JPH0740683B2 - gamma ray measurement - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a γ-ray measuring device, and more particularly, to a highly accurate measurement result even when a radiation generating place and a monitoring place are separated from each other such as a nuclear power plant. The present invention relates to a γ-ray measuring device suitable for showing to an observer.

[Background of the Invention]

The γ-ray measurement device outputs a radiation detection sensor, a pile-up rejector that removes the accumulation of the linear pulse waveform that is the output of this sensor, a baseline regenerator that returns the baseline to zero potential, and a baseline regenerator. It usually comprises a counting means for counting the number of pulses. When installing this gamma-ray counting device in a nuclear power plant, etc., the supervisor is usually outside the radiation generation area,
It is necessary to transmit the measurement result to the monitoring place where the monitoring staff is. However, even when performing signal transmission, since the transmission system is provided in the radiation generation region, there is a problem that the deterioration of the transmission system due to radiation exposure becomes a problem, and the accuracy of the received measurement result deteriorates.

[Object of the Invention]

It is an object of the present invention to provide a γ-ray measuring device capable of obtaining a highly accurate measurement result even in an environment where the radiation measuring place and the monitoring place are separated and the signal transmission system is exposed to radiation.

[Outline of Invention]

The above-mentioned object is a radiation detection sensor that detects γ-rays and outputs an electric signal of a corresponding linear pulse, a pile-up rejector that removes the waveform stack of the linear pulse, and a DC of the linear pulse signal processed by the pile-up rejector. In the γ-ray measuring apparatus, which includes a baseline regenerator that removes the component and returns the baseline to a true zero potential, and a counting unit that counts the linear pulse processed by the baseline regenerator, By providing a first photoelectric converter that converts an output signal into an optical signal, an optical cable that transmits the optical signal, and a second photoelectric converter that converts the optical signal transmitted by the optical cable into an electrical signal, A pile-up rejector, a baseline regenerator, and a counting means are provided on the optical signal receiving side, and the input signal to the first photoelectric converter is provided. Means for adding a predetermined DC level to the signal, and means for separating the DC component after passing the output signal of the second photoelectric converter through the pile-up rejector,
A means for multiplying the DC component separated by the means by a predetermined gain; a ratio of a signal component obtained after passing the output signal of the pile-up rejector through the baseline regenerator and a DC component multiplied by the predetermined gain. And a pulse signal obtained by taking a ratio by the means is counted by the counting means.

A first photoelectric converter for converting the output signal of the radiation detection sensor into an optical signal, an optical cable for transmitting the optical signal, and a second photoelectric converter for converting the optical signal transmitted by the optical cable into an electric signal. By providing the converter, the pile-up rejector, the baseline regenerator, and the counting means are provided on the receiving side of the optical signal, and the output signal of the second photoelectric converter passes through the pile-up rejector to generate a DC component. Means for separating, means for multiplying the direct current component separated by the means by a predetermined gain, signal components obtained after passing the output signal of the pile-up rejector through the baseline regenerator, and the predetermined gain. It is also achieved by providing a means for calculating the difference from the DC component and counting the pulse signal obtained by calculating the difference by the means by the counting means.

A pile-up rejector and a baseline regenerator are provided on the receiving side of the optical cable, and the ratio or difference between the signal component of the received signal and the DC component is taken, so various influences on the optical transmission system should be removed comprehensively. Therefore, it is possible to transmit a highly accurate measurement result over a long distance.

〔Example〕

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

When monitoring radiation in a nuclear power plant, the radiation measurement site and the monitoring site by workers are distant from each other, and signal transmission is performed by an optical fiber cable between the sites.

A scintillator is used for detecting radiation, for example, γ rays. This scintillator takes in gamma rays and instead outputs photons. The output photons are amplified into an electrical signal by a photoelectric converter, eg a photomultiplier. Instead of the photomultiplier, a semiconductor photoelectric converter (having a amplifying function) may be used.

The converted electric signal is sent to a center, which is a monitoring site, through an optical fiber cable. Optical transmission using an optical fiber cable has been used recently because it is less susceptible to noise and easier to perform high-speed multiplex transmission as compared with electric signal transmission using a transmission line.

Especially in the measurement of γ-rays, the pulse height depends on the energy of the radiation, and the pulse rate is 10 ^-1 to 10 ^-6 CPS.
It is a high-speed linear pulse signal with spread. Therefore, the use of the optical fiber cable is effective.

