Development of a Novel Laser Heated Thermoluminescent Dosimeter (LHTLD) for Dosimetry Measurements, in Situ and in Real Time

Thermoluminescence dosimetry (TLD) is a standard method for determining the radiation dose in different environments. This method involves irradiating Lithium Fluoride (LiF) crystals doped with different materials, then heating the crystals in a linear fashion with hot nitrogen, thereby inducing the irradiated crystals to emit visible radiation. The graph of the intensity as a function of temperature is called Glow Curve and the area underneath it is proportional to the dose. This may therefore be used for accurate dosimetry.

To circumvent the challenges inherent to the traditional method we propose a new idea for readout of the LiF crystal, based on lasers and optical fibers. After such a LiF crystal has been exposed to some dose, a laser beam transmitted through a suitable optical fiber heats the LiF crystal. The heated crystal then emits black-body infrared radiation that is transmitted by another fiber to an infrared detector, and the voltage generated by this detector is used to determine the temperature. A computer uses this voltage to control the laser heating so that the heating is linear. The heated crystal also emits visible radiation that is transmitted to a visible detector. The output of this detector as a function of temperature is again a Glow-Curve, the area under which could be used for dosimetry. This Laser Heated TLD (LHTLD) is based on lasers and optical fibers which make it more flexible useful in many applications. Several prototypes of this idea were operated successfully by us. Results of measurements with these methods will be presented.

Our goal in this work is to develop a small, portable, inexpensive and easy-to-use laser-heated and thermally-controlled TLD system. This system should make it possible to process such crystals in a remote location and in real-time without removing them from the measured environment. The LHTLD system would be useful for the nuclear industry and for environmental protection, where human-accessibility constraints prevent wide application of this standardized method of radiation dosimetry. In medicine, it will measure in real time the dose to which cardiologists are exposed during catheterization, or the dose to which patients undergoing CT are exposed to. This will prevent over-exposure, due to human error or a wrong calibration. It is expected that the new LHTLD system will revolutionize many areas of dosimetry.