JPS6261905B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal fluorescence dose reading device (hereinafter referred to as a TLD reader), and more specifically, a sensitivity detection and correction mechanism for automatically calibrating sensitivity and correcting sensitivity over time. It concerns a TLD reader with

When some types of phosphors are heated after being exposed to radiation, they emit thermal fluorescence (TL) that is proportional to the amount of radiation exposure.
emits. Thermal fluorescent dosimeter (TLD) takes advantage of this property, and consists of a thermal fluorescent dosimeter element (hereinafter referred to as TLD) made by molding a phosphor into an appropriate shape.
The TLD element that has been exposed to radiation is heated by the TLD reader, and the TL generated at that time is received by a photoelectric conversion element such as a photomultiplier tube. After photoelectric conversion, the exposure amount corresponding to this TL amount is displayed on the TLD reader in analog or digital form.

FIG. 1 is a block diagram showing an example of the circuit configuration of a conventional TLD reader.

In the TLD reader shown in FIG. 1, the TLD element 2 that has been exposed to radiation is first heated by a heating heater 3 provided on the sample stage 1.
The emitted TL is received by a photomultiplier tube 6 through a condensing lens 5, photoelectrically converted, and then amplified by an amplifier 8 and converted into a voltage. Then V-
The pulses are digitized by an F converter 9, counted by a counter 10, and displayed on a display 11. In this case, the TLD leader is TLD
In order to accurately display the amount of radiation that the element was exposed to,
Must be constantly calibrated. Therefore, when measuring a TLD element exposed to a known radiation dose, the TLD is designed to correctly display the exposure dose.
The reader needs to be adjusted (sensitivity calibrated).

This sensitivity calibration method uses a large number of TLD elements irradiated with a predetermined dose of radiation, and repeats this process so that the TLD reader displays this predetermined dose.
The task is to adjust the amplification of the TLD reader's electronic circuit and the voltage applied to the photomultiplier tube, and this work requires a great deal of time and effort.

Furthermore, even if the sensitivity is calibrated once, the sensitivity of the TLD reader may change due to changes in the sensitivity of the photomultiplier tube or the electric circuit system after photoelectric conversion over time. Sample stand 1
A standard light emitter 4, which is installed at If the values obtained by the measurements by the instrument 4 are compared and the two values are different, this means that the sensitivity has changed, and the sensitivity must be adjusted (sensitivity drift correction).

In this way, when calibrating the sensitivity of the TLD reader,
When measuring an element exposed to a known radiation dose,
The value displayed on the display 11 of the TLD reader is
TLD
High voltage power supply 7
The sensitivity of the TLD reader was adjusted by adjusting the voltage supplied to the photomultiplier tube 6 or by changing the gain of the amplifier 8, so the sensitivity adjustment operation was complicated. It was hot.

On the other hand, there is a thermal fluorescence dose reading device disclosed in Japanese Patent Application Laid-Open No. 53-63077 that automatically performs the above-mentioned sensitivity correction over time. Sensitivity correction for this device over time is performed by comparing the reference voltage value with the value obtained when measuring a light emitting device with a constant amount of light emission, and adjusting the sensitivity only when the relationship between these two values is within a predetermined range. This is done by storing the ratio of both values in a storage circuit, and then multiplying the actual value obtained by subsequent measurement of the TLD element to be measured by the ratio stored in this storage circuit.

However, the reference voltage is an analog quantity, and the reference voltage generating device that outputs it is mainly formed of elements such as resistors, transistors, and ICs whose characteristics change due to heat and aging. Therefore, it is difficult for a reference voltage generator formed from these elements to always output a constant reference potential.

In view of the above circumstances, an object of the present invention is to provide a TLD reader that can automatically perform sensitivity calibration in a short time, which conventionally requires a lot of time and effort, and can always accurately and automatically correct sensitivity changes over time. That is.

