ISO/ASTM 51431:2002
(Main)Practice for dosimetry in electron and bremsstrahlung irradiation facilities for food processing
Practice for dosimetry in electron and bremsstrahlung irradiation facilities for food processing
ISO/ASTM 51431 describes dosimetric procedures to be followed in facility characterization, process qualification and routine processing for electron beam and bremsstrahlung irradiation facilities for food processing in order to ensure that the product receives an acceptable range of absorbed doses. Other procedures related to facility characterization, process qualification and routine product processing that may influence and be used to monitor absorbed doses in the product are also discussed. The electron energy range covered in this practice is from 0,3 MeV to 10 MeV. Such electrons can be generated in continuous or pulse modes. The maximum electron energy of bremsstrahlung facilities covered in this practice is 10 MeV. A photon beam can be generated by inserting a bremsstrahlung converter in the electron beam path.
Pratique de la dosimétrie dans les installations de traitement des produits alimentaires irradiés par électrons et Bremsstrahlung
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Standards Content (Sample)
INTERNATIONAL ISO/ASTM
STANDARD 51431
First edition
2002-03-15
Practice for dosimetry in electron and
bremsstrahlung irradiation facilities for
food processing
Pratique de la dosimétrie dans les installations de traitement des
produits alimentaires irradiés par électrons et bremsstrahlung
Reference number
ISO/ASTM 51431:2002(E)
© ISO/ASTM International 2002
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ISO/ASTM 51431:2002(E)
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ii © ISO/ASTM International 2002 – All rights reserved
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ISO/ASTM 51431:2002(E)
Contents Page
1 Scope . 1
2 Referenced documents . 1
3 Terminology . 2
4 Significance and use . 3
5 Radiation source characteristics . 4
6 Irradiation facilities . 4
7 Dosimetry systems . 5
8 Installation qualification . 6
9 Process qualification . 7
10 Routine product processing . 8
11 Certification . 9
12 Measurement uncertainty . 9
13 Keywords . 10
Bibliography . 10
Figure 1 Diagram showing beam length and width for a scanned beam using a conveyor material
handling system . 2
Figure 2 Example of electron-beam dose distribution along the beam width . 2
Figure 3 A typical depth dose distribution for an electron beam . 3
Figure 4 A diagram of the parameter relationships for an electron or bremsstrahlung facility . 4
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ISO/ASTM 51431:2002(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to the member bodies for
voting. Publication as an International Standard requires approval by at least 75% of the member bodies
casting a vote.
ASTM International is one of the world’s largest voluntary standards development organizations with global
participation from affected stakeholders. ASTM technical committees follow rigorous due process balloting
procedures.
A pilot project between ISO and ASTM International has been formed to develop and maintain a group of
ISO/ASTM radiation processing dosimetry standards. Under this pilot project, ASTM Subcommittee E10.01,
Dosimetry for Radiation Processing, is responsible for the development and maintenance of these dosimetry
standards with unrestricted participation and input from appropriate ISO member bodies.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. Neither ISO nor ASTM International shall be held responsible for identifying any or all such
patent rights.
International Standard ISO/ASTM 51431 was developed by ASTM Committee E10, Nuclear Technology and
Applications, through Subcommittee E10.01, and by Technical Committee ISO/TC 85, Nuclear Energy.
iv © ISO/ASTM International 2002 – All rights reserved
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ISO/ASTM 51431:2002(E)
Standard Practice for
Dosimetry in Electron and bremsstrahlung Irradiation
1
Facilities for Food Processing
This standard is issued under the fixed designation ISO/ASTM 51431; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision.
