CN102879794A - Device used for reproduction of air kerma in radiation field of radioactive sources - Google Patents

Device used for reproduction of air kerma in radiation field of radioactive sources Download PDF

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CN102879794A
CN102879794A CN2012103504646A CN201210350464A CN102879794A CN 102879794 A CN102879794 A CN 102879794A CN 2012103504646 A CN2012103504646 A CN 2012103504646A CN 201210350464 A CN201210350464 A CN 201210350464A CN 102879794 A CN102879794 A CN 102879794A
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signal
module
radiation
measurement
air kerma
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CN102879794B (en
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王坤
杨小元
杨元第
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National Institute of Metrology
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Abstract

The invention aims to realize absolute measurement and magnitude reproduction of air kerma and traces the magnitude back to the International System of Units. The invention provides a device used for reproduction of the air kerma in a radiation field of radioactive sources, which comprises a ray radiation unit, a detector unit, a position control unit and a signal measurement and control unit, wherein the ray radiation unit is used for providing a ray radiation field of radioactive sources; the detector unit comprises an ionization chamber and a center collector electrode; the position control unit is used for adjusting the pitching and/or level angle of the detector unit relative to the ray radiation unit, and carrying out positioning and displacement control on the detector unit under ray bundle irradiation conditions; and the signal measurement and control unit comprises a signal storage module, a signal monitoring module, a signal compensation module, a signal measuring module and a magnitude traceability module. The device for reproduction of ray air kerma provided by the invention has the characteristics of 0.27% of the uncertainty of combined standard of the reproduction of air kerma, and 0.2% of the long-time stability.

