JPH0593685A - Measuring method of density and measuring apparatus of density using the same - Google Patents

Abstract

PURPOSE:To realize practical density measurement by conducting a corrective processing in consideration of the particle size of a sample to be measured. CONSTITUTION:A gamma-ray pulse is radiated from a radiation source 5 to a sample to be measured and a count value for a unit time of the gamma-ray pulse transmitted through the sample is determined for each of a plurality of energy ranges. Moreover, the value of a variable of the actual particle size of the sample is determined by substituting the count values in an approximation formula into which the variable of the particle size is introduced, and furthermore the true density is determined by substituting this value of the variable in an operation formula for calculating the density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention counts the number of γ-ray pulses that have radiated a γ-ray pulse to a sample to be measured and has passed through the sample to be measured, and the density of the sample to be measured is calculated from the counted value. The present invention relates to a density measuring method and a density measuring apparatus to be obtained, and more particularly, to a density measuring method and a density measuring apparatus for realizing a density measurement that is actually performed by performing a correction process in consideration of a particle size of a sample to be measured.

[0002]

2. Description of the Related Art Conventionally, there has been known a density measuring device for measuring the density of a sample such as asphalt for road paving or concrete. Such a density measuring device is designed to
A radiation source that emits a line pulse and a pair of detection sensors (NaI scintillation counters) arranged at different intervals from the radiation source are installed on the surface of the sample to be measured, and pass through the sample to be measured. The incoming γ-ray pulse is detected by each detection sensor, and the number of pulses per unit time is counted. Then, the sample density ρ is calculated by performing the calculation of the following equation (1) for each count value N1 and N2 of each detection sensor.

[0003]

[Equation 1]

Further, instead of using such a pair of detection sensors, the number of pulses is counted by only one detection sensor, and the counted value is applied to the following equation (2) to directly determine the density. There were things.

[0005]

[Equation 2]

[0006]

However, in such a conventional density measuring apparatus, it is considered that the particle size of the sample to be measured is not taken into consideration, that is, the particle size does not affect the γ-ray density measurement. Since the measurement was performed, there was an error from the actual density of the sample. Or, to minimize such an error, a sample similar to the sample to be measured was prepared in advance, and the density was measured after adjusting the sensitivity of the density measuring device for each sample, but it is extremely complicated. Met.

The necessity of considering the particle size of the sample when measuring the density of the sample will be explained. As shown in FIG.
A sample to be measured such as pavement asphalt or concrete can be regarded as a group of a large number of particle groups (q1, q2, etc.) distributed at intervals P, and it can be assumed that there are voids between the particles. Then, when a γ-ray pulse is emitted from the radiation source 1 provided on the surface of the sample to be measured and the number of γ-ray pulses that have passed through the sample to be measured is counted by the detection sensor 2, the γ-ray pulse of the sample to be measured is The scattering energy that is primarily scattered by the particle group q1 in the shallow portion (that is, the portion near the radiation source) and the γ-ray pulse is primarily scattered by the particle group q2 in the deep portion (that is, the portion far from the radiation source) of the sample to be measured. When the scattering energy is compared, the relationship between the energy Eγ of the γ-ray pulse scattered by the particle and the scattering angle θ is E0, where E0 is the known energy at the time of radiation of the radiation source 1.

[0008]

[Equation 3]

[0009]

[Equation 4]

It can be expressed by the equations (3) and (4), and in the primary scattering, the scattering energy changes according to the scattering angle θ. Therefore, as shown in FIG.
Considering the scattering model for 1 and q2, the γ-ray pulse emitted from the radiation source 1 toward the particle q1 having the depth D1 and the scattered γ-ray pulse scattered toward the detection sensor 2 by the primary scattering are considered. If the angle formed (scattering angle) is θ1, this angle θ1 becomes the circumferential angle of a triangular outer circle C1 having the positions of the radiation source 1, the detection sensor 2, and the particle q1 as vertices, and on this outer circle C1. The scattered energy of the primary scattering by the particles located is equal to any scattered energy.

