JPH04209461A - Linearity improvement method for photomultiplier tube - Google Patents

Abstract

PURPOSE:To improve the linearity of a voltage dividing circuit for a photomultiplier tube by applying voltage to each diode between the cathode and anode of the tube via a series of resistors having different resistance values. CONSTITUTION:Each of diodes D1 to D9 between the cathode C and anode A of a photomultiplier tube is applied with voltage via an optimum series of resistors R1 to R10 having different resistance values. As a result, the linearity of a voltage dividing circuit in the photomultiplier tube is improved, and the tube can be used with high accuracy via the application of simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for improving the linearity of a photomultiplier tube in order to use it with high precision.

[Prior Art] Currently, photomultiplier tubes, which are said to have high sensitivity and good response linearity, are often used as detectors in analytical instruments such as spectrophotometers. However, this detector also does not have perfect linearity, and its deviation (nonlinearity) is used without being calibrated. When measuring an optical filter (for example, 930D filter supplied by Nl5T (National Institute of Standards and Technology)), the transmittance is 30%.
Even with this filter, the transmittance is displayed as low by 0.2% or more.

In a photomultiplier tube used in a conventional spectrophotometer, in a voltage divider circuit as shown in Figure 1, the voltage between the electrodes is determined by resistors with equal resistance values (R, = R2 = ... = R,
. ) are often applied by a circuit that connects them in series. At that time, analysis by Land et al. (Land.

P,L,,Rev,Sci,Instrum,42.4
20-425 (19711), the amplification factor depends on the interstage voltage, so as the anode current increases, the interstage voltage at the subsequent stage decreases, and the linearity deteriorates.

On the other hand, Nl5T, NPL (National Physical Laboratory in the UK), and the Institute of Metrology of the Agency of Industrial Science and Technology have calibrated the nonlinearity of the detector by examining whether the additivity of light holds true, and are using high-precision spectrophotometers. (For example, Ninohe, Takahashi, Nishibata, Metrology Institute Report 39 (19901, P.
399-406). However, this method requires stability of the equipment, is time-consuming, and cannot be applied to equipment used in daily routine work.

[Problems to be Solved by the Invention] A technical problem to be solved by the present invention is to improve the method of applying the voltage between the electrodes in the photomultiplier tube described above, thereby increasing the linearity of the photomultiplier tube as a detector and making the photomultiplier tube highly accurate. The goal is to make it available for use.

[Means for Solving the Problems J] In order to solve the above problems, a method for improving the linearity of a photomultiplier tube according to the present invention provides a method for improving the linearity of a photomultiplier tube used as a detector. Applying a voltage between each dynode by providing a resistor between the cathode and each dynode and connecting the resistors in series,
At this time, the linearity of the response in the photomultiplier tube is improved by controlling the voltage by using resistors with different resistance values for at least some of the resistors.

[Operation] Considering the constants determined by the type of photomultiplier tube, etc., find the relationship between the current value between the cathode and the first stage dynode and the output current, and divide it so that the relationship is linear. By optimizing the resistance value, linearity as a detector is improved and the photomultiplier tube can be used with high precision.

[Examples] Examples of the present invention will be described in detail below with reference to FIG.

The present invention basically involves dividing the voltage between each dynode Dl-D between a cathode C and an anode A in a voltage dividing circuit of a photomultiplier tube used as a detector, as shown in FIG. , a resistance fR+-a+ between the cathode and each dynode. ) and by connecting those resistors in series, in which case only resistors with equal resistance values (R+=Rz=...=R,.) are connected in series as in the conventional method. Instead, at least some of these resistors have different resistance values to control the voltage, thereby improving the linearity of the response in the photomultiplier tube.

In the following, it will be specifically explained that the linearity can be improved by such a method.

Generally, in an electron multiplier tube, where η is the quantum efficiency, φ is the incident light flux, and G is the amplification factor, the output current IN is expressed as zs(φ)=ηGφ...fil.

Also, the amplification factor of the n-th stage dynode is δ. Then, D
The overall amplification factor G of the stage is the amplification factor δ. According to Land et al., empirically, δ. depends not only on the previous potential difference V,, but also on the next potential difference vn, I, and using parameters b, p, and q, δゎ=bVllV11. I...(
3). b, 1)+q are constants that differ depending on the type of photomultiplier tube, and the ratio of p and q also depends on the conditions of use of the photomultiplier tube.

Detector linearity can generally be improved as follows. First, equation (2) and parameters b, p
, q, and express the resistance divider circuit using Ohm's law and Kirchhoff's law. Therefore, the cathode and
The relationship between the current value i between the dynodes of the stage and the output current 9 is determined, and the dividing resistance value is optimized so that the relationship becomes linear.

Specifically, as shown in Figure 1, resistors (R
, -R,), if voltage ■ is applied to i+"l+"lz
+I. =...lN+INR+4+=V+, R2'I2
"V2...., RN'Ix"V-L+V2+
−−+VN=V δ−+=b・VN−+ JN 12・11・δ+, 1B=1i・δ2. ....

IN=IN-1・δN-1...(4) becomes.

By solving the above equations simultaneously, the relationship between 11 and iN can be determined, and by selecting appropriate R1, . . . , RH, linearity can be improved. In addition, the parameter p
, p, and q must be determined experimentally in advance.

Although the above two equations are difficult to solve analytically, they can be solved approximately as follows.

Since the amplification factor G depends on the luminous flux, G at low luminous flux is set to 60
Then, the amplification factor G is G=G, (1+△G(φl/Go) --・(5
1, and the second term on the right side, which depends on the luminous flux, is ΔG/
G is the deviation from linearity as a detector. ΔG/
From equation (2), G is as follows. Also, from equation (4), △V1+...+ΔVs-R+・△L+-+RN・ΔI
N:0.

