SIGMA projetor - Manual (Page 21)

OPERATING INSTRUCTIONS
2.10
STEP 4
Retracting
At the end of the required exposure time, set the brake to OFF and rapidly turn the crank handle in
the RETRACT (clockwise) direction until it no longer moves. You may hear the lock slide ‘click’
back into its original position depending on the ambient noise level at the job site. From the
control crank you may be able to observe the
GREEN MARKING on the slide bar.
Apply a slight amount of forward pressure on the crank handle as if to expose the source to
ensure that the positive locking mechanism has actuated.
Allow the crank handle to return to a neutral position, thereby relieving any tension (force) on the control
cable that would cause source movement when unlocking the projector. At this point the source cannot be
moved out of the stored position.
In the unlikely event the lock slide moves toward the lock position before the source is fully stored in the
exposure device, turn the crank handle in the RETRACT (clockwise) direction until it stops turning. (The
lock slide is designed to lock on the stop ball, not the control cable). Do not use excessive force. The
source assembly will be in the exposure device but not in the fully shielded position. Approach the
exposure device, from the rear, with a survey meter. The survey meter will measure approximately 400
µSv/hr (40 mR/hr) at the rear plate of the exposure device when a 3.7 TBq (100 Ci) Ir-192 source is in use.
CAUTION
Remain clear of the front of the exposure device (outlet port side) to minimize personal exposure. Reset
the lock slide to the open position. Return to the control crank and turn the crank handle in the RETRACT
(clockwise) direction and store the source assembly in the normal manner.
The odometer (if supplied) should read approximately zero when the source assembly has returned to the
projector.
Confirmatory Survey
Approach the exposure device while observing the survey meter – observe the GREEN MARKING on the
lock slide and survey the exposure device. The survey meter should indicate the same radiation level as
observed before the exposure. Note particularly the outlet port reading.
Survey the entire length of source guide tube with the survey meter. If the meter shows a sharp increase,
the source is exposed or incompletely shielded.
If the source is still exposed, attempt to store it properly by cranking the source a short distance towards
the exposure head and retracting it, repeating if necessary.
Locking the Exposure Device
When the source assembly is properly stored in the projected, rotate the selector ring from the OPERATE
position to the LOCK position and secure it with the plunger lock.
Remove and safeguard the key.
WARNING!
If after several attempts to return the source assembly, the selector ring cannot be rotated to the
lock position (do not use excessive force) or the lock slide is not actuated, one must suspect an
accident in which the source assembly may have become disconnected or stuck outside the
projector, giving rise to a very high radiation field. Treat the situation as an EMERGENCY.