JPH01219693A - Radiation detector - Google Patents

Abstract

PURPOSE:To reduce a cross talk to an adjacent sensor by a construction wherein a semiconductor radiation sensor is covered with a radiation shield having an opening so that an incident radiation may be incident on and absorbed by the central part of a sensitive part of the semiconductor radiation sensor. CONSTITUTION:A radiation detector is provided with a shield 4 having an opening 4a for the incidence of an X-ray 1, above a split-type electrode of an electrode 3 provided on the opposite sides of a radiation sensor array 2, i.e. an electrode on the side in the direction of the incidence of the X-ray. The widths l1 and l2 of the opening 4a of this shield 4 are set to be smaller than the corresponding widths n1 and n2 of the radiation-sensitive part of a semiconductor radiation sensor, respectively. Therefore part of the incident X-ray is cut and it falls only on an X-ray-sensitive incidence area 5, which is a hatched part. This constitution makes it possible to reduce an escape peak of a characteristic X-ray due to a material of the radiation, to reduce a cross talk and to improve the precision in measurement.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention consists of a micro radiation sensor capable of spectral analysis of radiation energy, a minimum radiation sensor array used in a diagnostic X-ray transmission imaging device, and a non-destructive inspection device. It relates to radiation detectors.

Prior Art First, the principle of absorption of radiation by the photoelectric effect will be shown using FIG.

When the incident radiation 71 enters the atom 72, it is mainly absorbed by the shell electrons 73 among the extra-shell orbital electrons, and the K-shell electrons are emitted outside the shell as excited electrons 74.

The excited electrons 74 generate electron-hole pairs in the semiconductor, and the number of photons of radiation can be detected by pulse-measuring the current or voltage generated by the electron-hole pairs. This state where there are no outer shell electrons can be achieved by the electrons in the outer shell entering the shell orbit. When this outer shell electron transits to the crab shell, the energy of the orbital energy difference is emitted as membrane characteristic X-rays 76. In addition, when the film characteristic X-ray 7e is also absorbed by atoms, electrons are emitted in the same way,
Electron-hole pairs are generated and can be measured as pulses of current or voltage.

FIG. 8 shows this phenomenon as a phenomenon within a semiconductor radiation sensor. The semiconductor radiation sensor shown in FIG. 8 is a fully depleted layer type sensor. Semiconductor radiation sensor 76
When radiation is absorbed in the film, the excited electrons 74 and the film properties
The excited electrons 74 that generate the rays 76 lose energy and generate electron-hole pairs in the semiconductor crystal, but when the K-shell characteristic X-rays 76 are generated near the crystal surface, they may be emitted outside the crystal. This phenomenon of the radiation exiting the crystal is called shell characteristic X-ray escape 77, and when this phenomenon occurs, the amount of charge output from the detector decreases, and the peak value of the optical coupler decreases. FIG. 9 shows this phenomenon using output pulse peak values.

In FIG. 8, reference numeral 8 indicates an electrode of the radiation semiconductor sensor. FIG. 9a shows the relationship between the energy of monoenergetic incident radiation and the number of photons. When such radiation with a single energy E is incident, the actual measurement of the output pulse height distribution from the semiconductor radiation sensor results in the 9th
It will look like the diagram. That is, it is divided into two groups of pulses: a pulse with a wave height corresponding to the incident energy E and a pulse with a wave height corresponding to the energy E-Ei (E: binding energy of shell electrons).

Problems to be Solved by the Invention As mentioned above, for a single incident radiation energy, the output pulse height is divided into a group of pulses with a size corresponding to the incident radiation energy and the incident radiation generated by the K film characteristic X-ray escape. There is a problem that the radiation energy is divided into two energy groups, a pulse group having a size corresponding to a low energy, and a large measurement error occurs when measuring a plurality of mixed radiation energy groups. In addition, in the sensor array, K film characteristic X-rays
If the signal is incident on and absorbed by an adjacent sensor, there will be a problem of crosstalk of the signal to the adjacent sensor.

In order to solve the above problem, it is necessary to reduce the escape 77 of the membrane characteristic X-rays to the outside of the semiconductor radiation sensor 76 of the membrane characteristic X-rays generated by the photoelectric effect, and to
It is sufficient that all the incident energy is absorbed within.

Based on the above-mentioned viewpoint, the present invention aims to provide a radiation detector that does not cause measurement errors due to X-ray escape.

