JPS58200186A - Gain stabilizer - Google Patents

Abstract

PURPOSE:To automate completely the compensation of the fluctuation of a pulse height value of a radiation detector, by measuring pulses having height values within a reference peak region on the distribution of the height of detection pulses, and by adjusting a gain of an ampflifier on the basis of the difference of a measured value from a set value. CONSTITUTION:A prescribed height value is set within the distribution of a reference peak of detector output pulse from a reference height value pulse generating source 1, only pulses having a prescribed height value or above out of the outputs of a pulse- height discriminator 10 are counted 11, and a gain 4 of a measuring system is adjusted roughly according to a control signal for adjustment of the gain which is obtained by calculating 12 the difference between a counted value and a reference count value set 13 beforehand. Moreover, two height value regions 5 and 6 are set within the distribution of the height of the reference peak, another control signal for adjustment of the gain is delivered on the basis of the comparison 9 between pulse counting rates 7 and 8 within the two height value regions, and thereby the gain 4 is adjusted. Then, whether or not the control signal for adjustment of the gain which is calculated 12 is within a prescribed range is discriminated 14, and either one of the control signals is selected according to the output of the discrimination.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain stabilizer for suppressing fluctuations in the output peak value of a radiation detector.

For detectors that use a radiation source built into the detector or installed outside the detector, or a photomultiplier tube, this applies to radiation detectors that can output pulses with a reference peak value from a pulsed light source for the photomultiplier tube. That is.

In the following, a NaI (Tj) scintillation detector doped with 4'/Am will be explained as an example. This detector requires pulse height analysis because the output peak value varies depending on the counting rate, temperature, long-term deterioration of the photomultiplier tube, etc.

When measuring the count value in a specific peak value section using a single channel analyzer, etc., an error may be introduced. As a conventional device for suppressing such fluctuations in peak value, there is a device shown in FIG.

In FIG. 1, / is 4'/Am-doped NaI ('
l) Scintillation detector 1.2 is the bias power supply for the detector, 3 is the preamplifier, Da is the main amplifier, S is the first
6 is a first single channel analyzer, ri is a first count rate meter, t is a first count rate meter, and D is a subtracter. Note that a gain stabilizer 100 is configured by the first and first single channel analyzers 3 and 6, the first and first count rate meters 7 and t, and the subtracter 9.

Next, the operation will be explained. jII/Am doped NaI (T
j) The r-rays incident on the scintillation detector l and the α-rays of 1 Da/Am built into the detector each generate optical pulses inside the detector, and as a result, an electrical pulse signal is generated as the output of the detector. This output is preamplifier 3. It is amplified and waveform shaped by the main amplifier and input to the normal measurement system, and is also input to the gain stabilizer/00C.

FIG. 2 shows the distribution of the output peak value of the main amplifier, with the horizontal axis showing the detector output pulse peak value and the vertical axis showing the counting rate. On the left side of the dashed-dotted line 1 is the measurement target r.
The counting rate is indicated by @, and Koda/A for wave height fluctuation correction is shown on the right.
The ma-ray peak P is shown, and as shown in Figure 1, the pulse height value of the r-ray is usually smaller than the pulse height value of the -da/Amα ray. The first single channel analyzer j is adjusted so as to output a pulse only in response to a pulse having a peak value between the peak value H/ and HJ in FIG.
The single channel analyzer 6 measures the peak value HJ in Figure 2.
It is adjusted so that a pulse is output only by burning a pulse having a peak value between and Hj.

H/, Hj and HJ, HJ are generally taken almost symmetrically with respect to the central wave height Hθ of the C41/Amα line peak.
1. The output of the single channel analyzer 3.6 is the count rate meter 7. f and outputs an output proportional to the counting rate. Counting rate now? , t's output as n/.

Let n2 be input to the subtracter 9 for both outputs, where n/, f
Output the difference Δn:n/-n between i and 4? Adjust the gain of the main amplifier by the edge value and sign. This adjustment will be explained in more detail below.

