KR20150093986A - Apparatus and method for measuring concentration of radon gas - Google Patents

Abstract

The present invention relates to a radon measuring apparatus and a radon measuring method. The radon measuring apparatus measures concentration of radon gas in the air in real-time. The radon measuring apparatus includes a radon detector which is electrically connected to an ionization chamber. The radon detector includes a transposition amplifier which is connected to the ionization chamber, an input resistor which is connected to the transposition amplifier that is grounded, first and second comparators which have first and second variable resistors to adjust each discrimination level, a pulse section analysis circuit, and a pulse counter circuit. The first and second comparators are provided to analyze a pulse form by filtering only alpha particles of radon. The present invention provides ability to exclude the influence of standby parameters and the possibility of operating in real time. According to the present invention, the influence of short electromagnetic noise is excluded, gamma line and beta particles are ignored, and correction is unnecessary.

Description

TECHNICAL FIELD [0001] The present invention relates to a radon measuring apparatus and a method of measuring radon,

The present invention relates to a radon measuring apparatus, and more particularly, to a radon measuring apparatus and method for detecting radon gas concentration in real time using an ionization chamber.

The present invention also relates to a radon measuring apparatus and method for detecting radon gas concentration in real time by pulse shape analysis.

The present invention also relates to a radon measuring device and a radon detecting method for measuring radon gas concentration by excluding all influences of atmospheric parameters and electromagnetic noise and detecting all the alpha particles introduced into the ionization chamber with optimum efficiency.

The present invention also relates to a radon measuring apparatus which does not require calibration and a radon detecting method therefor.

Radon corresponds to the sixth decay product of uranium-238 widely distributed in nature. Such radon corresponds to an alpha ray emitter of an inert gas which is liable to be released into the atmosphere, and therefore, when living in a room where the concentration of radon is high is long and exists in indoor and outdoor air, do. Therefore, it is necessary to measure the radon concentration. Especially, it is necessary to periodically measure and evaluate the space where the concentration of radon is likely to be high, for example, a building, a subway or an underground shopping street.

Detection of alpha radionuclide sources is an important radiological ecology and medically important factor, since alpha rays have a strong biological impact on humans, especially because they are deposited in the lungs through the respiratory tract. The annual dose for natural background radiation should not exceed 1 mSv (millisievert) per year.

The main source of this kind of radiation is, for example, Radon gas. The radon gas moves into the ground surrounded by permeable obstruction soil and gravel fields, and moves into the building through cracks and holes in the concrete. Building materials such as rock, brick and concrete also emit radon gas. These radon gases are water-soluble and also enter the room by water movement.

The level of risk for radon concentrations varies from country to country, but is generally between 60 and 200 Bq / ㎥ (Becquerel per cubic meter). Because of this fact, several detection systems and several measurement methods have been developed for the accurate evaluation of its radioactivity concentration in air.

Methods for the detection and determination of current radon concentrations include, for example, a method using a scintillation counter, a method using a gas counter including Geiger, a method using a proportional and ionization chamber type, a method using a solid state junction State junction: solid junction) counter and a method using an activated carbon detector are known. All of these methods are derived from methods for detecting alpha particles.

Among the devices for these methods, for example, scintillation counter has historically been the earliest used in experiments on radioactivity. The scintillation material is a photo cathode of a photomultiplier that amplifies the signal to provide information about the energy and count of the alpha particles. This device requires calibration, is expensive to manufacture, and is impractical for real-time monitoring of ambient radon gas concentrations.

The gas-filled alpha particle detector also depends on whether the Geiger counter or the ionizer / proportional counter is used in the operating mode, and a specific gas is used as the detector material. The device is in any case sealed with working gas for alpha or radon detection. Entry into the ionization zone by the incoming alpha particles is through thin, fragile plastic or metal windows. The presence of a vulnerable window at the entrance opening for the incoming alpha particles is a dissatisfactory factor to the counter in continuous use because the window can be easily damaged.

Also, if air is used as the counter gas, the amplitude of the output signal is very low due to trapping of electrons by negative atoms and molecules. The disadvantage of these detectors is that their readings are dependent on atmospheric conditions such as pulsed electromagnetic noise, vibrations of the fine anode, humidity and temperature, and high DC voltage requirements. To avoid the effects of background, atmospheric conditions, and pulse only, we use pulse-shape analysis in the pulse ionization chamber to detect only signals from alpha particles. However, this method is very complicated to manufacture and is impractical for real-time monitoring of ambient radon gas concentrations.

