JPS62207985A - Measuring instrument for position of radiation source - Google Patents

Abstract

PURPOSE:To easily measure the position of a radiation source in a three- dimensional space, by providing plural collimator elements that are placed to form an overall shape of a rotatable disc, inclined in accordance with the distance in the radial direction from the rotational center. CONSTITUTION:A collimator 2 is placed at the side of a radiation source 1 in the vicinity of a scintillator plate 3, and also, the two-dimensional intensity distribution of a fluorescent plate in the scintillator plate 3 is caught as an image by an ITV camera 4. As for the collimator 2, a shielding body 6 is inclined by an angle theta and provided, in a distance (r) from its rotational center axis 7, and only a radiant ray from a specified direction is made to pass through selectively. In this state, the collimator 2 is rotated by using the center axis 7 as a rotary axis, and in the optional place of each X and Y coordinate, the passing rate of the radiant ray is averaged from a discontinuous distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radiation source position measuring device for measuring the direction of a radiation source and the distance to the radiation source in a wide three-dimensional space.

[Conventional technology]

Conventional radiation monitors have used the ionization chamber method, and when evaluating the spatial distribution of dose, isolated chambers with isodirectional sensitivity are installed scattered in a three-dimensional space.

The line rate at each installation location is measured.

Furthermore, in the medical field, accidents in which radioactive isotopes are lost rarely occur, and in such cases, it is necessary to search for radioactive isotopes over a wide range of areas. 'Sakaribakoya G
The radiation source is searched for using an M tube, a scintillation detector, etc. Regarding radiation measurement, a publicly known document is the "Radiation Measurement Handbook" (November 30, 1981), translated by Itsube Kimura and Eiji Sakai.

Published by Nikkan Kogyo Shimbun, pp. 137-145).

[Problem that the invention seeks to solve]

However, in assessing the spatial distribution of dose,
In the case of ionization chambers installed at various locations, the measured value at each installation location indicates an average dose rate, so the dose distribution at that location cannot be known in detail.

Furthermore, even when searching for an S source, conventional radiation detectors have low directivity toward the source, and therefore a wide range of 3
The reality is that it takes more time and effort to search for a target source than in dimensional space.

The purpose of the present invention is...! The object of the present invention is to provide a radiation source position measuring device that can measure the spatial distribution of Lit in detail and easily measure the position of the radiation source in a three-dimensional space.

[Means for solving problems]

The above object can be achieved by using a collimator having a rotatable disc-like overall shape and having a plurality of collimator elements arranged at an angle according to the distance in the radial direction from the center of rotation. This is achieved by selectively allowing only radiation from the y+ direction to pass through and detecting it two-dimensionally.

[Effect]

Depending on each collimator element, radiation from a specific direction can be selectively passed through with a trowel-shaped five-point tilt. therefore.

When assuming radiation from a certain direction.

There is a collimator element that allows most of the radiation to pass through, but adjacent collimator elements also allow the radiation to pass through to a lesser extent. Therefore,
If the radiation passed through the collimator is detected two-dimensionally,
The direction of the radiation can be determined based on the position where the last radiation was detected. Further, the radiation from the collimator is detected two-dimensionally with a certain spread, and the distance to the radiation source can be determined from the extent of the spread.

〔Example〕

The present invention will be explained below with reference to FIGS. 1 to 11.
Before that, the preferred radiation detection means and IJ meter of the present invention, as well as the principle of the present invention, will be explained.

There are various types of radiation detection means, but in the present invention, since the radiation passing through the collimator needs to be detected two-dimensionally immediately after passing through the collimator, one of the radiation detection means according to the present invention is a scintillator plate. Alternatively, it is appropriate to have a plurality of semiconductor detectors arranged two-dimensionally. Although the detection principle is different, they can be used similarly. This will be explained later. A scintillator plate is used in the four-body example, and the detection principle of this scintillator is as follows.

In other words, radiation such as r-rays and X-rays acts as a scintillator.

It is well known that (fluorescence) occurs. The presence of this light allows us to confirm the presence of radiation.

Incidentally, in a scintillation detector, the radiation intensity is measured by converting fluorescence into a radiation signal using a photomultiplier tube, but in the device according to the present invention, the fluorescence intensity in the scintillator plate is captured as an image by an ITV camera, and its The two-dimensional fluorescent light intensity distribution is stored as updatable for various calculation processes to be performed later.

Furthermore, in order to selectively change the fluorescence intensity depending on the position of the radiation source, a method is known in which a collimator is used to improve sensitivity only to radiation incident from a predetermined direction. However, when increasing the directionality of the collimator, it is necessary to scan the measurement system in each direction. A feature of the collimator according to the present invention is that it is possible to measure the direction of radiation and further the distance to the radiation source without significantly increasing its directivity. A cross-sectional example of this collimator is shown in FIG. 2, and as shown in FIG. The dimensional intensity distribution can be captured as an image by the ITV camera 4. The collimator 2 is provided so that the shield 6 is inclined by an angle θ at a distance r from the rotation center axis 7 thereof. That is, the shielding body 6 forms a plurality of collimator elements.

