JPS6154488A - Measuring method of live time - Google Patents

Abstract

PURPOSE:To take an accurate measurement of live time through a simple circuit by stopping measuring the live time temporarily with a detection signal of radiation and also restarting the measuring operation with a busy signal outputted in the signal conversion ready state of an AD converter. CONSTITUTION:A linear amplifier 22 raises a piled-up pulse signal up to the level ULD of the AD converter so that AD conversion is disallowed, and excludes the piled-up signal from an object of measurement. When the linear amplifier 22 outputs a pulse signal 25, and AD converter outputs the busy signal 48 in a conversion ready signal level to convert a crest value into a digital signal, and the busy signal 48 is inputted to the set terminal S of a flip-flop circuit 41 to set the flip-flop. Simultaneously, a gate control signal 42 rises to a level H and a live time clock 44 is passed through an AND gate and counted by a counter timer 46; every time the pulse signal 21 arrives, the flip-flop circuit 41 is reset or set alternately to integrated the level time.

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention is a method for measuring only live time, excluding the period in which this signal exists, when a signal unsuitable for measurement arrives during radiation measurement. Concerning live time measurement method.

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

In such measurement fields, pile-up prevention is used during measurement to exclude signals from which accurate peak value information cannot be obtained due to pile-up from the measurement target. In such a case, in order to measure the total effective measurement time, ie, live time, for the signal for which measurement has been performed, it is necessary to subtract the time during which measurements are excluded due to pile-up, ie, dead time, from the total measurement time.

Figure 4 shows how to measure live time using U.S. Patent No. 38
This figure shows an outline of the circuit proposed by No. 14937. In this circuit, a pulse signal supplied to a line 1 provided on the output side of a preamplifier (not shown) is supplied to both a fast channel amplifier 2 and a slow channel amplifier 3. The pulse signal 4 output from the first channel amplifier 2 is subjected to a pile-up rejection section 5 to detect the presence or absence of pile-up. The output 1 word 6 of the pile-up rejection unit 5 becomes active every time a normal pulse signal in which no pile-up occurs, and remains inactive for a pulse signal in which a pile-up occurs.

On the other hand, the pulse signal 7 output from the slow channel amplifier 3 is input to the signal processing section 8.

(W processing [8Lt is composed of control logic, pulse stretcher, and linear gate. Of these, the linear gate is used to control the slow channel whose peak is bolded by the pulse stretcher every time the output signal 6 of the first channel becomes active. The signal is supplied to the multi-channel analyzer (MCA).The control logic uses the signal 7 input to the signal processing section 8.
A pulse signal 9 corresponding to the output signal 6 is generated on the condition that the peak value of the signal is within a normal signal level range.

Now, the pulse signal 4 is also supplied to the set terminal S of the flip-flop circuit 10, and this is set. When the flip-flop circuit 10 is set, the AND gate 12 is closed by the signal 11 output from its output terminal Q, and the counter timer 13 is activated by the clock generator 1.
The supply of the live time measurement tarokku 15 outputted by 4 is cut off. In this state, if the signal 17 supplied from the other AND gate 16 to the reset terminal R of the flip-flop circuit 10 is held at L (low) level, the live time measurement will remain suspended. It turns out. Such cases include: ■ When the pulse signal 9 that should be output in response to the pulse signal 4 is not output due to the reason mentioned above, or ■ When the multichannel analyzer is busy and its output signal 18 is kept at L level. It's time to be there.

In response to this, the flip-flop circuit 10 is immediately reset if the pulse signal 9 is output and the H (high) level signal indicating that the multi-channel analyzer is not busy is output. The live time measurement by the counter timer 13 is restarted.This live time measurement is continued until the next pulse signal 4 is detected, and the live time is accumulated by repeating the above operation.

"Problems to be Solved by the Invention" By the way, the previously proposed live time measurement methods described above have complicated circuit configurations, which is disadvantageous in terms of circuit reliability and cost.

In view of the above circumstances, an object of the present invention is to provide a live time measurement method that uses a simple circuit and enables accurate measurement.

"Means for solving the problem" In the present invention, in a predetermined case such as when a pileup occurs, the input signal is raised above the 0LD (upper level discriminator) level of the AD converter, During this time, live time measurement will be interrupted. Furthermore, while the live time measurement is temporarily stopped by the radiation detection signal, the measurement is restarted by the busy signal outputted when the AD converter is in the signal conversion enabled state.

According to this, the signal processing section shown in FIG. 4 is not required,
Significant simplification of the circuit can be achieved.

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

FIG. 1 shows a circuit portion that implements the live time measuring method of this embodiment. Every time a radiation detector (not shown) detects radiation, it outputs a pulse signal having a peak value proportional to its energy. These pulse signals 21 are supplied to an input terminal 23 of a linear amplifier 22 after passing through a preamplifier (not shown). An AD converter (not shown) is connected to the output terminal 24 of the linear amplifier 22, and detects the peak of the pulse signal 25 shaped into a Gaussian waveform and converts the peak value into a digital signal. It has become. A digital signal corresponding to each pulse signal is also written into a memory (not shown) as peak value information (energy information).

