X-ray Dynamic Defectoscopy (XRDD) Direct observation of damage development in time dependent gradually stressed materials by means of X-ray transmission measurements. Jan Jakubek a, Daniel Vavrik b, Stanislav Pospisil a, Jan Visschers c a IEAP CTU Prague, b ITAM CAS Prague, c NIKHEF Amsterdam Resolution and Stability Tests of Medipix-1 Pixel Detector Used for X-ray Dynamic Defectoscopy

Our Basic Experimental setup Hamamatsu rtg tube Medipix Stressed Al specimen With prefabricated slit Region of interest For sharp images we need point X-ray source => we use Hamamatsu microfocus X-ray source L with 5  m focal spot size. As X-ray imaging device the Medipix-1 Si detector were used with standard readout setup (Muros, two NI cards, PC and Medisoft) attached to water cooling system with controlled temperature °C (step 0.1 °C)

Projection of straight Edge Stress Slit (0.3 mm wide) Pb marks (1 mm wide) Al specimen (5 mm) Field of vision Projection of the slit is too wide ! Flat area between slit and mark seems to be skew !

Image of Ideal Edge Taken by Ideal Camera Let’s assume ideal camera: - each pixel integrates all light impacting its area. - there is no insensitive areas between pixels - there is no overlaps between adjacent pixels - pixels of equal area and shape Let’s assume ideal edge and lighting: - parallel rays - no light can pass through the material behind the edge - no scattering, no diffraction We measure values of function I’(x i ) in the pixel centers x i Where I’(x) is convolution of light intensity I(x) and “sampling” function q(x). where d is pixel size I(x) x 1 0 q(x) x 1 -d/2 d/2

Edge Profile Measurement With Sub Pixel Resolution Each row holds the samples of the same function but shifted. Shift is given by angle of the edge. I can combine rows to get more precise edge profile: Pb (1 mm) Detector matrix Count versus pixel order

It’s derivativeMeasured edge profile (normalized) Ideal response Measured Edge Profile – nearly ideal case Hamamatsu rtg tube at 35kV Medipix Lead plate (1 mm)

Edge profile – more real case Hamamatsu rtg tube at 35kV Medipix Led plate (1 mm thick) Al shielding (5 mm thick) ?

Scattering ? If the reason is scattering, the effect should depend on threshold (photons of lower energy). => We repeated measurement for different threshold values. The differences of edge profiles from the ideal one:

How to reduce influence of the “tails” around edges? - If possible use monochromatic X-ray source (often not available). - Precise tune the threshold level. - Prevent occurrence of big “parasite” contrasts in image near regions of interest. In case of our specimen for XRDD we filled the slit by absorbing tin paste.

Temperature Stability – Leakage Current

Temperature Stability – Noisy and Dead Pixels Noisy pixels = pixels which noise is more then two times bigger then dispersion of Poisson distribution Dead pixels = pixels giving les then half count of events. Conditions: Temperature 18°C, rtg at 35 kV, Vth=1.5V (minimum threshold was 1.35V)

Temperature Stability – Noisy Pixels, GaAs detector

Appendix I – Threshold scans

Appendix II – Edge Profile Versus Threshold Level Conditions: Temperature 18°C, rtg at 35 kV.