JPS63171387A - Discrimination of radiation energy - Google Patents

Abstract

PURPOSE:To discriminate radiation energy from which the measuring error due to K-shell characteristic X-ray escape is removed, in performing counting in such a state that incident radioactive rays are divided into two energy regions, by preliminarily determining a correction constant even when the K-shell characteristic X-ray escape peculiar to a semiconductive radiation detector is generated. CONSTITUTION:The photon energy is incident radioactive rays is divided into two kinds of energy bands using a discriminator to perform the counting of photons. Then, the photon count value of the high energy band is multiplied by predetermined coefficient to calculate the photon count value of K-shell characteristic X-ray escape and the value obtained by adding this photon count value to a high energy photon count value is set to a real high energy photon count value. Further, the value obtained by subtracting this photon count value from a low energy photon count value is set to a real low energy photon count value to perform the correction of the K-shell characteristic X-ray escape. By this method, even when there is the effect of the K-shell characteristic X-ray escape peak peculiar to the material of a semiconductive radiation detector, an energy band can be accurately separated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a radiation energy discrimination method in a data processing or image processing method used in an X-ray diagnostic device used in medical treatment or a non-destructive inspection device used in industry.

Prior Art Figure 2 shows the absorption mechanism of radiation due to the photoelectric effect. When incident radiation 1 enters an atom, it is mainly absorbed by shell electrons in the outer shell orbital electrons, and is emitted outside the membrane as K-shell electrons as excited electrons 2. This excited electron 2 is an electron in the semiconductor.
The number of photons of radiation can be detected by generating hole pairs and 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 3.

FIG. 3 shows this phenomenon as a phenomenon within a semiconductor radiation detector. When the radiation 1 is absorbed in the semiconductor detector 4, the excited electrons 2 and film characteristic X-rays 3 are generated, and the excited electrons 2 lose most of their energy due to the width of the semiconductor crystal, or
When the K film characteristic X-rays 3 are generated near the crystal plane, they may be emitted outside the crystal. This phenomenon of radiation exiting the crystal is called membrane characteristic X-ray escape, and when this phenomenon occurs, the amount of charge output from the detector decreases, and the peak value of the output pulse decreases. FIG. 4 shows this phenomenon in terms of output pulse peak values. FIG. 46 shows the energy of incident radiation and the number of photons. However, actual measurements show that when radiation of a single energy E' is incident, the wave height distribution from the semiconductor radiation detector is as shown in Figure 3.

That is, it is divided into two pulse groups: a pulse with a pulse height corresponding to the incident energy E, and a pulse with a pulse height corresponding to the energy EE, (E: binding energy of K-shell electrons).

Next, consider the case of irradiation with continuous energy radiation.

FIG. 5 shows the energy distribution emitted from the X-ray tube when X-rays are used as the radiation source.

When such continuous energy radiation is incident on a semiconductor radiation detector, the I(Russ output wave height distribution from the detector is as shown in the total spectrum shown by the solid line in Fig. 6. Its components are Binding energy of shell electrons E,
It consists of the summed spectral distribution of the L-shell photoelectric absorption spectrum, the K-shell photoelectric absorption spectrum, and the W-shell xs escape peak spectrum, with the boundary at .

Problems to be Solved by the Invention As mentioned above, when K-shell characteristic X-ray escape occurs,
For incident continuous energy radiation, the output wave height spectrum from a semiconductor radiation detector does not correspond to the incident radiation energy distribution, but has a spectral distribution shifted to the lower energy side. Even if it is divided into two energy bands using Noether, the data obtained therefrom does not correspond to the incident energy.

As a means to solve the problem, the shell characteristic X-ray escape peak spectrum is calculated by taking into consideration the material and shape used in the semiconductor radiation detector, and subtracting the count value of the K membrane characteristic X-ray escape peak toward the lower energy side. Correction is performed by adding to the high energy side.

That is, the photon energy of the incident radiation is divided into two types of energy bands using a discriminator and photon counting is performed, and the photon count value of the high energy band is multiplied by a predetermined coefficient to determine the photon of the film characteristic X-ray escape. The count value is calculated, and the value obtained by adding the shell characteristic X-ray escape photon count value to the high-energy photon count value is defined as the true high-energy photon count value. Furthermore, the K film characteristic X-ray escape peak is corrected by subtracting the shell characteristic X-ray escape photon count value from the low energy photon count value as the true low energy photon count value.

