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ROTAX, a spectrometer with a non-uniformly spinning analyser
PHYSICA[ ELSEVIER
Physica B 213&214 11995j 878 880
ROTAX, a spectrometer with a non-uniformly spinning analyser H. Tietze-Jaensch a'b' ¢,*, W. Schmidt a'b, R. Geick b, U. Steigenberger a alSIS Facilio', Rutherford Appleton Laboratoo,, Chilton, OXI I OQX, UK bphysikalisches lnstitut, Universit2it Wiirzburg, Am Hubland, 97074 WiJrzburg, German), ClFF der KFA Jiilich, 52425 Jiilich. Germany
Abstract
ROTAX, a new type of time-of-flight crystal analyser spectrometer for neutron inelastic scattering from single crystals is now installed at ISIS. By utilising its non-uniformly rotating crystal analyser, ROTAX provides a wide variety of time-of-flight scans through (Q, ug) space. A description of the instrument and its software is given as a practical guideline for the use of this novel instrument. P h o n o n scattering data obtained from a Cu single crystal are presented.
I. Introduction
Unlike other neutron spectrometers, ROTAX uses a programmable, non-uniformly spinning analyser crystal to scan the neutron energies scattered by a singlecrystal sample in a white pulsed beam. The advantage is a superior scan flexibility and versatility (cf. Ref. 1-1] and references therein) with high count rates due to multiplexing. Here, we emphasize practical guidelines for the use of ROTAX which needs no more presumptions to start than a triple-axis spectrometer. However, data interpretation is more complex, because of the variety of scans and because the time-of-flight and kr-information are gathered simultaneously in a two-dimensional detector data array. Conventional TAS-like figures are obtained by appropriate data-binning. The ROTAX instrument is installed on the N2 beam line of ISIS behind P R I S M A with an incident flight path to be varied from 13 16 m. The spectrometer components are remotely operated and move on air pads inside a blockhouse for shielding. Pyrolitic-graphite analyser
* Corresponding author.
crystals (3.5x5.5cm z, 0.7 ° ( F W H M ) mosaicity) are mounted in an aluminum frame and attached to the analyser motor shaft. The time- and position-sensitive J U L I O S detector 1-2] is used on ROTAX. The major instrument parameters are compiled in Table 1.
2. The software to start R O T A X
An experiment on ROTAX starts with the basic sample parameters. The ROTAX Instrument Control Program (Fig. l) asks to set-up/edit a file of sample lattice constants, scattering plane/geometry, angles, limits etc. The SCAN program is used to define a specific time-of-flight (TOF) scan through (Q, co) space. Various ROTAX scan types are offered, e.g. const-7j or const-ho9 [1] or linear Q scan 1-33. They differ in individual physical scan parameters, such as the TOF-trace, range of Q, energy transfer he) or incident energy Ei. Provisional dispersion data may be imported from a file for shared display together with the T O F scan. Being satisfied with a desired ROTAX scan, the program checks for its technical feasibility. If this fails, the user is requested to modify his scan, otherwise the Scan program produces
0921-4526/95/$09.50 .C 1995 Elsevier Science B.V. All rights reserved SSDI 0 9 2 1 - 4 5 2 6 ( 9 5 1 0 0 3 1 0 - X
H. Tietze-Jaensch et al. /Physica B 213&214 (1995) 878 880
Table 1 Major instrument parameters of ROTAX Incident energy Momentum transfer TOF window @ sample Moderator 3 sample positions Beam size Scattering angle Sample to analyser Analyser crystal Analyser scatt, angle Analyser to detector Detector Flux @ sample Resolution
I
I
I
11~350 meV (chopper defined) 0.5 20.0A 1 15ms 1 0 0 K C H 4 poisoned at 2.25 cm 13, 14, 16m from moderator height: 50mm × width: 30ram -160 <4,<120 variable distance 4(~ 100 cm pyrot. Graphite (00 1), 35 × 55 mm 2 -110 <20~< +110 variable distance > 48 cm JULIOS: .pos. sens. lin. Li-6 szint. length 68.2cm, Ad/d ~ 3 × 10 "~ 1 × 106n/cm2sec (Au foil activationl Ah~o: 1 10% of Ei Ef AQ: 1 10% of Q At: 2 las
I
Fig. 1. Logogram of the ROTAX software packages. Programs: round boxes: files: ellipses: essential hardware components: circle and corner boxes. three files of the desired R O T A X T O F - s c a n parameters in varying format. The scan.piw file is picked up by the P1W program (cf. Fig. 1) which is used to c o m m a n d the signal processor that runs and controls the R O T A X analyser drive electronics and the motor. The other files scan.asc, scan.dat are used by other programs for off-line data display and interpretation. Summarising, one simply needs to define the area of interest in the (Q, to) space for the sample and select the most favourable R O T A X scan. The Scan and Piw programs then deal with all the technical details and find out how best to run the spinning analyser. R O T A X is now ready to start. Two other
