D17, is a neutron reflectometer with horizontal scattering geometry (vertical surfaces) designed to be as flexible as possible in resolution and modes of operation. It is suitable for the study of surface structures in solids and solid/liquid interfaces over a wide range of length scales.

• The study of surfaces and buried interfaces of thin solid films and multilayers
• Solid-liquid interfaces and membranes
• Examination of off-specular reflectivity from atomic and magnetic in-plane structure
• Kinetic studies of interface evolution.

D17 operates in four modes:

Time-of-flight (TOF), non-polarised
This is achieved by a double chopper system using wavelengths from 2 to 27 Å with great flexibility in resolution. This mode can simultaneously cover an order of magnitude in q in less than a minute, allowing the time evolution of a sample to be followed (kinetics). TOF-GISANS is also possible.

Time-of-flight (TOF), polarised beam
This is achieved by using an S-bender polarising the TOF beam in a selectable wavelength range with high polarisation. Pol TOF-GISANS and kinetic studies also possible.

Monochromatic, non-polarised 
The non-poarised angle dispersive mode (high flux at 5.5 Å used over the entire q-range). Not suitable for kinetic studies as each point in q must be measured sequentially. GISANS possible.

Monochromatic, polarised beam
For the study of magnetic samples with a choice of polarisation analysis between a supermirror for the specular beam and a 3He cell covering the wide solid angle of the multidetector for off-specular studies. The instrument is ideal for the measurement of off-specular scattering arising from large scale in-plane structure, glancing incidence small angle scattering (GISANS) from smaller scale in-plane structure.