- Email: [email protected]
KWS-3, the new focusing-mirror ultra small-angle neutron scattering instrument and reflectometer at Jülich
ARTICLE IN PRESS
Physica B 350 (2004) e779–e781
KWS-3, the new focusing-mirror ultra small-angle neutron scattering instrument and reflectometer at Julich . E. Kentzinger*, L. Dohmen, B. Alefeld, U. Rucker, . J. Stellbrink, A. Ioffe, D. Richter, Th. Bruckel . Institut fur Forschungszentrum, Julich, Germany . Festkorperforschung, . .
Abstract In Julich, . a new high-resolution small-angle neutron scattering (SANS) instrument and reflectometer has been built. The principle of this instrument is a one-to-one image of an entrance aperture on a 2D position-sensitive detector by neutron reflection on a double-focusing toroidal mirror. It permits to perform SANS studies with a scattering wave ( 1 with considerable intensity advantages over pinhole-SANS instruments. vector resolution between 103 and 104 A To date, KWS-3 is the worldwide unique SANS instrument running on this principle. We present here the characterization of the image produced by the mirror and a measurement of the scattering from a diffraction grating. r 2004 Elsevier B.V. All rights reserved. PACS: 61.12.Ex Keywords: Focusing mirror; Small-angle neutron scattering; Reflectometry
1. Introduction
leading to the following relation:
At a 1 desired wave vector resolution ðdQÞ below ( ; focusing mirror small-angle neutron 103 A scattering (SANS) has considerable intensity advantages over a pinhole SANS instrument [1,2]. It comes from the fact that, for a pinhole SANS instrument, the intensity at sample position ðIP Þ is given by the product of the cross-sections of the entrance pinhole and the cross-section of the sample pinhole and that, for a focusing mirror SANS instrument, the intensity ðIF Þ is only given by the cross-section of the entrance pinhole,
IP 1 B 2: IF dQ
*Corresponding author. Fax: +49-2461-61-2610. E-mail address: [email protected] (E. Kentzinger).
Although the above idea being quite old [3], its technical realization has been possible only in the last decade, due to the manufacturing of very highquality soft X-ray mirrors for synchrotron sources and soft X-ray space telescopes (ROSAT), which fulfill the requirements needed for the smoothness and the slope errors of focusing-mirror SANS [1,4]. We present here KWS-3, the first and to date worldwide unique SANS instrument running on this principle.
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.203
ARTICLE IN PRESS e780
E. Kentzinger et al. / Physica B 350 (2004) e779–e781
2. Characterization of the instrument
105
Empty beam Empty beam with beam stop Background
104 Intensity [a.u]
A description of the instrument has already been given in Ref. [5]. The mirror is a 1:2 m long, 0:1 m wide and 5 cm thick toroidal double focusing Zerodur mirror, of 11 m focal length, and coated ( 65 Cu and 100 A ( Al as a protection with 1000 A layer. At such a short mirror length with respect to the focal length, the toroidal shape is a good enough approximation of an elliptical shape. The reflection plane has been chosen to be horizontal, reducing the deterioration of the image due to gravity. The entrance pinhole is at one focus of the mirror, the other focus is in the detection plane of a 2D position-sensitive detector. The detector is a scintillation detector with 1:5 mm space resolution. For small scattering angles 2y; the wave vector transfer resolution is given by 4p Dl 4p dQ ¼ y þ dy: l l l At the wavelength ðlÞ and wavelength spread ðDl=lÞ considered here (see next paragraph) the first term of this equation is negligible with respect to the second for scattering wave vectors smaller ( 1 : than 103 A The wave vector transfer resolution is therefore given by krE ; dQ ¼ L where k ¼ 2p=l; rE if the entrance aperture and L is the sample-to-detector distance ðL ¼ 9:3 mÞ: The wavelength spectrum at sample position (1:7 m after the mirror centre) has been measured ( to have a Gaussian shape centered around 12:7 A with a full-width at half-maximum of 9%. At this place, the beam is 0:1 m wide, 0:02 m high. The neutron intensity integrated over the complete beam cross-section is 180 n s1 per mm2 crosssection 1of the entrance aperture. At dQ ¼ ( 104 A (i.e. 2 2 mm2 aperture), the neutron intensity at sample position is therefore 720 n s1 : The first intensity profile in Fig. 1 shows the image of a 3 3 mm2 entrance aperture. It has a Gaussian profile over more than three orders of magnitude, with a full-width at half-maximum of 2:4 mm: Of particular importance is the determi-
106
aperture: 3*3 mm2
103 102 101 100
4Γ1/2
10-1 10-2 -40
-30 -20 -10 0 10 20 30 Distance from the beam center [mm]
40
Fig. 1. Intensity profile of the image of a 3 3 mm2 entrance aperture. The first curve is measured without beam stop. The second curve is measured with a beamstop stuck on the detector, reducing the level of scattering from the detector itself. The third curve is a background measurement with the beam shutter closed.
