The shutter is a large wedge of steel between the target and the instrument which stops the neutrons. When the wedge is in the beam (corresponding to 'shutter closed' position), neutrons are blocked from entering the beam. When the wedge is not in the beam (corresponding to 'shutter opened' position), neutrons go through the beamline to the sample. It allows safe access to the blockhouse and other areas of the beam during the cycle. Each instrument has its own shutter and this can be raised or lowered from controls found beside the instrument and inside the cabin. To prohibit access to areas of high radiation, a series of interlocks have to be completed before it is possible to open the shutter.
The interlock system is required such that:
1. Nobody is left inside high radiation areas.
2. All the sections of removable shielding have been replaced.
3. All the doors to the instrument are closed and locked.
The interlock systems on each instrument are configured according to the instrument layout; your local contact will help you understand the layout on the instrument you are using.
Instruments which have their sample positions inside a blockhouse will also have a search button or for more complicated beamlines multiple search buttons. These button must be pressed as the block house is searched by the last person to leaving the blockhouse to indicate to the system the search has been completed. For some beamlines there is an audible alarm during the search.
A noise will be made indicating the search is complete, and then you may then close and lock the door.
All interlock systems have the following features.
First, there are locks on various parts of the instrument. The photograph below shows the door lock on CRISP.
Second, there are one or more green boxes containing racks of keys. These are interlock keys which ensure the beamline is in a safe state for the shutter to be opened. When all the door keys are placed in these racks the master key will be released.
Third, there is a green master box – with a key labelled with an M. This is the box that controls the shutter – with the key in place the shutter is released and can be opened.
As the shutter opens a blue light comes on inside the high radiation area. This is linked to the shutter controls and to a radiation monitor. If you are working in a controlled area and the blue light comes on press the red beam off button or just leave the area as quickly as possible. Telephone the MCR and your local contact straight away.
Beam off buttons are found all over the hall; your Local Contact will point out the locations around your instrument. They are linked to the accelerator and can be used to trip the beam off in cases of emergency, such as if there is an individual within a blue light area.
In summary, make sure that you know:
1) Where the interlocks are and how they are operated.
2) Where the search button(s) are, if they exist.
3) How to complete a search and lock the blockhouse, if required
4) The purpose of a blue light and what to do if you are in an area where a blue light is on
5) Where the nearest red beam off buttons are.
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