Position sensitive multiwire proportional counter with integral delay line
United States Patent 3911279
A position sensitive multiwire proportional counter with integral delay line including a support carrying a plurality of anode wires and at least one cathode wire spaced in a predetermined relationship from the anode wires within the active volume of the counter to form an integral delay line. The counter is filled with a gas which ionizes upon interaction with ionizing radiation, the ionization of the gas being enhanced by the positive anode, such that an electrical charge is thereby induced in the cathode wire. Sensing of elapsed time between receipt of the induced charge at opposing ends of the cathode wire is utilized to determine the desired radiation positional data.
US Patent References:
Radioactivity measuring device
Simpson - May 1950 - 2509700
Method of suppressing photoelectric threshold
Friedman - October 1953 - 2657316
Detection and measurement of radiation
Teichmann - November 1954 - 2694152
POSITION-SENSITIVE RADIATION DETECTOR
Borkowski et al. - June 1970 - 3517194
COSMIC DUST OR OTHER SIMILAR OUTER SPACE PARTICLES IMPACT LOCATION DETECTOR
Auer - September 1972 - 3694655
Radioactivity measuring device
Simpson - May 1950 - 2509700
Method of suppressing photoelectric threshold
Friedman - October 1953 - 2657316
Detection and measurement of radiation
Teichmann - November 1954 - 2694152
POSITION-SENSITIVE RADIATION DETECTOR
Borkowski et al. - June 1970 - 3517194
COSMIC DUST OR OTHER SIMILAR OUTER SPACE PARTICLES IMPACT LOCATION DETECTOR
Auer - September 1972 - 3694655
Inventors:
Gilland, Jerry R. (Boulder, CO)
Emming, Jan G. (Boulder, CO)
Emming, Jan G. (Boulder, CO)
Application Number:
05/361134
Publication Date:
10/07/1975
Filing Date:
05/17/1973
View Patent Images:
Export Citation:
Assignee:
Ball Brothers Research Corporation (Boulder, CO)
Primary Class:
Other Classes:
250/389, 114/323, 313/93
International Classes:
H01J47/06; H01J47/00; G01T1/18
Field of Search:
313/93 250/385,389
US Patent References:
| 3772521 | RADIATION CAMERA AND DELAY LINE READOUT | November 1973 | Perez-Mendez |
Primary Examiner:
Dixon, Harold A.
Attorney, Agent or Firm:
Haynes, James D.
Claims:
What is claimed is
1. A position sensitive multiwire proportional counter comprising:
2. The position sensitive multiwire proportional counter of claim 1 wherein said counter includes grounding means positioned on opposite sides of said frame.
3. The position sensitive multiwire proportional counter of claim 1 wherein said cathode wire is wound around said second pair of side members.
4. The position sensitive multiwire proportional counter of claim 3 wherein each winding of said cathode wire is substantially equidistant from the most nearly adjacent anode wires.
5. The position sensitive multiwire proportional counter of claim 3 wherein said anode wires extend within the volume enclosed by said cathode wire wound around said second pair of side members.
6. The position sensitive multiwire proportional counter of claim 5 wherein each winding of said cathode wire is substantially equidistant from the most nearly adjacent anode wires.
7. The position sensitive multiwire proportional counter of claim 6 wherein said anode wires extend between said first pair of side members in a direction parallel to the axis of the winding defined by the cathode wire about said second pair of side members.
8. A position sensitive multiwire proportional counter, comprising
9. The position sensitive multiwire proportional counter of claim 8 further including
10. The position sensitive multiwire proportional counter of claim 8 wherein said cathode wire is wound about said second pair of side members to thereby define two substantially parallel planes and wherein said anode wires are parallel to each other and are connected to said first pair of side members to define another plane substantially parallel to the two parallel planes defined by said cathode wire.
11. The position sensitive multiwire proportional counter of claim 8 wherein said cathode wire acts as a delay line for the signal coupled to said signal processing circuitry.
12. A position sensitive radiation counter comprising
13. The position sensitive radiation counter of claim 12 wherein
1. A position sensitive multiwire proportional counter comprising:
2. The position sensitive multiwire proportional counter of claim 1 wherein said counter includes grounding means positioned on opposite sides of said frame.
