- Email: [email protected]
Bent Si monochromator—multi-detector neutron diffractometer installed at B4 super-mirror thermal guide tube in KUR
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 529 (2004) 169–171
Bent Si monochromator—multi-detector neutron diffractometer installed at B4 super-mirror thermal guide tube in KUR N. Achiwaa,*, S. Kawanob, M. Hinob, P. Mikulac, M. Onob, T. Fukunagab a
Graduate School of Science, Osaka University, Toyonaka, Osaka-fu 560-0043, Japan Research Reactor Institute, Kyoto University, Kumatori, Osaka-fu 590-0494, Japan c Nuclear Physics Institute, 250 68 Rez near Prague, Czech Republic
b
Abstract A new multi-detector neutron diffractometer has been installed at B4 thermal supermirror neutron guide in KUR, using a new bent Si monochromator developed by Mikula et al. and Ono et al.. Here we report resolutions of powder diffraction patterns by the multi-detector neutron diffractometer, which mainly depend on a radius of sample. Bragg diffraction optics by bent perfect crystal shows improvement of resolution without loss of luminosity and the multidetector on the same 2y arm can gain the intensity without loosing resolution. r 2004 Elsevier B.V. All rights reserved. PACS: 61.12.e; 61.12. Ex; 61.12.Ld Keywords: Neutron diffraction; Bragg diffraction optics; Focusing
1. Introduction A new powder neutron diffractometer with multi-detector has been installed at B4 thermal supermirror neutron guide, using a new perfect bent Si monochromator developed by Mikula et al. and Ono et al. [1–3]. Several advantages of bent
perfect crystal (BPC) against flat mosaic monochromator are summarized as follows: * *
*
*
*Corresponding author. Tel.: +81-724-52-7167; fax: +81724-51-2635. E-mail address: [email protected] (N. Achiwa).
*
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.04.199
Open beams without Soller collimators. Beam condensation due to asymmetric diffraction. Predictability and reproducibility of the reflectivity. Higher peak reflectivity than in case of mosaic crystals. Peak reflectivity does not depend on the thickness of the crystal.
ARTICLE IN PRESS 170 * *
N. Achiwa et al. / Nuclear Instruments and Methods in Physics Research A 529 (2004) 169–171
Focusing in real and momentum space. Increase of wavelength resolution without luminosity decrease.
Here we report resolutions of the powder diffractometer for different radii of sample with a monochromatic wavelength of 0.1632 nm.
2. Bragg reflection optics by bent perfect crystal Six slabs of Si monochromator crystals with dimensions of 20 cm 23 mm 3 mm of which (3 1 1) plane is parallel to the widest surface were bent so as to focus (3 1 1) Bragg reflection horizontally as well as vertically by tilting 3 stages of paired slabs [3]. The distance from the monochromator to the sample position is L ¼ 2 m [3]. The angle divergence of Bragg reflection of powder sample by the focused monochromatic beam is given by following equation[1,2]. L DW2 ¼ DW2 2aSM 1 1 : ð1Þ R sin WS Here, aSM ¼ tan yS =tan yM is the dispersion parameter, DW1 DW2 are divergence of monochromatic and sample reflections, WS ; WM are half of scattering angles for sample and monochromator,
RM is the bending radius, as shown in Fig. 1. Here for the radius RM ; RM ¼ 2LMS =½sin yM ð2 1=aSM Þ;
ð2Þ
D2W2 in Eq. (1) shows minimum at some value of the dispersion parameter aSM ¼ tan yS =tan yM : For a fixed RM ; a minimum Dd=d resolution take places at larger scattering angle compared with that of a flat monochromator. In the present paper the behavior is convinced by observing Bragg reflections of the powder samples in 2y-dependence of the resolution, Dd=d for different sample radius. The monochromatic bending radius RM is choosed as 9 m for L ¼ 2 m.