Description

A kind of device for reproduction radioactive source radiation field Air kerma
Technical field
The present invention relates to measurement and the reproduction of radioactive source radiation field Air kerma, belong to the basic measurement technology in ionising radiation metering field.
Background technology
Air kerma is defined as the summation of the initial kinetic energy of all charged ionizing particles that non-charged particle disengages in the unit mass air, be one of four SI derived quantitys in ionising radiation field, in 8 the crucial comparisons in the ionizing radiation dose field of International Bureau of Wieghts and Measurements's tissue, there are 6 to be the comparison of air kerma value.Air kerma is the important physical value of ionising radiation metering need of work reproduction, and it has following advantage:
1, kerma is used the SI legal unit of measurement, thereby has the superiority of SI unit, such as strict, simple and clear rationally, science is practical and general etc.;
2, kerma is applicable to describe any indirectly ionizing particles and interaction between substances;
3, the not tested energy restriction of kerma, applied range;
4, kerma and the biological effects of radiation are in close relations, and it just more is applicable to describe ray and matter interaction like this, and it is more extensive that it is used in the radiation therapy field.Because air kerma has above-mentioned advantage, so generally adopt in the world air kerma to substitute exposure as the physical quantity of transmission of quantity value.
Summary of the invention
The present invention is intended to realize absolute measurement and the realization of air kerma, and this amount is traced to the source to International System of Units.
The present invention adopts the graphite cavity ionization chamber as the ray detector unit, carries out the measurement of ionization current, finally realizes the realization of air kerma.Technical scheme of the present invention is:
A kind of device for reproduction radioactive source radiation field Air kerma comprises x radiation x unit, detector cells, position control unit and signal measurement and control unit,
Described x radiation x unit provides radioactive source x radiation x field;
Described detector cells comprises ionization chamber and center collector, is used for forming under the ionising radiation condition band point particle balance, satisfies the basic theory condition of measuring;
Described position control unit is used for adjusting pitching and/or the level angle of the relatively described x radiation x of described detector cells unit, under the beam radiation parameter described detector cells is positioned and the control that walks;
It is characterized in that,
The signal measurement and control unit comprises signal storage module, signal monitoring module, signal compensation module, signal measurement module and magnitude tracing module, wherein,
The signal storage module is used for the weak current of described detector cells constant output is accumulated storage;
The signal monitoring module is used for the variation of monitoring fixed point current potential, and judge whether this current potential satisfies equilibrium condition, namely whether revert to initial value and the certain hour that remains unchanged, when satisfying equilibrium condition, the signal monitoring module is sent the measurement instruction to signal measurement module;
The signal compensation module is used for the voltage of signal storage module output is applied a compensation rate, so that the current potential of the fixed point of monitoring returns initial value after measuring beginning;
Signal measurement module is used for according to the described measurement instruction from the signal monitoring module, the described compensation rate of described signal compensation module output is measured, and recorded described compensation rate Δ V and corresponding time t;
The magnitude tracing module is used for calculating the ionization current value that the center collector of described detector cells is collected according to the capacitance of the time t of described compensation rate Δ V, correspondence and measuring circuit, and according to the air kerma at air kerma realization formula calculation and measurement point place, and the physical quantity that comprises time, capacitance, magnitude of voltage and current value that relates in the measuring process traced to the source to the national standard of corresponding International System of Units.
Description of drawings
Fig. 1 shows the block diagram of apparatus of the present invention.
Fig. 2 is the signal of the ball-cylindrical air kerma ionization chamber in the detector cells.
Fig. 3 is according to measurement procedure synoptic diagram of the present invention.
Embodiment
See also Fig. 1, the inventive system comprises the x radiation x unit, detector cells, position control unit and signal measurement and control unit.Below will describe technical scheme of the present invention in detail according to each sequence of unit.
The x radiation x unit
As example, the x radiation x unit in the present embodiment adopts 60The Co gamma emitter, but it should be understood by those skilled in the art that adopting other suitable radiation sources is feasible equally.
Particularly, 60Co gamma ray radiator activity is 30TBq (on January 1st, 2006), is Russian import high specific activity 60Co radiation source, volume are φ 23.8mm * 34.8mm.Radiation source is fixed on that the source of Safety Irradiation device is indoor, and the chamber, source is made of tungalloy, and density is a little less than 18.95g/cm 3The chamber, source is that diameter is that 100mm, length are the cylinder of 100mm, and is coaxial with radioactive source.Go out beam hole over against radioactive source, also coaxial with it.Go out the diameter 45mm of beam hole, do not affect diaphragm system to the effect in source.Irradiation devices adopt electronic rotation shutter control radiation source beam, shutter is between chamber, source and collimating apparatus, when rotating shutter overlapped with radiation source and collimating apparatus exit portal, beam was open, when the axis in duct on the rotating shutter and beam axis at an angle of 90 the time beam close.Collimating apparatus is made by tungalloy, according to the ISO4037 standard design.The shell of irradiator adopts stainless steel material to make, and inner utilization lead adopts the single placingJi Shu as shielding material, guarantees seamless.
Detector cells
