JPH04131789A - Electric charge measuring apparatus and radiation value measuring apparatus using the same - Google Patents

Abstract

PURPOSE: To measure charges through a simple apparatus by generating an AC voltage on the upper surface of an electret in a badge through oscillation, supplying a DC voltage reversely to the outside of the bottom plate of the- housing of the badge and measuring the DC voltage at a moment of time when an electric field disappears. CONSTITUTION: When a mechanical oscillation is generated in the upper plate of a badge 10 through a solenoid 12, an AC signal appears across a load resistor 20. The magnitude of the AC signal is detected by an amplitude demodulator 16 which controls a ramp generator 18 sequentially and drives a high voltage amplifier 22 for forcibly imparting charges onto the bottom plate of the badge 10 sequentially. When charges are supplied to the bottom plate, an AC signal of reverse phase is detected by a potentiometer amplifier 14 and the AC signal generated in response to the oscillation of the bottom plate disappears. The null point is used for calculating the surface potential of the electret of the badge.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a radioactivity measuring device and an inspection device suitable for use in measuring radioactivity, and in particular, measuring the radiation dose received by a worker.

``Prior Art'' Some means are required by workers to detect the amount of dangerous radiation they emit. These workers are exposed to the above radiation. These workers include jobs in the health care field. In that area, X
There is a risk of exposure to radiation, which is no less dangerous than handling nuclear or radiological materials. For this reason, fairly sophisticated systems exist to monitor the exposure of such workers.

A typical method is to distribute radiation dose badges that measure radiation fields to workers who have been exposed to radiation for more than a certain period of time. These badges are checked periodically to ensure that the worker wearing the hat is not receiving more radiation than medically safe limits.

On the other hand, the precision procedures described above for all-day workers can be readily applied to temporary workers and visitors. This is particularly important for visitors to health care institutions and patients, as well as for visitors and construction workers to facilities that handle nuclear materials. The same applies to research institutions that use materials that contain radiation. Here, a problem arises regarding visitors.

Detection technology used for permanent facility workers involves the distribution and collection of radiation dose badges on a regular basis. Radiation doses are measured by more sophisticated equipment, such as equipment that is expensive, battery-powered, and has a hand-held reader. There is a need for a means to measure the radiation dose of permanent workers or even those who are in the facility for short periods of time, quickly and without unsuitable and complicated operations.

The devices described above are therefore operated by ordinary workers without special training in such areas.

On the other hand, in recent years, the use of electret ionization chambers for detecting radiation has increased. The ionization chamber has an electret, ie, residual electrostatic polarization, which is made of a material that transfers, receives, and holds charge. It retains its charge without loss for a relatively long period of time, regardless of the presence of radiation. When the electret is exposed to radiation, the radiation causes a decrease in charge in direct relation to its amount. The principle of charge reduction in this electret ionization chamber, especially for X-rays and gamma rays, is as follows:
The paper by Pretzch et al. (vol. 4)
．． p, 79. Radiation Potenti
al Dosimeter (1983)). Many designs have been proposed for this electret ionization chamber as a radiation dose measuring device for workers. Examples of these can be found in the article by Bauser et al. (Health Physics, vol. 34).
．． p. 97 (1978); Cameron
Proceedings on) et al.
the sixth conference on do
simetry (1980)) and Ikeya (Ikey
a) Literature by et al.
l, 39. p. 797 (1980)). However, these devices have not yet gained the trust of end users because they do not have sufficiently precise electronic measurement systems to read or record cumulative radiation doses.

Furthermore, the above-mentioned paper by Ikeya et al. describes a sonic method for measuring the electric charge of an engineered leftlet. This sonic method has inaccuracies with dimensional changes and environmental effects. According to this sonic method, electret charge is measured by detecting mechanical vibrations. Mechanical vibration of the electret generates an alternating current signal whose magnitude is proportional to the charge and the amplitude of the mechanical motion. Therefore, it indicates the response of the AC signal or the charge of the electret. The electret chamber does not suffer from the same problems as film and TLD badges. Even though it is difficult to use conventional equipment, it is easy to operate the equipment without charge loss to measure the charge reduction in the electret ionization chamber.