Junction counters also use a solid-state P-N junction with a reverse bias that collects the ionized charge in the path of the alpha particles through the depletion layer. This allows the device to be compact and portable. However, the cover area of the detector is low and requires long counting time to obtain accurate results. The limitations of the junction counter also depend on the stringent requirements to avoid scratching and abrasion of the detector metal electrode surface. This electrode is sensitive to light, and it blocks the ambient light by coating. However, there is a problem that a light leak due to a scratch occurs, and it is equally important that there is no moisture and dust to be an active surface.

Another means of detecting the radon gas concentration is an activated charcoal detector. However, this method is not applicable to continuous monitoring of radon gas concentration in real time.

1. Korean Patent Registration No. 10-1299405 (Published on Aug. 28, 2003) 2. Korean Patent Publication No. 10-2004-0071101 (published on Aug. 11, 2004) 3. Korean Patent Registration No. 10-0717953 (Published on May 17, 2007) 4. Korean Patent Registration No. 10-0936298 (Published on Jan. 12, 2010) 5. Korean Patent Registration No. 10-1040072 (Published on June 13, 2011) 6. Korean Patent Registration No. 10-1183064 (Published on September 20, 2012)

SUMMARY OF THE INVENTION An object of the present invention is to provide a radon measuring device and a radon detecting method for detecting radon gas concentration in real time using an ionization chamber.

Another object of the present invention is to provide a radon measuring apparatus and a radon detecting method for detecting radon gas concentration in real time by pulse shape analysis.

It is another object of the present invention to provide a radon measuring device and a radon detecting method for measuring the concentration of radon gas by excluding all influences of atmospheric parameters and electromagnetic noise and detecting all the alpha particles introduced into the ionization chamber with optimal efficiency will be.

It is still another object of the present invention to provide a radon measuring apparatus and a radon detecting method therefor that do not require calibration when detecting radon.

It is still another object of the present invention to provide a radon measuring device which can be miniaturized and portable, and is easy to operate and maintain.

In order to accomplish the above objects, the apparatus for measuring a radon of the present invention is characterized by measuring the radon gas concentration in real time by analyzing a pulse shape. Such a radon measuring device can eliminate the effects of atmospheric parameters and electromagnetic noise, and does not need to calibrate the radon concentration by detecting and measuring alpha particles with optimum efficiency.

The radon measuring apparatus of the present invention according to this aspect measures the concentration of radon gas in air in real time.

An apparatus for measuring a radon according to this aspect includes: an ionization chamber for introducing air and supplying an electric power to generate an ionization signal for radon; A preamplifier connected to the ionization chamber and having a parallel resistor grounded to the ionization chamber to amplify and output an ionized signal output from the ionization chamber; A first comparator having a first variable resistor for adjusting a discrimination level and receiving a signal amplified from the preamplifier to filter a background signal to output a rectangular signal to the alpha particles of radon; A pulse shape analyzing circuit having a second variable resistor for receiving a rectangular signal output from the first comparator and adjusting amplitude thereof; A second comparator having a third variable resistor for adjusting a discrimination level and outputting a signal corresponding to a rectangular signal having a large amplitude; A pulse count circuit for counting a signal corresponding to a rectangular signal having a large amplitude output from the second comparator; A controller that receives the counted value from the pulse count circuit and measures the radon concentration in real time; And an indicator for indicating the measured radon concentration under the control of the controller.

In one embodiment of this feature, the preamplifier comprises: And a collection time interval of the amplified signal is calculated by multiplying the parallel resistor and the parasitic capacitor of the parallel resistor.

In another embodiment, the collecting time period is not less than the sum of the electron collecting time period of the anode of the ionization chamber and the positive ion collecting time period of the cathode.

In yet another embodiment, the first comparator comprises: A noise pulse having a small amplitude, a gamma quantum, and a beta particle from the amplified signal of the preamplifier, and outputs a rectangular signal in the collection time period.

In another embodiment, the pulse duration analysis circuit comprises: A timer; The first comparator is switched on when a signal input from the first comparator has a low level and is switched off when a rectangular signal is input from the first comparator. - an optical relay being turned on; And a capacitor charged through the second variable resistor when the optical relay is switched off and discharged through the optical relay when the optical relay is switched on.

