hrvatski

Testiranje novih TLD sustava za mjerenje doze u okolini

The high gamma sensitivity demonstrated by LiF:Mg, Cu, P produced in China and Poland makes it appropriate for environmental applications. Recently a new version of this material has been produced in the United States in both loose chip and encapsulated card form. This study investigates the performance of the US material under conditions designed to simulate environmental insults as described in ANSI Draft Standard N13.29. Twenty dosimeters are placed in an environmental chamber that cycles twice through three 15 day periods of temperature and humidity conditions: -20 degrees C ; +50 degrees C with 20% relative humidity ; and +50 degrees with 90% relative humidity. Five randomly selected dosimeters are exposed to a 137Cs source to doses between 0.5 to 10.0 mSv at the beginning, middle, and end of the 90-day test. Two 40-watt fluorescent bulbs provide lighting in the chamber. Performance is measured by comparison with the proposed Draft N13.29 performance criteria that would require the absolute value of the bias and standard deviation to each be less than or equal to 0.35, while their sum must be less than or equal to 0.50. The performance criteria in ANSI Draft N.13.29 proved to be very useful for introducing new TLD systems in environmental monitoring. This standard is generic and not specific to the methods used to pass its criteria. The 7LiF:Mg, Cu, P chips and cards recently developed by Harshaw passed this performance test together with the Chinese LiF:Mg, Cu, P. The new chips seem to be very promising detectors for environmental dosimetry as they allow short exposure time, and ease in handling. However, the encapsulation of the cards needs changes to be more resistance against temperature and humidity effects. The fading of TL systems in extreme temperature and humidity conditions specified in ANSI Draft N13.29 call for further investigations.

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