Effect When using the method described above to separate incident radiation into two energy bands and perform photon counting, K Correct separation of energy bands becomes possible by correcting the membrane characteristic X-ray escape peak.

Example The incident X-ray energy spectrum as shown in Fig. 6 is f.
(6), the cumulative number of photons F(2) can be expressed by the following equation.

F (gradient=f″f@dE ・・・・・・・・・
(1) If the number of X-ray absorption photons absorbed by a semiconductor radiation detector is F'(El, then F'(E
) can be expressed by the following equation.

F '#-/''f(6)(1-scream(-μ(2)x))d
li: ...... (audience μ(6): Absorption coefficient of detector , when the output energy spectrum is divided according to Figure 6, the cumulative number of photons in the total spectrum is the sum of the following two equations, F# (6) +
F''(E-E,).

+ (1-A) 71 units (1-LEQ (-μm)) dE...
・(3) F#(EE-E,)=A/';, Q(1-ew(
-μ(Elri)dE・(4) Here, to explain the meaning of equation (3), the first term of lr//(6) is the shell photoelectric absorption energy spectrum in Figure 6, and the second term is The integrated number of photons in the shell photoelectric absorption spectrum, Fl'(g) in equation (4), represents the integrated number of photons in the shell characteristic X-ray escape beak spectrum. Here, the constant A is a constant of 1 or less, which is determined by considering both the absorption coefficient μ (gradient and shell electron binding energy E) and the effect of the detector shape. By determining A,
(3), (4) It becomes possible to convert the output pulse height spectrum from the semiconductor radiation detector into the X-ray energy spectrum absorbed by the semiconductor radiation detector shown in equation (2).

This conversion will be applied to actual energy discrimination.

Figure 1 shows the output pulse height spectrum of a semiconductor radiation detector) using discriminators E and E2.
It shows the respective components when separated into two types of energy regions. The low energy region of E1 to E2 consists of the sum of the L-shell photoelectric absorption spectrum (1), the sum of part of the shell photoelectric absorption spectrum (1), and the sum of the film characteristic X-ray escape peak spectrum (3) (rumor has it that more than 82 The high-energy region consists mostly of shell photoelectric absorption spectra (1) and (2) in the figure.

The sum of (3) is the output energy spectrum (b).

Here, based on the idea of energy discrimination, we stop calling it spectrum and rename it to integrated counts. Let the total count number be F), let the count number of area (1) be F(1), let the count number of area (below be F(g, area ('4)
When the count number of is F(3), the following equation holds true.

F (to) = F (1) + F (2) + F (3)
(6) If Ei and E2 are close, the second term of equation (3) and equation (4) can be rewritten as follows.

(1-A)fooAE) [1-go(-μ(Ii)x))
dE=F(2) −(6)E2 ・A/'M2f('')('-groan(-a(ax)dli:=
F(3) ・−”・・・(η(橢, From equation (7), (5), (F(1) = F from Shizuku equation) −F(Kabura −F(Shiro=F■− -F@・・・・・・・・・・・・・・・
...(9)-A (5), (8), @It is clear from the expression that the discriminator E4. By counting the output pulses from the semiconductor radiation detector using E2 and measuring the total count F(2) of 81 or more and the count F(2) of 82 or more, we can determine the true low value in the range of E1 to E2. This means that the energy photon count value F (1) and the true high energy count value F (2) + F (s) of 82 or more can be obtained, and the calculation formulas thereof are K as shown below.

F(1)=F)−TTfF(2)...
・・・・・・(9)F(Rumor+F(3)=F(2)+No-
By introducing the constant A in this way, the semiconductor radiation detector can be used even if the phenomenon of K-shell characteristic X-ray escape occurs. It becomes possible to accurately discriminate the energy of radiation photons absorbed by

The method for determining this constant A is to first irradiate a semiconductor radiation detector with radiation of a single energy E, as shown in FIG. 3a. As a result, in the output pulse height spectrum of the semiconductor radiation detector, in addition to the peak corresponding to the incident energy E, a peak due to shell characteristic X-ray escape occurs at a location corresponding to the energy E-. The total count of both peaks is the number of radiation photons absorbed by the semiconductor radiation detector, and the ratio of the count of the film characteristic X-ray escape peak to the total count is the value of A to be determined. The value of A depends on the absorption coefficient and shape (size, thickness) of the detector material and the shell electron binding energy Ei
It is a function of , and needs to be determined experimentally.

