CN109459780B - Flat ionization chamber for pulse X-ray and gamma-ray dose measurement - Google Patents
Flat ionization chamber for pulse X-ray and gamma-ray dose measurement Download PDFInfo
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- CN109459780B CN109459780B CN201811608416.6A CN201811608416A CN109459780B CN 109459780 B CN109459780 B CN 109459780B CN 201811608416 A CN201811608416 A CN 201811608416A CN 109459780 B CN109459780 B CN 109459780B
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- 230000005251 gamma ray Effects 0.000 title claims abstract description 17
- 238000005259 measurement Methods 0.000 title description 11
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 6
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 6
- 239000011248 coating agent Substances 0.000 claims description 10
- 238000000576 coating method Methods 0.000 claims description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 9
- 229910002804 graphite Inorganic materials 0.000 claims description 9
- 239000010439 graphite Substances 0.000 claims description 9
- 239000004696 Poly ether ether ketone Substances 0.000 claims description 7
- 229920003229 poly(methyl methacrylate) Polymers 0.000 claims description 7
- 229920002530 polyetherether ketone Polymers 0.000 claims description 7
- 239000004926 polymethyl methacrylate Substances 0.000 claims description 7
- 229920006324 polyoxymethylene Polymers 0.000 claims description 7
- 229930040373 Paraformaldehyde Natural products 0.000 claims description 5
- 229920000642 polymer Polymers 0.000 claims description 5
- -1 polyoxymethylene Polymers 0.000 claims description 5
- 229920001169 thermoplastic Polymers 0.000 claims description 5
- 239000004416 thermosoftening plastic Substances 0.000 claims description 5
- 239000011347 resin Substances 0.000 claims description 3
- 229920005989 resin Polymers 0.000 claims description 3
- 230000005684 electric field Effects 0.000 abstract description 8
- 230000000694 effects Effects 0.000 abstract description 4
- 230000004044 response Effects 0.000 abstract description 4
- 230000005855 radiation Effects 0.000 description 18
- 238000012937 correction Methods 0.000 description 7
- 150000002500 ions Chemical class 0.000 description 7
- 229960003965 antiepileptics Drugs 0.000 description 4
- 238000013461 design Methods 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 230000006798 recombination Effects 0.000 description 3
- 238000005215 recombination Methods 0.000 description 3
- 230000035945 sensitivity Effects 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 238000004547 X-ray dosimetry Methods 0.000 description 2
- 230000005865 ionizing radiation Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000003745 diagnosis Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000002601 radiography Methods 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/185—Measuring radiation intensity with ionisation chamber arrangements
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- High Energy & Nuclear Physics (AREA)
- Molecular Biology (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Measurement Of Radiation (AREA)
Abstract
The invention provides a flat ionization chamber for measuring pulse X-ray and gamma-ray doses. The ionization chamber can effectively shorten the polar distance, and under the same working voltage, secondary electrons can be accelerated better, so that the collection rate of the secondary electrons reaches microsecond magnitude; in addition, the ionization chamber adopts an energy compensation measure, and the aluminum layer sprayed on the inner wall can effectively promote the response of the ionization chamber to low-energy photons, so that the lower energy limit of the flat plate ionization chamber reaches 20keV; and the ionization chamber collector is designed with a protection ring, which has obvious effect on improving the uniformity of the electric field.
Description
Technical Field
The present invention relates to a measuring device, and more particularly to a flat ionization chamber for pulsed X, gamma ray dose measurement.
Background
Pulsed ionizing radiation is widely used in the fields of industrial flaw detection, X-ray diagnosis, flash X-ray radiography, security inspection, scientific research and the like. Pulsed ionizing radiation (hereinafter referred to as pulsed radiation) has the characteristics of short duration and high instantaneous dose rate, but active electron dosimeters (active electronic dosemeters, hereinafter referred to as AEDs) that are pulsed in a steady-state radiation field have difficulty in accurately measuring the dose of pulsed radiation. AEDs are widely used for dose monitoring of radiation fields, and their direct-reading display and alarm functions provide security to practitioners. AEDs have several problems in measuring the pulsed radiation field dose. Firstly, the instrument has an over-response problem, which necessarily affects the accuracy of the monitoring result; secondly, the interval between two measuring periods of the AED can reach several seconds, if pulse radiation happens just within the interval time of the measuring period of the instrument, a neglected event is likely to happen, so that the accuracy of a measuring result is greatly influenced, and the measuring result is seriously lower; finally, if a large-dose pulse happens in the measurement interval time of the instrument, a false alarm event is inevitably generated, and great potential safety hazards are brought to the injection staff. A flat ionization chamber needs to be developed for millisecond pulsed X and gamma rays for pulsed X and gamma ray dose measurement and personnel protection.