In another embodiment, when the rectangular signal is inputted from the first comparator, the amplitude of the potential of the capacitor is determined by the second variable resistance value and the capacitor value.

In another embodiment, the controller comprises: Measuring the radon concentration using the measurement time according to the ionization chamber and a conversion formula, the value counted from the pulse counting circuit; The measurement time is 1000 sec, and the conversion formula is a radon concentration I = 0.108n, where n is calculated as a count value.

According to another aspect of the present invention, there is provided a method of measuring a radon concentration in the air of a radon measuring apparatus having an ionization chamber and a radon detector to which a preamplifier is connected.

According to this aspect of the present invention, there is provided a method of measuring radon comprising the steps of supplying power to the ionization chamber and the radon detector, amplifying an ionized signal detected in the ionization chamber by the preamplifier, receiving the amplified signal from the preamplifier, A signal of a rectangular shape is filtered to analyze a pulse shape of a rectangular signal to transform it into a signal having a high amplitude and a signal corresponding to a signal for the alpha particles having a high amplitude is passed and counted, Measuring the radon concentration using the conversion time and measurement time according to the ionization chamber; The measurement time is 1000 sec, and the conversion formula is a radon concentration I = 0.108n, where n is calculated as a count value.

In one embodiment of this aspect, the method further comprises: The radon concentration is measured by filtering only the signals for the alpha particles of radon from the ionized signal.

As described above, the radon measuring apparatus of the present invention can detect the radon gas concentration by analyzing the pulse shape and can eliminate the influence of atmospheric parameters such as humidity, and can measure the radon concentration in real time This is possible.

In addition, the apparatus for measuring a radon of the present invention can be miniaturized, easy to carry, and low in manufacturing cost by analyzing pulse shapes of alpha particles of radon using an ionization chamber.

Further, the radon measuring apparatus of the present invention can eliminate the influence of noise from short electromagnetic noise such as static electricity, collector motor, fan, etc., and can detect alpha particles with efficiency of 100%, ignoring beta particles and gamma rays , No calibration required.

In addition, the radon measuring apparatus of the present invention can easily operate and maintain due to real-time radon concentration measurement.

1 is a block diagram showing a schematic configuration of a radon measuring apparatus for measuring a real time radon concentration according to the present invention;
FIG. 2 is a view showing a configuration of a radon measuring apparatus according to an embodiment of the present invention; FIG.
3 is a circuit diagram showing a configuration of the preamplifier shown in FIG. 2;
4 is a circuit diagram showing the configuration of the first comparator, the pulse interval analyzing circuit, and the second comparator shown in FIG. 2;
5 is a circuit diagram showing the configuration of the pulse count circuit shown in FIG. 2;
FIG. 6 is a waveform diagram showing input / output signals of the preamplifier and the first comparator shown in FIGS. 3 and 4; FIG.
FIG. 7 is a waveform diagram showing the amplitude of the alpha particle and the rectangular signal shown in FIG. 4 and the pulse corresponding thereto; FIG.
FIG. 8 is a waveform diagram showing a dependence of a signal interval and an amplitude on the input resistance of the preamplifier shown in FIG. 3; FIG.
9 shows a schematic configuration of an ionization chamber according to an embodiment of the present invention;
FIG. 10 is a perspective view showing a configuration of the ionization chamber shown in FIG. 9; FIG.
11 is an exploded perspective view showing a detailed configuration of the ionization chamber shown in FIG. 10; And
12 is a front view of the ionization chamber shown in FIG.

The embodiments of the present invention can be modified into various forms and the scope of the present invention should not be interpreted as being limited by the embodiments described below. The present embodiments are provided to enable those skilled in the art to more fully understand the present invention. Therefore, the shapes and the like of the components in the drawings are exaggerated in order to emphasize a clearer explanation.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a schematic configuration of a radon measuring apparatus for measuring a real-time radon concentration according to the present invention.

Referring to FIG. 1, the apparatus 2 for measuring a radon of the present invention includes an ionization chamber 100 for inputting air and outputting an ionized signal for radon to measure the concentration of radon gas in air in real time, And a radon detector 200 for measuring the concentration of the radon gas in real time by receiving the ionized signal from the ion source 100 and analyzing the pulse shape. The ionization chamber 100 and the radon detector 200 are electrically connected to each other.

The radon measuring apparatus 2 according to the present invention includes a compact ionization chamber 100 and can measure the radon concentration in real time by detecting only alpha particles of the radon gas using the radon detector 200, It is easy to operate and carry.

