RU2445648C2 - Method of stabilising and correcting transfer constant of scintillation detector and apparatus for realising said method - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: statistical sequence of detected pulses is obtained, which is converted to rectangular pulses whose amplitude is proportional to the amplitude of the detected pulses, and whose width is equal to the interval from the previous to the next statistically distributed pulse; a control signal is generated, which counteracts deviation of the controlled value from a given value; the control object (scintillation detector) is exposed to the control signal and its transfer constant is measured and corrected by varying supply voltage of a photomultiplier. The apparatus includes a zero-order extrapolator, whose input is connected to the output of a first amplifier, and the output to the input of an integrator, as well as a control signal regulator, one input of which is connected to a reference voltage source, the second input is connected to the output of the integrator, and the output to the input of the controlled photomultiplier power supply.

EFFECT: high accuracy of detecting ionising radiation.

4 cl, 4 dwg

Description

The invention relates to nuclear physics, and more particularly to methods and devices for adjusting and stabilizing the transfer coefficient of a scintillation detector of ionizing radiation, and can find application for constructing instrumentation and systems that use the interaction of a controlled object with radiation from radionuclide sources as a primary conversion to control technological parameters objects in various industries.

The instability of the transfer coefficient of the scintillation detector is due to the influence of factors such as changes in the ambient temperature, technical parameters of electronic circuit elements, and is one of the main reasons for the appearance of an error in the detection of ionizing radiation by a scintillation detector (inorganic crystalline scintillator - photomultiplier tube).

The known method of "Correction and stabilization using a radioactive source" (L1. V.V. Matveev, B.I. Khazanov. Instruments for measuring ionizing radiation. - M .: Atomizdat, 1987, p.624), and the device "Radioisotope device to control the density of liquids, pulps and high gas pressures "(L2. AS USSR No. 1118178, CL G01N 23/02, publ. June 8, 1984). Correction and stabilization

measuring parameters of the ionizing radiation detector, based on the use of a reference (reference) source, which consists in comparing the pulse sequence of the detected ionizing radiation with the pulse sequence from the control source. The disadvantage of this method and device is that its implementation requires a mechanical structure and an additional (reference) source of ionizing radiation.

A known method in which to stabilize using the radiation of a reference radioactive source or the peak of the measured radiation (L3. Tsitovich AP Nuclear electronics. - M .: Energoatomizdat, 1984, p. 47). Using differential amplitude analyzers, two stabilization windows are formed that are symmetrically located on the slopes of the reference peak, and then the counting speeds in the stabilization windows are compared on a comparison circuit to obtain a mismatch signal that is supplied to the actuator (controlled amplifier or PMT power supply). Along with the advantage of this method, namely, that the rapper has the same nature as the analyzed radiation, and in this case, the scintillator itself is also covered by stabilization, it has a number of significant drawbacks. The main of them can be attributed to the fact that the spectrum does not always have a peak suitable for use in the stabilization system, in addition, three or four threshold devices for forming stabilization windows is an additional hardware error.

There is also known a method "Method for differential stabilization of the spectrometric path of the scintillation unit for detecting gamma radiation according to the" reference peak "(L4. RF patent No. 2225017, G01T 1/40, BI No. 6 of 02.27.04).

The peak of the measured radiation is used as a reference source, using differential amplitude analyzers, two stabilization windows are formed symmetrically located on the slopes of the reference peak, and then the average count rates in the stabilization windows are compared to obtain a mismatch signal and a control signal for correction of the transmission coefficient of the detection path is generated, moreover as a reference source use the characteristic radiation flux generated by the measured gamma radiation in addition A real screen made of a material with a fixed atomic number surrounding the scintillation detector itself. That is, a screen of special material is needed, and there is also an additional hardware error in the formation of stabilization windows.

The closest in technical essence the prototype of the proposed device is the device "Device for stabilizing the transmittance of discrete pro-active detectors of ionizing radiation" (L5. RF Patent No. 2073887, CL G01T 1/40, published February 20, 1997). The device comprises an ionizing radiation detector, an amplifier, a sampling-storage device, an integrating chain, as well as a controlled detector power source.

