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Development of new neutron spin echo spectrometer based on neutron spin interferometry
Physica B 311 (2002) 102–105
Development of new neutron spin echo spectrometer based on neutron spin interferometry S. Tasakia,*, T. Ebisawaa, M. Hinoa, T. Kawaia, D. Yamazakia, N. Achiwab, R. Maruyamac, S. Kawakamic a
Research Reactor Institute Kyoto University, 1010 Kumatori-cho, Ossaka, 590-0494 Japan b Faculty of Science, Kyushu University, Japan c Faculty of Engineering, Kyoto University, Japan
Abstract A multilayer spin splitter (MSS) generates the phase difference between the two neutron spin states, one of which is parallel to the direction of the magnetic field and the other is anti-parallel to it. Since the phase difference is equivalent to the Larmor precession angle, MSS enables us to construct a new type of the neutron spin echo (NSE) spectrometer. The new NSE spectrometer has properties; (1) the size of the spectrometer is small compared with a conventional NSE spectrometer, since the phase shift originates from the neutron flight path difference through the gap layer of the MSS, (2) the neutron spin echo time is proportional to the neutron wavelength. The feasibility of the new NSE spectrometer to the pulsed neutron source and the renewal cold neutron beam line, C3-1-2 at the JRR-3M reactor in the Japan Atomic Energy Research Institute (JAERI ) are reported. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Neutron spin echo; Multilayer spin splitter
1. Introduction The multilayer spin splitter (MSS) is a neutron optical device consisting of a non-magnetic multilayer, a gap layer and a magnetic multilayer deposited in series on the silicon wafer as shown in Fig. 1. The top magnetic mirror reflects one spin state while the bottom non-magnetic mirror reflects the other spin state and the gap layer generates the path length difference between the two spin states. Its function is equivalent to the Larmor precession magnet in the conventional *Corresponding author. Tel.: +81-724-51-2340; fax: +81724-51-2620. E-mail address: [email protected] (S. Tasaki).
spin echo instrument [1]. A neutron polarized in the plane perpendicular to the magnetic field is regarded quantum-mechanically as the coherently superposed state of the two spin states, one of which has the spin direction parallel to that of the magnetic field and the other is anti-parallel to it. When such a polarized neutron is incident on a MSS, two neutron spin components are reflected separately and the relative phase shift is created through the gap layer of an order of 1 mm thickness. The relative phase shift is equivalent to the Lamor precession in a magnetic field and called the quantum precession of the neutron spin. The quantum precession, i.e. the phase shift by the MSS is produced by the path difference through the gap layer and thus it allow us to construct the
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 1 1 7 - 6
S. Tasaki et al. / Physica B 311 (2002) 102–105
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Fig. 1. Structure of MSS.
Fig. 2. Structure of spin echo spectrometer using MSS.
small size of the NSE instrument around 1 m in length. The basic idea for the new spin echo spectrometer is that the Larmor precession magnet is replaced by the MSS. The new NSE spectrometer utilizes four MSSs as shown in Fig. 2 [3]. In order to avoid polarization reduction due to the beam divergence, the (++) arrangement of MSS is adopted. In this set-up, the spin echo time tNSE is given by [2] tNSE ¼
4D sin y ; v
ð1Þ
where D; y and v are the thickness of the gap layer, an incident angle of neutron on the MSS and a neutron velocity [3]. The Eq. (1) shows that the thicker the gap layer and the larger the incident angle, the energy resolution becomes higher. However it is difficult to fabricate the MSS with a thick gap layer because it requires the overall uniformity over the surface of the gap layer
and the very small interface roughness between layers. The other problem is that the thick layer deposited on the silicon substrate is easy to peel off. In the recent investigation, [4] the MSS fabricated by the vacuum evaporation method had the homogeneity of the gap layer estimated to ( It should be lowered less than 50 A ( to be 66.2 A. construct a NSE spectrometer using MSSs. We have a plan to fabricate the MSS with the ionsputtering method. The MSS–NSE spectrometer has advantages as follows; (1) the very weak magnetic field is required to work the magnetic mirror of the MSS and the spin flip efficiency is also high, (2) ‘the number of precessions’ is independent of the magnetic field integral. These advantages enables us to construct the small size of the MSS–NSE spectrometer o1 m 1 m 1 m. The short length reduces the frame overlap region in a time of flight spectrum and for this reason the MSS–NSE spectrometer is suitable for the pulsed neutron source.
