ISO 20785-3:2015
(Main)Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 3: Measurements at aviation altitudes
Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 3: Measurements at aviation altitudes
The following documents, in whole or in part, are normatively referenced in ISO 20785-3:2015 and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO/IEC Guide 98‑1, Uncertainty of measurement ? Part 1: Introduction to the expression of uncertainty in measurement ISO/IEC Guide 98‑3, Uncertainty of measurement ? Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) ISO 20785‑1, Dosimetry for exposures to cosmic radiation in civilian aircraft ? Part 1: Conceptual basis for measurements ISO 20785‑2, Dosimetry for exposures to cosmic radiation in civilian aircraft ? Part 2: Characterization of instrument response
Dosimétrie pour les expositions au rayonnement cosmique à bord d'un avion civil — Partie 3: Mesurages à bord d'avions
L'ISO 20785-3:2015 donne les principes de base permettant de mesurer l'équivalent de dose ambiant aux altitudes de vol pour l'évaluation de l'exposition au rayonnement cosmique à bord d'un avion.
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INTERNATIONAL ISO
STANDARD 20785-3
First edition
2015-11-15
Dosimetry for exposures to cosmic
radiation in civilian aircraft —
Part 3:
Measurements at aviation altitudes
Dosimétrie pour les expositions au rayonnement cosmique à bord
d’un avion civil —
Partie 3: Mesurages à bord d’avions
Reference number
ISO 20785-3:2015(E)
©
ISO 2015
---------------------- Page: 1 ----------------------
ISO 20785-3:2015(E)
COPYRIGHT PROTECTED DOCUMENT
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ii © ISO 2015 – All rights reserved
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ISO 20785-3:2015(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Quantities and units . 1
3.2 Atmospheric radiation field . 4
4 General considerations . 6
4.1 General description of the cosmic radiation field in the atmosphere . 6
4.2 General considerations concerning the measurements . 8
4.2.1 General. 8
4.2.2 Selection of appropriate instruments . 8
4.2.3 Characterization of the responses of the instruments . 8
4.2.4 Measurements inside an aircraft . 8
4.2.5 Application of appropriate correction factors . 9
4.3 Safety and regulatory requirements for in-flight measurements . 9
5 Measurement at aviation altitude . 9
5.1 Parameters determining the dose rate. 9
5.1.1 Barometric altitude . 9
5.1.2 Geographic coordinates . 9
5.1.3 Solar activity .10
5.2 Possible influence quantities .10
5.2.1 General.10
5.2.2 Cabin air pressure .10
5.2.3 Cabin air temperature .10
5.2.4 Cabin air humidity .10
5.3 Specific considerations for active instruments .10
5.3.1 Power supply . .10
5.3.2 Vibrations and shocks .11
5.3.3 Electromagnetic interferences from the aircraft .11
5.4 Specific considerations for passive measurements .11
5.4.1 Security X-ray scanning .11
5.4.2 Background subtraction .11
6 Uncertainties .11
Annex A (informative) Representative particle fluence energy distributions for the cosmic
radiation field at flight altitudes for solar minimum and maximum conditions and
for minimum and maximum vertical cut-off rigidity .12
Bibliography .16
© ISO 2015 – All rights reserved iii
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ISO 20785-3:2015(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 2, Radiological protection.
ISO 20785 consists of the following parts, under the general title Dosimetry for exposures to cosmic
radiation in civilian aircraft:
— Part 1: Conceptual basis for measurements
— Part 2: Characterization of instrument response
— Part 3: Measurements at aviation altitudes
iv © ISO 2015 – All rights reserved
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ISO 20785-3:2015(E)
Introduction
Aircraft crews are exposed to elevated levels of cosmic radiation of galactic and solar origin and
secondary radiation produced in the atmosphere, the aircraft structure and its contents. Following
[1]
recommendations of the International Commission on Radiological Protection in Publication 60,
[2]
confirmed by Publication 103, the European Union (EU) introduced a revised Basic Safety Standards
[3]
Directive which included exposure to natural sources of ionizing radiation, including cosmic
radiation, as occupational exposure. The Directive requires account to be taken of the exposure of
aircraft crew liable to receive more than 1 mSv per year. It then identifies the following four protection
measures: (i) to assess the exposure of the crew concerned; (ii) to take into account the assessed
exposure when organizing working schedules with a view to reducing the doses of highly exposed
crew; (iii) to inform the workers concerned of the health risks their work involves; and (iv) to apply
the same special protection during pregnancy to female crew in respect of the ‘child to be born’ as to
other female workers. The EU Council Directive has to be incorporated into laws and regulations of
EU Member States and has to be included in the aviation safety standards and procedures of the Joint
Aviation Authorities and the European Air Safety Agency. Other countries such as Canada and Japan
have issued advisories to their airline industries to manage aircraft crew exposure.
