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High-speed time-resolved crystallography with neutrons: A feasibility study
Nuclear Instruments and Methods in Physics Research A292 (1990) 731-733 North-Holland
731
Letter to the Editor HIGH-SPEED TIMErRESOLVED CRYSTALLOGRAPHY WITH NEfu`TRONS : A FEASIBILITY STUDY P. CONVERT, R. HOCK and T. VOGT
Institut Laue-Langevin, B.P. 156 X, 38042 Grenoble Cedex, France Received 29 January 1990 With longitudinal ultrasound pulses matching the resonance frequency of a silicon-quartz transducer system, the transition between the vibrating and nonvibrating state is exvunined, using a stroboscopic method in which the intensity of the silicon 111 reflection is monitored against a variable delay time T2. The experiment demonstrates the feasibility of measuring reversible processes influencing nuclear or magnetic peaks within a time resolution of 15 to 40 ILs. In recent years substantial progress has been made in the field of highly time-resolved crystallography with neutrons; for example, Niimura and Muto were able to observe the transient phenomena of the polarization reversal of nitrogroups in sodium nitrate in an external electrical field using pulsed neutrons [1] . With time-resolved crystallography we observe processes in the microsecond range that involve reversible structurai changes within a crystallographic or magnetic lattice. We use a stroboscopic method applicable to all reversible processes, where the data collection in a short thâse' window can be repeated over a large number of synchronized cycles. Assuming that in a given time interval of the synchronized cycle the system under investigation is seen in the same physical state, the data collected with a constant delay time over a large number of cycles
14
0.1 MHz
can be added up. In the following we describe an experiment showing the limits of the applied method and its possible use in the near future. Stroboscopic measurements require certain instrument specifications which are well matched by the D20 diffractometer at the ILL [2] : a high flux (ca. 107 neutrons/ca? s) to collect data in a reasonable number of cycles, a multidetector (12 .8° in 29, wire spacing 0.1*) to observe a Bragg peak or even a part of a powder diffraction pattern, and adequate electronics. The time resolution is mainly governed by two factors: a neutron travelling with a certain velocity v gives rise to a time uncertainty 8t l while passing through a sample and detector with finite thickness (detector 40 mm, our sample 2.5 mm), and the incoming neutron beam has a wavelength spread leading to a spread in
p,1 16.36MHz
FREQUENCY [MHz] Fig. 1 . Frequency response of a vibrating silicon single crystal using 2.4 A neutrons .
0168-9002/90/$03.50 0 1990 - Elsevier Science Publishers 13.V. (North-Holland)
732
P. Convert et al. / Crystallography with neutrons
time 812 while travelling the distance 1=1 .46 m between the sample and detector. Considering this boundary condition, a time resolution of roughly 15 Ws is expected for a wavelength of 0.8 A, and 40 Ws for 2.4 A. To verify this, we studied the time response of a silicon single crystal to the application of a longitudinal sound wave. For that purpose D20 was used in its four-circle mode. The sound wave was generated in a 15 MHz x-cut quartz transducer glued onto one of the sides of a plate-shaped silicon single crystal with dimensions of 10 x 10 x 2.5 mm for the height, length and thickness, respectively. The 111 reflection was set up in Bragg geometry . In the first part of the experiment the frequency response of the coupled transducer-silicon system was determined by measuring the Bragg-peak intensity as a function of the applied rf frequency . Fig . 1 shows the obtained data. The resonance frequency indicated by the maximum reduction of extinction was found at 15.21 MHz. The reduction of extinction is due to an increase of the 8d/d of the crystal, increasing the acceptance 8X/11 via the interaction with the sound wave. A second intensity maximum is visible at 15 .63 MHz, probably caused by a second parasitic resonant mode of the system transducer-silicon. This reduction of extinction is a well-known phenomenon and was recently reviewed by Kulda [3] . In the second part of the experiment we were interested in the time response of the crystal to a pulsed sound field . The quartz transducer was excited with a rf pulse of 2500 Ws length and a repetition rate of 5000 Ws. This corresponds to one synchronized cycle. The frequency generator initialized the data acquisition electronics at the beginning of the first cycle. Two time slices of a length T3 = 