Speaker
Dr
Kukka Miikkulainen
(Oxford Instruments Analytical Oy)
Description
A side-illuminated GaAs strip detector prototype for inspecting welds on copper canisters has been designed and is being manufactured. The detector has 512 channels and the strips are focused towards the radiation source, the distance between source and detector being 2200 mm. The X-ray beam is collimated to an area of 100mm x 0.2um on the edge of the detector by a collimator 150 mm in length, making alignment issues rather demanding.
The copper canisters to be inspected will be used for final storage of spent nuclear fuel and therefore the imaging process needs to be fully automated and remote-controlled. The canisters are rotated in front of the detector at an angle of approximately 30 degrees. The thickness of copper that the X-rays need to pass through during weld inspection is up to 160 mm, which demands for a 9 MeV radiation source. The design goal is to be able to see volumetric defects as small as 1 x 1 x 1 mm 3. The 200 um strip pitch has been chosen to ensure this resolution and a strip length of 25 mm to offer enough stopping power for the high-energy X-rays in order to get a good signal. The strip detector is produced using high purity GaAs material grown by CVPE method (Chloride Vapour Phase Epitaxy) on n+ -type bulk GaAs wafers.
Readout is implemented with XCHIP readout ASICs and a high-speed DAQ module connected to a PC via Ethernet. The readout chips are protected from the incident X-rays by elevating them from the detector plane so that they are shielded by the collimator. This is achieved with a flex cable connection from the detector chip to the readout electronics. The final detector will be composed of two or three detectors similar to this prototype to facilitate stereoscopic radiography.
Author
Dr
Kukka Miikkulainen
(Oxford Instruments Analytical Oy)
Co-authors
Jorma Pitkänen
(Posiva Oy)
Kai Kuparinen
(Oxford Instruments Analytical Oy)
Seppo Nenonen
(Oxford Instruments Analytical Oy)
Stefan Sandlin
(VTT Technical Research Centre of Finland)