For regulatory and legislative purposes, the radiation protection quantities of interest are equivalent
dose (to the foetus) and effective dose. The cosmic radiation exposure of the body is essentially uniform
and the maternal abdomen provides no effective shielding to the foetus. As a result, the magnitude
of equivalent dose to the foetus can be put equal to that of the effective dose received by the mother.
Doses on board aircraft are generally predictable, and events comparable to unplanned exposure in
other radiological workplaces cannot normally occur (with the rare exceptions of extremely intense
and energetic solar particle events). Personal dosemeters for routine use are not considered necessary.
The preferred approach for the assessment of doses of aircraft crew, where necessary, is to calculate
directly effective dose rate, as a function of geographic location, altitude and solar cycle phase, and
to fold these values with flight and staff roster information to obtain estimates of effective doses for
individuals. This approach is supported by guidance from the European Commission, the ICRP in
[4] [5]
Publication 75 and the ICRU in Report 84.
The role of calculations in this procedure is unique in routine radiation protection and it is widely
accepted that the calculated doses should be validated by measurement. Effective dose is not directly
measurable. The operational quantity of interest is ambient dose equivalent, H*(10). Indeed, as
indicated in particular in ICRU Report 84, the ambient dose equivalent is considered to be a conservative
estimator of effective dose if isotropic or superior isotropic irradiation can be assumed. In order to
validate the assessed doses obtained in terms of effective dose, calculations can be made of ambient
dose equivalent rates or route doses in terms of ambient dose equivalent, and values of this quantity
determined by measurements traceable to national standards. The validation of calculations of ambient
dose equivalent for a particular calculation method may be taken as a validation of the calculation of
effective dose by the same computer code, but this step in the process may need to be confirmed. The
alternative is to establish, a priori, that the operational quantity ambient dose equivalent is a good
estimator of effective dose and equivalent dose to the foetus for the radiation fields being considered,
in the same way that the use of the operational quantity personal dose equivalent is justified for
the estimation of effective dose for radiation workers. Ambient dose equivalent rate as a function of
geographic location, altitude and solar cycle phase is then calculated and folded with flight and staff
roster information.
The radiation field in aircraft at altitude is complex, with many types of ionizing radiation present, with
energies ranging up to many GeV. The determination of ambient dose equivalent for such a complex
radiation field is difficult. In many cases, the methods used for the determination of ambient dose
equivalent in aircraft are similar to those used at high-energy accelerators in research laboratories.
Therefore, it is possible to recommend dosimetric methods and methods for the calibration of dosimetric
devices, as well as the techniques for maintaining the traceability of dosimetric measurements to
national standards. Dosimetric measurements made to evaluate ambient dose equivalent have to be
performed using accurate and reliable methods that ensure the quality of readings provided to workers
and regulatory authorities. This part of ISO 20785 gives procedures for the characterization of the
response of instruments for the determination of ambient dose equivalent in aircraft.
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ISO 20785-3:2015(E)
Requirements for the determination and recording of the cosmic radiation exposure of aircraft crew have
been introduced into the national legislation of EU Member States and other countries. Harmonization
of methods used for determining ambient dose equivalent and for calibrating instruments is desirable
to ensure the compatibility of measurements performed with such instruments.
This part of ISO 20785 is intended for the use of primary and secondary calibration laboratories for
ionizing radiation, by radiation protection personnel employed by governmental agencies, and by
industrial corporations concerned with the determination of ambient dose equivalent for aircraft crew.
vi © ISO 2015 – All rights reserved
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INTERNATIONAL STANDARD ISO 20785-3:2015(E)
Dosimetry for exposures to cosmic radiation in civilian
aircraft —
Part 3:
Measurements at aviation altitudes
1 Scope
This part of ISO 20785 gives the basis for the measurement of ambient dose equivalent at flight altitudes
for the evaluation of the exposures to cosmic radiation in civilian aircraft.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC Guide 98-1, Uncertainty of measurement — Part 1: Introduction to the expression of uncertainty
in measurement
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO 20785-1, Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 1: Conceptual basis
for measurements
ISO 20785-2, Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 2: Characterization of
instrument response
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 Quantities and units
3.1.1
particle fluence
fluence
Φ
at a given point of space, number dN of particles incident on a small spherical domain divided by the
cross-sectional area da of that domain:
dN
Φ=
da
-2 -2
Note 1 to entry: The unit of the fluence is m , a frequently used unit is cm .
