JP5879953B2 - Radiation inspection equipment - Google Patents

Description

  The present invention relates to an inspection apparatus using radiation (for example, beta rays, X-rays, gamma rays, etc.), and in particular, an object to be measured (hereinafter referred to as a sample) due to the influence of an air layer interposed between a radiation source and a radiation measuring instrument. The present invention relates to a radiation inspection apparatus that improves measurement accuracy.

  When radiation (hereinafter referred to as β-rays) passes through the material layer, it gradually loses energy due to ionization and excitation, and decays. In addition, it undergoes such inelastic scattering many times and changes its traveling direction. Therefore, as the physical quantity (for example, thickness) of the sample increases, the number of transmitted β rays decreases. Devices that measure the physical quantities of various sheet-like samples by applying such principles are known.

  In an inspection using radiation, it is common to place a sample (product, human body, etc.) between a radiation source and a detector, and detect, for example, the intensity of β rays from the transmittance to obtain a grayscale image. For this reason, a change in the air layer existing between the β-ray source and the detector directly affects the detected image (detection accuracy). That is, if a change in density occurs due to changes in temperature or pressure, this will directly lead to measurement errors.

  The β dose is monitored by feedback control and temperature control for stably driving the β-ray source. As prior art for monitoring fluctuations in temperature, pressure, etc., and feeding back to a measurement system to measure a measurement object with high accuracy, there are those disclosed in Japanese Patent Laid-Open Nos. 4-158209 and 2001-227918.

FIG. 4 is a perspective view showing an example of an in-line measuring instrument that measures the thickness and coating amount of a sheet-like sample by transmission characteristics using X-rays, β-rays, γ-rays, infrared rays, and the like.
The sheet-like sample 1 flows at a constant speed from the right to the left, and a radiation source head (lower side: hereinafter referred to as a radiation source) 2 and a detector head such as an ionization chamber (to be referred to as an ionization chamber) Measurement is performed in a form in which the sample 1 is scanned as a pair.

  Each head is supported by an O-type frame 4 called a gate type, and is driven up and down while maintaining the positional relationship of the opposing upper and lower heads. Each of the heads 2 and 3 repeats the measurement in a zigzag manner by repeatedly folding around the end of the sample. Further, each head is provided with a retracting position A on the right side of the O-shaped frame 4.

  This is because it is necessary to move to a position where there is no sample when the sample is set or when the radiation source head 2 or the detector head 3 is maintained or calibrated. In the thickness measurement, a plurality of standard samples whose thickness and material (basis weight) are known are measured in advance, and a calibration curve is obtained as a transmission characteristic with respect to the basis weight.

The thickness is converted by reversely drawing from the calibration curve and the transmission output value of the sample. Figure 4 shows the coating amount .
2 to 3 are installed in the production line, the permeation characteristics are measured before and after the coating process, and the difference can be obtained to determine the coating amount.

  In the system as shown in FIG. 4, since the heads 2 and 3 scan in the width direction with respect to the sample 1 flowing at high speed, it is possible to measure only partly on the zigzag line. For this reason, there is also a demand for full-scale measurement in recent years.

FIG. 5 shows a state in which a line type detector 3a in which detection elements (not shown) are arranged with a narrow pitch and without gaps is installed, and radiation is emitted radially from a radiation source separated by a predetermined distance to measure the entire surface. It is a perspective view. 2a is a radiation source, and 3a is a radiation detector (line camera).
Here, even if it is a scanning type measuring device shown in FIG. 4 or the whole surface measuring type measuring device shown in FIG. 5, the sample 1 must be once removed at the time of calibration.

  In other words, when calibrating against radiation source deterioration due to changes over time, detector sensitivity changes, air layer temperature / humidity changes (periodic fluctuations such as seasonal or morning / night due to poor air conditioning in the production line) Then, calibration is performed by measuring the state in which there is no sample 1 (= air layer).

In addition, it is also possible to re-determine a calibration curve by measuring a standard sample for a certain long term. In the conventional scanning type measuring instrument shown in FIG. 4 , the temperature between the sensor heads is measured in real time to compensate for the air temperature, and the air layer is measured at intervals of several tens of minutes to several hours.
Using this value, compensation of the measured value is performed.

