JPH0915336A - Alpha-ray dust monitor - Google Patents

Abstract

PURPOSE: To compensate the effect of radon-thoron existing in the natural world and thereby to realize an α-ray dust monitor of high sensitivity. CONSTITUTION: This monitor is equipped with a sampling system collecting dust in the air in an area to be measured, a radiation detector 7 detecting a radiation radiated from the dust 6, a first counting means 81 for counting a count value in the channel (first region) of a nuclide to be measured and a second counting means 82 for counting a count value in the channel (second region) of a radon-thoron daughter nuclide. It is equipped, besides, with a first arithmetic means 91 for computing and estimating a background value in the first region by using the count value of the second counting means 82 and a second arithmetic means 92 for subtracting the estimated background value from the count value of the first counting means 81 and compensating the background.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention passes air in a target atmosphere through a filter paper, collects dust (dust) present in the air on the filter paper, and collects α rays emitted from the dust. The present invention relates to an apparatus for monitoring the type and amount of dust (α-ray dust) that is measured by a measurement system including a radiation detector and that emits α-rays contained in the atmosphere.

[0002]

2. Description of the Related Art FIG. 14 is a conceptual diagram showing the structure of an .alpha.-ray dust monitor according to the prior art. The pump 1 depressurizes the dust collecting unit 3, sucks air in the work environment area to be monitored through the air supply pipe 2 into the dust collecting unit 3, passes the filter paper 4, and sends the air through the flow meter 5 to the exhaust system. The flow meter 5 is necessary to know the amount of air that has passed through the filter paper 4 and to obtain the dust concentration in the air of the work environment area to be monitored. Radiation emitted from the dust 6 collected on the filter paper 4 is detected by a radiation detector 7 arranged directly above the filter paper 4, and a measuring unit 8 having a built-in integral wave height discriminator has a set pulse wave height value or more. The number of radiations having the pulse wave height value (the pulse wave height value can be converted into energy) is measured, and the measured value is displayed on the display unit 10. An alarm may be issued if necessary.

In the case of this monitor, since all the radiations having the set pulse wave height value or more are counted and the pulse wave wave height values cannot be distinguished, even if the α rays emitted from some nuclides are included, the distinction can be made. I can't. FIG. 15 is a diagram for explaining the measurement by the above-mentioned conventional technique, and shows a pulse height spectrum when uranium and radon-thoron daughter nuclides coexist. The dotted line indicates the lower limit of the measurement range. The total count value corresponding to the area surrounded by the dotted line and the thick line on the right side of this spectrum and the portion surrounded by the horizontal axis (hatched portion) is the measured value. In the case of the figure, the sum of the counts of uranium and the daughters of Radon Thoron is the measured value.

In order to measure the nuclides emitting α-rays and their amounts, a pulse wave height spectrum of collected α-ray dust was measured using a multi-channel analyzer (see FIG. 15).
(As shown in 1) and the amount of individual nuclides must be determined by spectral stripping. In particular, when it is necessary to measure with high sensitivity, the effect of the daughter nuclide of radon thoron, which is a natural α-ray dust, cannot be ignored, so it is essential to compensate for the effect of the daughter nuclide of radon thoron. Become.

The reason will be described below. In the air, especially in the air of a somewhat closed space, there is dust containing natural radioactive material radon thoron (gas) and its daughter nuclide, and depending on the situation, the daughter nuclide of this radon thoron The amount of α-rays due to may become a non-negligible amount. Moreover, α emitted by Radon Tron's daughter nuclide
The energy of the rays is larger than the energy of the alpha rays emitted from uranium and plutonium, which are the objects of measurement. Furthermore, the dust containing the daughter nuclide of Radon Thoron contains many aerosol particles with a particle size of 1 micron or less, Some pass through the filter paper, some are collected inside the filter paper, and some are collected on the surface.

In the case of only collecting on the filter paper surface, the pulse height spectrum can be calculated and estimated if the environmental conditions for measurement are determined. However, as the amount of information collected inside the filter paper increases, the pulse wave height spectrum tends to have a large tail toward the low energy side, making calculation and estimation very difficult. This state is as shown in FIG.

Typical nuclides of interest as α-ray dust are uranium and plutonium, and the pulse height spectrum including these is shown in FIG. In this case, a collimator is used, and a component whose incident angle on the detector is more than 60 degrees is removed. As you can see from Figure 16, radon
The tails of Thoron's daughter nuclides RaA and ThC, RaC 'and ThC' are overlapping with the pulse height regions of uranium and plutonium. Therefore, it is necessary to separate each nuclide by spectral stripping.

On the other hand, the dust containing uranium and plutonium which are the target nuclides is usually larger in particle size than the dust of the daughter nuclide of Radon Thoron, and if the pore size of the filter paper is selected, most of it will be on the filter paper surface. Can be collected.
^The results measured with ²³⁹ Pu are shown by the dotted line in Fig. 16, but they show almost the same slope as the case of the ²⁴¹ Am surface source shown by the thin line, and it is assumed that most of it is collected on the surface. Can be judged to be correct. Therefore, since the dust containing these nuclides is collected on the surface of the filter paper, its pulse wave height region is
The environmental conditions, that is, the relative positional relationship between the filter paper and the radiation detector, the temperature, pressure, and humidity of the air between them, and the pulse wave height that can be uniquely determined by the collimator or protective film inserted between them The area becomes a relatively narrow width as seen in FIG.