Now, set the single channel analyzer s, 6 so that n/=n.If the output of subtracter 9 is negative, the main amplifier gain will be automatically lowered in proportion to its absolute value. If the number 9 is positive, its MI! To automatically increase the main amplifier gain in proportion to the relative value. A case where the output pulse height value decreases at a constant rate due to a decrease in the amplification factor of the photomultiplier tube will be explained with reference to FIGS. 3(a) and 3(b). In Figure 3, for simplification, H2=HJ=HO
As shown in Figure 3(a), which shows only the 21I/Ama line peak P, n/: n
After initial setting of J, when the peak value decreases as shown in Fig. 3(b), n/)n is therefore output from the subtractor D, Δn.
=n/-n is a positive number. As already mentioned, when Δn is positive, the main amplifier gain is automatically increased in proportion to its absolute value, so the peak value returns to its initial state.
n/=n, and as a result, Δn=0, and the gain adjustment operation ends.

When the peak value increases, a phenomenon opposite to that described above occurs, and gain adjustment is performed by a similar process.

Note that instead of adjusting the gain of the main amplifier, the pulse height value may be adjusted by adjusting the voltage of the bias power supply and changing the multiplication factor of the photomultiplier tube.

The conventional device has Km as described above, but if the peak value suddenly changes for some reason, or if the measurement system fails when the power is turned on, the initial peak value setting state is changed as shown in Figure 2(a). There are cases where the values of n/ and nJ become equal for different wave height values, and as shown in Figure (b), depending on the shape of the wave height distribution, the gain may not be able to be adjusted in the direction that should be adjusted.
//nJ or n/<n condition may not be resolved forever, and the ability to adjust to peak value fluctuations may eventually be lost. Although FIG. 9 shows the case where the peak value suddenly increases, a similar phenomenon may occur when the peak value suddenly decreases. Therefore, it was not possible to completely automatically correct wave height fluctuations.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it is possible to generate a pulse having a higher peak value than the pulse peak value due to the radiation to be measured through a radiation detector. In a radiation detector equipped with a constant reference pulse generation source, appropriate peak values are set at seven points within the reference peak region on the detector output pulse wave height distribution caused by the reference pulse generation source, and the peak values higher than that are set. After measuring only the pulses that have a value of From making adjustments, measurement system 11
It is an object of the present invention to provide a gain stabilizer that can fully automate the correction of fluctuations in pulse peak values, even when phenomena such as resolution deterioration occur.

An embodiment of the present invention will be described below with reference to FIG.

As with the conventional example, a co-Q/Am-doped NaI ('I'j) scintillation detector will be taken as an example. In FIG. 3, the gain stabilizer 10/ is replaced by the reference numerals 5 to 5 shown in FIG.
In addition to the element pointing to 90, elements 10 to /41 are newly provided, but the other components are the same as in Figure 1. Therefore, the output pulse height distribution of the main amplifier is also the same as in Figure 1. Same as shown. To explain an additional element, lθ is a pulse height discriminator, which is designed to produce an output only when the input pulse has a pulse height value greater than, for example, HQ in FIG. // is a count rate meter that receives the output of the pulse height discriminator and outputs a voltage proportional to the count rate of the pulse with a peak value of HII or higher as the count rate n3;
/2 is a first subtractor, which calculates the difference (Δn'==
n J = n30).

This output is also used to adjust the gain of the main amplifier.