Here, the relationship between the distance @r and the angle θ is as follows.

θ=α・r ・・・・・・・・・(1)
In FIG. 2, assuming that the radiation source 1 is located with respect to the collimator 2 as shown, among the ff1fl paths of radiation emitted from N[t, the radiation from path 5 is on the extension line of that path. Since the inclination angle of the shield 6 coincides with the inclination angle σ of the path 5 with respect to the central axis 7, the scintillator plate 3 can be reached without being blocked much by the shield 6. On the other hand, the radiation from the path 5' with another inclination angle θ' is caused by the inclination angle of the shield 6 on the extension line of the path and the inclination angle of the path 5' with respect to the central axis 7. 6, the intensity is attenuated and reaches the scintillator plate 3. In this way, radiation is emitted isotropically from the radiation source 1, but the radiation from a specific path is incident on the scintillator plate 3 without being blocked even once, and fluorescence is generated at the incident position. It is something that becomes. Therefore, it can be seen that the intensity of fluorescent light is high in the portion of the scintillator plate 3 where a large amount of incident radiation is exposed. For example, if the fluorescence on the scintillator plate 3 is observed with the ITV camera 4 in the state shown in FIG.

The relative intensity of the fluorescent light has a distribution pattern 8 as shown in FIG. In the figure, the vertical axis r indicates the position on the scintillator plate 3 from the central axis 7, and the horizontal @ indicates the relative intensity of the fluorescent light when the maximum value of the fluorescent light is normalized to 1.0. This is the place where the inclination angle of the shielding body 6 and the inclination angle of the radiation path with respect to the central axis 7 match where the intensity of the fluorescent light is maximum. The angle θ6 indicating the three-dimensional direction of the radiation source 1 is obtained using the equation.

θ, ÷α・``1 ・・・・・・・・・(2)
Now, when observing fluorescence, use collimator 2 as the center @7
The reason for rotating is as follows.

That is, in the case of the arrangement as shown in FIG.
An example of the fluorescence intensity distribution of the scintillator plate 3 as seen from the fifth
The result is as shown in Figure (a). this is.

Figure i@4 shows the fluorescent light intensity distribution when the collimator 2 is stationary. As shown in the figure, the fluorescent light is distributed according to the shape of the collimator element, and it can be seen that the fluorescent light spots are dispersed for one radiation source 1. Therefore, if the fluorescence intensity distribution is observed while rotating the collimator 2 about the central axis 7 in FIG. 4, it will be as shown in FIG. 5(b). Unlike the previous case, collimator 2 rotates, so
Each X, Yf! By averaging the radiation transmission rate from a discontinuous distribution at an arbitrary location, a continuous fluorescence intensity distribution is obtained. Therefore, the intensity distribution of the fluorescent light is a circular distribution with the highest intensity at the center as shown in Figure 5(b), whereas the intensity distribution of the fluorescent light is dispersed as shown in Figure 5(a). That is, when observing the fluorescent light intensity distribution of the seven antitilator plates 3 while rotating the collimator 2, one
One circular fluorescence intensity distribution can be obtained for rp, and the spread of the fluorescence intensity distribution, such as the radius Ro, can be easily evaluated.

Next, the method for determining the distance from the radius R0 of the fluorescence intensity distribution to the radiation source l is as follows: Take the length along the central axis 7 of the shield 6 shown in FIG. where d is the radius of the fluorescence intensity distribution when the value of d/h is, for example, 0.3, and the distance t from the collimator 2 to the source.
The relationship with is shown in FIG. In the figure, solid lines 10,
11.12 is α in equation (2), and the slope rate of the shield 6 is O deg/m, O, l deg/m, respectively.
Radius R of fluorescence intensity distribution when 0.2deg/H
0 and the distance t to the radiation source. α＝
Odeg/m, that is, when the shield 6 is not tilted.

The solid line 10 is a straight line. At this time, if the radius of the collimator 2 and the scintillator plate 30 is, for example, Loom, the limit of &R@ is 100 m, so the distance yBt can only be measured within 340 m at most.

However, as can be seen from the solid lines 11.12.

If the slope rate α is increased, the collimator 2. It can be seen that even if the scintillator plate 3 has a constant size, the range of measurable distance t is expanded.

Now, let me explain the contents of the present invention in more detail.