JP 61-11363 JP-A-4-158209 JP 2001-227918 A

  By the way, with respect to the change of the air layer that most affects the measurement accuracy in the short-term to medium-term, by performing the evacuation / calibration operation every several hours, there is no major problem in the normal measurement. However, when a short-term atmospheric change occurs due to a cold start of a factory or a typhoon passing, it may be difficult to maintain accuracy with a calibration operation in units of several hours.

Shortening the interval of the calibration operation is one of the solutions, but has a demerit that the sample cannot be measured during the calibration operation at the retracted position. Further, in the case of the whole surface measurement type as shown in FIG. 5 , since it is necessary to pull out the apparatus until it is detached from the sample, a width of about 2.5 times the width (W) of the apparatus itself is required. There is a situation where the evacuation operation itself is difficult to perform.

  Measures such as blowing constant temperature air to the air gap in the measurement gap are taken to reduce the temperature change that is relatively easy to affect the measured value, but air consumption is high. Heater power for constant temperature There is a problem such as.

  Accordingly, an object of the present invention is to improve the accuracy and stability of thickness measurement by compensating for variations in measurement signals caused by atmospheric variations such as temperature, humidity, and atmospheric pressure.

In order to achieve such a problem, the invention of the radiation inspection apparatus according to claim 1 of the present invention is:
In a radiation inspection apparatus that measures the basis weight by detecting radiation emitted from a radiation source and passing through a sample with a radiation detector,
A temperature sensor, an atmospheric pressure sensor, and humidity detection means are arranged in the vicinity of the inspection device, and the atmospheric weight is calculated based on the temperature detected by the temperature sensor and the atmospheric pressure detected by the atmospheric pressure sensor, and detected by the humidity detection means. A moisture weight is calculated based on the humidity, and an atmospheric weight calculating means for correcting the atmospheric weight based on the moisture weight is provided, and the basis weight is corrected based on the atmospheric weight calculated by the atmospheric weight calculating means. It is characterized by comprising.

In Claim 2, in the radiological examination apparatus of Claim 1,
The calculation of the moisture weight is performed based on an approximate expression of saturated water vapor pressure , a gas equation of state, and the humidity .

The present invention has the following effects.
When the distance between the radiation source and the detector is far and the amount of air present between them is greatly affecting the basis weight of the sample to be measured, or the basis weight of the sample to be measured is a thin film film The measurement accuracy can be increased when it is small and susceptible to atmospheric fluctuations.

In addition, even when using a full-surface measurement type measuring instrument, it is possible to perform continuous and accurate measurement with unnecessary or minimal evacuation operation, and stabilization of the basis weight measurement can be achieved.
In addition, a stable and accurate basis weight value can be measured even during a cold start where the temperature and humidity fluctuations in the factory are large or during a weather fluctuation such as the passage of a typhoon.
Further, there is no need to blow dry air that is kept at a constant temperature between the radiation source and the radiation detection apparatus, and it is possible to reduce compressed air and power.

It is a perspective view which shows an example of embodiment of this invention. The figure (a) which shows the change of the water vapor weight by the humidity change when temperature 30 degreeC humidity 50% is a reference, The figure which shows the change of the atmospheric weight by the humidity change when temperature 30 degreeC humidity 50% is a reference ( b). It is a flowchart which shows the flow of the signal processing by this invention. It is a perspective view which shows a prior art example. It is a perspective view which shows a prior art example.

  Hereinafter, the present invention will be described in detail with reference to the drawings. 1A and 1B are configuration diagrams showing an example of an embodiment of the present invention. FIG. 1A is a perspective view, and FIG. 1B is a schematic diagram showing a relationship among a detector head, a radiation source, a sample, and the atmosphere. The difference from FIG. 3 is that a temperature sensor 10, an atmospheric pressure sensor / humidity sensor 11 are arranged in the vicinity of the thickness measuring device and outputs from these sensors are input, and various calculations (a gas state equation, moisture weight, It is the point provided with the calculating means 12 which performs atmospheric weight, basic weight correction, etc.).

As shown in FIG. 1 (b), when a sample is placed between a radiation source and a detector, and the sample thickness is obtained from the radiation attenuation when passing through the sample, measurement is performed including attenuation due to the atmosphere. It will be. When it is desired to accurately determine the thickness of the sample, it is important to correct the attenuation due to the atmosphere.
Here, a method for accurately obtaining the sample weight by subtracting the value obtained by calculating the atmospheric weight from the weight including the sample and the atmosphere obtained by the detector by the following method will be described.

