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PICOSECOND SINGLE ELECTRON PULSES OF 35 MeVTODAI-LINAC AS IRRADIATION SOURCE
S.Tagawa, Y.Katsumura, T.Ueda, and Y.Tabata
Nuclear Engineering Research Lab., Univ. of Tokyo
A picosecond single pulse radiolysis system for emission
spectroscopy with a response down to 18 picoseconds(ps) wasachieved by a combination of fast detection techniques and anintense picosecond single electron pulse produced by 35 MeV
S-band Todai-Linac.(l) The technique of picosecond single pulse
radiolysis will provide a very strong means of studying onearly events in radiation chemistry, radiation biology, andradiation damage of ionic crystals.
During a span of 18 years, early events in radiationinduced reaction have been observed in shorter and shorter
times, starting with microsecond techniques, then followed bynanosecond and picosecond techniques. Picosecond pulse radiolysis has been started by using stroboscopic techniques, which
detect the absorption of reactive species at times from 20 to350 ps.C2)
Then radiation-induced emission has been detectedby a biplanar phototube at times from 60 to 770 ps.(3)The useof a train of picosecond pulses in above-mentioned two cases
leads to an uncertainty in age of a radiation-induced primary
product, if the product does not decay to zero between thepulses. Recently the absorption of reactive species has ~eendetected at times from 100 ps to 3.5 ns by using single }Ulse
stroboscopic pulse radiolysis, although there is still thelong-time limitation of 3.5 ns due to the necessity of using
Cerenkov radiation at analyzing light.(4)We have modified the above-mentioned picosecond pulseradiolysis systems to gain two significant experimental advantages. First, the decay of reactive species can be measured byonly one shot of picosecond single electron pulse and the fastdetection system, although sampling system is essential forabove-mentioned picosecond pulse radiolysis systems. Since aflow system is necessary to avoid overheating and builtup ofradiolytic products for sampling system, a lot of fresh solutions are necessary to be circulated through an irradiation
cell. Second, since a combination of fast detection system andpicosecond single electron pulse is used, there is no long-time
limitation for this picosecond single pulse radiolysis.
REQUIREMENT FOR ELECTRON BEAM AND DETECTION SYSTEM
The following characteristies of electron beam are required
for this picosecond single pulse radiolysis system.
(1) Single pulse without a satellite micropulse on either sideof the main pulse (as shown in Fig. 5)(2) Intense pulse enough to produce detectable concentrationof reactive species in irradiated sample.
(3) Focusing the electron beam to increase the current density.
( 4) Stability of the linac. (beam current and beam spot)(5)
Simple operation of the linac.
The following characteristics of the detection system are required.
(1) A very fast response(2) A wide-time range detection(3) Small jitter of the dection system itself.
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(4) Small timing jitter between the detection system and thepicosecond single pulse
PICOSECOND SINGLE PULSE RADIOLYSIS SYSTEM
Fig. 1 shows the schematic diagram of picosecond singlepulse radiolysis system for emission spectrosco py. Fig. 2 shows
the response of the picosecond single pulse radiolysis systemmeasured by using Cerenkov light induced from electron finestructure pulses of 10 ps duration (estimated value) produced
by a 35 MeV S-hand linac. The observed pulse width is 18 ps.
This pulse width is formed from two component s: the first one
is the pulse width of electron beam itself and the second one is
the rise and fall times of the detection system. Fig. 3 shows
the integrated signal of Cerenkov light pulses induced from one
hundred picosecond single electron pulses. The observed pulse
width is about 70 ps. This indicates the value of the timing
jitter between the detection system and the picosecond single
electron pulse in addition to the time resolution of the detection system and the real width of the single electron pulse.
STUDIES ON EXCITED STATES IN IRRADIATED LIQUID HYDROCARBON
BY USING PICOSECOND SINGLE PULSE RADIOLYSIS SYSTEM
A lot of work has been carried out on excited states ofliquid hydrocarbo ns by absorption and emission spectrosco py.
A number of reviews have been published on excited states ofhydrocarbo ns and energy transfer processes. (5) However, littlework has been done on kinetic behavior of excited states ofliquid hydrocarbo ns in the picosecond time range. The following
subjects have been carried out.
(1) Formation urocesses of excited states of irradiated liquid·hydrocarbo ns(2) Energy transfer mechanism from excited solvent molecules toboth solvent molecules and solute molecules
Fig. 4 shows the growth of the fluorescen ce of solute molecules in the picosecond single pulse radiolysis of irradiatedtoluene solutions by using picosecond single electron pulse
as shown in Fig. 5. The growth of the fluorescen ce of solutemolecules correspond s to the formation of excited solute molecules. As a result of analysis of the experimen tal data suchas the curve of the growth of fluorescen ce, quencher effects,
and temperatur e effects, two different very fast energy transfer processes are found to exist in irradiated liquidhydrocarbo ns. The rate constants of the slower energy transfer
process are an order of l~'M"'se~ 1 as shown in Fig. 4(a) and (b).
This reaction rate is one order faster than that of diffusioncontrolled reaction in these liquid hydrocarbo n solutions. Therate cons~ants of the faster energy transfer process are morethan 10 8 M-se~ 1 as shown in Fig. 4(c). This reaction rate is threeorder faster than that of the diffusion- controlled reaction inthese liquid hydrocarbo n solutions. These two kinds of very fast
energy transfer processes provides new concept of mechanism ofenergy transfer in irradiated liquid hydrocarbo ns. (6)