By the way, this linear amplifier 22 raises the piled-up pulse signal above the ULD level of the ΔD converter, thereby making AD conversion impossible and excluding the piled-up pulse signal from the measurement target. A control logic 27 is provided for this purpose. Control logic 27 is input terminal 2
This is a circuit for detecting pile-up by inputting the output signal 29 of the buffer 28 connected to the buffer 28.

FIG. 2 shows an example of this control logic. The control logic 27 is a signal detector 31
, a single shot circuit 32 and a pulse generator 33. The signal detector 31 detects the arrival of a pulse from the output signal 29 of the buffer, and outputs a pile-up detection pulse 3 with a predetermined time width from the single shot circuit 32.
Output 4. If the signal detector 31 detects the next pulse while this pile-up detection pulse is being output, the pulse generator 33 outputs a pile-up signal 35, indicating that a pile-up has occurred.

Note that since the single shot circuit 32 used here is a retriggerable circuit, when pile-up occurs continuously, the time width of the pile-up detection pulse is extended accordingly.

The pileup signal 35 is supplied to the linear amplifier 22. While this pile-up signal 35 exists, the linear amplifier 22 raises the pulse signal 25 in that portion above the ULD level (see the broken line 36 in FIG. 1). In this way, pileup is removed.

Now, when the pileup is removed in this way,
The live time must be corrected (shortened) by the removed time. The delay logic 37 and subsequent circuit parts in FIG. 1 represent a live time measurement circuit that performs such correction and measures live time. Of these, the delay logic 37 is configured to delay the buffer output signal 2 in consideration of the shaping time constant of the linear amplifier 22.
This is a circuit that delays 9. The flip-flop circuit 41 is reset by the pulse signal 39 output from the delay logic 37. As a result, the gate control signal 4 is output from the output terminal Q of the flip-flop circuit 41.
2 becomes L level, and the live time clock generator 43
The live time clock 44 supplied from the 2-input AND gate 45 is cut off by the 2-input AND gate 45. That is, in this state, the live time clock 44 for the counter timer 46
supply is cut off, and live time measurement is temporarily stopped.

On the other hand, when the pulse signal 25 is output from the linear amplifier 22, the subsequent AD converter outputs the busy signal 48 when the pulse signal 25 is at a convertible signal level, and converts the peak value into a digital signal. The busy signal 48 is input to the set terminal S of the flip-flop circuit 41 and is set.

At the same time, the gate control signal 42 becomes H level, and the live time clock 44 passes through the AND gate and is counted by the counter timer 46. In other words, live time measurement will be restarted. Live time measurement is performed using the flip-flop circuit 41 based on the next pulse signal 21.
will continue until it is reset again. Similarly, each time the pulse signal 21 arrives, the flip-flop circuit 4
1 repeats the reset state and set state, and the live time is accumulated. If a pile-up occurs during this integration operation, the busy signal 48 will be interrupted during this period, and the live time measurement will also be interrupted.

FIG. 3 shows the live time 1 . . . that exists between the numbers Ni, Ni+l . . . and the digital information written in the memory. ．． 1. . 1...
・It represents. Assuming that the average value of live time is T, this is expressed by the following equation.

However, the numerical value n refers to the total number of pulse signals written in the memory as peak value information, and does not include piled-up pulse signals.

"Effects of the Invention" As explained above, according to the present invention, live time measurement is started using the busy signal generated when the AD converter is performing conversion, and is based on the pulse signal without waveform shaping. Since the measurement is stopped when the timer is pressed, live time measurement can be easily and accurately performed. In addition, in the event of a pile-up, the signal level is raised above the ULD level and live time measurement is interrupted, so even if a high-level signal unsuitable for measurement arrives at the same time, these can be easily removed as not being measured. can do.

[Brief explanation of the drawing]

Fig. 1 is a professional diagram showing a circuit section that implements a live time measurement method in an embodiment of the present invention, Fig. 2 is a block diagram embodying the control logic in this circuit section, and Fig. 3 is a block diagram embodying the control logic in this circuit section. FIG. 4, which is an explanatory diagram showing the temporal relationship between digital information and live time, is a circuit block diagram for realizing a conventional live time measuring method. 22... Linear amplifier, 27... Control logic, 41...
... Flip-flop circuit, 43 ... Live time clock generator, 45 ... AND gate, 48 ... Busy signal. Applicant: Representative of Japan Atomic Energy Corporation
Person Patent Attorney Ume Yu Yamauchi Figure 1 Figure ÷ Akira 2 Figure 3 Figure 4

Claims (1)

[Claims] When the analog level of the signal input from the radiation measuring instrument to the AD converter does not exceed a predetermined signal convertible range, a busy signal indicating the signal conversion state of the AD converter allows live time measurement to continue, while radiation is detected. A method for measuring live time, characterized in that live time is accumulated by temporarily stopping measurement of live time every time the busy signal is present, and restarting the measurement depending on the presence of the busy signal.