JPH0568672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a pile-up reactor for removing from a measurement object pulses from which accurate peak value information cannot be obtained due to pile-up.

"Prior art" In the field of radiation spectroscopy, which measures the energy spectrum of radiation, the pulse output from a radiation detector is shaped and then the peak value is measured according to the energy. .

Figure 7a shows various pulses P1, P2, P output from the radiation detector and supplied to the linear amplifier.
It represents 3. For example, in a linear amplifier equipped with a Gaussian waveform shaping circuit, this pulse waveform is integrated and shaped into Gaussian waveforms G1, G2, and G3 (FIG. 4(b)). The peak deviation Δ between a and b in the figure is due to the shaping time constant.

By the way, each wave height value of Gaussian waveforms G1 and G2 is
They are each proportional to the energy of the radiation corresponding to the pulses P1 and P2, and can be converted into energy information by an AD converter (not shown). However, regarding the Gaussian waveform G3, the corresponding pulse P3 is piled up on the pulse P2, so the peak value information is excessive. Pulses from which accurate peak value information cannot be obtained due to pile-up must be removed from the measurement target.

FIG. 8 is for explaining one of the principles of a conventionally used pile up reactor for this purpose. Assume that pulses P4 and P5 are generated close to each other, causing a pileup, as shown in FIG. Conventionally, after performing the waveform shaping shown in FIG. 7b, a peak hold circuit (stretcher) added to the linear amplifier was used to hold the peak value information (FIG. 8b). When a peak is detected, a gate pulse (solid line c in the same figure) is output to supply the held peak value information to the AD converter, while when another peak is detected within a predetermined period of time after the peak is detected. The gate pulse (dotted line c in the figure) was not output, and the peak value information where the pile-up occurred was rejected before the AD converter. Another method is to digitally input pileup information to the AD converter and not store the conversion result in memory, or to digitally inhibit AD conversion.

``Problem that the invention seeks to solve'' However, for the former, AD converters originally have a built-in peak hold circuit;
Adding this to a linear amplifier means duplicating the same function. Therefore, measurement accuracy, noise resistance, and stability of the measuring device cannot be sufficiently improved.

The latter depends on the digital circuit of the AD converter, and can only be used with a specific combination of linear amplifier and AD converter.

In view of these circumstances, it is an object of the present invention to provide a pile-up reactor that can remove signal portions in which pile-up has occurred without using gates or digital interfaces.

"Means for Solving the Problem" As shown in principle in FIG. 1, the present invention includes a pile-up detection means 1 for detecting a pile-up, and an input signal 2 for a predetermined period of time after the pile-up is detected. The pile-up reactor is equipped with a level conversion means 4 for raising the output signal 3 to a signal level higher than a predetermined reference signal level, and the pile-up portion is substantially removed during AD conversion. That is, by raising the piled-up signal portions to a level higher than the ULD (upper level discriminator) level of the AD converter, these signal portions are excluded from AD conversion. Also
Even if AD conversion is performed, if the result is set to be a value higher than the maximum signal level of a normal input signal, this value can be ignored in the subsequent circuit and the same result can be obtained. can be obtained. Moreover, in this case, it is also possible to measure the incidence of pileups.

"Example" The present invention will be explained in detail with reference to Examples below.

FIG. 2 shows an example of a radiation measurement system using the pile up reactor of the present invention. In this system, the detector 11 outputs a pulse 13 having a peak value proportional to its energy every time it detects radiation emitted from a radiation source 12. The pulse 13 is supplied to a pile-up reactor 15 after passing through a preamplifier 14 .

Input terminal 1 of pile up reactor 15
The input signal 17 supplied to the linear amplifier 6 is input as is to the linear amplifier 18 and amplified, and a signal detector 19 detects the arrival of a pulse. Retriggerable single shot circuit 21
generates a pile-up detection pulse 22 having a predetermined time width every time the signal detector 19 detects a pulse. For example, the pile-up detection pulse 22 has a time width T (FIG. 3 b) that is longer than the maximum predictable time width from the start to the end of the shaped single Gaussian waveform G (FIG. 3 a). Set.

The pulse generator 23 is a single shot circuit 2
If the signal detector 19 detects the next pulse while the pile-up detection pulse 22 is being output from 1, it outputs a reject pulse 24, assuming that a pile-up has occurred. However, this reject pulse 24 can use a waveform with an optimal shape depending on the waveform shaping method, and does not need to be a square wave as shown in the figure. This reject pulse 24 is supplied to the linear amplifier 18, and while this pulse 24 exists, the signal level on the output side is within the conversion upper limit range (ULD) of the AD converter 26.
be raised to a higher value.