The opening and closing of the output gates of the subtracters 9 and 1 can be controlled by external signals. Further, n30 of the reference counting rate setter/3 is designed so that it can be set from the outside. The comparator/lI constantly receives an output from the output terminal/Ja of the subtracter/l, determines the magnitude relationship between the output and a numerical value set in advance in the comparator, and then outputs the subtracter D or l according to the result. Outputs cohegate signal. As a result, the output of the subtracter 9 or /2 is given to the main amplifier 4I for gain adjustment of the main amplifier. It is preferable to set the peak value of the α-ray pulse at 2II/km so as to be negligibly small. (K4 (/Amα ray pulse height value is NaI (Tj)
(This can be changed by controlling the amount of T1 in the small Na1(Tj) crystal doped with CollAm, which is optically bonded and embedded in the core.) Also, when initially setting the peak value, single channel 3
．． 6 and the pulse height discriminator IO are fidgety and output only for pulses with peak values between H/ and H3, between H and H3, and between H41 and higher as shown in Figure 2. Although it is common to set it so that it appears, here, for convenience of explanation, it is assumed that H3=HO and Ht=Hda. That is, in the case of a single channel, the wave height discriminator 6 and the wave height discriminator 10 each have a wave height value of H/-HO, a wave height value of HO to He, and a wave height value of It is set to output only for pulses having a peak value of H41 or higher. Therefore, the first. The outputs n/, n and H3 of the first and third count rate meters 7, f and // correspond to n/, n2 and H3 in Fig. 6 1a), (bl and (C), respectively) At the initial setting shown in Fig. 6(a), HO, H/ and Hda are n.
/==n, and the value of H3 at that time is n3=n30. The output of the reference counting rate setter 13 is set equal to this n30.

In the above configuration, the output Δn'=n3-n30 is always input from the output terminal l core a of the first subtractor 12 to the comparator ip, and this comparator satisfies the following condition -α ny-n3o
+β ・ ・ ・′(1) (α and β are O or positive numbers) The output is controlled as follows depending on whether they are satisfied.

(b) When condition (1) is satisfied, the output (gate signal) from the comparator/da closes the gate of the output terminal (l/b) of the subtracter/co, and then opens the output gate of the subtracter 9. The output of the subtracter 9 is used for gain adjustment of the main amplifier.

(b) If condition (1) is not satisfied, the output gate of the subtracter D is closed by the output (gate signal) from the comparator /+1, and then the output terminal of the subtracter l (/
Opening the gate b) allows the output of the subtracter l to be used for gain adjustment of the main amplifier.

The above (a) and (b) will be explained in detail with reference to FIGS. 6(b) and (c) K. FIG. 6(b) shows an example of a case where there is a sudden increase in the Norls wave height value when the energy resolution of the measurement system is deteriorating. Due to this sudden change in the peak value, the set peak value H/, HO of the single channel analyzer 3.6.

If H41 deviates significantly from the Koda/Amα line peak, as shown in Figure 6(b), it may become n/=n at a point away from the peak position, or the gain adjustment direction (increase or decrease) may be reversed. As mentioned above, the conventional gain stabilizer alone may lose its ability to correct peak value fluctuations. However, in such a case, for a properly chosen β value, ICnJ>nJθ+β (i.e., nj−n3
0>β) holds true. Therefore, since the condition (/) is not satisfied, the output signal of the subtracter l (Δn'=
nj-rx30) to adjust the gain of the main amplifier. As a result, when the Δn' value becomes equal to β, condition V) is satisfied, and the gain of the main amplifier is adjusted according to the above (A) using the output signal of the subtracter D (Δn=n/-n). become. The situation is the 6th
As shown in Figure (C). Figure 6 (n/=n in C1
From the premise that after J, becomes 1, n, )<nJO+β is satisfied and the resolution is degraded, n,?
＞n,? It can be seen that θ>n30−α is also satisfied, and the gain is subsequently adjusted by the output signal of the subtracter t for fluctuations in the peak value near this. Even if there is a sudden increase in the peak value similar to the above when the resolution is improved, the gain is basically adjusted by the same operation as above. However, considering the case where the gain of the main amplifier is adjusted in the form of n/''n by the output of the subtracter 9, n% < n 30 because the resolution has improved. By appropriately selecting α, all of the predetermined resolution improvement widths can be set to n3':2n30-α.Therefore, condition (1) is satisfied, and the gain is subsequently adjusted by the output of the subtracter 9. The same thing can be seen when a sudden decrease in the peak value occurs.