3. The position sensitive multiwire proportional counter of claim 1 wherein said cathode wire is wound around said second pair of side members.
4. The position sensitive multiwire proportional counter of claim 3 wherein each winding of said cathode wire is substantially equidistant from the most nearly adjacent anode wires.
5. The position sensitive multiwire proportional counter of claim 3 wherein said anode wires extend within the volume enclosed by said cathode wire wound around said second pair of side members.
6. The position sensitive multiwire proportional counter of claim 5 wherein each winding of said cathode wire is substantially equidistant from the most nearly adjacent anode wires.
7. The position sensitive multiwire proportional counter of claim 6 wherein said anode wires extend between said first pair of side members in a direction parallel to the axis of the winding defined by the cathode wire about said second pair of side members.
8. A position sensitive multiwire proportional counter, comprising
9. The position sensitive multiwire proportional counter of claim 8 further including
10. The position sensitive multiwire proportional counter of claim 8 wherein said cathode wire is wound about said second pair of side members to thereby define two substantially parallel planes and wherein said anode wires are parallel to each other and are connected to said first pair of side members to define another plane substantially parallel to the two parallel planes defined by said cathode wire.
11. The position sensitive multiwire proportional counter of claim 8 wherein said cathode wire acts as a delay line for the signal coupled to said signal processing circuitry.
12. A position sensitive radiation counter comprising
13. The position sensitive radiation counter of claim 12 wherein
Description:
BACKGROUND OF THE INVENTION
This invention relates in general to a position sensitive radiation counter system and, in particular, to a position sensitive multiwire proportional counter with integral delay line.
It is often times necessary in high energy physics research to obtain positional data with respect to ionizing radiation. While position sensitive radiation counter systems have been developed for such purposes, such systems have not proven to be completely successful due to a variety of factors.
Known systems are relatively complex and expensive, requiring a large amount of supporting electronics, and/or a variety of separate cathode connections at exact positions to external position encoding means.
Examples of known position sensitive radiation counter systems may be found in the following: U.S. Pat. No. 3,517,194, issued to C. J. Borkowski, et al., on June 23, 1970, and entitled "Position-Sensitive Radiation Detector"; U.S. Pat. No. 3,483,377, issued to C. J. Borkowski, et al., on Dec. 9, 1969, and entitled "Position-Sensitive Radiation Detector"; and in an article entitled "Electromagnetic Delay Line Readout for Proportional Wire Chambers", by R. Grove, K. Lee, V. Perez-Mendez, and J. Sperinde, published in NUCLEAR INSTRUMENTS AND METHODS, Volume 89, pages 257-262 (1970).
The above-referenced article teaches the use of an external delay line in conjunction with a multiwire proportional chamber in order to provide position sensitivity. The use of a delay line is also shown, by way of example, in U.S. Pat. No. 3,466,574, issued to E. Rutishauser, on Sept. 9, 1969, and entitled "Delay Lines".
With respect to the delay line readout system as described hereinabove, the generally used approach involves coupling the electrical output from the ionizing gas enclosed chamber, individually from a plurality of anode or cathode grid wires, to a separate external delay line element to achieve readout. The delay line then provides the timing differences used to determine position based upon the location at which the cathode wire carrying the charge is coupled into the delay line.
Thus, even the relatively newer prior art counter systems utilizing delay line readout require a plurality of cathode wires that are not continuous electrically, and, therefore, make system assembly more difficult. In addition, since an external delay line is utilized an electrical feedthrough for each cathode wire is necessary, and such systems often suffer signal loss due to inefficient coupling or signal variations, for example, from one cathode wire to another for a given and identical ionization stimulation in the chamber.
The instant invention is an improved position sensitive radiation counter system that is simple and yet reliable. The counter utilizes a single cathode winding that simplifies counter fabrication, assembly, and testing. The present invention eliminates the need for a separate external delay line, thereby eliminating undesirable and burdensome manufacturing characteristics and, thereafter, the handling and operational characteristics necessarily associated with prior art systems. The output from the cathode wire provides the necessary time differences by which the positional data of ionizing radiation interacting in the counter may be accurately ascertained.