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ISO 20785-3:2015(E)
Note 2 to entry: The energy distribution of the particle fluence, Φ , is the quotient dΦ by dE, where dΦ is the
E
fluence of particles of energy between E and E+dE. There is an analogous definition for the direction distribution,
Φ , of the particle fluence. The complete representation of the double differential particle fluence can be written
Ω
(with arguments) Φ (E,Ω), where the subscripts characterize the variables (quantities) for differentiation and
E,Ω
where the symbols in the brackets describe the values of the variables. The values in the brackets are needed
for special function values, e.g. the energy distribution of the particle fluence at the energy E = E is written as
0
Φ (E ). If no special values are indicated, the brackets may be omitted.
E 0
3.1.2
particle fluence rate
fluence rate
Φ
2
dΦ d N
Φ ==
dt ddat⋅
where dΦ is the increment of the particle fluence during an infinitesimal time interval with duration dt:
-2 −1 -2 −1
Note 1 to entry: The unit of the fluence rate is m s , a frequently used unit is cm s .
3.1.3
unrestricted linear energy transfer
linear energy transfer
LET
L
∞
for an ionizing charged particle, mean energy dE imparted locally to matter along a small path through
∞
the matter, minus the sum of the kinetic energies of all the electrons released, divided by the length dl
dE
∞
L =
∞
dl
−1 −1
Note 1 to entry: The unit of the linear energy transfer is J m , a frequently used unit is keV μm .
3.1.4
dose equivalent
H
at the point of interest in tissue
HD= Q
where D is the absorbed dose and Q is the mean quality factor at that point
Note 1 to entry: Q is determined by the unrestricted linear energy transfer, L (often denoted as L or LET), of
∞
charged particles passing through a small volume element (domains) at this point (the value of L is given for
∞
charged particles in water, not in tissue; the difference, however, is small). The dose equivalent at a point in tissue
is then given by:
∞
HQ= ()LD dL
L
∫
L−0
where D = dD/dL is the distribution in terms of L of the absorbed dose at the point of interest.
L
Note 2 to entry: The relationship of Q and L is given in Reference [2].
−1
Note 3 to entry: The unit of dose equivalent is J kg , called sievert (Sv).
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ISO 20785-3:2015(E)
3.1.5
ambient dose equivalent
H*(10)
dose equivalent at a point in a radiation field, that would be produced by the corresponding expanded and
aligned field, in the ICRU sphere at 10 mm depth on the radius opposing the direction of the aligned field
−1
Note 1 to entry: The unit of ambient dose equivalent is J kg , called sievert (Sv).
3.1.6
particle fluence-to-ambient dose equivalent conversion coefficient
h(10)*
Φ
quotient of the particle ambient dose equivalent, H*(10), and the particle fluence, Φ
H *(10)
h 10 * =
()
Φ
Φ
2 −1
Note 1 to entry: The unit of the particle fluence-to-ambient dose equivalent conversion coefficient is J m kg
2 2
with the special name Sv m , a frequently used unit is pSv cm .
3.1.7
correction factor
K
factor applied to the indication to correct for deviation of the measurement conditions from
reference conditions
3.1.8
atmosphere depth
X
v
mass of a unit-area column of air above a point in the atmosphere
-2 -2
Note 1 to entry: The unit of atmosphere depth is kg m ; a frequently used unit is g cm .
3.1.9
standard barometric altitude
pressure altitude
altitude determined by a barometric altimeter calibrated with reference to the International Standard
Atmosphere (ISA) (ISO, 1975) when the altimeter’s datum is set to 1 013,25 hPa
Note 1 to entry: The flight level is sometimes given as FL 350, where the number represents multiples of 100 feet
of pressure altitude, based on the ISA and a datum setting of 1 013,25 hPa. However, in some countries flight
levels are expressed in meters, in which case appropriate conversions should be made before applying the data
given in this part of ISO 20785.
3.1.10
magnetic rigidity
P
momentum per charge (of a particle in a magnetic field), given by:
p
P=
Ze
where p is the particle momentum, Z the number of charges on the particle and e the charge on the proton
–1
Note 1 to entry: The base unit of magnetic rigidity is the tesla metre (T m) (= V m s). A frequently used unit is V
(or GV) in a system of units where the values of the speed of light, c, and the charge on the proton, e, are both 1,
and the magnetic rigidity is given by pc/Ze.
Note 2 to entry: Magnetic rigidity characterizes charged-particle trajectories in magnetic fields. All particles having
the same magnetic rigidity have identical trajectories in a magnetic field, independent of particle mass or charge.
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ISO 20785-3:2015(E)
3.1.11
geomagnetic cut-off rigidity
cut-off rigidity
r
c
minimum magnetic rigidity an incident particle can have and still penetrate the geomagnetic field to
reach a given location above the Earth
Note 1 to entry: Geomagnetic cut-off rigidity depends on angle of incidence. Often, vertical incidence to the
Earth’s surface is assumed, in which case, the vertical geomagnetic cut-off rigidity is the minimum magnetic
rigidity a vertically incident particle can have and still reach a given location above the Earth.