Table 1 shows the values of the shell electron binding energy (K absorption edge energy) of the elements of the material of the semiconductor radiation detector that can be used in the present invention. St is E.

is as low as about 2 KeV (in the low energy region below 10 KeV, Go and GaAtr have an E of 10~10 KeV).
12 KeV, below 100 KeV, especially 50 Ke
In the energy range below V, the E of CdTe is about 30 KeV, and the radiation energy discrimination method of the present application is very effective in the energy range below 100-200 KeV. Also H9I! Ei of is about 33
Although it is a little complicated because the Ei of KeV and Hg are different from each other at about 83 KeV, it is effective for the energy range of ~200 KeV or less.

In Table 1 and below, a radiation energy discrimination method using a single detector is described. Detector row 1 with a plurality of detectors, for example -
When applying the radiation energy discrimination method of the present application to a dimensional detector array or a two-dimensional plane detector, the incident of K film characteristic X-ray escape to an adjacent detector, in other words, the film characteristic X emitted from an adjacent detector It is necessary to consider the incidence of line escapes. That is, crosstalk between adjacent detectors due to membrane characteristic X-ray escape appears in the phenomenon in which the count number of shell characteristic X-ray escape peaks increases as shown in FIG. In such a case, by changing the value of the constant A in consideration of the detector structure, it becomes possible to discriminate radiation energy while correcting crosstalk between adjacent detectors.

Effects of the Invention According to the present invention, when counting is performed by dividing the incident radiation into two energy regions, even when the shell characteristic It is possible to perform radiation energy discrimination without measurement errors due to X-ray escape due to the X-ray escape characteristic of the K film.

If the method according to the present application is used for X-ray image diagnosis, by irradiating the subject with X-rays once, it becomes possible to divide the radiation that has passed through the subject into images consisting of two energy regions. Furthermore, by taking the difference between these images, image processing called the energy difference method becomes possible. As a result, we have solved the problem of image deviation due to the difference in imaging time that occurs when irradiating twice with conventional energy radiation and taking the difference between the images.
This problem can be solved by the method according to the present application, and it becomes possible to obtain two images with no subject shift and a difference image thereof. Furthermore, in the case of conventional radiation with different energies, especially X-rays, the energy range is distributed over a wide range, so even if different energies are used, the actual energy spectrum distribution will have overlapping parts.
The energy discrimination according to the present invention has very high energy separation ability without any single layer.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the output pulse height distribution according to the present invention, Fig. 2 is a diagram showing the basic principle of the shell photoelectric effect, Fig. 3 is a schematic diagram of the shell characteristic X-ray escape phenomenon, and Fig. 4 is a diagram showing the simple principle of the shell photoelectric effect. FIG. 6 is a diagram showing the output pulse height distribution with respect to the incidence of one-energy radiation, FIG. 6 is a diagram showing the incident X-ray energy distribution, and FIG. 6 is a diagram showing the output pulse height distribution from the detector. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 5 Figure 6 Hire Rangi 1 Watari 1 cv)! Five capitals to the castle

Claims (4)

[Claims] (1) A method of counting radiation photons by using a semiconductor radiation detector, creating two discriminatory levels, and dividing incident radiation into two types of energy bands,
The high energy band count value is the high energy photon count value,
A count value in a low energy band is defined as a low-energy photon count value, a value obtained by multiplying the high-energy photon count value by a predetermined coefficient and added to the high-energy photon count value is defined as a true high-energy photon count value, and Radiation energy characterized in that the number of photons in two energy regions is obtained as a true low-energy photon count by subtracting a value obtained by multiplying the high-energy photon count by a predetermined coefficient from the low-energy photon count. Discrimination method. (2) The method for discriminating radiation energy according to claim 1, characterized in that photon numbers in two energy regions are obtained: a high-energy photon count value and a true low-energy photon count value. (3) The radiation energy discrimination method according to claim 1, wherein the radiation energy range to be detected is an energy range of 200 KeV or less. (4) The semiconductor crystal material used in semiconductor radiation detectors is G
2. The radiation energy discrimination method according to claim 1, wherein the radiation energy is one selected from e, GaAs, CdTe, and HgI.