Dual method of measurement of ionizing radiation doses in real time based on high sensitive luminescence crystals

The aim of the project entitled “Dual method of measuring doses of ionizing radiation in real-time based on highly sensitive luminescent crystals” was to develop a method of remote dose measurement in real-time using the phenomena of radioluminescence (RL) and optically stimulated luminescence (OSL) based on new highly sensitive luminescent crystals whose properties were optimized during the work progress by changing the doping and manufacturing conditions.

The project was implemented in two thematic areas. The first research path concerned the selection of the type of phosphor that could be used as a detector in the measurements. The next step was to optimize its luminescent properties by doping with various rare earth salts elements to obtain a phosphor with high sensitivity to ionizing radiation, both in terms of radioluminescence and optically stimulated luminescence, fast saturation time, and good signal repeatability. A photo of a terbium-doped lithium magnesium phosphate (LiMgPO4: Tb) crystal obtained by the micro-pull down method (PMD) is shown in the figure below on the right. The photo also shows a slice of phosphor crystal, which is the detector used in further measurements.

The second research path concerned the design of a measuring device for recording the radioluminescence signal in real-time during phosphor irradiation and measuring the optically stimulated luminescence signal immediately after the end of radiation exposure for the selected phosphor, i.e. for dual dose rate and dose measurement using one device with one detector. Based on the obtained initial measurement results, a small-sized measuring instrument was constructed for remote testing of RL and OSL signals, spectrally adjusted to measurements with the LiMgPO4 detector (photo on the left side of the figure). The measuring instrument was named PORTOS (portable RL / OSL). It consists of the following elements: an LMP detector with a diameter of 3 mm and a thickness of 1 mm placed at the end of a 15-meter quartz fiber, which, through a series of optical components with color filters, is connected to a Hamamatsu photomultiplier tube (type H10682-210). The system also uses a dichroic mirror to direct the laser beam onto the sample while blocking the laser wavelength in the light entering the photomultiplier tube.

Photo of the PORTOS measuring device and the crystal used as a detector

The PORTOS measuring device has been tested in a wide range of dose rates in the gamma radiation field, both on the Cs-137 source and on the Theratron E780 therapeutic device with the Co-60 source, and the proton beam generated by the AIC-144 cyclotron at the IFJ PAN. The use of the PORTOS measuring device for measuring the temporal structure of a proton beam turned out to be particularly interesting. Due to the very fast response time of the detector and the possibility of using a short sampling time (microseconds), it was possible to record the temporal structure with the isolation of individual pulses of a proton beam with an energy of 60 MeV.


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