3.1.12
vertical geomagnetic cut-off rigidity
vertical cut-off
cut-off
minimum magnetic rigidity a vertically incident particle can have and still reach a given location
above the Earth
3.1.13
deceleration potential
ϕ
cosmic ray modulation parameter deduced from space observations of the abundance variation of the
different species in function of the solar cycle epoch
Note 1 to entry: The deceleration potential could be deduced either from the sunspot index or from Climax
neutron monitor output, using simple linear formula depending upon the phase of the solar cycle.
3.2 Atmospheric radiation field
3.2.1
cosmic radiation
cosmic rays
cosmic particles
ionizing radiation consisting of high-energy particles, primarily completely ionized atoms, of extra-
terrestrial origin and the particles they generate by interaction with the atmosphere and other matter
3.2.2
primary cosmic radiation
primary cosmic rays
cosmic radiation incident from space at the Earth’s orbit
3.2.3
secondary cosmic radiation
secondary cosmic rays
cosmogenic particles
particles which are created directly or in a cascade of reactions by primary cosmic rays interacting
with the atmosphere or other matter
Note 1 to entry: Important particles with respect to radiation protection and radiation measurements in aircraft
are: neutrons, protons, photons, electrons, positrons, muons, and to a lesser extent, pions and nuclear ions
heavier than protons.
3.2.4
galactic cosmic radiation
galactic cosmic rays
GCR
cosmic radiation originating outside the solar system
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ISO 20785-3:2015(E)
3.2.5
solar cosmic radiation
solar cosmic rays
solar particles
cosmic radiation originating from the sun
3.2.6
solar particle event
SPE
large fluence rate of energetic solar particles ejected into space by a solar eruption
Note 1 to entry: Solar particle events are directional.
3.2.7
ground level enhancement
GLE
sudden increase of cosmic radiation observed on the ground by at least two neutron monitor stations
recording simultaneously a greater than 3 % increase in the five-minute-averaged count rate associated
with solar energetic particles
Note 1 to entry: A GLE is associated with a solar-particle event having a high fluence rate of particles with high
energy (greater than 500 MeV).
Note 2 to entry: GLEs are relatively rare, occurring on average about once per year.
3.2.8
solar modulation
change of the GCR field (outside the Earth’s magnetosphere) caused by change of solar activity and
consequent change of the magnetic field of the heliosphere
3.2.9
solar cycle
period during which the solar activity varies with successive maxima separated by an average interval
of about 11 years
Note 1 to entry: If the reversal of the Sun’s magnetic field polarity in successive 11 year periods is taken into
account, the complete solar cycle may be considered to average some 22 years, the Hale cycle.
Note 2 to entry: The sunspot cycle as measured by the relative sunspot number, known as the Wolf number, has
an approximate length of 11 years, but this varies between about 7 and 17 years. An approximate 11-year cycle
has been found or suggested in geomagnetism, frequency of aurora, and other ionospheric characteristics.
3.2.10
relative sunspot number
Wolf number
measure of sunspot activity, computed from the expression k(10g + f ), where f the number of individual
spots, g the number of groups of spots, and k a factor that varies with the observer’s personal experience
of recognition and with observatory (location and instrumentation)
3.2.11
solar maximum
time period of maximum solar activity during a solar cycle, usually defined in terms of relative
sunspot number
3.2.12
solar minimum
time period of minimum solar activity during a solar cycle, usually defined in terms of relative
sunspot number
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ISO 20785-3:2015(E)
3.2.13
cosmic ray neutron monitor
ground level neutron monitor
GLNM
large detector used to measure the time-dependent relative fluence rate of high-energy cosmic
radiation, in particular the secondary neutrons generated in the atmosphere
Note 1 to entry: Protons, other hadrons, and muons, may also be detected.
Note 2 to entry: Installed worldwide at different locations and altitudes on the ground (and occasionally placed
on ships or aircraft), cosmic radiation neutron monitors are used for various cosmic radiation studies and to
determine solar modulation.
4 General considerations
4.1 General description of the cosmic radiation field in the atmosphere
The primary galactic cosmic radiation (and energetic solar particles) interact with the atomic nuclei of
atmospheric constituents, producing a cascade of interactions and secondary reaction products that
contribute to cosmic radiation exposures that decrease in intensity with depth in the atmosphere from
[6] 20
aviation altitudes to sea level . Galactic cosmic radiation (GCR) can have energies up to 10 eV, but
lower-energy particles are the most frequent. After the GCR penetrates the magnetic field of the solar
system, the peak of its energy distribution is at a few hundred MeV to 1 GeV per nucleon, depending on
–2,7 15
solar magnetic activity, and the spectrum follows a power function of the form E eV up to 10 eV;
–3
above that energy, the spectrum steepens to E . The fluence rate of GCR entering the solar system is
fairly constant with time, and these energetic ions approach the Earth isotropically.