[0009]

As can be seen from the above description, the α-rays of the target nuclides (for example, uranium and plutonium) and the α-rays of the daughter nuclide of Radon Thong have pulse height spectra. Overlapping, the pulse height region of Radon Tron's daughter nuclide extends over the entire pulse height region of the target nuclide. for that reason,
Even if it is necessary to separate them, in the conventional technique, they are separated by using an expensive multi-channel analyzer to obtain the pulse height spectrum and spectrum stripping which requires a troublesome calculation process. There was a drawback that I could not.

In the present invention, a pulse height spectrum is taken by using a multi-channel analyzer, and the type and amount of α-ray dust are measured without separating the spectrum into individual nuclides by spectrum stripping. An object of the present invention is to provide an α-ray dust monitor capable of performing the above.

[0011]

In order to achieve the above-mentioned object, the present invention replaces a measuring section having a built-in function of an integral type wave height discriminator in the structure of a conventional α-ray dust monitor, First counting means for detecting α-rays in a first region including a pulse peak value corresponding to the peak position of the spectrum of the nuclide to be measured, and a pulse of a daughter nuclide of Radon-Tron that does not include the first region Radiation from daughter nuclides of radon thoron existing in the first region as background by using the second counting means for detecting α-rays in the second area including the peak value and the count value of the second counting means a first calculation means for estimating and calculating the count value of α rays;
The second calculation means for obtaining the α-ray emitted from the nuclide to be measured by subtracting the count value estimated and calculated by the first calculation means from the count value of the counting means.

Radon is a daughter radionuclide selected for compensation.
C '( ²¹⁴ Po) and ThC'
²¹² Po), or Radon ( ²¹⁸ Po) as the daughter of Radon, and ThC ( ²¹² Bi) as the daughter of Toron. In the first calculation means, when the count value of the second counting means is used to estimate and calculate the count value of α-rays emitted from the daughter nuclide of Radon Thoron existing as the background in the first region, As a coefficient for multiplying the count value of the counting means, a constant coefficient is adopted, a coefficient which is a function of the dust collecting time of the filter paper is adopted, and further, it is determined by an accumulated value of the count values of the second counting means. Adopt a coefficient.

Further, as the filter paper used for collecting dust, one which has been preliminarily collected for dust for a certain period of time under conditions close to actual use conditions is used. The time for this preliminary dust collection is 10 to 50% of the total dust collection time. Further, the second region is a region of any one or more nuclides of Radon Tron's daughter nuclides divided into a plurality of regions for each nuclide,
The first computing means multiplies the count value of the second counting means by a coefficient value determined as a function of the ratio of the count values between the divided regions for each nuclide, and the daughter of Radon Thong present in the first region as a background. It is also possible to adopt a configuration in which the count value of α rays emitted from the nuclide is estimated. In this case, RaC 'is the most effective daughter nuclide of Radon Thong selected to determine the coefficient value, and even if the division number is 2, sufficiently effective information can be obtained.

Furthermore, it is provided with means for keeping the temperature of the air layer between the filter paper and the radiation detector constant. In some cases, a sensor that measures any one or a combination of temperature, pressure, and humidity of the air layer between the filter paper and the radiation detector, and the measured values are used to measure the first region and the first region. The upper limit pulse peak value and the lower limit pulse peak value in two areas are compensated.

Furthermore, as the second region, a region containing the pulse peak value corresponding to the peak position of the spectrum of any one of the Radon and Tron daughter nuclides is the reference region. The width is the same, and the area where the pulse crest value is moved to the high pulse crest value side or the low pulse crest value side by a certain value is set as the comparison area,
Compare the count values in the reference area and the comparison area, and if the count value in the area on the low pulse peak value side is larger, move the set area of all nuclides including this nuclide to the low pulse peak value side. If the count value in the reference region on the low pulse crest value side is smaller, the set regions of all nuclides including this nuclide are moved to the high pulse crest side.

Alternatively, similarly, a reference region is set, and on the other hand, the width of the pulse peak value is the same, and the pulse peak value is moved by a constant value to the low pulse peak value side and the high pulse peak value side. Two areas are respectively set as comparison areas, the count values in these three areas are compared, and when the count value in the comparison area on the low pulse height side is the maximum,
Move the set area of all nuclides including this nuclide to the low pulse crest value side, and if the count value in the reference area is the maximum, leave the set area of all nuclides including this nuclide as it is, and set the high pulse When the count value in the comparison area on the peak value side is the maximum, the set areas of all nuclides including this nuclide are moved to the high pulse peak value side. In this case, RaD and Tron daughter nuclides for which it is most effective to set the comparison region are RaA and ThC.

[0017]

According to the present invention, in addition to the pulse wave height region (first region) of the nuclide to be measured, the daughter of radon thoron for grasping the amount of the daughter nuclide of radon thoron existing as the background A pulse wave height area (second area) dedicated to the nuclide is set, and the count value in each area is measured using the first counting means and the second counting means corresponding to these areas. That is, the count value of the second counting means is a count value representing the amount of the daughter nuclide of Radon Tron,
Since the count value of the first counting means is the total count value in the first region, the sum of the count value of the nuclide to be measured and the contribution (background) of the daughter nuclide of Radon Tron contained in that region. Has become. The contribution of the daughter nuclide of Radon Thoron is estimated using the first calculating means, and the output of the second calculating means is subtracted from the count value of the first counting means using the second calculating means to obtain a measurement target. It is possible to obtain the count value depending on the nuclide.