Further, even in the optical transmission, there is a problem of transmission with a digital waveform or an analog waveform. The output of the photoelectric conversion means or the preamplifier required thereafter is a high-speed pulse having analog information in the pulse height and having a spread of 10 ^-1 to 10 ^-6 CPS in the pulse rate as described above. Also requires double pulse resolution of about 0.25 μsec. Therefore, it seems that optical transmission by digital waveform is difficult. Therefore, optical transmission using an analog waveform is effective.

FIG. 1 is a configuration diagram of a γ-ray measuring device which is the basis of the present invention. The radiation detector 1 includes a scintillator and a photoelectric conversion unit (for example, Photomal), and outputs an electric signal corresponding to detected radiation. The transmitter 2 comprises a terminal preamplifier 21, a current driver 22, and a light emitting diode 23. The terminal preamplifier 21 receives the electric signal detected by the sensor 1 and performs a predetermined amplification, and the current driver 22 obtains a necessary amount of current. The light emitting diode 23 generates an optical signal corresponding to the amount of current.

The optical fiber cable 3 transmits the optical signal generated by the light emitting diode 23 to the receiver 4.

The receiving unit 4 includes a light receiving diode 41, a preamplifier 42, a pileup rejector 43, a baseline regenerator 44, a wave height discriminator 45,
It consists of a counting circuit 46 and a display 47. The light receiving diode 41 receives the optical signal transmitted through the cable 3 and converts it into an electric signal. The preamplifier 42 inputs the electric signal of the light receiving diode 41 and increases the predetermined gain. The pile-up rejector 43 performs a process of excluding the integration of pulses within the decomposition time in order to prevent waveform stacking. The baseline regenerator 44 regenerates the baseline. The wave height discrimination circuit 45 shapes the waveform in order to remove noise and the like outside the measurement target. Counting circuit
46 takes in the output pulse of the wave height discrimination circuit 45 and performs counting.
The display circuit 47 displays the count value after calculation such as arbitrary unit conversion.

With only the basic configuration shown in FIG. 1, the optical fiber cable is only required to be outside the radiation generating region, but when it is inside the radiation generating region, the problem of radiation resistance characteristics arises. In particular, as the scale of a nuclear power plant increases, it is often the case that an optical fiber cable is laid through the radiation generation area. It is possible to use an optical fiber having high radiation resistance among optical fiber cables, for example, an SI type optical fiber having a pure quartz core. However, even with this material,
When γ-rays are irradiated at a dose rate of 2 × 10 ² R / h up to an integrated dose of 10 ⁴ R, the increase in transmission loss will occur by about 1 to 2 dB / km. This is a non-negligible loss.

Further, the light emitting diode may also be affected by radiation, or may deteriorate in characteristics due to aging. Furthermore, the characteristics change even when used in places with high ambient temperature.

2 (a) and 2 (b) show the transmission characteristics.

(A) The figure shows the characteristics of transmission loss in an optical fiber cable. The characteristic l ₁ shows the characteristic of the light emitting diode 23, the horizontal axis represents the input current, and the vertical axis represents the outgoing light power. According to this characteristic, the output light B is obtained for the input current A.

The characteristic l ₂ shows the characteristic of the light receiving diode 41, the vertical axis shows the incident light power, and the horizontal axis shows the output current. In the normal state, assuming that the level (M1) is as shown by the solid line, the output current becomes D1 for the incident light C1. However, if it becomes N1 as indicated by the dotted line due to the influence of radiation, the incident light C1 becomes like C2, and the output current also becomes like D1 to D2. The DC levels b1 and b2 of the output current are the baseline.

On the other hand, a characteristic diagram when the characteristic of the light emitting diode 23 is deteriorated is shown in FIG. What was the initial characteristic l ₁₁ is the characteristic l ₁₂
It is supposed to be like. As a result, the optical signal is B2 rather than B1.
, The output light level also changes from M2 to N2, and the waveform changes from C3 to C4.

When the transmission characteristics or the characteristics of the light emitting diode are changed as described above, the passing crest value of the crest discrimination circuit is constant. I try to input a pulse based on unnecessary noise. As a result, it may be difficult to measure radiation accurately.