The magnetic fields of the Earth and Sun alter the relative number of GCR protons and heavier ions
reaching the atmosphere. The GCR ion composition for low geomagnetic cut-off and low solar activity
is approximately 90 % protons, 9 % He ions and 1 % heavier ions; at a vertical cut-off of 15 GV, the
[7]
composition is approximately 83 % protons, 15 % He ions and nearly 2 % heavier ions .
The changing components of ambient dose equivalent caused by the various secondary cosmic radiation
constituents in the atmosphere as a function of altitude are illustrated in Figure 1. At sea level, the
muon component is the most important contributor to ambient dose equivalent and effective dose. At
aviation altitudes, neutrons, protons, electrons/positrons, photons and muons are the most significant
components. At higher altitudes, nuclear ions heavier than protons start to
...
DRAFT INTERNATIONAL STANDARD
ISO/DIS 20785-3
ISO/TC 85/SC 2 Secretariat: AFNOR
Voting begins on: Voting terminates on:
2013-12-18 2014-03-18
Dosimetry for exposures to cosmic radiation in civilian
aircraft —
Part 3:
Measurements at aviation altitudes
Dosimétrie pour les expositions au rayonnement cosmique à bord d’un avion civil —
Partie 3: Mesurages à bord d’avions
ICS: 49.020;13.280
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 20785-3:2013(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2013
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ISO/DIS 20785-3:2013(E)
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ii © ISO 2013 – All rights reserved
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ISO/DIS 20785-3
Contents Page
Foreword .v
Introduction . vi
1 Scope .1
2 Normative references .1
3 Definitions .1
3.1 Quantities and units .1
3.2 Atmospheric radiation field .4
4 General considerations .6
4.1 General description of the cosmic radiation field in the atmosphere .6
4.2 General considerations concerning the measurements .8
4.3 Safety and regulatory requirements for in-flight measurements .9
5 Measurement at aviation altitude .9
5.1 Parameters determining the dose rate .9
5.2 Influence quantities . 10
5.3 Specific considerations for active instruments . 10
5.4 Specific considerations for passive measurements . 11
6 Uncertainties . 11
Annex A (informative) Representative particle fluence energy distributions for the cosmic
radiation field at flight altitudes for solar minimum and maximum conditions and for
minimum and maximum vertical cut-off rigidity . 12
iv © ISO 2013 – All rights reserved
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ISO/DIS 20785-3
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. 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.
ISO 20785-3 was prepared by Technical Committee ISO/TC 85, Nuclear Energy, Subcommittee SC 2,
Radiological protection.
ISO 20785 consists of the following parts, under the general title Dosimetry for exposures to cosmic radiation
in civilian aircraft:
Part 1: Conceptual basis for measurements
Part 2: Characterization of instrument response
Part 3: Measurements at aviation altitudes
© ISO 2013 – All rights reserved v
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ISO/DIS 20785-3
Introduction
Aircraft crews are exposed to elevated levels of cosmic radiation of galactic and solar origin and secondary
radiation produced in the atmosphere, the aircraft structure and its contents. Following recommendations of
[1] [2]
the International Commission on Radiological Protection in Publication 60 , confirmed by Publication 103 ,
[3]
the European Union (EU) introduced a revised Basic Safety Standards Directive which included exposure to
natural sources of ionizing radiation, including cosmic radiation, as occupational exposure. The Directive
requires account to be taken of the exposure of aircraft crew liable to receive more than 1 mSv per year. It
then identifies the following four protection measures: (i) to assess the exposure of the crew concerned; (ii) to
take into account the assessed exposure when organising working schedules with a view to reducing the
doses of highly exposed crew; (iii) to inform the workers concerned of the health risks their work involves; and
(iv) to apply the same special protection during pregnancy to female crew in respect of the ‘child to be born’ as
to other female workers. The EU Council Directive has already been incorporated into laws and regulations of
EU Member States and is being included in the aviation safety standards and procedures of the Joint Aviation
Authorities and the European Air Safety Agency. Other countries such as Canada and Japan have issued
advisories to their airline industries to manage aircraft crew exposure.