"Problem to be Solved by the Invention" By the way, the biggest drawback of the film and thermoluminescence detector (TDL) badge system mentioned above is (1)
) non-linear, low-elergy response; (2) loss of reading information; and (3) measurement equipment that is too formal for unregistered workers and visitors.

Furthermore, these devices have not yet gained the trust of end users because they do not have sufficiently precise electronic measurement systems to read or record the cumulative radiation dose.

On the other hand, the measurement method using an electret ionization chamber requires getting close to the film surface as a standard method for measuring the surface states of electrets. This is unsatisfactory as measurements cannot be repeated.

Furthermore, with the sonic (5onic) method of measuring the charge of an electret in the above-mentioned paper by Ikeya et al., it is often difficult to measure the true amplitude of the AC signal and to calculate the effect of mechanical vibration on the charge. become.

It would therefore be advantageous if the radiation dosimetry device could provide more than just an accurate reading of the accumulated dose, besides being able to be read by a very simple device.

This invention was made in view of the above-mentioned problems.
A charge measuring device that can measure the charge on an electret using a very simple device, and a charge measuring device that can easily measure the radiation dose even by an operator without special training, and can also measure and record the cumulative radiation dose. The purpose is to provide a radiation dose measuring device using a measuring device.

"Means for Solving the Problem" In order to solve the above-mentioned problem, the invention according to claim 1 includes: an electret charged with a predetermined electric charge;
, a first conductive plate installed away from the electret; a second conductive plate in contact with the opposite side of the electret and installed away from the first conductive plate; vibrating means for generating mechanical vibrations at a predetermined speed between the first conductive plate and the ground; a resistor connected between the first conductive plate and ground; and a voltage across the resistor. detection means for detecting the alternating current electric field generated by the vibration, comprising an amplifier for amplifying the alternating current electric field; applying means for applying a direct current voltage of opposite polarity to the charge on the electret to the second conductive plate; The invention according to claim 2, further comprising increasing means for increasing the direct current voltage by a predetermined control method until the detecting means indicates that the electric field has substantially disappeared. The invention according to item 1 further comprises: a measuring means for measuring the direct current voltage at a time when the alternating current electric field has substantially disappeared; and a display means for displaying the direct current voltage measured by the measuring means. The invention according to claim 3 is characterized in that the invention according to claim 2 further comprises converting the measured DC voltage into a charge represented by an initial charge on the electret and a charge represented by the measured DC voltage. The invention according to claim 4, further comprising conversion means for converting into a different signal equal to the difference between the electrets and relating the difference to the cumulative radiation transmitted and received by the electret. In the invention set forth in claim 5, the speed of the vibration is 60 Hz or more, in the invention set forth in claim 1, the detection means is an AC amplification modulation detection circuit. The invention according to claim 6 is characterized in that, in the invention according to claim 1, the applying means is a DC amplifier, and the increasing means is a ramp generator connected to the input of the DC amplifier. In the invention according to claim 7, characterized in that claim 1
The invention described further includes a converting means for converting the output of the applying means into a digital code, and the digital code outputted by the converting means is exchanged, and when the alternating current electric field substantially disappears, the digital code is converted into a digital code. a calculation means for storing a code and controlling the increasing means, and the increasing means is operated at the start of measurement by the applying means under the control of the controlling means, and the alternating current electric field is substantially The invention according to claim 8 is characterized in that the operation is terminated when the electret and the electret, which are supported in contact with the second conductive plate and the radiation monitoring means comprising the first conductive plate provided at a predetermined distance from the electret on a side facing the second conductive plate, the electret being charged to a predetermined potential; In the invention as set forth in claim 9, wherein the predetermined potential is related to the accumulated amount of radiation transmitted and received by the electret, in the invention as set forth in claim 8, the vibration speed is 180H2. The invention according to claim 1o is characterized in that, in the invention according to claim 8, the electret is formed from fluoroethylene propylene/tetrafluoroethylene. In the invention according to claim 8, the radiation monitoring means further includes the radiation monitoring means for forming a closed cavity around the electret.
The invention according to claim 12, further comprising an insulating spacer means for joining the second conductive plate together, the invention according to claim 11, wherein the insulating spacer means The invention as set forth in claim 13 is characterized in that it has an extension portion that supports attachment means for attaching the radiation monitoring means, wherein the extension portion is provided with readable personal identification information. The invention according to claim 14 is characterized in that the first and second conductive plates are made of a conductive plastic material, The invention as set forth in claim 15 is characterized in that the insulating spacer means is formed of an insulating plastic material. In the invention as set forth in claim 11, the first conductive plate detects radon gas. The invention according to claim 16 is characterized in that, in the invention according to claim 12, a hole is formed in order to operate the radiation monitoring means. In the invention according to claim 17, characterized in that the electrical connection between the first and second conductive plates is such that the electrical connection decreases depending on the cumulative amount of the transmitted and received radiation. a first conductive plate that supports the electret on a side that is not charged and in contact with the electret; and a first conductive plate that supports the electret on a side opposite to the first conductive plate; a second electrically conductive plate spaced apart from the electret; and a second electrically conductive plate for coupling the first and second electrically conductive plates together to form a closed cavity around the electret. an insulating spacer means and the coupling couples at least one of the first and second conductive plates vibrating with respect to the other and the insulating spacer means; The predetermined spacing between the first and second conductive plates is alternately increased and decreased, and in order to measure radiation, the predetermined spacing between the first and second conductive plates is increased or decreased such that the charge on the electret is decreased by the radiation. an extension providing an electrical connection between the first and second conductive plates, supporting an attachment means for attachment to an operator, and being of sufficient size to accommodate readable personal identification information; The invention according to claim 18 is characterized in that, in the invention according to claim 17, the first and second conductive plates are formed from a conductive plastic material, and the insulating spacer means The invention according to claim 19 is characterized in that the material is made of an insulating plastic material.
In the invention described in item 7, the second conductive plate is provided with holes for detecting radon gas.