1. Scope 2. Referenced Documents
1.1 This practice describes dosimetric procedures to be 2.1 ASTM Standards:
followed in facility characterization, process qualification, and E 170 Terminology Relating to Radiation Measurements
2
routine processing for electron beam and bremsstrahlung and Dosimetry
irradiation facilities for food processing to ensure that product E 177 Practice for Use of the Terms Precision and Bias in
3
receives an acceptable range of absorbed doses. Other proce- ASTM Test Methods
3
dures related to facility characterization, process qualification, E 456 Terminology Relating to Quality and Statistics
and routine product processing that may influence and be used E 666 Practice for Calculating Absorbed Dose from Gamma
2
to monitor absorbed dose in the product are also discussed. or X Radiation
Information about effective or regulatory dose limits for food E 668 Practice for Application of Thermoluminescence-
products is not within the scope of this practice (see ASTM Dosimetry (TLD) Systems for Determining Absorbed Dose
2
Guides F 1355 and F 1356). in Radiation-Hardness Testing of Electronic Devices
F 1355 Guide for the Irradiation of Fresh Fruits as a
NOTE 1—Dosimetry is only one component of a total quality assurance
2
Phytosanitary Treatment
program for adherence to good manufacturing practices used in the
F 1356 Guide for the Irradiation of Fresh and Frozen Red
production of safe and wholesome food.
Meat and Poultry to Control Pathogens and other Micro-
1.2 The electron energy range covered in this practice is
2
organisms
from 0.3 MeV to 10 MeV. Such electrons can be generated in
F 1736 Guide for the Irradiation of Finfish and Shellfish to
continuous or pulse modes.
2
Control Pathogens and Spoilage Microorganisms
1.3 The maximum electron energy of bremsstrahlung facili-
2.2 ISO/ASTM Standards:
ties covered in this practice is 10 MeV. A photon beam can be
51204 Practice for Dosimetry in Gamma Irradiation Facili-
generated by inserting a bremsstrahlung converter in the
2
ties for Food Processing
electron beam path (See ISO/ASTM Practice 51608).
51261 Guide for Selection and Calibration of Dosimetry
2
NOTE 2—For guidance in the selection, calibration, and use of specific
Systems for Radiation Processing
dosimeters and interpretation of absorbed dose in the product from dose
51275 Practice for Use of a Radiochromic Film Dosimetry
measurements, see the documents listed in ISO/ASTM Guide 51261 and
2
System
practices for individual dosimetry systems listed in 2.1.
51276 Practice for Use of a Polymethylmethacrylate Do-
NOTE 3—Bremsstrahlung from machine sources and gamma rays from
2
simetry System
radioactive isotopic sources are similar in characteristics, especially as
51310 Practice for Use of a Radiochromic Optical
dosimetry is concerned. See ISO/ASTM Practice 51204 for the applica-
2
tions of dosimetry in characterization and operation of gamma-ray Waveguide Dosimetry System
2
irradiation facilities for food processing. For information concerning
51539 Guide for Use of Radiation-Sensitive Indicators
electron beam irradiation technology and dosimetry, see ISO/ASTM
51608 Practice for Dosimetry in an X-ray (Bremsstrahlung)
Practice 51649.
2
Irradiation Facility for Radiation Processing
1.4 This standard does not purport to address all of the
51607 Practice for Use of the Alanine-EPR Dosimetry
2
safety concerns, if any, associated with its use. It is the
System
responsibility of the user of this standard to establish appro-
51631 Practice for Use of Calorimetric Dosimetry Systems
priate safety and health practices and determine the applica-
for Electron Beam Dose Measurements and Dosimeter
2
bility of regulatory limitations prior to use.
Calibrations
51649 Practice for Dosimetry in an Electron Beam Facility
for Radiation Processing at Energies Between 300 keV
2
and 25 MeV
1
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear
51650 Practice for Use of Cellulose Acetate Dosimetry
Technology and Applications and is the direct responsibility of Subcommittee
2
Systems
E10.01 on Dosimetry for Radiation Processing, and is also under the jurisdiction of
ISO/TC 85/WG 3.
51707 Guide for Estimating Uncertainties in Dosimetry for
Current edition approved Jan. 22, 2002. Published March 15, 2002. Originally
e1
published as E 143–91. Last previous ASTM edition E 1431–98 . ASTM E
1431–91 was adopted by ISO in 1998 with the intermediate designation ISO
2
Annual Book of ASTM Standards, Vol 12.02.