The TLD reader of the present invention includes a heating section that heats a thermal fluorescent dosimeter element, a standard light emitter that always emits a constant amount of light, a thermal fluorescent light emitted from the thermal fluorescent dosimeter element, and a standard light emitter that emits a constant amount of light. A photoelectric converter that converts the amount of light into a first electric signal, a dose information input means that outputs a second electric signal corresponding to a predetermined dose, and a value of the second electric signal and irradiation of the predetermined dose of radiation. a calculation means for calculating a calibration constant that is a ratio of the first electrical signal obtained when heating the reference thermal fluorescence dosimeter element to a reference value; a storage device for storing this calibration constant; and the reference value. a first storage means for storing an initial value of the first electric signal obtained by photometrically measuring the standard light emitter immediately before or after obtaining the initial value; The first photometer obtained by photometry of the standard light emitter immediately before photometry of the thermal fluorescence dosimeter element.
calculation means for calculating a drift correction coefficient which is the ratio of the electrical signal to the temporal value of the electric signal; a second storage means for storing the drift correction coefficient; The present invention is characterized by comprising a calculation means for multiplying the actual measured value of the electrical signal by the calibration constant and the drift correction coefficient, and a display device for displaying the output of the calculation means.

Note that the electrical signals obtained by photometry of the TLD element and the standard light emitter are converted into digital signals that are unaffected by external factors such as heat and aging, and then processed.

In this way, in the TLD reader of the present invention, a large number of reference TLD elements irradiated with a predetermined dose are used to repeatedly adjust the amplification degree of the electric circuit and the voltage applied to the photomultiplier tube so as to display the predetermined dose. Adjust the sensitivity calibration work to the value of the electrical signal corresponding to a predetermined dose and the reference TLD irradiated with a predetermined dose.
The ratio of the electric signal obtained by photometry of the element to the reference value is calculated, this is stored in the storage device as a calibration constant, and this calibration constant is automatically applied to the actual value of the electric signal obtained by photometry of the TLD element to be measured. In order to display an accurate dose by multiplying by

In addition, in the sensitivity drift correction that is performed when the amplification degree of the electric circuit and the characteristics of the photomultiplier tube change over time, manual work to change the amplification degree of the electric circuit and the voltage applied to the photomultiplier tube is performed as described above. The initial value of the electric signal obtained by photometry of a standard light emitter with a constant luminescence amount immediately before or after photometry of a standard TLD element irradiated with a predetermined dose (during sensitivity calibration), and the The ratio of the electrical signal obtained by photometry using this standard light emitter, which is performed immediately before photometry of the TLD element to be measured, to the elapsed value is calculated and stored in the storage device as a drift correction coefficient. Since the actual measured value of the electrical signal thus obtained is automatically multiplied by this drift correction coefficient, manual correction work is not required and accurate correction can always be performed.

In addition, since the initial value and the elapsed value for calculating the drift correction coefficient are obtained by the same photoelectric conversion system, and the initial value is obtained at the time of sensitivity calibration, the elapsed time correction can always be performed absolutely, easily and accurately. be able to.

Furthermore, since the configuration is such that the drift correction coefficient is calculated by obtaining the elapsed value immediately before the measurement of the TLD element under test, the drift correction coefficient is updated every time the measurement of each TLD element under test is performed, and as a result, each measurement is performed in a short time. It is also possible to sufficiently cope with changes over time in a short period of time when measurements are performed at home, and the reliability of each measurement can be improved.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing the circuit configuration of the TLD reader of the present invention.

On a slidable sample stage 1, a heater 3 for heating the TLD element and a standard light emitter (hereinafter simply referred to as a light emitter) 4 that always emits a constant amount of light are placed at different positions. TLD exposed to radiation
The element 2 is heated by a heater 3, and the fluorescent light emitted from the TLD element 2 at that time is photoelectrically converted by a photoelectric conversion element (photomultiplier tube) 6 via a lens 5. 7 is a high voltage power supply that supplies voltage to the photomultiplier tube 6. The output of the photomultiplier tube 6 is led to an amplifier 8 and converted into a voltage signal, which is then digitized by a voltage frequency converter (VF converter) 9 and counted by a counter 10. Counter 10
The counted value proportional to the integrated value of the amount of fluorescence from the TLD element is input to the microcomputer 11, where it is multiplied by various calibration constants stored in advance and then displayed on the display 13. .
Reference numeral 12 denotes an operation key which is a dose information input means for inputting various information into the microcomputer 11 from the outside in advance.