2 is a circuit diagram showing a configuration of a preamplifier shown in FIG. 2, and FIG. 4 is a circuit diagram showing a configuration of a radar apparatus according to an embodiment of the present invention, FIG. 5 is a circuit diagram showing the configuration of the pulse count circuit shown in FIG. 2; FIG. 5 is a circuit diagram showing the configuration of the first comparator, the pulse section analyzing circuit, and the second comparator; 6 is a waveform diagram showing the input and output signals of the preamplifier and the first comparator shown in FIGS. 3 and 4, FIG. 7 is a graph showing the amplitude of the alpha particles and the rectangular signals shown in FIG. 4, And FIG. 8 is a waveform diagram showing the dependence of the signal interval and the amplitude from the input register of the preamplifier shown in FIG.

Referring first to FIG. 2, a radon measuring apparatus 2 of the present invention includes a grounded ionization chamber 100 and a radon detector 200 electrically connected to the ionization chamber 100.

The ionization chamber 100 outputs an ionized signal to the preamplifier 204 for the radon gas introduced into the air. 9 and 10, the ionization chamber 100 includes a case 102 having a predetermined size and being grounded, a sensing electrode 108 and two power sources 108, (Voltage Electrode) 110 and 112, respectively. The contents of this ionization chamber 100 will be described in detail in the following Figs. 9 to 12.

The radon detector 200 includes a power supply unit 202 for supplying power of a predetermined magnitude to the power supply electrodes 110 and 112 of the ionization chamber 100 and a parallel input resistor 203 R, A preamplifier 204 connected in series with the ionization chamber 100 for receiving and amplifying the ionized signal outputted from the ionization chamber 100 and a first variable resistor 208 for adjusting the discrimination level are connected A first comparator 206 for filtering the background signal to output a rectangular signal, a pulse interval analyzing circuit 210 for receiving the rectangular signal from the first comparator 206 and adjusting the amplitude thereof, And a second comparator 220 connected to the second variable resistor 222 for adjusting the discrimination level and outputting a signal corresponding to the rectangular pulse signal having a large amplitude.

The radon detector 200 further includes a pulse count circuit 224 for counting a pulse signal having a large amplitude from the second comparator 220 and a pulse count circuit 224 for counting the count value from the pulse count circuit 224, A controller 228 for measuring the radon concentration in real time in response to the controller 228, and an indicator 230 for indicating the radon concentration measured from the controller 228.

Specifically, in this embodiment, the power supply unit 202 is connected to the power source of the radon detector 200, that is, the two-pole low voltage power source (± V) and the power source electrodes 110 and 112 of the ionization chamber 100, . For example, the power supply unit 202 supplies a power of about ± 5 V to the radon detector 200, and supplies power of about -70 to -80 V to the power supply electrodes 110 and 112 of the ionization chamber 100.

As shown in FIG. 3, the preamplifier 204 is composed of two stages and has an amplification degree of about 1,400 times in order to amplify signals for very weak alpha particles. That is, the preamplifier 204 includes a first preamplifier 204a, a second preamplifier 204b, and peripheral circuits R1 to R6, C1 to C6.

The first preamplifier 204a is connected to the non-inverting terminal (+) of the sensing electrode 108 of the ionization chamber 100 and the inverting terminal (-) is grounded to accept the ionized signal. At this time, the input of the first preamplifier 204a has a resistor 203 (R1) connected in parallel with the ground. In addition, a resistor 203 (R1) and a dummy capacitor (C in Fig. 2) are present by the ionization chamber 100 at the input end of the first preamplifier 204a. The output of the first preamplifier 204a is connected to the inverting terminal (-) and the non-inverting terminal (+) is connected to the resistor 203: R1 connected in parallel with the ground .

Therefore, when power is supplied from the power source unit 202 to the ionization chamber 100 and the radon detector 200, the ionized signal detected in the ionization chamber 100 is amplified through the preamplifier 204 do. At this time, the waveform of the amplified signal has the shape of the second signal S2 in Fig. The length T of the signal S2 includes the electron collecting time interval of the anode T ^- and the positive ion collecting time interval of the cathode T ⁺ . The interval of this signal S2 is adjusted by the values of the resistor R and the capacitor C shown in Fig.

