JPS6271880A - Radiation measuring instrument - Google Patents

Abstract

PURPOSE:To measure a radiation dose previously with a wide dynamic range by varying an integration time according to the level of a radiation detection output signal. CONSTITUTION:The output signal of a radiation detector 7 is integrated by an integrator 13, whose integral value is compared with a reference voltage V0 by a comparator 15. A counter 23 begins to count clock pulses from a reference clock generating part 17 on the start of the integration of the integrator 13 and an AND gate 21 is closed when the integral value reaches the V0, thereby stopping the counting operation. Count data is sent to an arithmetic control part to perform reciprocal arithmetic, finding the radiation dose. If the detection output of a detector 7 is small and the counter 23 overflows before the integral value reaches the reference value V0, a signal S5 is outputted through an FF 25, etc., to turn OFF the switch 13e of the integrator 13, so that the time up to when the integral value reaches the reference value V0 varies. Thus, the radiation dose is measured precisely with the wide dynamic range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a radiation measuring device that has a wide dynamic range and is capable of measuring OA lines with high accuracy.

[Technical background of the invention and its problems] In the radiation measuring device used in the xg1 thickness meter, the Data is collected for a predetermined period of time, and the thickness and tomographic image of the object to be inspected are obtained from the collected data.

By the way, if there are scratches, cavities, foreign objects, etc. in the object to be inspected, or depending on the type of material of the object to be inspected, the transmission line m will vary greatly.

However, in the conventional radiation measuring device described above, the transmitted radiation [
Since the data collection time was fixed regardless of the amount of [F] /N decrease.

There was a problem that artifacts were generated.

[Object of the Invention] The present invention has been made based on the above-mentioned circumstances, and its object is to provide a radioactive material that can accurately measure radiation regardless of the amount of transmitted radiation. ) II measurement device.

[Summary of the Invention] In order to achieve the above two objects, the present invention provides a radiation detector that transmits radiation generated by a radiation generator to an object to be inspected and detects the transmitted radiation wA1, and an output signal of this radiation detector. an integrating means for time-integrating the voltage, a clocking means for measuring the integration time until the output signal of the integrating means reaches a predetermined voltage, and a calculation means for calculating the transmission line layer from the integration time measured by the clocking means. It has

[Embodiment of the Invention] FIG. 1 is a block diagram showing the configuration of an embodiment of the apparatus according to the present invention, and FIG. 2 is a block diagram showing the configuration of an X-ray thickness meter to which the present invention is applied.

In FIG. 2, a radiation generator 1 is driven by a power source 3 to generate radiation, and this radiation is irradiated onto an object 5 to be inspected. The radiation transmitted through the inspected object 5 is detected by a detector 7, and the detection signal is supplied to a data/event collection section 9. The data collection section 9 time-integrates the output signal of the detector 7 as described later, and supplies the integrated data to the calculation/control section 11, which calculates the thickness of the object to be inspected 5. .

As shown in FIG. 1, the data collection section 9 includes an integrator 13 that integrates the output signal of the detector 7, a comparator 15 that compares the output voltage V of the integrator 13 with a reference voltage Vo,
a counting clock generator 17 for counting the integration time of the integrator 13; a three-man AND gate 21 that receives an inverted signal from the inverter 19, a comparison signal from the comparator 15, and a clock signal from the counting clock generator 17; Android Gate 2
8-bit counter 23 for counting clock signals from 8-bit counter 23, and a flip 70 block 25 for detecting overflow of 8-bit counter 23.

The integrator 13 has two integrators each inserted in parallel between an operational amplifier 13a and the input/output terminal of this A pair 13a.
2 capacitors 13b, 13c and these condensers +4
An analog switch 13d for discharging 13b and 13c,
Analog switch 1 that opens and closes the connection of capacitor i3b
3e.

Next, the operating principle of this embodiment configured as described above will be explained. The transmitted dose of radiation is uniquely determined by measuring the time it takes for the output voltage of the integrator to reach a predetermined constant voltage VO.

In other words, the output current i of the detector 7 is proportional to the intensity l of the radiation incident on the detector 7. Furthermore, the incident radiation intensity I includes temporal fluctuations due to radiation quantum noise and the like. Therefore, 1-kl(t) (1) (k is a conversion constant). Also, the output voltage V of the integrator 13 is the value obtained by dividing the charge Q accumulated in the capacitor by the capacitance RC. Therefore, from formulas (1) and (2>, V = Vo Assuming that the time it takes to reach is to, then the integral term in equation (4) above is the area of the shaded area in Figure 3.
If a rectangle whose base is 0 is drawn in Fig. 3, the height T of the rectangle is calculated from the time O of the incident radiation intensity to to,
This is the temporal average value up to.

Therefore, the time to until the output voltage V of the integrator reaches a constant voltage vO is the average of the radiation incident on the detector 7 during the time Q-to over time 0 to to. Since it is inversely proportional to the intensity I, by measuring this time to, the lower average intensity can be broadly determined. Transparent line ff1l
The time required for the output of the integrator 13 to reach the zero IEFV# reference N pressure 'JO is determined as shown in FIG.