879
programs take control of the rest of the instrument: (1) the MJS program sets and controls the general scattering geometry by moving stepping motors on all other axes of sample alignment, scattering angle, detector position etc. (2) J U L I O S controls the detector and produces the data files with neutron counts in a two-dimensional array, intensities versus total time-of-flight and detector position channels. In fact, the neutron scattering laws imply that every individual (t,x)-pixel of T O F and position channel of a detector data file is uniquely linked with a pixel element of (Q,~o) space, regardless of whether an inelastic or a diffraction (no rotating analyser) experiment is performed on ROTAX. Transforming the original (t, x) data into (Q,o~) data (diffraction data are always at co = 0) yields a machine independent data-set. This coordinate transformation from (t,x) to (Q,o~) is non-linear and, therefore, the intensity as a function of the pixel size needs to be renormalised. In addition, the incident flux k~ and position channel efficiency must be taken into account. These procedures are accomplished by different program sets: (1) diffraction data: D S P A C E is used to integrate along (t,x) lines with a constant Q or d-space value. The program produces ascii-files with the intensities versus d-spacing or T O F - v a l u e neutron energy or wavelength. Eventually, these files may be imported into G E N I E and/or other programs and, thus, open up the whole suite of existing RAL and alien software. (2) For inelastic data one must determine kf and T O F independently. Therefore, the actual analyser m o t o r curve must be included, using the program J U L D A T that reads the detector file in (t, x) coordinates and the scan.asc file of the analyser motor and plots an iso-line projection of the (Q, to) space into the detector (t, x) plane (Fig. 2). The Q E program transforms (t, x) detector data into a subplane of the four-dimensional (Q, ~o) space, e.g. (Q1, Q2) or (Qx, ~o). The resulting data are independent of the instrument and may be exported to other software.
3. Experimental results: inelastic scattering We present R O T A X inelastic data from a Cu single crystal sample using the PG-(004) analyser reflection. A const. IQ[/Q scan at constant angle ~ = 34 ° between k~ and Q was used to measure longitudinal LA (1 1 0) phonons of Cu throughout three different Brillouin zones, (2 2 0), (4 4 0) and (6 6 0). The scattering angle was set to ~b = - 110 ~. Fig. 2 presents a plot of the original data in (t, x) coordinates of the detector. The iso-lines are the (Q, to) space projections: long dashes for Qx = (1 00) and Qy = (0 1 0) direction, short dashes for energy transfer h~:) and the solid line for the R O T A X scan trace. Pronounced phonon scattering intensities are clearly vis-
880
H. Tietze-Jaensch et al.
/Physica B
213&214 (1995) 878-880
613 EZ ao © 2[3
I 2.05 HRI f'[)~,llff)N
140 (H%\NI!L
TOF
I)~D
I 2.00
DIRECTION
I 1.95
(OQO)
X
Fig. 2. Raw data of an inelastic ROTAX scan in primary detector coordinates with iso-lines of (Q,~o) space of Cu; long dashes: Q-lattice of scattering plane (0 1 0) × ( 10 0), short dashes: energy transfer hw, solid line: ROTAX TOF scan. INSERT: Enlargement of the top right corner. The boxes indicate the approximate size of the resolution elements for this ROTAX scan. ible. An e n l a r g e m e n t of the top right corner of Fig. 2 is inserted, revealing 2 distinct p h o n o n peaks a n d the app r o x i m a t e size of the resolution elements. Fig. 3 plots the p h o n o n intensities along the scan path of nearly c o n s t a n t energy transfer. The TOF-profile of the peaks reveals a const, kf plot, also well k n o w n in TAS-spectroscopy. In conclusion, we may summarise t h a t R O T A X has proved its capability a n d is feasible as an inelastic n e u t r o n scattering spectrometer that utilises best the pulsed time structure of the incident b e a m at ultimate flexibility in scan performance.
Fig. 3. Phonon peak profiles in the (1 10)-direction of Cu; ROTAX scan of Fig. 2.
R O T A X is funded by the G e r m a n B u n d e s m i n i s t e r fiJr F o r s c h u n g und Technologie, c o n t r a c t no. 0 3 - G E 3 - W U E .
References
[1] H. Tietze-Jaensch, W. Schmidt and R. Geick, Proc. ICANS XII 1993, Abingdon, U.K., RAL report no. 94-025 (1994) i-97.
[2] E. Jansen, W. Sch~ifer, A. Szepesvary, R. Reinartz, H. Tietze, G. Will, K.D. Miiller and U. Steigenberger, Physica B 180 181 (1992) 917. [3] W. Schmidt, H. Tietze-Jaensch and R. Geick, Proc. ICANS XII 1993, Abingdon, U.K., RAL report no. 94-025 (1994) 1-292.