SUMMARY OF INVENTION
It is, therefore, an object of this invention to improve position sensitive radiation counter systems.
It is another object of this invention to improve position sensitive radiation counter systems by indicating positional data through the use of an integral delay line.
Another object of this invention is to incorporate a delay line, which functions as the cathode, integral to the chamber of the counter.
It is still another object of this invention to combine the function of the cathode wire having an electrical charge induced therein with the function of delay of said charge to indicate the position at which the charge was induced.
A further object of this invention is to improve position sensitive multiwire proportional counters by utilizing cathode wires as integral counter delay lines in fixed spaced relationship from the anode wires.
It is still another object of this invention to improve position sensitive multiwire proportional counters by utilizing an integral delay line comprising a single cathode wire wound in a helical fashion and positioned parallel to a planar and parallel array of anode wires.
It is still another object of this invention to provide a position sensitive multiwire proportional counter with an integral delay line that is relatively simple yet reliable and requires little supporting electronics.
Yet another object of this invention is to improve position sensitive multiwire proportional counters by utilizing a continuous cathode integral delay line thereby requiring electrical attachment only at the ends thereof.
It is yet another object of this invention to improve position sensitive multiwire proportional counters by utilizing an inherent integral delay line thereby eliminating the necessity for an external delay line.
These and other objects are attained in accordance with the present invention wherein there is provided a position sensitive multiwire proportional counter with integral delay line including one or more integral cathode windings which provide effective delay lines to determine the desired particle positional data.
DESCRIPTION OF THE DRAWINGS
Further objects of the invention, together with additional features contributing thereto and advantages accruing therefrom, will be apparent from the following description of one embodiment of the invention having a single continuous integral delay line when read in conjunction with the accompanying drawings, wherein:
FIG. 1 is a perspective view, with the top ground plane partially cut away, showing the position sensitive multiwire proportional counter of this invention;
FIG. 2 is a top view, with the top ground plane removed, of the position sensitive multiwire proportional counter shown in FIG. 1;
FIG. 3 is a side view of the position sensitive multiwire proportional counter shown in FIG. 1;
FIG. 4 is a schematic representation illustrating the ionization of gas in the position sensitive multiwire proportional counter shown in FIG. 1 when ionizing radiation interacts with it;
FIG. 5 is a schematic representation illustrating the tendency for electron collection at the anode when ionizing radiation interacts with the position sensitive multiwire proportional counter shown in FIG. 1 to leave a net positive charge in the gas due to the positive ions; and
FIG. 6 is a schematic logic block diagram showing how the proportional counter may be utilized with processing circuitry to determine ionizing radiation positional data.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention provides an apparatus to establish electrical signal timing differences indicative of ionizing radiation positional data without requiring individual cathode wires coupled to external devices such as external delay lines or individual amplifiers. These timing differences provide the information to determine the point at which the ionizing radiation interacts with the gas in the counter. As heretofore described, the systems taught by the prior art couple the electrical output signal from individual cathode wires to devices mounted external of the basic multiwire counter, or do not use a delay line technique at all. In instances where external devices are used, the radiation position is determined based upon the location at which the cathode wire carrying the charge is tied into the external device. In the preferred embodiment of this invention, the cathode grid comprises a single wire wound on a frame in a generally rectangular and helical fashion, and carried parallel to a planar array of anode wires. The cathode wire thus wound exhibits electromagnetic delay line characteristics which thereby eliminates the need for an external delay line and provides the timing differences needed to establish radiation position in one direction.
