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Measurement of the decay time of scintillation intensity by correlation analysis
Volume 4, number 9
MEASUREMENT
CHEMICAL
OF
THE BY
DECAY
PHYSICS
TIME
CORRELATION
OF
SCINTILLATION
1970
XNTENSITY
ANALYSIS
F. AURICH lawn N.Strunski-~?lstftut, Technische Berlin
15 Januw
LETTERS
Uniuersitiit,
West, Gemmay
Received 3 Recomber 1969
The autocorrelation function of scintillations of an organic phosphor exoited by radioactive radiation was measured, yielding a luminescence decay time of 0.4 nsec for the scintillating compound. A correl&or with high time-resolution is described.
The fluctuation of the dark current 0E a pfiotomultiplier and the scintillation of a phosphor excited by radioactive radiation are random processes suitable for investigation by correlation analysis. This paper deals with the measurement of autocorrelation functions (acf) of these fluctuations in order to obtain information about the decay times of scintillation and dark current pulses [If. The mathematical expression for the auto-
Correlator
correlation
function E;eneraEIy rezis
*11(‘)
= & &-I(t)~~I(~
t
85
T)dt.
The dark current of a photomultiplier is composed of Poissson distributed pulses with rlseand falltime depending on the multiplier, Scintillations of an organic SCintiltator are ako composed of Poisson distributed pulses with a rise-
Electmmeter
~1hlcy r53
-
Recorder
Fig. 1. Upper part: block diagram of the electronic system. designed for measuring autocorrelation functions. Lower part: circuit diagram of the microwave corrcfator: D diode hp2375 matched quad. C capacitor IOOpf.Rd disc resistor 50 51, R resistor 10 Id&
CHEMICAL PHYSICS LETTERS
Volune 4. number 9
15 January 1970
built up to measure the autocorrelation functions. The lower part of fig. 1 shows a circuit diagram of the correlator. The input signal is parted equally in a system of coaxial transmission lines. One part of the signal is de!ayed by means of a trombone which is moved by a motor. Multiplication of the two signals is performed in a multiplying bridge circuit proposed by Wilcox [3]. For a complete block diagram of the electronic system see upper part of fig. 1. As a scintillator, a solution of 4,4”‘-bis(butyloctyloxy)-p-quaterphenyl* in xylene (1.4 g/l) was used [4]. The scintillations were excited by g&r J3 rays. Fig. 2b shows the autocorrelation function *II(T) of the dark current of the photomultiplier. It has been mentioned above that this acf is identical with the acf of a single dark current pulse. It is not possible to evaluate the shape of a single pulse from the acf, because phase information is missing. However, the basis width of a single pulse can be determined and the curve shows a width of 0.36 nsec. Assuming the pulse is Gaussian shaped, rise- and falltime are approximately 0.15 nsec.
L -T
Olnsec
2. a) Autocorrelation function of the scintillations of 4,4”‘-bis ( 2-butyloctylo.xy)-p-quaterphenyl in xylene (1_4g/l). b) Autocorrelation function of the dark current
Fig.
of the photomultiplier.
time depending on the photomultiplier with which the scintillations are measured. The falltime of these pulses is determined by the fluorescence decay time of the organic compound, provided that the fluorescence decay time is much longer than the photomultiplier decay. It is a result of statistical theory of communication [z] that the acf of the fluctuations is identical with the acf of a single pulse of which the fluctuating signal is composed. A correlator with high time-resolution was
Fig. 2a shows the acf of the scintillations of the quaterphenyl compound. As the risetime of the scintillation pulse is short compared with its falltime, the falltime of the acf can be compared directly with the falltime of the luminescence. This yields a luminescence decay time of 0.4
nsec.
The author is indebted to Dr. W. Volland for valuable help. * BIBUQ for scintillntion purposes, Merck, Darmstadt. REFERENCES [l] F. Aurich. Z. Angew. Physik 26 (1969) 374. [2] Y. W. Lee, Statistical theory of communication (Wiley, New York, 196’7). [3] R.H.Wilcox. Proc.1. R. E. 42 0954) 1512. [4] E. SchaumMffel and E. H. Graul, Atompraxis 13 (1967) 2.
