- Email: [email protected]
Absorption spectroscopy system based on picosecond single electron beams and streak camera
Radiat. Phys.Chem.Vol.23, No. 4, pp. 393-395,1984 Printedin Great Britain.
0146-5724/84 $3.00+ .00 PergamonPressLtd.
ABSORPTION SPECTROSCOPY SYSTEM BASED ON PICOSECOND SINGLE ELECTRON BEAMS A N D STREAK CAMERA H. KOBAVASHI, T. UEDA, T. KOBAYASHI, S. TAGAWA, Y. YOSHIDA and Y. TABATA Nuclear Engineering Research Laboratory, Faculty of Engineering, University of Tokyo, Tokai-mura, Ibaraki, 319-II, Japan (Recieved 20 March 1983)
Abstract--An absorption spectroscopy system with a time response of ~ 50 ps has been developed by using a streak camera with a gate option and picosecond single electron beams (35 MeV, ~ 10 ps pulse width, ,,~ 1.8 kraal/pulse) produced by an S-band linac. The absorption spectroscopy system has been applied to experiments on the recombination of geminate ion pairs in non-polar liquids.
1. I N T R O D U C T I O N A~ S-band linac which can produce picosecond single electron beams (35 MeV, ~ l0 ps pulse width, ~ 1.8 krad/pulse) has been operated since 1977fl ) The ultra short electron pulses generated by the linac and systems for both emission and absorption spectroscopies~2) have been used for studies on primary processes of radiation chemistry, o) A very powerful new absorption spectroscopy system with a time response of ~ 50 ps using the streak camera and 10ps beams has been developed. The absorption signal could be obtained even by single shot operation by using an intense light source. However, in the present experiments, more than 20 shots of the beam were needed to get good signal to noise ratio. 2. ABSORPTION SPECTROSCOPY SYSTEM The block diagram of the newly developed absorption spectroscopy system is shown in Fig. 1. An analyzing light produced by a xenon lamp with a pulse width of 6 #s passes through a monochromator and detected by a streak camera. The absorption signal is processed by a computer system. The intensity of analyzing light, the intensity of absorption and the intensity of Cerenkov light emitted from an irradiated sample are represented by I0, A and E respectively. The experimental procedure is as follows. (1) Only the analyzing light is detected (I0). (2) Both the analyzing light and the beam are introduced synchronously to the cell. The analyzing light, the Cerenkov light and the absorption are detected by the streak camera ( I 0 - A + E).
(3) Only the electron pulse beam is introduced to the cell. Cerenkov fight from the irradiated sample is detected by the streak camera (E). (4) The term of ( I 0 - A) is calculated by subtracting the term of(E) from the term of(I0 - ~,1 + E) and the optical density is calculated by using (I0) and (I0 - A). A rise time of this system has been measured by using the 2 ns sweep mode and was ~ 50 ps. 3. STREAK CAMERA WITH GATE OPTION A streak camera without a gate function is not suitable for detection of analyzing light with a pulse width of several microseconds, because of it's comparatively strong background. The streak camera (Hamamatsu T. V. ¢4)C979) with a gate option (Hamamatsu TV C1795X) has reduced the background and can be used for detection of analyzing light with a pulse width of several microseconds. The gate is opened in a time range of about 400 ns. The streak camera system has 256 channels of time axis. It was impossible to measure the intensity ratio of the background to the analyzing light at each channel of the time axis. The total background intensity of 256 channels could be measured and was compared with the total analyzing light intensity of the same channels. The intensity ratios of the background to the analyzing light at each streak speed are shown in Table 1. The gate option has two gate modes. Each mode is as follows. (a) Externally opened and internally closed mode The gate is opened by the external trigger and is closed by the internal trigger. The trigger for opening 393