15562:1998(E). The present International Standard ISO/ASTM 51431:2002(E) is a
3
revision of ISO 15562. Annual Book of ASTM Standards, Vol 14.02.
© ISO/ASTM International 2002 – All rights reserved
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ISO/ASTM 51431:2002(E)
2
Radiation Processing
2.3 International Commission on Radiation Units and
4
Measurements (ICRU) Reports:
ICRU Report 14 Radiation Dosimetry: X Rays and Gamma
Rays with Maximum Photon Energies Between 0.6 and 50
MeV
ICRU Report 34 The Dosimetry of Pulsed Radiation
ICRU Report 35 Radiation Dosimetry: Electron Beams
with Energies Between 1 and 50 MeV
ICRU Report 37 Stopping Powers for Electrons and
Positrons
ICRU Report 60 Radiation Quantities and Units
3. Terminology
3.1 Definitions:
3.1.1 absorbed dose (D)—Quantity of ionizing radiation
energy imparted per unit mass of a specified material. The SI
unit of absorbed dose is the gray (Gy), where 1 gray is
equivalent to the absorption of 1 joule per kilogram of the FIG. 1 Diagram Showing Beam Length and Width for a Scanned
Beam Using a Conveyor Material Handling System
specified material (1 Gy = 1 J/kg). The mathematical relation-
ship is the quotient of de¯by dm, where de¯ is the mean
incremental energy imparted by ionizing radiation to matter of
incremental mass dm (see ICRU 60).
D 5 de¯/dm (1)
3.1.1.1 Discussion—1. The discontinued unit for absorbed
dose is the rad (1 rad = 100 erg/g = 0.01 Gy).
2. Absorbed dose is sometimes referred to simply as dose.
3. For a photon source under conditions of charged particle equilib-
rium, the absorbed dose, D, may be expressed as follows:
D5F@E~μ /r!#, (2)
en
where:
2
F = particle fluence (particles/m ),
E = energy of the ionizing radiation (J), and
2
μ /r = mass energy absorption coefficient (m /kg).
en
4. If bremsstrahlung production within the specified material is
FIG. 2 Example of Electron-beam Dose Distribution Along the
negligible, the mass energy absorption coefficient (μ /r) is equal to the
en
4
Beam Width with the Width Noted at Some Defined Fractional
mass energy transfer coefficient (μ ), and absorbed dose is equal to air
tr
Level f of the Average Maximum Dose D
kerma. max
3.1.2 average beam current—time-averaged electron beam
current; for a pulsed machine, the averaging shall be done over
ing zone, for example, use of electromagnetic scanning of
a large number of pulses. pencil beam (in which case beam width is also referred to as
3.1.3 beam width—dimension of the irradiation zone per-
scan width), defocussing elements, and scattering foils.
pendicular to the beam length and direction of the electron 3.1.4 bremsstrahlung—broad-spectrum electromagnetic ra-
beam specified at a specific distance from where the beam exits
diation emitted when an energetic electron is influenced by a
the accelerator.
strong electric field such as that in the vicinity of an atomic
3.1.3.1 Discussion—For a radiation processing facility with
nucleus. Practically, bremsstrahlung is produced when an
a conveyor system, the beam width is usually perpendicular to
electron beam strikes any material (converter). The
the direction of motion of the conveyor (see Fig. 1). Beam
bremsstrahlung spectrum depends on the electron energy, the
width is the distance between the points along the dose profile
converter material and its thickness, and contains energies up
5
which are at a defined level from the maximum dose region in
to the maximum kinetic energy of the incident electrons (1, 2).
the profile (see Fig. 2). Various techniques may be employed to
3.1.5 compensating dummy—simulated product used during
produce an electron beam width adequate to cover the process-
routine production runs in process loads that contain less
5
4
Available from the International Commission on Radiation Units and Measure- The boldface numbers in parentheses refer to the bibliography at the end of this
ments, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A. standard.