"Operation" According to this invention, the radiation monitoring means is made of plastic.
It takes the form of an electret completely covered by a housing. The top and bottom surfaces of the housing consist of two conductive layers separated from each other by an insulating plastic spacer.
It's made from a piece of plastic. As a result, the electret installed inside the bottom plate is completely contained inside the housing, and therefore cannot be touched or contacted by dust. These contacts reduce the charge on the electret. The insulating spacer can be extended in one direction to form an attachment for the badge to the operator.

This elongated part is used for the personal identification code. The personal code may be printed or in the form of a 7<- code, or both.

Radiation dose badge (radiation monitoring means) characteristic of this invention
has an electret charged to a special potential, for example between 100 and 200 volts. This badge is
Worn by workers in areas exposed to radiation. The X-rays or gamma rays reduce the charge on the electret inside the badge. Whenever desired, the amount of charge reduction (an amount related to the cumulative amount of radiation) can be measured.

Measurements are accomplished by placing a hutch on top of a piebreak that vibrates up and down at approximately 180 Hz. Furthermore, the bottom plate of the badge is in contact with the electret. By vibrating, the electric field of the electret generates an alternating voltage on the top surface of the electret. Here, a reverse DC voltage is applied to the outside of the bottom plate of the badge housing. This DC voltage generates another AC signal on the top surface. The DC voltage outside the bottom plate is then increased to that level until it dissipates the electric field generated by the charge of the electret in contact with the inside of the bottom plate.

Since this method of dissipating the electric field is used, the charge on the electret does not decrease and the electret does not need to come into contact with anything. On the other hand, accurate measurement of the amount of charge is achieved by utilizing the fact that the voltage generated by the charge is equal to the voltage required to dissipate the electric field generated by the charge.

The above measurements do not concern the vibration amplitude or the separation between the electret and the top surface.