The filter paper used for collecting dust is collected by preliminary dust collection for a certain period of time under conditions close to actual use conditions.
The dust collection state of the filter paper becomes steady. Therefore, the first
Even if a constant coefficient is used as the coefficient used in the calculation means, the required accuracy can be obtained. If the region of one or more nuclides of Radon Thoron's daughter is divided into multiple regions for each nuclide and the ratio of the count values between the divided regions for each nuclide is calculated,
The dust collection state of the filter paper (dust collection ratio in the thickness direction of the filter paper) can be grasped. Therefore, the coefficient used in the first calculation means can be obtained from the ratio of the count values between the divided areas.

When the temperature of the air layer between the filter paper and the radiation detector is kept constant, fluctuations in the density of the air layer are reduced. On the other hand, if the temperature, pressure and humidity of the air layer between the filter paper and the radiation detector are measured, the density of the air layer can be estimated. Therefore, the upper limit pulse peak value and the lower limit pulse of the first region and the second region can be estimated. The fluctuation of the peak value can be calculated and estimated. Therefore, it is possible to ensure the accuracy of the set area by compensating for the variation.

One of the regions of Radon Tron's daughter nuclides
The two areas are used as the reference area, on the other hand, the width of the pulse peak value is the same, and the reference area is set by moving the pulse peak value to the high pulse peak value side or the low pulse peak value side by a certain value. Compare the count value in the area and the comparison area, or the width of the pulse peak value is the same as the reference area,
Setting two comparison areas where the pulse peak value is moved to the low pulse peak value side and the high pulse peak value side by a certain value, and comparing the count values in these three areas, the reference area is set appropriately. Can be optimized by determining whether or not

[0021]

1 is a conceptual diagram showing the construction of an .alpha.-ray dust monitor according to the present invention. Since the elements denoted by the same numbers as in FIG. 14 have the same functions, description thereof will be omitted. The difference from the conventional technique is that the measurement unit 8 includes a first counting unit that detects α rays in a first region including a pulse peak value corresponding to a peak position of a spectrum of a nuclide to be measured, and a first region. And a second counting means for detecting α-rays in a second region containing the pulse peak value of the Radon-Tron daughter nuclide, and further using the count value of the second counting means, First computing means for estimating and computing the count value of α-rays emitted from the daughter nuclide of Radon Thoron existing as a background in the region, and estimated and calculated by the first computing means from the count value of the first counting means This is to have an arithmetic processing unit 9 including a second arithmetic means for obtaining the α dose emitted from the nuclide to be measured by subtracting the estimated count value.

As a first embodiment, a case of monitoring plutonium by compensating for the background caused by Radon-Tron using three differential wave height discriminators will be described with reference to FIGS. 2 is a pulse wave height spectrum diagram showing the set region in this case, and FIG. 3 is a block diagram of the measuring unit 8 and the arithmetic processing unit 9 thereof. RaC 'as the daughter of Radon as the nuclide for the second region
, And ThC 'as the daughter nuclide of Tron. Region of Radon daughter nuclide (indicated as Radon-Channel in the figure)
(In this case, RaC 'channel) Count value A (RaC')
2 corresponds to the area of the hatching portion in the lower left of FIG. 2, and the count value A in the region of the daughter nuclide of thoron (in the figure, described as thoron-channel) (in this case, ThC ′ channel)
(ThC ') corresponds to the area of the rough hatching portion in the lower right direction in FIG. The count value in the first region, that is, the region of plutonium to be measured (in the figure, referred to as plutonium-channel), that is, the count value A (Pu) of the first counting means 81 is the dense right side in FIG. The area corresponds to the area of the hatched portion at the bottom.

As shown in FIG. 3, the measurement section 8 having three differential type wave height discriminators measures these three measurement values, and the first calculation means 91 of the calculation processing section 9 gives A (RaC '). The coefficient c (RaC ') for RaC' is multiplied by the coefficient c (ThC ') for ThC' to A (ThC ') to calculate the background component due to radon and thoron, that is, the estimated count value, 1 Counting means 81 count value A
The estimated count value is subtracted from (Pu) to obtain the plutonium count value.

In FIG. 4, in the first embodiment, as the lower limit pulse peak value of the Radon-channel, the pulse pulse peak value corresponding to 1/10 of the peak count value of RaC 'in the steady state of the filter paper is obtained. As the lower limit of the Tron-channel, the measurement result and the estimated count value actually measured by selecting the pulse wave crest value corresponding to 1/10 of the count value of ThC 'in the steady state of the filter paper are shown. . In this case, there is no plutonium dust. Since 1/10 of the peak count value is selected as the lower limit value, the Radon-channel and the Tron-channel are not continuous as shown in Fig. 2, and the lower limit values of each are shifted to the right of the case of Fig. 2. .

In FIG. 4, RaC'-ch is the Radon-channel count value A (RaC '), ThC'-ch is the thoron-channel count value A (ThC'), and Pu-ch is the plutonium-channel. Shows the count value A (Pu) of the
_est1 (Pu) is shown. The calculation formula used for the estimation is as follows.

