JP4164577B2 - High energy source direction discrimination system - Google Patents

Description

The present invention relates to a technique for detecting an incoming direction of high energy radiation.

There is one that detects the incident direction of radiation by calculating the mutual positional relationship of the signal output of radiation incidence by superimposing two or more two-dimensional sensors (see Patent Document 1). However, this can be calculated because a single radiation outputs a signal at a position corresponding to a specific pixel in each layer. As the number of incident radiations increases, it becomes difficult to distinguish. When a large number of radiations fly from a certain direction within a certain period of time. The integral values of each pixel in each layer are averaged, and the direction cannot be determined.
Japanese Examined Patent Publication No. 6-105303

  In the present invention, the shadow of the collimator is formed according to the radiation direction of radiation, and the direction of flight can be determined by calculating the distribution relationship of the output signal based on the positional relationship that the shadow can make. In the past, collimators were designed to allow the incidence of radiation in only one direction as much as possible, and were designed to avoid incidence at tilt angles. The present invention is based on a new idea of specifying the radiation direction of radiation using the shadow of a collimator with respect to incidence at an inclination angle.

An example in which two one-dimensional sensors A and B are spatially separated will be described. The collimator is placed so as to sandwich the sensor at a distance D1 that is a half of the length M of the sensitivity surface of the sensor. The material of the collimator shall have a shielding function against high energy rays (such as lead), and the collimator aperture shall be the same as the sensitivity surface of the sensor. Further, D1 = D2.
As shown in FIG. 1, sensor A (1) and sensor B (2) are placed at a distance of D2. Further, the collimator S (3) is placed on the upper surface of the sensor A (1) with a distance D1 and the collimator T (4) is placed on the lower surface of the sensor B (2) with a distance D1. The photosensitive surface of the sensor and the aperture of the collimator have the same dimensions. The dimensions here are examples, and can be arbitrarily set while paying attention to the light receiving angle.
2 shows the signal distribution of the sensor A (1) and the sensor B (2) when radiation is incident from the direction E1 in FIG. 1, ie, the vertical direction of the sensor. The second stage of FIG. 2 shows the signal distribution when radiation is incident from the direction E2 in FIG. 1, the third stage of FIG. 2 is E3 in FIG. 1, and the lowermost stage in FIG. 2 is E4 in FIG. The signal distribution of each sensor A (1) and sensor B (2) when radiation enters from each direction is shown.

When the radiation source is in the far direction of E1 and is incident with the vector E1, that is, when coming from the vertical (θ1 = 0) direction, the outputs of the sensors A and B are obtained from the entire sensor. That is, there is no lack of signal. When the radiation source is in the far direction of E2 and radiation comes from the vector of E2, collimator shadows are produced on sensors A and B. In this case, the direction of the radiation source can be obtained from the following simple relationship. However, the length of the sensitivity surface of the sensor A is M, and the length of the missing signal is m.
When the incident angle of radiation to the sensor is θ1 from the vertical line, D1 · Tanθ1 = m (1)
Therefore, Tan θ1 = m / D1 = 2 m / M (2)

At this time, assuming that the sensor B is arranged substantially in parallel with a distance of the sensors A and D2, and the incident angle of the radiation to the sensor is θ2 from the vertical line
(D1 + D2) Tanθ2 = n (3)
Therefore, Tanθ2 = n / (D1 + D2) = n / N (4)
However, the length of the sensitivity surface of the B sensor is N (= M), and the length where the signal is missing is n. The thickness of the sensor and collimator was negligible.
In this example, it is assumed that the radiation source comes from the upper direction. However, if it comes from the lower direction, m and n are compared to determine that the radiation source comes from the smaller side. Alternatively, it is assumed that M−m and N−n are compared and arrive from the larger one. Even in the vertical case, the signal amount can be easily determined because the signal amount of the sensor on the radiation arrival side is large.
If both sensor A and sensor B can detect radiation,
D2 · Tanθ3 = | n | − | m | (5)
However, when | n |> | m |, −45 ° ≦ θ3 ≦ 45 °
When | n | <| m |, 135 ° ≦ θ3 ≦ 225 °
Can also be obtained. If the sensor A and the sensor B are not the same sensor but have different frequency-sensitivity characteristics, a wide band can be obtained.
Further, if the third and fourth sensors and the collimator are provided by changing the angle, the direction in the vertical direction can be determined regardless of the difference in the signal amount.

  FIG. 3 shows how the shadow of the collimator is formed when two two-dimensional sensors A and B are arranged apart from each other. FIG. 3 shows a case where the sensor A (1) and the sensor B (2) are two-dimensional sensors. In this case, the one-dimensional case is expanded to two dimensions, and the concept is the same. Since the horizontal cross section is the same as FIG. 1, it is omitted. Fig.3 (a) is the figure seen from the upper side with the sensor A (1). There is a collimator S (3) in front, and the sensor A (1) is visible from the opening. Sensor B (2) is hidden behind sensor A (1) and cannot be seen. Similarly, the collimator T (4) cannot be seen behind the collimator S (3). The periphery of the collimator S (3) is omitted. This is an example in which the radiation from the outside is incident with the directionality of E5.