If RC = T = T ^- + T ⁺ (the electron collection time interval at the anode T ^- and the collection time interval of the positive charge ion at the cathode T ⁺ ), the signal is very long, but the alpha particles 100% alpha particles can actually be detected.

This is because the preamplifier 204 including the resistor 203 (R) between the output of the sensing electrode 108 of the ionization chamber 100 and the ground and the parasitic capacitor capacitance C therebetween is the product of the total input capacitance The parasitic capacitor capacitance C is determined to be a constant size, and the larger the value of the resistor 203 (R) is, the longer the collection time of electrons and positive charge ions becomes. Therefore, it should be close to the sum of the electron collection time interval at the anode T ^- and the collection time interval of the positive charge ion at the cathode T ⁺ . If the value of the resistor 203 (R) is too large, the signal becomes longer and the count rate becomes lower, so that the value of the resistor 203 (R) is about 500 M OMEGA.

4, the first comparator 206 is connected to the first variable resistor 208 (VR1) for adjusting the discrimination level to the non-inverting terminal (+) and the preamplifier 204 to the inverting terminal (- Respectively. The first comparator 206 receives the amplified signal from the preamplifier 204 and filters the background signal to output a rectangular signal.

That is, the first comparator 206 having the first variable resistor 208 (VR1) filters the background signal having the amplitude lower than that of the first signal S1 in Fig. This alpha particles with an approximately 5 MeV energy emitted by the radon about 10 ⁵ ions of the air and beta particle-gamma quanta with the generated e-pair, or the same energy (γ quantum) In other words, both are about 10 ² ions - < / RTI > electron pair, the signals from the beta particle or gamma quantum are filtered by the first comparator 206.

The output signal of the first comparator 206 is output to a rectangular signal (S3 in Fig. 6) having a length corresponding to the length of the output signal from the alpha particle of the preamplifier 204. [ The rectangular signal is output to the pulse section analysis circuit 210.

The pulse section analysis circuit 210 includes a transistor Q1, a timer 212, a photoreactor relay 214, a second variable resistor 216 (VR2), a capacitor 218 (C10) Circuits R7 to R12, R15, R16, C7 to C9. The second comparator 220 has a third variable resistor 222 (VR3) for adjusting the discrimination level.

When the signal input from the first comparator 206 has a low level, the pulse interval analyzing circuit 210 turns on the transistor Q1 to turn on the optical relay 214. [ When a rectangular signal is inputted from the first comparator 206, the pulse interval analyzing circuit 210 switches the optical relay 214 off and the capacitor 218 is charged through the second variable resistor 216 . The pulse section analysis circuit 210 also switches on the optical relay 214 at the falling edge of the rectangular signal and the capacitor 218 rapidly discharges through the optical relay 214. And the amplitude of the potential of the capacitor 218 varies depending on the value of the second variable resistor 216 and the capacitance of the capacitor 218. [

As a result, in the pulse interval analyzing circuit 210, the long rectangular signal S4 corresponding to the alpha particle is transformed into a pulse signal S5 having a high amplitude S6 and outputted as shown in Fig. The short rectangular signal S7 not corresponding to the alpha particle is transformed into a pulse signal S8 having a low amplitude S9 and outputted. The pulse signals S5 and S8 having the amplitudes of the amplitudes are output through the second comparator 220 having the third variable resistor 222 (VR3) by passing a signal corresponding only to the signal from the alpha particles having a large amplitude .

5, the pulse count circuit 224 is provided, for example, with a binary counter 224a. The pulse count circuit 224 receives the signal corresponding to the discriminated alpha particle from the second comparator 220, counts the signal corresponding to the alpha particle, and outputs it to the controller 228.

Referring again to Figure 2, the controller 228 compares the counted value from the binary counter 224a with the measurement time according to the shape (e.g., volume, etc.) of the ionization chamber 100, Measure the radon concentration. The controller 228 is provided, for example, as a PIC (Program Interrupt Control) controller. In this embodiment, the conversion formula is calculated with a measurement time of 1000 sec and a radon concentration I = 0.108n (where n is a count value). In addition, the controller 228 controls the indicator 230 to display the measured radon concentration data in real time by transmitting the measured radon concentration data and the accumulated data for a certain period of time to the indicator 230.

The controller 228 also includes a wake-up communication module such as Wi-Fi or serial wired communication (RS-485), and a notification function according to the measured radon concentration, (Not shown) such as a personal computer, a smart phone, and the like, and has a function of loading real-time or accumulated data through a data communication function.

