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A binary encoded position-sensitive scintillation hodoscope
NUCLEAR
INSTRUMENTS
AND METHODS
147 ( 1 9 7 7 )
465-469
; (~) N O R T H - H O L L A N D
P U B L I S H I N G CO.
A BINARY ENCODED POSITION-SENSITIVE SCINTILLATION HODOSCOPE* J. H. HOFTIEZER, G. S. MUTCHLER, J. A. BUCHANAN, W. P. MAD1GAN and G. C. PHILLIPS T. W. Bonner Nuclear Laboratories, Rice University, Houston, Texas, U.S.A. Received 23 May 1977 A position-sensitive scintillation hodoscope with reduced photomultiplier use has been built and used in experiments. This device is a fast, economical counter which has good timing characteristics and spatial resolution. Isolated strips of plastic scintillator (NE102) form a single layer (per coordinate) detecting surface, and are coupled by adiabatic light guides to photomultiplier tubes (RCA 8575). The light guides are encoded into a binary readout pattern, termed "'error-free", because the code identifies inefficient and multiple track events or the valid position measurement. These counters were successfully used to measure the incoming pion trajectories in a small angle scattering experiment.
I. Introduction The use of plastic scintillation counters is very common in particle physics experiments. These counters are often used without spatial resolution, but due to the complexity of certain experiments, hodoscopic arrays are sometimes necessary. Since such arrangements can become very elaborate and expensive, a number of schemes to simplify the hodoscopes and incorporate good spatial resolution have been proposedl4). The counter described here incorporates features of many previous proposals. It is similar to the multi-strip scintillation counters (MSSC) ~) but employs a new encoding scheme. 2. Strip counter concept The strip counter hodoscope consists of individual strips of scintillation material placed parallel, yet optically isolated from each other (fig. 1). These strips are coupled by adiabatic Plexiglas light guides to photomultiplier tubes from which the electronic signals that identify the detected position are received. In order to reduce the number of phototubes required from the conventional one per strip2), each strip must be coupled to more than one tube. In this manner a code for the strip position is developed. Interpretation of the code completes the position measurement by the detector system. The encoding scheme previously used in the MSSC-type device was that of binary counting (fig. 2). Light pipes connect each strip to one or more photomultiplier tubes, each of which produces one bit of a binary code. Thus the first strip is connected to the tube representing the first bi* Work supported in part by the U.S. Energy Research and Development Administration.
nary digit; the second to the second; and the third strip is connected to the tube representing the first binary digit and separately connected to the tube representing the second digit, etc. Because of this coding, the number of detectable positions using N phototubes is increased from N to 2'v- 1. During the use of the MSSCs, significant errors were found to be introduced into the data by this binary counting scheme. The errors occurred because false code words are created either when an
cintillator
ight Guide holomulfiplier Tube Fig. l. A schematic diagram of an eighteen element "errorfree" coded strip counter. Each strip is coupled to three photomultiplier tubes which identify its position.
466
Strip #
i 2 3 4 5 6 7 8 9 i0 ii 12 13 14 15
J . H . HOFTIEZER et al. Binary Code
0001 0010 0011 O100 0101 0110 0111 1000 1001 1 0 1 1011 1 1 0 1 1 0 1 1 1 1 1 1
0 0 1 0 1
Decimal
Strip #
I 2 3 /4 5 6 7 8 9 i0 ii 12 13 14 15
i 2 3 4 5 6 7 8 9 i0 ii 12 13 14 15
4321 Bit #
Gray Code Decimal
0001 0011 0010 0110 0111 0101 0100 1100 1101 1 1 1 1110 1 0 1 1 0 1 1 0 0 1 0 0
1 0 1 1 0
i 3 2 6 7 5 4 12 13 15 14 i0 ii 9 8
4321 Bit #
Fig. 2. Two possible encoding schemes which reduce the number of photomultiplier tubes required. The binary counting code was used in previous MSSC-type devices. event was inefficiently detected or when two events occurred within the resolving time of the system. An inefficient event is one in which the proper code for some reason is missing one or more bits; that is, a phototube connected to some strip does not detect the particle in the strip. If such an event occurs, the decoding will generate a false or invalid position measurement. Multiple events also produce false readings. For example, if two particles travel through the system during its resolving time, the arithmetic union of the two codes results. In a binary coding scheme this may be the same as a valid position code, although it will be incorrect. Similarly, if a particle travels at some angle to the counter and triggers two strips which are adjacent, a false position measurement may result. The use of a reflective Gray s) code (fig. 2) in the counter offers some improvement due to the removal of ambiguities near the strip edges; however, the effects of inefficiencies and multiple tracks remain. Thus, to analyze data from the MSSCs, some special method of removing the erroneous measurements is necessary. The major innovation of the present design is the coding employed, which identifies the position of valid readout events or reveals the occurrence
of inefficient and multiple track events. This is accomplished by requiring a specific n u m b e r of active bits for all strips in the counter. The n u m b e r of elements in such a code is given by its binomial coefficient. For N phototubes and of which M are required for a valid readout, the n u m b e r of positions is
-M!(N-M)!" Actually, due to physical considerations, the number detectable is somewhat less. The code elements are the permutations of the N phototubes when taken M at a time. Their order is arbitrary, and subsequently the usual increasing value was used to arrange the code elements. The code, termed " e r r o r f r e e " , can be analyzed accurately because inefficient or multiple events are apparent from the n u m b e r of active bits seen. In either case, it is not equal to M. Such a scheme does not allow as great a reduction in the number of phototubes required per detectable position as do other possible codes. Nevertheless, there is a substantial reduction compared to the more conventional method using one phototube per position.