[0026]

[ _Equation 1] A _est1 (Pu) = 0.051 × A (RaC ') + 0.180 × A (ThC') Since plutonium does not exist in this measurement, it is ideally the plutonium-channel of the Radon-Tron daughter nuclide. If the contribution to A _est1 (P
u) and A (Pu) should overlap. However, in reality, as shown in the figure, a deviation appears, which indicates the accuracy of monitoring. As you can see in the figure, a relatively large gap is seen during the first 3 days.
_est1 (Pu) is smaller. After the 4th day, the agreement is fairly good. This indicates that in the early stage of use of the filter paper, a large amount of Radon Thoron's daughter nuclide is collected inside the filter paper, and after the 4th day, it becomes almost in a steady state. Considering the square root of the count value, which is a statistical error, it can be said that there is a very good agreement after the fourth day.

FIG. 5 shows the measurement result and the estimated _count value according to the second embodiment. The measurement result and the estimated _count value A _est1 (Pu) of the first two days in FIG. in addition,
The estimated _count value A _est2 (Pu) (indicated by a thick line) corresponding to the plutonium-channel when the coefficient is corrected by the dust collection time is shown. As a correction, a coefficient B ₁ that corrects the difference in the accumulation state on the filter paper due to the difference in half-life of RaA and RaC 'and a coefficient B that corrects the collection state (difference between the surface and the inside) on the filter paper _{Using 2} and, the following equation was used.

[0028]

[ _Equation 2] A _est2 (Pu) = B ₂ × [B ₁ × 0.051 × A (RaC ') +
0.180 × A (ThC ')] An example of the coefficient values used is: 1 hour: B ₂ B ₁ = 3.15, 2 hours: B ₂ B ₁ = 1.85, 12
Time: B ₂ B ₁ = 1.48, 24 hours: B ₂ B ₁ = 1.24, 36 hours: B ₂ B ₁ = 1.00, B ₁ rapidly approaches ₁ in the first 4 hours and then B ₂ is the main correction factor.

Estimated count value A based on the time-corrected coefficient value
_est2 (Pu) is in good agreement with the _count value A (Pu). FIG.
7 and FIG. 7 are diagrams for explaining the third embodiment, which is an embodiment in which two differential wave height discriminators are used to compensate the background due to Radon-Tron and monitor plutonium. FIG. 6 is a pulse wave height spectrum diagram showing the setting of the region, and FIG. 7 is a measurement unit 8 and an arithmetic processing unit 9.
FIG. Radon-as a channel
Although RaA channel and ThC channel are selected as the Tron-channel, both channels are almost overlapping, resulting in one channel,
It can be measured by two differential wave height discriminators.

FIG. 8 shows a comparison between the count value of the first measuring means and the count value of the second measuring means and the estimated count value according to this embodiment. In this case as well, the measurement results are obtained in the absence of plutonium. The thin dotted line is the count value of the second measuring means,
That is, the count value A (RaA & T on the channel of RaA & ThC
hC), the thin line indicates the _count value of the first measuring means, that is, the plutonium-channel _count value A (Pu), the thick dotted line indicates the estimated _count value A _est3 (Pu) by a constant coefficient, and the thick line indicates the coefficient. The estimated _count value A _est4 (Pu) when the correction by the dust collection time is added to is shown. Also in this case, the estimated value by the constant coefficient is smaller than A (Pu) for the first three days, as in the first embodiment.

As can be seen from FIGS. 4 and 8, in the case of the estimation by the constant coefficient in the first and third embodiments, it depends on the use condition of the filter paper that the first 2-3 days _Count value A (Pu) and estimated _count value A _est1 (Pu) or A _est3
Although there is a significant difference with (Pu), the difference has become smaller after that. Therefore, if the dust paper is pre-collected before the filter paper is used and the collection state is stabilized, the estimated count value becomes more accurate. In the example of FIGS. 4 and 8, this period is 2 to 3 days. It is estimated that the period required to stabilize the collection state will vary greatly depending on the usage conditions of the filter paper, but in this case it is 2/6 (about 30%), and the filter paper used here is for 2 weeks. Since collection is possible, in that case it is 2/14 (about 15%). Therefore, it can be said that preliminary collection of 10 to 50% of the total usage time is effective.

9 and 10 show a fourth embodiment, FIG. 9 is a block diagram of the measuring section 8 and the arithmetic processing section 9, and FIG. 10 is a diagram showing the measurement result and the estimated count value. Is. As the count value of the second counting means, the count value A (RaA & ThC) in the channel of RaA & ThC is adopted, and the cumulative value ΣA (RaA of the count value A (RaA & ThC) is used as the coefficient for calculating the estimated count value.
& ThC) function is used. In the case of FIG. 10, the estimated _count value A _est5 (Pu) was obtained by the following formula.

