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High-intensity two-axis diffractometer with variable resolution D20

D20 is very high intensity 2-axis diffractometer equipped with a large microstrip detector. Due to the extremely high neutron flux, it opens up new possibilities for real-time experiments on very small samples.

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D20 Neutron optics

D20 Neutron optics

The path of the neutron beam from D2B/D20 beam shutter to sample position is controled by the following elements :
The path of the neutron beam from D2B/D20 beam shutter to sample position is controled by the following elements :

The "bouchon" H11

This rotor may shut the beam where it leaves the thermal source in the reactor for the beam tube H11, serving the instruments D19, D2B and D20 with neutrons. It is part of the security loop, so when this rotor is closed (red light off, green light on), the beam shutter OS2 (concerning only D20) will automatically be closed. Normally you won't ever manipulate the keybox for this shutter, situated on the protection wall of D20, near D2B. You may see events on this shutter in the last 48 hours.

The beam stop B2

This additional beam shutter between D19 and D2B concerns only D20 and D2B. It is not part of the security loop, so it won't be closed if H11 is closed.

The "barrillet"

This item which acts either as a beam shutter, isolating D20 monochromator housing from D2B, or as a collimator to define the divergence alpha1 of the beam before the monochromator. Three values of alpha1

are available :

- alpha1 = 27', the "natural" divergence of the beam

- alpha1 = 20'

- alpha1 = 10'

The last two values of the beam divergence are obtained by using vertical Soller slits. The flux of the beam is nearly proportional to the value of alpha 1. Changing the position of the barillet takes a few minutes. You may calculate the effect on the resolution function .

As there was a problem reported on peak shape using the smallest divergence of 10' and the copper monochromator (1.3 Angstroem), diagrams of a Silicium standard for several setups were recorded to find out the optimal setup.

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