Similarly, a particle q having a depth D2 (D2> D1)
If the angle (scattering angle) formed by the γ-ray pulse emitted toward 2 and the scattered γ-ray pulse scattered toward the detection sensor 2 by the primary scattering is θ2, this angle θ2 is
The circumferential angle of a triangular outer circle C2 whose vertices are the positions of the radiation source 1, the detection sensor 2, and the particle q2, and this outer circle C
The scattered energy of the primary scattering by the particles located on 2 is equal to any scattered energy.

If the depth is D2> D1, the scattering angle is θ2> θ1 and the depth D1 is
Energy of scattered γ-ray pulse Eγ1 and depth D2
In the case of, the relation of the energy Eγ2 of the γ-ray pulse is Eγ
1> Eγ2. Further, although FIGS. 6 and 7 are two-dimensional models, this relationship holds even in an actual three-dimensional case, and if D2> D1 and θ2> θ1, then Eγ1> Eγ.
Satisfies the relationship of 2.

As described above, the influence of the particles in the shallow portion and the deep portion of the sample on the γ-ray pulse is different, and this grain size must be taken into consideration in order to perform more practical density measurement. The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a density measuring method and a density measuring apparatus capable of actually measuring the sample density.

[0014]

In order to achieve such an object, the present invention is directed to a sample to be measured from a radiation source by γ
The present invention is directed to a density measuring method and a density measuring apparatus which count a number of γ-ray pulses per unit time that radiates a line pulse and has passed through a sample to be measured, and obtains the density of the sample from the counted value.

In the present invention, γ detected by the detection sensor
The count value of the line pulse is obtained for each of a plurality of energy ranges, and further, the variable value of the actual particle size of the sample is obtained by substituting these count values in the approximation formula described later in which the variable of the particle size is introduced. The true density is obtained by substituting the variable value into the arithmetic expression for density calculation.

[0016]

When the density calculated by the above-mentioned method is considered by the scattered γ-rays measured within two different energy ranges, the calculated densities are ρH and ρL. Due to the effect of particle size, the actual measured value is ρH
If ′, ρL ′,

[0017]

[Equation 5]

[0018]

[Equation 6]

As described above, it is assumed that an error is generated by EL and EH. At this time, if equation (6) is divided by equation (5),

[0020]

[Equation 7]

However, the value of ρL / ρH is assumed to be a constant value as long as the geometrical arrangement of the measurement system does not change, and is therefore a constant. Also, in general, when comparing EH and EL,

[0022]

[Equation 8]

If E L can be expressed as a function of second-order or higher of E H,

[0024]

[Equation 9]

As the equation (5),

[0026]

[Equation 10]

It can be written as As long as the shape of the function f (β) is invariant, if β, that is, ρL '/ ρH' can be obtained, the true density can be obtained. Therefore, by introducing an approximate expression that is considered valid as this function f (β) and correcting the influence of the granularity, it is possible to obtain a more realistic result as compared with the case where the conventional granularity is not considered. ..

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A density measuring device according to an embodiment of the present invention will be described below with reference to FIG. In FIG. 2, 3 is a surface-type density measuring device installed on the surface of the sample to be measured. Inside the housing 4, a radiation source 5 for irradiating the sample to be measured with γ-ray pulses is provided, and at the same time, a radiation source A pair of detection sensors 6 and 7 for detecting the γ-ray pulse that has passed through the sample to be measured are provided at different distances L1 and L2 from the position 5.

A NaI scintillation counter is applied to these detection sensors 6 and 7, and the detection level of energy is sequentially changed within a preset energy range (range of ET to EM in FIG. 1), and each of them is changed. The scanning process of counting the number of γ-ray pulses in the energy value is performed, or the count value corresponding to the pulse height diagram is obtained by collectively counting a plurality of windows in the entire measured scattered γ-ray energy range. ..

Further, γ counted by each detection sensor 6 and 7
As shown in FIG. 3, the line pulse count value data S1 and S2 are input to a processing unit having a first calculation unit 18 and a correction calculation unit 19, and output measurement data of the density ρ T.
The arithmetic units 18 and 19 are composed of arithmetic processing devices such as microprocessors. Further, the reference energy value EW for dividing into the energy ranges WL and WH shown in FIG. 1 is set appropriately.