Here, R1=R2-...=RN-, =R, FIN≠
Let R be the value of the current flowing through the resistor when the luminous flux is low. Then, equation (6) becomes...(7) If Rs/R=x, -ΔIN=lN, -
Since Δl1=11, ΔG/Go=[p・x−q・(X−tll−fzs/I
ol+q・fit/ro).

Since 11 is usually smaller than i and l, it is sufficient to consider ignoring the second term on the right side and setting only the first term on the right side to O. In other words, if the resistance at the final stage is selected as x=q/(p-q) (8) for the parameters p and q of the photomultiplier tube, linearity will be improved.

The inventor used a spectrophotometer (Hitachi U-3400) to investigate the linearity of the R928 photomultiplier tube manufactured by Hamamatsu Photonics, which is often used in spectrophotometers, and found that p = 0.
．． 7, q was found to be close to 0.2. Using this value, it can be seen from equation (8) that the linearity is better at x40.4.

The parameters b, p, and q are said to depend on the material of the photomultiplier tube, the applied voltage, the focusing state of light, etc., and must be determined empirically through experiments.

Next, numerical calculation results obtained when equation (4) is solved simultaneously are shown together with comparative examples using commercially available spectrophotometer settings. In Table 1, ΔT represents the maximum amount that must be corrected due to detector nonlinearity when transmittance T is measured.

Note that the parameter values are based on the R928 photomultiplier tube (Hamamatsu Photonics), which is normally used in spectrophotometers.
The value orange is assumed to be close to b・0.1, based on the experimental results of examining the nonlinearity of the output. p=0.69゜q=0.
It is set at 17. Also, the output current value is 18·l+.

- 1.2 μA, assuming that the dividing resistor is 10 stages in series.

■ in Table 1 is a numerical calculation of the resistance used in a commercially available spectrophotometer for comparison, but the experimental value of ΔT is thicker than the value in the table (Table 1 ■RI= -=R, when 0=330Ω (commercially available spectrophotometer setting value) Voltage (Vl 200 300 400Δmin(%l 0.18 0.17 0.13 ■R,
=...”If R*=150 is Ω, R1゜=50 is Ω, voltage (Vl 200 300 400
ΔD (%l O,000, old 0.O1■R,=
-=R,=1.50Ω, R9”RI.=10Ok
For Ω, voltage (Vl 200 300 4
00△T(%l -0,010,020,02■R+
”...: Ω to R7-150, Ω to R5-150, R,
= 150Ω.

RIO: Voltage (Vl 200' 300 400△T
(%l -0,010,020,03200v 0.
There are about 23. This is due to the inaccuracy of the parameters used. As shown in ■ in Table 1, the simplest method is to lower the resistance of the final stage, and it is possible to significantly lower the correction amount △T. It is also possible to improve the linearity over a fairly wide range of voltages by combining several resistors.

Although it is possible to improve linearity by nearly an order of magnitude by simple calculations as shown in Table 1, if the parameters cannot be obtained accurately or if you want to improve linearity even further, use numerical values. The value of resistance obtained from calculations can be fine-tuned experimentally.

Next, as an example, equation (4) is solved strictly by numerical calculation, and based on the result, from R1 to R in FIG.
By using a resistor whose resistance value is equal to 150Ω-, RI
A high-precision resistance socket in which only O is set to 61Ω resistance was fabricated as a prototype, and the experimental results are shown when this was applied to an R928 photomultiplier tube manufactured by Hamamatsu Photonics.

In the experiment, a new U-3400 spectrophotometer manufactured by Hitachi was used to compare the performance of a commonly used resistance socket and a prototype high-precision resistance socket.

Table 2 shows a comparison of the calibration values of the Nl5T 930D standard filter and the respective transmittance measurements.

Table 2 (nm) 440 465546.1590 63
5 Conventional socket 30.22 33.57 3
2.59 30.18 30.92 Difference with NIST -0,17-0,32-0,23-0,19-0
, 21 improved socket 30.39 33.78
32.83 30.39 31.35 Difference with NIST 0.00 -0.01 0.01
0゜02 0.02 As seen from Table 2, with a filter with a transmittance of 30%, the accuracy improves by about one order of magnitude, and it becomes 0.0
It agrees with the calibration value within 2%. In addition, using a high-precision spectrophotometer from the Institute of Metrology, Agency of Industrial Science and Technology, the output current value
When linearity was investigated by examining the additivity of light at μA and an applied voltage of 200 V, the calibration value of transmittance was 0.01.
It was found that it was within %.

In this way, the linearity of the photomultiplier tube as a detector can be improved by changing at least some of the resistances, and from calculations, one of the simplest methods is to change the resistance of the final stage. However, the optimum value of the resistance to be changed is not limited to that described above.

[Effects of the Invention] As detailed above, according to the method of the present invention, by simply improving the method of applying voltage between the electrodes in a photomultiplier tube, linearity as a detector is improved, and photomultiplier It becomes possible to use the tube with high precision.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a voltage dividing circuit for a photomultiplier tube to which the present invention is applied. Designated Agent Director, Metrology Research Institute, Agency of Industrial Science and Technology -＼： Osamu Hattori - -・-2■- Figure 1 V

Claims (1)

[Claims] 1. In a voltage dividing circuit for a photomultiplier tube used as a detector, the voltage between each dynode between the cathode and anode is determined by providing a resistor between the cathode and each dynode and connecting the resistors in series. The linearity of the response in the photomultiplier tube is improved by applying the voltage by connecting the photomultiplier tube and controlling the voltage by using at least some of the resistors with different resistance values. A method for improving the linearity of photomultiplier tubes.