[en] Full text: The XRD1 beamline is installed on D12B bending magnet (1.7 T) at the Brazilian Synchrotron Light Source (LNLS) and operates in the 5.5–14 keV range. The maximum photon flux is around 8 keV. The combination of a 3-circle diffractometer with the 24K Mythen detector and a robotic arm sample changer allows fast measurements. These capabilities are desirable for in situ experiments as well as industrial applications. The XRD1 beamline was first optimized for fast measurements (~ 100 s) of light-element materials in powder form, using glass capillaries in Debye-Scherrer geometry. The typical diameters of the capillaries vary between 0.3 and 1.0 mm. However, even 0.3-mm-diameter capillaries are too large for heavy-element materials, because of X-ray absorption. A different methodology — fixing the powder outside the capillary - was tested successfully with several materials. The powder of the multi-phase GdNd₄Si₄ compound was systematically studied by X-ray diffraction inside the 0.3-mm-diameter capillary and outside capillaries with different diameters (0.3, 0.5 and 0.7 mm). The data collected for this material in a capillary of 0.3 mm and energy of X-ray at 12 keV, has the absorption factor ; for factors , capillary geometry is not recommended. Comparing the peak intensities, we observe that the signal/background ratio related to the maximum of the (221) reflection of the tetragonal phase, for instance, is about 6.1 for the powder inside the 0.3-mm-diameter capillary and about 28.4 for the powder outside the same capillary, both measured with the same time (360 s). Many peaks of the second phase (orthorhombic) are barely seen in the diffraction pattern for the powder inside the capillary, while they are well observed for the powder outside the capillary. Nevertheless, Rietveld refinements present better GOF parameter for data collected from the sample inside capillary, but low e.s.d. on lattice parameters for every case. (author)