The effect of temperature and pressure on the basis weight can be derived from the “gas equation of state”.
PV = nRT = (W / m) RT (1)
W = m (PV / RT) ... (2)
Here, m = average molecular weight (air is composed of O ₂ and N ₂ nitrogen 1: 4, and the average molecular weight is 32 × 1/5 + 28 × 4/5 = 28.8)
W = weight [g]
n = number of moles R = Rydberg constant (1 mole of gas constant = 8.314472 (75) [J · mol-1 · K-1])
P = gas pressure [Pa]
V = volume [m ³ ]
T = temperature [K]

Let V be the volume of air present between the source and the detector. Here, since V is calculated as an amount corresponding to the basis weight, the distance between the radiation source and the detector head is calculated as the height with respect to the bottom surface of 1 m ² . By using atmospheric pressure as P and temperature as T, and using the average molecular weight of the atmosphere as m (average molecular weight), the weight of the atmosphere existing between the radiation source and the detector can be obtained from the equation (2).
If the calculated volume is previously set as the bottom surface (1 m ² ) corresponding to the basis weight, the atmospheric weight is equivalent to the atmospheric basis weight as it is.

The influence of humidity can be calculated as the weight of water vapor. Since the weight of water vapor is calculated as the product of the saturated water vapor amount and the humidity, the Antoine equation (Antoine equation) for obtaining the saturated water vapor pressure approximately is used here.
log ₁₀ P = A− (B / T + C)
Where P = vapor pressure (Pa)
T = temperature (K)
A, B, C = Antoine constants and constants depending on the substance, vapor pressure and temperature units For example, in water, Pa = scal as the unit of P, and Kelvin as the unit of T, A = 10.09 in the range of 333K to 423K , B = 1668.21, C = 45.15.

For example, if the saturated water vapor pressure is obtained using the Antoine equation, the saturated water vapor amount can be calculated by substituting the saturated water vapor pressure into P of the “gas state equation”. By taking the product of the saturated water vapor amount thus obtained and the measured humidity, the moisture weight in the atmosphere can be obtained. If the volume is calculated as the bottom surface of about 1 m ² as shown above, this is the basis weight due to the humidity in the atmosphere.

  So far, the calculation method of the basis weight of air and the basis weight of humidity has been described, but in actuality, the number of moles of dry air changes according to the partial pressure of water vapor caused by humidity. The amount of dry air corresponding to the molecular number ratio (about air 28.8 / water 18) is reduced with respect to an increase of 1 mol of water vapor. Therefore, in order to obtain the atmospheric basis weight in consideration of humidity, the moisture weight may be added after adding / subtracting the molecular number ratio corresponding to the change in humidity with respect to the dry air.

FIG. 2 is a diagram in which such a calculation is performed, and for example, a change in the amount of water vapor and a change in the atmospheric weight due to a change in humidity when the temperature is 30 ° C. and 50% are obtained. The thickness (basis weight) measuring device is provided with detection means that can measure temperature, humidity, and atmospheric pressure in or near it.
The dry air weight according to the distance between the radiation source and the detector is calculated from the temperature and the atmospheric pressure using the gas equation of state.

As a specific example, the saturated water vapor amount is obtained from an approximate equation of Antine or the like. The amount of moisture in the air can be obtained from the obtained saturated water vapor amount and the obtained humidity using the gas equation of state.
There are other approximate expressions such as Goff-Gratch expression, Magnus-Teten expression, Wexler-Hyland (Hyland and Wexler) expression, and various other expressions. And may be selected as appropriate.

After reducing the weight of dry air corresponding to the water vapor partial pressure, the moisture weight is added to determine the atmospheric weight according to the distance between the radiation source and the detector.
The obtained atmospheric weight is subjected to sensitivity correction in accordance with convenience in measurement such as detector sensitivity (for example, sensitivity correction represented by a different linear attenuation coefficient ratio between the atmosphere and the sample).
On the other hand, the amount by which irradiation from the radiation source attenuates when the sample is measured is measured, and the basis weight of the sample is obtained using a calibration curve prepared in advance.

