TSK 11 Göttingen 2006 Ullemeyer & Behrmann
 Neutron time-of-flight tex-
 ture measurements in Dubna:
 Status and developments
 Vortrag
 Klaus Ullemeyer1 Jan H. Behrmann1
 Introduction
 The multidetector texture diffractome-
 ter SKAT (from Russian: Spektrometer
 Kolitshestvennovo Analiza Tekstury) at
 the pulsed reactor IBR-2 in Dubna,
 Russia, started operation in March
 1997 and is open for users from all
 countries. Application of time-of-flight
 (TOF) diffraction to texture measure-
 ments offers the opportunity to record
 complete diffraction patterns, i.e., to
 measure several pole figures simulta-
 neously (Fig. 1(a)). To allow high
 spectral resolution for measurements on
 polyphase geological samples with many
 diffraction patterns, the instrument was
 placed at the end of an over 100m long
 flight path. In this paper, we will sum-
 marize advantages and disadvantages of
 the SKAT, as well as intended improve-
 ments.
 Characteristics of the SKAT — ad-
 vantages and disadvantages
 The main characteristics of the SKAT
 are as follows (Ullemeyer et al. 1998,
 Fig. 2):
 - 19 detector modules are arranged
 around the incident neutron beam
 at a unique angle of 2Θ = 90◦. Par-
 ticular Bragg peaks are assigned to
 one and the same neutron wave-
 length λ, hence, all λ and Θ de-
 pendent intensity corrections may
 be avoided.
 1 Geologisches Institut, Universität Freiburg,
 Albertstr. 23B, D-79104 Freiburg
 Figure 1: (a) Time-of-flight diffraction pat-
 tern of olivine (forsterite). Some Bragg re-
 flections are indicated. (b) Best possible
 experimental resolution ∆d/d, determined
 on quartz powder sample.
 - The sample is positioned in the cen-
 tre of the detector ring and rotated
 around an horizontal axis Z at an
 angle of 45° with respect to the in-
 cident neutron beam. Supposing
 that the detector modules include
 an angular range of 180°, complete
 pole figures may be measured by a
 single sample revolution (measure-
 ments are fast).
 - The goniometer angle of 45° al-
 lows installation of axial symmet-
 ric sample environment with min-
 imum restrictions to the incident
 and diffracted beams.
 1
Ullemeyer & Behrmann TSK 11 Göttingen 2006
 Figure 2: Photograph of the SKAT.
 Planned sample motions around X (α) and
 Y (β) are indicated.
 - Due to the long flight path, high
 resolution may be achieved by colli-
 mation of the diffracted beam (Fig.
 1 (b)).
 - The beam cross section of 50 ×
 85mm2 allows application of large
 sample volumes.
 Although the SKAT is well-suited for
 the measurement of bulk textures on ge-
 ological samples, restrictions are valid.
 Due to the pulse repetition rate of 5Hz
 at the IBR–2 reactor, the maximum ac-
 cessible lattice spacing dmax is restricted
 to about 4.9Å. This may be sufficient
 for texture analyses even on three-phase
 samples (e.g., carbonate rocks consist-
 ing of calcite + dolomite + quartz).
 On the other hand, successful texture
 analysis may be hampered (e.g., in
 case of ultrabasic rocks or phyllosilicate-
 bearing gneisses).
 Intended upgrading of the SKAT
 Expansion of accessible d-range im-
 proves the possibilities for texture mea-
 surements. From Bragg’s law,
 λ = 2d sinΘ
 and invariability of λ follows that ex-
 pansion of dmax may be achieved by de-
 crease of 2Θ only. We consider construc-
 tion of a second detector system with
 2Θ = 65°, keeping the old detector sys-
 tem for alternative use. Accessible d-
 range extends to about 6.5Å, allowing
 access to more non-overlapped Bragg re-
 flections. Inevitable deterioration of res-
 olution ∆d/d by about 15–20% (com-
 pare to Fig. 1(b)) appears to be accept-
 able. In addition, the scanning possi-
 bilities will be improved by two more
 sample rotations around an horizontal
 and a vertical axis, respectively (Fig.
 2). Thus, the recording of orientational
 data even for alternative methods of
 quantitative texture analysis (Bernstein
 et al. 2005) will be possible. Upgrad-
 ing of the SKAT is scheduled contem-
 poraneously with modernization of the
 IBR-2 reactor (2007–2009).
 Acknowledgements Operation of
 the SKAT is supported by the German
 Ministry of Education and Research
 through grant 03DU03FB. Valuable
 support of the Frank Laboratory of
 Neutron Physics – Joint Institute of
 Nuclear Research (Dubna) is also
 gratefully acknowledged.
 Literatur
 Bernstein S, Hielscher R & Schaeben H (2005)
 The Generalized Spherical Radon Transform
 and Its Application in Texture Analysis.
 Preprint 2005-2, Fakultät für Mathematik
 und Informatik, TU Bergakademie Freiberg
 Ullemeyer K, Spalthoff P, Heinitz J, Isakov NN,
 Nikitin AN & Weber K (1998) The SKAT
 texture diffractometer at the pulsed reactor
 IBR-2 at Dubna: experimental layout and
 first measurements. Nucl Instr Meth Phys
 Res A412, 80–88
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