Optical fibres Part 1-54: Measurement methods and test procedures Gamma irradiation
|Publication Date:||1 June 2003|
|ICS Code (Fibres and cables):||33.180.10|
This part of IEC 60793 outlines a method for measuring the steady state response of optical fibres and optical cables exposed to gamma radiation. It can be employed to determine the level of radiation-induced attenuation produced in single-mode or multimode optical fibres, in either cabled or uncabled form, due to exposure to gamma radiation.
The attenuation of cabled and uncabled optical fibres generally increases when exposed to gamma radiation. This is primarily due to the trapping of radiolytic electrons and holes at defect sites in the glass (i.e. the formation of "colour centers"). This test procedure focuses on two regimes of interest: the low dose rate regime suitable for estimating the effect of environmental background radiation, and the high dose rate regime suitable for estimating the effect of adverse nuclear environments. The testing of the effects of environmental background radiation is achieved with an attenuation measurement approach similar to method IEC 60793-1-40A, cut-back. The effects of adverse nuclear environments are tested by monitoring the power before, during and after exposure of the test sample to gamma radiation. The depopulation of color centers by light (photobleaching) or by heat causes recovery (lessening of radiation induced attenuation). Recovery may occur over a wide range of time which depends on the irradiation time. This complicates the characterization of radiation induced attenuation since the attenuation depends on many variables including the temperature of the test environment, the configuration of the sample, the total dose and the dose rate applied to the sample and the light level used to measure it.
This test is not a material test for the non-optical material components of a fibre optic cable. If degradation of cable materials exposed to irradiation is to be studied, other test methods will be required.
NOTE Background information on this subject is given in IEC/TR 622831.
Attention is drawn to the fact that strict regulations and suitable protective facilities are adopted in the laboratory for this test. Carefully selected trained personnel are used to perform this test. It can be extremely hazardous to test personnel if it is improperly performed or without qualified conditions.
1 IEC 62283, Nuclear radiation - Fibre optic guidance.