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ISO/ASTM 51431:2002(E)
product than specified in the documented product loading incident surface of a homogeneous material where the electron
configuration, or simulated product used at the beginning or beam enters to the point where the tangent at the steepest point
end of a production run, to compensate for the absence of (the inflection point) on the almost straight descending portion
product. of the depth-dose distribution curve meets the depth axis.
3.1.5.1 Discussion—Simulated product or phantom material 3.1.13.1 Discussion—See Fig. 3.
may be used during irradiator characterization as a substitute 3.1.14 process load—a volume of material with a specified
for the actual product, material or substance to be irradiated. loading configuration irradiated as a single entity.
3.1.6 depth-dose distribution—variation of absorbed dose 3.1.15 production run—a series of process loads consisting
with depth from the incident surface of a material exposed to of materials, or products having similar radiation-absorption
a given radiation. characteristics, that are irradiated sequentially to a specified
3.1.7 dose uniformity ratio—ratio of the maximum to the range of absorbed dose.
minimum absorbed dose within the process load. The concept 3.1.16 reference material—homogeneous material of
is also referred to as the max/min dose ratio. known radiation absorption and scattering properties used to
3.1.8 dosimetry system—a system used for determining establish characteristics of the irradiation process, such as scan
absorbed dose consisting of dosimeters, measurement instru- uniformity, depth-dose distribution, throughput rate, and repro-
ments and their associated reference standards, and procedures ducibility.
for the system’s use. 3.1.17 reference plane—a selected plane in the radiation
3.1.9 electron energy spectrum—particle fluence distribu- zone that is perpendicular to the electron beam axis.
tion of electrons as a function of energy. 3.2 Definitions of other terms used in this standard that
3.1.10 electron range—penetration distance in a specific, pertain to radiation measurement and dosimetry may be found
totally absorbing material along the beam axis of the electrons in ASTM Terminology E 170. Definitions in ASTM E 170 are
incident on the material (equivalent to practical electron range, compatible with ICRU 60; that document, therefore, may be
R ). used as an alternative reference.
p
3.1.10.1 Discussion—See Fig. 3—R can be measured from
p
4. Significance and Use
experimental depth-dose distributions in a given material.
4.1 Food products may be processed with accelerator-
Other forms of electron range are found in the dosimetry
generated radiation (electrons and bremsstrahlung) to derive
literature, eg., extrapolated range derived from depth-dose data
public health or economic benefits, or both. Examples include
and the continuous-slowing-down-approximation range (the
parasite and pathogen control, insect disinfestation, growth and
calculated pathlength traversed by an electron in a material in
maturation inhibition, and extension of shelf-life. Food irradia-
the course of completely slowing down). Electron range is
−2
tion specifications usually include an upper and lower limit of
usually expressed in terms of mass per unit area (kg·m ), but
absorbed-dose, and may also include an upper limit on overall
sometimes in terms of unit thickness (m) for a specified
average. For a given application, one or both of these values
material.
may be prescribed by regulations that have been established on
3.1.11 half-value depth (R )—depth in homogeneous ma-
50
the basis of available scientific data. Therefore, it is necessary
terial at which the absorbed dose has decreased to 50 percent
to determine the capability of an irradiation facility to process
of its maximum value.
within these absorbed-dose limits prior to the irradiation of the
3.1.11.1 Discussion—See Fig. 3—The half-value depth
food product. Once this capability is established, it is necessary
usually applies to electrons.
to monitor and document the maximum and minimum ab-
3.1.12 optimum thickness (R )—depth in homogeneous
opt
sorbed dose in the irradiated product for each production run to
material at which the absorbed dose equals the absorbed dose
verify compliance with the process specifications with an
at the surface where the electron beam enters.
acceptable level of confidence.
3.1.12.1 Discussion—See Fig. 3.
3.1.13 practical electron range (R )—distance from the
p
NOTE 4—The Codex Alimentarius Commission (9) uses the term
“overall average absorbed dose” in discussing broad concepts such as the
wholesomeness of foods irradiated to an overall average absorbed dose of
less than 10 kGy. The overall average dose should not, however, be used
in place of minimum or maximum absorbed doses for specific applica-
tions. The CAC confirms this in the following statement from CAC/RCP
19-1979, Annex A: “(T)he design of the facility and the operational
parameters have to take into account minimum and maximum dose values
required by the process.”