[0033]

[ _Equation 3] A _est5 (Pu) = 5.4 × [ΣA (RaA & ThC)] ^-0.221 ×
A (RaA & ThC) As shown in FIG. 10, the count value A (Pu) (shown by a thin line) and the estimated _count value A _est5 (Pu) (shown by a thick line) show a very good agreement. FIG. 11 shows a fifth embodiment, which is an embodiment including means for estimating the collection status of radon and thoron inside the filter paper. In this case, five differential wave height discriminators are used. In the figure, the nuclides to be measured are uranium and plutonium, and the second region is RaA & ThC in order to obtain the count value corresponding to the amount of the daughter nuclide of Radon Thoron.
In addition to setting the channel, the channel of RaC 'is divided into two in order to grasp the condition of the filter paper and obtain the coefficient by which the count value in the RaA & ThC channel is multiplied.
The ratio of the count value A (I) in the high pulse peak value side area I and the count value A (II) in the low pulse peak value side area II of this RaC 'divided channel is calculated, and the ratio of RaA & ThC channel Determine the coefficient by which the count value is multiplied. In the state where the set pulse crest value of area I and area II is fixed, A (I)
As / A (II) is larger, the spectrum is steeper, so the coefficient value is smaller, and conversely, A (I)
It can be easily understood that the coefficient value becomes large when / A (II) is small.

Since the accuracy of A (I) / A (II) becomes higher as each count value becomes larger, it is most effective to adopt the channel of RaC 'having the largest count value. In addition, the pulse peak values of Region I and Region II are
If you set the count value corresponding to the amount of Tron's daughter nuclide relative to the pulse height region of the nuclide and the pulse height region of the target nuclide, the estimated count value will be calculated without changing the ratio. Can be a coefficient for

This point will be described in more detail with reference to FIG. In Fig. 11, the lower limit pulse crest value of the channel of plutonium, which is the nuclide to be measured, is p ₁ , the upper limit pulse crest value is p _2, and the RaA & ThC channel for the count value corresponding to the amount of the daughter nuclide of Radon Thoron. The lower limit pulse peak value is p ₂ (same as the upper limit pulse peak value of the plutonium channel), and the upper limit pulse peak value is r ₂ . The divided region is the RaC 'channel, the region I is the region corresponding to the RaA & ThC channel, the lower limit pulse crest value is d ₂ , the upper limit pulse crest value is d ₃ , and the region II is the plutonium channel. And the lower limit pulse peak value
d ₁ and the upper limit pulse crest value are d ₂ . The widths of the regions I and II can be approximately determined by the following equations depending on the average stopping power of α rays in the corresponding regions.

[0036]

[Formula 4] [Width of region I: d ₃ −d ₂ ] / [Channel width of RaA & ThC: r ₂ −p ₂ ] = SP (I) / SP (RaA & ThC)

[0037]

[Formula 5] [Width of region II: d ₂ −d ₁ ] / [width of plutonium channel: p ₂ −p ₁ ] = SP (II) / SP (Pu) where SP (I) is the region I Average stopping power of α rays at
SP (RaA & ThC) is α in RaA & ThC channel
The average stopping power of rays, SP (Pu) is the average stopping power of α rays in the plutonium channel, and SP (II) is the average stopping power of α rays in region II.

With this setting, the count value A _est6 (Pu) estimated to count α rays due to the Radon-Tron daughter nuclide in the plutonium channel is given by the following equation.

[0039]

[ _Equation 6] A _est6 (Pu) = [A (II) / A (I)] × A (RaA & ThC) From this, the coefficient for obtaining the estimated count value can be obtained from the count values in the regions I and II. You can see that. The coefficient for obtaining the estimated count value in the uranium channel is obtained as a simple function of this coefficient, for example, the n-th power.

When no uranium is present in the atmosphere to be measured, the measurement accuracy is improved by expanding the lower limit pulse peak value of the plutonium channel to p ₀ and the lower limit pulse peak value of region II to d _0. To do. FIG. 12 is a conceptual diagram showing the sixth embodiment. In this embodiment, an atmosphere measuring sensor 12 for measuring any one of temperature, pressure and humidity or a combination thereof is provided in a space including the filter paper 4 of the dust collecting section 3 and the radiation detector 7. The density of the air in this space is estimated by the output signal of this sensor 12, and the upper and lower limit pulse crest values of the area for the measurement value of the first counting means and the measurement value of the second counting means are estimated by the estimated air density. The set value is compensated, and the set pulse wave height region is effectively kept constant even if the state of the atmosphere changes.

When the temperature, pressure or humidity of the air layer between the filter paper 4 and the radiation detector 7 fluctuates, the density of the air layer changes. There is an air layer between the filter paper and the radiation detector,
If the density changes, even if α-rays with the same energy are emitted from the dust 6, α-rays when reaching the radiation detector 7
The energy of the line loses energy proportional to the density of the air layer, and the energy value becomes different. That is, the pulse crest values differ. Speaking of the pulse height spectrum, the spectrum moves in the horizontal axis direction. Therefore, if each pulse crest value region is fixed, the change in the state of the air layer causes a change in the measured value. Therefore, when high accuracy is required, the set values of the upper and lower limit pulse crest values of the set pulse crest value region are compensated by the temperature, pressure and humidity of the air layer between the filter paper 4 and the radiation detector 7. Is necessary.

The effect of temperature on the air density is about -1/300 per degree Celsius, the effect of pressure is about + 1 / 1,000 per 1 hPa, and the humidity is about -1/260 per 1% of water vapor present in the air,
Since the usual fluctuation range can be regarded as temperature ± 10 ° C, pressure ± 10hPa, and water vapor concentration ± 2%, it is expected that temperature will have the greatest effect and humidity will have the least effect. The accuracy can be greatly improved by controlling.