When calibrating the sensitivity of the TLD reader of the present invention, the reference TLD element 2 is irradiated with a known dose [Z] using a reference radiation source, and the operation key 12 is used to confirm that the irradiation dose is [Z]. After inputting to the computer 11, this TLD element 2 is measured with a TLD reader. The light emitted from the reference TLD element 2 is digitized after photoelectric conversion, and
0, the reference value [X] at the counter 10 is input to the microcomputer 11, where the sensitivity calibration constant [Y] (= [Z]/[X]) is immediately calculated. The counted reference value [X] is multiplied by the sensitivity calibration constant [Y] and displayed on the display 13 as the exposure dose of the TLD element 2. At this time, the sensitivity calibration constant [Y] calculated by the microcomputer 11 is stored in the microcomputer 11 unless some instruction is given from the outside or the sensitivity calibration operation is performed again according to the above procedure. When measuring a TLD element 2 whose exposure dose is unknown, the actual measurement value [X'] counted by the counter 10 is multiplied by the sensitivity calibration constant [Y] to make corrections, and then the exposure dose of that TLD element is calculated. Is displayed.

Furthermore, in order to know the sensitivity of the photoelectric conversion element 6 of the TLD reader and changes in the sensitivity of the TLD reader due to changes over time in the electrical circuit system after the photoelectric converter, a sensor is installed at one end of the sample stage 1, similar to the conventional TLD reader. In addition, the light emitted from the light emitter 4 that emits light with a constant intensity is measured for a certain period of time and the integrated value of the light intensity is constantly monitored. However, with the TLD reader of the present invention, even if the sensitivity changes over time, the measurement is possible. Sensitivity drift correction is performed so as not to affect the value (so that the overall sensitivity of the TLD reader remains unchanged).
To correct the sensitivity drift, first, immediately before or after storing the sensitivity calibration constant [Y] obtained by the sensitivity calibration of the TLD reader in the microcomputer 11, the light emitter 4 is placed directly below the photomultiplier tube 6. The light emitted from the light emitter 4 is received by the photomultiplier tube 6, and thereafter, the light is measured for a certain period of time through the same electric circuit system as when measuring the TL from the TLD element 2, and the initial value [X _CAL ] is counted by the counter 10. is led to the microcomputer 11 and stored, and this value [X _CA
L ] is stored together with the [Y] value until the sensitivity calibration constant [Y] is changed.

After a certain period of time has elapsed, when measuring the TLD element 2 to be measured, the amount of light from the light emitter 4 is measured again, and the elapsed value [X′ _CAL ] is counted by the counter 10 at that time.
is guided by the computer 11, and the ratio _{( [} X _CA
L ]/[X′ _CAL ]) is calculated and stored as a sensitivity drift correction coefficient ([A]). After this, when the TLD element to be measured is measured with this TLD reader, the TL from this TLD element is photoelectrically converted and digitized, and after being counted by the counter 10, the actual measured value is first transferred to the microcomputer 1.
1 and is displayed on the display 13 after being multiplied by the sensitivity calibration constant [Y] and the drift correction coefficient [A].

Note that the initial value [X _CAL ] of the amount of light emitted from the light emitter 4 measured when calculating the above calibration constants [Y] and [Y] is once stored in the microcomputer 11 and used to calculate the calibration constant [Y]. It will not be erased until it is repaired, but if the light emitter 4 is placed directly below the photomultiplier tube 6 and the light intensity of the light emitter 4 can be measured, the light emitter 4 will be erased at regular intervals.
The emitted light is measured for a certain period of time, and the counted value [X'' _CAL ] counted by the counter 10 at that time is input to the microcomputer 11, replacing the previously stored elapsed value [X' _CAL ]. The newly stored result is the drift correction coefficient [A] ([X _CAL ]/
[X′ _CAL ] changes to ([X _CAL ]/[X″ _CAL ]).In this way, once the sensitivity is calibrated,
Even if the sensitivity of the photoelectric conversion element and electric circuit system changes over time, the TLD reader will eventually
The sensitivity of the TLD reader when measuring the TLD element is automatically adjusted to be the same as during calibration.