20 Rs separated by Ti = 2500 ILs were shifted over the transition between vibrating and norivibrating crystal, using a delay time T2 varying from 880 to 1120 ps in steps of 20 p.s. The total counting time for a peak was t = 0 .5 s, corresponding to n = 25 000 cycles. By plotting the intensity of the Bragg peak against the delay time T2, the evolution of the intensity as a function of the sound excitation strength can be reconstructed as shown in fig. 2. Here a time slice of T3 = 20 his was used, showing one intermediate peak between vibrating and nonvibrating state, indicating a time resolution of roughly 40 us using neutrons with J1 = d  We have also represented schematically the time scale employed in the measurement, indicating how the two time slices move. Using neutrons with 0.8 A wavelength and T3 = 5 Ws, two intermediate intensity values between the vibrating and nonvibrating state can be observed . The response of the crystal to the sound excitation is almost instantaneous . The transducer should vibrate resonantly after approximately 3 rf periods, corresponding do 0.2 Ws at 15 MHz. Thus the intensity increase is solely due to the reduction of extinction by
2500Ns
ON 26
`ÎÎÎlÎ,ÎÎ,1'11I wwWWI
1
,
4s* T3-20ps
i rf -pulse
25ma
I I
1l I n
I I I
uulllnlll ~~ ultulu n 111111111111 ~ 111111111111''
LTI-.442 acquisition
I l
K2-n T3
n _3 slic@ 2
n
alite, pulse-length-TI .2.6 ms slice " T3 - 20 ps delay ; T2 1, fry ° v-vv iv 1120 Ps by steps of 20 ps
st
.t
Fig. 2. Time response of a silicon single crystal to a pulsed ultrasonic field using 2.4 A neutrons. increasing the acceptance of the crystal. This process is faster than the time resolution of this setup. The method allows a very precise r.casure.ment of the time resolution of the used experimental setup . The current data acquisition system had been realized five years ago by Epaud [5]. It consists of one synchronization CAMAC module and four CAMAC sealer units. Each sealer unit has 32 sealers with 24 bits parallel in the entrance, allowing a very high counting rate from the independent 128 cells of the PSD. The 32 sealers are followed by a microprocessor (Intel 8085) with 4K EPROM for the program and 16K RAM to record up to 160 spectra, or slices, of 32 numbers . The four sealer units are driven by the synchronization module which contains 160 x 4 memories for the time and three monitors. This module controls the complete tirnino 1T_ 'T'_ T_ n»miuar nf c1i- .nA -, ..'t if nan »~~"-"" a ~ - l , " Z , e 3 , ""~ "uvv. v a vaawu auav v'vavv~. a ~ vasaa also follow external synchronization signals in a slave or half-slave mode. The minimum length of the time window T3 is 2 Ws with a minimum spacing of Ti = 2500 jis between two slices . An improved acquisition system to be used with the 1600-cell PSD (160 ° in 20, wire spacing 0.1° ) is under construction . The minimum span ing between two slices (T1 ) will be reduced to about 30 1,s. This experiment was meant to be a first feasibility study to determine the time resolution achievable on
P. Convert et al. / Crystallography with neutrons
D20. In the near future, especially with the availability of a larger multidetector [4], this type of measurement should lead to the observation of new interesting phenomena such as transient and metastable phases, relaxation processes triggered by electric or magnetic fields, and might allow the separation of overlapping processes due to their different time response to an external perturbation. Even though we are not able to reach the nanosecond time resolution possible on modern synchrotron sources (see e.g. refs. [6,7]), high-speed crystallography with neutrons offers the advantages that neutrons, compared to X-rays, are a better probe of the bulk and sample environments like furnaces or cryostats, and electric or magnetic fields are relatively straightforward. We also hope to use the neutrons' unique interaction with the magnetic spin to probe relaxation processes, e.g. of magnetic domains. The first studies are promising.
733
References [1] N. Niimura and M. Muto, J. Phys. Soc. Japan 35 (1973) 628 . [2] The Yellow Book - Guide To The Neutron Research Facilities At The ILL -, eds. H. Blank and B. Maier (Grenoble, 1988). [3] J. Kulda, M. Vrana and P. Mikula, Physica B151 (1988) 122 . [4] A. Oed, P. Convert, M. Bemeron, H. Junk, C. Budtz-Joergensen, M.M. Madsen, P. Jonasson and H.W. Schnopper Nucl. Instr. and Meth. A284 (1989) 223. [5] F. Epaud, diplom-engineer thesis, Conservatoire National des Arts et Metiers Centre Agree (CUEFA) (Grenoble, 1984). [6] D. Mills, Phys. Today (April 1984) 22. [7] H. Bartunik, Rev. Phys. Appl. 19 (1984) 671 .