3. High luminosity of the powder diffractometer A combination of supermirror thermal guide [4], bent perfect Si monochromator and multiple detectors can serve higher luminosity of the powder diffractometer and lower back ground comparing that in the reactor room in KURRI. The diffractometer is shown in Fig. 2. Monochromator angle 2WM can be varied from 45 to 90 which covers wave length from 0.1253 to 2.316 nm. The 2WS range from 5 to 150 can cover Q range from 3.35 to 54.4 nm1 for l ¼ 0:1632 nm. Since the multiple detectors locate on the same 2ys arm, each detector collects neutrons of
Supermirror thermal neutron guide
Thermal neutron guide
Monochromator
Polycrystalline sample L ∆ 2
∆ 1
Si (311) Bent perfect crystal Monochromator
Detectors
Goniometer Detectors
Fig. 1. Sketch of a powder diffractometer with the BPC monochromator in combination with multiple detectors.
Fig. 2. A multi-detector neutron diffractometer with bent perfect monochromator installed at B4 thermal supermirror neutron guide.
ARTICLE IN PRESS N. Achiwa et al. / Nuclear Instruments and Methods in Physics Research A 529 (2004) 169–171 0.09
Fe3O4
14000
5mmphi 8mmphi
5mmphi 8mmphi
0.08 0.07
10000
0.06
8000
∆d/d
Intensity / 120 sec
12000
6000
0.05 0.04 0.03
4000
0.02
2000
0.01 0.00
0 0
20
40
60
80
100
120
140
0
20
Fig. 3. Powder patterns of magnetite Fe3O4 sample of which diameters are 5 and 8 mm, respectively. 1.8
5mmphi
1.6
40
60
80
100
120
140
2 Theta (degree)
2 Theta (degree)
Fig. 5. 2y-dependence of resolution, Dd=d of the diffractometer for two sample diameters of 5 and 8 mm.
The resolution is not directly proportional to the sample diameter. Since the slit just before the detectors is 5 mm and the distance from the sample to detector is 62 cm, an additional Dy of 0.46 is included in the angular width of each Bragg reflections.
8mmphi
1.4
FWHM (degree)
171
1.2 1.0 0.8 0.6 0.4
Acknowledgements
0.2 0.0 0
20
40
60
80
100
120
140
2 Theta (degree) Fig. 4. 2y-dependence of full-width at half-maximum(FWHM) of each Bragg reflection for the data in Fig. 3.
different angles during the scanning. Each neutron counts are added after correction of the each 2ys angles. 4. Performance of the powder diffractometer Fig. 3 shows powder patterns of magnetite Fe3O4 for l ¼ 0:1632 nm for two sample diameters 5 and 8 mm. The 2y-dependences of FWHM of each Bragg reflections for the data in Fig. 3 are shown in Fig. 4. The resolutions, Dd=d¼ Dy=tan y were calculated by using the data in Fig. 4 are shown in Fig. 5.
We thank Dr. Toru Ebisawa of JAERI for the arrangement of the supermirror guide at B4 beam hole in KUR and Professor Yuji Kawabata of KURRI for continuous supporting through the experiment. The Bragg diffraction optics investigations are also in the Czech Republic supported by the grants of GA-CR (No. 202/03/0891), GACAS (No. A1048003) and COST-OC P7.003.
References [1] P. Mikula, J. Kulda, P. Lukas, M. Ono, J. Saroun, M. Vrana, V. Wagner, Physica B 283 (2000) 289. [2] P. Mikula, K. Lukus, J. Saroun, M. Vrana, V. Wagner, J. Phys. Soc. Jpn. 70 (Suppl. A) (2001) 477. [3] M. Ono, P. Mikula, S. Harjo, J. Sawano, J. Phys. Soc. Japan. 70 (Suppl. A) (2001) 486. [4] T. Akiyoshi, T. Ebisawa, T. Kawai, F. Yoshida, M. Ono, S. Tasaki, S. Mitani, T. Kobayashi, S. Okamoto, J. Nucl. Sci. Technol. 29 (1992) 939.