nation of the level of the diffuse halo around the image. It is characterized by determining the contrast ratio I2G1=2 ; defined by the ratio between the intensity measured at 72G1=2 from the beam centre (where G1=2 is the full-width at halfmaximum of the image) and the maximum intensity of the image. We deduce a value of 9:3 104 : In that case, the main contribution to the halo intensity does not come from off-specular scattering from the mirror but from scattering events taking place inside the detector. This can be proven by installing a beamstop in front of the detector, thus strongly reducing the primary beam intensity. As can be seen from the second intensity profile in Fig. 1, the halo intensity is in that case strongly reduced, leading to I2G1=2 ¼ 1:4 104 : The level of the background (third curve in Fig. 1) tells us that an even smaller value can be reached by designing a more efficient beam stop. We would like to point out at this place that a reduction in size of the entrance aperture leads systematically to a reduction of the image size,
ARTICLE IN PRESS E. Kentzinger et al. / Physica B 350 (2004) e779–e781
104 2
aperture: 2*2 mm
Intensity [a.u.]
103
102
101
100 -1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Q [10-3 A-1] Fig. 2. Intensity profile obtained with a diffraction grating placed at sample position (2 2 mm2 entrance aperture).
down to an entrance aperture of 1:5 mm; equal to the spatial resolution of our detector. Therefore, our limitation in wave-vector resolution does not come from our mirror, but from our detector. As a further check of the Q-resolution of the instrument, we show in Fig. 2 the intensity profile of the scattering from a diffraction grating. Up to six diffraction orders are detected. From the distance between the intensity maxima, we deduce a period of 3:6 mm; in good agreement with its nominal value ð3 mmÞ:
3. Applications and future developments KWS-3 can be used to perform high Q-resolution SANS studies on systems with expected correlations ranging from 0.6 to 6 mm: This can be, for example, assemblies of large colloids or of biological molecules. In this range, KWS-3 deli-
e781
vers complementary informations to its neighbour pinhole SANS instruments KWS-1 and KWS-2, which cover the range below 0:6 mm: KWS-3 can also be used as a medium-resolution reflectometer with horizontal sample surfaces. It is therefore well suited for liquid samples. Grazing incidence SANS (GISANS) studies can also be performed to study in-plane correlations in thin films, giving access to an intermediate length scale (0.6–6 mm) between the length scales reachable to GISANS at a pinhole SANS (10–600 nm) and to off-specular scattering at a reflectometer (1–50 mm) [6]. We are now equipping the instrument with polarized neutrons and a polarization analysis covering the whole detector area. For soft matter studies, it will enable to easily separate coherent and incoherent scattering, thus permitting the wider use of nondeuterated samples. It will also broaden its use in the area of magnetism, for example for the study of critical magnetic fluctuations or of systems with dipolar interactions. The instrument is now open to external users. Special funding exists for European user groups in the framework of the program ‘‘Access to research infrastructures’’ supported by the European Union (http://www.neutronscattering.de).
References [1] B. Alefeld, D. Schwann, T. Springer, Nucl. Instrum. Methods A 274 (1989) 210. [2] B. Alefeld, L. Dohmen, D. Richter, Th. Bruckel, . Physica B 276–278 (2000) 52. [3] B. Henke, J.W.M. DuMond, Phys. Rev. 89 (1953) 1300. [4] B. Aschenbach, Rep. Prog. Phys. 48 (1985) 579. [5] B. Alefeld, L. Dohmen, D. Richter, Th. Bruckel, . Physica B 283 (2000) 330. [6] C. Fermon, F. Ott, B. Gilles, A. Marty, A. Menelle, Y. Samson, G. Legoff, G. Francinet, Physica B 267–268 (1999) 162.