NOTE 5—In addition to regulations specifying minimum and maximum
absorbed dose limits for a food, some countries have regulations requiring
that an overall average dose should not exceed a specified value, which is
the mean of the specified minimum and maximum limits. The overall
average dose absorbed by the food is the mean value of the measured
minimum and maximum absorbed dose values.
4.2 Some food products are processed in the chilled or
FIG. 3 A Typical Depth Dose Distribution for an Electron Beam
frozen state. Therefore, it is necessary to confirm that the
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ISO/ASTM 51431:2002(E)
dosimeters used for routine monitoring are useable at low clude the electron beam accelerator system; material handling
temperature and that the dosimeter temperature during irradia- systems; a radiation shield with personnel safety system;
tion is sufficiently stable to allow correction for temperature product staging, loading, and storage areas; auxiliary equip-
effects on the dosimeter response. ment for power, cooling, ventilation, etc.; equipment control
4.3 For more detailed discussions of radiation processing of room; a laboratory for dosimetry and product testing; and
foods, see ASTM Guides F 1355, F 1356 and F 1736. personnel offices. Bremsstrahlung facilities also include an
4.4 Regulations in some countries limit the maximum elec- X-ray converter (see ISO/ASTM Practice 51608). The electron
tron energy to 10 MeV and photon energy to 5 MeV for the beam accelerator system consists of the radiation source (see
purpose of food irradiation to avoid induced radioactivity in the ISO/ASTM Practice 51649), equipment to disperse the beam
food. on product and associated equipment (11).
4.5 To ensure that products are irradiated with reproducible 6.2 Process Parameters:
doses, routine process control requires documented product 6.2.1 There are various process parameters that play essen-
handling procedures before, during, and after the irradiation, tial roles in determining and controlling the absorbed dose in
consistent orientation of the products during irradiation, moni- radiation processing at an irradiation facility. They should,
toring of critical process parameters, routine product dosim- therefore, be considered when performing the absorbed-dose
etry, and documentation of the required activities and func- measurements required in Sections 8, 9, and 10.
tions. 6.2.2 Process parameters include process load characteris-
4.6 Accelerator-generated radiation can be in the form of tics (for example, size, bulk density, and heterogeneity),
electrons or photons (bremsstrahlung) produced by the elec- irradiation conditions (for example, processing geometry,
trons. Penetration into the product required to accomplish the multi-sided exposure and number of passes through the beam),
intended effect is one of the factors affecting the decision to use and operating parameters. (see Fig. 4).
electrons or photons. Penetration of 5-MeV bremsstrahlung 6.2.3 Process parameters that will achieve the absorbed
radiation in water or plastic materials is slightly greater than dose within the specified limits are established during process
that of Co-60 gamma rays (1-4). qualification (see Section 9).
6.2.4 During routine product processing (see Section 10),
NOTE 6—More detailed discussion of food irradiation processing may
the facility operating parameters are controlled and monitored
be found in Refs 5-10.
to maintain all values that were set during process qualifica-
5. Radiation Source Characteristics
tion.
6.3 Operating Parameters:
5.1 Electron Facilities:
6.3.1 Operating parameters include beam characteristics
5.1.1 Radiation sources for electrons with energies greater
(controlled by accelerator parameters: for example, energy,
than 300 keV considered in this practice are either direct action
average beam current, and pulse rate); conveyor speed and
(potential-drop) or indirect-action (microwave-powered) accel-
performance characteristics of material handling; and beam
erators. The radiation fields depend on the characteristics and
dispersion parameters (for example, beam width and frequency
the design of the accelerators. Included among these charac-
at which scanned beam is swept across product). Operating
teristics are the electron beam parameters, that is, the electron
parameters are measurable, and their values depend on the
energy spectrum, average electron beam current and beam
current distribution on the product surface.
