JPH059753B2 - - 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 particularly to a TLD reader equipped with a correction mechanism for automatically correcting sensitivity over time. It is.

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, which is 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 reader is adjusted (sensitivity calibration) to display the irradiation dose correctly.

However, 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 electrical circuit system after photoelectric conversion over time, so it is necessary to monitor these changes in sensitivity. Therefore, a light emitter 4 installed on the sample stage 1 that always emits light with a constant amount of light is guided directly below the photomultiplier tube 6 to measure the amount of light emitted, and the value and sensitivity obtained by this measurement are During calibration, the values obtained by measuring the light emitter 4 are compared, and if these two values are different, this means that a change has occurred in the sensitivity, so the sensitivity must be adjusted (sensitivity drift correction).

In this way, when the TLD reader experiences a sensitivity drift, the high-voltage power supply 7 is adjusted by manually turning the sensitivity correction variable volume installed in the TLD reader each time. Since the sensitivity of the TLD reader was adjusted by changing the voltage supplied to the TLD reader or by changing the gain of the amplifier 8, there was a problem in that the sensitivity adjustment operation was complicated. Therefore, instead of manually correcting the changes in the TLD reader over time, we have developed a system that uses a calibration light source that emits a constant amount of light to detect changes in the sensitivity of the measurement system and compensates for changes in measured values due to changes in the TLD reader's components over time. A TLD reader equipped with a
There is still the inconvenience of having to set it in a TLD reader and calibrate changes over time, and an improvement has been desired.

In view of the above circumstances, it is an object of the present invention to provide a TLD reader that can always accurately and automatically correct sensitivity changes over time.

Thermal fluorescence dose reading device (TLD reader) of the present invention
consists of a slidable sample stage on which a thermal fluorescence dosimeter element is placed, a heating section that heats the thermal fluorescence dosimeter element, and a constant amount of light emitted at a position different from the heating section. a standard light emitter having: a photoelectric converter that converts thermal fluorescence emitted from the thermal fluorescence dosimeter element into a first electrical signal; and dose information that outputs a value of a second electrical signal corresponding to a predetermined dose. input means, the ratio of the value of the second electrical signal to the reference value of the first electrical signal obtained when heating the reference thermal fluorescence dosimeter element irradiated with the predetermined dose of radiation; A calculation means for calculating a calibration constant, a storage device for storing this calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating a calibration constant, and a calculation means for calculating the calibration constant, and a calculation means for calculating the calibration constant. A thermal fluorescence dose reading device comprising a display device that displays the product of a first electrical signal and an actual measurement value, the first electrical signal obtained by photometry of the standard light emitter immediately before or after obtaining the reference value. a calculation means for calculating a correction coefficient consisting of the product of the initial value of the electric signal and the calibration constant;
storage means, a second storage means for storing the temporal value of the first electric signal obtained by photometrically measuring the standard light emitter immediately before the measurement of the thermal fluorescence dosimeter element to be measured; Multiplying the actual measured value of the first electric signal obtained by photometry of a fluorescent dosimeter element by the correction coefficient stored in the first storage means, and the elapsed value stored in the second storage means. and inputting the calculated value to the display device, and when the measurement target thermal fluorescence dosimeter element is not being measured, the standard light emitter and the photoelectric converter face each other. The present invention is characterized in that the amount of light from the standard light emitter is automatically measured at regular intervals by sliding the sample stage, and the value over time is updated one after another.

Note that the electrical signals obtained by photometry of the TLD element and the standard light emitter are converted into digital signals that are not affected by external factors such as heat and aging, and then processed. Further, the above-mentioned correction coefficient is obtained by simultaneously obtaining a calibration constant and multiplying this calibration constant by the above-mentioned initial value.