Such signal processing will be explained with reference to FIG.
As an input signal 17 to the input terminal 16 of the pile up reactor, a pulse P4 as shown in FIG.
Assume that P5 is input. The amplifier 18 shapes the first pulse P4 and sends it to the output terminal 29 as an output signal 28 (FIG. 4b) having a Gaussian waveform G4. On the other hand, the signal detector 19 detects the arrival of the pulse P4 and outputs the output terminal Q of the single shot circuit 21.
Along with this, the pile-up detection pulse 22
(Fig. 4c) is output. During the time that this pile-up detection pulse 22 is being output, the signal detector 19 detects the next pulse P5 and supplies the detection output to the pulse generator 23. Pulse generator 23
This detects pile-up and generates a reject pulse 24. Furthermore, the retriggerable single shot circuit 21 extends the pile-up detection pulse 22 by a new time width T from this point.

Now, the reject pulse 24 is supplied to the linear amplifier 18, and its output is sent to the AD converter 26.
(4th ULD level)
Figure b). In the case of the previous pulse P4, when the AD converter 26 detects the shaped peak, it converts the peak value into a digital signal and writes it into the memory 31. In the case of pulse P5, linear amplifier 18
output level is higher than the ULD level. Accordingly
The AD converter 26 does not perform the conversion, and no peak value information (energy information) is written to the memory 31.

When the reject pulse 24 falls, the portion beyond the peak of the Gaussian waveform G5 after shaping is AD
It is input to converter 26. In this part, the signal level is attenuated over time, so the AD converter 26 cannot detect the peak value.
Similarly, no conversion into digital signals is performed. As a result, the work of measuring energy information for pulse P5 is completely rejected. Note that the duration of the pileup detection pulse 22 is extended due to the presence of the pulse 5, so if a new pulse arrives during this duration, it is assumed that a pileup has occurred. In other words, in this case as well, the AD conversion work will be rejected.

"Modified Example" By the way, in the embodiment described above, in order not to measure the pile-up pulse, the signal in which the pile-up has occurred is raised to a level higher than the ULD level of the AD converter 26, but the present invention is not limited to this. do not have. That is, it may be lower than the ULD level as long as it is higher than the highest signal level expected for a signal that is not piled up. FIG. 5 corresponds to FIG. 4 and shows an example in which the ULD level is raised to a level lower than the ULD level.

In this case, the AD converter 26 also converts the pulse in which the pileup has occurred into a digital signal. The converted pulse height information is written into the memory 31, and can be used as reject information (pileup occurrence information) separate from energy information about pulses in which no pileup has occurred. FIG. 6 shows an example of the contents stored in the memory 31 in such a case. In the memory 31, information regarding the measurement time and information on rejected pulses are stored in a multi-channel manner together with the original energy information.

``Effects of the Invention'' As explained above, according to the present invention, the signal causing the pileup is raised to a predetermined signal level to be distinguished from other signals. There is no need to provide a hold circuit, and AD
There is no need for an output gate circuit to control on/off the signal supplied to the converter. Furthermore, the logic is simpler than the conventional pile-up reactor, and since no processing is performed on pulses in which no pile-up has occurred, it is advantageous in terms of measurement accuracy, noise, and circuit stability. Also, since the digital signal of the AD converter is not used,
Any AD converter can be used as long as it is equipped with a ULD, and as explained in the modification example, it is also possible to measure the occurrence of pulses that have caused pile-up, reducing the number of pulses that are omitted due to pile-up. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic configuration of the present invention, and Figs. 2 to 4 show an embodiment of the present invention, of which Fig. 2 shows a radiation measurement system using a pile up reactor. , Figure 3 is various waveform diagrams showing the relationship between the shaped pulse and the pile-up detection pulse, Figure 4 is a waveform diagram showing the waveforms of each part of the pile-up reactor, and Figure 5 is the output of the linear amplifier. A waveform diagram showing a modified example of the signal, FIG. 6 is an explanatory diagram showing the memory configuration in this modified example, FIG. 7 is a various waveform diagram showing various pulses and waveforms after shaping, and FIG. 8 is a diagram showing a conventional pileup. FIG. 6 is various waveform diagrams for explaining processing operations of a rejector. DESCRIPTION OF SYMBOLS 1... Pile-up detection means, 2... Input signal, 3... Output signal, 4... Level conversion means, 1
8...Linear amplifier, 19...Signal detector, 23
...Pulse generator, 26...AD converter.

Claims (1)

[Scope of Claims] 1. Pile-up detection means for detecting pile-up, and level conversion for raising the input signal to a signal level higher than a predetermined reference signal level for a predetermined period of time from when the pile-up is detected and outputting the signal. 1. A pile-up reactor, comprising means for removing pile-up by raising the signal level of the level converting means. 2. The pile up reactor according to claim 1, wherein the reference signal level is at or higher than an upper limit value for signal conversion of an AD converter. 3. The pile-up according to claim 1, wherein the reference signal level is lower than the upper limit value for signal conversion of the AD converter and higher than the maximum signal level of a normal input signal. Rejecta.