Other variations of use are given in (L6. RF patent for PM No. 23105, L7. Catalog “Berthold technologies”, L8. Catalog “SRP-97 device”).

The objective of the invention is the stabilization of the operational characteristics of the scintillation detector, such as the ability to set the gain of the control signal, which will provide the optimal mode of stabilization of the transmission coefficient of the scintillation detector; setting the required level of the controlled spectrum of pulses, as well as maintaining these parameters when replacing a photomultiplier tube with a different gain without adjustment. As well as the preservation of the established parameters of the registration of ionizing radiation under the influence of various destabilizing factors, which is important when operating instrumentation and process control systems using a scintillation detector.

Figure 1 shows a block diagram of a device that implements the proposed method of stabilization and adjustment of the transfer coefficient of the scintillation detector:

figure 2 is a graphical representation of time diagrams at the corresponding points of the device explaining the method of adjusting the measurement parameters of the threshold device;

figure 3 is an example implementation of an extrapolator;

figure 4 is an example implementation of a control signal controller.

The presented figures depict:

1 - scintillation detector,

2 - PMT - photomultiplier tube,

3 - the first (linear) amplifier,

4 - extrapolator,

5 - integrator

6 - source of reference voltage

7 - control signal controller,

8 - controlled power source of the PMT (photomultiplier tube),

9 - output of the first amplifier 3,

10 - output extrapolator 4,

11 - amplitude (peak) detector,

12 - shaper gating (control) pulses,

13 is a sampling device with memory,

14 - second (differential) amplifier.

V _y - signal from amplifier 3,

V _e - signal from the output of the extrapolator 4.

The essence of the proposed method for stabilizing and adjusting the transfer coefficient of the scintillation detector is that they obtain a statistical sequence of pulses, convert this sequence into rectangular pulses with amplitudes proportional to the amplitudes of the detected pulses and a width equal to the interval from the previous to the next. statistically distributed impulses; a sequence of generated pulses is integrated. The voltage obtained during integration can be considered representative, since it carries all the basic properties of the set of pulses of the recorded spectrum (i.e., their spectral distribution). This voltage is compared with the reference voltage source setting, which determines the required level of the recorded spectrum, and thus a control signal is obtained that counteracts the deviation of the controlled variable (spectral distribution of the detected pulses) from the set value. By influencing the control signal on the control object (controlled photomultiplier power supply), the transmission coefficient of the scintillation detector is adjusted by changing the supply voltage to match the voltage obtained by integrating the sequence of generated pulses with the reference voltage setting, thereby preserving the set level of the recorded spectrum, the change of which can be caused various destabilizing factors.

A stabilization and adjustment coefficient for the transmission coefficient is also proposed, which implements the proposed method for adjusting the measurement parameters of a discrete threshold threshold radioisotope. The novelty of which is that an extrapolator is introduced into the device, the input of which is connected to the output of the first amplifier, and the output to the input of the integrator, and also a control signal regulator is introduced, the second (differential) amplifier, which is connected to the integrator output by a non-inverting input; inverting - to the source of the reference voltage, and the output is connected to the control input of the regulated power source of the photoelectronic multiplier.

A device that implements the proposed method works as follows. The flow of measured ionizing radiation is recorded and converted by a scintillation detector (inorganic crystalline scintillator 1 - photoelectron multiplier 2) and amplifier 3 into a pulse train with the amplitude proportional to the energy lost by the ionizing radiation particle in inorganic crystalline spingillator 1 in accordance with diagram 9 (V _y ). Extrapolator 4 provide the conversion of the recorded pulses into a sequence of pulses with amplitudes proportional to the amplitudes of the recorded pulses and a width equal to the interval from the previous to the next, statistically distributed pulses, in accordance with diagram 10 (V _e ).

The area of the step function of the generated pulses is practically independent of the pulse repetition rate, i.e. from changes in the intensity of recorded ionizing radiation. The change in the area is caused by the dependence of the change in the spectral distribution of the amplitudes of the detected pulses caused by the influence of destabilizing factors (temperature and time drift, voltage fluctuations of the power supply, aging of the detector, change in the light contact of the scintillation detector, etc.).