Although not shown in the drawings as an embodiment, as an effective embodiment having a relatively simple structure, the accuracy can be improved without compensating the set values of the upper and lower limit pulse peak values of the set pulse peak value region. The temperature of the air layer can be controlled by, for example, winding a heater around the air supply pipe 2 to control the temperature. FIG. 13 is a pulse wave height spectrum diagram for explaining the seventh embodiment. This is for checking and optimizing the set pulse crest value of the area. FIG. 13 shows an attempt to check and optimize the state of set values by RaA & ThC channels.

First, the preset area is set as a reference area (lower limit pulse peak value = l ₀ , upper limit pulse peak value = h ₀ ), and the count value in this area is set to A ₀ (RaA & ThC). Set a comparison area (lower limit pulse peak value = l ₂ , upper limit pulse peak value = h ₂ ) in which this reference area is moved to the high pulse peak value side by a certain pulse peak width, and the count value in this area is set to A ₂ ( RaA & ThC) and set a comparison area (lower limit pulse height = l ₁ , upper limit pulse height = h ₁ ) in which the reference area is moved to the low pulse peak value side by a constant pulse peak value, and the count value in this area is set to A ₁ (RaA & ThC).

By comparing these count values, the standard
Area can be checked and the setting area can be optimized.
it can. This will be explained below. In Figure 13, the reference
The channel moves to the low pulse peak side and the low pulse peak
If the comparison area on the value side is reached, the count value will be the upper limit.
Area S on the high side of the pulse wave _h1Is reduced by the amount corresponding to
Area S at the lower limit of the pulse wave peak_l1Increase by the amount equivalent to
I do. As is clear from the figure, S_h1> S_l1Because
The count value decreases as it moves. Furthermore, on the low pulse peak side
Moving to the peak area of the nuclide on the left,
State continues.

On the contrary, if the reference area moves to the high pulse crest value side and becomes the state of the comparison area on the high pulse crest value side, the count value is the upper limit pulse wave crest value side, and is equal to the area S _h2. And increases by the amount corresponding to the area S _l2 on the lower limit pulse height side. As is clear from the figure, S _l2 >
Since it is S _h2 , the _count value decreases in this case as well. Further, this state continues even if the pulse value moves to the high pulse crest value side.

As can be seen from the above description, the reference area in the figure has the maximum count value, and the count value decreases when moving to either direction. The state with the maximum count value is an ideal setting state. In the case of optimization with one comparison area, when the count value of the comparison area is larger, the upper and lower limit pulse crest values of all the setting areas are shifted to the comparison area side, and the count value of the comparison area is changed. When is small, the pulse peak value of the channel can be optimized by shifting the upper and lower limit pulse peak values of all the setting areas to the side opposite to the comparison area. When both count values are the same, the upper and lower limit pulse crest values of all setting areas may be left unchanged.

When the comparison areas are provided above and below for optimization, the upper and lower limit pulse crest values of all the set areas are shifted to the side of the area having the maximum count value, thereby changing the pulse crest values of the areas. Can be optimized. It goes without saying that when the reference area is the maximum, the upper and lower limit pulse crest values of all the setting areas are left unchanged.

[0049]

According to the present invention, in addition to the pulse wave height region (first region) of the nuclide to be measured, the radon thoron for grasping the amount of the daughter nuclide of radon thoron existing as the background is obtained. The dedicated pulse height area (second area) is set for the daughter nuclides of
The counting value in each area is measured using the counting means and the second counting means. That is, since the count value of the second counting means is a count value representing the amount of the daughter nuclide of Radon Tron, and the count value of the first counting means is the total count value in the first region, the nuclide to be measured It is the sum of the count value by and the contribution (background) of the daughter nuclide of Radon Thong contained in that region. The contribution of the daughter nuclide of Radon Thoron is estimated using the first calculating means, and the output of the second calculating means is subtracted from the count value of the first counting means using the second calculating means to obtain a measurement target. It is possible to obtain the count value depending on the nuclide.

Therefore, according to the present invention, the pulse height spectrum is obtained using a multi-channel analyzer, and the type and amount of α-ray dust are measured without separating the spectrum into individual nuclides by spectral stripping. can do. Let RaC 'be the daughter nuclide of Radon selected to obtain the count value of the second counting means, and ThC' be the daughter nuclide of Tron, and the differential wave height discriminator for obtaining the count value of the second counting means. Two are required, but if RaA is the daughter nuclide of Radon and ThC is the daughter nuclide of Tron, the number can be one.

Second of each of Radon Tron's daughter nuclides
The coefficient by which the count value of the counting means is multiplied can be properly used depending on the required measurement accuracy. Adopting a constant coefficient is the easiest to calculate, and is suitable when the effect of Radon-Tron is small or when high accuracy is not required. If the filter paper used for collecting dust is used for dust collection in advance for a certain period of time under conditions close to the actual use condition, higher accuracy can be obtained by a simple calculation using a certain coefficient. The time for collecting the preliminary dust may be appropriately selected according to environmental conditions and required accuracy.