BINARY ENCODED SCINTILLATION HODOSCOPE Error Free Code
Strip #
Entrc Wi
6 7 8 9
Alum f
Fig. 3. An isometric drawing of the completed strip counter. The counter is quite large ( - 1 m) and heavy ( - 35 kg), yet reasonable sturdy.
3. Construction and implementation T w o hodoscope counters have been constructed. Each consists of identical X and Y coordinates oriented perpendicular to one another (fig. 3). For this application, six (N = 6) phototubes were provided for each coordinate, of which three ( M = 3) were coupled to any given strip. This implies twenty possible code elements, but given the obvious choice of three phototubes on each end of the counter, two code e l e m e n t s (111000 and 000111) were eliminated as special cases. For these codes the corresponding phototubes are all located at one end of the counter. T h u s , the three light guides m u s t all be attached to one end of the scintillation strip. In the remaining cases two phototubes couple to one strip end and the third tube couples to the other. The final code s c h e m e e m ployed is s h o w n in fig. 4. T h e active region of the hodoscope consists of eighteen strips of scintillation plastic (NE102, Pilot F), of either 0.64 c m × 0 . 4 7 c r u x 14.0 cm (the larger counter) or 0 . 3 8 × 0 . 3 2 x 11.5 cm (small counter). The smallest dimension is the counter thickness. Each strip is highly polished for good light transmission and wrapped with aluminized mylar to isolate it optically from the other strips. Light guides are of two types; those which attach
467
i0 ii 12 13 14 15 16 17 18
001 001 00 0 1 Ol 0 1 0 1 0 1 0 1 1 ! 1 1 1 1 1 1 1
0 0 0 0 0 0 1 1 1
654
Decimal Value
1 0 0 0 1 1 1
0 1 1 0 1 1 0 0 1
i 0 i i 0 i 0 1 0
I 1 0 i 1 0 1 0 0
ii 13 14 19 21 22 25 26 28
0 0 0 1 1 1 0 0 0
0 1 1 0 0 1 0 0 1
i 0 1 0 1 0 0 1 0
I 1 0 1 0 0 1 O 0
35 37 38 41 42 44 49 50 52
3 2 1 Bit #
Fig. 4. The "'error-free'" code as used in the strip counter. The code identifies eighteen counter positions or the occurrence of inefficient and multiple track events with six photomultiplier tubes. to the strips singly and those which attach in pairs (fig. 5). T h e s e were arranged according to the error-flee code and bent along the m o s t convenient path to the appropriate photomultiplier tube position. T h e light guides were also wrapped in aluminized mylar and epoxied (using NE580) to the scintillation strips. This a r r a n g e m e n t was m o u n t e d and light-sealed in an a l u m i n u m frame to which the phototubes (RCA 8575) and their bases were attached. Light
Light Guide Scintillator~
~ p,
-
I ~
.22 rn
~
.12 m
'
I
~
.22 m
t
Fig. 5. A drawing of a typical element of the strip counter. The elements could be individually removed from the counter; however, it was found that each coordinate was most easily built as a unit.
468
J.H.
HOFTIEZER
et al.
