Activity Depth Profiling

The importance of depth profile data 

Data on the depth profile of contamination within any structure is fundamental to evaluating decontamination options and deciding upon decommissioning strategy.  Decisions on the depth of removal not only affect the selection of the techniques to be used, but are critical to the waste categorisation of both removed and remaining materials, and often has a bearing on the radiation dose to which those decommissioning the structure will receive. Such segregation is not optional, as in most cases it will be a condition of the waste producers EPR Permit or RSA Authorisation. Although individual Permits differ, there will generally be a requirement to use BAT to a) minimise the volume of radioactive waste disposed of, and b) to characterise, sort and segregate solid radioactive waste to facilitate their disposal by optimised disposal routes.  ALARP will also be a consideration for material removal, in terms of optimising dose to decommissioning workers. 

Depth Profiling at IRAS Active Analytics

IRAS Active Analytics offer both non-destructive and destructive facilities for determining the depth profile of radionuclides in concrete cores and other substrates. 

For non-destructive testing, the IRAS RadProfiler™ series of instruments provide accurate and high precision data on the depth distribution of gamma emitting radionuclides. Depending on selected options, the IRAS RadProfiler™ is used with either one or four gamma spectrometry detectors, of low resolution NaI(Tl) or high resolution HPGe types.  Both the low resolution and high resolution detector options provide an industry standard digital detector interface, and link to standard computer controlled Multi-Channel Analyser functions.  

The system allows the depth profile of gamma emitting radionuclides to be determined, either in absolute terms (Bq/g) or where more appropriate, by making relative photopeak count rate measurements to determine the exponential decay factor (mm-1) which describes the shape of the exponential decrease in activity concentration from a contaminated core face.  The system does so with standard operating depth resolutions of 1, 2, 5 and 10 mm, although other collimator slit sizes can be accommodated. 

The system provides for totally non-destructive testing of cores, providing highly reliable and reproducible data, with an impressive depth resolution.  Long term measurement reproducibility tests have shown that the residual standard deviations of repeated measurements to be approximately 2%.

IRAS Active Analytics operate two IRAS RadProfiler ™ MkII collimated gamma spectrometer systems.  Recently re-designed, the MkII retains the same performance characteristics but with improvements in operability and portability, of particular importance for deployment at site.