CN104681390B - Graphite cake ionisation chamber - Google Patents
Graphite cake ionisation chamber Download PDFInfo
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- CN104681390B CN104681390B CN201510112764.4A CN201510112764A CN104681390B CN 104681390 B CN104681390 B CN 104681390B CN 201510112764 A CN201510112764 A CN 201510112764A CN 104681390 B CN104681390 B CN 104681390B
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Abstract
The present invention relates to a kind of graphite cake ionisation chamber, the graphite cake ionisation chamber includes：Outer wall, the outer wall are round pie, and material is graphite；Passive electrode, for flake, material is graphite, is insulated in the outer wall, and with the outer wall；Electrode connecting rod, material are graphite, are connected with the passive electrode, and are insulated with the outer wall；First protected level, it is socketed on the outside of the electrode connecting rod, and is insulated with the electrode connecting rod；Second protected level, it is connected with first protected level, is socketed on the outside of the electrode connecting rod, and is insulated with the electrode connecting rod；High compression ring, it is connected with the outer wall.The graphite cake ionisation chamber of the present invention, machining and assembly precision are high, are easy to Modeling Calculation.Improve stability and the degree of accuracy of benchmark reproduction value.
Description
Technical field
The present invention relates to a kind of graphite cake ionisation chamber, more particularly to a kind of graphite cake ionisation chamber.
Background technology
Air kerma is the powered electricity of whole that uncharged ionizing particle discharges in the air of unit mass
It is that one of most important physical quantity is learned in ionising radiation metering from the summation of the initial kinetic energy of particle.Air kerma is also to inhale
Dosage and the Research foundation of dose equivalent are received, is changed through value, the absorbed dose of radiation and dose equivalent value of application field can trace to the source
To Kerma benchmark.It is the existing legality measurement system in China that air kerma amount, which passes system, treatment for radiation-caused disease, radiation protection
All traced to the source to air kerma benchmark with the dose measurement device of environmental monitoring.Accurate reproduction air kerma value, it is
One of horizontal important symbol of national ionising radiation scientific research.And the measurement of air kerma needs to use ionisation chamber.
The content of the invention
The purpose of the present invention is the defects of being directed to prior art, there is provided a kind of graphite cake ionisation chamber, mechanical precision is high, carries
The precision that high air kerma calculates.
To achieve the above object, the invention provides a kind of graphite cake ionisation chamber, the graphite cake ionisation chamber to include：
Outer wall, the outer wall are round pie, and material is graphite；
Passive electrode, for flake, material is graphite, is insulated in the outer wall, and with the outer wall；
Electrode connecting rod, material are graphite, are connected with the passive electrode, and are insulated with the outer wall；
First protected level, it is socketed on the outside of the electrode connecting rod, and is insulated with the electrode connecting rod；
Second protected level, be connected with first protected level, be socketed on the outside of the electrode connecting rod, and with the electricity
Pole connecting rod insulation；
High compression ring, it is connected with the outer wall.
Further, the passive electrode is connect with outer wall insulation by the neck that insulate and set.
Further, the electrode connecting rod passes through the first insulation division and outer wall, the first protected level and the second protection
Class B insulation, which connects, to be set.
Further, the outer wall is connect with the described first protection class B insulation by the second insulation division and set.
Further, the high compression ring is connect with the described first protection class B insulation by the 3rd insulation division and set.
Further, the graphite cake ionisation chamber also includes HV Terminal, is connected with the high compression ring.
The graphite cake ionisation chamber of the present invention, machining and assembly precision are high, are easy to Modeling Calculation.Improve benchmark reproduction
The stability of value and the degree of accuracy.
Brief description of the drawings
Figure 1A is the front view of graphite cake ionisation chamber of the present invention；
Figure 1B is the side view of graphite cake ionisation chamber of the present invention；
Fig. 2 is volt-ampere characteristic curve figure.
Embodiment
Below by drawings and examples, technical scheme is described in further detail.
60It is 10cm that the development of Co gamma-rays air kerma ionisation chambers, which is realized using nominal volume,3Ball-cylinder
Measurement of the cavity ionization chamber to air kerma.
Compared with ball-cylindrical cavity ionisation chamber, cake ionisation chamber has the advantages that easier to process, and the invention provides one
Set is using cake type ionisation chamber as measuring unit60Co gamma-rays air kerma measurement apparatus, the high pressure of the cake ionisation chamber
Pole and collector use graphite material, and device is operated in 50TBq60In Co irradiation fields, and obtained using weak current acquisition system
Obtaining current signal.The each physical parameter of method acquisition device and correction term for intending being combined using testing and covering snap gauge.
