JP3083534B2 - Dead time adjustment method for X-ray detector system of two-counter EXAFS measurement device and two-counter EXAFS measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention measures the X-ray absorption coefficient fine vibration (hereinafter, referred to as EXAFS) near the X-ray absorption edge of a substance, The present invention relates to an X-ray structure analysis apparatus for elucidating a local structure, and more particularly to adjustment of a dead time of an X-ray detector system suitable for structural analysis of amorphous, quasi-crystal and the like.

(Prior art) When performing EXAFS measurement, first, the energy of the incident X-ray is continuously changed without setting the sample, the incident X-ray intensity is measured with an X-ray counter, and then the sample is set. The energy of the incident X-ray is continuously changed, and the intensity of the incident X-ray is measured by an X-ray counter. The X-ray absorption coefficient of the sample is obtained by dividing the incident X-ray intensity when the sample is not installed by the transmitted X-ray intensity when the sample is installed.

In general, when performing EXAFS measurement in a laboratory system using a sealed tube or a rotating anti-cathode type X-ray generator, the absorption coefficient curve is affected by characteristic X-rays superimposed on white X-rays, and spike-like noise ( Glitch) appears. The energy of certain characteristic X-rays due to impurities contained in the opposite cathode of such an X-ray tube may be located in the region of EXAFS measurement,
This has been a major obstacle to obtaining accurate information such as the local structure around the line-absorbing atoms, particularly the distance between adjacent atoms and the coordination number of the atoms. The main reason for this is that the coefficient loss characteristics of the counter for monitoring the incident X-ray intensity and the counter for measuring the X-ray transmitted through the sample are inconsistent. As a result, the difference in the tendency of counting down becomes remarkable in both counters, and as a result, spike-like noise appears on the absorption coefficient curve.

Therefore, the movable radiopaque barrier is installed on the cylinder of the counter for measuring the sample transmission X-rays, and the volume of the sample gas in the cylinder is changed to make the count loss characteristic of the sample transmission X-ray counter. It has been proposed that the noise of the absorption coefficient curve be eliminated by making the noise loss match the counting loss characteristic of the monitor counter (see Japanese Patent Application Laid-Open No. 60-151573).

The C ₂ of Fig. 6 is a sample transmitted X-ray counter, C ₁ is a counter for monitoring and partial CA surrounded by the broken line is EXAFS counter proposed in JP 60-151573. FIG. 6 shows a two-counter EXAFS measuring apparatus using the proposed EXAFS counter. However, in this two-counter EXAFS measuring device, the volume of the gas in the cylinder is large enough to absorb X-rays because it is adjusted to match the counting loss characteristic of the counter for monitoring the volume of gas in the cylinder. However, there is an inconvenience that the measurement is usually performed in an insufficient X-ray absorption state in the sample transmission X-ray counter.

In order to solve this inconvenience, the moving partition is stopped from being installed on the cylinder of the sample transmission X-ray measurement counter, and the volume of the cylinder is fixed to a size sufficient for gas to absorb X-rays. _1, mismatch count loss characteristics C ₂ are both counter
It has been proposed that the dead time determined by the waveform shaping time constants τ ₀ and τ of the amplifiers AMP belonging to C ₁ and C ₂ be separately adjusted (Japanese Patent No. 2921854).

That is, in FIG. 6, the detection and counting system for the incident X-ray monitor includes a detector C ₁ , a preamplifier PA, an amplifier AMP, a wave height discriminator SCA, and a scaler ST. Detector C ₂ , preamplifier PA, amplified amplifier AMP,
It consists of wave height discriminator SCA 'and scaler ST. The both strains, respectively tau ₀ the dead _time, and _{^{τ, R t = I 0 t}} / I t to (R ^t is determined by the sample material value, I ₀ ^t, I ^t respectively I _0,
True (no counting loss) counting rate in I counter).

R ^t = τ / τ ₀ must be satisfied in order to eliminate glitches. Japanese Patent No. 2921854 satisfies the above expression by continuously changing the waveform shaping time constant τ _AMP of the AMP that determines the dead time τ.

(Problems to be Solved by the Invention) In the method of the patent, these variable elements must be simultaneously changed and tuned as several capacitors and resistors of the amplifier are variable, and the operation is complicated.