Next, the operation of this embodiment having the above operating principle will be explained with reference to the time chart of FIG.

Detection signal 81 output from detector 7 (the output current i
) is integrated by the integrator 13. When the integrator 13 starts operating, the analog switch 13e is closed and the analog switch 13d is open. Therefore, the integral is determined by a time constant determined by the parallel capacitance of the capacitors 1'3b and 13G, and the output π pressure V of the integrator 13 increases as shown in FIG. 5(2). Until the output signal 82 (output voltage V) of the integrator 13 reaches the reference voltage ■0, the output signal S3 of the comparator 15 is 1'' (see FIG. 5 (3)).

Meanwhile, the 8-bit counter 23 receives the clock signal from the counting clock generator 17 via the AND gate 2°1, and supplies the count data to the arithmetic/control unit 11. The counting operation of this counter 23 is performed by the integrator 1.
Since the output voltage V of the integrator 13 reaches the standard voltage v0 and the output signal S3 of the comparator 15 becomes ``0'', the output voltage V of the integrator 13 is determined to be the reference voltage vO from the count data of the counter 23. The time t1 until it reaches is known.

Therefore, the transmitted radiation dose of the inspected object 5 is determined from time t1, and the thickness of the inspected object 5 is determined by the calculation/control unit 1.
It can be found by 1.

When the count data has been transferred to the calculation/control unit 11, the calculation/control unit 11 outputs a reset signal S6 (
(See FIG. 5(6)), the analog switch 13d is closed by this reset signal S6.

This causes capacitors 13b and 13c to discharge. Further, the counter 236 and the flip-flop 25 are reset by the reset signal S6.

When the preparation for the next data collection is completed, the calculation/control unit 11
The reset signal S6 is released, and the integrator 13 starts integrating again.

When the amount of transmitted radiation is small, it takes a long time for the output voltage 'J of the integrator 13 to reach the reference voltage (2)0. Therefore, after a certain period of time t2 has elapsed after the start of integration, the anacog switch 13e is opened to disconnect the capacitor 13b.
Integration is performed only by the capacitor 13c, so that the output of the integrator 13 quickly reaches the reference voltage VO. This operation is performed as follows.

That is, when the count number of the 8-pitch counter 23 reaches 256, an overflow occurs (0, F.

) terminal becomes °1°', and the flip-flop 25 is set. The output of the flip tab 25 is 11 i I
When the signal becomes +, this output signal is inverted by the inverter 277 and becomes an inverted signal S5, which opens the analog switch 13e. This disconnects the capacitor 131) and integrator '
Since charging of I3 is performed only by the capacitor 13C, '' increases in the constant in equation (6). The increase m per unit time in the output voltage V of the integrator 13 increases, and the reference voltage V quickly increases.
Reach O. The time t3 until reaching this Vo is determined by the following equation.

t2 turtle296・p (p is the period of 17 clock pulses l1
l) In this way, in this embodiment, the integration time can be varied even when the number of transmitted lines m is small, so that problems caused by a shortage of lines m can be solved.

Further, while the analog switch 13e of the integrator 13 is closed, the voltages across the capacitors 13b and 13c are always equal, so even if the analog switch 13e is opened and the capacitor 13b is disconnected after the time t2 has elapsed, No spike-like noise occurs.

FIG. 6 shows the configuration of a second embodiment of the device according to the present invention.

In the first embodiment, the capacitor was switched only - times, but in this embodiment, the capacitor was switched n times, forming an integrator having a so-called zero-order polygonal line.

In the figure, n+1 capacitors C1 to On+1 are connected in parallel between the input and output terminals of the operational amplifier 13 of the integrator 13. Additionally, a blog switch S W + to SWn is provided in series with each of the circuits C+ to C+011.

Further, an n-bit shift register 29 is connected to an overflow terminal of the 8-bit counter 23 instead of the flip-flop 25. This n-bit shift register 2
Switching signals for the analog switch SW+=SWn are supplied from the output terminals D1 to □n of 9 through inverters, respectively.

This n-bit shift register 29 responds by setting n outputs of output terminals D1 to [)n to "1" in this order every time °1" is output from the overflow terminal of the 8-bit counter. 'C analog switch SW +~SW
n are opened in this order.

After starting the integration now, until time t2, the analog switch S
All the switches W + to S W n are closed, and if the output voltage V of the integrator 13 has not reached the reference voltage VO when the integration time reaches time t2, the 8-bit counter 23 will overflow. Overflow terminal is 1
''.Now, the output terminal DI of the two n-bit shift registers becomes ``1°'', and the analog switch SV
V+ is opened and capacitor C1 is disconnected. Therefore, as shown in FIG. 7, between t 2 and 2t 2, C2+C3+
-+Cn''+The integration is performed with the combined capacitance.

Furthermore, if the output voltage V of the integrator 13 does not reach the reference voltage Vo even after time t2, the output terminal D2 of the n-bit shift register 29 also becomes "1", thereby also disconnecting the capacitor C2. In this way, integrator 1
The capacitors C1 to On are sequentially disconnected until the output voltage V of No. 3 reaches the reference voltage Vo, thereby forming an integrator having a maximum of n bending points as shown in FIG.

