All strongly absorbing atoms are also incoherent neutron scatters scatterers. The very first thing you will observe is the huge background scattering. Now for many compounds containing  Gd, Sm, Eu etc. neutron diffraction experiments will be almost useless unless you use very thin annular cylindrical sample holders. You can still however  study thin single crystals. It would be convenient to use shorter wavelengths (hot neutrons). Absorption corrections will be necessary for all neutron diffraction experiments. The absorption correction will depend on the path lengths of the incoming and diffracted beam inside the sample. The Gaussian absorption correction will be appropriate for single crystal experiments. You must be able to index the faces of the crystal and the distances between them. There are standard single crystal programs (CCSL, Shelx, Fullprof etc) that will do the job for you. For powder diffraction the shape of the sample older will determine the absorption correction. The cylindrical absorption correction is the simplest. The absorption correction for neutron diffraction is very similar to that for X-ray diffraction. For powder diffraction low-Q reflections will be more affected than the high-Q reflections and that will cause your Debye Waller factor to be negative unless do the absorption correction properly. For the calculation of the absorption coefficients of your sample consult and any standard book of neutron diffraction viz, Bacon and also the International Tables of Crystallography. If you wish to understand then read these books carefully but if you wish to do just the correction without understanding then use Fullprof which will do the job for you.

For Li there are two istopes 6Li and 7Li for which the nuclear spins are I = 1 and 3/2 respectively. Their absorption cross sections are 70.5 and 940 barns. So 7Li will be very strongly ansprbing whereas 6Li will be managable. Fortunately what Li you buy is already depleted of 7Li and you get almost pure 6Li. This is convenient for neutron diffraction but even then the absorption is rather high. So if you study neutron diffraction from compounds with 6Li you have to use annular cylindrical sample holders and also do absorption correction.

Thank you Professor, the system under studied is a glass modified by lithium oxide. Studied using the isotopic substitution method with the GEM at ISIS UK. Half of the samples are enriched with the highly absorbing Li isotope. GEM is very excellent for such experiments. I appreciate your opinion on data analysis (correction and optimisation) very much. Thank you!

Yes isotope substitution is a very powerful method especially for diffraction from amorphous and glassy materials. The coherent scattering lengths fot 6Li and 7Li are 2.0 x 10^-13 and -2.22 x 10^-13 cm, respectively. So if you substitute Li sites only by isotopes then difference of the S(Q) wil give you information about the Li positions only. That is very convinient and useful.

Since you are doing diffraction from glassy sample I do not advise you to use Fullprof or GSAS. The best would be to use the standard absorption correction from the programs used by glass and amorphous community. Professor Salmon from the University of Bath is a specialist for such studies. You can contact him. Otherwise you should talk to David Keen or other ISIS guys.