First, the principle of density measurement according to the embodiment is shown in FIG.
It will be described together with the pulse height diagram shown in FIG. In FIG. 1, a radiation source that emits a γ-ray pulse is installed on the surface of a sample to be measured, and different distances L1 and L2 from the radiation source are set.
(However, a pair of detection sensors are installed at the position of L1 <L2), the number of scattered γ-ray pulses reaching each detection sensor per unit time is counted, and the horizontal axis represents the energy of scattered γ-ray pulses, The vertical axis is shown as the count value for each energy. Graph (A) shows the measurement result by the detection sensor installed at a distance L1 close to the radiation source, and graph (B) shows the measurement result by the detection sensor installed at a distance L2 far from the radiation source. Further, the discrimination energy level EM and energy level ET of the γ-ray pulse emitted from the radiation source are the measurement limits of the density measuring device, and the measurement results within this range are shown.

In such a pulse height diagram, when an appropriate energy level EW is used as a reference, EW and E
The count value in the energy range WH between M is predominant in the shallow part of the measured sample, and the count value in the energy range WL between ET and EW is predominant in the deep part of the measured sample. Become. Therefore, first, the total count value in the energy range WH for the graph (A) is NH1, the total count value in the energy range WL is NL1,
If the total count value in the entire range WL ÷ WH is N1 and the graph (A) is the function f (Eγ), the following equation (11),
It can be represented by (12) and (13).

[0033]

[Equation 11]

[0034]

[Equation 12]

[0035]

[Equation 13]

Similarly, for the graph (B), the total count value in the energy range WH is NH2, the total count value in the energy range WL is NL2, the total count value in the total range WL + WH is N2, and the graph (B) is a function g. (Eγ)
It can be expressed by equations (14), (15) and (16).

[0037]

[Equation 14]

[0038]

[Equation 15]

[0039]

[Equation 16]

The respective count values N1, NH1, NL1,
When the density is calculated for each energy range from N2, NH2, and NL2, the density ρH from the measurement result of the range WH, the range WL
The density ρ L from the measurement result of and the density ρ HL from the measurement result of the range WH + WL are

[0041]

[Equation 17]

[0042]

[Equation 18]

[0043]

[Formula 19]

It can be obtained from In addition, the above formulas (17) to (1
In 9), AH, AL, A, BH, BL, and B are constant values. Here, when the density measurement is performed assuming that there is no influence of the particle size as in the conventional case, ρH = ρL = ρHL holds, but in the actual sample measurement, the particle size is considered as described above. There is a need to.

Therefore, according to the principle of this embodiment, the following equation (2
As shown by the approximation formulas 0) to (22), it was assumed that the relation between the density of the sample before correction and the true density is satisfied by the approximation formula in which the parameter related to the particle size of the sample is introduced.

[0046]

[Equation 20]

[0047]

[Equation 21]

[0048]

[Equation 22]

ΡT is the true density of the sample to be measured and is proportional to the reciprocal of the mass absorption coefficient of the sample to be measured. Further, ρH is the measured density before correction obtained from the measurement result of the energy range WH, ρL is the measured density before correction obtained from the measurement result of the energy range WL, and ρHL is the measured density before correction obtained from the measurement result of the energy range WHL. Is the density of. Furthermore,
RD is an unknown variable relating to the particle size of the sample to be measured, XH, XL
, XHL are constants.

Here, the densities ρH, ρL, ρHL obtained for each energy range of the sample to be measured (that is, for each sample depth).
Assuming that Eqs. (20) to (22) hold, the ratio of Eqs. (20) and (21) above gives

[0051]

[Equation 23]

The approximate expression (3) holds and the third and subsequent terms on the right side of expression (23) have extremely small values, so if they are ignored, the value of the unknown variable RD relating to the granularity can be obtained.
Then, the variable value RD thus determined is expressed by the above equation (2)
Substituting into 2), the true density ρT can be obtained.