S. Tasaki et al. / Physica B 311 (2002) 102–105
104
In this report, we discuss the characteristics of the MSS–NSE spectrometer applied to a pulsed neutron source. A renewal cold neutron beam line at JRR-3M in JAERI is also presented.
2. Applicability to the pulsed neutron sources In order to apply the MSS–NSE spectrometer to the pulsed neutron source, the following technical problems should be solved. 1. Polarizer and analyzer mirrors should be supermirrors. The Permalloy (PA)/Ge multilayer ( is with a stacking thickness above 8000 A required. This problem is expected to be resolved by using the ion-sputtering method for the fabrication. 2. Both magnetic and non-magnetic mirrors of MSS should be supermirrors applicable to the pulsed neutron with a wide wavelength range. 3. The spin flippers should be also applicable to the pulsed neutron beam with a very wide wavelength range and the time-of-flight measurement. For the MSS–NSE spectrometer, the spin echo time tNSE is represented by the following equation: tNSE
4D sin y ; ¼ v
ð2Þ
where v is the velocity of the neutron, y the neutron incident angle on the MSS. The significant difference from the other spin echo methods is that the spin echo time is inversely proportional to v; not v3 : Assuming that the quasi-elastic scattering spectrum from the sample obeys the Gaussian distribution with standard deviation s; the polarization PNSE of the spin echo signal is represented with tNSE ; 2 t s : ð3Þ PNSE pexp NSE _2 A polarizability of NSE signal simulated for the MSS–NSE spectrometer as a function of neutron wavelength is shown in Fig. 3. Here we assume the gap layer thickness of the MSS to be 10 mm, a neutron incident angle 1.11, and s are 100 and
Fig. 3. Polarization of NSE signal for MSS–NSE as a function of neutron wavelength.
1000 neV. The MSS–NSE spectrometer with a gap layer of 10 mm could distinguish the quasi-elastic scattering involved in the energy of several hundreds neV. Since the tNSE is inversely proportional to v; the MSS–NSE spectrometer has its advantages that it can give detailed information on the quasi-elastic scattering.
3. A renewal cold neutron beam line at JRR-3M reactor We have renewed the C3-1-2 beam line at JRR3M reactor in Japan Atomic Energy Research Institute (JAERI) for developing the new type of the spectrometer. In the previous arrangement of the C3-1-2 beam line, a quadruple monochroma( tor system (QUAD) was installed and 12.6 Amonochromatized neutron beam was extracted for neutron reflectometry and spin interferometry [6]. QUAD has been replaced by a bender system to get three beam lines with more intense beam. We are installing; (1) a neutron refractometer with an intense magnetic field, (2) a new type of the neutron spin echo instrument, and (3) a neutron reflectometer/a neutron spin interferometer. The detail is reported elsewhere [7]. The schematic view of the neutron bender is shown in Fig. 4. The neutron beam from the main cold neutron guide is devided into two parts, each
S. Tasaki et al. / Physica B 311 (2002) 102–105
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of the next element [8]. These concaved elements allow the bender to accept the beam with a large divergence angle. We are now constructing the neutron reflectometer and the test bench for polarized neutrons at the monochromatic beam line to perform tests of optical elements in the spectrometers, and the spin interferometory system at the second beam line. Fig. 4. A new neutron bender installed at C3-1-2 port of JRR3M reactor.