“Embodiments” The present invention discloses an apparatus and a device for measuring the amount of charge reduction depending on the amount of radiation received. This invention accomplishes multiple objectives through special electret dosimetry badges and advanced measurement techniques.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the null detection method of the present invention.

As shown in FIGS. 1 and 2, the mechanical vibration of the upper plate 11 of the Hajj 10 is, for example, 180H2
It is generated by a small solenoid 12 operating at . In addition, if a high quality AC signal is generated,
The frequency may be, for example, 60 Hz or even higher. This oscillation generates an alternating current signal across the load resistor 20 at the input of the electrometer amplifier 14. This electrometer amplifier 14 is related to the amount of charge on the electret 13. The magnitude of this AC signal is detected by the amplitude demodulator 16. This amplitude demodulator 16 has a feedback
A ramp generator 18 is composed of a differential amplifier, etc., which are connected so as to be integrated by inserting a capacitor 19 into the loop.
are controlled sequentially.

This lamp generator 18 is connected to the bottom plate 1 of the badge 10.
The high-voltage amplifier 22 that forcibly applies charge onto the high voltage amplifier 5 is sequentially driven. The effect of the charge applied to the bottom plate 15 of the badge 10 is to lower the influence field within the electret ionization chamber. This produces a reduced AC signal.

Finally, electret 1 of the electret ionization chamber
3 and on the bottom plate 15 of the same size,
And the presence of opposite charges produces a zero electric field in the air gap 34 (see FIG. 3) within the electret ionization chamber.

Therefore, the AC signal generated in response to the vibration of the upper plate is eliminated. This is the null point and is used in a simple way to calculate the surface potential on the electret. Furthermore, the charge is applied to the bottom plate 1 of the badge 10.
5, an anti-phase alternating current signal is detected by the electrometer amplifier 14.

The output of the amplitude modulation detector 16 is transmitted to the microcomputer 2.
Connected to 4. This microcomputer 24 is connected to a lamp generator 18, and this lamp generator 1
8 determines when to start measuring the charge on badge 10.

The DC signal given to the bottom of the badge 10 is A/D (
is converted into a digital code by an analog/digital converter 26. This digital code is sequentially supplied to the microcomputer 24. Therefore, when the microcomputer 24 detects zero input from the amplitude demodulator 16, the microcomputer 24 outputs the digital signal from the A/D converter 26.
Memorize the code. This digital code is Badge 1
Represents a null voltage above the bottom of 0. This null voltage corresponds to the charge on the electret within the badge 10. Badge 1
The data regarding the amount of charge of 0 can be displayed on a simple display device 28 and/or printed on the printer 3o. A computer spreadsheet is processed by the microcomputer 24 to incorporate standard functions for the decrease in electret charge as a function of radiation dose.

The design of badge 10 is shown in FIGS. 3 and 4.

In this figure, the electret is housed in a container arranged between two electrically conductive top plates 11 and bottom plates 15 that are insulated from each other. This container has a top plate 11 and a bottom plate 1.
5 is arranged to vibrate using only a small force. If possible, the container should be made of a material that is as similar to the body's tissues as possible and is protected from chemical and environmental influences.

As shown in FIG. 3, the top plate 11 and bottom plate 15 of the container are each made of a conductive plastic material, and an insulating plastic material (for example, P
, V, C) are separated by a gasket 32. This plastic material ensures the required insulation between the top plate 11 and the bottom plate 15 and acts as a spacer to form a specific air gap 34 inside the electret ionization chamber.

The spacer forming this insulation can be stretched as shown by a portion 35 thereof. This extension part 35 is
Badge 10 is attached to the user by attachment 37, forming an extended surface 39 on which personal identification information is printed. This personal identification information is, for example, a barcode or handwritten information. The attachment (clip) 37 is
Made of conductive material, when used, the badge 10
It has elongated legs 40 electrically connected to plates 11 and 15 for actuation. This fixture 37 is moved during the measurement. Furthermore, the badge 10 excluding the attachment 37 does not affect radiation measurement. .

The electret material may be any convenient material, preferably fluoroethylenepropylene/tetrafluoroethylene (F E P/TFE) because of its excellent charge retention properties.

