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A semiautomatic scanning system for nuclear emulsions
NUCLEAR INSTRUMENTS
AND METHODS 89 0 9 7 0 )
289-290;
(~) NORTH-HOLLAND
PUBLISHING CO.
A S E M I A U T O M A T I C SCANNING SYSTEM FOR NUCLEAR E M U L S I O N S c. YAMAGUCHI, T. SHINTOMI and M. MASUDA Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
Received 14 September 1970 An electric apparatus for semiautomatic scanning of nuclear emulsions has been developed. It provides a high stability, a low drift and a good reproducibility.
The pattern of a track is expressed in Cartesian coordinates, namely those of the top and end points of the track (also the intermediate points for a curved one). These are measured and digitized by electrical means and memorized on a paper tape. By feeding this information to a computer, the energy and incident angle of the track can be calculated and also one can exclude the duplicate measurement of the same track. The methods for measuring each coordinate are as follows: For X-coordinate: X-displacement is measured by a successive passage of Moire fringes, the diffraction patterns produced by two gratings which convert a small displacement to a large one. The passage of the fringes is counted by means of photoelectric ceils. For Y-coordinate: The displacement is measured by a linear transformer. The inside movable ferrite core changes a mutual coupling constant of the linear transformer, hence the output voltage of the secondary coil. The output voltage is digitized by a digital voltmeter onto a paper tape. For Z-coordinate: A helical potentiometer is connected with a focusing shaft of a microscope, and the depth is measured by the rotating angle of the shaft. The voltage corresponding to the rotating angle is measured by the same digital voltmeter. The block diagram for the system is shown in fig. I. The main problem for the apparatus was to develop
a power supply for the linear transformer. To obtain an accuracy of measurement of position within a micron extending over 10 mm, the voltage stability of the oscillator for the linear transformer must be controlled within 1 x 10 -4. To acquire this accuracy the whole electrical equipment must be stabilized within the same order of stability, and, therefore, the negative feedback was fully employed. The whole circuit of the voltage-stabilized oscillator is shown in fig. 2. The special notice must be paid for the standard voltage supply and the rectifier circuit. It goes without saying that the standard voltage supply must have an extremely high stability. For this purpose the special Zener diode ZD and resistor R4 whose temperature coefficient is 2 x 10 -5 (20 ppm)/°C have been used. The equal stability is required for the gain of the dc amplifier and the rectifier. This requirement has been satisfied by using resistors with low temperature coefficient for R1, R 2 and R a. The amount of feedback of the de amplifier is 60 dB with its open loop gain of 75 dB. This reduces the temperature coefficient of the rectifying diodes D 1. The ten turn helical potentiometer and the 1 kHz power supply are used for Z coordinate measurement. 1 k Hz Oscillator + ~2v • '......
CdS
Power Amplifier A
Linear Transformer
Identification of Trad~ ~, "7' ]
I P°teoti°I meter
+I~V
.~ y____J Linear JTransforrner,
°~""~x4 Ernutsion
I
MoireFfing~ +25V
[3 C. Amplifier
Fig. 1. Block diagram
of the
system.
Fig. 2. Circuit
289
Rectifier
o f the 1 k H z
-ISV
Standard Source voltage-stabilized
oscillator.
290
c. YAMAGUCHI et al.
Since the nuclear particles come into the emulsion with its glancing angle of about 15 ° , the contribution of Z coordinate to the total length of a track is a tenth of that of the X and/or Y coordinates. Therefore, no such high stability is required for this power supply, and a mechanical oscillator has been used. As for helical potentiometer, it provides a linearity of 0.1%. The resolving power of the equipment of Moire fringes was 1 #m and its reproducibility was extremely good. The jittering of the voltage power supply for the linear transformer was 1.5 mV (fwhm) at 3.5 V (r.m.s.) output, i.e. the stability of 4 x 10 -4. This
|00
v) El 0
U
5 (/~m) D ( ~ ) ~< - x 100. L(#m)
6O
Os~
ss2o
s~z~
Output Voltage (mY) Fig. 3. Jittering of the output of the 1 kHz voltage-stabilized oscillator.
XlO~ *° •
7~ /;'.'.. ~ '/D(%)= o
or...\ ~5 U
•
'('~' x ,0o
, e
•
[ ' .".: . - 2
"
---12.
t. 'i,.