The above-mentioned α and β are obtained by changing the state of the gate signal of the comparator/4I due to the gain adjustment using the output of the subtracter 9.
, is a value set with hysteresis characteristics in order to prevent vibration between the two controls by switching to gain adjustment using the output of 2, and as mentioned above, the core atp, 6n due to the expected degradation or improvement of resolution when there is no position variation.
It must be set to a value large enough to include the range of increase/decrease in the j value and when condition (1) is satisfied (the output signal of the subtractor de should be set so that the gain can be adjusted correctly. If β is large, even if the situation shown in Figure 6(b) K occurs, nj × n30 + β, and the gain adjustment is continued using the output signal of the subtractor D. In this case, n/=n, so the peak value fluctuation correction ability is achieved. Note that in the above embodiment, the case where the gain of the main amplifier is controlled by the signal of the subtracter 9 or / is explained, but instead of the gain of the main amplifier, other Gain change element 1 For example, in scintillation detection a, the voltage of the bias power supply may be controlled.
Although the wave height discrimination @10 was used in the above embodiment, any other device may be used as long as it functions substantially equivalently. Also.

In the above embodiment, the count rate meter 7, t, // is connected to the single channel analyzer 3.6 and the pulse height discriminator 10, but this is used as a counter and a subtracter is used for each count for a fixed period of time. Or load it into /.

In addition, the same operation as in the embodiment may be performed by making the reference output from the reference needle wheel setter/3 correspond to the fixed time. Such a change can be easily handled by changing the setting value inside the counter or subtracter or the reference count rate setter. Furthermore, subtractor 9 or /co.

The reference counting rate setter, the comparator/da, etc. may be replaced with a computer, a microprocessor, etc., and all the calculations and controls described in the above embodiments may be performed by software, and the same effects as in the above embodiments can be obtained.

Furthermore, in the above embodiment, Co4(/Am-doped NaI(T)
j) The explanation was given using a scintillation detector as an example.

Wave height distribution as shown in Figure 1 by 411Ama line-51 A peak is formed on the wave height distribution that has a wave height value similar to the above peak, but is higher than that, and there are no pulses with varying intensity. A reference peak value pulse with constant intensity such as a source (a nuclide that emits alpha rays with appropriate energy and a long half-life is sufficient).

24 (in addition to /Am, for example, it is possible to increase 3tPu), any detection system may be used to achieve the same effect as the above embodiment. As such a detection system, for example, instead of a NaI (TJ) scintillation detector, a C5I (Tj), anthracene, plastic scintillator, BO2 wheel)/scintillation detector generates a reference peak value pulse with a constant intensity as described above. It is possible to raise a doped source,
Alternatively, the inner wall surface of the gas proportional counter tube may be coated with an α detection nuclide such as CoII/Am.

An α spectrum similar to that obtained with a scintillation detector doped with 41/Am can be obtained.

As described above, according to the present invention, radiation 1 to be measured
A reference peak value pulse with a constant intensity that can be generated via a radiation detector using a pulse having a pulse peak value higher than that of the pulse peak value by IjVC. Wave value Set an appropriate wave height value at point K1 within the reference peak area on the detector output pulse wave height distribution caused by the pulse generation source [7. Use a wave height discriminator to measure only pulses with wave heights higher than By roughly adjusting amplifier gain or gain change factors such as bias voltage according to the difference or ratio with the set value, fluctuations in the pulse peak value are roughly corrected, and then a conventional gain stabilizer is used to accurately stabilize the pulse wave. By correcting fluctuations in high prices, the following effects can be obtained.

(1) Even if a sudden and large change in peak value occurs, the ability to correct the change in peak value can be corrected without losing the ability to correct the change.

(,2) When the measurement system is powered on, no matter what the initial state of the peak value is, it is possible to automatically correct the peak value to the set value.

(3) Items (1) and (2) allow complete automation of pulse height value fluctuation correction.