In this way, in the TLD reader of the present invention,
Sensitivity drift correction, which is performed when the amplification degree of the electric circuit and the characteristics of the photomultiplier tube change over time, can be performed instead of the manual work of changing the amplification degree of the electric circuit and the voltage applied to the photomultiplier tube. The initial value of the electrical signal obtained by photometry of the standard light emitter with a constant luminescence amount installed in the TLD reader immediately before or after photometry of the reference TLD element irradiated with the above prescribed dose (during sensitivity calibration) and the above-mentioned calibration constant, and the time-lapse value of the electrical signal obtained by the photometry of this standard light emitter, which is performed immediately before the photometry of the TLD element under test that has been irradiated with an arbitrary dose (this value is (automatically updated at regular intervals while the TLD element is not being measured) are stored separately in the storage device, and the actual measured value of the electrical signal obtained by photometry of the TLD element to be measured. is multiplied by the correction coefficient stored in the storage device and divided by the elapsed value to automatically correct the drift of the measurement system. Therefore, manual correction work is not required and accurate correction can always be performed.

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

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

A slidable sample stage 1 is equipped with a heater 3 for heating the TLD element and a light emitter 4 that always emits a constant amount of light.
are placed in different positions. The TLD element 2 exposed to radiation is heated by the heater 3,
At this time, the fluorescent light emitted from the TLD element 2 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 (V-F converter) 9 and counted by a counter 10. The count value proportional to the integral value of the amount of fluorescence from the TLD element counted by the counter 10 is input to the microcomputer 11, where it is multiplied by various calibration constants stored in advance, and then displayed on the display 13.
will be displayed. 12 is microcomputer 1
1 is an operation key which is a dose information input means for inputting various information from the outside in advance.

When correcting the sensitivity change over time 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,
After inputting that the irradiation dose is [Z] into the microcomputer 11 using the operation key 12,
Measure this TLD element 2 with a TLD reader. The light emitted from the reference TLD element 2 is photoelectrically converted and digitized, counted by a counter 10, and the reference value [X] at the counter 10 is inputted to the microcomputer 11, where it is immediately converted into a sensitivity calibration constant [Y] ( =
[Z]/[X]) is calculated, and immediately before or after obtaining this sensitivity calibration constant [Y], the sample stage 1 is slid to place the light emitter 4 directly under the photomultiplier tube 6, and the light emitter 4 is The emitted light is received by a photomultiplier tube 6,
After that, photometry is carried out for a certain period of time through the same electric circuit system as when measuring TL from TLD element 2, and counter 10
The initial value [X _CAL ] counted by is led to the microcomputer 11, where the initial value [X _CAL ]
The above-mentioned calibration constant [Y] calculated in advance as
A correction coefficient [X _CAL・Y] consisting of the product of is memorized and saved in the microcomputer 11.
Furthermore, when measuring the TLD element 2 to be measured after a certain period of time has elapsed, just before that, the sample stage 1 is slid to move the light emitter 4 directly below the photomultiplier tube 6, and the light intensity of the light emitter 4 is automatically adjusted. The elapsed value [ _X'CAL ] which is measured and counted by the counter 10 at that time is also led to the computer 11, where it is memorized and temporarily saved. Then, when the TLD element under test is measured with this TLD reader, the TL from this TLD element is photoelectrically converted and then digitized.
After being counted by the counter 10, the actual value is the product of the sensitivity calibration constant [Y] previously stored in the microcomputer 11 and the initial value [X _CAL ] obtained by measuring the light emission of the light emitter 4. The display is multiplied by a correction coefficient [X _CAL・Y], and then divided by the elapsed value [X' _CAL ] of the amount of light emitted from the light emitter 4, which is also stored in the microcomputer 11, to perform drift correction. 13 is displayed. Naturally, at this time, conversely, the TL from the TLD element under test
The actual measured value is divided by the elapsed value of the amount of light emitted from the light emitter 4 [X′ _CAL ], and then the correction coefficient [X _CAL・
Y] and then displayed on the display 13.