When a coefficient which is a function of the dust collection time of the filter paper is adopted, the calculation becomes slightly complicated, but more accurate measurement can be performed. If a coefficient determined by the cumulative value of the count values of the second counting means is adopted, the calculation becomes complicated, but more accurate measurement is possible. The above coefficients are
It is given as an experientially determined constant or function. On the other hand, a region for dividing one or more nuclides of Radon Tron's daughter nuclide into multiple regions for each nuclide and estimating the estimated count value by the ratio of the count values between the divided regions for each nuclide. You can also decide the numerical value. Since the coefficient determined by this method is a result of directly measuring the actual use state of the filter paper, the coefficient with the highest accuracy can be obtained. In this case, it is necessary to add a differential wave height discriminator, and if the area for the count value of the second counting means and the high pulse wave height area I are made common, the number of additions can be reduced by one.

The most effective Radon Thong daughter nuclide selected to determine the coefficient value by this method is Ra
It is C '. The reason is that the count value is large and thus the measurement accuracy is high, and furthermore, the width of the pulse peak value of the channel is wide, so that various ratio regions can be set. Next, the effect of improving the measurement accuracy by controlling the state of the air layer between the filter paper 4 and the radiation detector 7 or by measuring and compensating the state of the air layer will be described.

A means for keeping the temperature of the air layer between the filter paper 4 and the radiation detector 7 constant is provided, and if the temperature of the air layer is kept constant, it is the largest factor that changes the density of the air layer. Since the density change due to temperature is small, the change in energy lost by the α rays emitted from the dust 6 in the air layer is small, and the variation in the energy of the α rays when reaching the radiation detector 7 is small, and the measurement accuracy is reduced. Is improved.

The density of the air layer depends not only on temperature but also on pressure and humidity. Therefore, the temperature, which is related to the density of air,
One of pressure and humidity or a combination of them is selected according to the situation of the area to be monitored, and the measurement result compensates for the pulse peak value that can be converted into α-ray energy, thereby improving measurement accuracy. Can be improved.

One of the regions of Radon Tron's daughter nuclide
With one channel as the reference area, the width of the pulse peak value is the same, and the reference area is set by moving the pulse peak value to the high pulse peak value side or the low pulse peak value side by a certain value. The count values in the area and the comparison area are compared, and the width of the pulse peak value is the same as that of the reference area, and the pulse peak value is moved to the low pulse peak value side and the high pulse peak value side by a certain value. By setting one comparison area and comparing the count values in these three areas, it can be determined whether or not the reference area is in an appropriate setting state, and the accuracy of measurement can be improved.

This method does not rely on controlling the state of the air layer between the filter paper 4 and the radiation detector 7 or by measuring and compensating for the state of the air layer to compare one or two comparisons. By setting the region, it is possible to optimize the upper and lower limit pulse crest values of the setting regions of all nuclides. In this case, it is most effective to set the comparison area to RaA and ThC. The reason is that it is a daughter nuclide of Radon Thoron that emits α-rays having the energy closest to the energy of α-rays emitted by plutonium or uranium to be measured, and that the measurement value of the second counting means is Since only one region is needed, the total number of differential type wave height discriminators required is small.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration of an α-ray dust monitor according to the present invention.

FIG. 2 is a pulse wave height spectrum diagram showing a set region according to the first embodiment.

FIG. 3 is a measurement unit 8 and a calculation processing unit 9 according to the first embodiment.
Block diagram showing

FIG. 4 is a diagram showing measurement results and calculation results according to the first embodiment.

FIG. 5 is a diagram showing measurement results and calculation results according to the second embodiment.

FIG. 6 is a pulse height spectrum diagram showing a set area according to a third embodiment.

FIG. 7 shows a measuring unit 8 and an arithmetic processing unit 9 according to the third embodiment.
Block diagram showing

FIG. 8 is a diagram showing measurement results and calculation results according to the third embodiment.

FIG. 9 is a measuring section 8 and an arithmetic processing section 9 according to a fourth embodiment.
Block diagram showing

FIG. 10 is a diagram showing measurement results and calculation results according to the fourth embodiment.

FIG. 11 is a pulse wave height spectrum diagram showing a set region according to a fifth embodiment.

FIG. 12 is a conceptual diagram showing a configuration of an α-ray dust monitor according to a sixth embodiment.

FIG. 13 is a pulse wave height spectrum diagram showing a set region according to a seventh embodiment.

FIG. 14 is a conceptual diagram showing a configuration of an α-ray dust monitor according to a conventional technique.

FIG. 15 is a pulse wave height spectrum diagram showing a measurement range of an α-ray dust monitor according to a conventional technique.

FIG. 16: Pulse height spectrum diagram showing pulse height spectra of Radon Thoron daughter nuclide, plutonium and uranium

[Brief description of reference numerals]

 1 Pump 2 Air Pipe 3 Dust Collection Part 4 Filter Paper 5 Flow Meter 6 Dust 7 Radiation Detector 8 Measurement Unit 81 First Counting Means 82 Second Counting Means 9 Calculation Processing Unit 91 First Calculation Means 92 Second Calculation Means 10 Display Unit 12 Atmosphere measurement sensor

Claims (16)