~|ir
Cove~ . MAX I
v Trailer
MAX
2 3 4
" MAX 6 • MAY I MAY
5
MAX MAY
t e -_,L_~
6 I
," MAY 6 • MBX I 3
Scale MAB
54
~• MBX 6 • MBY I
MAY
MAYS
MAB
6 __CLR
" ~BY s
MABE Cave
MBY 2
Trailer •
3 4 65 ~
MBYS
MBY
Fig. 6. T h e electronic layout for the strip c o u n t e r s as they were i m p l e m e n t e d during one experiment.
The electronic implementation is shown in fig. 6. When a GATE signal is received, the 6-bit pattern is saved. There are sixty-four possibilities which contain all the output information from the hodoscope. This information can be sorted in a number of ways which are meaningful to the operation of the counter. To monitor the operation three histograms were used. The histogram of valid readout positions [i.e., output containing exactly three (N = 3) active bits] is the most interesting. This profile is the shape of the beam incident on the counter (fig. 7a). A histogram of the number of non-zero digits per event, ranging from zero to six, was useful in determining the efficiency of the hodoscope. Ideally all counts should appear in the three bit column, corresponding to valid position codes. In practice, the occurrence of valid codes was much greater than other types of readouts (fig. 7b). A histogram of the activity of individual phototubes was used to locate noisy or inefficient tubes. For symmetric beams centered on the counter the tubes are equally active.
4. Discussion
The error-free counting efficiency is the primary means of assessing the strip counter performance. This efficiency is given by the ratio of events with exactly three active bits to the total number of events, since only this data can be analyzed
3000
c o
~
~ 75
2000
.~
50
o u
,ooo
: J
-L
125456789101112151415161718 Strip Position
0 123456 -#'Bits
Fig. 7. A b e a m profile h i s t o g r a m (a) and the corresponding efficiencies (b) for one coordinate of the strip counter, taken with a 140 MeV zr beam.
BINARY
ENCODED
SCINTILLATION
uniquely. Remaining event readout patterns are divided into two groups, those which are truly inefficient (containing less than three active bits), and those which are classed with multiple readouts (containing more than three active bits). In the large counter efficiency was 88% error-free, 5% inefficient, and 7% multiple readout events. The small counter was somewhat less efficient; its efficiency was 81% error-free, 15% inefficient, and 4% multiple readout events. While these errorfree efficiency levels are acceptable, levels approaching unity (100%) are much more desirable because the total efficiency of a sequence of strip counter coordinates is a multiplicative function which rapidly decreases. Improvement in the efficiency of the larger counter is most likely to result from a decrease in multiple event readouts. There are indications that many of these are due to adjacent strips in the counter detecting the same traversing particle. If it is assumed that all multiple readout patterns are due to adjacent strips, these events can be assigned a position and added into the data, increasing the efficiency of a sequence of coordinates substantially without distorting the measured distributions. However, using this assumption, the counters are no longer " e r r o r - f r e e " .
HODOSCOPE
469
elastic scattering of pions (both positive and negative) at pion energies from 100 MeV to 300 MeV for various target nuclei6). The counters were used to define the incoming pion trajectory by locating the traversing particle at two points in space. Using the counters, an instantaneous beam intensity of - 3 x 1 0 6 particles per second was possible. Thus, reasonable statistics were obtained in a relatively short time. 6. Conclusion This article describes the development o f a new type of scintillation hodoscope. These devices successfully approach the current limits in both spatial and time resolution of similar instruments. They are safeguarded by the nature of the encoding scheme against the systematic introduction of errors into the data. Further, the counters exhibit n u m e r o u s desirable features such as their reliability and ease of operation, making them appropriate for experimental use. The most severe limitation on the strip counters is imposed by the moderate efficiency of their coordinates, caused not by the concepts involved in the counter design, but rather by the physical dimensions. The use of the strip counter hodoscopes in a small angle scattering experiment has demonstrated successfully the application of the device.
5. Application The strip counter hodoscope is a versatile instrument with applications in many experiments which require spatial knowledge of the trajectories as well as fast timing of high energy particles. A typical application was illustrated in a recent experiment performed at the Los Alamos Meson Physics Facility. This experiment measured the
References 1) L. Y. Lee et al., Nucl. Instr. and Meth. 119 (1974) 29. 2) L. W. AIvarez, Rev. Sci. Instr. 31 (1960) 76. 3) M. W. Collins et al., Nucl. Instr. and Meth. 117 (1974) 339. 4~ D. E. Pellett et al., Nucl. Instr. and Meth. 115 (1974) 135. 5) M. Gardner, Sci. Am. (30 August 1972) 106. 6) W. H. Dragoset, Ph. D. Thesis (Rice University, 1977) unpublished.
