SIGMA projetor - Manual (Page 20)

OPERATING INSTRUCTIONS
2.9
STEP 4
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, 7 ft (2.1 m) 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.