Referring now to the drawings, in which like numerals have been used for like characters, the numeral 9 refers generally to the position sensitive multiwire proportional counter system of this invention. As shown in FIGS. 1, 2 and 3, this counter system includes a frame 11 of conventional nonconductive material or any other means of mechanically supporting the wire structure hereinafter described having ground planes 13 and 14 disposed parallel thereto and spaced therefrom in any conventional manner. As best shown in FIG. 1, frame 11 has a plurality of equally spaced anode wires 16 extending therethrough between two opposite sides of the frame with the anode wires positioned parallel to the two remaining sides of the frame and connected to a lead 17 coupled to anode terminal 18 leading from the counter. Anode terminal 18 is commonly connected to a source of positive voltage. The anode wires may be mounted to the frame in any conventional manner, but as shown in FIG. 1, are between and attached to the two opposite sides of the frame.
In addition, a cathode wire, or winding, 20 is wound across the two remaining opposite sides of the frame such that the axis of the winding is positioned parallel to the anode array wires and spaced therefrom. The cathode wire extends across the top and bottom of the frame, as shown best in FIGS. 1 and 3. The cathode wire terminates at terminals 22 and 23, which lead from the counter, as shown in FIGS. 1 and 2.
Alternately the cathode wire, or winding, 20 is wound on a separate frame similar in size to the anode array. This cathode winding is then mounted parallel to and on either side of the anode array. Depending upon the specific application, the cathode wires can be placed at any angle with respect to the anode wires.
For operation, the counter is enclosed by a housing (not shown) and a suitable gas (i.e., a gas, such as Argon and Methane mixed in a 9 to 1 ratio, which may be ionized and will produce secondary ionization near the anode) is inserted within the housing as is well known in the art. Ionizing radiation is then passed through the counter and the position of the interaction determined. Position sensitive radiation counters are well known in the art, and hence, additional structure of the frame or other support techniques and their operation have not been set forth in more detail herein. Details of these structures and their operation are set forth in the prior art and the above-identified patents and articles may be referred to for example of a more detailed description.
As shown in FIG. 4, after the counter is filled with an appropriate gas, the gas is ionized as ionizing radiation interacts within the counter. Since the anode is positive, the free electrons are accelerated to high energy near the anode and secondary ionization is produced. This results in a multiplication of the initial number of free electrons and, as indicated in FIG. 5, produces a region of intense ionization near the anode. Most of the electrons created are collected on the anode leaving a net positive charge in the gas due to the positive ions. This positive charge induces a voltage on the cathode wires which is inversely related to the distance of the cathode wire from the positive charge. This induced voltage profile is then time-analyzed, as hereinafter described, and the position of the instant ionizing radiation thereby determined. Heretofore, such measurement was done by externally mounted devices. This invention, however, achieves such measurement directly from the cathode wire 20 which acts inherently as a delay line.
The signal induced on the delay line (cathode wire 20) propagates down the wire at a velocity which is characteristic of the delay line constants. Therefore, the time of arrival of the pulse at the output is a measure of the instant position of the ionizing radiation. Since the voltage is induced at multiple positions on the cathode wire, it is possible to interpolate the radiation position between these wires. The ultimate system accuracy is a function of energy deposition, gas gain, wire spacing and electronic noise which will vary in different applications.
The cathode wire is wound as a continuous coil (as shown in FIGS. 1, 2 and 3) and acts as an inductor (L) whose inductance is proportional to the number of turns and the cross sectional area of the coil. The coil also has stray capacitance (C) to the anode wires and to the ground planes. This results in the cathode wire acting as an electromagnetic delay line with the following idealized characteristics:
Delay = √LC
Characteristic Impedance = √L/C
The position of the instant ionizing radiation is determined by observing the elapsed time required for the pulse to reach the output terminal or may be measured by measuring the time difference between the pulses at the two output terminals.