FIG. 3 is an explanatory diagram of the principle adopted in the present invention to solve the above-mentioned problems. The attenuator 61 is a part corresponding to an optical transmission system and has a predetermined attenuation characteristic. This attenuator
The addition signal (S1 + S2) of the radiation linear pulse signal S1 to be measured and the DC component signal S2 is input to 61. The output X2 of the attenuator 61 corresponding to the signal (S1 + S2) corresponds to the output side signal of the optical transmission system. If the attenuation rate is α, then X2 = α (S1 + S2) (1).

The discriminator 62 separates the signal X2 into a DC component αS2 and a linear pulse component αS1. The relationship at this time is X3 = αS1 (2) X4 = αS2 (3).

The threshold control circuit 63 has a set value β for correcting various noise components, and the relationship between the input X4 and the output V1 is as follows.

V1 = βX4 = βαS2 (4) The comparison circuit 64 takes the ratio of X3 and V1.

As is clear from the equation (5), the output X5 has a value that does not include α. That is, the output X5 of the comparator 64 has a value that is not affected by the attenuation rate α due to the characteristic variation.

FIG. 4 is a configuration diagram of a γ-ray measuring device according to an embodiment of the present invention. The main points different from the basic configuration shown in FIG. 1 are that the DC signal S2 is input to the current driver 22, the low-pass filter 51 and the threshold control circuit 52 in the receiving unit 4.
And the wave height discriminator 45 is a baseline regenerator.
The configuration is such that the output of the threshold value control circuit 52 is input in addition to the output of 44. Other differences will become apparent in the description below.

The radiation detection sensor 1 includes a scintillator and a photoelectric conversion unit. Radiation is converted into an optical signal by the scintillator, and photoelectric conversion is performed by the photoelectric conversion unit. The preamplifier 21 increases a predetermined gain of the electric signal after photoelectric conversion. This output is a linear pulse and becomes the signal S1.

The current driver 22 superimposes the linear pulse S1 and the DC component S2 to obtain a drive current. The light emitting diode 23 inputs this drive current and generates light corresponding to the drive current. The emitted light enters the optical fiber cable 3 and propagates in the fiber 3.

The light receiving diode 41 receives the transmitted light from the optical fiber cable 3 and converts it into an electric signal. The preamplifier 42 increases the electric signal by a predetermined gain.

The pile-up rejector 43 attempts to eliminate the pulse overlap phenomenon. That is, the electric output waveform of the radiation detection sensor 1 decays logarithmically with time. Therefore, when the radiation intensity is high, that is, when the output pulses of the sensor 1 are closely connected, a pulse overlapping phenomenon occurs. The receiving unit 4 receives the signal in which the pinching phenomenon occurs through the cable 3.

FIG. 5 (a) is a diagram showing a pulse overlapping phenomenon.
This overlapping phenomenon of pulses causes an error when measuring the peak value (magnitude of energy) from the baseline.

The pile-up rejector 43 is for preventing this pinch-over phenomenon, and is configured by using an RC differentiating circuit or a delay line having a short time constant. Pile-up rejector at this time
The waveform diagram after the processing by 43 is shown in FIG.

The baseline regenerator 44 removes the direct current component and regenerates the baseline. When the CR circuit in the pile-up rejector 43 is used to shape the waveform, AC coupling results in AC coupling, so the baseline carrying the pulse waveform signal falls below the actual level and above and below the zero axis. The areas of the waveform are equal. This baseline shift causes an error when measuring the peak value with reference to the zero potential. FIG. 6 shows an example thereof. For the true zero axis,
A waveform showing a baseline shift is shown. The baseline regenerator 44 eliminates the baseline shift,
Bring the baseline back to true zero potential in as short a time as possible.

The low pass filter 51 removes an AC component and extracts a DC component. This DC component is the DC component S2 applied from the outside.
A considerable amount corresponds.

The baseline regenerator 44 and the low-pass filter 51 described above correspond to the discriminator 62 in FIG.

The threshold control circuit 52 has a gain β, takes in the output of the filter 51, integrates the gain, and outputs it. The threshold control circuit 52 corresponds to the threshold control circuit 63 shown in FIG.

The gain β has the following meaning. The optical analog signal transmitted from the transmitter (terminal device) 2 is the sensor 1, the preamplifier.
21, Includes noise components generated by current driver 22, etc.
The amount of this noise is greatly influenced by the individual characteristics of the sensor 1, the preamplifier 21 and the like, and if this is ignored and the radiation dose is counted, the count value will contain a large error. In order to correct this and suppress variations in the count value, it is necessary to consider the optical analog signal below a specific level as a noise component and remove it. The conversion constant that gives the voltage level to be removed is the gain β. For example, in FIG. 5B, when the pulses to be actually detected are two tall pulses, the gain β that sets the voltage level at which the four short pulses are removed is set.