5.1.2 These aspects are further discussed in ISO/ASTM
Practice 51649.
5.2 Bremsstrahlung Facilities:
5.2.1 A high-energy X-ray (bremsstrahlung) generator emits
short-wavelength electromagnetic radiation, which is analo-
gous to gamma radiation from radioactive isotopic sources.
Although their effects on irradiated materials are generally
similar, these kinds of radiation differ in their energy spectra,
angular distribution, and dose rates.
5.2.2 The physical characteristics of the X-ray field depend
on the design of the X-ray converter and the parameters of the
electron beam striking the target, that is, the electron energy
spectrum, average electron beam current, and beam current
distribution on the target.
5.2.3 The physical characteristics of an X-ray source and its
suitability for radiation processing are further discussed in
ISO/ASTM Practice 51608.
6. Irradiation Facilities
6.1 Facility Components:
FIG. 4 A Diagram of the Parameter Relationships for an Electron
or Bremsstrahlung Facility
6.1.1 Electron and bremsstrahlung irradiation facilities in-
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ISO/ASTM 51431:2002(E)
facility controlling parameters (see row (4) in Fig. 2). During uct being irradiated may be affected by the configuration of
installation qualification (see 8), absorbed dose characteristics material handling.
over the expected range of the operating parameters are 6.4.2 Bremsstrahlung Facilities—The penetrating quality of
established for a reference material. high-energy X rays permits the treatment of large containers or
6.3.2 Beam Characteristics: full pallet loads of products. The container size for optimum
photon power utilization and dose uniformity depends on the
6.3.2.1 The three principal beam characteristics that affect
maximum energy and product density. The narrow angular
dosimetry are the electron energy spectrum, average beam
distribution of the radiation favors the use of continuously
current, and pulse beam current. The electron energy spectrum
moving conveyors rather than shuffle-dwell systems to enhance
affects the depth-dose distribution within the product (see
dose uniformity.
ISO/ASTM Practice 51649). The average and pulse beam
6.4.3 Electron Facilities—Two different configurations
currents, in addition to several other operating parameters,
commonly used are:
affect the average and peak dose rates, respectively.
Conveyors or Carriers—Boxes, with thickness comparable
NOTE 7—If the accelerator does not have an energy analyzing system
to the electron range, containing food products are placed upon
(for example, an analyzing magnet), the electron energy spectrum of the
carriers or conveyors for passage through the electron beam.
beam can be specified in a practical way by two parameters: the average
The speed of the conveyor or carriers is controlled in conjunc-
electron energy (E ) and the most probable electron energy (E ). The
a p
tion with the electron beam current and beam width so that the
values of these two parameters at the surface of water-equivalent product
may be measured experimentally (see ISO/ASTM Practice 51649). required dose is delivered.
Bulk-flow System—For irradiation of liquids or particulate
6.3.3 Beam Dispersion:
materials like grain, bulk-flow transport through the irradiation
6.3.3.1 Dispersion of the electron beam to produce a beam
zone may be used. Because the flow of fluids and particulate
width adequate to cover the processing zone may be achieved
materials through the irradiation zone may be turbulent and the
by various techniques. These include electromagnetic scanning
path and the velocity of individual elements are not control-
of a pencil beam or use of defocussing elements or scattering
lable, an average dose may be derived from average velocity
foils.
and dose field in the irradiation zone in order that the required
6.3.3.2 The beam width, in addition to several other oper-
dose is applied. In case where adherence to minimum and
ating parameters, affects the dose rate. Scanning of a pencil
maximum dose is required more sophisticated dosimetry tech-
beam can produce pulsed dose at points along the beam width.
niques should be applied (see Ref (13) and also 9.2.4).
This can influence the dosimeters’ performance when they are
sensitive to dose rate variations.
7. Dosimetry Systems
6.3.3.3 See ISO/ASTM Practice 51649 for determination of
7.1 Dosimetry systems are used
...
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