Physica B 350 (2004) e779–e781
KWS-3, the new focusing-mirror ultra small-angle neutron scattering instrument and reflectometer at Julich . E. Kentzinger*, L. Dohmen, B. Alefeld, U. Rucker, . J. Stellbrink, A. Ioffe, D. Richter, Th. Bruckel . Institut fur Forschungszentrum, Julich, Germany . Festkorperforschung, . .
Abstract In Julich, . a new high-resolution small-angle neutron scattering (SANS) instrument and reflectometer has been built. The principle of this instrument is a one-to-one image of an entrance aperture on a 2D position-sensitive detector by neutron reflection on a double-focusing toroidal mirror. It permits to perform SANS studies with a scattering wave ( 1 with considerable intensity advantages over pinhole-SANS instruments. vector resolution between 103 and 104 A To date, KWS-3 is the worldwide unique SANS instrument running on this principle. We present here the characterization of the image produced by the mirror and a measurement of the scattering from a diffraction grating. r 2004 Elsevier B.V. All rights reserved. PACS: 61.12.Ex Keywords: Focusing mirror; Small-angle neutron scattering; Reflectometry
1. Introduction
leading to the following relation:
At a 1 desired wave vector resolution ðdQÞ below ( ; focusing mirror small-angle neutron 103 A scattering (SANS) has considerable intensity advantages over a pinhole SANS instrument [1,2]. It comes from the fact that, for a pinhole SANS instrument, the intensity at sample position ðIP Þ is given by the product of the cross-sections of the entrance pinhole and the cross-section of the sample pinhole and that, for a focusing mirror SANS instrument, the intensity ðIF Þ is only given by the cross-section of the entrance pinhole,
IP 1 B 2: IF dQ
*Corresponding author. Fax: +49-2461-61-2610. E-mail address: [email protected] (E. Kentzinger).
Although the above idea being quite old [3], its technical realization has been possible only in the last decade, due to the manufacturing of very highquality soft X-ray mirrors for synchrotron sources and soft X-ray space telescopes (ROSAT), which fulfill the requirements needed for the smoothness and the slope errors of focusing-mirror SANS [1,4]. We present here KWS-3, the first and to date worldwide unique SANS instrument running on this principle.
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.203
ARTICLE IN PRESS e780
E. Kentzinger et al. / Physica B 350 (2004) e779–e781
2. Characterization of the instrument
105
Empty beam Empty beam with beam stop Background
104 Intensity [a.u]
A description of the instrument has already been given in Ref. [5]. The mirror is a 1:2 m long, 0:1 m wide and 5 cm thick toroidal double focusing Zerodur mirror, of 11 m focal length, and coated ( 65 Cu and 100 A ( Al as a protection with 1000 A layer. At such a short mirror length with respect to the focal length, the toroidal shape is a good enough approximation of an elliptical shape. The reflection plane has been chosen to be horizontal, reducing the deterioration of the image due to gravity. The entrance pinhole is at one focus of the mirror, the other focus is in the detection plane of a 2D position-sensitive detector. The detector is a scintillation detector with 1:5 mm space resolution. For small scattering angles 2y; the wave vector transfer resolution is given by 4p Dl 4p dQ ¼ y þ dy: l l l At the wavelength ðlÞ and wavelength spread ðDl=lÞ considered here (see next paragraph) the first term of this equation is negligible with respect to the second for scattering wave vectors smaller ( 1 : than 103 A The wave vector transfer resolution is therefore given by krE ; dQ ¼ L where k ¼ 2p=l; rE if the entrance aperture and L is the sample-to-detector distance ðL ¼ 9:3 mÞ: The wavelength spectrum at sample position (1:7 m after the mirror centre) has been measured ( to have a Gaussian shape centered around 12:7 A with a full-width at half-maximum of 9%. At this place, the beam is 0:1 m wide, 0:02 m high. The neutron intensity integrated over the complete beam cross-section is 180 n s1 per mm2 crosssection 1of the entrance aperture. At dQ ¼ ( 104 A (i.e. 2 2 mm2 aperture), the neutron intensity at sample position is therefore 720 n s1 : The first intensity profile in Fig. 1 shows the image of a 3 3 mm2 entrance aperture. It has a Gaussian profile over more than three orders of magnitude, with a full-width at half-maximum of 2:4 mm: Of particular importance is the determi-
106
aperture: 3*3 mm2
103 102 101 100
4Γ1/2
10-1 10-2 -40
-30 -20 -10 0 10 20 30 Distance from the beam center [mm]
40
Fig. 1. Intensity profile of the image of a 3 3 mm2 entrance aperture. The first curve is measured without beam stop. The second curve is measured with a beamstop stuck on the detector, reducing the level of scattering from the detector itself. The third curve is a background measurement with the beam shutter closed.