The conversion of the pulse sequence into a step function is performed as follows. The amplitude (peak) detector 11 measures the amplitude of the detected pulse. The voltage equal to the amplitude of the pulse from the output of the amplitude detector 11 is stored for a set time by the sampling device with memory 13, after which the amplitude detector is reset by the control pulse of the gate pulse generator 12. The sampling device with memory 13 provides storage of the current voltage value for a time interval T to the supply of the control signal of the driver of the strobe pulses 12, which will prepare the sampling device with memory 13 for sampling the subsequent signal from the amplitude detector 11.

By integrating the signal generated by the extrapolator 4, the integrator 5 provides a signal that carries information about the properties of the set of pulses of the recorded spectrum and reflects the change in the controlled parameter under the influence of destabilizing factors. This voltage V _and from the output of the integrator 5 is compared with the setting V _{mouth of the} source of the reference voltage 6, which determines the required level of the recorded spectrum. The controller of the control signals 7 generate a control signal that counteracts the deviation of the controlled variable (spectral distribution of the detected pulses) from the set value currently observed. Voltage V _and supplied to non-inverting input of the second (differential) amplifier 14, the voltage V of the reference voltage source 6 _mouth - on the inverting input. According to the state of the imbalance of these voltages, the control signal regulator 7 generates an output signal V _control , which counteracts the deviation of the controlled variable from the set value, V _control = -R ₂ V _set / R ₁ + (R ₂ / R ₁ +1) V _and .

The control signal V _control allows you to set the value of V _{height of the} controlled power source 8 of the photoelectronic multiplier 2, such that the transmission coefficient of the scintillation detector will provide the spectrum level specified by the set voltage of V _set reference voltage source 6, since the equilibrium of the system is determined by the condition V _set = V _and .

According to the above formula, the gain of the second differential amplifier

K _u = -R ₂ / R ₁ ,

where R ₁ is the input resistance in the circuit of the inverting signal of the second differential amplifier connected to the reference voltage source 6,

R ₃ is the resistance of the input second differential amplifier from the extrapolator 4 and integrator 5,

R ₂ is the resistance in the feedback circuit of the second differential amplifier, which is shown in Fig.4.

In this way, a device for stabilization and adjustment of the transfer coefficient of the scintillation detector is formed, characterized in that a second (differential) amplifier with a transmission coefficient K _u = -R ₂ / R ₁ , a non-inverting input connected to the integrator output, and inverting-to the reference voltage source, and the output of the second amplifier is connected to the control input of the regulated power supply of the photoelectronic multiplier.

When replacing a scintillation detector with a different transmission coefficient, a different value of V _{height of the} power supply 8 of the photoelectronic multiplier 2 will be automatically set, which will provide a given level of the spectrum. In the case where the temperature and other instability force change V _and the output voltage of the integrator 5, the output signal V _Ctrl regulator control signal 7 will set the voltage V _height controllable power source 8 photomultiplier 2, in which is adhered the system V equilibrium _mouth = V _and, most compensate for the influence of destabilizing factors.

Thus, the proposed method for adjusting and stabilizing the transfer coefficient of the scintillation detector of ionizing radiation and a device for its implementation provide:

a) improving the accuracy of control of the level of flow of ionizing particles;

b) automatic adjustment of the spectrum level when replacing a photoelectron multiplier;

c) compensation for the influence of destabilizing factors and aging of the scintillation detector by adjusting the transmission coefficient of the scintillation detector of ionizing radiation.

The proposed method for adjusting the measurement parameters of a discrete threshold isotope recorder is new, it does not follow from the prior art, it has an inventive step, as new stages are added: a statistical sequence of detected pulses is obtained, which is converted into rectangular pulses with amplitudes proportional to the amplitudes of the recorded pulses, and a width equal to the interval from the previous to the next statistically distributed pulses; generate a control signal that counteracts the deviation of the controlled variable from the set value, affects it on the control object (scintillation detector), changes, adjusts its transmission coefficient through a change in the supply voltage of the photoelectronic multiplier.