An object of the present invention is to eliminate a glitch by a simple operation.
A counter type EXAFS measuring device is provided.

(Means for solving the problem) The purpose of this is to set the time constant of the output stage IC that determines the TTL level output pulse width of the wave height discriminator at the subsequent stage of the amplifier (determined by the capacitance of the resistor and capacitor, usually a fixed value This is achieved by matching the count loss characteristics of both counter systems by making one fixed resistor, which determines the above (1), a variable resistor.

(Operation) FIG. 5 shows signals of the X-ray detection counting system. The linear amplifier (AMP) receives a signal from the preamplifier (PA) and shapes the signal into a Gaussian waveform by a built-in differentiating circuit and an integrating circuit. In the wave height discriminator SCA, the signal of the amplifier (AMP) in the preceding stage is wave height discriminated by an LLD (Lower Level Discriminator) and output as a rectangular digital pulse. FIG. 4 (A) schematically shows the normal (as in the above-mentioned patent) relationship of the pulse signal in the linear amplifier (AMP) and the pulse height discriminator (SCA), and FIG. 4 (B) schematically shows the relationship in the present invention. Show. As shown in FIG. 4A, in a normal X-ray detection counting system, τ _AMP > τ _SCA , and in this case, τ _AMP becomes τ. If τ _AMP <τ _SCA , τ _SCA determines τ. Therefore, the τ _AMP of the linear amplifier (AMP) is reduced so that τ _AMP <τ _SCA as shown in FIG. 4B, and then the τ _{SCA of the} pulse height discriminator (SCA) is made continuously variable. If you remodel,
The dead time τ can be adjusted with only one variable resistor.

This linear amplifier (AMP) and wave height discriminator (SCA) are applied to an I counter, and the dead time τ of the detection and counting system is actually determined by a single thin film method (T. Fukamachi: Jpn. J. Appl. Phys. 8 (1969)). ) Measured according to 851). FIG. 3 shows the results.

In this experiment, τ _SCA was changed between 0.2 and 2 μsec.
Τ was obtained for each τ _SCA . As can be seen from the figure, 0.2
When <τ _SCA <0.8 μsec, τ _d is constant at 0.7 μsec, but when τ _SCA > 0.8 μsec, τ = τ _SCA . That is, by using the wave height discriminator _SCA having a continuously variable τ _SCA , the dead time τ of the detection and counting system can be continuously varied at τ> 0.7 μsec.

(Effect) According to the present invention, the dead time of the X-ray detection / counting system can be adjusted with only one variable resistor, and the dead time of the other X-ray detection / counting system is matched to make the counting loss characteristics match, and there is no glitch. A smooth absorption curve can be obtained. This makes it possible to acquire accurate information such as the distance between atoms and the coordination number of atoms from the sample substance.

(Example) Hereinafter, the present invention will be described in detail.

The present invention relates to a two-counter EXAFS measuring apparatus shown in FIG.
It is used as a pulse height discriminator (SCA ') for a counter, and a normal output pulse width fixed pulse height discriminator (SCA) is used for an _I0 counter.

FIG. 1 shows a circuit diagram of the output stage of the wave height discriminator of the present invention. The SCA removes noise (signal below a certain level) of the analog signal input from the preceding stage AMP, converts it into a TTL level digital pulse, and receives it at the subsequent stage scaler. TTL
The time width of the level output pulse is usually determined by the resistance and the capacitance of the output stage IC. In conventional commercial wave height discriminators, the resistance and the capacitor are fixed, and thus the output pulse width is fixed. In the present invention, this is made variable so that the output pulse width can be continuously changed.

