JP2008123767A - Photomultiplier tube, light measurement method, and device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow measurement of very weak light with reliability even if sensitivity of a photomultiplier tube changes due to aging or in temperature at measurement. <P>SOLUTION: Since the sensitivity characteristics of a photomultiplier tube 1 changes as time elapses, after a certain time has elapsed since initial calibration, a switch 16 is turned on to heat a heater 14, so that the temperature of the photomultiplier tube 1 is forcedly changed. The photomultiplier tube 1 is irradiated with a reference light from a reference light source 22; a photocount value is acquired with a counter 6, and a sensitivity change rate per unit temperature of the photomultiplier tube is calculated to calibrate the photomultiplier tube. With such a configuration, even if the sensitivity of the photomultiplier tube changes due to aging, reliable measurements of very weak light can be made. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photomultiplier tube that detects weak light from an object to be measured and outputs a measurement value, and an optical measurement method and apparatus that measures the light intensity from the object to be measured using the photomultiplier tube.

  A photomultiplier tube performs photocounting of incident faint light, and can accurately measure the intensity of the faint light incident from the count value. For example, the photomultiplier tube is used in a fine particle measuring apparatus or an ophthalmic measuring apparatus.

  In such a measuring device that needs to detect the intensity of weak light, the number of output pulses (signal pulses) per unit time included in the output signal of the photomultiplier tube that has received weak light is the number of photons of the incident light. The intensity of faint light is measured by a photon counting method that counts as if it were. The counted number of output pulses is also referred to as a photocount value. The output pulse is identified by cutting the noise component by binarizing the output signal obtained by current / voltage conversion and amplification of the output current of the photomultiplier tube with the threshold voltage.

  However, the sensitivity (= count value / weak light intensity) of the photomultiplier tube changes depending on the temperature environment. As an example, when the ambient temperature changes by -0.3% / ° C., that is, by 1 ° C., the count value changes by 0.3% even if light of the same intensity is measured. That is, when the environmental temperature increases by 10 degrees, the measured value changes by about 3%.

  Therefore, if the ambient temperature is not taken into account, it is impossible to suppress the measurement error to 3% in a use environment of 10 to 40 degrees, for example. As a countermeasure, the temperature of the photomultiplier tube is always measured, the photomultiplier tube sensitivity is corrected from the photomultiplier tube temperature, and the sensitivity is applied to the result of the measured value. Is usually performed (see, for example, Patent Documents 1 to 4 below).

  Therefore, the “temperature sensitivity change rate = sensitivity change rate / temperature” of the photomultiplier tube is measured in advance, stored in the measuring instrument, and the stored value is read out at the time of measurement, and the measured value is corrected. Yes.

  However, there is an individual difference in the sensitivity change rate of the photomultiplier tube, for example, the sensitivity change rate is -0.1% / ° C or -0.8% / ° C, and this individual difference is small in measurement accuracy. It has an influence. Therefore, in order to correct the measurement value obtained using the photomultiplier tube, it was necessary to measure the “sensitivity change rate” in advance for each photomultiplier tube.

  Furthermore, there is no guarantee that this coefficient “sensitivity change rate / temperature” will not change over a long period of time, that is, it will change over time, so if you want to make an accurate measurement, periodically obtain “sensitivity change rate / temperature” again. There is a problem of having to. For example, periodically (for example, once a year), the photomultiplier tube (unit) or the device that uses it is pulled up from the place of use, placed in a thermostat, etc., measured with the reference light, and again the coefficient It was necessary to rewrite “sensitivity change rate / temperature”.

  As a result, there were problems in the operation of the device for users and the burden of after-sales service.

  The present invention has been made to solve such a problem, and even when the sensitivity of the photomultiplier tube changes due to the temperature at the time of measurement or the change over time, the reliable weak light is not affected. It is an object of the present invention to provide a photomultiplier tube capable of measurement and a light measurement method and apparatus using the photomultiplier tube.

The present invention
A photomultiplier tube that detects weak light from an object to be measured and outputs a measured value,
A temperature adjusting means for changing the temperature of the photomultiplier tube is provided,
The rate of change in sensitivity per unit temperature of the photomultiplier tube can be calculated by changing the temperature of the photomultiplier tube by the temperature adjusting means.