°o
I,
stability corresponds to about 3/~m in length. Fig. 3 shows this short time drift of the power supply. The time constant of the rectifier circuit was 1.5 x 10 -2 sec. The larger the gain of the differential amplifier is, the more stable the output of the power amplifier will be, but it would cause an unstable result for the differential amplifier. The gain was chosen 26 dB. The long time drift was 7 x 10-4/10 h. Since the measurement of a track is completed in not more than a minute, the long time drift is less important than the jittering. To examine the performance of the apparatus, the proton tracks from the 4°Ca(y,p) reaction were measured. Fig. 4 shows a relation of the length of the track to the difference of the length when each track was measured twice in a random time interval. In this reaction the nuclear plates were set so that the protons enter the emulsion in the direction of X-coordinate. It is seen that for most of the tracks the length L and the difference D in two measurements are in the relation of:
~
• .'*-.
~'
~
Difference(%) Fig. 4. A relation of the length of proton tracks from the 4°Ca (7, p) reaction to the difference of the lengths in measurements when each track was measured twice by this apparatus.
This suggests that the difference of lengths in two measurements is almost independent of the length of a track. The dots in the upper region of the curve are expected due to the misunderstanding of the incident point of the track where the grains were hard to be detected. The error of measurement is mathematically expected as half of the difference in two measurements. The relative error tends to become smaller for measuring the longer tracks, i.e. less than 0.25% for 700 pm proton tracks and 1.3% for 200/~m, which correspond to 20 keV for 12 MeV tracks and 40 keV for 5.5 MeV. Thus the tracks were measured almost within the difference of 5/~m, and therefore an error less than 2.5/~m was expected. Since the reading error in measurement is fairly large, this apparatus itself provides a much smaller error then 2.5/~m. Appreciable results have been obtained. This apparatus conferred a great benefit to the scanner reducing his prodigious labour and saving much time. This was significantly efficient when there were many tracks in a microscope view. The time of scanning including the following data process was reduced to about a quarter of the previous one. Providing this apparatus, the artificial error in measurement was certainly eliminated to a great extent. The authors would like to express their thanks to the Itoh Science Foundation for financial support.
AND METHODS 89 0 9 7 0 )
289-290;
(~) NORTH-HOLLAND
PUBLISHING CO.
A S E M I A U T O M A T I C SCANNING SYSTEM FOR NUCLEAR E M U L S I O N S c. YAMAGUCHI, T. SHINTOMI and M. MASUDA Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
Received 14 September 1970 An electric apparatus for semiautomatic scanning of nuclear emulsions has been developed. It provides a high stability, a low drift and a good reproducibility.
The pattern of a track is expressed in Cartesian coordinates, namely those of the top and end points of the track (also the intermediate points for a curved one). These are measured and digitized by electrical means and memorized on a paper tape. By feeding this information to a computer, the energy and incident angle of the track can be calculated and also one can exclude the duplicate measurement of the same track. The methods for measuring each coordinate are as follows: For X-coordinate: X-displacement is measured by a successive passage of Moire fringes, the diffraction patterns produced by two gratings which convert a small displacement to a large one. The passage of the fringes is counted by means of photoelectric ceils. For Y-coordinate: The displacement is measured by a linear transformer. The inside movable ferrite core changes a mutual coupling constant of the linear transformer, hence the output voltage of the secondary coil. The output voltage is digitized by a digital voltmeter onto a paper tape. For Z-coordinate: A helical potentiometer is connected with a focusing shaft of a microscope, and the depth is measured by the rotating angle of the shaft. The voltage corresponding to the rotating angle is measured by the same digital voltmeter. The block diagram for the system is shown in fig. I. The main problem for the apparatus was to develop
a power supply for the linear transformer. To obtain an accuracy of measurement of position within a micron extending over 10 mm, the voltage stability of the oscillator for the linear transformer must be controlled within 1 x 10 -4. To acquire this accuracy the whole electrical equipment must be stabilized within the same order of stability, and, therefore, the negative feedback was fully employed. The whole circuit of the voltage-stabilized oscillator is shown in fig. 2. The special notice must be paid for the standard voltage supply and the rectifier circuit. It goes without saying that the standard voltage supply must have an extremely high stability. For this purpose the special Zener diode ZD and resistor R4 whose temperature coefficient is 2 x 10 -5 (20 ppm)/°C have been used. The equal stability is required for the gain of the dc amplifier and the rectifier. This requirement has been satisfied by using resistors with low temperature coefficient for R1, R 2 and R a. The amount of feedback of the de amplifier is 60 dB with its open loop gain of 75 dB. This reduces the temperature coefficient of the rectifying diodes D 1. The ten turn helical potentiometer and the 1 kHz power supply are used for Z coordinate measurement. 1 k Hz Oscillator + ~2v • '......
