JP4178232B2 - Incident position detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the incident position detecting DeSo location for detecting the position of the center of gravity of the event to be input over a plurality of detector cells, in particular, reduce the size of the pixels than the spread of the charged particles and light generated by the event suitable for use in detecting the radiation or light with oversampling techniques take relates the incident position detection DeSo location.
[0002]
[Prior art]
Conventionally, when dealing with a large number of pixels in front-end electronics for radiation detectors using an ASIC or the like, a chip for a low count rate simply records and holds a signal for each pixel and reads it later. On the other hand, in the case of operating at a high count rate, in order to suppress simultaneously occurring events, as shown in FIG. 1, for example, from a radiation detector (for example, a scintillator) 10 input via an amplifier 12, In general, the signal is processed using the priority encoder 14 and the incident pixel number N is output as a digital value.
[0003]
Conventionally, mainly due to hardware limitations such as detectors and circuits, the pixel size cannot be made very small, and even when individual signals are read, events often fall within one pixel, In many cases, this method was in time.
[0004]
However, recently, in order to observe the event occurring in the detector 10 in more detail from the trend toward higher resolution, as shown in FIG. 2, the size of the pixel is determined from the spread of charged particles or light caused by the event. An oversampling technique is being carried out. Furthermore, high-level information is being included by projecting three-dimensional information on a two-dimensional position by such oversampling (see Patent Documents 1 and 2).
[0005]
With this configuration, not only when radiation or the like reacts only within one pixel and outputs a signal, but also as shown in FIG. 3, a large number of pixels react substantially simultaneously to one event. The case comes out.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-142523 [Patent Document 2]
Japanese Patent Laid-Open No. 11-142524
[Problems to be solved by the invention]
However, in the priority encoding method, the order of incidence on the priority encoder 14 is not necessarily the order in which the intensity is strong, and even if the intensity is weak, detection is performed if the threshold value is exceeded. Therefore, the position of the center of gravity could not be detected accurately.
[0008]
On the other hand, in order to perform the center-of-gravity calculation between pixels, not only hardware is usually required for the calculation, but in order to perform this later, for example, the output of each pixel is stored in a capacitor or the like. Since it is necessary to read serially after integration, if the data rate increases, the overall throughput is impaired. Although it is possible to call the signals stored in the capacitor in parallel, the circuit becomes too large. Furthermore, when outputting the pixel number as a digital value, there is a problem that a large number of signal lines are required.
[0009]
The present invention has been made to solve the above-described conventional problems, and it is an object of the present invention to accurately detect the position of the center of gravity of an incident incident across a plurality of detection cells with a relatively simple circuit configuration.
[0010]
[Means for Solving the Problems]
The present invention relates to a wave height discriminating means for discriminating the level of an input signal of each detection cell in an incident position detecting device for detecting the barycentric position of an event incident across a plurality of detection cells, and the discriminated level. An encoder that generates a pulse of a predetermined width having a wave height in accordance with the signal, a resistance ladder to which the pulse is input at a position corresponding to the channel to which the signal is input, and reading means connected to both ends of the resistance ladder. The problem is solved by comparing the magnitude of the output of the reading means to detect the position of the center of gravity of the event.
[0013]
Further, the wave height discriminating means is a discriminator having a plurality of threshold values.
[0014]
Further, a plurality of resistance ladders are connected in series to be scalable, so that a larger-scale position detection system can be constructed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
As shown in FIG. 4, the first embodiment of the present invention uses a scintillator including a number of detection cells in a detector, and for each channel corresponding to each detection cell, an individual preamplifier 20, and A wave height discriminator (discriminator) 26 including a shaping amplifier 22, a variable amplification amplifier 24, and a plurality (three in the figure) of comparators 28A, 28B, 28C is prepared.
[0017]
The outputs of the comparators 26A, 26B, and 26C are connected to a common encoder 30.
[0018]
One encoder 30 is prepared for each channel. The encoder 30 determines the magnitude of the signal output and, as shown in FIG. 5, has a short width t (for example, 100 nsec) having several different voltage values h1 to h4 (four in the embodiment) corresponding to the magnitude. Hereinafter, a pulse P is generated. The pulse output via the amplifier 32, is connected to the switch En-shaped resistor ladder 34.
[0019]