Nuclear Instruments and Methods in Physics Research A 529 (2004) 169–171
Bent Si monochromator—multi-detector neutron diffractometer installed at B4 super-mirror thermal guide tube in KUR N. Achiwaa,*, S. Kawanob, M. Hinob, P. Mikulac, M. Onob, T. Fukunagab a
Graduate School of Science, Osaka University, Toyonaka, Osaka-fu 560-0043, Japan Research Reactor Institute, Kyoto University, Kumatori, Osaka-fu 590-0494, Japan c Nuclear Physics Institute, 250 68 Rez near Prague, Czech Republic
b
Abstract A new multi-detector neutron diffractometer has been installed at B4 thermal supermirror neutron guide in KUR, using a new bent Si monochromator developed by Mikula et al. and Ono et al.. Here we report resolutions of powder diffraction patterns by the multi-detector neutron diffractometer, which mainly depend on a radius of sample. Bragg diffraction optics by bent perfect crystal shows improvement of resolution without loss of luminosity and the multidetector on the same 2y arm can gain the intensity without loosing resolution. r 2004 Elsevier B.V. All rights reserved. PACS: 61.12.e; 61.12. Ex; 61.12.Ld Keywords: Neutron diffraction; Bragg diffraction optics; Focusing
1. Introduction A new powder neutron diffractometer with multi-detector has been installed at B4 thermal supermirror neutron guide, using a new perfect bent Si monochromator developed by Mikula et al. and Ono et al. [1–3]. Several advantages of bent
perfect crystal (BPC) against flat mosaic monochromator are summarized as follows: * *
*
*
*Corresponding author. Tel.: +81-724-52-7167; fax: +81724-51-2635. E-mail address: [email protected] (N. Achiwa).
*
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.04.199
Open beams without Soller collimators. Beam condensation due to asymmetric diffraction. Predictability and reproducibility of the reflectivity. Higher peak reflectivity than in case of mosaic crystals. Peak reflectivity does not depend on the thickness of the crystal.
ARTICLE IN PRESS 170 * *
N. Achiwa et al. / Nuclear Instruments and Methods in Physics Research A 529 (2004) 169–171
Focusing in real and momentum space. Increase of wavelength resolution without luminosity decrease.
Here we report resolutions of the powder diffractometer for different radii of sample with a monochromatic wavelength of 0.1632 nm.
2. Bragg reflection optics by bent perfect crystal Six slabs of Si monochromator crystals with dimensions of 20 cm 23 mm 3 mm of which (3 1 1) plane is parallel to the widest surface were bent so as to focus (3 1 1) Bragg reflection horizontally as well as vertically by tilting 3 stages of paired slabs [3]. The distance from the monochromator to the sample position is L ¼ 2 m [3]. The angle divergence of Bragg reflection of powder sample by the focused monochromatic beam is given by following equation[1,2]. L DW2 ¼ DW2 2aSM 1 1 : ð1Þ R sin WS Here, aSM ¼ tan yS =tan yM is the dispersion parameter, DW1 DW2 are divergence of monochromatic and sample reflections, WS ; WM are half of scattering angles for sample and monochromator,
RM is the bending radius, as shown in Fig. 1. Here for the radius RM ; RM ¼ 2LMS =½sin yM ð2 1=aSM Þ;
ð2Þ
D2W2 in Eq. (1) shows minimum at some value of the dispersion parameter aSM ¼ tan yS =tan yM : For a fixed RM ; a minimum Dd=d resolution take places at larger scattering angle compared with that of a flat monochromator. In the present paper the behavior is convinced by observing Bragg reflections of the powder samples in 2y-dependence of the resolution, Dd=d for different sample radius. The monochromatic bending radius RM is choosed as 9 m for L ¼ 2 m.
