JPS59100885A - Array for detecting element of radiant rays - Google Patents

Abstract

PURPOSE:To shorten the traveling time of an electron and to obtain a high speed pulse with narrow pulse width by forming the crystal of a semiconductor detector thinly and arranging electrodes on the opposed surfaces inserting the thin crystals between them to shorten the traveling distance of the electron and positive holes to the electrodes. CONSTITUTION:Radiant rays detecting elements 1 consisting of semiconductors are linearly arranged on a substrate 2, and upper electrodes 3 are formed on the opposed crystal surfaces of the elements to form an array and to count up incident and absorbed radiant ray photons as the electric pulse. The number 4 is a lower common electrode. Denoting that the effective atomic No. of an element material to photoelectric absorption is >=30 and the thickness of the crystal, i.e. the interval of the electrodes, is <=0.5mm.. If the array is moved along a subject, two-dimensional radiant ray picture signals can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a radiation detection element array that can be used in an X-ray diagnostic device, an X-ray inspection device for nondestructive testing, and the like.

Conventional structure and its problems Traditionally, X-ray photographs have been used for many X-ray inspections, but
Sensitivity was not sufficient, so there was a need to reduce the exposure dose during medical examinations, and contrast agents were still used to add contrast due to lack of contrast resolution.

In recent years, computerized tomography equipment has been developed, which not only allows for tomography, but also has good contrast resolution and can identify substances with slightly different radiation absorption coefficients, such as muscle and fat, as well as large-sized cancers. It is now possible to identify them without a contrast agent.

The reason for this is that the accuracy of radiation-sensitive sensors has improved, but it is still insufficient and it has not been possible to identify even small cancers. Furthermore, the exposure dose could not be said to be low, and there was a need to further reduce it.

OBJECTS OF THE INVENTION An object of the present invention is to provide a new radiation detection element array that has good radiation sensitivity, low exposure dose, and good contrast resolution.

Structure of the Invention The present invention comprises linearly arranging radiation detection elements made of semiconductors on a substrate, providing electrodes on opposing crystal planes of the elements to form an array, and counting incident and absorbed radiation photons as electrical pulses. The effective electron number for photoelectric absorption of the element material is 30 or more, and the crystal thickness, that is, the electrode opening is set to be less than o, s. A two-dimensional radiographic image signal can be obtained by moving the array over the subject.

Description of Examples In the method of obtaining an image by counting pulses, the higher the number of pulses for one pixel, the better the contrast resolution can be obtained.
Ru. For this purpose, it is necessary to narrow the detection pulse width and count many pulses within a certain period of time. For this reason, the crystal thickness is reduced to shorten the hole transit time. Since the pulse width is proportional to the square of the thickness, there is a practical pulse width limit at about 0.5 mm, and if the thickness is less than this, a product quality image of 105 to 106 counts/pixel can be obtained. It will be done.

On the other hand, if the crystal is thin, the absorption rate of X-rays will be poor. If a material with an effective atomic number of 30 or more regarding photoelectric absorption is used, 0
・Absorption rate of 30% or more can be obtained with 6 having a thickness of about the size of a scrap.

We have found a radiation-sensitive element that is designed to meet these conditions and has high sensitivity and good contrast resolution.

The radiation detection element array of the present invention will be described by way of examples. FIGS. 1a and 1b are configuration diagrams of a radiation detection element array according to an embodiment of the present invention, where a is a plan view and FIG. 1b is a front view. In the figure, 1 is a semiconductor detection element crystal, 2 is its substrate, 3 is an upper electrode of the element, and 4 is a lower common electrode. By measuring the radiation dose while driving this element array along the subject, a two-dimensional image signal can be read.

That is, the radiation incident on the semiconductor detector element crystal 1 is
When a photoelectric effect or Compton effect reaction occurs within a semiconductor material, secondary electrons are generated. This secondary electron moves within the semiconductor and generates electron-hole pairs around its path. The number of electron-hole pairs is proportional to the initial energy of the second order-one child.

FIG. 2 shows a diagram for explaining the principle. In the figure, 6
is a semiconductor detector element crystal, 6 is an electrode, and 7 is another electrode. When a strong electric field is applied to the semiconductor sensing layer, electrons and holes move at high speed toward their respective electrodes, generating charge pulses. The time during which secondary electrons and electron-hole pairs are generated by radiation is very short, and is 10-
It takes about 12 seconds. However, because it takes a long time for electrons and holes, especially holes, to move within a semiconductor, it has conventionally been difficult to obtain a high-speed pulse output with a narrow pulse width. When obtaining an X-ray transmission image of a human body, etc., move the play along the human body for a short time of at least 10 Sec, and
It is necessary to read array measurement values at positions of 0 or more points, and for this purpose, the time required for one measurement with one element is short, at least 1001960.

However, when the pulse width is wide, the number of pulses that can be counted within this time decreases, the dynamic range of the pixel decreases, and the accuracy of counting decreases. Therefore, in order to improve counting accuracy, etc., it is necessary to obtain high-speed pulses with as narrow a pulse width as possible. conventionally,
There is no solution in this respect, and the pulse measurement method is not used, only the current measurement method (References: Y, Nar,
useat al,, IERE Trans,
N5-27(1), p, 2.52°1000 years). When using the current method, the radiation sensitivity decreases by more than two orders of magnitude compared to the pulse method.