FIGS. 3B and 3C show the signal detection areas of the sensor A (1) and the sensor B (2), but the hatched portion shows an area without a signal due to the shadow of the collimator. . In the sensor A (1), an area where no radiation can be detected is classified into an area (5) where there is no signal and an area (6) where there is a signal where radiation can be detected. Similarly, in the sensor B (2), an area where no radiation can be detected is classified into an area (7) where there is no signal and an area (8) where there is a signal where radiation can be detected.
In this case as well, as in the case of the one-dimensional case, the angle of the arrival direction is obtained for each of the vertical and horizontal directions, so the angle on the two-dimensional surface is obtained.

By arranging a plurality of ones that can detect the one-dimensional or two-dimensional directions, the directions of the radiation sources in all directions can be specified. The system can be tailored to the purpose by adjusting the length of the one-dimensional sensor as needed, or modifying the symmetry of the two-dimensional length.
Further, as an example of modification, it is conceivable that the sensor is arranged in a spherical shape so that radiation can be detected from all directions. In this case, a two-dimensional sensor is used as the sensor and is arranged in a substantially spherical shape. A sphere is formed of a material having a radiation shielding effect as an outer shell of the sensor assembly. A hole serving as a collimator is formed at a position corresponding to substantially the center of each two-dimensional sensor, and the shadow of the incoming radiation is projected onto each two-dimensional sensor. Here, it is assumed that the two-dimensional sensor is discretely arranged, and a hole is made at a position corresponding to the approximate center of each two-dimensional sensor. However, in the case where the two-dimensional sensor is continuously arranged in a spherical shape, Is to make a hole in any location of the outer shell. Preferably, holes are made at several points equally divided on the spherical surface. In addition, although the two-dimensional sensor is arranged in a substantially spherical shape, it should be considered to be a polyhedral solid from the viewpoint of manufacturing. For example, if the structure is a regular dodecahedron with twelve two-dimensional sensors fixed to each surface and twelve holes in the outer shell, it will be easy to manufacture. Further, it is arbitrary whether the outer shell is a sphere or a polyhedral solid.
As another modification, it is conceivable to arrange a unit formed by integrating a two-dimensional sensor and a collimator unit made of a material having a radiation shielding effect in a substantially spherical shape.

According to the present invention, a large number of incoming radiation is measured as an integrated intensity distribution, and the amount of radiation incident and the direction of arrival can be obtained at an appropriate time interval and arbitrarily within that time, so the calculation method is also simple. Also, the circuit configuration can be greatly simplified.
In the monitoring of nuclear facilities and monitoring of nuclear waste, it will function extremely effectively in identifying the source direction.

Side view of sensor and collimator arrangement Diagram showing sensor output for each radiation source Front view showing arrangement and collimator shadow in 2D sensor

Explanation of symbols

1 Sensor A
2 Sensor B
3 Collimator S
4 Collimator T
5,7 Area without signal 6,8 Area with signal

Claims (3)

A one-dimensional or two-dimensional sensor that detects a high-energy ray and outputs a signal is placed in the space, and a collimator that has a shielding function for the high-energy ray and has an opening is placed at a certain distance from the sensor. The front surface of the sensor and the opening are arranged parallel to the sensor so that the size of the collimator opening and the sensitivity surface of the sensor are the same, and the direction of arrival of the high energy beam The shadow distribution formed on the sensitivity surface of the sensor is acquired based on the output signal distribution of the sensitivity surface and the direction of the high energy radiation source is estimated based on the acquired shadow distribution. A high energy source direction discriminating system . The sensor is a parallel arrangement of two or more one-dimensional sensors that are spatially separated, and the distribution of shadows formed on the sensitivity surface of the plurality of sensors depending on the direction of arrival of the high energy rays. The direction of the high energy radiation source according to claim 1, wherein the direction of the high energy radiation source is obtained based on the distribution of output signals of the plurality of sensitivity surfaces, and the direction of the high energy radiation source is estimated based on the obtained distribution of shadows. Discriminating system . The two or more two-dimensional sensors are spatially separated in parallel and the shadow distribution formed on the sensitivity surface of the plurality of sensors depends on the direction of arrival of the high energy rays. The direction of the high energy radiation source according to claim 1, wherein the direction of the high energy radiation source is obtained based on the distribution of output signals of the plurality of sensitivity surfaces, and the direction of the high energy radiation source is estimated based on the obtained distribution of shadows. Discriminating system.

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