• Attenuators are installed on all beamlines in the experimental hutches and most users are now familiar with their use. We particularly recommend their use on the tunable beamlines 14-4, 23-1 and 29 to minimise radiation damage to your samples. A quick guide for the tunable beamlines is to use 1 second exposures and alter the transmission level to give your required intensities (watch out for overloads) on your images.

    Control of the attenuator insertion is done via mxcube. Simply type the transmissed beam level you desire and press enter/return. The transmission is set as close as possible to the given values.

    They can also be controlled manually via the SPEC session. If you're not sure about the SPEC sessions, please ask your local contact for help.

    The exception is BM29 where the absorbers are controlled via the BsxCuBE software with "transmission brick" similar to mxCuBE one.

    There are two boxes with a total of eight attenuator slots giving a wide variety of attenuation factors. If the transmission mode of MXCuBe is not working type in the appropriate SPEC session mattset <number> where mattset number is given in the tables below. Type mattset 0 to remove all attenuators. The current state of the attenuators can be found with the command mattstatus. Please remember to remove the attenuators after your experiment is finished!
     

    Monochromatic Beam Attenuators

    mattset 1 2 4 8 16 32 64 128
    thickness 0.32mm 0.84mm 1.82mm 0.09mm 0.09mm 0.09mm 0.09mm 0.09mm
    material Al foil Al foil Al foil Al foil Al foil Al foil Al foil Al foil

The following settings could be useful for data collection on ID14-4. E.g. for MAD data collection so that the crystal will not be dead after one wavelength. Attentuation is also recommended for a low-resolution pass where an attenuator would be much better than sub-second exposure times that might be needed to prevent overloads, as the beamline is optimised for exposure times around 1 second. Attenuation is also needed for manual energy-scans where one needs to find an appropriate attenuation factor such that the MCA gives a proper signal without being saturated. Start with a high attenuation factor and work towards a smaller attenuation factor:

 

Attenuators Inserted Transmission (%) at Os LIII-edge (10.87 keV) Transmission (%) at Se K-edge (12.66 keV) Transmission (%) at 13.2 keV mattset
1 2 4 8 16 32 64 128
OUT OUT OUT OUT OUT OUT OUT OUT 100 100 100 0
OUT OUT OUT IN OUT OUT OUT OUT 61 73 75 8
OUT OUT OUT IN IN OUT OUT OUT 37 53 57 24
OUT OUT OUT IN IN IN OUT OUT 22 39 43 56
IN OUT OUT OUT OUT OUT OUT OUT 17 32 37 1
OUT OUT OUT IN IN IN IN OUT 14 28 32 120
OUT OUT OUT IN IN IN IN IN 8 20 25 248
IN OUT OUT IN IN OUT OUT OUT 4 12 16 25
OUT IN OUT OUT OUT OUT OUT OUT 1.0 5.1 7.2 2
IN IN OUT OUT OUT OUT OUT OUT 0.2 1.6 2.7 3
OUT OUT IN OUT OUT OUT OUT OUT 4e-3 0.2 0.3 4
IN OUT IN OUT OUT OUT OUT OUT 7e-4 5e-2 0.1 5
OUT IN IN OUT OUT OUT OUT OUT 4e-5 8e-3 2e-2 6
IN IN IN OUT OUT OUT OUT OUT 7e-6 3e-3 9e-3 7

You should now be able to work out your own combination that you consider to be ideal for your application. All numbers given above are based on calculations and might not agree with the actual situation, since the beam likes to burn holes in the attenuators.