Next, the linear amplifier of the present invention was converted to an amorphous CuTa alloy EXAFS.
Here is an example applied to measurement. The experimental conditions are as follows. In the two-counter EXAFS measuring apparatus, the variable output pulse width type pulse height discriminator of the present invention was used as the pulse height discriminator for the I counter. An ordinary fixed type was used as the wave height discriminator of the _I0 counter. Actually, amorphous CuTa alloy Ta
Examples of EXAFS measurement on the LIII absorption edge are shown in FIGS. 2A and 2B. I ₀ and the dead time of the I counter are as follows: (a) τ _SCA (I ₀ ) = 1 μsec, τ _SCA (I) = 20 μsec (b) τ _SCA (I ₀ ) = 1 μsec, τ _SCA (I) = 5 μsec (c ) _SCA (I ₀ ) = 5 μsec, and τ _SCA (I) = 1 μsec. The FIG. 2B, the characteristic X-ray WLbeta ₂ has appeared due to impurities contained in the anticathode X-ray tube. Looking at the X-ray absorption coefficient curves in Figure 2A, corresponding to the X-ray WLbeta _2, data glitches chevron when the (a) is a data glitch valley occurs when the (c) (B)
In the case of, no data glitch has occurred.

As described above, it has been shown that the continuously variable pulse width discriminator according to the present invention is extremely effective in completely eliminating data glitches in a two-counter EXAFS measuring apparatus.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIGS. 2A and 2B are X-ray absorption coefficient curves obtained by performing a two-counter EXAFS measurement using an amorphous CuTa alloy as a sample. , FIG. 3 is a plot of τV.S.τ _SCA determined by a single thin film method, FIG. 4 is an output pulse waveform of a linear amplifier and a pulse height discriminator, and FIG. 5 is an X-ray detector system. FIG. 6 is a block diagram of a two-counter EXAFS measuring apparatus. (Explanation of symbols) XS: X-ray tube, SS: Solar slit, DS: Divergent slit, MC: Dispersive crystal, GM: Goniometer, RS: Emitting slit, C _{1: I0} counter, C ₂ ...... I counter, CS ...... N ₂ dewar, SP ...... sample, HV ...... high voltage power supply, CA ...... counter arm, PA ...... preamplifier, AMP ...... linear (main) amplifier, SCA, SCA ' …… A wave discriminator, ST …… Channel scaler, μCP …… A microcomputer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-40574 (JP, A) JP-A-60-151573 (JP, A) Fully open 63-58771 (JP, U) Really open 58773 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01T 1/17 G01N 23/08

Claims (3)

(57) [Claims] An incident X including an amplifier connected to a monitor counter and a pulse height discriminator connected to the amplifier.
A two-counter EXAFS measuring apparatus comprising a detection counting system for X-ray monitoring, a detection counting system for transmission X-ray measurement including an amplifier connected to a sample transmission X-ray counter, and a wave height discriminator connected to the amplifier. In the dead time adjusting method of the X-ray detector system, the dead time of the amplifier of one of the detection and counting systems is made shorter than the dead time of the pulse height discriminator connected to the amplifier, and the output pulse waveform of the pulse height discriminator is used. And the width of the output pulse waveform of the peak discriminator of one of the detection and counting systems is changed so as to eliminate the discrepancy in the counting loss characteristic with the other detection and counting system. A dead time adjusting method for an X-ray detector system of a two-counter EXAFS measuring apparatus, characterized in that: 2. τ / τ ₀ = R ^t (where τ is the dead time of the detection and counting system for transmission X-ray measurement, τ ₀ is the dead time of the detection and counting system for incident X-ray monitoring, R ^t = I ₀ ^t / I ^t, the where I ₀ ^t is the true count rate detection counting system for the incident X-ray monitor, I ^t is such to satisfy the true count rate) of detection counting system for transmitting X-ray measurement The two-counter system according to claim 1, wherein the width of the output pulse waveform of the wave height discriminator of one of the detection counting systems is changed.
The dead time adjustment method for the X-ray detector system of the EXAFS measurement device. 3. An incident X including an amplifier connected to a monitor counter and a pulse height discriminator connected to the amplifier.
In a two-counter EXAFS measuring apparatus having a detection counting system for X-ray monitoring, a detection counting system for transmission X-ray measurement including an amplifier connected to a sample transmission X-ray counter, and a wave height discriminator connected to the amplifier, The dead time of the amplifier of one of the detection and counting systems is made smaller than the dead time of the pulse height discriminator connected to the amplifier, and the width of the output pulse waveform of the pulse height discriminator is continuously changed; A two-counter EXAFS measuring apparatus characterized in that the width of the output pulse waveform of the wave height discriminator of one of the detection and counting systems is changed so as to eliminate the discrepancy of the counting loss characteristic that occurs with the other detection and counting system. .