Disclosure of Invention
Aiming at the technical problem that the existing pulse X-ray and gamma-ray radiation dose cannot be accurately measured, the invention provides the flat ionization chamber for measuring the pulse X-ray and gamma-ray dose, which can measure the pulse X-ray and gamma-ray dose rate and solve the millisecond-level pulse X-ray and gamma-ray reference radiation requirement.
The flat ionization chamber for pulse X and gamma ray dose measurement is characterized by comprising working gas, an incident window, a protection ring, a flat electrode and a base; wherein a cylindrical ionization chamber cavity is formed in the base for accommodating the working gas; the incident window is a cylinder with one end open and one end closed, the outer side wall of the incident window is provided with threads, and the open end is buckled on the bottom of the cavity of the ionization chamber; threads matched with the threads on the incident window are formed on the inner side wall of the ionization chamber cavity, so that the incident window is fixed on the base through a knob; the bottom of the ionization chamber cavity is provided with a circular plate electrode, the plate electrode is provided with an annular groove along the outer edge of the plate electrode, and the protection ring is arranged in the annular groove.
Preferably, the entrance window is made of polymethyl methacrylate or polyoxymethylene thermoplastic crystalline polymer.
Preferably, the working surface of the plate electrode is sprayed with a graphite coating or an aluminum coating.
Preferably, the plate electrode is made of polymethyl methacrylate or polyoxymethylene thermoplastic crystalline polymer.
Preferably, the height of the protection ring is equivalent to the height of the ionization chamber, and the width of the protection ring is in the range of 2-6 mm; the protection ring is made of PEEK polyether-ether-ketone resin.
Preferably, the thickness of the coating is in the range of 0.002-0.008 mm.
Preferably, the ionization chamber is characterized in that a graphite layer is formed on the inner side wall of the ionization chamber, and the thickness of the graphite layer is 0.002-0.1mm.
The device can measure the pulse X-ray and gamma-ray dose rate, and solves the millisecond-level pulse X-ray and gamma-ray reference radiation requirement. The device can effectively shorten the polar distance, and under the same working voltage, secondary electrons can be accelerated better, so that the collection rate of the secondary electrons reaches microsecond magnitude; secondly, the ionization chamber adopts an energy compensation measure, and the aluminum layer sprayed on the inner wall can effectively promote the response of the ionization chamber to low-energy photons, so that the lower energy limit of the flat ionization chamber reaches 20keV; finally, the ionization chamber collector is designed with a 2mm guard ring for improving the uniformity of the electric field.
Drawings
Fig. 1 is a schematic view of a planar cavity ionization chamber structure according to the present invention.
Fig. 2 is a graph of the equipotential lines of an ionization chamber according to the present invention when the ionization chamber is measured.
It should be noted that the drawings are not necessarily to scale, but are merely shown in a schematic manner that does not affect the reader's understanding.
Detailed Description
Embodiments of the present invention will be further described with reference to the accompanying drawings.
The ionization chamber according to the invention has the design principle that:
when the ionization chamber is placed in a pulsed X-ray radiation field, the air kerma Kpulse and the generated charge Jg of the pulsed X-rays in the sensitive volume of the ionization chamber satisfy the bragg-gray equation, assuming that the charged particle balance is satisfied:
wherein K pulse is the pulsed X-ray air kerma, W is the average energy consumed to generate a pair of ions in the gas; j g is the total charge of ions of one sign released per unit mass of gas in the cavity, Q g is obtained by electronic system measurements;
Jg＝Qg/mg (2)
m g is the mass of the gas in the cavity, m g ＝ V.rho, V is the cavity volume, and rho is the gas density in the cavity; For the ratio of the mass-impact-prevention power of the medium to the mass-impact-prevention power of the gas generating charged ionized particles, the medium should be the outer wall of the cavity ionization chamber, and this value can be found by referring to ICRU report. W is the average energy consumed to generate a pair of ions in the gas, and can be obtained through ICRU report, and e is the unit ion charge; The ratio of the mass energy absorption coefficients of the cavity gas and the outer wall of the ionization chamber can be obtained through ICRU report; pi k i is a correction factor, pi k i＝kh·kTP·ks. Wherein k h is a correction of the air humidity effect; k TP is the correction of the air temperature and air pressure effects; ks is the ionization loss correction for particle recombination.