of which has a 10 mm 50 mm beam cross section. One of beams is reflected four times by the 2.1 Qsupermirror led to the neutron refractometer. The neutron wavelength for this beam is longer than ( The beam intensity is about 4 105 n/cm2 s. 9.2 A. The other beam is incident on the bender at the incident angle slightly larger than that of the former beam and reflected six times by the 2.1 Qsupermirror. The neutron wavelength of this beam ( The beam intensity is about is longer than 9.8 A. 5 2 2 10 n/cm s. Near the end of the second beam line, a triple monochromator system is inserted to take out the monochromatized beam. The monochromators are multilayer mirrors with a d( and the number of layers of 100 spacing of 134 A which was fabricated with the vacuum evaporation instrument in the KUR [5]. The wavelength and its resolution of the monochromatized beam is ( 12.5 A75.5%. Typical beam intensity is 1000 cps with 1/1000 rad beam divergence. Each supermirror element of the bender is concaved to focus the reflected beam on the center
Acknowledgements This work is supported by the inter-university program for common use KURRI and JAERI facility, and financially supported by a Grant-inAid for Scientific Research from the Japanese Ministry of Education, Science and Culture (No. 11480124, No. 08404014, No. 10440122).
References [1] T. Ebisawa, S. Tasaki, T. Kawai, M. Hino, T. Akiyoshi, N. Achiwa, Y. Otake, H. Funahashi, J. Phys. Soc. Japan 65 (Suppl. A) (1996) 66–70. [2] F. Mezei, Neutron Spin Echo, Lecture Notes in Physics, Springer, Berlin, 1980. [3] S. Tasaki, T. Ebisawa, M. Hino, J. Phys. Chem. Solid (1999) 1607. [4] S. Tasaki, et al., J. Phys. Soc. Japan, in press. [5] S. Tasaki, T. Ebisawa, T. Akiyoshi, T. Kawai, S. Okamoto, Nucl. Instrum. Methods A 355 (1995) 501. [6] T. Ebisawa, S. Tsaki, Y. Otake, H. Funahashi, K. Soyama, N. Torikai, Y. Matsushita, Physica B 213–214 (1995) 901. [7] J. Suzuki et al., in press. [8] T. Ebisawa et al., in press.
Development of new neutron spin echo spectrometer based on neutron spin interferometry S. Tasakia,*, T. Ebisawaa, M. Hinoa, T. Kawaia, D. Yamazakia, N. Achiwab, R. Maruyamac, S. Kawakamic a
Research Reactor Institute Kyoto University, 1010 Kumatori-cho, Ossaka, 590-0494 Japan b Faculty of Science, Kyushu University, Japan c Faculty of Engineering, Kyoto University, Japan
Abstract A multilayer spin splitter (MSS) generates the phase difference between the two neutron spin states, one of which is parallel to the direction of the magnetic field and the other is anti-parallel to it. Since the phase difference is equivalent to the Larmor precession angle, MSS enables us to construct a new type of the neutron spin echo (NSE) spectrometer. The new NSE spectrometer has properties; (1) the size of the spectrometer is small compared with a conventional NSE spectrometer, since the phase shift originates from the neutron flight path difference through the gap layer of the MSS, (2) the neutron spin echo time is proportional to the neutron wavelength. The feasibility of the new NSE spectrometer to the pulsed neutron source and the renewal cold neutron beam line, C3-1-2 at the JRR-3M reactor in the Japan Atomic Energy Research Institute (JAERI ) are reported. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Neutron spin echo; Multilayer spin splitter
1. Introduction The multilayer spin splitter (MSS) is a neutron optical device consisting of a non-magnetic multilayer, a gap layer and a magnetic multilayer deposited in series on the silicon wafer as shown in Fig. 1. The top magnetic mirror reflects one spin state while the bottom non-magnetic mirror reflects the other spin state and the gap layer generates the path length difference between the two spin states. Its function is equivalent to the Larmor precession magnet in the conventional *Corresponding author. Tel.: +81-724-51-2340; fax: +81724-51-2620. E-mail address: [email protected] (S. Tasaki).