When Kerma refers to uncharged ionizing particle with matter interaction, it is transferred in unit mass material secondary
Level charged particle initial kinetic energy summation, owns caused by the bremstrahlen energy and medium quadratic effect including ionizing particle
The energy of charged particle such as auger electrons.Assuming that all bands that uncharged particle discharges in the medium that quality is dm (units/kg)
The initial kinetic energy sum of charged particle is dEtr(unit J), then Kerma K can be defined as below：
Wherein K unit is Jkg-1；Special entitled gray(Gy) (Gy).
Photon can not directly cause ionization, and pass through caused by photoelectric effect, Compton scattering and pair effect etc. times
Level electronics causes ionization.When secondary electron passes through air, it can be had an effect with the orbital electron of atom in air, loss section itself
Point or whole energy so that atom is ionized or excited in air, forms electronics and cation pair, experimentally by ionization electricity
The measurement of stream can obtain the dose of radiation of photon.Bragg-Gray aperture theories assume that gas cavity size is much smaller than secondary electrical
During the range of son, the ionization of photon caused secondary electron in the cavities can be neglected；The introducing of cavity does not change secondary electron
Fluence and spectral distribution；Radiation field is equally distributed in material around cavity.Graphite etc. and the effective atom of air need to be used
Material development similar in ordinal number ionizes locular wall, to meet aperture theory condition as far as possible, carries out air kerma measurement.
For cavity ionization chamber, reproduction air kerma K formula is as follows：
It in density is ρ (unit kgm that wherein Q, which is,-3) and volume be V (unit m3) dry air in production given birth to
Total electrical charge, unit C；W/e is to produce the average ionization work(required for the ion pair of a pair of unit charges, unit JC-1；g
For the share for not being collected the energy that pole is collected into consumed by bremstrahlen；(μtr/ρ)a,cFor the mass-energy of air and graphite
Transfer ratio ratio is related to ionisation chamber graphite material；sc,aFor graphite and the stopping-power ratio of air, with ionisation chamber graphite material
And geometry is related；ΠkiIt is to include the various correction terms related to ionisation chamber geometry, measuring condition etc..
Figure 1A is the front view of graphite cake ionisation chamber of the present invention, and Figure 1B is the side view of graphite cake ionisation chamber of the present invention
Figure, as illustrated, graphite cake ionisation chamber of the present invention specifically includes：Outer wall 1, passive electrode 2, electrode connecting rod 3, first are protected
The 4, second protected level 5 of level and high compression ring 6.
Outer wall 1 is round pie, and material is graphite.Passive electrode 2 is flake, and material is also graphite, in outer wall 1,
And insulated with outer wall 1.Electrode connecting rod 3, material are graphite, are connected with passive electrode 2, and are insulated with outer wall 1.First protects
Shield level 4 is socketed in the outside of electrode connecting rod 3, and is insulated with electrode connecting rod 3.Second protected level 5 is connected with the first protected level 4
Connect, be socketed in the outside of electrode connecting rod 3, and insulate with electrode connecting rod 3.High compression ring 6 is connected with outer wall 1.
Set specifically, passive electrode 2 is connect by the neck 7 that insulate with the insulation of outer wall 1.Electrode connecting rod 3 passes through the first insulation
Portion 81 connects with the insulation of outer wall 1, the first protected level 4 and the second protected level 5 and set.Outer wall 1 passes through the second insulation division 82 and the first protection
The insulation of level 4, which connects, to be set.High compression ring 6 is connect with the insulation of the first protected level 4 by the 3rd insulation division 83 and set.
In addition, graphite cake ionisation chamber of the present invention also includes HV Terminal 9, it is connected with high compression ring 6.
Ionization chamber outer wall 1, passive electrode 2, the material of electrode connecting rod 3 use monoblock density as 1.85gcm-3Stone
Ink, to ensure the even density of various pieces.Again as shown in figure 1, the outer wall 1 of ionisation chamber is made up of cylindrical box and upper lid, receive
Colelctor electrode 2 is cylindrical sheets that are centrally located and being insulated with ionization chamber outer wall 1.The main geometric parameters of ionisation chamber are listed in table 1
In.
Table 1
| Geometric parameter | Numerical value |
| External diameter (mm) | 50.955 |
| Internal diameter (mm) | 45.115 |
| Upper cover thickness (mm) | 2.753 |
| Interior height (mm) | 5.208 |
| Passive electrode diameter (mm) | 40.948 |
| Passive electrode thickness (mm) | 0.966 |
| Neck and electrode connecting rod volume (mm3) | 71.3 |
| Cavity volume (mm3) | 6981.6 |
Support section is made up of three parts.Foremost is high compression ring 6 made of copper, electrode connecting rod 3 and the part of outer wall 1, high
There is gold-plated copper HV Terminal 9 on pressure ring 6, be connected by scolding tin with high-voltage power-line.