FIG. 6 shows, in block form, processing circuitry 28 which may be connected to terminals 22 and 23 of counter 9 to accomplish this end. As shown in FIG. 6, terminals 22 and 23 (connected to the ends of the cathode wire 20) are coupled to amplifiers 30 and 31, which amplifiers are, in turn, connected to discriminators 33 and 34. The output from the discriminators are coupled to a time-to-height converter 36, the output of which is coupled to a pulse height analyzer 38. Such processing circuits are known in the art and a more detailed description of such circuitry may be found, for example, in U.S. Pat. Nos. 3,483,377 and 3,517,194 as well as in the article above referenced.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. For example, it is not necessary that the cathode winding encompass the anode array. More particularly, the anodes array could be positioned outside the space encompassed by the cathode winding 20, but adjacent thereto. Further, the delay line feature of the cathode wire can be achieved by other than a helical-rectangular configuration; for instance, the cathode wire 20 could be disposed between the sides of frame 11 in a single plane instead of being wrapped around the opposing sides thereof as previously described. Further, the anode wires 16 may be nonparallel to the axis of the cathode winding 20; for instance, the anode wires 16 could be disposed normal to the axis of the cathode winding 20. Then, one may combine these above modifications wherein two cathode windings are used in parallel planes, but with their axes mutually perpendicular, with the anode wires 16 extending in a plane between the two cathode wire planes, thereby providing positional information in two orthoganal axes. One will also recognize that many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
This invention relates in general to a position sensitive radiation counter system and, in particular, to a position sensitive multiwire proportional counter with integral delay line.
It is often times necessary in high energy physics research to obtain positional data with respect to ionizing radiation. While position sensitive radiation counter systems have been developed for such purposes, such systems have not proven to be completely successful due to a variety of factors.
Known systems are relatively complex and expensive, requiring a large amount of supporting electronics, and/or a variety of separate cathode connections at exact positions to external position encoding means.
Examples of known position sensitive radiation counter systems may be found in the following: U.S. Pat. No. 3,517,194, issued to C. J. Borkowski, et al., on June 23, 1970, and entitled "Position-Sensitive Radiation Detector"; U.S. Pat. No. 3,483,377, issued to C. J. Borkowski, et al., on Dec. 9, 1969, and entitled "Position-Sensitive Radiation Detector"; and in an article entitled "Electromagnetic Delay Line Readout for Proportional Wire Chambers", by R. Grove, K. Lee, V. Perez-Mendez, and J. Sperinde, published in NUCLEAR INSTRUMENTS AND METHODS, Volume 89, pages 257-262 (1970).
The above-referenced article teaches the use of an external delay line in conjunction with a multiwire proportional chamber in order to provide position sensitivity. The use of a delay line is also shown, by way of example, in U.S. Pat. No. 3,466,574, issued to E. Rutishauser, on Sept. 9, 1969, and entitled "Delay Lines".
With respect to the delay line readout system as described hereinabove, the generally used approach involves coupling the electrical output from the ionizing gas enclosed chamber, individually from a plurality of anode or cathode grid wires, to a separate external delay line element to achieve readout. The delay line then provides the timing differences used to determine position based upon the location at which the cathode wire carrying the charge is coupled into the delay line.
Thus, even the relatively newer prior art counter systems utilizing delay line readout require a plurality of cathode wires that are not continuous electrically, and, therefore, make system assembly more difficult. In addition, since an external delay line is utilized an electrical feedthrough for each cathode wire is necessary, and such systems often suffer signal loss due to inefficient coupling or signal variations, for example, from one cathode wire to another for a given and identical ionization stimulation in the chamber.
The instant invention is an improved position sensitive radiation counter system that is simple and yet reliable. The counter utilizes a single cathode winding that simplifies counter fabrication, assembly, and testing. The present invention eliminates the need for a separate external delay line, thereby eliminating undesirable and burdensome manufacturing characteristics and, thereafter, the handling and operational characteristics necessarily associated with prior art systems. The output from the cathode wire provides the necessary time differences by which the positional data of ionizing radiation interacting in the counter may be accurately ascertained.
SUMMARY OF INVENTION
It is, therefore, an object of this invention to improve position sensitive radiation counter systems.
It is another object of this invention to improve position sensitive radiation counter systems by indicating positional data through the use of an integral delay line.
Another object of this invention is to incorporate a delay line, which functions as the cathode, integral to the chamber of the counter.
It is still another object of this invention to combine the function of the cathode wire having an electrical charge induced therein with the function of delay of said charge to indicate the position at which the charge was induced.
A further object of this invention is to improve position sensitive multiwire proportional counters by utilizing cathode wires as integral counter delay lines in fixed spaced relationship from the anode wires.