nation of the level of the diffuse halo around the image. It is characterized by determining the contrast ratio I2G1=2 ; defined by the ratio between the intensity measured at 72G1=2 from the beam centre (where G1=2 is the full-width at halfmaximum of the image) and the maximum intensity of the image. We deduce a value of 9:3 104 : In that case, the main contribution to the halo intensity does not come from off-specular scattering from the mirror but from scattering events taking place inside the detector. This can be proven by installing a beamstop in front of the detector, thus strongly reducing the primary beam intensity. As can be seen from the second intensity profile in Fig. 1, the halo intensity is in that case strongly reduced, leading to I2G1=2 ¼ 1:4 104 : The level of the background (third curve in Fig. 1) tells us that an even smaller value can be reached by designing a more efficient beam stop. We would like to point out at this place that a reduction in size of the entrance aperture leads systematically to a reduction of the image size,
ARTICLE IN PRESS E. Kentzinger et al. / Physica B 350 (2004) e779–e781
104 2
aperture: 2*2 mm
Intensity [a.u.]
103
102
101
100 -1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Q [10-3 A-1] Fig. 2. Intensity profile obtained with a diffraction grating placed at sample position (2 2 mm2 entrance aperture).
down to an entrance aperture of 1:5 mm; equal to the spatial resolution of our detector. Therefore, our limitation in wave-vector resolution does not come from our mirror, but from our detector. As a further check of the Q-resolution of the instrument, we show in Fig. 2 the intensity profile of the scattering from a diffraction grating. Up to six diffraction orders are detected. From the distance between the intensity maxima, we deduce a period of 3:6 mm; in good agreement with its nominal value ð3 mmÞ:
3. Applications and future developments KWS-3 can be used to perform high Q-resolution SANS studies on systems with expected correlations ranging from 0.6 to 6 mm: This can be, for example, assemblies of large colloids or of biological molecules. In this range, KWS-3 deli-
e781
vers complementary informations to its neighbour pinhole SANS instruments KWS-1 and KWS-2, which cover the range below 0:6 mm: KWS-3 can also be used as a medium-resolution reflectometer with horizontal sample surfaces. It is therefore well suited for liquid samples. Grazing incidence SANS (GISANS) studies can also be performed to study in-plane correlations in thin films, giving access to an intermediate length scale (0.6–6 mm) between the length scales reachable to GISANS at a pinhole SANS (10–600 nm) and to off-specular scattering at a reflectometer (1–50 mm) [6]. We are now equipping the instrument with polarized neutrons and a polarization analysis covering the whole detector area. For soft matter studies, it will enable to easily separate coherent and incoherent scattering, thus permitting the wider use of nondeuterated samples. It will also broaden its use in the area of magnetism, for example for the study of critical magnetic fluctuations or of systems with dipolar interactions. The instrument is now open to external users. Special funding exists for European user groups in the framework of the program ‘‘Access to research infrastructures’’ supported by the European Union (http://www.neutronscattering.de).
References [1] B. Alefeld, D. Schwann, T. Springer, Nucl. Instrum. Methods A 274 (1989) 210. [2] B. Alefeld, L. Dohmen, D. Richter, Th. Bruckel, . Physica B 276–278 (2000) 52. [3] B. Henke, J.W.M. DuMond, Phys. Rev. 89 (1953) 1300. [4] B. Aschenbach, Rep. Prog. Phys. 48 (1985) 579. [5] B. Alefeld, L. Dohmen, D. Richter, Th. Bruckel, . Physica B 283 (2000) 330. [6] C. Fermon, F. Ott, B. Gilles, A. Marty, A. Menelle, Y. Samson, G. Legoff, G. Francinet, Physica B 267–268 (1999) 162.