3. High luminosity of the powder diffractometer A combination of supermirror thermal guide [4], bent perfect Si monochromator and multiple detectors can serve higher luminosity of the powder diffractometer and lower back ground comparing that in the reactor room in KURRI. The diffractometer is shown in Fig. 2. Monochromator angle 2WM can be varied from 45 to 90 which covers wave length from 0.1253 to 2.316 nm. The 2WS range from 5 to 150 can cover Q range from 3.35 to 54.4 nm1 for l ¼ 0:1632 nm. Since the multiple detectors locate on the same 2ys arm, each detector collects neutrons of
Supermirror thermal neutron guide
Thermal neutron guide
Monochromator
Polycrystalline sample L ∆ 2
∆ 1
Si (311) Bent perfect crystal Monochromator
Detectors
Goniometer Detectors
Fig. 1. Sketch of a powder diffractometer with the BPC monochromator in combination with multiple detectors.
Fig. 2. A multi-detector neutron diffractometer with bent perfect monochromator installed at B4 thermal supermirror neutron guide.
ARTICLE IN PRESS N. Achiwa et al. / Nuclear Instruments and Methods in Physics Research A 529 (2004) 169–171 0.09
Fe3O4
14000
5mmphi 8mmphi
5mmphi 8mmphi
0.08 0.07
10000
0.06
8000
∆d/d
Intensity / 120 sec
12000
6000
0.05 0.04 0.03
4000
0.02
2000
0.01 0.00
0 0
20
40
60
80
100
120
140
0
20
Fig. 3. Powder patterns of magnetite Fe3O4 sample of which diameters are 5 and 8 mm, respectively. 1.8
5mmphi
1.6
40
60
80
100
120
140
2 Theta (degree)
2 Theta (degree)
Fig. 5. 2y-dependence of resolution, Dd=d of the diffractometer for two sample diameters of 5 and 8 mm.
The resolution is not directly proportional to the sample diameter. Since the slit just before the detectors is 5 mm and the distance from the sample to detector is 62 cm, an additional Dy of 0.46 is included in the angular width of each Bragg reflections.
8mmphi
1.4
FWHM (degree)
171
1.2 1.0 0.8 0.6 0.4
Acknowledgements
0.2 0.0 0
20
40
60
80
100
120
140
2 Theta (degree) Fig. 4. 2y-dependence of full-width at half-maximum(FWHM) of each Bragg reflection for the data in Fig. 3.
different angles during the scanning. Each neutron counts are added after correction of the each 2ys angles. 4. Performance of the powder diffractometer Fig. 3 shows powder patterns of magnetite Fe3O4 for l ¼ 0:1632 nm for two sample diameters 5 and 8 mm. The 2y-dependences of FWHM of each Bragg reflections for the data in Fig. 3 are shown in Fig. 4. The resolutions, Dd=d¼ Dy=tan y were calculated by using the data in Fig. 4 are shown in Fig. 5.
We thank Dr. Toru Ebisawa of JAERI for the arrangement of the supermirror guide at B4 beam hole in KUR and Professor Yuji Kawabata of KURRI for continuous supporting through the experiment. The Bragg diffraction optics investigations are also in the Czech Republic supported by the grants of GA-CR (No. 202/03/0891), GACAS (No. A1048003) and COST-OC P7.003.
References [1] P. Mikula, J. Kulda, P. Lukas, M. Ono, J. Saroun, M. Vrana, V. Wagner, Physica B 283 (2000) 289. [2] P. Mikula, K. Lukus, J. Saroun, M. Vrana, V. Wagner, J. Phys. Soc. Jpn. 70 (Suppl. A) (2001) 477. [3] M. Ono, P. Mikula, S. Harjo, J. Sawano, J. Phys. Soc. Japan. 70 (Suppl. A) (2001) 486. [4] T. Akiyoshi, T. Ebisawa, T. Kawai, F. Yoshida, M. Ono, S. Tasaki, S. Mitani, T. Kobayashi, S. Okamoto, J. Nucl. Sci. Technol. 29 (1992) 939.