PorTL – The next step in TL Dosimetry

Thermoluminescent Dosimeters (TLD) are one of the most commonly used detectors for monitoring the radition exposure of personnel. TLD, together with closely related Optically Stimulated Luminescent Dosimeter (OSLD), is used in virtually all passive radiation monitoring “badges” and dosimeters worn by radiation workers. TLD is also commonly used for many other dosimetric applications including environmental dose assessment around accelerator facilities, nuclear power stations, and nuclear fuel processing and storage facilities.

Some advantages of TLD include:

  • Small size – an individual detector consisting of 10 mg of TL material is sufficient for most purposes;
  • Inexpensive – individual TLDs are many times less expensive than active detectors such as Geiger Counters or Ion Chambers;
  • Large dynamic range - TLD is able to measure from as low as 5 μGy to as high as 10000 Gy
  • Some TL materials are nearly tissue-equivalent;
  • TL detectors are able to measure the dose over long periods times without requiring power or periodic maintenance;
  • TL dosimeters are insensitive to most of the environmental agents (humidity, pressure, atmospheric composition) or they can be easily packaged or calibrated in such a way that they are made insensitive (temperature);
  • TLD evaluation is easily automated;
  • TLDs can be used for many forms of radiation, including mixed fields (β-γ, n-γ) or even electromagnetic radiation (UV, visible);
  • TLDs can be annealed and reused many hundreds of times, with only a very gradual change in efficiency and calibration.

In summary, TLD offers a relatively inexpensive, stable, and highly reproducible dosimetry technology for measuring cumulative exposure to ionizing radiaton by means of a compact, light-weight detector that requires no power during exposure.

Naturally there are some disadvantages of traditional TLD:

  • Using traditional TLD systems, the TLD detectors must be both annealed (prepared prior to radiation exposure) and evaluated (following exposure) in a laboratory equipped with both a large and expensive TLD reader and a high temperature annealing oven that must be operated by qualified personnel;
  • With traditional TLD systems, the need to process TLD in the laboratory introduces a delay in obtaining results;
  • In traditional TLD systems, the individual TLD dosimeters are often either in the form of chips, ribbons, powder, or embedded in cards or badges – making it difficult to track or trace individual detectors;
  • For applications requiring accuracy, each TL crystal (individual detector) must be calibrated individually;
  • For all TLD systems, heating and annealing methods must be defined accurately, be highly reproducible, and must be used consistently.

Most of these limitations are overcome by the new PorTL TLD System:

  • Because PorTL is small, light, portable, and battery powered, the individual PorTL detector cells can be both annealed and read out in the field, eliminating the need for the laboratory-based reader and annealing oven;
  • Readout and annealing of the PorTL cells in the field permits instant access to the dose results and immediate reuse of the PorTL cells;
  • All measured data and operational parameters (calibration information) are stored either in each individual PorTL cell or in the reader;
  • The PorTL system is easy to use, requiring only a minimum of training;
  • The PorTL dosimeter cells are more durable and robust than the individual TLD badges, cards, ribbons, or chips used in most traditional TLD systems.