spin echo instrument [1]. A neutron polarized in the plane perpendicular to the magnetic field is regarded quantum-mechanically as the coherently superposed state of the two spin states, one of which has the spin direction parallel to that of the magnetic field and the other is anti-parallel to it. When such a polarized neutron is incident on a MSS, two neutron spin components are reflected separately and the relative phase shift is created through the gap layer of an order of 1 mm thickness. The relative phase shift is equivalent to the Lamor precession in a magnetic field and called the quantum precession of the neutron spin. The quantum precession, i.e. the phase shift by the MSS is produced by the path difference through the gap layer and thus it allow us to construct the
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 1 1 7 - 6
S. Tasaki et al. / Physica B 311 (2002) 102–105
103
Fig. 1. Structure of MSS.
Fig. 2. Structure of spin echo spectrometer using MSS.
small size of the NSE instrument around 1 m in length. The basic idea for the new spin echo spectrometer is that the Larmor precession magnet is replaced by the MSS. The new NSE spectrometer utilizes four MSSs as shown in Fig. 2 [3]. In order to avoid polarization reduction due to the beam divergence, the (++) arrangement of MSS is adopted. In this set-up, the spin echo time tNSE is given by [2] tNSE ¼
4D sin y ; v
ð1Þ
where D; y and v are the thickness of the gap layer, an incident angle of neutron on the MSS and a neutron velocity [3]. The Eq. (1) shows that the thicker the gap layer and the larger the incident angle, the energy resolution becomes higher. However it is difficult to fabricate the MSS with a thick gap layer because it requires the overall uniformity over the surface of the gap layer
and the very small interface roughness between layers. The other problem is that the thick layer deposited on the silicon substrate is easy to peel off. In the recent investigation, [4] the MSS fabricated by the vacuum evaporation method had the homogeneity of the gap layer estimated to ( It should be lowered less than 50 A ( to be 66.2 A. construct a NSE spectrometer using MSSs. We have a plan to fabricate the MSS with the ionsputtering method. The MSS–NSE spectrometer has advantages as follows; (1) the very weak magnetic field is required to work the magnetic mirror of the MSS and the spin flip efficiency is also high, (2) ‘the number of precessions’ is independent of the magnetic field integral. These advantages enables us to construct the small size of the MSS–NSE spectrometer o1 m 1 m 1 m. The short length reduces the frame overlap region in a time of flight spectrum and for this reason the MSS–NSE spectrometer is suitable for the pulsed neutron source.
S. Tasaki et al. / Physica B 311 (2002) 102–105
104
In this report, we discuss the characteristics of the MSS–NSE spectrometer applied to a pulsed neutron source. A renewal cold neutron beam line at JRR-3M in JAERI is also presented.
2. Applicability to the pulsed neutron sources In order to apply the MSS–NSE spectrometer to the pulsed neutron source, the following technical problems should be solved. 1. Polarizer and analyzer mirrors should be supermirrors. The Permalloy (PA)/Ge multilayer ( is with a stacking thickness above 8000 A required. This problem is expected to be resolved by using the ion-sputtering method for the fabrication. 2. Both magnetic and non-magnetic mirrors of MSS should be supermirrors applicable to the pulsed neutron with a wide wavelength range. 3. The spin flippers should be also applicable to the pulsed neutron beam with a very wide wavelength range and the time-of-flight measurement. For the MSS–NSE spectrometer, the spin echo time tNSE is represented by the following equation: tNSE
4D sin y ; ¼ v
ð2Þ
where v is the velocity of the neutron, y the neutron incident angle on the MSS. The significant difference from the other spin echo methods is that the spin echo time is inversely proportional to v; not v3 : Assuming that the quasi-elastic scattering spectrum from the sample obeys the Gaussian distribution with standard deviation s; the polarization PNSE of the spin echo signal is represented with tNSE ; 2 t s : ð3Þ PNSE pexp NSE _2 A polarizability of NSE signal simulated for the MSS–NSE spectrometer as a function of neutron wavelength is shown in Fig. 3. Here we assume the gap layer thickness of the MSS to be 10 mm, a neutron incident angle 1.11, and s are 100 and
Fig. 3. Polarization of NSE signal for MSS–NSE as a function of neutron wavelength.
