ISO/ASTM 51818:2002

INTERNATIONAL ISO/ASTM
STANDARD 51818
First edition
2002-03-15
Practice for dosimetry in an electron
beam facility for radiation processing at
energies between 80 KeV and 300 KeV
Pratique de la dosimétrie dans une installiation de traitement par
irradiation utilisant un faisceau d’électrons d’énergies comprises
entre 80 keV et 300 keV
Reference number
ISO/ASTM 51818:2002(E)
© ISO/ASTM International 2002

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ISO/ASTM 51818:2002(E)
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ii © ISO/ASTM International 2002 – All rights reserved

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ISO/ASTM 51818:2002(E)
Contents Page
1 Scope . 1
2 Referenced documents . 1
3 Terminology . 1
4 Significance and use . 2
5 Dosimetry system . 3
6 Installation qualification and t esting . 3
7 Frequency of dosimetric measurements . 3
8 Throughput calculations . 4
9 Certification . 4
10 Measurement uncertainty . 4
11 Keywords . 4
ANNEX . 5
Bibliography . 7
Figure 1 Depth dose curves . 2
Figure A1.1 Depth dose curve 300 kV . 6
Figure A1.2 Electron beam width dose uniformity . 7
Table1 Calculated K values at the product surface . 3
Table A1.1 Example of depth dose distribution at 300 kV . 5
© ISO/ASTM International 2002 – All rights reserved iii

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ISO/ASTM 51818:2002(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 51818 was developed by ASTM Committee E10, Nuclear Technology and
Applications, through Subcommittee E10.01, and by Technical Committee ISO/TC 85, Nuclear Energy.
Annex A1 of this International Standard is for information only.
iv © ISO/ASTM International 2002 – All rights reserved