The present invention also provides:
A light measurement method and apparatus for measuring light intensity from a measurement object using a photomultiplier tube that detects weak light from the measurement object and outputs a measurement value,
Providing a temperature adjusting means for changing the temperature of the photomultiplier;
Calculating the sensitivity change rate per unit temperature of the photomultiplier tube by changing the temperature of the photomultiplier tube by the temperature adjusting means;
From the relationship between the calculated rate of change in sensitivity per unit temperature and the amount of light incident on the photomultiplier tube determined from the ambient temperature of the photomultiplier tube at the time of measurement, and the measured value of the photomultiplier tube, the light intensity from the object to be measured It is characterized in that a value indicating is calculated.

  In the present invention, since the sensitivity change rate per unit temperature of the photomultiplier tube can be easily obtained, it is possible to calculate a value indicating the intensity of weak light from the object to be measured in consideration of the sensitivity change rate, Even in the case where the sensitivity of the photomultiplier tube changes due to the temperature at the time of measurement or changes with time, it is possible to measure weak light with reliability.

  Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

  FIG. 1 shows a configuration of a light measurement device that measures the intensity of weak light from a measurement object. The light measuring device 8 is used in a fine particle measuring device or the like, and outputs the intensity of weak scattered light from the measurement object 24, for example, fine particles, as a photocount value.

  The photomultiplier tube 1 is disposed in the main body (housing) 9 of the light measuring device 8, and an objective lens 10, a mirror 11, a diaphragm 12, and the like are disposed on the photocathode (cathode) of the photomultiplier tube 1. The weak measurement light from the object to be measured 24 enters through the condensing optical system consisting of

  A pulse current corresponding to the intensity of the measurement light is output from the photomultiplier tube 1, converted into a pulse-shaped output signal by the current / voltage conversion and amplification circuit 3, and input to the pulse binarization circuit 4. . The pulse binarization circuit 4 compares the voltage of the output signal from the photomultiplier tube with a threshold voltage, and if it is lower than the threshold voltage, it is regarded as a noise component and cut as “0”, and if higher, the signal component The pulse signal is output as “1”.

  The pulse signal from the pulse binarization circuit 4 is input to the pulse number counter 6. The counter 6 is configured by software executed by a CPU (not shown) or by dedicated hardware, and counts the number of output pulses per unit time. The count value is also called a photocount value, and indicates the intensity of measurement light from the object to be measured 24. Then, the count value is corrected and calculated by an arithmetic circuit (arithmetic unit) 19 to be described later, and displayed as a measurement result on a display unit (monitor) 7 including a liquid crystal display device.

  As shown in FIG. 2, the photomultiplier tube 1 is attached to a socket 1a and is disposed in a housing 2 having an opening 2a for guiding measurement light. The photomultiplier tube 1, the socket 1a, the housing A photomultiplier tube unit is constituted by the body 2 and the like.

  By the way, the sensitivity (photocount value / light reception amount) of the photomultiplier tube 1 varies depending on the temperature, and therefore the measurement value is affected. The sensitivity of the photomultiplier tube changes due to the influence of the ambient temperature where the photomultiplier tube is installed, and the temperature constantly fluctuates due to the heat generated by the photomultiplier tube itself even during startup of the device. The sensitivity of the multiplier varies.

  In this embodiment, a temperature sensor 15 is detachably attached to the housing 2 of the photomultiplier tube 1 for calibrating the photomultiplier tube, and the temperature of the photomultiplier tube 1 is forcibly changed. Therefore, a heat source as a temperature adjusting means is detachably attached to the housing 2 of the photomultiplier tube 1. This heat source is realized, for example, as a heater 14 and can be turned on and off by a switch 16.

  Now, let us consider calibration of a photomultiplier tube unit that is considered to be measured in an environment of 10 ° C. to 40 ° C. At the time of this calibration, in FIG. 1, instead of the measurement light from the object to be measured 24, reference light from the reference light source 22 having an output of about 10 nW made of LED or the like is made incident on the light measurement device 8, and this is increased by photoelectron amplification. Light is received by the double tube 1 and the photocount value is examined.

  First, at the time of manufacture of the photomultiplier tube unit or at the time of shipment from the manufacturer, the temperature of the photomultiplier tube unit is adjusted to 15 ° C. and 35 ° C. by adjusting with a constant temperature layer or the like. The photocount value when light is received is obtained. The result is illustrated in FIG.

