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Fibre-Optic Dosimeters

#3092


Development of Fibre-Optic Dosimeters for Civil Nuclear Industry, Environmental Monitoring, and Medicine

Tech Area / Field

  • INS-DET/Detection Devices/Instrumentation
  • BIO-RAD/Radiobiology/Biotechnology
  • MED-RAD/Radiomedicine/Medicine
  • PHY-OPL/Optics and Lasers/Physics

Status
3 Approved without Funding

Registration date
10.08.2004

Leading Institute
Institute of General Physics named after A.M. Prokhorov RAS / Fiber Optical Research Center, Russia, Moscow

Supporting institutes

  • VNIITF, Russia, Chelyabinsk reg., Snezhinsk\nCancer Research Center, Russia, Moscow

Collaborators

  • SCK-CEN, Belgium, Mol\nFraunhofer-INT, Germany, Euskirchen

Project summary

Under the action of nuclear radiation, point defects (colour centers) arise in the fibre glass network. As a consequence, the absorption of light propagating in the fibre increases. Hence, the possibility exists of measuring the dose of radiation by measuring the optical loss in the fibre.

Fibre-optic dosimeters would have a number of essential advantages over conventional dosimeters and a wide field of potential uses in the civil nuclear industry, medicine, and environmental monitoring. In contrast to the conventional dosimeters and radiation detectors, optical fibers feature a small weight and transverse size, as well as immunity to electromagnetic interferences. Fiber-optic dosimeters can be fabricated using relatively inexpensive components. The operation of a fibre-optic dosimeter does not require any electric powering of the sensor probe; therefore, sparks and fire hazard are fully eliminated.

By using optical time domain reflectometry (OTDR), one can create a distributed fibre dosimeter to monitor a vast territory or building with just one fibre. In this case, a single fibre substitutes numerous point dosimeters. Distributed fibre dosimeters might be installed inside and around nuclear hazard facilities, in radioactive waste disposals , and in contaminated areas to allow remote monitoring of the radiation field in both normal and accidental conditions. If such a dosimeter has been installed around a nuclear hazard facility in advance, a remote operator will be able to determine the coordinates and activity of radioactive falls in the event of an emergency.

A short length of a radiation-sensitive fibre spliced with a radiation-resistant fibre pigtail constitutes a point fibre dosimeter. Such a dosimeter holds much promise for radiotherapy. In contrast to the dosimeters currently used in clinical practice and radiological research (ionization chambers, semiconductor and thermoluminescence dosimeters), a point fibre dosimeter would have a far smaller size of the sensing element, which permits a high spatial resolution. Owing to a low weight and the absence of heavy wire cables, a fibre dosimeter would be much more convenient in clinical practice than, for a example, semiconductor dosimeter. Fibre dosimeters would allow on-line, in-vivo dose monitoring immediately in the process of irradiation. The latter feature is important, among other things, for timely revealing mistakes in the patient’s position and radiation beam parameters. Fibre dosimeters do not require prolonged preparation for irradiation and post-irradiation treatment to read the dose value. Finally, fibre dosimeters would enable invasive dose measurements. By now, several pioneering experiments to demonstrate the possibility of using fibre dosimeters in radiotherapy have been staged.

Although the above concept of fibre dosimeter dates back to 1978, the investigations have not yet yielded a product. The major problem consists in the fact that the physical pattern of the formation, thermal decay, and interconversion of radiation-induced colour centres (RICC) is rather complicated and has not been adequately explored. The chemical composition of radiation-sensitive fibres, their radiation sensitivity, fabrication regimes, the operation wavelength(s), and the algorithm of dose reconstruction from the induced absorption measurements have not been optimized. The Project is aimed at solving the above so far unsolved problems, which will permit fabrication of two prototype fibre dosimeters.

Specifically, the objectives of the Project are as follows:

- to optimize the chemical composition and technological fabrication regimes of optical fibres for distributed fibre dosimeters and radiotherapeutic point fibre dosimeters;

- to determine the optimal operation wavelength(s) of fibre dosimeters and algorithms of dose reconstruction from multiple wavelength induced absorption measurements, to determine the accuracy of dose determination in the presence of temperature and dose rate variations; to determine experimentally the critical maximal and minimal doses between which a required accuracy is achieved;

- to make a prototype distributed fibre dosimeter;

- to make a prototype point fibre dosimeter for radiotherapy and to test it in clinical conditions.

