SIGMA 150Ci - Manual (Page 20)

STEP 4
OPERATING INSTRUCTIONS
2.10
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 40mR/hr (400µSv/hr) at the rear
plate of the exposure device when a 100Ci. (3.7TBq) 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 toward the exposure head and retracting it, repeating if necessary.
Locking the exposure device
When the source assembly is properly stored in the projector, rotate the selector ring
from the OPERATE position to the LOCK position and secure it with the plunger lock.
Remove and safeguard 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.