X-ray Interlock Check Methodology

These tests should only be done by experienced designated personnel while there is no user in the X-ray room. The tests must be done at least once every six months and entered into the log book. They cannot and must not be done while data collection is ongoing.

Test the X-ray Tower lamps

There are three tower lamps of relevance:

• Red "X-ray On" lamp that is lit whenever the generator makes X-rays
• Yellow "shutter open" lamp for RIGHT port
• Yellow "shutter open" lamp for LEFT port - this should not be present
• Green "ready" light has no relevance for interlock purposes.

There is also a red "X-ray On" lamp on the generator front panel.

Make sure the backstop is installed and nobody else is inside the enclosure. You can do this test while standing inside the hutch with the door closed - if you stand behind (to the left of) the collimator the scatter is minimal even with the beam on - I have surveyed this in the past and it is barely above background. Close the enclosure door to enable the interlock. Reduce the X-ray power to 20 Kv and 10 mA to reduce scatter. With the X-rays on, manually open the (right) shutter via the front panel shutter switch to check that it works. Remove the shutter bulb on the tower. Verify that the shutter will not open without that bulb in place and functioning. Also verify that there is no bulb in the left shutter bulb socket.

Turn off the X-rays via the front panel (from 20kV/10mA). This will also stop the anode spinning, so hit TREV ON to start it spinning again. The green Ready light should be lit on the light tower. Remove the X-ray On bulb from the front panel. The Ready light should go out. Verify that you cannot turn on X-rays without the front panel bulb in place. Replace the front panel bulb.

Remove the X-ray On bulb in the tower. The Ready light should go out. Verify that you cannot turn on X-rays without the bulb in place. Replace the tower bulb and turn the X-rays on again.

Testing the Enclosure Interlock

Close the door of the enclosure. With the X-rays on and nobody except yourself in the enclosure, flip open the shutter briefly via the front panel toggle switch. Verify that the yellow tower light and the red rotary shutter light are lit. Close the shutter.

Open the enclosure door. Verify that the shutter will not open while the enclosure door is open. . Close that door and unlock and open the second enclosure door (where applicable). Verify that the shutter will not open while either enclosure door is open. . With the IIc generator, close all enclosure doors, open the metal access door and verify that the shutter will not open while the access door is open. Close that door and lock it from the inside.

Return the shutter toggle switch to the EXT (external control) position on the front panel.

Testing the Enclosure Interlock Override

For this you need the override keys, and if you don't know where the override keys are you shouldn't be doing the test....only the Facility Manager, Fred Hughson or Yigong Shi should ever do these tests.

With no-one else in the room: for each machine, enable the override with the override keys, open an enclosure door, flip open the shutter using the front panel. Close the shutter, returning the toggle switch to EXT, and re-arm the interlock and remove the keys.

Note that the override keys are of questionable relevance even for maintenance since you can do everything else without them by simply closing the door behind you while you are in the hutch.