[Claims] 1. Dust contained in an atmosphere of interest is collected on a filter paper, and α rays emitted from the dust are measured by a radiation detector to measure α ray dust existing in the atmosphere. In a monitoring device, a first counting means for detecting α-rays in a first region including a pulse peak value corresponding to a peak position of a spectrum of a nuclide to be measured, and a radon-tron that does not include the first region Second counting means for detecting α-rays in the second region containing the pulse peak value of the daughter nuclide of the above, and the daughter value of Radon Thong present in the first region as a background by using the count value of the second counting means. First calculation means for estimating and calculating the count value of α-rays emitted from the nuclide, and by subtracting the count value estimated and calculated by the first calculation means from the count value of the first count means, the measurement target Tosu Second computing means and, alpha rays dust monitor, characterized in that it consists of obtaining the alpha dose that is released from nuclide. 2. The α-ray dust monitor according to claim 1, wherein the daughter nuclide of radon selected for the second region is RaC ′ ( ²¹⁴
Po), and ThC '( ²¹² Po) is the daughter nuclide of Tron. 3. The α-ray dust monitor according to claim 1, wherein the daughter nuclide of radon selected for the second region is RaA ( ^218).
Po), and the daughter nuclide of TRON is ThC ( ²¹² Bi), an α-ray dust monitor. 4. The α-ray dust monitor according to any one of claims 1 to 3, wherein the first computing means multiplies the count value of the second counting means by a constant coefficient and is the daughter of Radon Tron. An α-ray dust monitor characterized by estimating and calculating an estimated count value of a nuclide. 5. The α-ray dust monitor according to any one of claims 1 to 3, wherein the first calculation means is a function of the count value of the second counting means and the dust collection time of the filter paper. An α-ray dust monitor characterized by multiplying a coefficient to estimate and calculate an estimated count value of Radon-Tron daughter nuclides. 6. The α-ray dust monitor according to any one of claims 1 to 4, wherein the filter paper used for dust collection has a preliminary dust collection under a condition close to an actual use condition for a predetermined time in advance. The alpha ray dust monitor characterized by using the thing. 7. The α-ray dust monitor according to claim 6, wherein the preliminary dust collection time is 10 to 50% of the total dust collection time. 8. The α-ray dust monitor according to any one of claims 1 to 3, wherein the first computing means adds the count value of the second counting means to the cumulative value of the count value of the second counting means. An α-ray dust monitor characterized by multiplying a coefficient determined by the above to estimate and calculate an estimated count value of Radon Tron's daughter nuclide. 9. The α-ray dust monitor according to any one of claims 1 to 3, wherein the second region is any one of radon and thoron daughter nuclides.
The region of one or a plurality of nuclides is divided into a plurality of regions for each nuclide, and the first computing means sets the coefficient value determined as a function of the ratio of the count values between the divided regions of each nuclide to the count value of the second counting means. An α-ray dust monitor characterized by multiplying by and calculating the estimated count value of Radon Tron's daughter nuclide. 10. The α-ray dust monitor according to claim 9, wherein Radon is the daughter nuclide of Radon-Tron selected for determining the coefficient value, and the division number is 2. Dust monitor. 11. The α-ray dust monitor according to any one of claims 1 to 10, further comprising means for keeping a temperature of an air layer between the filter paper and the radiation detector constant. Α ray dust monitor characterized by. 12. The α-ray dust monitor according to any one of claims 1 to 10, wherein any one of temperature, pressure and humidity of an air layer between the filter paper and the detector is used. Alternatively, the α-ray dust monitor is provided with means for measuring a combination thereof, and the upper limit pulse peak value and the lower limit pulse peak value of the first region and the second region are compensated by the measured value. 13. The α-ray dust monitor according to any one of claims 1 to 12, wherein the second region is located at a peak position of a spectrum of any one of radon and thoron daughter nuclides. The region containing the corresponding pulse crest value is the reference region, while the width of the pulse crest value is the same, and the region where the pulse crest value is moved to the high pulse crest value side or the low pulse crest value side by a fixed value Set as a comparison area, compare the count values in the reference area and the comparison area, and if the count value in the area on the low pulse peak side is larger, set areas for all nuclides including this nuclide. Move to the low pulse peak value side, and if the count value in the low pulse peak value side area is smaller, move the set area of all nuclides including this nuclide to the high pulse peak value side. α-rays dust monitor which is characterized. 14. The α-ray dust monitor according to any one of claims 1 to 12, wherein the second region is located at a peak position of a spectrum of any one of radon and thoron daughter nuclides. The region containing the corresponding pulse crest value is the reference region, on the other hand, the width of the pulse crest value is the same, and the pulse crest value is moved to the low pulse crest value side and the high pulse crest value side by a certain value. Each region is set as a comparison region, the count values in these three regions are compared, and if the count value in the comparison region on the low pulse peak side is the maximum, the setting region for all nuclides including this nuclide is set. If the count value in the reference area is the maximum, the setting area for all nuclides including this nuclide is left unchanged, and the count value in the comparison area on the high pulse peak value side is left unchanged. Greatest in the case, the setting area of all species, including the species move to a higher pulse height side, alpha rays dust monitor, characterized in that. 15. The α-ray dust monitor according to claim 13 or 14, wherein Radon and Tron's daughter nuclides that set the reference region are RaA and
An α-ray dust monitor characterized by being ThC. 16. The α-ray dust monitor according to any one of claims 1 to 15, wherein the second region corresponds to each of the radon daughter nuclide and the thoron daughter nuclide. An α-ray dust monitor characterized by being set as.