The rate of change in sensitivity per unit temperature (sensitivity change rate / temperature) of the photomultiplier tube is the measured value (photocount value) when the ambient temperature of the photomultiplier tube 1 is changed from temperature 1 to temperature 2. Assuming that the measured value 1 has changed to the measured value 2, the sensitivity change rate calculating means 17 in FIG.
(Measured value 2-Measured value 1) / (Measured value 1) / (Temperature 2-Temperature 1)
Is calculated as

In the case of the measurement results shown in FIG. 3, the sensitivity change rate per unit temperature is
(90-110) / {(35 ° C.-15 ° C.) × 110} = − 0.9% / ° C.
It becomes. The calculated sensitivity change rate / temperature is stored in the storage device (storage means) 18 together with measurement parameters such as measurement value 2, measurement value 1, temperature 2, and temperature 1.

Next, the intensity of faint light from the object to be measured 24 is measured when the ambient temperature is 20 ° C. When the ambient temperature is 20 ° C., the sensitivity of the photomultiplier tube 1 changes. Therefore, the sensitivity characteristic is obtained at that temperature. At this time, if the sensitivity change rate / temperature obtained from FIG. 3 is unchanged,
(20 ° C.-15 ° C.) × (−0.9% / ° C.) × 110 + 110 = 105
Thus, the relationship (sensitivity characteristic) between the photocount value and the amount of received light at an ambient temperature of 20 ° C. as shown by the solid line in FIG. 4 is obtained.

  From this relationship, for example, when the photocount value of the pulse number counter 6 is C1, the light amount W1 is measured. The measured light quantity W1 can be obtained by the arithmetic circuit 19 using the ambient temperature measured by the temperature sensor 15 and the value stored in the storage device 18 in FIG.

  At the time of the first calibration described above, the obtained sensitivity change rate / temperature is −0.9% / ° C. When the sensitivity change rate / temperature is not changed, it is measured by the temperature sensor 15 as described above. Using the ambient temperature and the value stored in the storage device 18, the intensity of light from the object to be measured can be measured from the count value from the counter 6.

  However, it has been confirmed that when a predetermined time (for example, one year) elapses from the time of the first calibration, a change with time occurs in the photomultiplier tube 1 and the sensitivity characteristic at the measurement temperature changes.

Now, for example, assume that the temperature when measurement is performed after one year has passed since the first calibration is 25 ° C., and the rate of change in sensitivity / temperature is −0.9% / ° C. as in the first calibration. Then, the photocount value for the reference light amount is
(25 ° C.-15 ° C.) × (−0.9% / ° C.) × 110 + 110 = 100
Actually, however, as shown in FIG. 5, the photocount value with respect to the reference light amount is 95, which is different from the above value.

  This is considered that the rate of change in sensitivity per unit temperature of the photomultiplier tube has changed over time, and thus the measured value is also affected. Even if calibration is performed with the reference light amount every time measurement is performed, the temperature changes as it is between the end of calibration and before measurement.

  In addition, a method of uniformly correcting from the previous calibration result, for example, a method in which the photocount value is changed from 100 to 95 at 25 ° C. at this time, it is not suitable for a method of uniformly reducing each temperature by 5%. I understand. If the cause is that the photomultiplier tube sensitivity itself has deteriorated, the problem can be solved by determining that the temperature has been uniformly reduced by 5% at all temperatures. However, if the sensitivity change rate / temperature of the photomultiplier tube due to temperature change is not the cause, not the sensitivity deterioration of the photomultiplier tube, for example, there is no sensitivity decrease at a temperature of 15 ° C., and −5% sensitivity decrease at 25 ° C., 35 There may be a decrease in sensitivity of -10% at ℃.

  For this reason, since correct measurement becomes impossible after a certain period of time, when a predetermined time has elapsed since the first calibration, the sensitivity change rate / temperature of the photomultiplier tube is recalculated. Therefore, when a predetermined time has elapsed since the first calibration, the switch 16 is turned on to cause the heater 14 to generate heat, and the temperature of the photomultiplier tube 1 is forcibly changed to cause the photomultiplier tube 1 to be supplied with the reference light source 22. Then, the reference light is incident, and the rate of change in sensitivity / temperature is calculated by calculating the count value, and the photomultiplier tube unit is calibrated.

