JPS6128109B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermoluminescence measuring device for measuring radiation exposure dose.

Certain substances (CaSO ₄ :Tm, Li ₂ B ₄ O ₇ :Cu,
It is known that when materials (such as Ag) are irradiated with radiation and then heated with light or hot air, they emit light that corresponds to the amount of radiation they were exposed to. A thermoluminescence measurement device is a device that utilizes this property to convert the generated light into an electrical signal using a photoelectric conversion device to determine the amount of radiation exposure. Such a thermoluminescence measurement device is a thermoluminescence dosimeter (hereinafter referred to as TLD) containing the above-mentioned substance.
A heating system for heating the TLD element (called a TLD element), a drive system for moving the TLD element to the heating system, a photoelectric conversion system consisting of photomultiplier tubes, etc., and a system for guiding the light generated in the heating system to the charger multiplier tube. It is equipped with an optical system, a signal processing system for processing the output of the photoelectric conversion system, and a display system for displaying or recording measured values. Among these systems, optical systems and photoelectric conversion systems (especially photomultiplier tubes) are subject to large changes over time due to dust and dirt, so for the same amount of generation,
It is necessary to perform appropriate calibration to obtain the same measurement output.

Conventionally, in order to perform such calibration, a calibration light source that always emits constant light (for example, β from C
Instead of a TLD element, a device (which is made by irradiating a fluorescent material with a ray of light to emit a constant amount of light) is inserted into a thermoluminescence measuring device to record the output from the light emitted by the calibration light source obtained through the optical system and others. Then, later, the measured value from the TLD element was corrected, or the gain of the photomultiplier tube etc. was adjusted so that the light emission output of the calibration light source became a constant reference value.

However, in an apparatus that measures a large number of TLD elements such as the present apparatus, both methods require a lot of effort and are a major problem. In addition, when this measuring device is first started up, the amount of light emitted from the TLD element corresponds to the amount of radiation exposure of the TLD element (value setting), which means that variations in the amount of light emitted by the TLD element and the heat source can be avoided. It was a labor-intensive task, as it required measuring multiple TLD elements.

The present invention provides a thermoluminescence measuring device that can easily and automatically perform calibration to compensate for the above-mentioned changes over time and pricing.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows the device of the present invention, in which the TLD element 1 stored in the magazine 4
is taken out, moved to a measurement position, and stopped. There are four TLD elements 1, which are attached to an element plate 2, and are normally stored in a magazine 4 while being housed in a holder 3 (this is called a TL badge). Magazine 4 can store 50 TL badges. Push up this TL badge with a push-up rod (not shown) and read the number hole 5 provided on the holder 3 with a number reading unit 6. Thereafter, the slide 7 is used to pull out the element plate 2, and the TLD element 1 is sequentially moved to a measurement position where the photomultiplier tube 10 and the light guide 11 are located for measurement. At that time,
Heating is performed in a pulsed manner using 12 infrared lamps, and 13 silicon filters are installed so that only the hot rays of the lamp light are incident on the TLD element 1.

Furthermore, the slide 7 is provided with a TLD element (referred to as a zero point element) 8 which is not exposed to radiation, and a calibration light source 9. Before measuring the TLD element 1, it is necessary to measure the TLD element 1 with the aforementioned measurement system and check the device. Let's do it.

In FIG. 2, reference numeral 20 denotes an object to be measured, which is the TLD element 1, the zero point element 8, or the calibration light source 9. 21 is a photoelectric conversion unit for converting light generated by the object to be measured 20 into an electrical signal (in this case, the number of pulses), and for example, a photomultiplier tube is used. 22 is a pulse counting circuit;
The output of the photoelectric conversion section 21 is applied. The output of the pulse counting circuit 22 is applied to a buffer 23 which is a temporary memory. The output of the buffer 23 is connected to a fixed contact 37 of a changeover switch 36. The changeover switch 36 is composed of three changeover contacts a, b, and c. Switching contact a is the conversion coefficient generating circuit 29
The output signal of the irradiation dose setting unit 27 is applied to the other input of the conversion coefficient generation circuit 29. The output of the conversion coefficient generation circuit 29 is connected to the input side of the memory ( ) 30. The output of memory ( ) 30 is supplied as one input to multiplier 31 . This memory 30 needs to be nonvolatile, and magnetic core memory, wire memory, etc. can be considered, but as an example, a semiconductor nonvolatile memory using MNOS has a simple circuit configuration and a small memory capacity. It's convenient. Switching contact b is connected as one input signal of multiplier 31. The switching contact C is the calibration coefficient generating circuit 3.
2, and the output signal of the calibration standard setting section 34 is applied to the other input of the calibration coefficient generating circuit 32. The output of the calibration coefficient generation circuit 32 is connected to the input side of the memory ( ) 33. The output of memory ( ) 33 is applied as one input to multiplier 31 . This memory ( ) 33 is nonvolatile like the memory ( ) 30 described above. In addition, the irradiation dose setting section 27 and the calibration standard value setting section 34
is composed of a digital SW or the above-mentioned nonvolatile memory.

