SIGMA 150Ci - Manual (Page 19)

STEP 4
2.9
OPERATING INSTRUCTIONS
Projecting
Rapidly rotate the control crank handle in the EXPOSE direction (counter-clockwise) to move
the source assembly out of the exposure device to the radiographic focal position.
The control crank handle will stop turning when the source reaches the source stop.
Do not use excessive force.
The odometer (if fitted) will indicate the approximate total distance traveled,
7ft (2.1m) for each guide tube section.
Set the brake to ON to prevent movement of the source assembly during the
radiographic exposure.
Start timing the radiographic exposure from the moment the source assembly reaches
the exposure head.
Survey meter readings observed during the projection operation should increase
rapidly from background to a high level as the source emerges from the projector.
Then readings should fall as the source moves out towards the focal point,
fall sharply as the source enters a collimator (if used) and remain steady throughout
the exposure.
Actual survey meter readings will depend on the source activity, distance, collimators
and shielding. The sequence of changes should be observed and the readings noted.
During retraction of the source assembly from the exposure head to the exposure device,
the sequence will reverse. The survey meter should indicate a continually increasing
radiation level as the source assembly is retracted, then drop to background when the
source assembly is stored in the exposure device.
During the radiographic exposure, use the survey meter to check the boundary dose
rate, but spend as little time as possible in and near the restricted area to minimize
personal exposure.