Means for Solving the Problems In order to achieve the above object, the radiation detector of the present invention covers a semiconductor radiation sensor with a radiation shielding member having an opening, so that incident radiation is directed to the central part of the sensitive part of the semiconductor radiation sensor. It is designed so that the X-rays incident on the semiconductor radiation sensor are absorbed in the central part, and the resulting film characteristic X-rays are reabsorbed before they reach the vicinity of the surface of the semiconductor radiation sensor or before they are incident on adjacent sensors. .

Effect With the above configuration, by reabsorbing most of the X-rays generated within the semiconductor radiation sensor, the output pulse height distribution becomes a distribution corresponding to the incident energy, and the signal component due to characteristic X-ray escape is suppressed. This makes it possible to reduce crosstalk to adjacent sensors.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing the structure of an embodiment of the radiation detector of the present invention. In response to the incidence of X-rays 1 from the direction of arrow a, electrodes '3 provided on both sides of the radiation sensor array 2
Above the split electrode, that is, the electrode on the side of the X-ray incident direction,
A shield 4 is provided having an opening 4a for X-rays.

The widths 11 and 12 of the opening 4a of the shield 4 are set smaller than the corresponding widths n1 and n2 of the radiation sensitive portion of the semiconductor radiation sensor. Therefore, a part of the incident X-rays are cut off and are incident only on the X-ray sensitive incident area 6, which is the shaded area in FIG. That is, the incidence of X-rays on the peripheral edge portion of the sensor and the boundary portion with an adjacent sensor is blocked. A sectional view of the radiation detector shown in FIG. 1 is shown in FIG. Incident X-rays 1 are blocked by a shielding body 4,
The light is incident on an X-ray sensitive volume 6a indicated by diagonal lines. When X-rays are absorbed within the X-ray sensitive volume 5a, K film characteristic X-rays 6 are generated, and some of them exit outside the X-ray sensitive volume 6a, which is the shaded area. The part shielded by the shielding body 4 is also a part sensitive to radiation, but since the shielding width d is provided for each sensor, the film characteristic X of the radiation generated in the sensor 7 is
The line 6 does not reach the neighboring sensor 7a, most of it is absorbed again in the sensor 7, and the height of the pulse output from the electrode of the sensor 7 is that of the pulse output without the K-film characteristic X-ray escape.

The larger the shielding width d is, the better the escape can be prevented; however, in the case of a sensor array, the size of each sensor is determined based on the required spatial resolution, etc. This results in a decrease in sensitivity. Therefore, the half-value layer width for the shell characteristic X-ray photon energy can be used as a guideline.

FIG. 3 shows an example of measuring characteristics when a shield is attached to the sensor and when the shield is not attached. FIG. 3A shows the pulse height distribution with a shield, and FIG. 3B shows the pulse height distribution with no shield. As is clear from these distributions A and B, the number of pulses decreased due to the presence of the shielding body, but the second peak with a lower pulse height, that is, the shell characteristic X-ray escape peak, It can be seen that it has decreased. Note that the presence of a peak in distribution A is due to membrane characteristic X-rays emitted from the electrode direction. In addition, the valley width m1゜m2 of the polarized electrode 3 of the semiconductor sensor array 2 on the X-ray incident side in FIGS. In order to absorb effectively, the larger the electrode is, the better, as long as it does not cause interference between the electrodes. Therefore, it is preferable that the valley width m19m2 of the electrode 3 is greater than or equal to the corresponding widths 11 and 12 of the opening 4a of the shield 4.

By the way, so far we have explained the quadrilateral shape of the opening 4a of the shielding body 4 shown in FIG. The same can be said. Also, the opening 4
It is clear that a may not be hollow or may be filled with radiolucent material.

FIG. 6 shows another embodiment of the invention. Figure 1.

In the example shown in Fig. 2, a method was described in which a shield is provided to reduce the escape of characteristic X-rays in a semiconductor radiation sensor, to make the output pulse height distribution correspond to the incident energy, and to reduce crosstalk to adjacent sensors. . However, when high spatial resolution is required, the shape of each semiconductor sensor becomes minute, and sufficient shielding @d of the shielding body 4 cannot be achieved, and even if a sufficient shielding width d is provided, the needle barrel 3 As mentioned above, this leads to deterioration of sensitivity, which is a fatal drawback in micro-shaped sensors. FIG. 6 shows a configuration suitable for a semiconductor sensor array consisting of a plurality of semiconductor sensors that requires such high spatial resolution. Radiation enters the radiation sensor array 2 from the top to the bottom of the drawing. The radiation sensor array 2 is provided with electrodes on both upper and lower surfaces as in FIGS. 1 and 2, and has a split electrode 3 on the radiation incident side. A shielding body 4 having an opening 4a is provided above the radiation sensor array 2 (on the radiation incident direction side). Valley width 1 of opening 4a of shielding body 4
1 and 12 are set smaller than the corresponding valley width n1;n2 of the radiation sensitive portion of each sensor of the radiation sensor array 2. Further, the valley widths of the split electrodes 3 are greater than or equal to the widths of the openings 4a of the corresponding shields 4 and less than the widths of the radiation sensitive portions of the respective sensors.