Specifically, when the second calibration is performed and the ambient temperature measured by the temperature sensor 15 is 25 ° C., as shown in FIG. 6, a photocount value 95 for the reference light amount 10 nW at that time is obtained. Thereafter, the switch 16 is turned on to operate the heater 14 to forcibly raise the temperature of the photomultiplier tube unit. When the temperature reaches an equilibrium state to some extent, the sensitivity change rate calculation means 17 in FIG. 1 obtains the temperature 45 ° C. of the photomultiplier tube 1 obtained by the temperature sensor 15 at that time and the pulse number counter 6 as shown by a one-dot chain line. From the photocount value 70 with respect to the obtained reference light amount, the rate of change in sensitivity per unit temperature,
(70-95) / {(45 ° C.-25 ° C.) × 95} = − 1.3% / ° C.
Is calculated. The calculated new sensitivity change rate / temperature is stored in the storage device 18 in the form of being overwritten with the previous one.

  Subsequent measurements are made using the new rate of sensitivity change / temperature. That is, feeble light from the object to be measured 24 is received by the photomultiplier tube 1, and the pulse number counter 6 outputs, for example, a photocount value C2. As shown in FIG. 7, the arithmetic circuit 19 assumes that the ambient temperature at the time of measurement from the temperature sensor 15 is 20 ° C., from this temperature and a new sensitivity change rate of −1.3% / ° C. read from the storage device 18. The measured light quantity W2 for the count value C2 is calculated from the sensitivity characteristic indicated by the solid line indicating the relationship between the light quantity at 20 ° C. and the photocount value. Then, the calculated measurement light amount is displayed on the display unit 7 as a value indicating the intensity of the weak light from the measurement object 24.

  In this way, by calibrating the photomultiplier tube every time a predetermined time elapses, even if the sensitivity of the photomultiplier tube changes, it is possible to reliably measure weak light. Become.

  In the above-described embodiment, the weak light from the object to be measured 24 is scattered light scattered from the fine particles by, for example, the fine particle measuring device, but the configuration of the light measuring device 8 is from the anterior chamber of the eye to be examined. The present invention can also be applied to an ophthalmic measurement apparatus that analyzes scattered light and performs ophthalmic measurements such as flare measurement and cell measurement. For example, in flare measurement, cells or proteins existing in the anterior chamber are irradiated with laser light, and scattered light scattered from the cells or proteins is applied to a photomultiplier tube having a configuration similar to that of the light measurement device 8 shown in FIG. The number of cells in the measurement volume in the anterior chamber is measured from the measured value (photocount value), and the protein concentration (flare value) is measured. Even in such a device, since the sensitivity change rate / temperature can be easily updated by periodically calibrating the device, it is reliable even when the sensitivity of the photomultiplier tube changes due to a change over time. Flare measurement is possible.

  In the above-described embodiment, the heater 14 is attached to the outside of the housing 2 or the photomultiplier tube unit that houses the photomultiplier tube itself, but is detachably attached to the inside of the housing 2. May be. Moreover, it can also arrange | position in the place which can change the temperature of a photomultiplier tube in the place away from the storage housing | casing 2 thru | or a photomultiplier tube unit.

  Further, the temperature adjusting means for changing the temperature of the photomultiplier tube may be an air conditioner in a room where the light measuring device 8 is installed, instead of a heat source such as the heater 14, and houses the entire light measuring device. It may be a temperature-controlled thermostat.

  The temperature sensor 15 for measuring the ambient temperature of the photomultiplier tube is not attached to the housing for the photomultiplier tube, but is disposed at a predetermined location around the photomultiplier tube where the temperature can be measured. May be.

  In the embodiment described above, the reference light is generated using the reference light source 22, but the reference light is generated using a normal light source and a filter having a predetermined density selected from a plurality of density filters. May be.

It is the block diagram which showed the structure of the optical measurement apparatus. It is explanatory drawing which showed the attachment state of the temperature sensor and heater in a photomultiplier tube unit. It is a graph explaining the method of calculating | requiring a sensitivity change rate / temperature. It is a graph which shows the relationship between the incident light quantity in the sensitivity change rate / temperature calculated | required in FIG. 3, and a photo count value. It is a graph which shows the shift | offset | difference of the photocount value when the sensitivity characteristic of a photomultiplier tube changes. It is a graph explaining the method of calculating | requiring the sensitivity change rate / temperature again when the sensitivity characteristic of a photomultiplier tube changes. It is a graph which shows the relationship between the incident light quantity in the sensitivity change rate / temperature calculated | required in FIG. 6, and a photo count value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photomultiplier tube 8 Light measuring device 14 Heater 15 Temperature sensor 17 Sensitivity change rate calculation means 18 Memory | storage device 19 Calculation circuit (calculation means)
22 Reference light source 24 DUT

