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Reflectometer D17

D17 is the first ILL dedicated reflectometer and it has been designed to be as flexible as possible in resolution and modes of operation. The instrument is suitable for the analysis of surface structures in solids and solid/liquid interfaces. Horizontal surface experiments, such as free liquids, will suffer from a severe restriction in Q-range and flux and are thus not recommended for this instrument.

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www > Instruments & Support > Instruments & groups > D17 > Documentation > D17 LAMP Book > COSMOS > Machine Options

D17 LAMP Book

The Machine Options pop-up window contains  very important parameters that come from the calibration of time-of-flight parameters on D17.  Make sure that they are correct with respect to your measurement! 

 

You can ask your local contact for the correct parameters. 

 

Alternatively, the correct values should be saved in the data file.  After you have loaded a raw data file in to LAMP, click on the Data Parameters button in the lower part of the LAMP window.  This will open a pop-up window with useful information on the measurement.  You can find the values for POFF and the Opening Offset for your file by using the scroll bar to choose the workspace containing your data.


Offset Poff:  This is a parameter giving the angle between a pickup on the chopper (from which the time-of-flight is calculated) and the opening edge of the chopper.

Offset d0:  This is the distance between the choppers and the sample position, given in metres.

Opening Offset:  If the choppers are phased to this value, the beam has no direct line of sight from the guide to the sample position.

Pixel Width:  This is the width of an x-pixel, given in millimetres.

Override numor values:  The above values should be saved in the data file, and they should be read automatically when COSMOS is run.  If you suspect that the values are wrong, you may click this option and manually enter the values.

You have the possibility to have different values for each angle measured.

On D17 these values are usually the same for all angles.  They will sometimes change between cycles if there has been an intervention on the instrument.  The only time you would need to have different values for different angles would be if you wanted to analyse sets of data from the same sample, measured in separate experiments (this is generally inadvisable anyway).

On FIGARO these values will change between angles.  Make sure you keep a record of the right values.


Ask your local contact and/or the instrument responsible for more details.

Because changing these values will change the way that the wavelength and resolution is calculated, you need to be absolutely sure that you're doing the right thing.

 

For that reason, we've put a warning in that pops up once you click the 'OK' window

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