731
Letter to the Editor HIGH-SPEED TIMErRESOLVED CRYSTALLOGRAPHY WITH NEfu`TRONS : A FEASIBILITY STUDY P. CONVERT, R. HOCK and T. VOGT
Institut Laue-Langevin, B.P. 156 X, 38042 Grenoble Cedex, France Received 29 January 1990 With longitudinal ultrasound pulses matching the resonance frequency of a silicon-quartz transducer system, the transition between the vibrating and nonvibrating state is exvunined, using a stroboscopic method in which the intensity of the silicon 111 reflection is monitored against a variable delay time T2. The experiment demonstrates the feasibility of measuring reversible processes influencing nuclear or magnetic peaks within a time resolution of 15 to 40 ILs. In recent years substantial progress has been made in the field of highly time-resolved crystallography with neutrons; for example, Niimura and Muto were able to observe the transient phenomena of the polarization reversal of nitrogroups in sodium nitrate in an external electrical field using pulsed neutrons [1] . With time-resolved crystallography we observe processes in the microsecond range that involve reversible structurai changes within a crystallographic or magnetic lattice. We use a stroboscopic method applicable to all reversible processes, where the data collection in a short thâse' window can be repeated over a large number of synchronized cycles. Assuming that in a given time interval of the synchronized cycle the system under investigation is seen in the same physical state, the data collected with a constant delay time over a large number of cycles
14
0.1 MHz
can be added up. In the following we describe an experiment showing the limits of the applied method and its possible use in the near future. Stroboscopic measurements require certain instrument specifications which are well matched by the D20 diffractometer at the ILL [2] : a high flux (ca. 107 neutrons/ca? s) to collect data in a reasonable number of cycles, a multidetector (12 .8° in 29, wire spacing 0.1*) to observe a Bragg peak or even a part of a powder diffraction pattern, and adequate electronics. The time resolution is mainly governed by two factors: a neutron travelling with a certain velocity v gives rise to a time uncertainty 8t l while passing through a sample and detector with finite thickness (detector 40 mm, our sample 2.5 mm), and the incoming neutron beam has a wavelength spread leading to a spread in
p,1 16.36MHz
FREQUENCY [MHz] Fig. 1 . Frequency response of a vibrating silicon single crystal using 2.4 A neutrons .
0168-9002/90/$03.50 0 1990 - Elsevier Science Publishers 13.V. (North-Holland)
732
P. Convert et al. / Crystallography with neutrons
time 812 while travelling the distance 1=1 .46 m between the sample and detector. Considering this boundary condition, a time resolution of roughly 15 Ws is expected for a wavelength of 0.8 A, and 40 Ws for 2.4 A. To verify this, we studied the time response of a silicon single crystal to the application of a longitudinal sound wave. For that purpose D20 was used in its four-circle mode. The sound wave was generated in a 15 MHz x-cut quartz transducer glued onto one of the sides of a plate-shaped silicon single crystal with dimensions of 10 x 10 x 2.5 mm for the height, length and thickness, respectively. The 111 reflection was set up in Bragg geometry . In the first part of the experiment the frequency response of the coupled transducer-silicon system was determined by measuring the Bragg-peak intensity as a function of the applied rf frequency . Fig . 1 shows the obtained data. The resonance frequency indicated by the maximum reduction of extinction was found at 15.21 MHz. The reduction of extinction is due to an increase of the 8d/d of the crystal, increasing the acceptance 8X/11 via the interaction with the sound wave. A second intensity maximum is visible at 15 .63 MHz, probably caused by a second parasitic resonant mode of the system transducer-silicon. This reduction of extinction is a well-known phenomenon and was recently reviewed by Kulda [3] . In the second part of the experiment we were interested in the time response of the crystal to a pulsed sound field . The quartz transducer was excited with a rf pulse of 2500 Ws length and a repetition rate of 5000 Ws. This corresponds to one synchronized cycle. The frequency generator initialized the data acquisition electronics at the beginning of the first cycle. Two time slices of a length T3 = 20 Rs separated by Ti = 2500 ILs were shifted over the transition between vibrating and norivibrating