Detector cells mainly comprises ionization chamber and center collector.In the present embodiment, preferably, 60Co gamma-rays air kerma ionization chamber can be designed to ball-cylindrical structural, as shown in Figure 2, its two ends are spherical, the middle part is cylindrical, this structure combines cylindricality and spherical advantage, can effectively reduce the corner effect of plunderring of cylindricality ionization chamber, reduce the uncertainty of the physical parameters measurement in the realization.Ionization chamber inside is provided with the center collector.Center collection very end is spherical cylinder, and the terminal center that is positioned at the ionization chamber internal cavities.As example, the nominal collected volume of ionization chamber is 10cm 3, effectively collected volume is 9.542cm 3, the detail parameters of ionization chamber and center collector sees Table 1.
The detail parameters of table 1 ball-cylindrical air kerma ionization chamber
Figure BSA00000780244700031
Position control unit
Position control unit is used for the control survey platform, realizes the accurate location of benchmark.In the present embodiment, long 3.0 meters of the guide rail of measuring table, platform is wide to be 1.1 meters, can realize three-dimensional mobile manual or electronic control, wherein moves forward and backward 3 meters of scopes, 1.5 meters of move left and right.Adopt the driven by motor ball-screw to rotate as transfer motion power.Fully emit in order to make guide rail steel internal stress, V-way and the closed slide combination of effect released in employing naturally through 3 years, and adopt ground furrow irrigation bath mud method fixedly the I-shaped steel as the ground of guide rail, so that stable performance (not deformation) behind the guide rails assembling guarantees that like this ionization chamber bearing accuracy is better than 0.3mm.Scale on the guide rail can computerized control with platform, and it advances, retreats, raises and reduce at guide rail.Also can utilize button on the manual control box on guide rail next door to control its scale is advancing, is retreating, is raising and reducing at guide rail with platform.On control desk and manual control box next door be separately installed with big or small monitor, can see very easily on the screen ionization chamber apart from the radiation source center, upper and lower, about position (scale monitors on the guide rail) and laboratory overall picture.
The signal measurement and control unit
The signal measurement and control unit comprises signal storage module, signal monitoring module, signal compensation module, signal measurement module and magnitude tracing module, wherein,
The signal storage module is used for the weak current of described detector cells constant output is accumulated storage;
The signal monitoring module is used for the variation of monitoring fixed point current potential, and judge whether this current potential satisfies equilibrium condition, namely whether revert to initial value and the certain hour that remains unchanged, when satisfying equilibrium condition, the signal monitoring module is sent the measurement instruction to signal measurement module;
The signal compensation module is used for the voltage of signal storage module output is applied a compensation rate, so that the current potential of the fixed point of monitoring returns initial value after measuring beginning;
Signal measurement module is used for according to the described measurement instruction from the signal monitoring module, the described compensation rate of described signal compensation module output is measured, and recorded described compensation rate Δ V and corresponding time t;
The magnitude tracing module is used for calculating the ionization current value that the center collector of described detector cells is collected according to the capacitance of the time t of described compensation rate Δ V, correspondence and measuring circuit, and according to the air kerma at air kerma realization formula calculation and measurement point place, and the physical quantity that comprises time, capacitance, magnitude of voltage and current value that relates in the measuring process traced to the source to the national standard of corresponding International System of Units.
In the present embodiment, 60The gamma-ray air kerma realization of Co formula is:
K · = I Vρ W e 1 1 - g ‾ ( μ en ‾ ρ ) a , c s ‾ c , a Π k i
In the formula,
Figure BSA00000780244700042
Air kerma rate for measurement point; I is the ionization current that the center collector of detector cells is collected; V is the ionization chamber volume of detector cells; ρ is dry air density; W/e is in dry air, the average energy that consumes during with a pair of ion pair of electron production of an electron charge;
Figure BSA00000780244700043
Account for the share of its zero energy for the energy that is consumed in bremsstrahlung;
Figure BSA00000780244700044
Be the mass energy absorption coefficient ratio of air with graphite;
Figure BSA00000780244700045
Average stopping-power ratio for graphite and air; k iFollowing each modifying factor of expression:
k s-ion recombination losses modifying factor;
k h-humidity modifying factor;
k St-ionization chamber bar Scattering correction the factor;
k Att-wall weakens modifying factor;
k Sc-wall scattering modifying factor;
k CEPThe mean place modifying factor of-generation electronics;
k An-axial heterogeneity modifying factor;
k Rn-heterogeneity modifying factor radially.
Measurement procedure as shown in Figure 3.As preferably, in order to make the abundant return-to-zero of measurement mechanism, measure the time interval that finishes with measurement beginning next time is 1 minute at every turn, and the positive and negative polarization voltage transitions time interval of ionization chamber is 5 minutes.Each polarizing voltage of ionization chamber is measured ionization electric charge (ionization current) ten times, calculates measured value, mean value, the relative standard deviation of measurement result and the mean value of positive-negative polarity of each polarizing voltage after temperature, pressure correction, and 60The measured value of Co gamma-rays air kerma and 60The Co gamma-rays half life period is revised.Measurement result is as shown in table 2.
Each physical parameter of table 2 and uncertainty evaluation thereof
Figure BSA00000780244700061
(1) s iRepresent the u (x that category-A is estimated with statistical method i)/x iRelevant criterion uncertainty u iRepresent the u (x that category-B is estimated with other method i)/x iThe relevant criterion uncertainty
(2) under 0 ℃ and 101.325kPa condition
(3) Result's synthetic uncertainty, (4) k Attk ScCompany's value of taking advantage of.
Adopt ray air kerma reproducing apparatus of the present invention, reproduction air kerma combined standard uncertainty is 0.27%, long-time stability 0.2%; Participate in the BIPM.RI of International Bureau of Wieghts and Measurements (I)-K1 International key comparison, and compare reference value 0.08% interior coincideing, the result enters the KCDB database, obtains international equivalence.Through for a long time test, the support equipments such as benchmark ionization chamber and radiation field possess gamma-rays air kerma realization and transmission of quantity value ability, meet the technical requirement of National primary standard device.