During measurement, ionization electricity is formed with passive electrode 2 in ionization chamber outer wall 1 plus positive or negative voltage by high compression ring 6
, passive electrode electric current is exported from the circular hole of outer wall 1 by electrode connecting rod 3.
Insulation neck 7, the first insulation division 81, the second insulation division 82, the 3rd insulation division 83 are that material is the exhausted of PTFE material
Edge material.First protected level 4, the second protected level 5 play a part of signal shielding.Finally, signaling interface part is designed to mark
Accurate Q9 bases, by Q9 connector sending out signals.
Graphite cake ionisation chamber pair60The gamma-ray responses of Co.Weak current measuring system is by electrometer, temperature humidity air pressure
Meter and industrial computer composition.Electrometer is controlled by the system controlling softwares of Labview programmings with realize bias adjustment and from
Dynamicization measures, and can realize two kinds of measurement patterns of charge measurement and current measurement.Temperature humidity barometer passes through RS232 and industry control
Machine is connected, and directly reads ambient parameter, and the amendment of the temperature humidity air pressure for electric current.Electrometer and temperature humidity air pressure
Meter is traced to the source to correlate values National primary standard.
Ionisation chamber active centre is away from the preceding surface 430mm of source container external diaphragm in measurement process, and wafer thickness 3.4mm, source has
The preceding surface 555mm of centre-to-centre spacing source container external diaphragm (drawing nominal value) is imitated, the preceding surface in the geometrical center to center source in source is
11.25mm, the distance of the geometrical center to center ionisation chamber active centre (a reference value reproduction measurement point) in source is 999.25mm.
Electrometer selects 200nC ranges in measurement process.It is illustrated in figure 2 volt-ampere characteristic curve figure, horizontal seat in figure
It is designated as being added high pressure, ordinate is the ionization current of measurement, is blocked in 27V-30V scopes in figure.Determine polarizing voltage
For 150V, now curent change ± 50V, curent change are less than 0.4%.Measured value is carried out in real time by software programming in measurement
Temperature and air pressure humidity amendment.
The physical parameter and correction term of the graphite cake ionisation chamber experiment measurement of the present invention are summarized in table 2.First in table 2
It is classified as physical parameter and correction term, including measurement electric current, atmospheric density, ionization building volume, ionization work(, compound modifying factor, handle
Modifying factor and field uniformity modifying factor, corresponding value is provided respectively in secondary series, include A classes in tertial uncertainty
Standard uncertainty and type B standard uncertainty.A class uncertainties come from statistics and calculated；B class uncertainties come from measurement
Instrument is traced to the source, or from used measuring method, subitem hereafter is listed into occurrence and the bibliography of measuring method.
Calculated by side and root method, all the Composite Seismogram of 7 physical parameters and correction term is 0.17%.
Atmospheric density ρ selects BIPM recommendations, i.e., at 0 DEG C of temperature, pressure 101.325kPa, the density of dry air
1.2930kg·m-3, for uncertainty with the assessment of B classes method, its value is 0.01%.
Wherein temperature correction factor：
kT=(273.15+T)/293.15 (3-1)
Air pressure modifying factor：
kP=101.325/P (3-2)
T is temperature in above-mentioned formula, unit for DEG C, P is atmospheric pressure, unit kPa.Humidity is by being adapted to dry gas
Correction factor be 0.9970.Measuring system of the present invention is directly adapted to measurement electric current under the status of criterion, therefore temperature and air pressure is wet
Degree amendment is not comprised in correction factor, in order to avoid compute repeatedly.
The ionization work(that a pair of ion pairs are produced in dry air selects CCRI (I) recommendations 33.97JC-1.By W/e and
Sc,aUncertainty COMPREHENSIVE CALCULATING, (W/e) Sc,aUncertainty is assessed in B classes method, and its value is 0.11%.
Compound modifying factor ksFrom ion and electronics measured preceding further in conjunction with without being collected simultaneously through collector
Measure.Obtaining calculation formula by Boag methods is：
IU/IU/n=1+ (n-1) A/U+ (n2-1)m2(g/U2)IU (3-1)
ks=1+ Α/U+m2(g/U2)IU (3-2)
Be in formula A rely on ionisation chamber type constant, IUIt is the ionization current measured when operating voltage is U, IU/nIt is work
The ionization current that voltage measures when being U/n, g are the factors relevant with ionisation chamber physical dimension, m2For the migration with negative ions
The related physical quantity of rate.
