). Performance of PA‐HEC sensors was compared to commercial A12 Farmer ionization chamber as well as to radiation transport simulations using CEPXS/ONEDANT with nanometer‐to‐micrometer spatial resolution. The computations included periodic and single‐element structures N x (Al‐PA‐Ta‐PA‐Al) with variable layer thicknesses. Results Signal from PA‐HEC sensors was proportional to the simulated net leakage electron current (averaged over the PA thickness). Experimental response was linear with dose and independent of dose rate. Detector responses to different x‐ray sources show higher signals for kVp photon energies, as expected, though a strong signal was obtained for MV energies as well. The signal scaled with total effective area inside the multielemental structures; for example, the yield of a multielement sensor made with 20 Ta layers compared to a single‐element structure with 1 Ta layer of the same total thickness of Ta was 10 times greater for 6 MV beam and 23 times greater for 120 kVp. Beam attenuation per element in the detector was 0.5%, 1%, 3%, and 46%, respectively for 6 MV, 6 MV FFF, 2.5 MV, and 120 kVp. Conclusion We demonstrated the feasibility of aerogel‐based multilayer HEC radiation detector and its application for flux/dose monitoring of kVp and radiotherapy MV beams with small beam attenuation.

Self‐powered multilayer radioisotope identification device

“…Furthermore, the sensor has been shown to work in high-dose rate environments. 8,9 Therefore, it could become an important auxiliary RIID to identify sources in the conditions other instrumentation fail or is difficult to use.…”

“…The simple and reproducible physics of the radiation interaction with this detector and the ease of signal collection suggest that this device may not require recalibration. Furthermore, the sensor has been shown to work in high‐dose rate environments 8,9 . Therefore, it could become an important auxiliary RIID to identify sources in the conditions other instrumentation fail or is difficult to use.…”

“…Using the computed fast electron current in the detector we calculated the spatial average of the net current in the aerogel. As detailed elsewhere, 8,9 the signal measured by each electrode is determined based on electrodynamic equations 16 and it is the difference between the downstream and the upstream spatially averaged currents in the aerogel layers neighboring the electrode.…”

“…[7][8][9][10][11] An important difference between existing commercial RIIDs and our device is that we use a low-cost and simple multilayer detector structure, which leads to a rugged device with simple operation. 8,9 Instead of photon counting and energy discrimination, which requires pulse height analysis, we measure fast electron current profiles across the multilayer electrode structure from which we derive spectral information. It is noteworthy that the fast electron current as a function of depth in the multilayer detector structure is different in shape, magnitude and meaning from dose as function depth in a heterogeneous medium.…”

“…In this paper, we explore a new RIID device employing a multilayer aerogel‐based HEC detector. The operation principle and the experimental demonstration of self‐powered nanoporous aerogel High Energy Current (HEC) detectors is detailed elsewhere 7–11 …”