The activity in the framework of this Project will be as follows. Silica optical fibres with non-standard dopants producing long-lived RICC will be fabricated. The induced loss spectra in such fibres will be measured during and after -irradiation; thereafter, the induced loss spectra will be analyzed numerically with the aim to determine one or several wavelengths at which the induced absorption allows accurate determination of dose. In the most favorable case, a single wavelength will be determined at which the induced absorption is uniquely related to the absorbed dose. However, if the required accuracy of dose determination in the presence of dose rate and temperature variations cannot be achieved in this way, a more complicated algorithm of dose determination from the induced absorption values at two or several wavelengths will be searched for. Depending on the results of the numerical analysis of the induced absorption spectra, the fibre technology will be modified. As the result, the chemical composition and technological regimes of optical fibres for distributed fibre dosimeter and radiotherapeutic point fibre dosimeters, the operating wavelengths of the dosimeters, and the algorithm of dose determination from the induced loss values will be optimized.

The optimized fibres will be studied in more detail to determine the accuracy of dose determination, the critical maximal and minimal doses between which this accuracy is achieved, and the correlation between the measured and the tissue-equivalent doses.

Based on the optimized fibres a prototype distributed fibre dosimeter and a prototype point radiotherapeutic fibre dosimeter will be fabricated and demonstrated to the international scientific community. The radiotherapeutic dosimeter will be tested in clinical conditions.

This Project does meet the ISTC goals. The distributed fibre dosimeters to be developed are intended for environmental monitoring in concatenated areas and around nuclear hazard facilities. They can also be applied inside nuclear power plants to ensure safety of personnel. The distributed fibre dosimeters appear to be a promising tool for long-term monitoring of nuclear waste storage sites. Thus, the Project relates to the priority R&D fields of ISTC: environmental monitoring, energy production, and nuclear safety. The development and testing of a radiotherapeutic dosimeter will contribute to the solution of an important international technical problem, namely, quality assurance in radiotherapy and minimization of radiation injury to the patient in the course of radiotherapy.

Owing to this Project, weapon scientists and engineers of the Russian Federal Nuclear Centre – Zababakhin All-Russian Research Institute of Technical Physics will have an opportunity to pass on to a civil research and development area and to join the international scientific community.

Three Russian institutes will join forces to fulfill this Project. The Fibre Optics Research Centre at the A.M.Prokhorov General Physics Institute of the Russian Academy of Sciences (FORC), the leading institution of the Project, embarked on a study of radiation-sensitive fibres in the 1990-ies. By now, preliminary investigations of the kinetics of radiation-induced absorption in P-, Al-, and rare-earth-doped fibres have been performed. New principles of operation of fibre dosimeters of high doses have been proposed. A number of investigations have been carried out in cooperation with the SCK*CEN Belgian Nuclear Research Centre, a Collaborator of this Project. FORC possesses all the necessary equipment for fibre preform fabrication (MCVD-process), for fibre drawing and characterization as well as technological know-hows of special fibres to be studied in this Project.

The Russian Federal Nuclear Centre – Zababakhin All-Russian Research Institute of Technical Physics (RFNC-VNIITF) is one of the major nuclear research establishments in Russia. The RFNC-VNIITF scientists participating in the Project possess a 60Со source and dosimetric equipment. They have a wide experience in measuring induced optical absorption in fibres under nuclear irradiation using a set-up based on a diode array spectrometer. RFNC-VNIITF also has technological equipment to produce fibre preforms and to draw fibres.

The N.N.Blokhin Russian Cancer Research Centre of the Russian Academy of Medical Sciences (RCRC) is one of the two leading oncological research centres in Russia. The RCRC’s team possesses a wide clinical experience in radiotherapy and is conducting research on technical, dosimetric, and biophysical problems of radiotherapy, on quality assurance in radiotherapy and minimization of radiation injury to patient. RCRC’s participants of the Project possesses equipment to test the fibres and the prototype medical fibre dosimeter under radiation: namely, a ROKUS therapeutic cobalt source, thermoluminescence and semiconductor dosimeters, ionization chambers, and various phantoms.

The Foreign Collaborators, the SCK*CEN Belgian Nuclear Research Centre and the Fraunhofer – Institute for Technological Trend Analysis, have been involved in the research of fibres for dosimetry for many years. Their role in this Project will consist in exchange of research results and independent testing of the fibres developed in the framework of this Project.


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