The indicator 230 is provided, for example, with a digital indicator or an LCD display module to receive and display the measured radon concentration and accumulated data from the controller.

The construction and operation of the ionization chamber according to the present invention will be described in detail with reference to FIGS. 9 to 12. FIG. 9 is a perspective view showing the configuration of the ionization chamber shown in FIG. 9, and FIG. 11 is a cross-sectional view showing the ionization chamber shown in FIG. 10, And FIG. 12 is a front view of the ionization chamber shown in FIG. 10 according to a state in which the front surface of the ionization chamber is opened. FIG.

Referring to FIGS. 9 to 12, the ionization chamber 100 of the present invention is provided with a shape capable of introducing air. The ionization chamber 100 of this embodiment has a generally rectangular parallelepiped case 102, a sensing electrode 108 fixedly mounted inside the case 102, and two power supply electrodes 110 and 112. The case 102 is electrically grounded. To this end, the ionization chamber 100 insulates the case 102, the sensing electrode 108, and the power supply electrodes 110 and 112 from both sides of the inner side of the case 102 and connects the sensing electrode 108 and the power supply electrodes 110, 112 are insulated from each other so as to be installed at predetermined intervals in the vertical direction.

The insulator 120 is, for example, made of synthetic resin or the like and is screwed on both sides of the inner surface of the case 102. The insulator 120 is formed with a plurality of mounting grooves 120a so as to maintain a constant distance (D in FIG. 12) between the sensing electrode 108 and the power supply electrodes 110 and 112.

The sensing electrode 108 is disposed at the center of the insulator 120 and each of the power supply electrodes 110 and 112 is disposed above and below the sensing electrode 108.

The sensing electrode 108 is electrically connected to the preamplifier 204 and each of the power supply electrodes 110 and 112 is electrically connected to the power supply unit 202. To this end, the sensing electrode 108 and the power source electrodes 110 and 112 are formed with first to third terminal portions 118a, 110a, and 112a, respectively, each of which partially protrudes in the horizontal direction. The first terminal portion 108a is connected to the preamplifier 204 and a resistor R1 connected in parallel with the ground using soldering or the like. The second and third terminal portions 110a and 112a are connected to the power supply portion 202 and are supplied with power of a predetermined size (for example, -70 to -80 V).

The sensing electrode 108 and the power source electrodes 110 and 112 are formed in a metal plate shape such as stainless steel to generate an ionized signal for the alpha particles of the radon, ), ≪ / RTI > and the like.

In addition, the ionization chamber 100 is opened at the rear side where the air is introduced or at the rear by mounting a mesh network 104 made of metal. The sensing electrode 108 and the power supply electrodes 110 and 112 are isolated from each other on the front surface of the ionization chamber 100 and the insulation plate 106 is insulated from the radon detector 200 including the preamplifier 204 Respectively. A plurality of through holes are formed in the insulating plate 106 so that the first to third terminal portions 118a, 110a, and 112a protrude from the front surface. The insulating plate 106 is made of synthetic resin or the like and forms a space 130 having a certain depth so that the preamplifier 204 and the radon detector 200 can be installed in the front surface of the case 102 do.

The ionization chamber 100 may have various shapes such as a rectangular parallelepiped or a cylindrical shape. The ionization chamber 100 may be provided with various sizes or volumes. In this embodiment, the ionization chamber 100 is provided in a rectangular parallelepiped shape having a volume of 125 ml, 250 ml or the like so as to be suitable for a place or an application for measuring the radon concentration and capable of miniaturization.

As described above, the radon measuring apparatus 2 of the present invention is proved by an experimental model through the following embodiments.

That is, the radon measuring apparatus 2 according to the embodiment of the present invention is suitable for detecting a radon gas of a relatively narrow range of 0.1 pCi / L (3.7 Bq / m 3) to 100 pCi / L (3700 Bq / m 3). In the ionization chamber 100, there are three plate electrodes made of stainless steel. These plate electrodes, which are comprised of two power supply electrodes and one sensing electrode, are located in a grounded metal box (i.e., case) to reduce external electromagnetic radiation and are used to separate these electrodes from fixed and grounded metal boxes Insulators are installed with PVC or anti-static plastic.

