**Pavol Mikula \*, Vasyl Ryukhtin, Jan Šaroun and Pavel Strunz**

Department of Neutron Physics, Nuclear Physics Institute ASCR, v.v.i., 250 68 Rež, Czech Republic; ˇ ryukhtin@ujf.cas.cz (V.R.); saroun@ujf.cas.cz (J.Š.); strunz@ujf.cas.cz (P.S.)

**\*** Correspondence: mikula@ujf.cas.cz; Tel.: +420-2-6617-3159

Received: 2 November 2020; Accepted: 27 November 2020; Published: 30 November 2020

**Abstract:** Resolution properties of the unconventional high-resolution neutron diffraction three-axis setup for strain/stress measurements of large bulk polycrystalline samples are presented. Contrary to the conventional two-axis setups, in this case, the strain measurement on a sample situated on the second axis is carried out by rocking the bent perfect crystal (BPC) analyzer situated on the third axis of the diffractometer. Thus, the so-called rocking curve provides the sample diffraction profile. The neutron signal coming from the analyzer is registered by a point detector. This new setup provides a considerably higher resolution (at least by a factor of 5), which however, requires a much longer measurement time. The high-resolution neutron diffraction setting can be effectively used, namely, for bulk gauge volumes up to several cubic centimeters, and for plastic deformation studies on the basis of the analysis of diffraction line profiles, thus providing average values of microstructure characteristics over the irradiated gauge volume.

**Keywords:** residual stresses; neutron diffraction; three axis setting; high resolution; bent crystal monochromator; bent crystal analyzer