MEASUREMENT
CHEMICAL
OF
THE BY
DECAY
PHYSICS
TIME
CORRELATION
OF
SCINTILLATION
1970
XNTENSITY
ANALYSIS
F. AURICH lawn N.Strunski-~?lstftut, Technische Berlin
15 Januw
LETTERS
Uniuersitiit,
West, Gemmay
Received 3 Recomber 1969
The autocorrelation function of scintillations of an organic phosphor exoited by radioactive radiation was measured, yielding a luminescence decay time of 0.4 nsec for the scintillating compound. A correl&or with high time-resolution is described.
The fluctuation of the dark current 0E a pfiotomultiplier and the scintillation of a phosphor excited by radioactive radiation are random processes suitable for investigation by correlation analysis. This paper deals with the measurement of autocorrelation functions (acf) of these fluctuations in order to obtain information about the decay times of scintillation and dark current pulses [If. The mathematical expression for the auto-
Correlator
correlation
function E;eneraEIy rezis
*11(‘)
= & &-I(t)~~I(~
t
85
T)dt.
The dark current of a photomultiplier is composed of Poissson distributed pulses with rlseand falltime depending on the multiplier, Scintillations of an organic SCintiltator are ako composed of Poisson distributed pulses with a rise-
Electmmeter
~1hlcy r53
-
Recorder
Fig. 1. Upper part: block diagram of the electronic system. designed for measuring autocorrelation functions. Lower part: circuit diagram of the microwave corrcfator: D diode hp2375 matched quad. C capacitor IOOpf.Rd disc resistor 50 51, R resistor 10 Id&
CHEMICAL PHYSICS LETTERS
Volune 4. number 9
15 January 1970
built up to measure the autocorrelation functions. The lower part of fig. 1 shows a circuit diagram of the correlator. The input signal is parted equally in a system of coaxial transmission lines. One part of the signal is de!ayed by means of a trombone which is moved by a motor. Multiplication of the two signals is performed in a multiplying bridge circuit proposed by Wilcox [3]. For a complete block diagram of the electronic system see upper part of fig. 1. As a scintillator, a solution of 4,4”‘-bis(butyloctyloxy)-p-quaterphenyl* in xylene (1.4 g/l) was used [4]. The scintillations were excited by g&r J3 rays. Fig. 2b shows the autocorrelation function *II(T) of the dark current of the photomultiplier. It has been mentioned above that this acf is identical with the acf of a single dark current pulse. It is not possible to evaluate the shape of a single pulse from the acf, because phase information is missing. However, the basis width of a single pulse can be determined and the curve shows a width of 0.36 nsec. Assuming the pulse is Gaussian shaped, rise- and falltime are approximately 0.15 nsec.
L -T
Olnsec
2. a) Autocorrelation function of the scintillations of 4,4”‘-bis ( 2-butyloctylo.xy)-p-quaterphenyl in xylene (1_4g/l). b) Autocorrelation function of the dark current
Fig.
of the photomultiplier.
time depending on the photomultiplier with which the scintillations are measured. The falltime of these pulses is determined by the fluorescence decay time of the organic compound, provided that the fluorescence decay time is much longer than the photomultiplier decay. It is a result of statistical theory of communication [z] that the acf of the fluctuations is identical with the acf of a single pulse of which the fluctuating signal is composed. A correlator with high time-resolution was
Fig. 2a shows the acf of the scintillations of the quaterphenyl compound. As the risetime of the scintillation pulse is short compared with its falltime, the falltime of the acf can be compared directly with the falltime of the luminescence. This yields a luminescence decay time of 0.4
nsec.
The author is indebted to Dr. W. Volland for valuable help. * BIBUQ for scintillntion purposes, Merck, Darmstadt. REFERENCES [l] F. Aurich. Z. Angew. Physik 26 (1969) 374. [2] Y. W. Lee, Statistical theory of communication (Wiley, New York, 196’7). [3] R.H.Wilcox. Proc.1. R. E. 42 0954) 1512. [4] E. SchaumMffel and E. H. Graul, Atompraxis 13 (1967) 2.