For a given range (measurement range) of radiation, it is possible to calculate all combinations of dimensions that satisfy the present invention. Note that the badge 10 is made small to facilitate attachment. For example, the thickness is less than 5 am. In addition, the electric field range of useful electrets is
Select between 10,000 and 40.0 OOV/m. In this way, for an electret charged with 100 volts as an initial charge, when the device uses an electret with a thickness of 1.6 mm and a gap of 2.5 + nm,
A radiation range of 28 msv is obtained. The range of this radiation is adjusted by varying the dimensions to suit the desired requirements.

Radiation sensitivity depends on the resolution with which the surface potential is measured. Typically, the level of sensitivity may be required to drop to 0,001 m5v. This requires a measured voltage of more than six times the amplitude to achieve the desired range.

In one experiment, the present test apparatus is equipped with a plurality of series connected electrets supplied with different surface potentials ranging from 20 to 200 volts. The invention is capable of reading voltages (occurring repeatedly three times in a row) for four important values in each case. Moreover, the surface potential measurements were consistent with other conventional methods.

It was also proven that this measurement procedure does not affect the charge. These tests make it possible to create a system with a sensitivity better than 0,01 m5v and a range of 100 mSv using a single electret and badge. This range can be extended both by utilizing two badges or by incorporating two electrets of different thicknesses and/or surface potentials within an electret ionization chamber. good.

A new system according to this invention is created for the measurement of surface potentials on an electret film inside a shielded badge designated as an electret ionization chamber. This system is for worker radiation dosimeter,
Used in a given environment. By using the null method, the charge within the badge that decreases due to exposure to radiation can be measured by a worker without special training.

While the invention has been particularly shown and described by reference to examples. This is understood by these techniques within the specification. Various changes in the form of the embodiment and its details may be made without departing from the spirit and scope of the invention. For example, by providing a plurality of holes 44, 44, 44, 44 in plate 11 as shown in Figure 4, the badge can be used to detect radon gas.

"Effects of the Invention" As explained above, according to the present invention, an AC voltage is generated on the top surface of the electret by placing a badge device on the top surface of the vibrator that vibrates up and down, and an electric field generated by the charge of the electret is generated. By supplying a DC voltage in the opposite direction to the outside of the bottom plate of the badge housing so that the electric field disappears, and measuring the DC voltage at the point when the electric field disappears, we can calculate the charge on the electret using a very simple device. The radiation dose can be easily measured even by workers without special training, and the accumulated radiation dose can be measured and recorded.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a charge measuring system according to an embodiment of the present invention, FIG. 2 is a schematic circuit diagram showing the configuration of a charge measuring circuit, and FIG. 3 is a cross section of an ionization device having an electret according to the present invention. 4(a) is an exploded view of the electret ionization device shown in FIG. 3, and FIG. 4(b) is an exploded view of a modification of the present invention. f/"t+" in the drawing ('1'' inside: no change) 10...Badge (radiation monitoring means), 11...
Upper plate (first conductive plate), 12...
・Solenoid (vibrating means), 13...Electret, 14...Electrometer amplifier, 15...
Bottom plate (second conductive plate), 16...
Amplitude demodulator, 20... Resistor (resistor), 22.
... High voltage amplifier (applying means), 24 ... Microcomputer (increasing means), 26 ... A/D converter (conversion means) 28 ... Display device, 30 ... Printer, 32... Gasket (insulating spacer means), 34
...Void, 35...Expansion, 37...
... Attachment, 39... Expansion surface, 40...
...Leg, 44...hole.