INSTRUMENTS
AND METHODS
147 ( 1 9 7 7 )
465-469
; (~) N O R T H - H O L L A N D
P U B L I S H I N G CO.
A BINARY ENCODED POSITION-SENSITIVE SCINTILLATION HODOSCOPE* J. H. HOFTIEZER, G. S. MUTCHLER, J. A. BUCHANAN, W. P. MAD1GAN and G. C. PHILLIPS T. W. Bonner Nuclear Laboratories, Rice University, Houston, Texas, U.S.A. Received 23 May 1977 A position-sensitive scintillation hodoscope with reduced photomultiplier use has been built and used in experiments. This device is a fast, economical counter which has good timing characteristics and spatial resolution. Isolated strips of plastic scintillator (NE102) form a single layer (per coordinate) detecting surface, and are coupled by adiabatic light guides to photomultiplier tubes (RCA 8575). The light guides are encoded into a binary readout pattern, termed "'error-free", because the code identifies inefficient and multiple track events or the valid position measurement. These counters were successfully used to measure the incoming pion trajectories in a small angle scattering experiment.
I. Introduction The use of plastic scintillation counters is very common in particle physics experiments. These counters are often used without spatial resolution, but due to the complexity of certain experiments, hodoscopic arrays are sometimes necessary. Since such arrangements can become very elaborate and expensive, a number of schemes to simplify the hodoscopes and incorporate good spatial resolution have been proposedl4). The counter described here incorporates features of many previous proposals. It is similar to the multi-strip scintillation counters (MSSC) ~) but employs a new encoding scheme. 2. Strip counter concept The strip counter hodoscope consists of individual strips of scintillation material placed parallel, yet optically isolated from each other (fig. 1). These strips are coupled by adiabatic Plexiglas light guides to photomultiplier tubes from which the electronic signals that identify the detected position are received. In order to reduce the number of phototubes required from the conventional one per strip2), each strip must be coupled to more than one tube. In this manner a code for the strip position is developed. Interpretation of the code completes the position measurement by the detector system. The encoding scheme previously used in the MSSC-type device was that of binary counting (fig. 2). Light pipes connect each strip to one or more photomultiplier tubes, each of which produces one bit of a binary code. Thus the first strip is connected to the tube representing the first bi* Work supported in part by the U.S. Energy Research and Development Administration.
nary digit; the second to the second; and the third strip is connected to the tube representing the first binary digit and separately connected to the tube representing the second digit, etc. Because of this coding, the number of detectable positions using N phototubes is increased from N to 2'v- 1. During the use of the MSSCs, significant errors were found to be introduced into the data by this binary counting scheme. The errors occurred because false code words are created either when an
cintillator
ight Guide holomulfiplier Tube Fig. l. A schematic diagram of an eighteen element "errorfree" coded strip counter. Each strip is coupled to three photomultiplier tubes which identify its position.
466
Strip #
i 2 3 4 5 6 7 8 9 i0 ii 12 13 14 15
J . H . HOFTIEZER et al. Binary Code
0001 0010 0011 O100 0101 0110 0111 1000 1001 1 0 1 1011 1 1 0 1 1 0 1 1 1 1 1 1
0 0 1 0 1
Decimal
Strip #
I 2 3 /4 5 6 7 8 9 i0 ii 12 13 14 15
i 2 3 4 5 6 7 8 9 i0 ii 12 13 14 15
4321 Bit #
Gray Code Decimal
0001 0011 0010 0110 0111 0101 0100 1100 1101 1 1 1 1110 1 0 1 1 0 1 1 0 0 1 0 0
1 0 1 1 0
i 3 2 6 7 5 4 12 13 15 14 i0 ii 9 8
4321 Bit #
Fig. 2. Two possible encoding schemes which reduce the number of photomultiplier tubes required. The binary counting code was used in previous MSSC-type devices. event was inefficiently detected or when two events occurred within the resolving time of the system. An inefficient event is one in which the proper code for some reason is missing one or more bits; that is, a phototube connected to some strip does not detect the particle in the strip. If such an event occurs, the decoding will generate a false or invalid position measurement. Multiple events also produce false readings. For example, if two particles travel through the system during its resolving time, the arithmetic union of the two codes results. In a binary coding scheme this may be the same as a valid position code, although it will be incorrect. Similarly, if a particle travels at some angle to the counter and triggers two strips which are adjacent, a false position measurement may result. The use of a reflective Gray s) code (fig. 2) in the counter offers some improvement due to the removal of ambiguities near the strip edges; however, the effects of inefficiencies and multiple tracks remain. Thus, to analyze data from the MSSCs, some special method of removing the erroneous measurements is necessary. The major innovation of the present design is the coding employed, which identifies the position of valid readout events or reveals the occurrence
of inefficient and multiple track events. This is accomplished by requiring a specific n u m b e r of active bits for all strips in the counter. The n u m b e r of elements in such a code is given by its binomial coefficient. For N phototubes and of which M are required for a valid readout, the n u m b e r of positions is
-M!(N-M)!" Actually, due to physical considerations, the number detectable is somewhat less. The code elements are the permutations of the N phototubes when taken M at a time. Their order is arbitrary, and subsequently the usual increasing value was used to arrange the code elements. The code, termed " e r r o r f r e e " , can be analyzed accurately because inefficient or multiple events are apparent from the n u m b e r of active bits seen. In either case, it is not equal to M. Such a scheme does not allow as great a reduction in the number of phototubes required per detectable position as do other possible codes. Nevertheless, there is a substantial reduction compared to the more conventional method using one phototube per position.