In this way, the actual measured value of TL from the TLD element is photoelectrically converted and then digitized, and after being counted by the counter 10, various calculations for sensitivity correction are performed, and the calculated values are displayed on the display 13. be done. At this time, this calculated value is sequentially stored in the microcomputer 11 again together with the identification number of the TLD element to be measured, and saved as data. You can output the desired data and display it again on the display 13, output the data to another display device such as a printer via an interface, or store the measured values all at once and display them later. These measured values may be taken out and input into the microcomputer 11 to calculate the average value, standard deviation value, etc. In this way, by providing a storage means to store all the measured values of the TLD element under test and deleting the data when it is no longer needed, it is possible to prevent errors in recording measured values and loss of measured data. This is more preferable because troubles can be avoided. In addition, the above correction coefficient [X _CAL・
Once the calibration constant [Y] is stored in the microcomputer 11, it will not be erased until the calibration constant [Y] is recalculated.
You can replace the TLD element 2 under test above with another element,
By sliding the sample stage 1 when interrupting the measurement, the light emitter 4 is placed directly below the photoelectric conversion element 6, and when the light intensity of the light emitter 4 is set in a measurable state, it is automatically adjusted to a certain level. The emitted light from the light emitter 4 is constantly measured for a certain period of time at time intervals, and the elapsed value [X'' _CAL ] counted by the counter 10 at that time is input to the microcomputer 11 one by one and is not stored in advance. A new value is stored in place of the elapsed time value [X′ _CAL ], and the calculation for drift correction of the actual measured value of the TLD element under test is automatically performed in accordance with the above-mentioned order. Therefore, once the sensitivity of the TLD reader has been calibrated, even if the sensitivity of the photoelectric conversion element or electric circuit changes over time,
Finally, the sensitivity is automatically adjusted to be the same as during calibration.

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 power of the TLD reader is turned off or during a power outage, so that the data is not erased at all times. The operability of this TLD reader is improved by holding it in
Reliability will improve.

As explained in detail above, TLD according to the present invention
The reader corrects sensitivity changes due to drift, which is changes in characteristics of electric circuits over time, simply by sliding the sample stage on which the TLD element is placed.
The light from the standard light emitter installed in the TLD reader is measured using the same photoelectric conversion path as when measuring the light emitted from the TLD element, and the rate of change is calculated to obtain the photometry of the TLD element to be measured. Since the actual measured values are automatically corrected, there is no need to manually correct the characteristics of the electric circuit in the electric circuit, which was required in the past, and operability is improved, which is of great practical value.

[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)

[Scope of Claims] 1. A slidable sample stage on which a fluorescent dosimeter element is placed, a heating section that heats the thermal fluorescent dosimeter element, and a heating section that is always arranged at a different position from the heating section. A standard light emitter that emits a constant amount of light, a photoelectric converter that converts the thermal fluorescence emitted from the thermal fluorescence dosimeter element into a first electrical signal, and a value of the second electrical signal that corresponds to a predetermined dose. Dose information input means for outputting, the value of the second electrical signal and the reference value of the first electrical signal obtained when heating the reference thermal fluorescence dosimeter element irradiated with the predetermined dose of radiation; a calculation means for calculating a calibration constant that is a ratio of A thermal fluorescence dose reading device comprising a display device that displays the product of the first electric signal obtained at a calculation means for calculating a correction coefficient consisting of the product of the initial value of the first electrical signal and the calibration constant;
storage means, a second storage means for storing the temporal value of the first electric signal obtained by photometrically measuring the standard light emitter immediately before the measurement of the thermal fluorescence dosimeter element to be measured; Multiplying the actual measured value of the first electric signal obtained by photometry of a fluorescent dosimeter element by the correction coefficient stored in the first storage means, and the elapsed value stored in the second storage means. and inputting the calculated value to the display device, and when the measurement target thermal fluorescence dosimeter element is not being measured, the standard light emitter and the photoelectric converter face each other. 1. A thermal fluorescence dose reading device, characterized in that the sample stage is slid, the light intensity of the standard light emitter is automatically measured at regular intervals, and the value over time is updated one by one.