The control section 28 switches the changeover switch 37 to a, b, and c based on the output signal of the operation section 26 and the output signal of the magazine detection section 38. Magazine detection section 3
8 is a device for detecting when the head of the magazine has come to the position of the element push-up rod. As explained in FIG. 1, the mechanical drive unit 25 is a drive unit that moves the magazine and pulls out the TLD element.
8 control section. 24 is a heating device for heating the object to be measured 20, and TLD
The element and the zero point element are controlled so that they are heated only when they come to the measurement position.

Since the light intensity of the calibration light source can be read in advance with another measuring device, the read value is set in the calibration standard value setting section 34.

Further, the outputs of the switching contact b and the calibration standard value setting section 34 are applied to a calibration standard value comparison circuit 39, and the output of the comparison circuit 39 is applied to the alarm output section 40.

Next, the overall operation of this embodiment will be explained. First, the case of pricing will be explained. Generally, the following relationship exists between the irradiation dose Dc and the number Nc of pulses obtained by the pulse counting circuit 22 when there are no fluctuations in the optical system or photoelectric conversion system.

Dc＝Cs・Nc... However, Cs is a conversion coefficient.

Pricing involves finding the value of Cs. First, the control section 28 is operated using the operation section 26, and the switching contact is set to a. Approximately 20 TL badges are irradiated with a fixed amount of radiation, the value Rs is set in the irradiation dose setting section 27, and the TL badges are stored in a magazine and measured. As shown in Figure 1,
The TLD element is extracted from the TL batch and placed in the heating device 24.
The measured value is temporarily stored in a buffer 23 through a photoelectric conversion device 21 and a pulse counting circuit 22. When all TLD elements (20×4=80) are measured and stored, the measured values are applied to the conversion coefficient generation circuit 29 through the switching contact a. The conversion coefficient generation circuit 29 calculates the average value of the data stored in the buffer 23, Na, and calculates Cs from the output value Rs from the irradiation dose setting section 27. That is, since Rs∝Ns, Rs/Ns is calculated and this is set as Cs. Memory ( ) 30 stores the value of Cs, and the output signal of memory ( ) 30 is applied to multiplier 31 . By measuring approximately 20 TL badges and assigning a price based on the average value, it is possible to determine the correct price since variations in TLD elements and sources are eliminated. next,
Consider the case of calibration measurement. Assuming that there are fluctuations in the optical system and photoelectric conversion system, the equation becomes the following relational expression: Dc=Sr・Cs・Nc... However, Sr is a calibration coefficient for calibrating the optical system and photoelectric conversion system.

The calibration measurement involves measuring the calibration light source 9 shown in FIG. 1 a fixed number of times (for example, 10 times) for each magazine. That is, the switching contact is switched to c by the magazine detection section 38 that detects the head of the magazine. When the TL button is pushed up, the slide 7 pulls the element plate 2, and the calibration light source 9 comes to the measurement position, the light from the calibration light source 9 is measured a certain number of times, and the value of 23 is measured in the same way as the above value setting. Temporarily stored in Batsuhua. However, in this case, the heating device 24 does not operate. When measured a certain number of times (for example, 10 times) and stored, it is applied to the calibration coefficient generation circuit 32 through the switching contact c. The calibration coefficient generation circuit 32 calculates the average value of the data stored in the buffer 23 and outputs Nr, the output value from the calibration standard value setting section 34.
Calculate Sr from Rr. That is, Sr=Rr/Nr is generated and applied to the memory 33. Memory is Sr.
The value of is stored and the output signal is applied to the multiplier 31.