BINARY ENCODED SCINTILLATION HODOSCOPE Error Free Code
Strip #
Entrc Wi
6 7 8 9
Alum f
Fig. 3. An isometric drawing of the completed strip counter. The counter is quite large ( - 1 m) and heavy ( - 35 kg), yet reasonable sturdy.
3. Construction and implementation T w o hodoscope counters have been constructed. Each consists of identical X and Y coordinates oriented perpendicular to one another (fig. 3). For this application, six (N = 6) phototubes were provided for each coordinate, of which three ( M = 3) were coupled to any given strip. This implies twenty possible code elements, but given the obvious choice of three phototubes on each end of the counter, two code e l e m e n t s (111000 and 000111) were eliminated as special cases. For these codes the corresponding phototubes are all located at one end of the counter. T h u s , the three light guides m u s t all be attached to one end of the scintillation strip. In the remaining cases two phototubes couple to one strip end and the third tube couples to the other. The final code s c h e m e e m ployed is s h o w n in fig. 4. T h e active region of the hodoscope consists of eighteen strips of scintillation plastic (NE102, Pilot F), of either 0.64 c m × 0 . 4 7 c r u x 14.0 cm (the larger counter) or 0 . 3 8 × 0 . 3 2 x 11.5 cm (small counter). The smallest dimension is the counter thickness. Each strip is highly polished for good light transmission and wrapped with aluminized mylar to isolate it optically from the other strips. Light guides are of two types; those which attach
467
i0 ii 12 13 14 15 16 17 18
001 001 00 0 1 Ol 0 1 0 1 0 1 0 1 1 ! 1 1 1 1 1 1 1
0 0 0 0 0 0 1 1 1
654
Decimal Value
1 0 0 0 1 1 1
0 1 1 0 1 1 0 0 1
i 0 i i 0 i 0 1 0
I 1 0 i 1 0 1 0 0
ii 13 14 19 21 22 25 26 28
0 0 0 1 1 1 0 0 0
0 1 1 0 0 1 0 0 1
i 0 1 0 1 0 0 1 0
I 1 0 1 0 0 1 O 0
35 37 38 41 42 44 49 50 52
3 2 1 Bit #
Fig. 4. The "'error-free'" code as used in the strip counter. The code identifies eighteen counter positions or the occurrence of inefficient and multiple track events with six photomultiplier tubes. to the strips singly and those which attach in pairs (fig. 5). T h e s e were arranged according to the error-flee code and bent along the m o s t convenient path to the appropriate photomultiplier tube position. T h e light guides were also wrapped in aluminized mylar and epoxied (using NE580) to the scintillation strips. This a r r a n g e m e n t was m o u n t e d and light-sealed in an a l u m i n u m frame to which the phototubes (RCA 8575) and their bases were attached. Light
Light Guide Scintillator~
~ p,
-
I ~
.22 rn
~
.12 m
'
I
~
.22 m
t
Fig. 5. A drawing of a typical element of the strip counter. The elements could be individually removed from the counter; however, it was found that each coordinate was most easily built as a unit.
468
J.H.
HOFTIEZER
et al.