Ionization chamber recombination is a major factor affecting collection efficiency, and positive and negative ions may recombine at the site of generation or conform during migration due to insufficient electric field between electrodes. The collection efficiency of the ionization chamber can easily reach more than 99.9% in the case of continuous pulse radiation, however, the collection efficiency of the pulse radiation needs to be corrected according to the dose value obtained by pulse radiation, and the ions generated by one pulse are completely collected in the interval time of two pulses as far as possible according to the pulse duration and the pulse interval. In the field of pulsed X-ray dosimetry research, the main factor interfering with standard ionization chambers is ion recombination. According to theoretical calculation, the collection efficiency of the flat ionization chamber is related to the polar distance of the ionization chamber and high-pressure tight cutting, for example, the polar distance of 1.5mm is selected, the collection voltage is 320V, the collection efficiency of single pulse (the dosage is 10 mGy) exceeds 96%, and therefore the polar distance of the flat ionization chamber is designed to be 1.5mm.
In addition, the material, thickness and coating of the inner walls of the flat ionization chamber can have an effect on the energy response characteristics of the flat ionization chamber.
Based on this, as shown in fig. 1, the flat ionization chamber for pulsed X, gamma ray dose measurement according to the present invention includes a working gas 1, an incident window 2, a guard ring 3, and a collector 4 and a susceptor 5. Preferably, the ionization chamber further comprises an insulator disposed at the ionization chamber wire connection and made of polyetheretherketone resin (PEEK). For reducing leakage current and improving the sensitivity of measurement.
Wherein the working gas 1 is air.
Wherein the entrance window 2 is transparent polymethyl methacrylate (PMMA) or polyoxymethylene thermoplastic crystalline polymer (POM, also known as super steel or siren steel). The incident window 2 is a cylinder with one end open and one end closed, threads are arranged on the outer side wall of the incident window 2, and the open end is buckled on the bottom of the cavity of the ionization chamber. The inner layer of the susceptor 5 is formed with a cylindrical ionization chamber cavity for accommodating the working gas 1. Threads matched with the threads of the incident window 2 are formed on the inner side wall of the cavity of the ionization chamber, so that the incident window is fixed on the base 5 in a knob mode. Preferably, the ionization chamber cavity has an outer diameter of 100-110mm and the sensitive region has a diameter of 80-90mm.
Preferably, a graphite layer is formed on the inner side wall of the ionization chamber, and the thickness is 0.002-0.1mm. The bottom of the cavity in the base 5 is provided with a plate electrode 4. The flat electrode is also called a collector, is made of POM or PMMA, and is sprayed with a graphite or aluminum coating on the working surface. The thickness of the coating is in the range of 0.002-0.008 mm. More preferably, both the upper and lower surfaces of the plate electrode are coated with a graphite or aluminum coating.
The thickness of the plate electrode is preferably 0.5mm to 3mm. The plate electrode 4 is circular, and along the circumference of the plate electrode, an annular groove is provided in which the guard ring 3 is embedded. The height of the protection ring is equivalent to the cavity height of the ionization chamber, and the thickness of the protection ring is in the range of 2-6 mm. The protection ring is made of polyether-ether-ketone (PEEK).
In ionization chamber designs, the uniformity of the electric field within the sensitive volume region has a significant impact on the ionization chamber performance. To check the rationality of the ionization chamber design and whether the electric field between the plates is uniform, electric field analysis software can be used to simulate the distribution of the electric field between the plates at 400V, as shown in fig. 2.
From the simulation result of fig. 2, it can be seen that the potential line between the two polar plates of the ionization chamber has a certain distortion at the edge of the electrode, so that a protection ring is designed above the flat plate electrode 4 of the flat plate ionization chamber, and the uniformity of the electric field is greatly improved.
When the ionization chamber is tested, the flat ionization chamber is placed in a steady 137Cs gamma-ray reference radiation field, so that the axis of the ionization chamber is coincident with the axis of the ray bundle. The radiation field reference conditions are shown in table 2. And determining the sensitivity factor of the flat ionization chamber, establishing the relation Re between the ionization radiation dose and the ionization charge, and testing the electric leakage, the saturation characteristic, the repeatability and the linearity of the flat ionization chamber.
Table 2 reference conditions in gamma-ray reference radiation field
(3) Pulsed X-ray dosimetry
And measuring the air kerma convention true value of the pulse X-ray and gamma-ray reference radiation field by adopting a flat ionization chamber and an electrometer.
The measurement results are shown in the following formula:
Ka＝NK×M×CT，P×Ch (3)
wherein:
NK is the sensitivity factor of the plate ionization chamber;
m is the charge reading of the plate ionization chamber;
CT, P is the air temperature and air pressure correction factor, given by equation (4);
Ch is a correction factor for the difference in relative humidity between the reference and measured conditions, which correction is typically small, so for the range of relative humidity that is typically achieved, ch=1 is assumed.