H. KoBAYASmet al.
394
~
LAMP
'~ LENS
BEAM CATCHER
2C
U MIRROR
o'
~
m Cyclohexane
MONOCHROMATOR STREAK @
~
CAMERA
0 i0
GRAPHIC DISPLAY
FIG. 1. The block diagram of the absorption spectroscopy system using the streak camera. TABLE 1. THE INTENSITYRATIOSOF BACKGROUNDTO ANALYZING LIGHT. TtIE TOTALBACKGROUNDINTENSITYOF 256 TIMEAXISCHANNELSHAS BEENcoMPAREDWITH THE TOTAL ANALYZINGLIGHTINTENSITYOF THE SAMECHANNEL FULL TIME SCALE
BACKGROUND/ ANALYZINGLIGHT
t20
%
sc
in Cyclohexane
0
o'.o ! ns
0.56ns
7.6 %
2 ns
t.tns
5.2 %
5 ns
2.7 ns
1.7 %
10 ns
4.7 ns
0.9 %
the gate is applied externally. The streak trigger is applied after about 250 ns of this triger and a streak voltage is generated immediately. The trigger for closing the gate is generated internally by picking up the signal of the streak voltage. Since the trigger circuits mounted in the streak camera have their intrinsic delay time, the minimum gate time duration of this mode is about 400 ns as described above. This mode has been used during the experiments. The intensity ratios of the background to the analyzing light at each streak speed of this trigger mode have been measured and are shown in Table 1. (b) Externally opened and externally closed mode The gate is opened by the external ~ g g e r and is closed also by the external trigger. In this mode, two triggers for the gate function and the streak trigger have to be prepared. One trigger for the gate function is used for opening the gate and other is used for closing the gate. Time interval between these two triggers decides the gate time duration. The minimum gate time duration of this mode is about 100 ns. This
2.0 ' (ns)
FIG. 2. Absorption vs time trace observed at 415 nm for 5 mM biphenyl solution in cyclohexane system. The dotted line represent the calculated curve obtained by using the time constant of 53 ps for anion radical formation and the rise time of 50 ps for the detection system.
o' 4C
STREAK SWEEP MODE
t.0 ' Time
,.'o Time
21o (ns)
FIG. 3. Absorption vs time trace observed at 415 nm for 300 mM biphenyl solution in cyclohexane system.
mode should make an advantage to improve the intensity ratio of the background to the analyzing light. The expected intensity ratios of the background to the analyzing light are calculated. These ratios are expected to become less than 2.0~ over the streak sweep modes from 1 to 10 ns and should be small enough for experiments. 4. EXPERIMENTAL RESULTS Here we present some experimental results on the recombination of geminate ion pairs in non-polar liquids. The 10 ns streak sweep mode was used for these experiments. (a) Solution of biphenyi in cyclohexane Figures 2 and 3 show typical absorptions vs time trace observed at 415nm for 5raM and 300ram biphenyl solutions in cyclohexane respectively. Since the rate constant for the reaction of biphenyl with electron in cyclohexane is 2.6 x 1012M - 1sec- i(s) formarion times of the anion radical of biphenyl are 53 and 0.9 ps for 5 and 300 mM biphenyl solutions in cyclohcxane respectively. The details of analysis of the geminate recombination of biphenyl anion radical on the basis of Smoluchowski equation will be pubfished elsewhere. The formation process of anion
Absorption spectroscopy system
m '0 40
i
0,0
i
i
,
LO "
l
2.0
Time (ns)
FxG. 4. Absorption vs time trace observed at 480 nm for
carbon tetrachloride.