~|ir
Cove~ . MAX I
v Trailer
MAX
2 3 4
" MAX 6 • MAY I MAY
5
MAX MAY
t e -_,L_~
6 I
," MAY 6 • MBX I 3
Scale MAB
54
~• MBX 6 • MBY I
MAY
MAYS
MAB
6 __CLR
" ~BY s
MABE Cave
MBY 2
Trailer •
3 4 65 ~
MBYS
MBY
Fig. 6. T h e electronic layout for the strip c o u n t e r s as they were i m p l e m e n t e d during one experiment.
The electronic implementation is shown in fig. 6. When a GATE signal is received, the 6-bit pattern is saved. There are sixty-four possibilities which contain all the output information from the hodoscope. This information can be sorted in a number of ways which are meaningful to the operation of the counter. To monitor the operation three histograms were used. The histogram of valid readout positions [i.e., output containing exactly three (N = 3) active bits] is the most interesting. This profile is the shape of the beam incident on the counter (fig. 7a). A histogram of the number of non-zero digits per event, ranging from zero to six, was useful in determining the efficiency of the hodoscope. Ideally all counts should appear in the three bit column, corresponding to valid position codes. In practice, the occurrence of valid codes was much greater than other types of readouts (fig. 7b). A histogram of the activity of individual phototubes was used to locate noisy or inefficient tubes. For symmetric beams centered on the counter the tubes are equally active.
4. Discussion
The error-free counting efficiency is the primary means of assessing the strip counter performance. This efficiency is given by the ratio of events with exactly three active bits to the total number of events, since only this data can be analyzed
3000
c o
~
~ 75
2000
.~
50
o u
,ooo
: J
-L
125456789101112151415161718 Strip Position
0 123456 -#'Bits
Fig. 7. A b e a m profile h i s t o g r a m (a) and the corresponding efficiencies (b) for one coordinate of the strip counter, taken with a 140 MeV zr beam.
BINARY
ENCODED
SCINTILLATION
uniquely. Remaining event readout patterns are divided into two groups, those which are truly inefficient (containing less than three active bits), and those which are classed with multiple readouts (containing more than three active bits). In the large counter efficiency was 88% error-free, 5% inefficient, and 7% multiple readout events. The small counter was somewhat less efficient; its efficiency was 81% error-free, 15% inefficient, and 4% multiple readout events. While these errorfree efficiency levels are acceptable, levels approaching unity (100%) are much more desirable because the total efficiency of a sequence of strip counter coordinates is a multiplicative function which rapidly decreases. Improvement in the efficiency of the larger counter is most likely to result from a decrease in multiple event readouts. There are indications that many of these are due to adjacent strips in the counter detecting the same traversing particle. If it is assumed that all multiple readout patterns are due to adjacent strips, these events can be assigned a position and added into the data, increasing the efficiency of a sequence of coordinates substantially without distorting the measured distributions. However, using this assumption, the counters are no longer " e r r o r - f r e e " .
HODOSCOPE
469
elastic scattering of pions (both positive and negative) at pion energies from 100 MeV to 300 MeV for various target nuclei6). The counters were used to define the incoming pion trajectory by locating the traversing particle at two points in space. Using the counters, an instantaneous beam intensity of - 3 x 1 0 6 particles per second was possible. Thus, reasonable statistics were obtained in a relatively short time. 6. Conclusion This article describes the development o f a new type of scintillation hodoscope. These devices successfully approach the current limits in both spatial and time resolution of similar instruments. They are safeguarded by the nature of the encoding scheme against the systematic introduction of errors into the data. Further, the counters exhibit n u m e r o u s desirable features such as their reliability and ease of operation, making them appropriate for experimental use. The most severe limitation on the strip counters is imposed by the moderate efficiency of their coordinates, caused not by the concepts involved in the counter design, but rather by the physical dimensions. The use of the strip counter hodoscopes in a small angle scattering experiment has demonstrated successfully the application of the device.
5. Application The strip counter hodoscope is a versatile instrument with applications in many experiments which require spatial knowledge of the trajectories as well as fast timing of high energy particles. A typical application was illustrated in a recent experiment performed at the Los Alamos Meson Physics Facility. This experiment measured the
References 1) L. Y. Lee et al., Nucl. Instr. and Meth. 119 (1974) 29. 2) L. W. AIvarez, Rev. Sci. Instr. 31 (1960) 76. 3) M. W. Collins et al., Nucl. Instr. and Meth. 117 (1974) 339. 4~ D. E. Pellett et al., Nucl. Instr. and Meth. 115 (1974) 135. 5) M. Gardner, Sci. Am. (30 August 1972) 106. 6) W. H. Dragoset, Ph. D. Thesis (Rice University, 1977) unpublished.