The proposed device, a scintillation detector, is also new and has an inventive step, as new elements and their connections are used: a zero-order extrapolator, the input of which is connected to the output of the first amplifier, and the output to the input of the integrator, as well as a control signal regulator, one input which is connected to a reference voltage source, the second input to the integrator output, and the output to the input of a regulated photoelectric multiplier power source.

The proposed method and device is industrially applicable and feasible, will allow the use of scintillation detectors of ionizing radiation as a primary transducer of the interaction of the controlled object with the radiation of radionuclide sources, to control the parameters of technological objects in various industries, without the use of complex devices to stabilize their gain, which in turn will increase the accuracy of process control.

Literature

1. V.V. Matveev, B.I. Khazanov. Devices for measuring ionizing radiation. Atomizdat, 1987, p. 644.

2. A.S. USSR No. 1118178, class G01N 23/02 publ. June 8, 1984

3. Tsitovich A.P. Nuclear Electronics. - M .: Energoatomizdat, 1984, p. 47.

4. RF patent No. 2225017, G01T 1/40, BI No. 6 of 02.27.04.

5. RF patent No. 2073887, cl. G01T 1/40, published February 20, 1997

6. RF patent for PM No. 23105, cl. G01N 23/02, published 05/20/2002

7. Catalog “Berthold technologies”, “Radiometric measurement of technological processes, level measurement” 2005. Id. No. 32528 PR60Rev 01.

8. Catalog “Scintillation exploration device SRP-97” MPR RF, 2006

Claims (4)

1. A method for stabilizing and adjusting the transfer coefficient of a scintillation detector, which consists in recording a sequence of pulses whose amplitudes reflect the spectral distribution of the detected ionizing radiation, which carries information about the stability of the transfer coefficient of the detector, in extracting the control signal obtained from this pulse sequence and its effect on the object control the gain of the detector to restore a given gain, different t we note that a sequence of pulses carrying information about the spectral distribution is converted into a sequence of rectangular pulses with amplitudes proportional to the amplitudes of the detected pulses and a width equal to the interval from the previous to the next statistically distributed pulses; a sequence of formed rectangular pulses is integrated; comparing the voltage obtained during integration with the reference voltage setting, which determines the required level of the recorded spectrum; determine the imbalance of these voltages, generate a control signal for the detector supply voltage, which corrects the transfer coefficient of the scintillation detector; set the transmission coefficient at which the spectral distribution of the pulses will correspond to the level determined by the reference voltage setting, thereby preserving the set level of the recorded spectrum, the change of which can be caused by various destabilizing factors. 2. A device for stabilizing and adjusting the transfer coefficient of a scintillation detector, comprising a scintillator optically coupled to a photoelectron multiplier, a first amplifier of the recorded pulse spectrum, the input of which is connected to the output of the photoelectron multiplier, an adjustable power supply of the photoelectron multiplier, and also a reference voltage source with a setting that determines the specified scintillation detector transmittance level, characterized in that an extrapolator zero is introduced into the device of the first order, the input of which is connected to the output of the first amplifier, and the output to the input of the integrator, and a control signal regulator is introduced, one input of which is connected to the reference voltage source, the second input of the controller to the integrator output, and the output to the input of the regulated power source photomultiplier tube. 3. The device for stabilizing and adjusting the transfer coefficient of the scintillation detector according to claim 2, characterized in that the zero-order extrapolator contains a series-connected amplitude (peak) detector and a sampling device with memory, as well as a gate (control) pulse shaper, the shaper input being connected to the input of the amplitude (peak) detector, the first output with the control input of the amplitude detector, the second output of the driver with the control input of the sampling device with memory. 4. The device for stabilization and adjustment of the transfer coefficient of the scintillation detector according to claim 2, characterized in that a second (differential) amplifier with a transmission coefficient K _u = -R ₂ / R ₁ , a non-inverting input connected to the integrator output, is introduced as a control signal controller inverting - to the source of the reference voltage, and the output of the second amplifier is connected to the control input of the regulated power source of the photoelectronic multiplier.

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