In addition, the sensitivity of TLD elements differs depending on the type and shape of the phosphor used in the element, so
Even when exposed to the same dose of radiation, if the type and shape of the phosphor used in the TLD element differs,
The amount of TL differs, and even if TLD elements of the same shape are manufactured using the same phosphor, the sensitivity will differ due to processing precision, etc.
The microcomputer 11 calculates the sensitivity calibration constant [Y] for each TLD element.
If you specify which TLD element to measure at the time of measurement using the operation key 12, etc., you will not have to perform complicated corrections of measured values for each TLD element with different sensitivities. It disappears.

In addition, in the TLD reader of the present invention, the various data stored in the memory section of the microcomputer 11 is provided with a built-in backup battery so that it will not be erased when the TLD reader is turned off or during a power outage, so that the data is not erased at all times. The operability and reliability of this TLD reader will be improved if it is held in this position.

As explained in detail above, TLD according to the present invention
In the past, the sensitivity calibration process of the reader required a lot of time and effort to manually adjust the amplification of the electric circuit and the voltage applied to the photomultiplier tube, but the sensitivity calibration work was performed using information input from outside and the photometry of the reference TLD element. Calibration constants are automatically determined based on the reference values provided.
Calibration is performed by automatically multiplying the actual measured value obtained by photometry of the TLD element under test by this calibration constant, eliminating the need for a circuit for sensitivity calibration, which greatly simplifies the circuit configuration and reduces manufacturing costs.
In addition, to compensate for sensitivity changes due to drift, which is a change in the characteristics of an electrical circuit over time, a standard light emitter is used to automatically determine the drift correction coefficient.
Since the actual value obtained by photometry of the TLD element is automatically multiplied and corrected, there is no need to manually correct the characteristics of the electric circuit in the electric circuit, which was required in the past, improving operability. In addition, the calibration constant of each TLD element to be measured is memorized even in the sensitivity correction of individual TLD elements with different sensitivities, and the calibration constant corresponding to the TLD element to be measured is selected from the dose information input means at the time of measurement.
Since the actual measurement value obtained by photometry of the TLD element is automatically multiplied and corrected, the voltage applied to the photomultiplier tube can be changed or the amplification factor can be changed depending on the type of TLD element with different sensitivity, which was previously required. There is no need to incorporate an extra switching circuit to change the sensitivities, and the complexity of the circuit configuration and decrease in accuracy when measuring TLD elements with greatly different sensitivities or a large number of TLD elements with different sensitivities can be improved. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one circuit configuration of a conventional TLD reader, and FIG. 2 is a block diagram showing one embodiment of the present invention. 1... Sample stage, 2... TLD element, 3... Heater, 4... Standard light emitter, 5... Lens,
6...Photomultiplier tube, 7...High voltage power supply, 8...Amplifier, 9...Voltage frequency converter, 10...Counter, 11...Microcomputer, 12...
Operation keys, 13...Display.

Claims (1)

[Claims] 1. A heating unit that heats a thermal fluorescence dosimeter element, a standard light emitter that always emits a constant amount of light, and a first electrical A photoelectric converter for converting into a signal, a dose information input means for outputting a second electric signal corresponding to a predetermined dose, a value of the second electric signal and a reference thermal fluorescent beam irradiated with the predetermined dose of radiation. The first amount obtained when the metering element is heated.
a calculation means for calculating a calibration constant which is the ratio of the electric signal of 1 to a reference value; a storage device for storing this calibration constant; a first storage means for storing an initial value of an electric signal, and a first storage means for storing an initial value of an electric signal obtained by photometry of the standard light emitter immediately before photometry of a thermal fluorescence dosimeter element to be measured that has been irradiated with an arbitrary dose of radiation; a calculation means for calculating a drift correction coefficient which is a ratio of the first electrical signal to the temporal value of the first electrical signal; a second storage means for storing the drift correction coefficient;
A calculation means for multiplying the actual measured value of the first electric signal obtained by photometry of the thermal fluorescence dosimeter element to be measured by the calibration constant and the drift correction coefficient, and a display device for displaying the output of the calculation means. A thermal fluorescence dose reading device characterized by the following.