For regulatory and legislative purposes, the radiation protection quantities of interest are equivalent dose (to
the foetus) and effective dose. The cosmic radiation exposure of the body is essentially uniform and the
maternal abdomen provides no effective shielding to the foetus. As a result, the magnitude of equivalent dose
to the foetus can be put equal to that of the effective dose received by the mother. Doses on board aircraft are
generally predictable, and events comparable to unplanned exposure in other radiological workplaces cannot
normally occur (with the rare exceptions of extremely intense and energetic solar particle events). Personal
dosemeters for routine use are not considered necessary. The preferred approach for the assessment of
doses of aircraft crew, where necessary, is to calculate directly effective dose per unit time, as a function of
geographic location, altitude and solar cycle phase, and to fold these values with flight and staff roster
information to obtain estimates of effective doses for individuals. This approach is supported by guidance from
, [4] [5]
the European Commission the ICRP in Publication 75 and the ICRU in Report 84 .
The role of calculations in this procedure is unique in routine radiation protection and it is widely accepted that
the calculated doses should be validated by measurement. Effective dose is not directly measurable. The
operational quantity of interest is ambient dose equivalent, H*(10). In order to validate the assessed doses
obtained in terms of effective dose, calculations can be made of ambient dose equivalent rates or route doses
in terms of ambient dose equivalent, and values of this quantity determined by measurements traceable to
national standards. The validation of calculations of ambient dose equivalent for a particular calculation
method may be taken as a validation of the calculation of effective dose by the same computer code, but this
step in the process may need to be confirmed. The alternative is to establish, a priori, that the operational
quantity ambient dose equivalent is a good estimator of effective dose and equivalent dose to the foetus for
the radiation fields being considered, in the same way that the use of the operational quantity personal dose
equivalent is justified for the estimation of effective dose for radiation workers. Ambient dose equivalent rate
as a function of geographic location, altitude and solar cycle phase is then calculated and folded with flight
and staff roster information.
The radiation field in aircraft at altitude is complex, with many types of ionizing radiation present, with energies
ranging up to many GeV. The determination of ambient dose equivalent for such a complex radiation field is
difficult. In many cases, the methods used for the determination of ambient dose equivalent in aircraft are
similar to those used at high-energy accelerators in research laboratories. Therefore, it is possible to
recommend dosimetric methods and methods for the calibration of dosimetric devices, as well as the
techniques for maintaining the traceability of dosimetric measurements to national standards. Dosimetric
measurements made to evaluate ambient dose equivalent shall be performed using accurate and reliable
methods that ensure the quality of readings provided to workers and regulatory authorities. This standard
gives procedures for the characterization of the response of instruments for the determination of ambient dose
equivalent in aircraft.
Requirements for the determination and recording of the cosmic radiation exposure of aircraft crew have been
introduced into the national legislation of EU Member States and other countries. Harmonization of methods
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ISO/DIS 20785-3
used for determining ambient dose equivalent and for calibrating instruments is desirable to ensure the
compatibility of measurements performed with such instruments.
This part of ISO 20785 is intended for the use of primary and secondary calibration laboratories for ionizing
radiation, by radiation protection personnel employed by governmental agencies, and by industrial
corporations concerned with the determination of ambient dose equivalent for aircraft crew.
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DRAFT INTERNATIONAL STANDARD ISO/DIS 20785-3
Dosimetry for exposures to cosmic radiation in civilian
aircraft — Part 3: Measurements at aviation altitudes
1 Scope
This part of ISO 20785 gives the basis for the measurement of ambient dose equivalent at flight altitudes for
the evaluation of the exposures to cosmic radiation in civilian aircraft.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO/IEC Guide 98-1:2009, Uncertainty of measurement — Part 1: Introduction to the expression of uncertainty
in measurement
ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO 20785-1, Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 1: Conceptual basis for
measurements
ISO 20785-2, Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 2: Characterization of
instrument response
3 Definitions
3.1 Quantities and units
3.1.1
particle fluence
fluence
at a given point of space, the number dN of particles incident on a small spherical domain divided by the
cross-sectional area da of that domain:
dN
da
-2 -2
Note 1 to entry: The unit of the fluence is m , a frequently used unit is cm .
Note 2 to entry: The energy distribution of the particle fluence, , is the quotient d by dE, where d is the fluence of
E
particles of energy between E and E+dE. There is an analogous definition for the direction distribution, , of the particle
fluence. The complete representation of the double differential particle fluence can be written (with arguments) (E,),
where the subscripts characterize the variables (quantities) for differentiation and where the symbols in the brackets
describe the values of the variables. The values in the brackets are needed for special function values, e.g. the energy
distribution of the particle fluence at the energy E = E is written as (E ). If no special values are indicated, the brackets
0 E 0
may be omitted.
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ISO/DIS 20785-3
3.1.2
particle fluence rate
fluence rate
…
2
d d N
dt dadt
where dis the increment of the particle fluence during an infinitesimal time interval with duration dt:
-1 -1
-2 -2
Note 1 to entry: The unit of the fluence rate is m s , a frequently used unit is cm s .