[0053]

[Equation 24]

As described above, according to the principle of the present embodiment, the actually measured sample density determined for each depth is defined by the true sample density, the particle size, and the depth variable, and the particle size in the approximate expression is related. The unknown variable and the unknown variable related to the depth are specified, and the true density is obtained from the measured sample density.
That is, further explaining according to the actual processing procedure, first,
When calibrating the density measuring device at an initial point, etc., each energy range WH, WL, WHL of a sample to be measured (hereinafter referred to as a reference sample) whose density ρT is known in advance and whose particle size is uniform
The densities ρ H, ρ L and ρ HL are measured, then the measurement results are substituted into the equations (20) to (22) and back calculated to obtain unknown constants X H, XL and XHL. That is,
In the known sample, the variable RD is a constant, and the densities ρT and ρH, ρL, ρHL are known, so that unknown constants XH, XL, XHL are obtained here. Then, these obtained variables are substituted into the above equations (20) to (22).

Next, the sample to be measured for which the density is to be actually obtained is measured, and the densities ρ H, ρ L, ρ for the respective energy ranges WH, WL, WHL actually measured by this measurement are measured.
The unknown variable value RD of the sample to be measured is obtained by substituting HL into the above equations (20) to (22) and using the previously obtained constants XH, XL, XHL to further perform the operation of the equation (23).
That is, the variable value RD of the particle size of the sample to be measured for which the density is actually obtained by performing the calculation of the equation (23) here
Will be confirmed.

Then, by substituting the variable value RD and the constants XHL and ρHL previously obtained in the equation (24), the true density ρT of the sample to be actually measured can be obtained. Become. Further, another embodiment will be described with reference to FIG. This embodiment is a case where another type of detection sensor is applied.

In the previous embodiment, the above equations (17) to (19) are used.
As shown in FIG. 3, a pair of detection sensors is provided and the density is obtained from the ratio of the respective count values. However, only one detection sensor is provided, and the measured count value NL for each energy range obtained from the detection sensor is obtained. , NH, NHL are expressed by the following equations (25) to (2
Substituting into 7), the density ρL before correction obtained from these equations
, .Rho.H, .rho.HL can be applied to the above equations (20) to (24) to perform the correction process considering the granularity.

[0058]

[Equation 25]

[0059]

[Equation 26]

[0060]

[Equation 27]

Thus, the above approximate expressions (20) to (24)
Introducing the above, the unknown variables in these equations are specified, and the measured values of the density that are actually measured are substituted into these equations and arithmetic processing is performed. It is possible to obtain accurate and accurate results. That is, in the figure, 3 is a surface-type density measuring device installed on the surface of the sample to be measured, and in the housing 4, a radiation source 5 for emitting a γ-ray pulse to the sample to be measured is provided, A detection sensor (NaI scintillation counter) 8 for detecting the γ-ray pulse that has passed through the sample to be measured is provided at an appropriate interval from the radiation source 5.

The detection sensor 8 performs a scanning process in which the detection level of energy is sequentially changed within a preset energy range and the number of γ-ray pulses at each energy value is counted, or all the measured scattered γ-rays are used. Collective counting is performed on a plurality of windows in the energy range to obtain count value data corresponding to the pulse height diagram as shown in FIG.

In this embodiment, since there is only one detection sensor 8, one type of count value data is obtained. Then, a calculation unit (not shown) measures the count values NL and NH for each energy range obtained from the detection sensor 8.
, NHL into the above equations (25) to (27) and applying the uncorrected densities ρ L, ρ H, and ρ HL obtained from these equations to the above equations (20) to (24), the true density ρ T
Is calculated.

Further, the arithmetic unit (not shown) is provided with the above equation (2).
The unknown variables in 3) and (24) are applied in advance to the approximation formulas (20) to (22) as described in the above-described embodiment, and are determined in advance when the device is calibrated, and the actual measurement process after the calibration is performed. In (1), the true density of the unknown sample to be measured is calculated by performing the correction process only with the equations (23) and (24).

Still another embodiment will be described with reference to FIG. In this density measuring device 3, a radiation source 5 is provided in a housing 4, and a pair of GM tubes 10 and 11 housed in a shielding material 9 having a collimator function are provided at different positions. Then, an arithmetic unit (not shown) performs arithmetic processing based on the count values obtained from these detection sensors to calculate the density of the sample. The GM tubes 10 and 11 are arranged so that the incident angles θ1 and θ2 of the γ-ray pulse are different.