The thickness of the sample can be obtained with high accuracy by subtracting the atmospheric weight after sensitivity correction from this basis weight. The calculation of the atmospheric weight based on temperature, humidity, and atmospheric pressure may be performed by preparing a reference table of values prepared in advance, a calibration curve, or a dedicated approximate expression in addition to the above calculation method.
Further, when the atmospheric weight is corrected, normally, there is a tendency that the atmospheric pressure is low when the humidity is high and the atmospheric pressure is high when the humidity is low. For this reason, accuracy can be improved even if correction is performed using a measured value of either humidity or atmospheric pressure as a value including the other factor.

  3A to 3C are flowcharts showing the flow of signal processing using the radiation measuring apparatus of the present invention. In the figure, (a) is a signal processing flow measured by a sample measuring sensor, (b) is a signal flow measured by a temperature measuring device and an atmospheric pressure measuring device, and (c) is a signal flow measured by a humidity measuring device. FIG. In addition, each sensor by these (a-c) shall start a measurement simultaneously at the time of starting a measurement with a radiation measuring device.

In FIG. 3 (a),
Step 1: The signal from the radiation source when the sample is transmitted by the sample detector is measured.
Step 2: Use a sample calibration curve,
Step 3: Determine thickness (basis weight).

In FIG. 3B,
Step 1 ′: The signal measured by the temperature sensor / barometric pressure sensor 11 is input to the calculation means 12,
Step 2 ′: Using the gas equation of state,
Step 3 ′: Calculate the dry air weight.

In FIG. 3C,
Step 1 ″: Measure humidity with a humidity sensor,
Step 2 '': Calculate saturated water vapor pressure.
Step 3 ″: Using the gas state equation from the saturated water vapor pressure,
Step 4 ″: Calculate the moisture weight.

Proceed to step 4 ′ of FIG.
Step 4 ′: The partial pressure of water vapor is subtracted from the dry air weight determined in Step 3 ′ and the moisture weight determined in Step 4 ″.
Step 5 ′: Calculate the atmospheric weight from the value obtained by subtracting the water weight determined in Step 4 ″ and the water vapor partial pressure determined in Step 4 ′.
Step 6 ′: Atmospheric weight sensitivity correction is performed.

Returning to FIG.
Step 4: Atmospheric weight is subtracted from the basis weight determined at Step 3 and the atmospheric weight sensitivity correction value determined at Step 6 ′.
Step 5: Obtain the corrected basis weight,
Step 6: The corrected basis weight is output as a measured value.
The thickness measurement can be compensated by the above steps.

The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention. In the embodiment, an example using values measured by a temperature sensor, an atmospheric pressure sensor, and a humidity sensor has been shown. However, since the decrease in measurement accuracy due to changes in atmospheric pressure and humidity is small compared to temperature changes, a certain average atmospheric pressure is used. By using it, there is no need to have an atmospheric pressure sensor. Further, although the measurement accuracy is lowered, it is possible to perform compensation without using the humidity sensor if the atmospheric pressure sensor is operated so as to incorporate a representative correlation of humidity.
Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

1 Sample 2 Radiation source 2a Radiation source 3 Detector head (ionization chamber)
3a Radiation detector (line camera)
4 O-type frame 5 Thickness measuring device 6 Line-type detector 10 Temperature sensor 11 Pressure / humidity sensor 12 Calculation means

Claims (2)

In a radiation inspection apparatus that measures the basis weight by detecting radiation emitted from a radiation source and passing through a sample with a radiation detector,
A temperature sensor, an atmospheric pressure sensor, and humidity detection means are arranged in the vicinity of the inspection device, and the atmospheric weight is calculated based on the temperature detected by the temperature sensor and the atmospheric pressure detected by the atmospheric pressure sensor, and detected by the humidity detection means. A moisture weight is calculated based on the humidity, and an atmospheric weight calculating means for correcting the atmospheric weight based on the moisture weight is provided, and the basis weight is corrected based on the atmospheric weight calculated by the atmospheric weight calculating means. Radiation inspection apparatus characterized by comprising. The radiation inspection apparatus according to claim 1 , wherein the calculation of the moisture weight is performed based on an approximate expression of a saturated water vapor pressure , a gas equation of state, and the humidity .