The distance between the power supply electrode and the sensing electrodes is generally uniform. About 2 cm in this embodiment. One end of the metal box is open to allow air to easily pass into the ionization chamber, or closed by a stainless steel grid or mesh network. The volume of the ionization chamber can be varied in various ways such as 125 ml and 250 ml. The power supply electrode is connected to a DC power source of -70 V to -80 V. The sensing electrode is grounded through a resistor R having a parasitic capacitor C and is connected to a preamplifier located in a small metal box grounded to prevent the influence of external electromagnetic radiation.

The total input capacitance, C, of the preamplifier, including the capacitance of the ionization chamber, is about 30 pF. FIG. 8 shows a waveform diagram showing the dependence of the signal interval and the amplitude from the input resistance of the preamplifier. Increasing the input resistance value of this preamplifier increases the signal interval and amplitude.

That is, the signals S10, S11, and S12 in FIG. 7 correspond to the input resistance values R = 100 MΩ, 200 MΩ, and 500 MΩ, respectively, of the preamplifier. Since the signal is lengthened and the counting rate is limited by further increasing this value, the input resistance of the preamplifier is selected to be R = 500 ㏁ so that the radon concentration can be measured in real time.

Therefore, in the pulse section analysis circuit of FIG. 4, the RC value of the second variable resistor 216 (VR2) and the capacitor 218 is about 30 to 35 msec. This value is very close to the sum of the electron collection time interval of the anode T ^- and the positive ion collection time interval of the cathode T ⁺ . This means that the efficiency of alpha particle detection is virtually 100% and that there is no need for a separate calibration for the measured radon concentration values of the radon measuring device.

Also, the alpha activity concentration I, pCi / L can be calculated by the formula I = n / (0.03tv), where n is the count number for the measurement time t sec by the radon detector having an ionization chamber volume of v, L to be. In this example, the radon detector can be measured to have a measurement time of 1000 sec and an alpha radioactivity of radon concentration I = 0.108n.

In the embodiment of the present invention, the volume of the ionization chamber is tested on the basis of 125 ml and 250 ml, and if the volume or shape of the ionization chamber is changed, it is possible to appropriately change the measurement time and the conversion formula.

The calibration of the radon detector was made by comparing the readings of the expensive accurate radiometer, AlphaGUARD and the developed radon detector. These comparative devices were placed in a container and different amounts of 3 mg to 10 g of UO ₂ (NO ₃ ) ₂ were placed in the container. Each measurement was repeated 5 times and the results were used to calculate the dependence of the radon concentration determination error Δ (1 σ (standard deviation) around the mean value for the concentration value c.

For the developed laboratory radon detector, the calibration curve is approximated by the function c = 0.11n. Where c is the radon concentration pCi / L. This is in fact consistent with the formula given above and confirms that the efficiency of alpha particle detection is 100% and the calibration of the radon measuring device is unnecessary. The radon concentration determination error is c = 0.11√n. Also, the total gain of the preamplifier is 1400, and the discrimination levels of the first and second comparators are 0.3 V and 1.0 V, respectively.

In addition, the influence of air temperature and humidity on the stability of the radon detector was tested in a climatic chamber. For this purpose, an alpha particle source ²³⁹ Pu, which emits alpha particles with energies of 5.107 MeV, 5.145 MeV and 5.157 MeV, was used. This source was placed in front of the grid of the ionization chamber and the counts (times) detected in different air were compared. In these experiments, the air humidity h and the temperature t were varied in the range of 28% to 95% and 25 ° C to 40 ° C. The measurement time was 1000 sec. Some test results are shown in Table 1 below.

These results show that the number n of the counted pulses is not changed in the range of the measurement error, nor is it related to temperature and humidity.

Influence of Air Temperature and Humidity on the Stability of Detection System No herb, oC h, % n No herb, oC h, % n One


2

25
35
40
25
35
40 28
31
32
50
48
51 1796 ㅁ 43
1843 ㅁ 43
1804 ㅁ 43
1798 ㅁ 43
1815 ㅁ 43
1799 ㅁ 43 3


4

25
35
40
25
35
40 75
80
78
88
90
95 1812 ㅁ 43
1802 ㅁ 43
1826 ㅁ 43
1800 ㅁ 43
1833 ㅁ 43
1830 ㅁ 43

In addition, the effects of gamma quantum and beta particle emission on alpha particle detection were investigated. The radioactive sources ⁶⁰ Co, ¹³⁷ Cs and ⁹⁰ Sr- ⁹⁰ Y, which emit gamma quantum and beta particles, were placed in front of the grid in the ionization chamber. The energies of the gamma quanta and beta particles of these radioactive sources are given in Table 2. Experiments have shown that the radon detector is not sensitive to gamma quanta and beta particles and does not detect any radioactivity. These results demonstrate that the radon detector is sensitive only to alpha particles.