The GM tube itself does not directly count the counted values of the scattered energy of the γ-ray pulse, but the scattered γ-ray energy Eγ of the γ-ray pulse reaching the GM tubes 10 and 11 through the sample to be measured. And the scattering angle θ have the characteristics that can be expressed by the equations (3) and (4).
Therefore, the γ-rays corresponding to the energy Eγ corresponding to the respective scattering angles are detected in these GM tubes 10 and 11 set to different incident angles θ1 and θ2.
The count value can be obtained with the respective GM tubes 10 and 11 as in the first embodiment.

Then, with respect to the count values by the GM tubes 10 and 11, a calculation unit (not shown) uses the equations (20) to (2).
The true density ρT is obtained by performing the calculation of 4).
As to the unknown variables in the above equations (23) and (24), the arithmetic unit (not shown) applies the approximate equations (20) to (22) to the device in advance, as described in the above description of the principle. Is confirmed at the time of calibration, etc., and in the actual measurement work after the calibration, the true density of the unknown sample to be measured is calculated by performing the correction processing only by the equations (23) and (24).

[0068]

As described above, according to the present invention, the γ-ray pulse is emitted from the radiation source to the sample to be measured, and the number of γ-ray pulses passing through the sample to be measured per unit time is calculated. In the density measuring method and the density measuring apparatus for counting and determining the density of the sample from the counted value, the counted value of the γ-ray pulse detected by the detection sensor is calculated for each of a plurality of energy ranges, and a variable of particle size is introduced. The variable value of the actual particle size of the sample is obtained by substituting these count values into the approximated equation, and the true density is obtained by substituting this variable value into the calculation formula for density calculation. It is possible to obtain a sample density that is actually suitable by introducing the parameter of particle size.

[Brief description of drawings]

FIG. 1 is a pulse height diagram for explaining the principle of density measurement of the present invention.

FIG. 2 is a schematic configuration explanatory diagram showing a configuration of a density measuring device according to an embodiment of the present invention.

3 is a block diagram showing a configuration of an arithmetic processing unit of the density measuring device shown in FIG.

FIG. 4 is a schematic configuration explanatory view showing a configuration of a density measuring device according to another embodiment of the present invention.

FIG. 5 is a schematic configuration explanatory view showing a configuration of a density measuring device according to still another embodiment of the present invention.

FIG. 6 is an explanatory diagram for explaining that particle size should be considered in density measurement.

FIG. 7 is another explanatory diagram for explaining that the particle size should be considered in the density measurement.

[Explanation of symbols]

 WL; low energy range of scattered γ-ray pulse WH; high energy range of scattered γ-ray pulse 3; density measuring device 4; housing 5; radiation source 6, 7; detection sensor 10, 11; GM tube 18; first Calculation unit 19; Correction processing calculation unit

Front page continuation (72) Inventor Tatsuo Oyama 2-16-46 Minami-Kamata, Ota-ku, Tokyo Within Tokimetsuku Co., Ltd.

Claims (2)

[Claims] 1. A γ-ray pulse is emitted from a radiation source to a sample to be measured, the number of γ-ray pulses passing through the sample to be measured per unit time is counted, and the density of the sample is calculated from the counted value. In the density measurement method for obtaining the above, the count value is obtained for each of a plurality of energy ranges, the variable value of the particle size of the sample is obtained by substituting these count values into the approximate expression introducing the variable of the particle size, and the variable value is A density measuring method, characterized in that a corrected density is obtained by substituting it in an arithmetic expression for density calculation. 2. A γ-ray pulse is emitted from a radiation source to the sample to be measured, the number of γ-ray pulses passing through the sample to be measured is counted, and the density of the sample is calculated from the counted value. In the density measuring device for determining, the detection means for detecting the count value of the γ-ray pulse per unit time for each of a plurality of energy ranges, and the count value from the detection means is substituted into an approximate expression introducing a variable of particle size. The density measurement is characterized by having a first calculation means for obtaining a variable value of the particle size of the sample by the above, and a correction calculation means for obtaining a corrected density by substituting the variable value into an arithmetic expression for density calculation. apparatus.