The wave height discriminator 45 takes the ratio between the AC output of the baseline regenerator 44 and the DC output of the threshold control circuit 52. By taking this ratio, a detection signal that is not affected by the waveform attenuation in the optical transmission system is obtained. This detection signal is waveform shaped, and the counting circuit 46 counts the pulse after waveform shaping.

According to this example, a detection signal irrelevant to the attenuation factor in the optical transmission system could be obtained.

When the optical fiber cable is uniformly deteriorated in the length direction, the influence of the attenuation factor of the optical fiber cable can be removed by taking the ratio of the signal component and the direct current component as in the above-described embodiment. On the other hand, when the optical fiber cable is locally damaged by radiation exposure or the like, this effect can be removed by taking the difference between the signal component and the DC component.

FIG. 7 is a block diagram of an embodiment for obtaining the difference. in this case,
Superposition of the DC component S2 is not always necessary. This is because the ratio is not taken. Differential amplifier 45A instead of wave height discriminator 45
Was set up. The waveform diagram at this time is shown in FIG. The output a of the pile-up rejector 43 has a DC component and a signal component (AC component). The baseline regenerator 44 removes this DC component and detects only the signal component as the signal b. The low-pass filter 51 removes the signal component and passes only the DC component as the DC signal c. The threshold control circuit 52 multiplies β and compensates for drift and the like to obtain the output d. This output d becomes the threshold level. The differential amplifier 45A takes the difference between the signals b and d and waveform-shapes the positive component of the difference value d to obtain the output e.

According to this embodiment, when the waveform distortion due to the optical transmission system is not in the form of multiplication but in the form of addition (or subtraction), it is effective in correcting the distortion. Here, the multiplication is a case where the uniform attenuation rate α is multiplied in the cable length direction as in the equation (1), and the addition (or subtraction) is a local attenuation rate α, and X2 = (Α + S1) + (α + S2) (6) This is the case expressed by the relational expression.

In the case of this addition, if the difference between the signal component and the DC component is calculated, the attenuation rate α at the locally damaged portion can be removed. In the present embodiment, this idea is used as it is, and the differential amplifier 45A functions. In this embodiment, the DC component d becomes the threshold value.

FIG. 9 is a detailed embodiment diagram. This embodiment corresponds to FIG. The baseline regenerator 44 comprises a differentiating circuit composed of a capacitor 71 and a resistor 72. The low pass filter 51 is composed of a resistor 73 and a capacitor 74 and has a kind of integration function. The threshold control circuit 52 is composed of resistors 75 and 76 and an operational amplifier 77, and the gain β is set by the ratio of the resistors 76 and 75. The differential amplifier 45 takes in b and d, (b-d)
And the waveform of only the positive component is shaped and output e
Issue as.

FIG. 10 shows another embodiment of the threshold control circuit 52. A potentiometer 78 was inserted in series with the resistor 76. There is an advantage that the value of the gain β can be variously changed by changing the value of the potentiometer 78.

FIG. 11 shows another modification of the embodiment shown in FIG. The different point is the configuration of the threshold control circuit 52. The threshold control circuit 52 includes voltage dividing resistors 81 and 82 and a series resistor 81. The voltage dividing resistor 82 is a potentiometer. The gain β can be changed by changing the value of the voltage dividing resistor 82.

FIG. 12 shows another embodiment. The present embodiment is characterized in that an upper limit level detection circuit 53 is added. The upper limit level detection circuit 53 takes in the upper limit level set value Vh and the output of the threshold control circuit 52, and when the output of the threshold control circuit 52 becomes larger than Vh, generates an alarm output Vo. When it is smaller than Vh, the alarm output Vo is not generated.

FIG. 13 shows an embodiment of the upper limit level detection circuit 53. The upper limit level setting value Vh is set by the ratio of the voltage dividing resistors 86 and 87.
The voltage dividing resistor 87 is a potentiometer. Comparator 85 is Vd
And Vh are compared, and when Vb ≧ Vh, an H level output is output. The current driver 88 generates a current corresponding to this H level and drives the relay 89. The contact 90 is turned on (or off) by the excitation of the relay 89, and an alarm is displayed.