3.1.3
unrestricted linear energy transfer
linear energy transfer
LET
L
for an ionizing charged particle, the mean energy dE imparted locally to matter along a small path through
the matter, minus the sum of the kinetic energies of all the electrons released with kinetic energies in excess
of , divided by the length dl
dE
L
dl
Note 1 to entry: This quantity is not completely defined unless is specified, i.e., the maximum kinetic energy of
secondary electrons whose energy is considered to be “locally deposited.” may be expressed in eV.
Note 2 to entry: Linear energy transfer is often abbreviated LET, but to which should be appended the subscript or its
numerical value.
Note 3 to entry: The unit of the linear energy transfer is J m-1, a frequently used unit is keV m-1.
Note 4 to entry: If no energy cutoff is imposed, the unrestricted linear energy transfer, L , is equal to the linear electronic
∞
stopping power, S , and may be denoted simply as L.
el
3.1.4
dose equivalent
H
at the point of interest in tissue
H = D Q
where D is the absorbed dose, and Q is the quality factor at that point
Note 1 to entry: Q is determined by the unrestricted linear energy transfer, L (often denoted as L or LET), of charged
∞
particles passing through a small volume element (domains) at this point (the value of L is given for charged particles in
∞
water, not in tissue; the difference, however, is small). The dose equivalent at a point in tissue is then given by:
H Q(L)D dL
L
L0
where D = dD/dL is the distribution in terms of L of the absorbed dose at the point of interest.
L
Note 2 to entry: The relationship of Q and L is given in ICRP Publication 103 (ICRP, 2007).
-1
Note 3 to entry: The unit of dose equivalent is J kg , with the special name sievert (Sv).
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ISO/DIS 20785-3
3.1.5
ambient dose equivalent
H*(10)
dose equivalent at a point in a radiation field, that would be produced by the corresponding expanded and
aligned field, in the ICRU sphere at 10 mm depth on the radius opposing the direction of the aligned field
-1
Note 1 to entry: The unit of ambient dose equivalent is J kg with the special name sievert (Sv).
3.1.6
particle fluence-to-ambient dose equivalent conversion coefficient
h*
quotient of the particle ambient dose equivalent, H*(10), and the particle fluence,
H *(10)
h *
-1
2
Note 1 to entry: The unit of the particle fluence-to-ambient dose equivalent conversion coefficient is J m kg with the
2 2
special name Sv m , a frequently used unit is pSv cm .
3.1.7
atmosphere depth
X
v
mass of a unit-area column of air above a point in the atmosphere
-2 -2
Note 1 to entry: The unit of atmosphere depth is kg m ; a frequently used unit is g cm .
3.1.8
standard barometric altitude
pressure altitude
altitude determined by a barometric altimeter calibrated with reference to the International Standard
Atmosphere (ISA) (ISO, 1975) when the altimeter's datum is set to 1013,25 hPa.
Note 1 to entry: The flight level is sometimes given as FL 350, where the number represents multiples of 100 feet of
pressure altitude, based on the ISA and a datum setting of 1013,25 hPa. However, in some countries flight levels are
expressed in meters, in which case appropriate conversions should be made before applying the data given in this Report.
3.1.9
magnetic rigidity
P
momentum per charge (of a particle in a magnetic field), given by:
P p/Ze
where p is the particle momentum, Z the number of charges on the particle and e the charge on the proton
–1
Note 1 to entry: The base unit of magnetic rigidity is the tesla metre (Tm) ( Vm s). A frequently used unit is V (or GV) in
a system of units where the values of the speed of light, c, and the charge on the proton, e, are both 1, and the magnetic
rigidity is given by pc/Ze.
Note 2 to entry: Magnetic rigidity characterizes charged-particle trajectories in magnetic fields. All particles having the
same magnetic rigidity have identical trajectories in a magnetic field, independent of particle mass or charge.
3.1.10
geomagnetic cut-off rigidity
cut-off rigidity
r
c
minimum magnetic rigidity an incident particle can have and still penetrate the geomagnetic field to reach a
given location above the Earth
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ISO/DIS 20785-3
Note 1 to entry: Geomagnetic cut-off rigidity depends on angle of incidence. Often, vertical incidence to the
Earth’s surface is assumed, in which case, the vertical geomagnetic cut-off rigidity is the minimum magnetic
rigidity a vertically incident particle can have and still reach a given location above the Earth.
3.1.11
vertical geomagnetic cut-off rigidity
vertical cut-off
cut-off
minimum magnetic rigidity a vertically incident particle can have and still reach a given location above
the Earth.