Claims (2)

1. a device that is used for reproduction radioactive source radiation field Air kerma comprises x radiation x unit, detector cells, position control unit and signal measurement and control unit,
Described x radiation x unit provides radioactive source x radiation x field;
Described detector cells comprises ionization chamber and center collector, is used for forming under the ionising radiation condition band point particle balance, satisfies the basic theory condition of measuring;
Described position control unit is used for adjusting pitching and/or the level angle of the relatively described x radiation x of described detector cells unit, under the beam radiation parameter described detector cells is positioned and the control that walks;
It is characterized in that,
The signal measurement and control unit comprises signal storage module, signal monitoring module, signal compensation module, signal measurement module and magnitude tracing module, wherein,
The signal storage module is used for the weak current of described detector cells constant output is accumulated storage;
The signal monitoring module is used for the variation of monitoring fixed point current potential, and judge whether this current potential satisfies equilibrium condition, namely whether revert to initial value and the certain hour that remains unchanged, when satisfying equilibrium condition, the signal monitoring module is sent the measurement instruction to signal measurement module;
The signal compensation module is used for the voltage of signal storage module output is applied a compensation rate Δ V, so that the current potential of the fixed point of monitoring returns initial value after measuring beginning;
Signal measurement module is used for according to the described measurement instruction from the signal monitoring module, and the described compensation rate Δ V that described signal compensation module is exported measures, and records described compensation rate Δ V and corresponding time t;
The magnitude tracing module is used for calculating the ionization current value that the center collector of described detector cells is collected according to the capacitance of the time t of described compensation rate Δ V, correspondence and measuring circuit, and according to the air kerma at air kerma realization formula calculation and measurement point place, and the physical quantity that comprises time, capacitance, magnitude of voltage and current value that relates in the measuring process traced to the source to the national standard of corresponding International System of Units.
2. reproducing apparatus according to claim 1, wherein, described x radiation x unit adopts 60The Co gamma emitter, described air kerma realization formula is:
Figure FSA00000780244600011
In the formula,
Figure FSA00000780244600012
Air kerma rate for measurement point; I is the ionization current that the center collector of detector cells is collected; V is the ionization chamber volume of detector cells; ρ is dry air density; W/e is in dry air, the average energy that consumes during with a pair of ion pair of electron production of an electron charge;
Figure FSA00000780244600021
Account for the share of its zero energy for the energy that is consumed in bremsstrahlung;
Figure FSA00000780244600022
Be the mass energy absorption coefficient ratio of air with graphite; Average stopping-power ratio for graphite and air; k iFollowing each modifying factor of expression:
k s-ion recombination losses modifying factor;
k h-humidity modifying factor;
k St-ionization chamber bar Scattering correction the factor;
k Att-wall weakens modifying factor;
k Sc-wall scattering modifying factor;
k CEPThe mean place modifying factor of-generation electronics;
k An-axial heterogeneity modifying factor;
k Rn-heterogeneity modifying factor radially.
CN201210350464.6A 2012-09-20 2012-09-20 A kind of device for reappearing air kerma in radioactive source radiation field Expired - Fee Related CN102879794B (en)