Physica B 213&214 11995j 878 880
ROTAX, a spectrometer with a non-uniformly spinning analyser H. Tietze-Jaensch a'b' ¢,*, W. Schmidt a'b, R. Geick b, U. Steigenberger a alSIS Facilio', Rutherford Appleton Laboratoo,, Chilton, OXI I OQX, UK bphysikalisches lnstitut, Universit2it Wiirzburg, Am Hubland, 97074 WiJrzburg, German), ClFF der KFA Jiilich, 52425 Jiilich. Germany
Abstract
ROTAX, a new type of time-of-flight crystal analyser spectrometer for neutron inelastic scattering from single crystals is now installed at ISIS. By utilising its non-uniformly rotating crystal analyser, ROTAX provides a wide variety of time-of-flight scans through (Q, ug) space. A description of the instrument and its software is given as a practical guideline for the use of this novel instrument. P h o n o n scattering data obtained from a Cu single crystal are presented.
I. Introduction
Unlike other neutron spectrometers, ROTAX uses a programmable, non-uniformly spinning analyser crystal to scan the neutron energies scattered by a singlecrystal sample in a white pulsed beam. The advantage is a superior scan flexibility and versatility (cf. Ref. 1-1] and references therein) with high count rates due to multiplexing. Here, we emphasize practical guidelines for the use of ROTAX which needs no more presumptions to start than a triple-axis spectrometer. However, data interpretation is more complex, because of the variety of scans and because the time-of-flight and kr-information are gathered simultaneously in a two-dimensional detector data array. Conventional TAS-like figures are obtained by appropriate data-binning. The ROTAX instrument is installed on the N2 beam line of ISIS behind P R I S M A with an incident flight path to be varied from 13 16 m. The spectrometer components are remotely operated and move on air pads inside a blockhouse for shielding. Pyrolitic-graphite analyser
* Corresponding author.
crystals (3.5x5.5cm z, 0.7 ° ( F W H M ) mosaicity) are mounted in an aluminum frame and attached to the analyser motor shaft. The time- and position-sensitive J U L I O S detector 1-2] is used on ROTAX. The major instrument parameters are compiled in Table 1.
2. The software to start R O T A X
An experiment on ROTAX starts with the basic sample parameters. The ROTAX Instrument Control Program (Fig. l) asks to set-up/edit a file of sample lattice constants, scattering plane/geometry, angles, limits etc. The SCAN program is used to define a specific time-of-flight (TOF) scan through (Q, co) space. Various ROTAX scan types are offered, e.g. const-7j or const-ho9 [1] or linear Q scan 1-33. They differ in individual physical scan parameters, such as the TOF-trace, range of Q, energy transfer he) or incident energy Ei. Provisional dispersion data may be imported from a file for shared display together with the T O F scan. Being satisfied with a desired ROTAX scan, the program checks for its technical feasibility. If this fails, the user is requested to modify his scan, otherwise the Scan program produces
0921-4526/95/$09.50 .C 1995 Elsevier Science B.V. All rights reserved SSDI 0 9 2 1 - 4 5 2 6 ( 9 5 1 0 0 3 1 0 - X
H. Tietze-Jaensch et al. /Physica B 213&214 (1995) 878 880
Table 1 Major instrument parameters of ROTAX Incident energy Momentum transfer TOF window @ sample Moderator 3 sample positions Beam size Scattering angle Sample to analyser Analyser crystal Analyser scatt, angle Analyser to detector Detector Flux @ sample Resolution
I
I
I
11~350 meV (chopper defined) 0.5 20.0A 1 15ms 1 0 0 K C H 4 poisoned at 2.25 cm 13, 14, 16m from moderator height: 50mm × width: 30ram -160 <4,<120 variable distance 4(~ 100 cm pyrot. Graphite (00 1), 35 × 55 mm 2 -110 <20~< +110 variable distance > 48 cm JULIOS: .pos. sens. lin. Li-6 szint. length 68.2cm, Ad/d ~ 3 × 10 "~ 1 × 106n/cm2sec (Au foil activationl Ah~o: 1 10% of Ei Ef AQ: 1 10% of Q At: 2 las
I
Fig. 1. Logogram of the ROTAX software packages. Programs: round boxes: files: ellipses: essential hardware components: circle and corner boxes. three files of the desired R O T A X T O F - s c a n parameters in varying format. The scan.piw file is picked up by the P1W program (cf. Fig. 1) which is used to c o m m a n d the signal processor that runs and controls the R O T A X analyser drive electronics and the motor. The other files scan.asc, scan.dat are used by other programs for off-line data display and interpretation. Summarising, one simply needs to define the area of interest in the (Q, to) space for the sample and select the most favourable R O T A X scan. The Scan and Piw programs then deal with all the technical details and find out how best to run the spinning analyser. R O T A X is now ready to start. Two other