radical of biphenyl can be observed in 5 mM biphenyl solution in cyclohexane and the result is shown in Fig. 2. The dotted line shows the calculated value obtained by using the time constant of 53 ps for anion radical formation and the rise time of 50 ps for detection system. While the anion radical of biphenyl decays immediately after a pulse in the case of 300 mM biphenyl solution. (b) Carbon tetrachloride Figure 4 shows the typical absorption vs time trace observed at 480 nm for carbon tetrachloride. Although the identification of the species with the absorption maximum at 480 nm observed in pulse radiolysis of liquid carbon tetrachloride is very controversial at present, the species would be formed from the genimate ion recombination. Figure 4 shows the formation process of the intermediate due to geminate ion recombination in the picosecond time region, although the formation process has been observed in the time region of nanosecond (6) and sub-nanosecondfl)
395
5. C O N C L U S I O N The absorption spectroscopy system with a rise time of ~ 50 ps based on picosecond single electron beams and a streak camera with gate function has been developed. The system has been applied to experiments on the recombination of geminate ion pairs in non-polar liquids. It is basically possible to get an absorption trace by single shot operation. This is the advantageous point of this system, comparing with a stroboscopic pulse radiolysis system (s) which needs a lot of repeated pulsed beams with high repetition rate. REFERENCES 1. (a) H. KOBAYASHI,T. UEDA, T. KOBAYASm,S. TAGAWA and Y. TABATA,Nucl. lnstrum. Mete 1981, 179, 223; (b) H. KOSAY~,~m,T. UEDA,T. KOSAYASm,S. TAOAWA and Y. T~mATA3". Fac. Engng Univ. Tokyo 1981, 36B, 85; (c) Y. TABATA,J. TANAKA,S. TAGAWA,Y. KATSUMU~, T. UI~DAand K. HAS~GAWA,J. Fac. Engng Univ. Tokyo 1978, 34B, 619. 2. H. KOBAYASm,T. UEDA,T. KDBAYASHI,M. WASmOand Y. TABATA,RodioL Phys. Chem. 1983, 21, 13. 3. (a) S. TAGAWA,Y. KA~t.n~rov.Aand Y. TABATA,Radiot. Phys. Chem. 1982, 19, 25; (b) S. TAGAWA,Y. TAnATA,H. KOBAVASmand M. WASmO, Radiat. Phys. Chem. 1982, 19, 193; (c) S. TAGAWA,M. WAsmo, Y. TAnATAand H. KOBAYASm,Radiat. Phys. Chem. 1982, 19, 227. 4. Hamamatsu TV Co., Ltd. 1126-1. Ichino-Cho, Hamamatsu City, Japan. 5. G. BECKand J. K. THOMAS,Chem. Phys. Lett. 1972, 13, 295. 6. (a) C. A. M. VAN DEN ENDE, L. H. LU~I~NS, J. M. WAR-~.Nand A. HUMMEL,Radiat. Phys. Chem. 1982, 19, 455; 03) R. E. BOHLER, Radiat. Phys. Chem. 1983, 21, 139. 7. M. WASHIO,S. TAGAWAand Y. TABATA,Radiat. Phys. Chem. 1982, 21, 239. 8. (a) M. J. BRONSKILL,W. B. TAYLOR, R. K. WOLFF and J. W. HUNT, Rev. Sci. Instrum. 1970, 41, 333; (b) CHARLES D. JONAH Rev. Sci. Instrum. 1975, 46, 62.
0146-5724/84 $3.00+ .00 PergamonPressLtd.
ABSORPTION SPECTROSCOPY SYSTEM BASED ON PICOSECOND SINGLE ELECTRON BEAMS A N D STREAK CAMERA H. KOBAVASHI, T. UEDA, T. KOBAYASHI, S. TAGAWA, Y. YOSHIDA and Y. TABATA Nuclear Engineering Research Laboratory, Faculty of Engineering, University of Tokyo, Tokai-mura, Ibaraki, 319-II, Japan (Recieved 20 March 1983)
Abstract--An absorption spectroscopy system with a time response of ~ 50 ps has been developed by using a streak camera with a gate option and picosecond single electron beams (35 MeV, ~ 10 ps pulse width, ,,~ 1.8 kraal/pulse) produced by an S-band linac. The absorption spectroscopy system has been applied to experiments on the recombination of geminate ion pairs in non-polar liquids.
1. I N T R O D U C T I O N A~ S-band linac which can produce picosecond single electron beams (35 MeV, ~ l0 ps pulse width, ~ 1.8 krad/pulse) has been operated since 1977fl ) The ultra short electron pulses generated by the linac and systems for both emission and absorption spectroscopies~2) have been used for studies on primary processes of radiation chemistry, o) A very powerful new absorption spectroscopy system with a time response of ~ 50 ps using the streak camera and 10ps beams has been developed. The absorption signal could be obtained even by single shot operation by using an intense light source. However, in the present experiments, more than 20 shots of the beam were needed to get good signal to noise ratio. 2. ABSORPTION SPECTROSCOPY SYSTEM The block diagram of the newly developed absorption spectroscopy system is shown in Fig. 1. An analyzing light produced by a xenon lamp with a pulse width of 6 #s passes through a monochromator and detected by a streak camera. The absorption signal is processed by a computer system. The intensity of analyzing light, the intensity of absorption and the intensity of Cerenkov light emitted from an irradiated sample are represented by I0, A and E respectively. The experimental procedure is as follows. (1) Only the analyzing light is detected (I0). (2) Both the analyzing light and the beam are introduced synchronously to the cell. The analyzing light, the Cerenkov light and the absorption are detected by the streak camera ( I 0 - A + E).