Therefore, the outputs per chip are two, A and B, as shown in FIG. 6. For example, the outputs of the amplifiers 36A and 36B are obtained by the divider 38 connected via the amplifiers 36A and 36B for reading. Can be obtained from which channel the signal is output. Specifically, by dividing an analog value such as A / (A + B) by the charge division method between the outputs A and B, the position of the center of gravity of the incident radiation is obtained, and the number of the channel into which the signal is input is obtained. An analog signal can be encoded and output.
[0020]
Since the throughput of this method uses only the rising portion of the input signal, high throughput can be expected without being affected by the fluorescence decay time. Furthermore, the S / N ratio in the charge division method is extremely high because it is once pulsed by a comparator and digitized, and can be encoded up to about 10,000 channels.
[0021]
In addition, when the signal charge is spread over many channels, there may be a time difference in the pulses output from the detector. This can be dealt with by using a sufficiently wide pulse width, as well as between adjacent channels. This can also be avoided by providing a synchronization circuit for a certain period of time in order to synchronize the timing of generation of the encoded pulse.
[0022]
Furthermore, when encoding is performed for a large number of channels, the outputs of the chips may be connected in series. For example, as in the second embodiment shown in FIG. 7, if the output of chip 1 is A1 and B1, and the output of chip 2 is A2 and B2, B1 and A2 are connected in series, and signals are read from A1 and B2. Just put it out. In this way, the number of channels of 100 to 200 per chip can be increased by the number of chips. Such a feature is suitable for use in space limited front end electronics.
[0023]
In the above-described embodiment, the number of comparators is three, and the output wave height of the encoder 30 is high, medium, low, and zero. However, the number of comparators and the number of wave height types are limited to this. Not.
[0024]
In the above embodiment, the shaping amplifier 22 and the variable amplification amplifier 24 are provided. However, these amplifiers can be omitted.
[0025]
In the above embodiment, the scintillator is used as the detector. However, the type of detector is not limited to this, and a radiation detector using a semiconductor sensor such as germanium or a compound semiconductor, a multi-wire proportional counter ( The same applies to a multi-anode type photomultiplier tube in which a gas counter) and dynodes are made of fine mesh .
[0026]
【The invention's effect】
According to the present invention, even when a plurality of channels react simultaneously, the position of the center of gravity can be easily obtained because the resistance ladder performs hardware calculation based on DA conversion. In addition, a channel that does not respond does not output a signal, and a channel that has already output a signal pulse does not output a signal for a while, so that the throughput as the number of pulses that can be processed per unit time is impaired. There is nothing. Furthermore, since the number of signal lines necessary for reading a large number of detection cells is encoded into analog information, it has an excellent effect that it may be extremely small, such as only two.
[0027]
The application target of the present invention is not limited to a one-dimensional array of detection cells, but can be similarly applied to a two-dimensional array or more, and is highly effective when the number of dimensions is large. In particular, it is suitable for combining with the techniques of Patent Documents 1 and 2.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of an incident position detecting device using a conventional priority encoder. FIG. 2 is an explanatory diagram showing a state of oversampling. FIG. 3 is a time chart showing a problem of a priority encoder during oversampling. FIG. 4 is a circuit diagram showing the configuration of the first embodiment of the present invention. FIG. 5 is a time chart showing an example of the shape of a pulse output from the encoder in the first embodiment. FIG. 7 is a block diagram showing the overall configuration of the second embodiment of the present invention.
DESCRIPTION OF SYMBOLS 10 ... Radiation detector 20 ... Preamplifier 22 ... Shaping amplifier 24 ... Variable amplification amplifier 26 ... Wave height discriminator 28A, 28B, 28C ... Comparator 30 ... Encoder P ... Pulse 34 ... Resistance ladder 38 ... Divider

Claims (3)

An incident position detection device for detecting the position of the center of gravity of an incident incident across a plurality of detection cells,
Wave height discriminating means for discriminating the level of the input signal of each detection cell;
An encoder for generating a pulse of predetermined width having a height corresponding to the discriminated level,
A resistor ladder to which the pulses are entered in the position corresponding to the channel signal is input,
Reading means connected to both ends of the resistance ladder,
An incident position detecting apparatus for detecting the position of the center of gravity of an event by comparing the magnitude of the output of the reading means. The incident position detecting device according to claim 1 , wherein the wave height discriminating means is a discriminator having a plurality of threshold values. Incident position detecting device according to claim 1 or 2 wherein the resistor ladder are more connected in series.

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