It is still another object of this invention to improve position sensitive multiwire proportional counters by utilizing an integral delay line comprising a single cathode wire wound in a helical fashion and positioned parallel to a planar and parallel array of anode wires.
It is still another object of this invention to provide a position sensitive multiwire proportional counter with an integral delay line that is relatively simple yet reliable and requires little supporting electronics.
Yet another object of this invention is to improve position sensitive multiwire proportional counters by utilizing a continuous cathode integral delay line thereby requiring electrical attachment only at the ends thereof.
It is yet another object of this invention to improve position sensitive multiwire proportional counters by utilizing an inherent integral delay line thereby eliminating the necessity for an external delay line.
These and other objects are attained in accordance with the present invention wherein there is provided a position sensitive multiwire proportional counter with integral delay line including one or more integral cathode windings which provide effective delay lines to determine the desired particle positional data.
DESCRIPTION OF THE DRAWINGS
Further objects of the invention, together with additional features contributing thereto and advantages accruing therefrom, will be apparent from the following description of one embodiment of the invention having a single continuous integral delay line when read in conjunction with the accompanying drawings, wherein:
FIG. 1 is a perspective view, with the top ground plane partially cut away, showing the position sensitive multiwire proportional counter of this invention;
FIG. 2 is a top view, with the top ground plane removed, of the position sensitive multiwire proportional counter shown in FIG. 1;
FIG. 3 is a side view of the position sensitive multiwire proportional counter shown in FIG. 1;
FIG. 4 is a schematic representation illustrating the ionization of gas in the position sensitive multiwire proportional counter shown in FIG. 1 when ionizing radiation interacts with it;
FIG. 5 is a schematic representation illustrating the tendency for electron collection at the anode when ionizing radiation interacts with the position sensitive multiwire proportional counter shown in FIG. 1 to leave a net positive charge in the gas due to the positive ions; and
FIG. 6 is a schematic logic block diagram showing how the proportional counter may be utilized with processing circuitry to determine ionizing radiation positional data.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention provides an apparatus to establish electrical signal timing differences indicative of ionizing radiation positional data without requiring individual cathode wires coupled to external devices such as external delay lines or individual amplifiers. These timing differences provide the information to determine the point at which the ionizing radiation interacts with the gas in the counter. As heretofore described, the systems taught by the prior art couple the electrical output signal from individual cathode wires to devices mounted external of the basic multiwire counter, or do not use a delay line technique at all. In instances where external devices are used, the radiation position is determined based upon the location at which the cathode wire carrying the charge is tied into the external device. In the preferred embodiment of this invention, the cathode grid comprises a single wire wound on a frame in a generally rectangular and helical fashion, and carried parallel to a planar array of anode wires. The cathode wire thus wound exhibits electromagnetic delay line characteristics which thereby eliminates the need for an external delay line and provides the timing differences needed to establish radiation position in one direction.
Referring now to the drawings, in which like numerals have been used for like characters, the numeral 9 refers generally to the position sensitive multiwire proportional counter system of this invention. As shown in FIGS. 1, 2 and 3, this counter system includes a frame 11 of conventional nonconductive material or any other means of mechanically supporting the wire structure hereinafter described having ground planes 13 and 14 disposed parallel thereto and spaced therefrom in any conventional manner. As best shown in FIG. 1, frame 11 has a plurality of equally spaced anode wires 16 extending therethrough between two opposite sides of the frame with the anode wires positioned parallel to the two remaining sides of the frame and connected to a lead 17 coupled to anode terminal 18 leading from the counter. Anode terminal 18 is commonly connected to a source of positive voltage. The anode wires may be mounted to the frame in any conventional manner, but as shown in FIG. 1, are between and attached to the two opposite sides of the frame.
In addition, a cathode wire, or winding, 20 is wound across the two remaining opposite sides of the frame such that the axis of the winding is positioned parallel to the anode array wires and spaced therefrom. The cathode wire extends across the top and bottom of the frame, as shown best in FIGS. 1 and 3. The cathode wire terminates at terminals 22 and 23, which lead from the counter, as shown in FIGS. 1 and 2.