1000 neV. The MSS–NSE spectrometer with a gap layer of 10 mm could distinguish the quasi-elastic scattering involved in the energy of several hundreds neV. Since the tNSE is inversely proportional to v; the MSS–NSE spectrometer has its advantages that it can give detailed information on the quasi-elastic scattering.
3. A renewal cold neutron beam line at JRR-3M reactor We have renewed the C3-1-2 beam line at JRR3M reactor in Japan Atomic Energy Research Institute (JAERI) for developing the new type of the spectrometer. In the previous arrangement of the C3-1-2 beam line, a quadruple monochroma( tor system (QUAD) was installed and 12.6 Amonochromatized neutron beam was extracted for neutron reflectometry and spin interferometry [6]. QUAD has been replaced by a bender system to get three beam lines with more intense beam. We are installing; (1) a neutron refractometer with an intense magnetic field, (2) a new type of the neutron spin echo instrument, and (3) a neutron reflectometer/a neutron spin interferometer. The detail is reported elsewhere [7]. The schematic view of the neutron bender is shown in Fig. 4. The neutron beam from the main cold neutron guide is devided into two parts, each
S. Tasaki et al. / Physica B 311 (2002) 102–105
105
of the next element [8]. These concaved elements allow the bender to accept the beam with a large divergence angle. We are now constructing the neutron reflectometer and the test bench for polarized neutrons at the monochromatic beam line to perform tests of optical elements in the spectrometers, and the spin interferometory system at the second beam line. Fig. 4. A new neutron bender installed at C3-1-2 port of JRR3M reactor.
of which has a 10 mm 50 mm beam cross section. One of beams is reflected four times by the 2.1 Qsupermirror led to the neutron refractometer. The neutron wavelength for this beam is longer than ( The beam intensity is about 4 105 n/cm2 s. 9.2 A. The other beam is incident on the bender at the incident angle slightly larger than that of the former beam and reflected six times by the 2.1 Qsupermirror. The neutron wavelength of this beam ( The beam intensity is about is longer than 9.8 A. 5 2 2 10 n/cm s. Near the end of the second beam line, a triple monochromator system is inserted to take out the monochromatized beam. The monochromators are multilayer mirrors with a d( and the number of layers of 100 spacing of 134 A which was fabricated with the vacuum evaporation instrument in the KUR [5]. The wavelength and its resolution of the monochromatized beam is ( 12.5 A75.5%. Typical beam intensity is 1000 cps with 1/1000 rad beam divergence. Each supermirror element of the bender is concaved to focus the reflected beam on the center
Acknowledgements This work is supported by the inter-university program for common use KURRI and JAERI facility, and financially supported by a Grant-inAid for Scientific Research from the Japanese Ministry of Education, Science and Culture (No. 11480124, No. 08404014, No. 10440122).
References [1] T. Ebisawa, S. Tasaki, T. Kawai, M. Hino, T. Akiyoshi, N. Achiwa, Y. Otake, H. Funahashi, J. Phys. Soc. Japan 65 (Suppl. A) (1996) 66–70. [2] F. Mezei, Neutron Spin Echo, Lecture Notes in Physics, Springer, Berlin, 1980. [3] S. Tasaki, T. Ebisawa, M. Hino, J. Phys. Chem. Solid (1999) 1607. [4] S. Tasaki, et al., J. Phys. Soc. Japan, in press. [5] S. Tasaki, T. Ebisawa, T. Akiyoshi, T. Kawai, S. Okamoto, Nucl. Instrum. Methods A 355 (1995) 501. [6] T. Ebisawa, S. Tsaki, Y. Otake, H. Funahashi, K. Soyama, N. Torikai, Y. Matsushita, Physica B 213–214 (1995) 901. [7] J. Suzuki et al., in press. [8] T. Ebisawa et al., in press.