In FIG. 6, each sensor of the radiation sensor array 2 is
Unlike the figure, they are arranged alternately in two rows in a staggered manner. Therefore, unlike the case where they are arranged in one row, one adjacent sensor can be used as the shielding part 2d, and the size of the opening 4a of the shielding body 4 can be set to the size of the sensor when there is no shielding body. Can be done. FIG. 6 shows the output characteristics of the sensor with this configuration.

FIG. 6B shows the pulse height distribution without a shield similar to FIG. 3B, and C shows the pulse height distribution of the sensor with this configuration. In the sensor output of this configuration, the number of pulses matches that of the case without the shield, and the peak C1 with low pulse height, that is, the shell characteristic X-ray escape peak, has also decreased to the same extent as the characteristic peak in Figure 3A. I understand that. The presence of peak C is the first
This is due to shell characteristic X-rays emitted from the direction of the electrodes, similar to the configurations shown in FIGS. In Figure 6, the sensor is 2
Although the method of arranging in columns has been described, it is also possible to arrange in two or more columns.

Although a radiation sensor array has been described above, it is clear that the present invention can be applied to a single radiation sensor. In addition, in the above explanation, the characteristic X-rays were discussed only for the crab shell, but the characteristic x4 produced by the photoelectric effect with good outer shells such as L and M has low energy, and the probability of characteristic X-ray escape is small and does not pose a problem. Therefore, I omitted it.

Note that cadmium telluride (CdTe) and silicon (Si) are used as semiconductor materials for semiconductor radiation sensors.

Ge7y manium (Go), gallium arsenide (GaAs)
.

Either mercury iodide (H9I) can be used. Also tungsten and lead as shielding materials.

It is effective to use materials with high atomic numbers such as gold and platinum.

In the above explanation, the output characteristics of the sensor were explained as the number of pulses having a pulse height value corresponding to the energy of the incident radiation. , it can also be applied to a detection method that obtains an output corresponding to the incident energy.

Effects of the Invention According to the present invention, most of the characteristic It is possible to reduce the escape peak of characteristic X-rays and improve the energy resolution of the radiation sensor. Furthermore, crosstalk between adjacent sensors in the radiation sensor array can be reduced and measurement accuracy can be improved.

In addition, by arranging the sensors of the radiation sensor array in multiple rows, it has high spatial resolution and high sensitivity.
It becomes possible to realize a radiation sensor array with less escape.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a semiconductor radiation detector according to an embodiment of the present invention, FIG. 2 is a cross-sectional view thereof, FIG. 3 is a characteristic diagram showing changes in pulse height depending on the presence or absence of a shield, and FIG. 5 is a plan view of a semiconductor sensor array according to another embodiment of the present invention; FIG. 6 is a pulse height characteristic diagram of the sensor having the configuration shown in FIG. 5; and FIG. 7 is a crab shell. FIG. 8 is a schematic diagram showing the principle of photoelectric absorption, FIG. 8 is a sectional view showing the principle of a semiconductor radiation sensor, and FIG. 9 is a characteristic diagram showing the output pulse height distribution of the radiation sensor with respect to incidence of a single energy. 2... Radiation sensor array, 4... Shielding body, 4a... Opening, 6... X-ray sensitive incident area. Name of agent: Patent attorney Toshio Nakao and 1 other person1-
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Claims (2)

[Claims] (1) Comprising a semiconductor radiation sensor that responds to radiation photons, an electrode disposed on the radiation incident side of the semiconductor radiation sensor, and a radiation shield having an opening disposed on the radiation incident side of the electrode. , the opening area of the opening in the radiation shield is smaller than the area of the opposing radiation-sensitive portion of the semiconductor radiation sensor, and the area of the electrode facing the opening is smaller than the opening area of the opening. A radiation detector characterized by: (2) A semiconductor sensor array formed by arranging a plurality of semiconductor radiation sensor sections in a staggered manner, an electrode disposed on the radiation incident side for each of the sensor sections, and an opening corresponding to each of the sensor sections. A radiation shielding plate provided with a radiation shielding plate, wherein the opening area of the opening of the radiation shielding body is made smaller than the area of the radiation-sensitive portion of the opposing sensor unit.