879
programs take control of the rest of the instrument: (1) the MJS program sets and controls the general scattering geometry by moving stepping motors on all other axes of sample alignment, scattering angle, detector position etc. (2) J U L I O S controls the detector and produces the data files with neutron counts in a two-dimensional array, intensities versus total time-of-flight and detector position channels. In fact, the neutron scattering laws imply that every individual (t,x)-pixel of T O F and position channel of a detector data file is uniquely linked with a pixel element of (Q,~o) space, regardless of whether an inelastic or a diffraction (no rotating analyser) experiment is performed on ROTAX. Transforming the original (t, x) data into (Q,o~) data (diffraction data are always at co = 0) yields a machine independent data-set. This coordinate transformation from (t,x) to (Q,o~) is non-linear and, therefore, the intensity as a function of the pixel size needs to be renormalised. In addition, the incident flux k~ and position channel efficiency must be taken into account. These procedures are accomplished by different program sets: (1) diffraction data: D S P A C E is used to integrate along (t,x) lines with a constant Q or d-space value. The program produces ascii-files with the intensities versus d-spacing or T O F - v a l u e neutron energy or wavelength. Eventually, these files may be imported into G E N I E and/or other programs and, thus, open up the whole suite of existing RAL and alien software. (2) For inelastic data one must determine kf and T O F independently. Therefore, the actual analyser m o t o r curve must be included, using the program J U L D A T that reads the detector file in (t, x) coordinates and the scan.asc file of the analyser motor and plots an iso-line projection of the (Q, to) space into the detector (t, x) plane (Fig. 2). The Q E program transforms (t, x) detector data into a subplane of the four-dimensional (Q, ~o) space, e.g. (Q1, Q2) or (Qx, ~o). The resulting data are independent of the instrument and may be exported to other software.
3. Experimental results: inelastic scattering We present R O T A X inelastic data from a Cu single crystal sample using the PG-(004) analyser reflection. A const. IQ[/Q scan at constant angle ~ = 34 ° between k~ and Q was used to measure longitudinal LA (1 1 0) phonons of Cu throughout three different Brillouin zones, (2 2 0), (4 4 0) and (6 6 0). The scattering angle was set to ~b = - 110 ~. Fig. 2 presents a plot of the original data in (t, x) coordinates of the detector. The iso-lines are the (Q, to) space projections: long dashes for Qx = (1 00) and Qy = (0 1 0) direction, short dashes for energy transfer h~:) and the solid line for the R O T A X scan trace. Pronounced phonon scattering intensities are clearly vis-
880
H. Tietze-Jaensch et al.
/Physica B
213&214 (1995) 878-880
613 EZ ao © 2[3
I 2.05 HRI f'[)~,llff)N
140 (H%\NI!L
TOF
I)~D
I 2.00
DIRECTION
I 1.95
(OQO)
X
Fig. 2. Raw data of an inelastic ROTAX scan in primary detector coordinates with iso-lines of (Q,~o) space of Cu; long dashes: Q-lattice of scattering plane (0 1 0) × ( 10 0), short dashes: energy transfer hw, solid line: ROTAX TOF scan. INSERT: Enlargement of the top right corner. The boxes indicate the approximate size of the resolution elements for this ROTAX scan. ible. An e n l a r g e m e n t of the top right corner of Fig. 2 is inserted, revealing 2 distinct p h o n o n peaks a n d the app r o x i m a t e size of the resolution elements. Fig. 3 plots the p h o n o n intensities along the scan path of nearly c o n s t a n t energy transfer. The TOF-profile of the peaks reveals a const, kf plot, also well k n o w n in TAS-spectroscopy. In conclusion, we may summarise t h a t R O T A X has proved its capability a n d is feasible as an inelastic n e u t r o n scattering spectrometer that utilises best the pulsed time structure of the incident b e a m at ultimate flexibility in scan performance.
Fig. 3. Phonon peak profiles in the (1 10)-direction of Cu; ROTAX scan of Fig. 2.
R O T A X is funded by the G e r m a n B u n d e s m i n i s t e r fiJr F o r s c h u n g und Technologie, c o n t r a c t no. 0 3 - G E 3 - W U E .
References
[1] H. Tietze-Jaensch, W. Schmidt and R. Geick, Proc. ICANS XII 1993, Abingdon, U.K., RAL report no. 94-025 (1994) i-97.
[2] E. Jansen, W. Sch~ifer, A. Szepesvary, R. Reinartz, H. Tietze, G. Will, K.D. Miiller and U. Steigenberger, Physica B 180 181 (1992) 917. [3] W. Schmidt, H. Tietze-Jaensch and R. Geick, Proc. ICANS XII 1993, Abingdon, U.K., RAL report no. 94-025 (1994) 1-292.