CdS
Power Amplifier A
Linear Transformer
Identification of Trad~ ~, "7' ]
I P°teoti°I meter
+I~V
.~ y____J Linear JTransforrner,
°~""~x4 Ernutsion
I
MoireFfing~ +25V
[3 C. Amplifier
Fig. 1. Block diagram
of the
system.
Fig. 2. Circuit
289
Rectifier
o f the 1 k H z
-ISV
Standard Source voltage-stabilized
oscillator.
290
c. YAMAGUCHI et al.
Since the nuclear particles come into the emulsion with its glancing angle of about 15 ° , the contribution of Z coordinate to the total length of a track is a tenth of that of the X and/or Y coordinates. Therefore, no such high stability is required for this power supply, and a mechanical oscillator has been used. As for helical potentiometer, it provides a linearity of 0.1%. The resolving power of the equipment of Moire fringes was 1 #m and its reproducibility was extremely good. The jittering of the voltage power supply for the linear transformer was 1.5 mV (fwhm) at 3.5 V (r.m.s.) output, i.e. the stability of 4 x 10 -4. This
|00
v) El 0
U
5 (/~m) D ( ~ ) ~< - x 100. L(#m)
6O
Os~
ss2o
s~z~
Output Voltage (mY) Fig. 3. Jittering of the output of the 1 kHz voltage-stabilized oscillator.
XlO~ *° •
7~ /;'.'.. ~ '/D(%)= o
or...\ ~5 U
•
'('~' x ,0o
, e
•
[ ' .".: . - 2
"
---12.
t. 'i,.
°o
I,
stability corresponds to about 3/~m in length. Fig. 3 shows this short time drift of the power supply. The time constant of the rectifier circuit was 1.5 x 10 -2 sec. The larger the gain of the differential amplifier is, the more stable the output of the power amplifier will be, but it would cause an unstable result for the differential amplifier. The gain was chosen 26 dB. The long time drift was 7 x 10-4/10 h. Since the measurement of a track is completed in not more than a minute, the long time drift is less important than the jittering. To examine the performance of the apparatus, the proton tracks from the 4°Ca(y,p) reaction were measured. Fig. 4 shows a relation of the length of the track to the difference of the length when each track was measured twice in a random time interval. In this reaction the nuclear plates were set so that the protons enter the emulsion in the direction of X-coordinate. It is seen that for most of the tracks the length L and the difference D in two measurements are in the relation of:
~
• .'*-.
~'
~
Difference(%) Fig. 4. A relation of the length of proton tracks from the 4°Ca (7, p) reaction to the difference of the lengths in measurements when each track was measured twice by this apparatus.
This suggests that the difference of lengths in two measurements is almost independent of the length of a track. The dots in the upper region of the curve are expected due to the misunderstanding of the incident point of the track where the grains were hard to be detected. The error of measurement is mathematically expected as half of the difference in two measurements. The relative error tends to become smaller for measuring the longer tracks, i.e. less than 0.25% for 700 pm proton tracks and 1.3% for 200/~m, which correspond to 20 keV for 12 MeV tracks and 40 keV for 5.5 MeV. Thus the tracks were measured almost within the difference of 5/~m, and therefore an error less than 2.5/~m was expected. Since the reading error in measurement is fairly large, this apparatus itself provides a much smaller error then 2.5/~m. Appreciable results have been obtained. This apparatus conferred a great benefit to the scanner reducing his prodigious labour and saving much time. This was significantly efficient when there were many tracks in a microscope view. The time of scanning including the following data process was reduced to about a quarter of the previous one. Providing this apparatus, the artificial error in measurement was certainly eliminated to a great extent. The authors would like to express their thanks to the Itoh Science Foundation for financial support.