Note that 31 is a binary conversion unit, and when transferring data to the arithmetic/control unit 11, in order to reduce the number of signal lines, '
1” (for example, D1 to D3 are “1”).
i'', Dn~Dn is ``0'', C3 is the most significant digit).
). Further, this binary number converter 31 only needs to have an output bit number of [10Q2 n , l + 1. Here, [] is a Gaussian symbol and represents the largest integer that does not exceed the number in [].

Next, when the characteristic curve of FIG. 7 is made exponential, the ratio of the capacitances required for the capacitors C1 to Cn +l is derived as follows.

. The numerical characteristic is when the ratio of the slopes of the graphs of time at2- (a-1) t2 and time (a-1) t2- (a-2>t2 is always constant over a-2 to n) In this case, the resolution is always the same ratio over the full scale, so there is no sacrifice in resolution.

Substituting the above equation (5) into equation (4), we get: Therefore, the escape pressure VO that can be reached during a certain period of time is inversely proportional to the capacitance of the capacitor. Therefore, each polygonal line section (O to t
2, in order to keep the slope ratio m between t2 and 2[2,...) constant, the capacitance C of the capacitor should be set at 1/m increments. Therefore, C1+C2+C3+C4+-+Cm +Cn+1=
1 C2+C3+C4+・+Cn +Cn −4−+=1/
m C3+C4+-+Cn +Cn ++ -1/m 2 Therefore ° C+=1-1/m (,2=1/m -1/m2- C3=1/m2-i/113 Cn =1/m ''-1/ m” = (m-1)/No'...(9) Roaring, C1~
By setting the On condenser to the value of equation (9), the device can be constructed without sacrificing resolution. Also, in this case, Cil'', -H=1/m' Tel
) Le.

In this way, in this embodiment, the integrator 13 having the n-th order polygonal line can be configured with an extremely simple configuration, and therefore the dynamic range of the device is wide.

In addition, the clock pulses are constantly counted in the 8-bit counter 23, and the overflow can be used repeatedly, so from this point of view as well, the device configuration is 1! I
It becomes simpler and its usefulness increases.

In each of the above embodiments, a radiation thickness meter was used as an example, but
The present invention is not limited to this, and as shown in FIG.
It can also be used as a T-scanner.

In the figure, radiation from an X-ray generator 1 is focused into a pencil beam by a collimator 32a, and then irradiated onto an object 5 to be inspected, and its transmission time is input to a detector 7 via a collimator 32b. The output signal of the detector 7 is then supplied to the data acquisition section 9. In the data collection section 9, the collected data is integrated as described above, and the transmitted dose is determined by the 51 sieve 33 based on the integration time. Based on this transmitted dose, a tomographic image of the object to be inspected 5 is displayed on the operating section 3.
The image is displayed on the CRT 39 via 7. Reference numeral 35 denotes a system control unit that operates the data table on which the object to be inspected 5 is placed and controls the data collection unit 9.

When the present invention is applied to a radiation CT scanner, artefaction due to insufficient transmitted line segment? This has excellent effects in that it is possible to prevent the occurrence of blemishes and to keep the integration time to the necessary minimum.

[Effects of the Invention] As explained in detail above, according to the present invention, the output signal of the radiation detector is integrated over time and the transmitted dose is determined from this integration time. For example, with an X-ray thickness meter, accurate thickness measurement is possible, and with a CT scanner, image S/' can be resolved.
It is possible to improve N and prevent the occurrence of artifacts due to insufficient transmission rays.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an apparatus according to the present invention, FIG. 2 is a block diagram showing the configuration of an X-ray thickness meter to which the present invention is applied, and FIGS. 3 and 4 are A diagram for explaining the operating principle of the present invention, FIG. 5 is a time chart for explaining the operation of the device shown in FIG. 1, and FIG.
FIG. 7 is a block diagram showing the configuration of the embodiment; FIG. 7 is a diagram showing the integral characteristic of the device shown in FIG. 6; and FIG. 8 is a block diagram showing the configuration of the radiation C scanner to which the present invention is applied. DESCRIPTION OF SYMBOLS 1... Radiation generator 5... Inspection object 7... Radiation detector 9... Data collection part 11... Calculation/control part 13... Integrators 13b, 13c, C1~
Cn ++ -'::I Indenser 15...Comparator 1
7... Counting clock generator 23... 8-bit counter 25... Flip-flop 29... n-bit shift register Figure 2 Figure 3 Figure 4 Figure 5 Figure 7 Figure 8

Claims (2)

[Claims] (1) A radiation detector that transmits the radiation generated by the radiation generator to the object to be inspected and detects the transmitted dose; an integrating means that integrates the output signal of the radiation detector over time; and an output signal of the integrating means. a timer for measuring the integration time until a preset reference voltage is reached; a variable means for varying the integration time depending on the magnitude of the output signal of the radiation detector; A radiation measuring device comprising calculation means for determining a transmitted dose. (2) The radiation measuring device according to claim 1, wherein the variable means is a means for varying the n-time integration time until the output signal of the radiation detector reaches a reference voltage.