The present invention uses current value when changing voltage with ionisation chamber distance as U and U/n by changing source, draws IU/
IU/n-IUFigure, A/U and m are drawn from slope and intercept2(g/U2), compound modifying factor is then drawn according to formula 3-2.The present invention
Choose n=3 (U=150V, U/n=50V) and calculate compound modifying factor with two kinds of conditions of n=5 (U=150V, U/n=30V)
ksIt is 0.004% for 1.0009, A classes uncertainty, the correction term is determined with Same Way with ARPANSA, its B class uncertainty
For 0.05%.
Handle amendment kstThe scattering item brought from ionisation chamber support section.By in ionisation chamber support section relative to ionization
A size material identical support section is placed at the Central Symmetry of room and obtains handle correction value.Testing obtained handle correction value is
0.9976, for uncertainty with type A evaluation, its value is 0.06%.
Field uniformity amendment passes through 1 PTW models TW31014, volume 0.015cm3Ionisation chamber measure, survey respectively
The average current value with ionisation chamber centre distance for 4 points of 2.1cm in ionisation chamber central plane is measured, at cake ionisation chamber center
Current value compares.Measure field uniformity correction factor krnFor 1.0016, for uncertainty with type A evaluation, its value is 0.09%.
Table 2：The physical parameter and correction term of graphite cake ionisation chamber experiment measurement
Simulation calculating, the physics ginseng of acquisition are carried out to the graphite cake ionisation chamber of this work development using DSMC
Number and correction term are listed in Table 3 below.The statistical error that the A classes uncertainty of 5 physical parameters and correction term provides to cover snap gauge to intend,
The value that B classes uncertainty is provided with reference to NRC using the article of identical calculations method.By side and root method obtain each analog parameter and
The Composite Seismogram of the Composite Seismogram of correction term, 5 physical parameters and correction term is 0.17%.
Monte carlo method program thereby of the present invention is EGSnrc, and each physical parameter and amendment are calculated by different subprograms
.The bremstrahlen factor is calculated by g programs in EGSnrc, the graphite material density of cake ionisation chamber used is during calculating
1.85g·cm-3.By in EGSnrc DOSRZnrc subprograms distinguish mock standard situation under air kerma relative value with
1.85g·cm-3Graphite material Kerma relative value, the two ratio are the mass energy transfer coefficient ratio (μ of air and graphitetr/
ρ)a,c.By SPRRZnrc programs simulation ionization chamber wall materials in EGSnrc, (present invention is selected under the status of criterion with specified material
Air) stopping-power ratio, the analogy method will not provide the absolute value of stopping power.Wall modifying factor kwallCalculating select
CAVRZnrc subprograms, " Aatt and Ascat " options are selected in it calculates type.Axial uniformity amendment passes through
DOSRZnrc simulation parallel beams are incident to measure the ratio between air absorbed dose of radiation with ionisation chamber under the condition of incidence of 100cm far points source.Prevent
Ability than simulation, kwallSimulation and the simulation of axial uniformity be required to be modeled cake ionisation chamber.
Table 3：Graphite cake ionisation chamber covers the physical parameter and correction term that snap gauge is intended obtaining
The same measurement point in radiation field, by the measurement result of cake ionisation chamber after half-life period is adapted on the same day, with
Country based on ball-cylindrical cavity ionisation chamber60Co gamma-rays air kerma standard apparatus measurement results are compared, preceding
The ratio of person and the latter are 0.9987.The method for calculating and comparing uncertainty is reported with reference to international comparison, removes same source not
After degree of certainty component, the combined standard uncertainty of the ratio is 0.23%.The relevant parameter of stream oriented device absolute measurement is listed in table 4
In, because two ionization building volumes and structure are different, part correction term value difference is larger.The wall modifying factor K of cake ionisation chamberwall
For 1.0011, less than the 1.0186 of ball-columnar ionization room, wall effect can be reduced by illustrating the design of patty ionisation chamber.
Because cake ionisation chamber design feature causes it to be more than ball-columnar ionization room by irradiation solid angle, therefore analyze its axial uniformity
Parameter kanMore than ball-columnar ionization room, the supposition is confirmed by comparing in table.
