Investigation has been made of the radioluminescence dose response of Ge-doped silica flat and cylindrical fibers subjected to 6 and 10 MV photon beams. The fibers have been custom fabricated, obtaining Ge dopant concentrations of 6 and 10 mol%, subsequently cut into 20 mm lengths. Each sample has been exposed under a set of similar conditions, with use made of a fixed field size and source to surface distance (SSD). Investigation of dosimetric performance has involved radioluminescence linearity, dose-rate dependence, energy dependence, and reproducibility. Mass for mass, the 6 mol% Ge-doped samples provided the greater radioluminescence yield, with both flat and cylindrical fibers responding linearly to the absorbed dose. Further found has been that the cylindrical fibers provided a yield some 38% greater than that of the flat fibers. At 6 MV, the cylindrical fibers were also found to exhibit repeatability variation of <1%, superior to that of the flat fibers, offering strong potential for use in real-time dosimetry applications.
In previous work we investigated the real-time radioluminescence (RL) yield of Ge-doped silica fibres and Al2O3 nanodot media, sensing electron- and x-ray energies and intensities at values familiarly obtained in external beam radiotherapy. The observation of an appreciable low-dose sensitivity has given rise to the realisation that there is strong potential for use of RL dosimetry in diagnostic radiology. Herein use has been made of P-doped silica optical fibre, 2 mm diameter, also including a 271 µm cylindrical doped core. With developing needs for versatile x-ray imaging dosimetry, preliminary investigations have been made covering the range of diagnostic x-ray tube potentials 30 kVp to 120 kVp, demonstrating linearity of RL with kVp as well as in terms of the current-time (mAs) product. RL yields also accord with the inverse-square law. Given typical radiographic-examination exposure durations from tens- to a few hundred milliseconds, particular value is found in the ability to record the influence of x-ray generator performance on the growth and decay of beam intensity, from initiation to termination.
Review is provided of a number of low-dose, low dose rate situations that in study require advances in the development of dosimetric facilities. Using a clinical linac set up to provide doses down to the few mGy level, the performance of a real-time radioluminescence system has then been illustrated, accommodating pulsed as well as continuous dose delivery. The system gate times provide for tracking of the pattern of dose delivery, allowing detailed account of dose and dose-rate variations. The system has been tested in both x-ray and electron mode dose delivery.
We have developed a radioluminescence-based survey meter for use in industries in which there is involvement in naturally occurring radioactive material (NORM), also in support of those needing to detect other weak emitters of radiation. The functionality of the system confronts particular shortcomings of the handheld survey meters that are currently being made use of. The device couples a LYSO:Ce scintillator with a photodetector via a polymer optical fibre waveguide, allowing for "intrinsically safe" inspection within pipework, separators, valves and other such component pieces. The small-diameter optical fibre probe is electrically passive, immune to electromagnetic interference, and chemically inert. The readout circuit is entirely incorporated within a handheld casing housing a silicon photomultiplier (SiPM) detection circuit and a microprocessor circuit connected to an LCD display. A 15 m long flexible PMMA optical fibre waveguide is butt coupled to an ABS plastic probe that retains the LYSO:Ce scintillator. Initial tests have included the use of lab-based mixed gamma-ray sources, measurements being made in concert with a reference conventional GM survey-meter. Characterization, via NORM sources at a decontamination facility, has shown useful sensitivity, covering the dose-rate range 0.10- to 28 µSv h-1 (R-squared 0.966), extending to 80 µSv/h as demonstrated in use of a Cs-137 source. The system is shown to provide an effective tool for detection of radioactivity within hard to access locations, in particular for sources emitting at low radiation levels, down to values that approach background.