JPH0431785A - Dead time adjustment method for X-ray detector system of 2-counter EXAFS measurement device and 2-counter EXAFS measurement device - Google Patents

Abstract

PURPOSE:To make it possible to adjust dead time of an X-ray detector system only by one variable resistor and to know the dead time simply as the length of a TTL digital pulse by an oscilloscope or the like, by changing continuously the width of an output pulse waveform outputted from a pulse-height discriminator of the X-ray detector system. CONSTITUTION:Receiving a signal from a preamplifier, a linear amplifier (AMP) shapes its waveform to be of a Gaussian type by a differentiating circuit and an integrating circuit incorporated therein. In a pulse-height discriminator (SCA), a signal of the AMP in the front stage is subjected to pulse-height discrimination by LLD (Lower Level Discriminator) and outputted as a rectangular digital pulse. By using a variable resistor in place of a fixed resistor determining a time constant (which is determined by a resistance and the capacity of a capacitor and takes a fixed value generally) of output-stage IC which determines an output pulse width of a TTL level, in the pulse-height discriminator of an X-ray counter, the output pulse width is changed continuously.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to the use of extended X-ray absorption coefficients near the X-ray absorption edge of a substance.
Ti.

An X-ray detector that is particularly suitable for analyzing the structure of amorphous, quasi-crystalline materials, etc. This invention relates to a system dead time adjustment method and a pulse height discriminator.

(Prior art) Generally, when performing EXAFS measurements in a laboratory system using a sealed tube or rotating anode-type X-ray generator, the absorption coefficient curve is affected by the characteristic X-rays superimposed on the white X-rays. A spike-like noise (glitch) appears. Some characteristic This has been a major obstacle in obtaining accurate information such as the distance between matching atoms and the coordination number of atoms. The main reason for this is the counting loss (
(due to finite dead time).

One of the inventors of the present invention developed a two-force counter type EXAFS measurement device with the aim of obtaining a glitch-free and smooth absorption curve in a laboratory EXAFS measurement device.
This was proposed in Japanese Patent Application Laid-open No. 151573/1983. FIG. 6 is a configuration diagram of the two-force counter type EXAFS measuring device. In particular, by moving the partition wall of the I counter (C2) that can continuously vary the detection area (effective length) for sample-transmitting X-rays, this device By balancing the counting rate and eliminating the effect of counting loss due to the unfavorable time of the two counters,
It was intended to eliminate the problem. However, in the above two-force counter type EXAFS measurement, the detection efficiency of the I counter is originally 1.
Although it is desirable that the detection efficiency be 00%, there is a drawback in that the detection efficiency of the I counter is forced to drop below 100% in order to satisfy the matching condition of the count loss characteristics. By continuously varying the waveform shaping time constant of the linear amplifier (AMP) of the counter, the pulse width of the electrical signal, that is, the dead time of the X-ray detector system, can be continuously varied, and a counter such as a semiconductor detector can be used. Waveform shaping that provides a smooth X-ray absorption coefficient curve that is not affected by characteristic X-rays, even when the length of the I counter is fixed at its maximum length and used with almost 100% detection efficiency. Developed a linear amplifier with a continuously variable time constant.
- Proposed in No. 112627.

(Problem to be solved by the invention) The principle of the glitch cancellation method is as follows.

EXAFS measurement device (Figure 6) detector, preamplifier (
(hereinafter referred to as AMP), a pulse height discriminator (hereinafter referred to as SCA), and a scaler. ,
■Tau for each delay time of the counter detector system. , τ, and RL=IOt/It (here ■).
It is Io, the true counting rate (when there is no counting loss) at the I counter, respectively), and to eliminate the glitch, RL - τ/τ. ...(1) must be satisfied. RL is a value determined by the sample material.

In the above XvA detector system, the dead time τ is usually A
MP waveform shaping time constant τ0. Since it is determined by
No. 12627 introduces an AMP in which τ□ can be continuously varied.
It was used as a counter to continuously change τ to satisfy the +11 formula. However, in this method, several variable capacitors and variable resistors had to be tuned simultaneously in order to change τA□, making the operation complicated.

(Means for solving the problem) The above problem is solved by the output stage I which determines the output pulse width of the TTL level in the pulse height discriminator of the X-ray counter.
By using a variable resistor instead of a fixed resistor, which determines the time constant of C (which is determined by the capacitance of the resistor and capacitor and usually takes a fixed value), the output pulse width can be changed continuously. This can be achieved by the configured present invention.

(effect) The present invention will be explained in more detail below.

FIG. 5 is a signal flow diagram of the X-ray detector system.

The linear amplifier (AMP) receives a signal from the preamplifier (PA), and its waveform is shaped into a Gaussian shape by a built-in differentiation circuit and an integration circuit. In SCA, the signal of the previous stage AMP is
LD (Lower LevelD 1scria+
1nator) and outputs it as a rectangular digital pulse. FIGS. 4(A) and 4(B) show a linear amplifier (AMP) and a pulse height discriminator (S C
The relationship of pulse signals in A) is shown schematically. As shown in Figure 4 (A), in a normal X-ray detector system, τAMP
>τSeA, and in this case τ0. becomes τ. If τAMP <τSCA, τ3CA determines τ. Therefore, AMP's τ8. As shown in the same figure (B), τ0. 〈τ,. If we make it as small as possible and then modify the SCA so that τSCA can be continuous, the dead time τ can be adjusted with only one variable resistor.