Table 4：Cake ionisation chamber and the comparison of ball-columnar ionization room
The present invention, by the development of cake ionisation chamber, realizes from the design of different structure ionisation chamber60Co gamma-rays
The absolute measurement of air kerma.This work reappear air kerma value with60Co gamma-rays air kermas state
The ratio of family's benchmark is 0.9987, combined standard uncertainty 0.23%.Institute's development ionisation chamber uses full graphite pied geometry,
Machining and assembly precision are high, are also easy to Monte Carlo Modeling Calculation, reduce the uncertainty of correction term.The ionisation chamber will
Ionisation chamber group is formed with existing benchmark, to improve the stability of benchmark reproduction value and the degree of accuracy.In addition, ionized for the set cake
Room devises anti-Water ball so that the cake ionisation chamber can be used for ionization method absolute measurement60Co gamma-rays water absorbent amounts, phase
Close work and also achieve good result.
Above-described embodiment, the purpose of the present invention, technical scheme and beneficial effect are carried out further
Describe in detail, should be understood that the embodiment that the foregoing is only the present invention, be not intended to limit the present invention
Protection domain, within the spirit and principles of the invention, any modification, equivalent substitution and improvements done etc., all should include
Within protection scope of the present invention.
Claims (6)
1. a kind of graphite cake ionisation chamber, it is characterised in that the graphite cake ionisation chamber includes：
Outer wall, the outer wall are round pie, and material is graphite；
Passive electrode, for flake, material is graphite, is insulated in the outer wall, and with the outer wall；
Electrode connecting rod, material are graphite, are connected with the passive electrode, and are insulated with the outer wall；
First protected level, it is socketed on the outside of the electrode connecting rod, and is insulated with the electrode connecting rod；
Second protected level, it is connected with first protected level, is socketed on the outside of the electrode connecting rod, and connects with the electrode
Extension bar insulate；
High compression ring, it is connected with the outer wall.
2. graphite cake ionisation chamber according to claim 1, it is characterised in that the passive electrode by insulate neck with
The outer wall insulation, which connects, to be set.
3. graphite cake ionisation chamber according to claim 1, it is characterised in that the electrode connecting rod passes through the first insulation
Portion connects and set with the outer wall, the first protected level and the second protection class B insulation.
4. graphite cake ionisation chamber according to claim 1, it is characterised in that the outer wall passes through the second insulation division and institute
State the first protection class B insulation and connect and set.
5. graphite cake ionisation chamber according to claim 1, it is characterised in that the high compression ring by the 3rd insulation division with
The first protection class B insulation, which connects, to be set.
6. graphite cake ionisation chamber according to claim 1, it is characterised in that the graphite cake ionisation chamber also includes height
Pressure side, is connected with the high compression ring.
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| CN105589503B (en) * | 2016-01-27 | 2017-11-07 | 中国计量科学研究院 | A kind of production method and constant-current source device of direct current continuous current signal |
| CN107576979B (en) * | 2017-09-01 | 2024-04-12 | 山东省计量科学研究院 | Dose rate range simulation expanding device |
| CN108550516B (en) * | 2018-05-24 | 2021-01-01 | 上海联影医疗科技股份有限公司 | Multi-channel ionization chamber of medical linear accelerator and collector thereof |
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| CN204424202U (en) * | 2015-03-13 | 2015-06-24 | 中国计量科学研究院 | Graphite cake ionization chamber |
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| US20110095199A1 (en) * | 2009-10-27 | 2011-04-28 | Institute Of Nuclear Energy Research Atomic Energy Council, Executive Yuan | Method to measure current using parallel plate type ionization chamber with the design of guard electrode |
| CN103311086B (en) * | 2012-03-15 | 2016-03-30 | 中国原子能科学研究院 | Multi-layer cavity ionization chamber |
| CN102879794B (en) * | 2012-09-20 | 2015-09-30 | 中国计量科学研究院 | A kind of device for reappearing air kerma in radioactive source radiation field |
| TWI497102B (en) * | 2012-10-31 | 2015-08-21 | Iner Aec Executive Yuan | Ionization chamber with built-in temperature sensor |
| CN203055855U (en) * | 2012-11-13 | 2013-07-10 | 北京中科加华科技有限公司 | Graphite gas ionization detector |
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| CN204424202U (en) * | 2015-03-13 | 2015-06-24 | 中国计量科学研究院 | Graphite cake ionization chamber |
Non-Patent Citations (3)
| Title |
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| Performance evaluation of graphite pancake ionization chamber by comparing the absorbed dose to water calibration;Lee, JH etal;《RADIATION MEASUREMENTS》;20060331;第41卷(第3期);第306-316页 * |
| 球形石墨空腔电离室内部电场的研究;邬蒙蒙等;《中国测试》;20121130;第38卷(第6期);第30-33页 * |
| 用于60Coγ射线照射量基准的石墨空腔电离室的研制;徐沔等;《计量学报》;19861030;第7卷(第4期);第245-251页 * |
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