One of the key points of the present invention is that, in order to measure high-speed pulses, a semiconductor detector crystal is formed thinly, as shown in FIG. 1, and electrodes are provided on opposing surfaces with the thin crystal in between. , by shortening the traveling distance of electrons and holes to the electrode,
The goal is to shorten the travel time and obtain high-speed pulses with a narrow pulse width. This point will be explained in detail with reference to FIG. Electron-hole pairs generated in the semiconductor by radiation quanta follow the electric field applied to the semiconductor,
Electrons move to the anode and holes move to the cathode. This causes a pulsed current to flow externally. It is known that the time width t of this pulse signal is expressed by the first equation.

t-d2/μ, Va (a) where t: pulse duration d: thickness of semiconductor detection layer μ: mobility of electrons or holes va: application to semiconductor detection layer According to the voltage equation, the pulse duration is proportional to the square of the thickness of the semiconductor layer. . This results in a pulse width of .

Let's look at this with a real example: CdTa (effective atomic number ZX=49) and GILAS (ZR=s 1). The hole mobility of CaTe is μh=8”/
V, sec.

Further, for GaAs, μ11=400. voltage to 10
Assuming that 0V is applied, the pulse width is plotted against the thickness as shown in Figure 3. One thickness of CdTe is approximately 1p.
Sf90. GaAs is O-25p S el C+
For O-6NN thickness, CaTe is 0.3 ps6a,
GaAs becomes 0-06pSeQ. 1 Tomo Atsushi and O,S
The sheath thickness causes a several-fold difference in pulse width. In this way, 0.
At a depth of 5 or less, the pulse width is less than 0.2 μsec, and the time resolution of the pulse approaches the limit that can be processed by modern practical circuit technology. Now, if the pulse integration time for one pixel is 10o m5ec, the pulse width is 0.1μS.
The number of eC pulses is 100 m5ec ÷ 0.1 μs6
0 = nearly 106 pieces can be obtained. In the case of a radiation pulse, the error due to statistical fluctuations is 1r;7;103, and the measurement error at that pixel is 0.1%. It is said that the difference in the X-ray absorption coefficients of biological soft tissue constituents such as muscle, fat, and water is less than a few lines, and it is said that a pixel measurement accuracy of 0.1% is required to detect this difference. .

Therefore, it can be said that the error factor due to the statistical fluctuation of the incident xk described above is at a level that maintains this accuracy.

However, if the semiconductor layer is made thinner, the absorption rate of radiation decreases, causing the opposite problem of worsening radiation sensitivity. Figure 4 shows the crystal thickness of CaTe and GaAs and the 69 keV
FIG. 3 is a diagram showing the relationship between X-ray absorption rate (%). The X-rays used for diagnosis are within or outside of eo keV.

In the case of a thickness of 0.511 ff, CaTe has an effective atomic number of 49 for photoelectric absorption, which has an absorption efficiency of about ao%, which is sufficiently large. Even a thickness of 0.1111jl can be practically used at about 30%. GaAs has an effective atomic number of 31 and 0.5
In the case of Tomatsu, the absorption efficiency is about 30%, which is lower than that of CdTe, but
It can be used practically. Crystals with an effective atomic number smaller than 30 have low X-ray absorption efficiency, in other words, have low sensitivity to X-rays, and cannot be put to practical use.

To summarize the above, if the semiconductor crystal has an effective atomic number of 30 or more and a thickness of 0.6 degrees, the X-ray absorption for diagnosis is sufficient and the sensitivity is high. Furthermore, as mentioned previously, a thickness of 0.6 ffW or less results in a short pulse width.

FIGS. 5a and 5b show another embodiment of the present invention different from that shown in FIG. This is an example with electrodes attached. This is a simplified manufacturing method. As such, the array may take on a variety of configurations.

FIG. 6 shows an example of an X-ray image receiving apparatus using the array. The fan beam X-rays exiting the X-ray tube 5 pass through the object 6 and enter the semiconductor detection element array 7, the X-ray signal is detected by each element, and the pulse number signal is sent to the counter circuit system 8. Next, image processing/memory and display system 9
and displayed or filed as an image. Although this is a normal X-ray radiograph, this array can also be applied to computerized tomography and can also obtain cross-sectional images.

Effects of the Invention The radiation detecting element of the present invention as described above can provide a new radiation receiver (X-ray diagnostic equipment, etc. with high intersection and high contrast resolution by using the II element.
．． Using a radiation detection element array of 5717m CdTe, which has an absorption efficiency of 80% for 60 keV X-rays, has a sensitivity close to the theoretical limit.

An X-ray image with good contrast can be obtained at 0.1=1 mR. This corresponds to 100 times the sensitivity of silver radiography. Furthermore, when an image is obtained at a level of 106 counts per pixel, the contrast resolution is very good and minute differences in living tissue can be distinguished.

[Brief explanation of the drawing]

Figures 1 (a> and (b) are respectively a plan view and a front view of a radiation detection element array according to an embodiment of the present invention, Figure 2 is an explanatory diagram of the principle of radiation detection, and Figure 3 is an illustration of the elements FIG. 4 is a diagram showing the relationship between thickness and output pulse width. FIG. 4 is a diagram showing the relationship between element thickness and absorption rate of 60 keV X-rays. FIG. A plan view and a front view of the radiation detection element array of FIG. 6 are diagrams showing the application of the element array to an X-ray diagnostic device. electrode, 4
...Other electrodes. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2: Mouth Figure 3: Weight (mm) Figure 4: Thickness (m force)

Claims (3)

[Claims] (1) The effective atomic number for photoelectric absorption of the element material of a detection element made of a semiconductor that counts absorbed radiation photons as electric pulses is 30 or more, and a plurality of the elements are arranged in a line on a substrate, and A plurality of electrodes are attached to opposing surfaces of the elements arranged in the array to form an array consisting of a plurality of elements, and the spacing between the opposing electrodes is 0.61Hm or less and 0.1mff+ or more. Features radiation detection element play. (2) The radiation detection element array according to claim 1, wherein the semiconductor is gallium arsenide. (3) The radiation detection element array as set forth in claim 1, wherein the semiconductor is cadmium chloride.