Claims (17)

A photomultiplier tube that detects weak light from an object to be measured and outputs a measured value,
A temperature adjusting means for changing the temperature of the photomultiplier tube is provided,
A photomultiplier tube characterized in that the rate of change in sensitivity per unit temperature of the photomultiplier tube can be calculated by changing the temperature of the photomultiplier tube by the temperature adjusting means.   2. The photomultiplier tube according to claim 1, wherein the temperature adjusting unit is detachably attached to the inside or outside of the housing of the photomultiplier tube. 3.   2. The photomultiplier tube according to claim 1, wherein the temperature adjusting means is disposed outside a housing for the photomultiplier tube.   The temperature adjusting means is a heat source for heating the photomultiplier tube, and changes in temperature of the photomultiplier tube when the heat source is turned on, and a photomultiplier tube that receives the reference light from the reference light source when the heat source is turned off and on The photomultiplier tube according to any one of claims 1 to 3, wherein a rate of change in sensitivity per unit temperature is calculated based on the measured value.   The photomultiplier tube according to any one of claims 1 to 4, wherein a temperature sensor for measuring an ambient temperature of the photomultiplier tube is attached to a housing of the photomultiplier tube. A light measurement method for measuring light intensity from a measurement object using a photomultiplier tube that detects weak light from the measurement object and outputs a measurement value,
A temperature adjusting means for changing the temperature of the photomultiplier tube is provided in the photomultiplier tube,
Calculate the rate of change in sensitivity per unit temperature of the photomultiplier tube by changing the temperature of the photomultiplier tube with the temperature control means,
From the relationship between the calculated rate of change in sensitivity per unit temperature and the amount of light incident on the photomultiplier tube determined from the ambient temperature of the photomultiplier tube at the time of measurement, and the measured value of the photomultiplier tube, the light intensity from the object to be measured A light measurement method characterized by calculating a value indicating   The optical measurement method according to claim 6, wherein the temperature adjusting means is detachably attached to the inside or outside of the housing of the photomultiplier tube.   The light measuring method according to claim 6, wherein the temperature adjusting means is disposed outside a housing of the photomultiplier tube.   The temperature adjusting means is a heat source for heating the photomultiplier tube, and changes in temperature of the photomultiplier tube when the heat source is turned on, and a photomultiplier tube that receives the reference light from the reference light source when the heat source is turned off and on The light measurement method according to claim 6, wherein a rate of change in sensitivity per unit temperature is calculated based on the measured value.   10. The light measurement method according to claim 6, wherein a temperature sensor for measuring the ambient temperature of the photomultiplier tube is attached to the housing for the photomultiplier tube.   The light measurement method according to claim 6, wherein the sensitivity change rate per unit temperature is calculated every elapse of a predetermined time. A light measurement device that measures light intensity from a measurement object using a photomultiplier tube that detects weak light from the measurement object and outputs a measurement value,
Temperature adjusting means for changing the temperature of the photomultiplier;
A calculation means for calculating a sensitivity change rate per unit temperature of the photomultiplier tube by changing the temperature of the photomultiplier tube by the temperature adjusting means;
From the relationship between the calculated rate of change in sensitivity per unit temperature and the amount of light incident on the photomultiplier tube determined from the ambient temperature of the photomultiplier tube at the time of measurement, and the measured value of the photomultiplier tube, the light intensity from the object to be measured Computing means for computing a value indicating
A light measuring device comprising:   13. The optical measurement apparatus according to claim 12, wherein the temperature adjusting means is detachably attached to the inside or outside of the housing for the photomultiplier tube.   13. The light measuring device according to claim 12, wherein the temperature adjusting means is disposed outside a housing for the photomultiplier tube.   The temperature adjusting means is a heat source for heating the photomultiplier tube, and changes in temperature of the photomultiplier tube when the heat source is turned on, and a photomultiplier tube that receives the reference light from the reference light source when the heat source is turned off and on The optical measurement apparatus according to claim 12, wherein a rate of change in sensitivity per unit temperature is calculated based on a measured value of the above.   16. The light measuring device according to claim 12, wherein a temperature sensor for measuring an ambient temperature of the photomultiplier tube is attached to a housing for the photomultiplier tube.   The optical measurement apparatus according to claim 12, wherein the sensitivity change rate per unit temperature is calculated every elapse of a predetermined time.

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