crystal, using a delay time T2 varying from 880 to 1120 ps in steps of 20 p.s. The total counting time for a peak was t = 0 .5 s, corresponding to n = 25 000 cycles. By plotting the intensity of the Bragg peak against the delay time T2, the evolution of the intensity as a function of the sound excitation strength can be reconstructed as shown in fig. 2. Here a time slice of T3 = 20 his was used, showing one intermediate peak between vibrating and nonvibrating state, indicating a time resolution of roughly 40 us using neutrons with J1 = d  We have also represented schematically the time scale employed in the measurement, indicating how the two time slices move. Using neutrons with 0.8 A wavelength and T3 = 5 Ws, two intermediate intensity values between the vibrating and nonvibrating state can be observed . The response of the crystal to the sound excitation is almost instantaneous . The transducer should vibrate resonantly after approximately 3 rf periods, corresponding do 0.2 Ws at 15 MHz. Thus the intensity increase is solely due to the reduction of extinction by
2500Ns
ON 26
`ÎÎÎlÎ,ÎÎ,1'11I wwWWI
1
,
4s* T3-20ps
i rf -pulse
25ma
I I
1l I n
I I I
uulllnlll ~~ ultulu n 111111111111 ~ 111111111111''
LTI-.442 acquisition
I l
K2-n T3
n _3 slic@ 2
n
alite, pulse-length-TI .2.6 ms slice " T3 - 20 ps delay ; T2 1, fry ° v-vv iv 1120 Ps by steps of 20 ps
st
.t
Fig. 2. Time response of a silicon single crystal to a pulsed ultrasonic field using 2.4 A neutrons. increasing the acceptance of the crystal. This process is faster than the time resolution of this setup. The method allows a very precise r.casure.ment of the time resolution of the used experimental setup . The current data acquisition system had been realized five years ago by Epaud [5]. It consists of one synchronization CAMAC module and four CAMAC sealer units. Each sealer unit has 32 sealers with 24 bits parallel in the entrance, allowing a very high counting rate from the independent 128 cells of the PSD. The 32 sealers are followed by a microprocessor (Intel 8085) with 4K EPROM for the program and 16K RAM to record up to 160 spectra, or slices, of 32 numbers . The four sealer units are driven by the synchronization module which contains 160 x 4 memories for the time and three monitors. This module controls the complete tirnino 1T_ 'T'_ T_ n»miuar nf c1i- .nA -, ..'t if nan »~~"-"" a ~ - l , " Z , e 3 , ""~ "uvv. v a vaawu auav v'vavv~. a ~ vasaa also follow external synchronization signals in a slave or half-slave mode. The minimum length of the time window T3 is 2 Ws with a minimum spacing of Ti = 2500 jis between two slices . An improved acquisition system to be used with the 1600-cell PSD (160 ° in 20, wire spacing 0.1° ) is under construction . The minimum span ing between two slices (T1 ) will be reduced to about 30 1,s. This experiment was meant to be a first feasibility study to determine the time resolution achievable on
P. Convert et al. / Crystallography with neutrons
D20. In the near future, especially with the availability of a larger multidetector [4], this type of measurement should lead to the observation of new interesting phenomena such as transient and metastable phases, relaxation processes triggered by electric or magnetic fields, and might allow the separation of overlapping processes due to their different time response to an external perturbation. Even though we are not able to reach the nanosecond time resolution possible on modern synchrotron sources (see e.g. refs. [6,7]), high-speed crystallography with neutrons offers the advantages that neutrons, compared to X-rays, are a better probe of the bulk and sample environments like furnaces or cryostats, and electric or magnetic fields are relatively straightforward. We also hope to use the neutrons' unique interaction with the magnetic spin to probe relaxation processes, e.g. of magnetic domains. The first studies are promising.
733
References [1] N. Niimura and M. Muto, J. Phys. Soc. Japan 35 (1973) 628 . [2] The Yellow Book - Guide To The Neutron Research Facilities At The ILL -, eds. H. Blank and B. Maier (Grenoble, 1988). [3] J. Kulda, M. Vrana and P. Mikula, Physica B151 (1988) 122 . [4] A. Oed, P. Convert, M. Bemeron, H. Junk, C. Budtz-Joergensen, M.M. Madsen, P. Jonasson and H.W. Schnopper Nucl. Instr. and Meth. A284 (1989) 223. [5] F. Epaud, diplom-engineer thesis, Conservatoire National des Arts et Metiers Centre Agree (CUEFA) (Grenoble, 1984). [6] D. Mills, Phys. Today (April 1984) 22. [7] H. Bartunik, Rev. Phys. Appl. 19 (1984) 671 .