Characteristics of the radioactive source used for testing of the ionization chamber Radioactive source Energy of gamma quantum, MeV Energy of beta particles, MeV ⁶⁰ Co
¹³⁷ Cs
⁹⁰ Sr- ⁹⁰ Y   1.33, 1.17
  0.662
  0.318
  1.175
  0.546

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. It is possible.

2: Radon measuring apparatus 100: ionization chamber
102: Case 104: Mesh Network
106: insulating plate 108: sensing electrode
110, 112: power supply electrode 120: insulator
200: Radon detector 202: Power source
204: Preamplifier 206: First comparator
208: first variable resistor 210: pulse section analysis circuit
212: Timer 214: Light Relay
216: second variable resistor 218: capacitor
220: second comparator 222: third variable resistor
224: pulse count circuit 228: controller
230: Indicator

Claims (9)

A radon measuring device for measuring a radon gas concentration in air in real time, comprising:
An ionization chamber for introducing air and supplying an electric power to generate an ionization signal for radon;
A preamplifier connected to the ionization chamber and having a parallel resistor grounded to the ionization chamber to amplify and output an ionized signal output from the ionization chamber;
A first comparator having a first variable resistor for adjusting a discrimination level and receiving a signal amplified from the preamplifier to filter a background signal to output a rectangular signal to the alpha particles of radon;
A pulse shape analyzing circuit having a second variable resistor for receiving a rectangular signal output from the first comparator and adjusting amplitude thereof;
A second comparator having a third variable resistor for adjusting a discrimination level and outputting a signal corresponding to a rectangular signal having a large amplitude;
A pulse count circuit for counting a signal corresponding to a rectangular signal having a large amplitude output from the second comparator;
A controller that receives the counted value from the pulse count circuit and measures the radon concentration in real time;
And an indicator for indicating the measured radon concentration under the control of the controller. The method according to claim 1,
The preamplifier comprising:
And a collection time interval of the amplified signal is calculated by multiplying the parallel resistor and the parasitic capacitor of the parallel resistor. 3. The method of claim 2,
Wherein the collection time period is not less than a sum of an electron collection time interval of the anode of the ionization chamber and a positive ion collection time interval of the cathode. The method according to claim 2 or 3,
The first comparator comprising:
Wherein a noise pulse, a gamma quantum, and a beta particle having a small amplitude are filtered from the amplified signal of the preamplifier, and a rectangular signal is output in the collection time period. 5. The method of claim 4,
The pulse section analysis circuit comprising:
A timer;
The first comparator is switched on when a signal input from the first comparator has a low level and is switched off when a rectangular signal is input from the first comparator. - an optical relay being turned on;
And a capacitor charged through the second variable resistor when the optical relay is switched off and discharged through the optical relay when the optical relay is switched on. 6. The method of claim 5,
Wherein the amplitude of the potential of the capacitor is determined by the second variable resistance value and the capacitor value when a rectangular signal is input from the first comparator. 6. The method of claim 5,
The controller comprising:
Measuring the radon concentration using the measurement time according to the ionization chamber and a conversion formula, the value counted from the pulse counting circuit;
Wherein the measurement time is 1000 sec and the conversion formula is a radon concentration I = 0.108 n, wherein n is calculated as a count value. A method for measuring radon concentration in air of a radon measuring apparatus having an ionization chamber and a radon detector connected to a preamplifier, the method comprising:
A power source is supplied to the ionization chamber and the radon detector to amplify an ionized signal detected in the ionization chamber by the preamplifier and a signal amplified by the preamplifier to filter a background signal to output a rectangular signal , A pulse shape of a rectangular signal is analyzed and transformed into a signal having a high amplitude, a signal corresponding to a signal for the alpha particles having a high amplitude is passed and counted, and the counted value is measured according to the ionization chamber Measure the radon concentration using time and conversion formula;
Wherein the measurement time is 1000 sec and the conversion formula is a radon concentration I = 0.108n, wherein n is a count value. 9. The method of claim 8,
The method comprising:
Wherein the radon concentration is measured by filtering only the signal for alpha particles of radon from the ionized signal.

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