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REFERENCES
Y.Tabata, J.Tanaka, S.Tagawa, Y.Katsumura, and T.Ueda,J .Atomic Energy Soc. Japan, (1978) ,to be published
M. J.Bronskill and J. W.Hunt, J.Phys. Chern., 72, 3762,(1968)
G.Beck and J. K.Thomas, J.Phys. Chern., 76, 3856, (1972)
C. D.Jonah, Rev. Sci. Instrum., 46, 62 TI975)"Organic Molecular Photophysics", J. B.Birks ed.,Wiley-Interscience, New York, (1973)
S.Tagawa, Y.Katsumura, T.Ueda, and Y.Tabata, Symp. Radiation Chemistry, Sapporo, (1977), Annual Meeting Chern. Soc.,
Yokohama, (1978)

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Fig.l Schematic diagram of apicosecond single pulse radiolysis
system~350ps~

Fig.2 Response of the picosecond
single pulse radio}ysis systemmeasured by using Cerenkov light
induced from electron fine-structure
pulses of 10 ps duration (estimated value) Electron fine-structurepulses are produced by a 35 MeV
S-band linac. The observed pulse
width is 18 ps.

Fig. 3 The integrated signal ofCerenkov light pulses induced
from electron pulses. One hundred
picosecond single electron pulses
are used. The observed pulse widthis about 70 ps.

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~2ns~ ~ 790 ps --.j(a)

(b)

(c)

Fig. 4 Growth of the fluorescence of solute molecules in irradiatedtoluene solutions measured by the picosecond single pulse
radiolysis system(a) 10 mM 1)(-NPO toluene solution
the signal obtained fran one shot of the electron pulse(b) 4 mM DM-POPOP toluene solution
the integrated signal obtained from 256 electron pulses(c) 7. 5 m.l\1[ TPB toluene solution
the signal obtained fran one shot of the electron pulse
a-NPO: 2-(1-naphthyl) -5-phenyloxazo leIl1-POPOP: 1,4-bis-2-(4-m ethyl-5-phenyl oxazole)benzen e
TPB: 1,1,4,4-tetraph enyl-1,3-butad iene
Fig.5 Picosecond single electron pulse
achieved by Tbdai-Linac withsubharmonic buncher used for thepicosecond single pulse radiolysis
system238