FIG. 1 shows the configuration of an imaging section according to the present invention. In the imaging unit, a collimator 2 having a 13ft gear on the outer periphery is rotatably held on the front surface of the case 16, and a motor 15
The collimator 2 is rotationally driven by the rotation of a small gear 14 fixed to a rotating shaft.

Further, a scintillator plate 3 is fixedly arranged behind the collimator 2.

The ITV camera 4 is arranged so as to look over the entire surface of the scintillator plate 3. The case 16 houses the above-mentioned components therein, and also functions to shield radiation.

Note that if the radiation passing through the collimator 2 is strong,
An imaging section having a configuration as shown in FIG. 7 can be considered. In FIG. 7, a mirror 17 is installed behind the scintillator plate 3), so that the entire surface of the scintillator plate 3 is reflected by the mirror 17 and seen by the ITV camera 4.

With this configuration, the radiation that has passed through the collimator 2 and the scintillator plate 3 does not directly enter the ITV camera 4, and the ITV camera 4 is less likely to be damaged by the radiation.

Collimator 2 used in the imaging section shown in Figures 1 and 7
A more detailed structure is shown in FIG. In the figure.

A gear 13 is formed on the outer peripheral edge of the collimator 2, and a large number of transmission holes 18 are drilled on its surface. The angle 0 formed by each transmission hole 18 with the central axis 7 has a directly proportional relationship to the distance r from the central axis 7 of the transmission hole 18 as shown in equation (1).

FIG. 9 shows another structure of the collimator 2 having the same effect as that shown in FIG. The one shown in FIG. 9 has a structure in which a shielding rod 19 is pasted on the disk surface. The angle θ of each shielding rod 19 with the central axis 7 has a proportional relationship with the distance r of the shielding rod 19 from the central axis 7 as shown in equation (1). In such a structure, each shielding rod 19
This means that radiation passes through the gap unshielded.

Note that the transmission hole 18 in FIG. 8 and the shielding rod 19 in FIG. 89 are both shown in a conical shape.

Of course, a cylindrical shape or a regular polygonal prism can have the same function.

Next, to explain the signal processing system, Fig. 10 shows the first
7 shows a signal processing system including the imaging section 20 shown in FIG. According to this, the terminal 21 of the imaging section 20 is an output terminal of the ITV camera 4, and is configured so that the fluorescent light intensity distribution on the scintillator plate 3 is outputted as a VTR signal. conversion! 30 converts the VTFL signal into digital information, that is, a coordinate value t representing the sweep time and an intensity value P representing the brightness at that time, and outputs the converted information to the arithmetic unit 31. On the other hand, the motor control device 13
5 rotates the collimator 2 by supplying a drive pulse to the motor 15 through the terminal 22. Start signal 5 at the start of supply of the drive pulse
After outputting TART to the arithmetic unit 31, drive pulses are output at a constant cycle, but after a predetermined number of drive pulses required for one rotation of the collimator 2 are output, the end signal END is output to the arithmetic unit 31. and then outputs the start signal 5TART again after a predetermined time elapses.
The same output procedure is repeated.

Now, in the arithmetic unit 31, when the start toy No. 8 is input from the motor 'filj [35], frame memo 1J is input.
32, and the intensity value P from the converter 30;
and coordinate value t. Strength value P
and the degree K when the coordinate value t is manually input.

These values are first processed to be converted into the values P+ and i shown in equations (3) and (4).

i=βt ・・・・・・・・・(3
) Pi=P/+P ・・・・・・・・・
- (4) However, β is an address conversion constant, and P1' is the written content at address i. Scanning start point on both sides of the frame (
The elapsed time t from the time origin (every 7 frames) directly represents the X and Y coordinate position on the frame V-frame screen, and this also represents the coordinate value in the rask scan, so it can be used in an nxn size frame memory. The address for that is equation (3)
This is what is required.

Now, the value i obtained as a result of the processing shown in equations (3) and (4)
.

According to P+, the value P+ is stored as updatable at address i of the frame memory 32, as shown in Equation 1 (3).

The processing according to (4) is performed so that the fluorescent light intensity distribution on the frame memory 32 is as shown in Figure 5 (b), and is performed for as many frames as possible during one rotation of the collimator 2. There is. This allows frame memory 3
From the cumulatively added fluorescence intensity distribution data on 2, the center and spread of the distribution can be determined as follows.

That is, when a termination signal is manually input from the motor control device 1i35, the arithmetic device 31 selects the forging size value P1. from the values P+ stored in the frame memory 32. ! address value i with
, but this process is based on equation (5). P@
, the initial value of Pn is 0, and by performing the process according to equation (5) every time the address i is updated in the range of O%n''-1, the maximum value Pn@R*1 Therefore, the address value 10 is It is what is required.

Once the address i is determined as described above, the angle θ indicating the direction of the radiation source is then determined using equation (6).