FIG. 14 is realized by using a transistor, and is different in that a transistor 93 and base resistors 91 and 92 are provided.

The application of the DC component S2 does not need to be performed by the current driver 22. It may be the light emitting diode 23 or the preamplifier 21.

〔The invention's effect〕

According to the present invention, it is possible to compensate for the influence of the change in the transmission characteristics during the analog transmission of the linear pulse when detecting the radiation.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is a waveform explanatory diagram thereof, FIG. 3 is a principle explanatory diagram of the present invention, FIG. 4 is an embodiment diagram of the present invention, and FIG. 5 is a pile-up rejector. FIG. 6 is an explanatory diagram of processing waveforms of FIG.
FIG. 7 is a diagram of another embodiment of the present invention, FIG. 8 is a waveform diagram of each part thereof, and FIG. 9, FIG. 10, FIG. 11, FIG. 12, FIG. 13, FIG. Here is an example. 1 …… Radiation detection sensor, 2 …… Transmitter, 3 …… Optical fiber cable, 4 …… Receiver, 21 …… Op Amp, 22 …… Current driver, 23 …… Light emitting diode, 41 …… Receiving diode, 4
2 …… Preamplifier, 43 …… Pile-up rejector, 44…
… Baseline regenerator, 45 …… Wave height discriminator, 46 …… Counting circuit, 47 …… Indicator, 51 …… Low pass filter, 52 …… Threshold control circuit.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H04B 10/02 10/18 15/00 9298-5K (72) Inventor Yuzaburo Iwasa 5 Omika-cho, Hitachi City, Ibaraki Prefecture No. 2-1 Incorporated company Hitachi Ltd. Omika Plant (56) Reference JP-A-55-135441 (JP, A) JP-A-58-166836 (JP, A) JP-A-50-141386 (JP, A) JP-A-47-27077 (JP, A) JP-B-50-9312 (JP, B2)

Claims (2)

[Claims] 1. A radiation detection sensor that detects γ-rays and outputs an electric signal of a corresponding linear pulse, a pile-up rejector that removes waveform stacking of the linear pulse, and a linear pulse signal processed by the pile-up rejector. In the gamma ray measuring apparatus, the radiation detecting sensor comprises a baseline regenerator for removing a direct current component and returning the baseline to a true zero potential, and a counting means for counting the linear pulses processed by the baseline regenerator. By providing a first photoelectric converter for converting the output signal of the optical signal into an optical signal, an optical cable for transmitting the optical signal, and a second photoelectric converter for converting the optical signal transmitted by the optical cable into an electric signal. The pi-up rejector, the baseline regenerator, and the counting means are provided on the optical signal receiving side, and the input signal to the first photoelectric converter is provided. Means for adding a predetermined DC level, means for separating the DC component after passing the output signal of the second photoelectric converter through the pile-up rejector, and multiplication of the DC component separated by the means by a predetermined gain. Means and means for obtaining a ratio of a signal component obtained after passing the output signal of the pile-up rejector through the baseline regenerator and a direct current component multiplied by the predetermined gain are provided, and the ratio is obtained by the means. A gamma ray measuring device characterized in that the pulse signal obtained by the above is counted by the counting means. 2. A radiation detection sensor that detects γ-rays and outputs an electric signal of a corresponding linear pulse, a pile-up rejector that removes piled-up waveforms of the linear pulse, and a DC of a linear pulse signal processed by the pile-up rejector. In the γ-ray measuring apparatus, which includes a baseline regenerator that removes the component and returns the baseline to a true zero potential, and a counting unit that counts the linear pulse processed by the baseline regenerator, By providing a first photoelectric converter that converts an output signal into an optical signal, an optical cable that transmits the optical signal, and a second photoelectric converter that converts the optical signal transmitted by the optical cable into an electrical signal, A pile-up rejector, a baseline regenerator, and a counting means are provided on the optical signal reception side, and the output signal of the second photoelectric converter is provided. Means for separating a direct current component after passing through the pile-up rejector, means for multiplying the direct current component separated by the means by a predetermined gain, and an output signal of the pile-up rejector obtained after passing through the baseline regenerator. Means for obtaining the difference between the signal component to be generated and the DC component multiplied by the predetermined gain, and the pulse signal obtained by taking the difference by the means is counted by the counting means. apparatus.