Digital Tomography (THATIR)        

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Gamma-ray source and frame supporting the detector-head of the gamma-ray spectrometer. The detector is programmed to move along the two axes perpendicular to the source-detector axis.




Gamma-ray intensity as a function of position measured for various sweeps of the spectrometer head.  The valleys correspond to iron bars intercepting the radiation. The red curves show the results of fitting these data with a mathematical function that takes into account the position and diameter of the iron bars.



Results of applying the tomographic reconstruction program developed by THASA to the section of a structural element containing three reinforcing bars.



Computer screen for the control program that controls the motion and operation of the spectrometer.






Pulses due to the gamma radiation detected by the spectrometer viewed using an oscilloscope.


Internal mode

This mode is used in cases of concrete thicknesses in excess of about  30 cm .

An example was the determination of the vertical position of a post tensioned duct inside a large beam. The detector was displaced along a hole drilled vertically at some distance of the expected horizontal coordinate of the duct (see figure). In this case it was only necessary to use a fixed weak external source.



  View of the system used tp locate a duct in the interior of a beam. In this case the source was fixed externally (by request of Riva S.A.)



Another example was the determination of the rebars in the bottom of a 1m deep concrete platform with  no access from below.  In this case both the source and the detector were displaced inside holes drilled  every  30 cm  (by requestof Lontra S.A.).  A similar configuration was used to study the grouting in deep PT ducts (see Defective grouting in post tensioned structures).

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