Claims (19)

[Claims] (1) An electret that is charged with a predetermined charge, a first conductive plate that is placed away from the electret, and a first conductive plate that is in contact with the opposite side of the electret and that is placed away from the first conductive plate. two conductive plates; a vibration means for generating mechanical vibrations at a predetermined speed between the electret and the first conductive plate; and a vibrating means connected between the first conductive plate and ground. detection means for detecting an alternating current electric field generated by the vibration, the detecting means comprising a resistor and an amplifier for amplifying the voltage across the resistor; applying means for applying a conductive plate; and increasing means for increasing the DC voltage by a predetermined control method until the detection means indicates that the AC electric field has substantially disappeared. Electric charge measuring device. (2) Further comprising a measuring means for measuring the DC voltage at the time when the AC electric field has substantially disappeared, and a display means for displaying the DC voltage measured by the measuring means. The charge measuring device according to claim 1, characterized in that: (3) further converting the measured DC voltage into a different signal equal to the difference between the initial charge on the electret and the charge represented by the measured DC voltage;
3. The charge measuring device according to claim 2, further comprising conversion means for relating the difference to cumulative radiation transmitted and received by the electret. (4) The charge measuring device according to claim 1, wherein the speed of the vibration is 60 Hz or more. (5) The charge measuring device according to claim 1, wherein the detection means is an AC amplification modulation detection circuit. (6) The charge measuring device according to claim 1, wherein the applying means is a DC amplifier, and the increasing means is a ramp generator connected to an input of the DC amplifier. (7) Further, a converting means for converting the output of the applying means into a digital code, and transmitting and receiving the digital code outputted by the converting means, and converting the digital code when the alternating current electric field substantially disappears. and a calculation means for controlling the increasing means, wherein the increasing means operates under the control of the controlling means at the start of measurement, and the alternating current electric field is substantially 2. The electric charge measuring device according to claim 1, wherein the electric charge measuring device terminates its operation when the electric charge disappears. (8) Furthermore, the electret is supported in contact with the second conductive plate, and the first A radiation monitoring means comprising a conductive plate, wherein the electret is charged to a predetermined potential, and the predetermined potential is related to the cumulative amount of radiation delivered and received by the electret. Item 1. The radiation dose measuring device according to item 1. (9) The radiation dose measuring device according to claim 8, wherein the speed of the vibration is 180 Hz. (10) The radiation dose measuring device according to claim 8, wherein the electret is made of fluoroethylene propylene/tetrafluoroethylene. (11) The radiation monitoring means further comprises insulating spacer means for joining the first and second conductive plates together to form a closed cavity around the electret. The radiation dose measuring device according to claim 8, characterized in that: (12) The radiation dose measuring device according to claim 11, wherein the insulating spacer means has an extension portion that supports attachment means for attaching the radiation monitoring means to a worker. (13) The radiation dose measuring device according to claim 12, wherein the expanded portion is large enough to be provided with readable personal identification information. (14) The first and second conductive plates are made of a conductive plastic material, and the insulating spacer means is made of an insulating plastic material. Radiation dose measuring device. (15) Claim 1, wherein the first conductive plate has holes for detecting radon gas.
1. The radiation dose measuring device according to 1. (16) The attachment means is characterized in that the attachment means is electrically connected between the first and second conductive plates such that the charge on the electret is reduced by the radiation in order to activate the radiation monitoring means. The radiation dose measuring device according to claim 12. (17) An electret that is charged to a predetermined potential that is discharged according to the cumulative amount of radiation transmitted and received, and a first conductor that supports the electret on a side that is not charged and in contact with the electret. a second conductive plate provided on a side facing the first conductive plate at a predetermined distance from the electret; and for forming a closed cavity around the electret. , insulating spacer means for coupling said first and second electrically conductive plates together, said coupling being with at least one of said first and second electrically conductive plates, one of which vibrates relative to the other; The vibration alternately increases and decreases the predetermined spacing between the first and second conductive plates, thereby transmitting radiation. providing an electrical connection between the first and second conductive plates such that the charge on the electret is reduced by the radiation, and supporting attachment means for attachment to an operator for measurement; 1. A radiation dose measuring device comprising: an extension portion having a sufficient size to allow readable personal identification information. (18) The first and second conductive plates are made of a conductive plastic material, and the insulating spacer means is made of an insulating plastic material. Radiation dose measuring device. (19) Claim 1, wherein the second conductive plate has holes for detecting radon gas.
7. The radiation dose measuring device according to 7.