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ISO/ASTM 51818:2002(E)
Standard Practice for
Dosimetry in an Electron Beam Facility for Radiation
1
Processing at Energies Between 80 and 300 keV
This standard is issued under the fixed designation ISO/ASTM 51818; 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 2.3 International Commission on Radiation Units and
4
Measurements (ICRU) Reports:
1.1 This practice covers dosimetric procedures to be fol-
ICRU Report 37 Stopping Powers for Electrons and
lowed to determine the performance of low energy (300 keV or
Positrons
less) single-gap electron beam radiation processing facilities.
ICRU Report 60 Radiation Quantities and Units
Other practices and procedures related to facility characteriza-
2.4 Methods for Calculating Absorbed Dose and Dose
tion, product qualification, and routine processing are also
5
Distribution:
discussed.
ZTRAN Monte Carlo Code
1.2 The electron energy range covered in this practice is
Integrated Tiger Series (ITS) Monte Carlo Codes
from 80 keV to 300 keV. Such electron beams can be generated
Energy Deposition in Multiple Layers (EDMULT) Electron
by single-gap self-contained thermal filament or plasma source
Gamma Shower (EGS43) Monte Carlo Codes
accelerators.
1.3 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions:
responsibility of the user of this standard to establish appro-
3.1.1 Definitions of terms used in this practice may be found
priate safety and health practices and determine the applica-
in ASTM Terminology E 170 and ICRU Report 60.
bility of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
2. Referenced Documents 3.2.1 absorbed dose (D)—quantity of ionizing radiation
energy imparted per unit mass of a specified material. The SI
2.1 ASTM Standards:
unit of absorbed dose is the gray (Gy), where 1 gray is
E 170 Terminology Relating to Radiation Measurements
2 equivalent to the absorption of 1 joule per kilogram of the
and Dosimetry
specified material (1 Gy = 1 J/kg). The mathematical relation-
E 177 Practice for Use of the Terms Precision and Bias in
3 ship is the quotient of d e¯ by dm, where d e¯ is the mean
ASTM Test Methods
3
incremental energy imparted by ionizing radiation to matter of
E 456 Terminology Relating to Quality and Statistics
incremental mass dm (see ICRU Report 33).
2.2 ISO/ASTM Standards:
51261 Guide for Selection and Calibration of Dosimetry de¯
D 5 (1)
2
Systems for Radiation Processing dm
51275 Practice for Use of a Radiochromic Film Dosimetry
3.2.1.1 Discussion—The discontinued unit for absorbed
2
System
dose is the rad (1 rad = 100 erg/g = 0.01 Gy). Absorbed dose is
51276 Practice for Use of a Polymethylmethacrylate Do-
sometimes referred to simply as dose.
2
simetry System
3.2.2 air gap—the distance between the product plane and
51607 Practice for Use of the Alanine-EPR Dosimetry
the electron beam window.
2
System
3.2.3 backscatter—the term used to describe additional
51650 Practice for Use of a Cellulose Acetate Dosimetry
absorbed dose caused by scatter of the primary electron beam
2
System
from nearby material.
51707 Guide for Estimating Uncertainties in Dosimetry for
3.2.4 beam current—time-averaged electron beam current
2
Radiation Processing
delivered from the accelerator.
3.2.5 beam length— non-scanned electron beam, the active
length of the cathode assembly in vacuum parallel to the
1
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear
product flow and perpendicular to the beam width.
Technology and Applications and is the direct responsibility of Subcommittee
3.2.6 beam power—the product of the average electron
E10.01 on Dosimetry for Radiation Processing, and is also under the jurisdiction of
beam energy and the average beam current (unit kW).
ISO/TC 85/WG 3.
Current edition approved Jan. 22, 2002. Published March 15, 2002.Originally
e1
published as ASTM E 1818–96. Last previous ASTM edition E 1818–96 . ASTM
e1
E 1818–96 was adopted in 1998 with the intermediate designation ISO
4
15573:1998(E). The present International Standard ISO/ASTM 51818:2002(E) is a Available from the International Commission on Radiation Units and Measure-
revision of ISO 15573. ments, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.
2 5
Annual Book of ASTM Standards, Vol 12.02. Available from the Radiation Shielding Information Center (RSIC), Oak Ridge
3
Annual Book of ASTM Standards, Vol 14.02. National Laboratory (ORNL), P.O. Box 2008, Oak Ridge, TN 37831, U.S.A.
© ISO/ASTM International 2002 – All rights reserved
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ISO/ASTM 51818:2002(E)
3.2.7 beam width—non-scanned electron beam, the active inflection point) on the almost straight descending portion of
width of the cathode assembly in vacuum perpendicular to the the depth dose distribution curve meets the depth axis.
product flow and beam length. 3.2.16 process load—a volume of material with a specified
3.2.8 bulk processing rate—mass throughput rate based on loading configuration irradiated as a single entity.
the output power in watts of the electron beam, the mass of the 3.2.17 production run— continuous-flow irradiation, a se-
irradiated material and the dose. Expressed in kilogray kilo- ries of process loads, consisting of materials or products having
grams per kilowatt hour or Megarad pounds per kilowatt hour. similar radiation-absorption characteristics, that are irradiated
3.2.9 depth-dose distribution—variation of absorbed dose sequentially to a specified range of absorbed dose.
with depth from the incident surface of a material exposed to 3.2.18 product plane—the plane corresponding to the top
a given radiation (see Fig. 1 for calculated values). surface of the product being irradiated.
3.2.10 dose uniformity ratio—ratio of the maximum to the 3.2.19 self-shielded accelerator—an electron beam source
minimum absorbed dose within the process load. The concept that is integrally designed with radiation shielding, product
is also referred to as the max/min dose ratio. transport system, and irradiation chamber.
3.2.11 dosimeter—a device that, when irradiated, exhibits a 3.2.20 single-gap accelerator—an electron beam source
quantifiable change in some property of the device which can consisting of a vacuum tube and a high voltage power supply
be related to absorbed dose in a given material using appro- that can accelerate a dispersed beam of electrons from a high
priate analytical instrumentation and techniques. voltage potential to ground potential in one stage.
3.2.12 dosimetry system—a system used for determining 3.2.21 surface area rate coeffıcient (K)— a quantity relating
absorbed dose, consisting of dosimeters, measurement instru- area irradiated per unit time to beam current and absorbed
