Measurement of residual radioactive surface contamination by 2-D laser heated TLD

The feasibility of applying and adapting a two-dimensional laser heated thermoluminescence dosimetry system to the problem of surveying for radioactive surface contamination was studied. The system consists of a CO2 laser-based reader and monolithic arrays of thin dosimeter elements. The arrays consist of 10,201 thermoluminescent phosphor elements of 40 micron thickness, covering a 900 cm2 area. Array substrates are 125 micron thick polyimide sheets, enabling them to easily conform to regular surface shapes, especially for survey of surfaces that are inaccessible for standard survey instruments. The passive, integrating radiation detectors are sensitive to alpha and beta radiation at contamination levels below release guideline limits. Required contact times with potentially contaminated surfaces are under one hour to achieve detection of transuranic alpha emission at 100 dpm/100 cm2. Positional information obtained from array evaluation is useful for locating contamination zones. Unique capabilities of this system for survey of sites, facilities and material include measurement inside pipes and other geometrical configurations that prevent standard surveys, and below-surface measurement of alpha and beta emitters in contaminated soils. These applications imply a reduction of material that must be classified as radioactive waste by virtue of its possibility of contamination, and cost savings in soil sampling at contaminated sites