CT,P＝(P0×T)/(P×T0) (4)
Wherein P and T are the pressure and temperature of the air at the time of measurement; p0 and T0 are the sum of pressures under reference conditions
Temperature, p0=101.3 kP a, t0=293.15K.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
The present invention is not limited to the above embodiments, but the scope of the invention is defined by the claims.
Claims (6)
1. The flat ionization chamber for measuring the pulse X-ray and gamma-ray dose is characterized by comprising working gas, an incident window, a protection ring, a flat electrode and a base; wherein a cylindrical ionization chamber cavity is formed in the base for accommodating the working gas; the incident window is a cylinder with one end open and one end closed, the outer side wall of the incident window is provided with threads, and the open end is buckled on the bottom of the cavity of the ionization chamber; threads matched with the threads on the incident window are formed on the inner side wall of the ionization chamber cavity, so that the incident window is fixed on the base through a knob; the bottom of the ionization chamber cavity is provided with a circular flat electrode, the flat electrode is provided with an annular groove along the outer edge of the flat electrode, and the protection ring is arranged in the annular groove;
the height of the protection ring is equivalent to that of the ionization chamber;
A graphite layer is formed on the inner side wall of the ionization chamber;
a graphite coating or an aluminum coating is sprayed on the working surface of the flat electrode;
the width of the protection ring is in the range of 2-6 mm.
2. The flat panel ionization chamber according to claim 1, wherein the entrance window is made of polymethyl methacrylate or polyoxymethylene thermoplastic crystalline polymer.
3. The flat panel ionization chamber according to claim 1, wherein the flat panel electrode is made of polymethyl methacrylate or polyoxymethylene thermoplastic crystalline polymer.
4. The flat panel ionization chamber of claim 1 wherein said guard ring is made of polyetheretherketone resin.
5. The flat panel ionization chamber according to claim 1, wherein the thickness of the coating is in the range of 0.002-0.008 mm.
6. The flat panel ionization chamber according to claim 1, wherein the thickness of the graphite layer formed on the inner side wall of the ionization chamber is 0.002 to 0.1mm.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201811608416.6A CN109459780B (en) | 2018-12-26 | 2018-12-26 | Flat ionization chamber for pulse X-ray and gamma-ray dose measurement |
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| CN201811608416.6A CN109459780B (en) | 2018-12-26 | 2018-12-26 | Flat ionization chamber for pulse X-ray and gamma-ray dose measurement |
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| CN109459780A CN109459780A (en) | 2019-03-12 |
| CN109459780B true CN109459780B (en) | 2024-09-06 |
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103474323A (en) * | 2012-06-08 | 2013-12-25 | 中国原子能科学研究院 | Ionization chamber for directly measuring personal dose equivalent |
| CN209387885U (en) * | 2018-12-26 | 2019-09-13 | 中国原子能科学研究院 | It is a kind of for pulse X, the plane ionization chamber of gamma-rays dosage measurement |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| HU176837B (en) * | 1979-03-12 | 1981-05-28 | Orszagos Meresuegyi Hivatal | Ionization chamber applicable as secondary dozimetric standard |
| AT394456B (en) * | 1990-04-17 | 1992-04-10 | Oesterr Forsch Seibersdorf | SECOND IONIZATION CHAMBER FOR MEASURING PHOTON RADIATION |
| CN101158723A (en) * | 2006-02-10 | 2008-04-09 | 中国人民解放军63960部队 | End window ionization chamber |
| CN103472475B (en) * | 2012-06-08 | 2015-09-30 | 中国原子能科学研究院 | A kind of transmission-type monitor ionization chamber being suitable for low energy X ray and measuring |
| CN106783503B (en) * | 2017-03-10 | 2018-05-25 | 山东中测校准质控技术有限公司 | A kind of hollow cylindrical collector diagnoses ionisation chamber |
| CN107992699B (en) * | 2017-12-14 | 2021-03-19 | 中国计量科学研究院 | Simulation detection method for radiation dose of eye lens |
| CN108562931A (en) * | 2018-02-02 | 2018-09-21 | 中国原子能科学研究院 | A kind of energy compensating type Neutron Ambient Dose Equivalent secondary standard ionisation chamber |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103474323A (en) * | 2012-06-08 | 2013-12-25 | 中国原子能科学研究院 | Ionization chamber for directly measuring personal dose equivalent |
| CN209387885U (en) * | 2018-12-26 | 2019-09-13 | 中国原子能科学研究院 | It is a kind of for pulse X, the plane ionization chamber of gamma-rays dosage measurement |
Non-Patent Citations (1)
| Title |
|---|
| 平板电离室的研制及改进;陈义珍 等;原子能科学技术;20080930;第42卷;380-384 * |
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