Alternately the cathode wire, or winding, 20 is wound on a separate frame similar in size to the anode array. This cathode winding is then mounted parallel to and on either side of the anode array. Depending upon the specific application, the cathode wires can be placed at any angle with respect to the anode wires.
For operation, the counter is enclosed by a housing (not shown) and a suitable gas (i.e., a gas, such as Argon and Methane mixed in a 9 to 1 ratio, which may be ionized and will produce secondary ionization near the anode) is inserted within the housing as is well known in the art. Ionizing radiation is then passed through the counter and the position of the interaction determined. Position sensitive radiation counters are well known in the art, and hence, additional structure of the frame or other support techniques and their operation have not been set forth in more detail herein. Details of these structures and their operation are set forth in the prior art and the above-identified patents and articles may be referred to for example of a more detailed description.
As shown in FIG. 4, after the counter is filled with an appropriate gas, the gas is ionized as ionizing radiation interacts within the counter. Since the anode is positive, the free electrons are accelerated to high energy near the anode and secondary ionization is produced. This results in a multiplication of the initial number of free electrons and, as indicated in FIG. 5, produces a region of intense ionization near the anode. Most of the electrons created are collected on the anode leaving a net positive charge in the gas due to the positive ions. This positive charge induces a voltage on the cathode wires which is inversely related to the distance of the cathode wire from the positive charge. This induced voltage profile is then time-analyzed, as hereinafter described, and the position of the instant ionizing radiation thereby determined. Heretofore, such measurement was done by externally mounted devices. This invention, however, achieves such measurement directly from the cathode wire 20 which acts inherently as a delay line.
The signal induced on the delay line (cathode wire 20) propagates down the wire at a velocity which is characteristic of the delay line constants. Therefore, the time of arrival of the pulse at the output is a measure of the instant position of the ionizing radiation. Since the voltage is induced at multiple positions on the cathode wire, it is possible to interpolate the radiation position between these wires. The ultimate system accuracy is a function of energy deposition, gas gain, wire spacing and electronic noise which will vary in different applications.
The cathode wire is wound as a continuous coil (as shown in FIGS. 1, 2 and 3) and acts as an inductor (L) whose inductance is proportional to the number of turns and the cross sectional area of the coil. The coil also has stray capacitance (C) to the anode wires and to the ground planes. This results in the cathode wire acting as an electromagnetic delay line with the following idealized characteristics:
Delay = √LC
Characteristic Impedance = √L/C
The position of the instant ionizing radiation is determined by observing the elapsed time required for the pulse to reach the output terminal or may be measured by measuring the time difference between the pulses at the two output terminals.
FIG. 6 shows, in block form, processing circuitry 28 which may be connected to terminals 22 and 23 of counter 9 to accomplish this end. As shown in FIG. 6, terminals 22 and 23 (connected to the ends of the cathode wire 20) are coupled to amplifiers 30 and 31, which amplifiers are, in turn, connected to discriminators 33 and 34. The output from the discriminators are coupled to a time-to-height converter 36, the output of which is coupled to a pulse height analyzer 38. Such processing circuits are known in the art and a more detailed description of such circuitry may be found, for example, in U.S. Pat. Nos. 3,483,377 and 3,517,194 as well as in the article above referenced.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. For example, it is not necessary that the cathode winding encompass the anode array. More particularly, the anodes array could be positioned outside the space encompassed by the cathode winding 20, but adjacent thereto. Further, the delay line feature of the cathode wire can be achieved by other than a helical-rectangular configuration; for instance, the cathode wire 20 could be disposed between the sides of frame 11 in a single plane instead of being wrapped around the opposing sides thereof as previously described. Further, the anode wires 16 may be nonparallel to the axis of the cathode winding 20; for instance, the anode wires 16 could be disposed normal to the axis of the cathode winding 20. Then, one may combine these above modifications wherein two cathode windings are used in parallel planes, but with their axes mutually perpendicular, with the anode wires 16 extending in a plane between the two cathode wire planes, thereby providing positional information in two orthoganal axes. One will also recognize that many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.