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X-ray energy

X-ray energy

Changing beamline energies

Users have access to the following energy ranges from the ShutterFlux GUIs:

MX1 - 8.5 keV to 17.5 keV

MX2 (Double Crystal Monochromator) - PX 8.5 keV to 15.5 keV or CX 17.44 keV
MX2 (Channel Cut Crystal Monochromator) - 12 keV to 13.5 keV

If you require access to energies outside of this range, speak with staff.

MX2 - Changing between CC and DCM

MX2 has two monochromatic options that can swapped depending on the type of experiment you are doing. This is usually set for the length of your experiment on setup, as it requires MX staff to setup and align, as well as a period of thermal equilibration to assure quality beam intensity and position. If you’re not sure which option you need, talk to staff.

MX2 - Changing between energies

To change between energies:

  1. Firstly ensure you are on the correct monochromator option for the desired energy.
    Channel Cut (CC) → 12.0 keV to 13.5 keV
    Double Crystal (DCM) → 5.5 keV to 18 keV

  2. Open beamcam:8080/BEAM.IDL.mjpg in a new tab in firefox to visualise the beam

  3. On the MX2 User controls GUI, enter your desired energy, hit enter, then press “change energy”

  4. Wait for the beam to come back on the beam camera, the you’re ready to collect!

Standard Collection Energies

Structural Biology (PX) - Protein crystal datasets are typically collected at 13 keV (0.9537 Å ). The MX beamlines are set up and equilibrated for this energy unless researchers request otherwise.

Chemical Crystallography (CX) - To achieve the required resolution for chemical crystallography structures, the energy is set to 17.444 keV (Mo K_alpha emission) and the detector is brought to closest approach.
Chemical Crystallography Resolution Requirements

 

Excitation scans and metal identification

To run excitation scans, go to the MAD and Excitation Scan module and follow the steps below:

  1. Select ‘excitation scan’ mode

  2. Fill out prefix for your scan (this will be the name of the generated file)

  3. Provide scan time in seconds (this will vary, we recommend starting with 5 seconds)

  4. Click ‘Scan’ to start

Keep the scan browser active!!

Check log once scan is in progress

 

MAD scans

To run MAD scans, go to the MAD and Excitation Scan module (only accessible on site or via remote access desktops) and follow the steps below:

  1. Select ‘MAD scan’ mode

  2. Choose an element or enter an energy value manually

  3. Fill out prefix for your scan (this will be the name of the generated file)

  4. Provide scan time in seconds (this will vary, we recommend starting with 5 seconds)

  5. Click ‘Scan’ to start

Keep the scan browser active!!

Check log once scan is in progress

Choosing MAD scan energies

This depends on several factors: what the anomalous scatterer is, how strong the signal is, and how radiation-sensitive your crystals are. For most Se-Met crystals a two-wavelength MAD experiment with the high energy remote (from 5-500 eV above the peak) collected first and followed by the inflection point is highly successful. Be careful to collect enough data at each wavelength to have an anomalous multiplicity of at least 4 (>7 is preferable).

Remember that radiation damage within a dataset will destroy your signal so it is better to attenuate heavily and collect redundant MAD data. For example, it is worth sacrificing 0.2 Å in resolution (by attenuating more) to reduce radiation damage for your MAD datasets. Most users collect a high-res native dataset as well.  

Useful tool for picking energies: X-ray absorption edges

Example of MAD scan interface

 

Example of MAD scan output