(3) Only the electron pulse beam is introduced to the cell. Cerenkov fight from the irradiated sample is detected by the streak camera (E). (4) The term of ( I 0 - A) is calculated by subtracting the term of(E) from the term of(I0 - ~,1 + E) and the optical density is calculated by using (I0) and (I0 - A). A rise time of this system has been measured by using the 2 ns sweep mode and was ~ 50 ps. 3. STREAK CAMERA WITH GATE OPTION A streak camera without a gate function is not suitable for detection of analyzing light with a pulse width of several microseconds, because of it's comparatively strong background. The streak camera (Hamamatsu T. V. ¢4)C979) with a gate option (Hamamatsu TV C1795X) has reduced the background and can be used for detection of analyzing light with a pulse width of several microseconds. The gate is opened in a time range of about 400 ns. The streak camera system has 256 channels of time axis. It was impossible to measure the intensity ratio of the background to the analyzing light at each channel of the time axis. The total background intensity of 256 channels could be measured and was compared with the total analyzing light intensity of the same channels. The intensity ratios of the background to the analyzing light at each streak speed are shown in Table 1. The gate option has two gate modes. Each mode is as follows. (a) Externally opened and internally closed mode The gate is opened by the external trigger and is closed by the internal trigger. The trigger for opening 393
H. KoBAYASmet al.
394
~
LAMP
'~ LENS
BEAM CATCHER
2C
U MIRROR
o'
~
m Cyclohexane
MONOCHROMATOR STREAK @
~
CAMERA
0 i0
GRAPHIC DISPLAY
FIG. 1. The block diagram of the absorption spectroscopy system using the streak camera. TABLE 1. THE INTENSITYRATIOSOF BACKGROUNDTO ANALYZING LIGHT. TtIE TOTALBACKGROUNDINTENSITYOF 256 TIMEAXISCHANNELSHAS BEENcoMPAREDWITH THE TOTAL ANALYZINGLIGHTINTENSITYOF THE SAMECHANNEL FULL TIME SCALE
BACKGROUND/ ANALYZINGLIGHT
t20
%
sc
in Cyclohexane
0
o'.o ! ns
0.56ns
7.6 %
2 ns
t.tns
5.2 %
5 ns
2.7 ns
1.7 %
10 ns
4.7 ns
0.9 %
the gate is applied externally. The streak trigger is applied after about 250 ns of this triger and a streak voltage is generated immediately. The trigger for closing the gate is generated internally by picking up the signal of the streak voltage. Since the trigger circuits mounted in the streak camera have their intrinsic delay time, the minimum gate time duration of this mode is about 400 ns as described above. This mode has been used during the experiments. The intensity ratios of the background to the analyzing light at each streak speed of this trigger mode have been measured and are shown in Table 1. (b) Externally opened and externally closed mode The gate is opened by the external ~ g g e r and is closed also by the external trigger. In this mode, two triggers for the gate function and the streak trigger have to be prepared. One trigger for the gate function is used for opening the gate and other is used for closing the gate. Time interval between these two triggers decides the gate time duration. The minimum gate time duration of this mode is about 100 ns. This
2.0 ' (ns)
FIG. 2. Absorption vs time trace observed at 415 nm for 5 mM biphenyl solution in cyclohexane system. The dotted line represent the calculated curve obtained by using the time constant of 53 ps for anion radical formation and the rise time of 50 ps for the detection system.
o' 4C
STREAK SWEEP MODE
t.0 ' Time
,.'o Time
21o (ns)
FIG. 3. Absorption vs time trace observed at 415 nm for 300 mM biphenyl solution in cyclohexane system.