Next, consider the case of measuring TL badges. In this case, the switching contact is switched to b. As shown in FIG. 1, the TL button is pushed up by the element push-up rod, and the TLD element 1 attached to the element plate 2 pulled out by the slide 7.
When it reaches the measurement position, it is heated by the lamp 12 and received by the photoelectric conversion section 21, and the pulse counting circuit 22
It is counted and temporarily stored in the buffer 23. The read data is multiplied by 31 with the output values Cs and Cr of the memory 30 and the memory 33, respectively, to a correctly calibrated and valued value (that is, if the count value is N _M , the exposure amount D _M is D _M = Sr × Cs× _NM ) is output from the multiplier 31 and applied to the display output section 35. The calibration light source 9 is measured for each magazine, and the measurement interval is short in terms of time, so aging changes between magazines can be ignored, and it can be considered that the TLD elements during that period are correctly calibrated.

Note that the calibration light source 9 is measured once just before the TL badge measurement, and the reading value is applied to the calibration reading value comparison circuit 38 via the contact b of the changeover switch 36, and is applied to the calibration standard value setting section 34. The standard value is compared with the calibration reading value comparison circuit 38 to check whether the reading value is within a certain range. When the measurement device is out of a certain range, the measuring device is stopped and the alarm output section 3 is activated.
9 to prevent future erroneous measurements of the TLD element. Further, the control unit 28 controls the calibration reading value comparison circuit 38 so that it operates only in this case, and does not operate when performing calibration measurement and measuring the TLD element.

As is clear from the above explanation, calibration to compensate for changes over time is automatically performed for each magazine and the calibration light source is measured for each TL badge, which simplifies the calibration work and improves the reliability of the data. rises. Furthermore, since the pricing is done automatically, there is an advantage that there is no need for complicated work at the time of starting the device.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a thermoluminescence measuring device according to an embodiment of the present invention, and FIG. 2 is a block diagram of the same device. 1...Thermoluminescence dosimeter (TLD element),
2... Element plate, 3... Holder, 4...
... Magazine, 5 ... Number hole, 6 ... Number reading unit, 7 ... Slide, 8 ... Zero point element, 9 ...
... Calibration light source, 10 ... Photomultiplier tube, 11 ... Light guide, 12 ... Infrared lamp, 13 ... Silicon filter, 20 ... Measurement object, 21 ... Photoelectric conversion section, 22 ... Pulse counting circuit , 23... Buffer, 24... Heating device, 25... Mechanical drive section, 26... Operation section, 27... Irradiation dose setting section, 28... Control section, 29... Conversion coefficient generation circuit, 30... Memory, 31... Multiplier, 32...
...Calibration coefficient generation circuit, 33...Memory, 34...
...Calibration standard value setting section, 35...Display output section, 36
...Selector switch, 37...Fixed contact, 38...
Magazine detection unit, 39... Calibration standard value comparison circuit,
40... Alarm output section.

Claims (1)

[Claims] 1. A magazine containing a plurality of TL badges having one or more thermoluminescent dosimeters, means for heating the thermoluminescent dosimeter, a calibration light source, and the thermoluminescent dosimeter and the calibration light source. means for moving the thermoluminescent dosimeter to a measurement position; means for measuring the amount of light from the linear luminescent dosimeter and the calibration light source; a first memory for storing the measured values; an irradiation dose setting unit for storing the dose to be applied, a means for calculating a conversion coefficient between the light amount and the dose, a second memory for storing the conversion coefficient, and a calibration standard value for setting the calibration standard value of the calibration light source. The device includes a setting unit, a means for calculating a calibration coefficient, a third memory for storing the calibration coefficient, a multiplier, and a comparator, and is configured to set a predetermined dose to a plurality of thermoluminescent dosimeters at the time of pricing. A conversion coefficient is calculated from the light intensity measurement value of this thermoluminescence dosimeter and the above-mentioned predetermined dose value, and when calibrating each magazine, the multiple measurement values of the light intensity of the above-mentioned calibration light source and the above-mentioned light intensity are calculated. A calibration coefficient is calculated from the standard value, and at the time of measurement, the light intensity measurement value of the dosimeter, the conversion coefficient, and the calibration coefficient are multiplied, and this multiplication result is used as the exposure dose, and the above
A thermoluminescence measurement device characterized in that for each TL badge, the amount of light from the calibration light source is measured, compared with a calibration standard value, and checked to see if it is within an allowable range.