(6) However, [ ] is a Gauss symbol, C is a constant, and α is the inclination rate of the collimator 2.

Incidentally, if we explain equation (6) here, address i
, is located on the frame memory 32 as [t*/
') yo), and the line number is i, -(j, /n)
・It is more known than n. Frame memory 32
If you set the upper xt Y-axis origin (upper left corner) t - the center of the array, the address i, the corresponding x, y @ mark (x*,
ye ) is coordinate transformed as follows.

x @-C(i,-(i,/n)-n-n/2) ・”
(7)y,=c((i,/n)-n/2)...
......(8) Therefore, the distance between the newly set origin and the address i, the corresponding x, (6) is required.

The direction of the radiation source can be determined three-dimensionally from equations (7) and (8) as described above, but the distance to the primary radiation source can be determined by determining the radius ratio described above. , to find this radius rL1, first the frame memory 3
The average value P a t of the recorded contents in step 2 is calculated according to the following formula.

+12-1 P, 3 Σ p 1 / n ” ” =
(9) After the average value Pat is determined in this manner, the radius ratio of 4 is determined according to the flow shown in FIG. , Xag y in the processing in Figure 1
The value of a is shown in equations (7) and (8), and sXl
+YI is obtained by replacing i in formulas (7) and (8) with i.

On the frame memory 32, the positions atX* are RP, .

There are positions where Pl is close to CP, , ] with y, ) as the center, and if these positions are connected, they form a circle. However, the value of the circumference is not necessarily CP,, ). This is because P includes statistical variation. Therefore.

By extracting positions that are close to P, 8 and whose value is CP, , ), and then finding the root mean square distance between each of these positions and the position of P, 8.

The radius R0 is determined. , is determined in this way because the distance between the position of h P 86M and each of these positions is exactly 1%, and is not incremented.

If the radius R1 is found as described above.

Next, based on this, the distance t to the radiation source is determined from the relationship shown in FIG. The obtained angle θ and radius R are displayed on the display 36 as the source direction and distance, while the address i in the frame memory 33 is
By recording numbers only on display 3
4, the position of the radiation source is displayed as a bright spot.

This allows the radiation intensity distribution in a wide three-dimensional space to be known compared to the size of the aperture of the scintillator plate.

Although the fluorescence intensity distribution of the scintillator plate 3 is detected by the ITV camera 4 in the imaging section 20, it is of course possible to detect it by a two-dimensionally arranged photodiode or the like.

〔Effect of the invention〕

As explained above, in the case of the present invention, radiation from a wide range of three-dimensional space can be measured by radiation monitoring of the l system, and the direction of the radiation source and the distance from the position on the line at can be measured while the system is installed at that position. Are you stupid enough to measure S at the same time?
This has the effect of being able to measure the three-dimensional spatial distribution of the quantity rate.

[Brief explanation of drawings]

1 and 7 are diagrams showing the configuration of an imaging section related to the main part of the present invention, FIG. 2 is a diagram showing a cross section of a collimator as an example of a component of the present invention, and FIG. FIG. 4 is a diagram showing the fluorescent light intensity distribution on the scintillator plate, FIG. 4 is a diagram showing a perspective appearance of the one shown in FIG. 2, and FIG.
A diagram showing the fluorescence intensity distribution on the scintillator plate during rotation, Figure @6 is a diagram showing the relationship between the spread of the fluorescence intensity distribution and the distance to the source. FIG. 8 and FIG. 9 are diagrams showing a collimator with a more detailed structure according to the present invention in a partially broken and perspective view, respectively.
FIG. 10 is a diagram showing a signal processing system in an example of the apparatus according to the present invention, and FIG. 11 is a diagram showing the flow of processing for determining the spread of the fluorescence intensity distribution. 2...Collimator, 3...Scintillator [,4...
・ITV camera, 1.5... Motor (for collimator rotation drive), 20... Imaging section, 30... Converter, 31
...Arithmetic unit, 32...Frame memory, 34...
・Display, 35...Motor control device, 36...
·display.

Claims (1)

[Claims] 1. A collimator having a rotatable disk-like overall shape and comprising a plurality of collimator elements tilted according to the distance in the radial direction from the center of rotation; radiation detection means for detecting radiation two-dimensionally; collimator rotation drive means for rotationally driving the collimator; and radiation detection means that detects radiation two-dimensionally;
Based on the dimensional radiation detection signal, a two-dimensional distribution of radiation intensity on the radiation detection means is determined, and from this distribution, the position where the radiation intensity is maximum and the size of the spread of the intensity distribution around this position are determined. It is characterized by a configuration consisting of a processing means for detecting the radiation, and a display means for displaying the extent of the spread of the intensity distribution centered at the position as the distance to the radiation source, with the position where the radiation intensity is maximum as the direction of the radiation source. radiation source position measurement device.