[Brief explanation of the drawing]

Figure 1 is a block diagram schematically showing a conventional gain stabilizer.
j) Waveform diagram showing an example of wave height distribution of scintillation detector output, Figures 3 (a) and (b) are waveforms for explaining the operating principle when the conventional gain stabilizer shown in Figure 1 is used. Figure 1 (a) and (bl are the first
FIG. 3 is a waveform diagram for explaining the drawbacks of the conventional gain stabilizer shown in FIG.
a), (bl and (C) are waveform diagrams for explaining the operation of Fig. 3. In the figure, l is 2'l/km doped NaI (Tj)
Scintillation detector, 2 is a bias power supply, 3 is a preamplifier, DA is a main amplifier, 3 and 6 are each the first
and the first single channel analyzer, 7 and l are the seventh and first count rate needles, 9 is the subtractor, 10 is the pulse height discriminator, 7/ is the third count rate needle, and l is the third count rate needle. is a first subtractor, /j is a reference counting rate setter, /41 is a comparator, and 10/ is a gain stabilizer. In Figure 1, the same reference numerals indicate the same or equivalent parts. Homura Figure 3 (b) Draft 4 Procedural Amendment (Voluntary) Mr. Commissioner of the Japan Patent Office 1, Indication of the Case Patent Application Sho I Cou # Reference J4-No. 2,
Name of the invention Gay VXI Busyzu 3, VA representative Hitoshi Katayama Part 4, agent Subject of amendment (1) Scope of claims in the specification (2) Details of the invention in the specification Abuse of explanation Contents of amendment (1) The scope of claims is amended as shown in the attached sheet. (2) “Insulation value” on page 3 of the specification shall be corrected to “absolute value”. (3) "Standard counting rate" on page 1j, line d of the same page is changed to "Standard counting rate".
and correct it. (4) Correct it to the "fixed time count value" of "fixed time" on page 13, line Sj. (5) "α Detection" in the I column of page 1A' is corrected to "α ray emission", and "e1 spectrum" in the / D row of the same page is corrected to "α ray spectrum". (6) "(J) From items (1) and (2)...O can be automated." on page 17, line 4-It is corrected as follows. rcJ) Items (1) and (2) can be corrected even if the energy resolution of the III constant system changes. (4) From items (1), (2), and (3), it is possible to completely automate the correction of fluctuations in pulse height values. ” Pulses from a reference peak value pulse generation source that generates pulses with a reference peak wave height distribution higher than the pulse height value due to the radiation to be measured are generated via the radiation detector used for measurement, and this is In a gain stabilizer that adjusts the gain of the measurement system by monitoring the reference peak wave height distribution output from the radiation detector obtained by A predetermined pulse height value is set within the clock, and a device Y having a pulse height discrimination function is used to count only the pulses having a pulse height value greater than or equal to the predetermined pulse height value. A first control system that roughly adjusts the gain of the measurement system using a gain adjustment control signal that takes the difference or ratio of The control signal for gain adjustment is determined by comparing the pulse count rate within
a first control system that outputs a signal No. 1 and adjusts the gain of the measurement system, and sets a range of a gain adjustment control signal of the first control system so that the gain adjustment control signal is within the range. Whether it's there or not! A gain stabilizer characterized in that the outputs of the first and first control systems are selected by determining the outputs, and the gain of the measurement system is thereby adjusted.

Claims (1)

[Claims] Pulses from a reference peak value pulse generation source that generates pulses with a reference peak height distribution higher than the pulse peak value of the radiation to be measured are passed through the radiation detector used for measurement. , a gain stabilizer that adjusts the gain of the measurement system by monitoring the reference peak wave height distribution output from the radiation detector thus obtained.
Set a certain predetermined peak value within the reference peak peak height distribution of the detector output pulse from the reference peak value pulse generation source,
Using a device having a pulse height discrimination function, only pulses having a pulse height value equal to or higher than the predetermined pulse height value are counted. A first control system that roughly adjusts the gain of the measurement system using a gain adjustment control signal that takes the difference or ratio between the counted value and a preset reference counted value; Two peak value regions are set, and a control signal for gain adjustment is output by comparing the pulse count rates within the five peak value regions. and a second control system that adjusts the gain of the measurement system, sets a range of a gain adjustment control signal of the seventh control system, and determines whether the gain adjustment control signal is within the range. A gain stabilizer characterized in that the outputs of the first and second control systems are selected, thereby adjusting the gain of the measurement system.