a trainee and an instructor make a shot on a Weld. After exposure, the instructor retracts the source and completes a survey .While setting up for the next shot, the source, due to tube compression, moves from the shielded position. The instructor moves to the camera for his survey meter and notices the 'reading. He immediately leaves the tank and realizes the crank is half a turn off. What is the possible cause in the above situation??
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