2
ments, and their associated reference standards and procedures dose. Typically this value is expressed in kGy meters per
2
for the system’s use. milliampere minute, or Megarad feet per milliampere minute.
3.2.13 electron energy—kinetic energy of the accelerated Calculated values using Monte Carlo simulation are shown in
electron beam (units—eV (electron volts)). Often, acceleration Table 1. In the literature, this processing rate concept is
voltage in kV is used to characterize beam energy in keV. The sometimes called the processing coefficient.
maximum energy of the beam inside the accelerator is equal to 3.2.22 uncertainty—a parameter associated with the result
the acceleration voltage but expressed in keV units. The beam of a measurement that characterizes the dispersion of the
energy at the product surface is less than the maximum energy values that could reasonably be attributed to the measurand or
derived quantity (see ISO/ASTM Guide 51707).
inside the accelerator due to losses in the beam path, such as
the window and the air gap.
4. Significance and Use
3.2.14 traceability—the documentation demonstrating by
means of an unbroken chain of comparisons that a measure- 4.1 A variety of processes use low energy electron beam
ment is in agreement within acceptable limits of uncertainty accelerators to modify product characteristics. Dosimetry re-
with comparable nationally or internationally recognized stan- quirements, the number and frequency of measurements, and
dards. record keeping requirements will vary depending on the type
3.2.15 practical electron range—distance from the incident and end use of the products being processed. In many cases
surface of a homogeneous material where the electron beam dosimetry may be used in conjunction with physical, chemical,
enters to the point where the tangent at the steepest point (the or biological testing of the product. In many cases reference
FIG. 1 Depth Dose Curves (0.5 mil Ti Window, 0.5 in. Air Gap)
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ISO/ASTM 51818:2002(E)
TABLE 1 Calculated K Values at the Product Surface
irradiation facility is to determine that the processing equip-
2 2
Electron Beam Kilogray Metres / Megarad Feet /Milliampere ment performs in accordance with design specifications. The
A A
Acceleration Voltage Milliampere Minute (K) Minute (K)
process should include mechanical and electrical testing of the
100 kV 6.0 6.5
electron beam accelerator and related processing equipment,
125 kV 14.9 16.0
and should include, but not be limited to, the following:
150 kV 24.3 25.1
6.1.1 Operation of all safety interlocks,
175 kV 23.4 25.2
200 kV 23.3 25.1
6.1.2 Operation of all system interlocks,
225 kV 22.7 24.4
6.1.3 An extended demonstration of system performance at
250 kV 21.4 23.0
specified ratings,
275 kV 18.7 20.1
300 kV 18.5 19.9
6.1.4 Operation of the system over the full range of voltage
A
Based on Monte Carlo Integrated Tiger Series simulation, assuming Far West and beam current,
(FWT 60-00) film dosimeters and 12.7 mm (0.5 in.) air gap.
6.1.5 Radiation survey at maximum operating voltage and
current,
standards may be developed, comparing dosimetry results with
6.1.6 Mechanical inspection of the system,
other quantitative product testing; for example, sterility, gel
6.1.7 Electrical inspection of the system,
fraction, melt flow, modulus, molecular weight distribution, or
6.1.8 Performance of the inert gas system, if applicable,
cure analysis tests can be used to determine radiation dose in
6.1.9 Performance of the ozone exhaust system, if appli-
specific relevant materials. Wherever possible, the results of
cable, and
quantitative physical testing should be used in conjunction with
6.1.10 Testing and calibration of product handling system
dosimetry in commercial radiation processing applications.
over the full performance range.
4.2 Radiation processing specifications usually include a
6.2 The second phase of qualifying an irradiation facility is
minimum or maximum absorbed dose limit, or both. For a
to characterize the performance of the equipment using dosim-
given application these limits may be set by government
etry. The purpose of these measurements is to qualify the dose
regulation or by limits inherent to the product itself.
delivering characteristics of the equipment for performance
4.3 Critical process parameters must be controlled to obtain
acceptance and for future reference. The process should
reproducible dose distribution in processed materials. The
include, but not be limited to, the following:
electron beam energy (in eV), beam current (in mA), spatial
6.2.1 Surface Area Rate Measurements— minimum of five
distribution of the beam, and exposure time or process line
measurements over the voltage range of interest with at least
speed all affect absorbed dose (see Section 5). In some
five dosimeters equally spaced across the width of the beam at
liquid-to-solid polymerization applications (often referred to as
the product plane at a nominal dose level. The surface area rate
radiation curing), the residual oxygen level during irradiation
measurement should be repeated at a typical operating voltage
must be controlled to achieve consistent results. A high level of
level at several different beam current levels to establish and
residual oxygen can affect product performance in these curing
test the linearity between beam current and surface dose (see
applications, but it will not affect the absorbed dose.
Annex A1).
4.4 Before any radiation process can be utilized, it must be
6.2.2 Beam Uniformity Measurements—minimum of one
validated to determine its effectiveness. This involves testing of
dosimeter per 2.5 cm over full width. Three measurements
the process equipment, calibrating the measuring instruments,
should be made at the product plane (see Annex A1).
and demonstrating the ability to deliver the desired dose within
6.2.3 Depth-dose Measurements—A minimum of three
the desired dose range in a reliable and reproducible manner.
measurements should be made at each voltage covering the
The desired improvements, as well as any undesirable effects
voltage range of interest measured with the dosimetry stack at
due to radiation damage to a specific product, should be
the product plane (see Annex A1).
understood.
7. Frequency of Dosimetric Measurements
5. Dosimetry System
7.1 Initial facility performance evaluation dosimetry should
5.1 The documents listed in Section 2 provide detailed
be conducted in accordance with Section 6.
information on the selection and use of appropriate dosimetry
7.2 Product Validation—Surface area rate measurement
...