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Cited By (10)

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CN103278838A (en) * 2013-05-24 2013-09-04 四川中测辐射科技有限公司 Protection level gamma ray air kerma standard device
CN104330815A (en) * 2014-11-26 2015-02-04 中国工程物理研究院核物理与化学研究所 Method applied to detection of air kerma conventional true value
CN104681390A (en) * 2015-03-13 2015-06-03 中国计量科学研究院 Graphite round-cake ionization chamber
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CN105589503A (en) * 2016-01-27 2016-05-18 中国计量科学研究院 Method for generating DC constant-current current signals and constant current source device
CN108387921A (en) * 2018-03-06 2018-08-10 中国计量科学研究院 The system and method for measuring the fluence rate of K fluorescent X-rays
CN111487662A (en) * 2020-06-02 2020-08-04 中国计量科学研究院 Free air ionization chamber and air kerma measuring method
CN111551980A (en) * 2020-05-27 2020-08-18 中国计量科学研究院 Detection method based on irradiator system
CN111982344A (en) * 2020-08-17 2020-11-24 中国工程物理研究院激光聚变研究中心 Laser inertial confinement fusion hot spot high-spatial resolution detection system and method
CN115300814A (en) * 2022-09-19 2022-11-08 中国计量科学研究院 I-125 rotating bracket with low scattering structure

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Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103278838A (en) * 2013-05-24 2013-09-04 四川中测辐射科技有限公司 Protection level gamma ray air kerma standard device
CN105092609A (en) * 2014-05-16 2015-11-25 中国核动力研究设计院 Radiation protective door shielding performance test device and method thereof
US10031240B2 (en) 2014-11-26 2018-07-24 Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics Air kerma conventional true value determining method
CN104330815A (en) * 2014-11-26 2015-02-04 中国工程物理研究院核物理与化学研究所 Method applied to detection of air kerma conventional true value
WO2016082294A1 (en) * 2014-11-26 2016-06-02 中国工程物理研究院核物理与化学研究所 Measurement method for air kerma conventional true value
CN104330815B (en) * 2014-11-26 2016-09-07 中国工程物理研究院核物理与化学研究所 Air kerma conventional true value assay method
CN104681390A (en) * 2015-03-13 2015-06-03 中国计量科学研究院 Graphite round-cake ionization chamber
CN105589503A (en) * 2016-01-27 2016-05-18 中国计量科学研究院 Method for generating DC constant-current current signals and constant current source device
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
CN108387921A (en) * 2018-03-06 2018-08-10 中国计量科学研究院 The system and method for measuring the fluence rate of K fluorescent X-rays
CN111551980A (en) * 2020-05-27 2020-08-18 中国计量科学研究院 Detection method based on irradiator system
CN111487662A (en) * 2020-06-02 2020-08-04 中国计量科学研究院 Free air ionization chamber and air kerma measuring method
CN111487662B (en) * 2020-06-02 2022-04-29 中国计量科学研究院 Free air ionization chamber and air kerma measuring method
CN111982344A (en) * 2020-08-17 2020-11-24 中国工程物理研究院激光聚变研究中心 Laser inertial confinement fusion hot spot high-spatial resolution detection system and method
CN111982344B (en) * 2020-08-17 2022-04-22 中国工程物理研究院激光聚变研究中心 Laser inertial confinement fusion hot spot high-spatial resolution detection system and method
CN115300814A (en) * 2022-09-19 2022-11-08 中国计量科学研究院 I-125 rotating bracket with low scattering structure

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