By applying this AMP and SCA to the I counter, we can actually calculate the dead time τ of the detector system using the single thin film method (T).

Fukamachi: Jpn, J, Appl.
Fhys, 8 (1969) 851). The results are shown in FIG. In this experiment, τ5cA
τ was obtained for each τSCA by changing between -0, 2 and 2 μsec. As can be seen from the figure, ■ 0.2〈τ
If sca <0.8 μsec, τ, = 0.7 μsec
However, when τSCA〉0.8 μsec, τ
=rSeA. In other words, τSCA is continuously variable S
By using CA, the dead time τ of the detector system can be reduced to τ〉
It can be seen that it is sufficient to continuously vary the value in 0.7 μsec.

(Effects of the Invention) According to the present invention, the dead time of the X-ray detector system can be adjusted using only one variable resistor, and the dead time can be easily determined as the length of a TTL digital pulse using an oscilloscope or the like. Therefore, it has become possible to obtain accurate information such as the distance between atoms and the coordination number of atoms from the sample substance. Furthermore, in order to completely remove high-order harmonics, it is also effective when it is necessary to use a semiconductor detector with excellent energy resolution.

The present invention is suitable for atomic structure analysis of amorphous materials, quasicrystal materials, liquid solutions, etc., and is therefore expected to be used in the development of new materials such as various ceramics and amorphous alloys.

(Example) The present invention will be explained in detail below.

The present invention uses the continuously variable output pulse width type pulse height discriminator of the present invention as a pulse height discriminator (SCA') for the I counter in the two-force counter type EXAFS measuring device shown in FIG. A wave height discriminator (SCA) is used for the I0 counter.

A circuit diagram of the output stage of the pulse height discriminator of the present invention is shown in FIG.
The SCA removes noise (a signal with a constant amplitude) from the manually generated analog signal from the AMP at the front stage, converts it into a TTL level digital pulse, and receives it from the scaler at the rear stage.

The time width of the TTL level output pulse is normally determined by the output stage IC.
It is determined by the resistor and capacitor capacity used. Conventional pulse height discriminators on the market have fixed resistors and capacitors, and therefore the output pulse width is fixed. In the present invention,
This is made variable so that the output pulse width can be changed continuously.

Next, the linear amplifier of the present invention was constructed using an amorphous CuTa alloy EX.
An example of application to AFS measurement will be shown. The experimental conditions are as follows. In the two-force counter type EXAFS measuring device, the variable output pulse width type pulse height discriminator of the present invention was used as the pulse height discriminator for the I counter. A normal fixed type was used as a 10-counter wave height discriminator. In fact, an example of EXAFS measurement on the absorption edge of Ta Ln of an amorphous CuTa alloy is shown in FIGS. 2A and 2B. Io, the dead time of the I counter is (al r 5CA(10) −1 u sec, τ
5cA(I) = 20 p 5ec(b) τ5c
A(L) −1 μsec, τ5ctt (I) = 5
μ5ec(C1τ5cA(Io) = 5μSec %
It was adjusted as follows: τ5cA(1) = 1 μsec.

In FIG. 2B, a characteristic X-ray WLβ2 due to impurities contained in the anticathode of the X-ray tube appears. Looking at the X-ray absorption coefficient curve in FIG. 2A, it can be seen that (a) corresponds to the X-ray WLβ2.
In the case of , a mountain-shaped data glitch occurs, in the case of (C), a valley-shaped data glitch occurs, but in the case of (b), no data glitch occurs.

As described above, the output pulse width continuously variable pulse height discriminator of the present invention has the following features:
It has been shown that this method is extremely effective in completely eliminating data glitches in a two-force counter type EXAFS measuring device.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an embodiment of the present invention, and Figures 2A and 2B are X-ray absorption coefficients obtained by performing two-force counter EXAFS measurement using an amorphous CuTa alloy as a sample. Figure 3 is a plot of τV, S, and τSCA determined by the single thin film method. Figure 4 is the output pulse waveform of the linear amplifier and pulse height discriminator. Figure 5 is the output pulse waveform of the X-ray detector system. The signal flow diagram, Figure 6, is 2
FIG. 2 is a configuration diagram of a force counter type EXAFS measuring device. (Explanation of symbols) XS...X-ray tube, SS...Solar slit,
DS...Divergent slit, MC...Spectroscopy crystal, GM
...Goniometer, R3...Light emitting slit, C1
...I0 counter, C2...1 counter, C8...
...N2 dewar-SP...sample, HV...high voltage power supply, CA...counter arm, PA...preamplifier, AMP...linear (main) amplifier, SCA, S
CA'... Wave height discriminator, ST... Channel scaler - μCP... Microcomputer. "-- SCA -11" Figure 4 (△) (B) AMP 〉 te SCA te MP down scA

Claims (2)

[Claims] (1) X characterized by continuously changing the width of the output pulse waveform output from the pulse height discriminator of the X-ray detector system
Dead time adjustment method for line detector system. (2) An X-ray detector system comprising a pulse height discriminator having means for continuously adjusting a time constant, thereby making it possible to adjust dead time.