mode should make an advantage to improve the intensity ratio of the background to the analyzing light. The expected intensity ratios of the background to the analyzing light are calculated. These ratios are expected to become less than 2.0~ over the streak sweep modes from 1 to 10 ns and should be small enough for experiments. 4. EXPERIMENTAL RESULTS Here we present some experimental results on the recombination of geminate ion pairs in non-polar liquids. The 10 ns streak sweep mode was used for these experiments. (a) Solution of biphenyi in cyclohexane Figures 2 and 3 show typical absorptions vs time trace observed at 415nm for 5raM and 300ram biphenyl solutions in cyclohexane respectively. Since the rate constant for the reaction of biphenyl with electron in cyclohexane is 2.6 x 1012M - 1sec- i(s) formarion times of the anion radical of biphenyl are 53 and 0.9 ps for 5 and 300 mM biphenyl solutions in cyclohcxane respectively. The details of analysis of the geminate recombination of biphenyl anion radical on the basis of Smoluchowski equation will be pubfished elsewhere. The formation process of anion
Absorption spectroscopy system
m '0 40
i
0,0
i
i
,
LO "
l
2.0
Time (ns)
FxG. 4. Absorption vs time trace observed at 480 nm for
carbon tetrachloride.
radical of biphenyl can be observed in 5 mM biphenyl solution in cyclohexane and the result is shown in Fig. 2. The dotted line shows the calculated value obtained by using the time constant of 53 ps for anion radical formation and the rise time of 50 ps for detection system. While the anion radical of biphenyl decays immediately after a pulse in the case of 300 mM biphenyl solution. (b) Carbon tetrachloride Figure 4 shows the typical absorption vs time trace observed at 480 nm for carbon tetrachloride. Although the identification of the species with the absorption maximum at 480 nm observed in pulse radiolysis of liquid carbon tetrachloride is very controversial at present, the species would be formed from the genimate ion recombination. Figure 4 shows the formation process of the intermediate due to geminate ion recombination in the picosecond time region, although the formation process has been observed in the time region of nanosecond (6) and sub-nanosecondfl)
395
5. C O N C L U S I O N The absorption spectroscopy system with a rise time of ~ 50 ps based on picosecond single electron beams and a streak camera with gate function has been developed. The system has been applied to experiments on the recombination of geminate ion pairs in non-polar liquids. It is basically possible to get an absorption trace by single shot operation. This is the advantageous point of this system, comparing with a stroboscopic pulse radiolysis system (s) which needs a lot of repeated pulsed beams with high repetition rate. REFERENCES 1. (a) H. KOBAYASHI,T. UEDA, T. KOBAYASm,S. TAGAWA and Y. TABATA,Nucl. lnstrum. Mete 1981, 179, 223; (b) H. KOSAY~,~m,T. UEDA,T. KOSAYASm,S. TAOAWA and Y. T~mATA3". Fac. Engng Univ. Tokyo 1981, 36B, 85; (c) Y. TABATA,J. TANAKA,S. TAGAWA,Y. KATSUMU~, T. UI~DAand K. HAS~GAWA,J. Fac. Engng Univ. Tokyo 1978, 34B, 619. 2. H. KOBAYASm,T. UEDA,T. KDBAYASHI,M. WASmOand Y. TABATA,RodioL Phys. Chem. 1983, 21, 13. 3. (a) S. TAGAWA,Y. KA~t.n~rov.Aand Y. TABATA,Radiot. Phys. Chem. 1982, 19, 25; (b) S. TAGAWA,Y. TAnATA,H. KOBAVASmand M. WASmO, Radiat. Phys. Chem. 1982, 19, 193; (c) S. TAGAWA,M. WAsmo, Y. TAnATAand H. KOBAYASm,Radiat. Phys. Chem. 1982, 19, 227. 4. Hamamatsu TV Co., Ltd. 1126-1. Ichino-Cho, Hamamatsu City, Japan. 5. G. BECKand J. K. THOMAS,Chem. Phys. Lett. 1972, 13, 295. 6. (a) C. A. M. VAN DEN ENDE, L. H. LU~I~NS, J. M. WAR-~.Nand A. HUMMEL,Radiat. Phys. Chem. 1982, 19, 455; 03) R. E. BOHLER, Radiat. Phys. Chem. 1983, 21, 139. 7. M. WASHIO,S. TAGAWAand Y. TABATA,Radiat. Phys. Chem. 1982, 21, 239. 8. (a) M. J. BRONSKILL,W. B. TAYLOR, R. K. WOLFF and J. W. HUNT, Rev. Sci. Instrum. 1970, 41, 333; (b) CHARLES D. JONAH Rev. Sci. Instrum. 1975, 46, 62.