3.2 Atmospheric radiation field
3.2.1
cosmic radiation
cosmic rays
cosmic particles
ionizing radiation consisting of high-energy particles, primarily completely ionized atoms, of extra-terrestrial
origin and the particles they generate by interaction with the atmosphere and other matter
3.2.2
primary cosmic radiation
primary cosmic rays
cosmic radiation incident from space at the Earth’s orbit
3.2.3
secondary cosmic radiation
secondary cosmic rays
cosmogenic particles
particles which are created directly or in a cascade of reactions by primary cosmic rays interacting with the
atmosphere or other matter
Note 1 to entry: Important particles with respect to radiation protection and radiation measurements in aircraft are:
neutrons, protons, photons, electrons, positrons, muons, and to a lesser extent, pions and nuclear ions heavier than
protons.
3.2.4
galactic cosmic radiation
galactic cosmic rays
GCR
cosmic radiation originating outside the solar system
3.2.5
solar cosmic radiation
solar cosmic rays
solar particles
cosmic radiation originating from the sun
3.2.6
solar particle event
SPE
large fluence rate of energetic solar particles ejected into space by a solar eruption
Note 1 to entry: Solar particle events are directional.
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ISO/DIS 20785-3
3.2.7
ground level enhancement
GLE
sudden increase of cosmic radiation observed on the ground by at least two neutron monitor stations
recording simultaneously a greater than 1 % increase in the five-minute-averaged count rate associated with
solar energetic particles.
Note 1 to entry: A GLE is associated with a solar-particle event having a high fluence rate of particles with high energy
(greater than 500 MeV).
Note 2 to entry: GLEs are relatively rare, occurring on average about once per year. GLEs are numbered; the first number
being given to that occurring in February 1942.
3.2.8
solar modulation
change of the GCR field (outside the Earth's magnetosphere) caused by change of solar activity and
consequent change of the magnetic field of the heliosphere
3.2.9
solar cycle
period during which the solar activity varies with successive maxima separated by an average interval of
about 11 years
Note 1 to entry: If the reversal of the Sun’s magnetic field polarity in successive 11 year periods is taken into account, the
complete solar cycle may be considered to average some 22 years, the Hale cycle.
Note 2 to entry: The sunspot cycle as measured by the relative sunspot number, known as the Wolf number, has an
approximate length of 11 years, but this varies between about 7 and 17 years. An approximate 11-year cycle has been
found or suggested in geomagnetism, frequency of aurora, and other ionospheric characteristics. The u index of
geomagnetic intensity variation shows one of the strongest known correlations to solar activity.
3.2.10
relative sunspot number
Wolf number
measure of sunspot activity, computed from the expression k(10g + f), where f the number of individual spots,
g the number of groups of spots, and k a factor that varies with the observer's personal experience of
recognition and with observatory (location and instrumentation)
3.2.11
solar maximum
time period of maximum solar activity during a solar cycle, usually defined in terms of relative sunspot number
3.2.12
solar minimum
time period of minimum solar activity during a solar cycle, usually defined in terms of relative sunspot number
3.2.13
cosmic ray neutron monitor
ground level neutron monitor
GLNM
large detector used to measure the time-dependent relative fluence rate of high-energy cosmic radiation, in
particular the secondary neutrons generated in the atmosphere. Protons, other hadrons, and muons, may also
be detected
Note 1 to entry: Installed worldwide at different locations and altitudes on the ground (and occasionally placed on ships or
aircraft), cosmic radiation neutron monitors are used for various cosmic radiation studies and to determine solar
modulation.
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ISO/DIS 20785-3
4 General considerations
4.1 General description of the cosmic radiation field in the atmosphere
The primary galactic cosmic radiation (and energetic solar particles) interact with the atomic nuclei of
atmospheric constituents, producing a cascade of interactions and secondary reaction products that contribute
to cosmic radiation exposures that decrease in intensity with depth in the atmosphere from aviation altitudes
[6] 20
to sea level . Galactic cosmic radiation (GCR) can have energies up to 10 eV, but lower-energy particles
are the most frequent. After the GCR penetrates the magnetic field of the solar system, the peak of its energy
distribution is at a few hundred MeV to 1 GeV per nucleon, depending on solar magnetic activity, and the
–2,7 15
spectrum follows a power function of the form E eV up to 10 eV; above that energy, the spectrum
–3
steepens to E . The fluence rate of GCR entering the solar system is fairly constant with time, and these
energetic ions approach the Earth isotropically.
The magnetic fields of the Earth and sun alter the relative number of GCR protons and heavier ions reaching
the atmosphere. The GCR ion composition for low geomagnetic cut-off and low solar activity is approximately
90 % protons, 9 % He ions and 1 % heavier ions; at a vertical cut-off of 15 GV, the composition is
[7][8]
approximately 83 % protons, 15 % He ions and nearly 2 % heavier ions .
The changing components of ambient dose equivalent caused by the various secondary cosmic radiation
constituents in the atmosphere as a function of altitude are illustrated in Figure 1. At sea level, the muon
component is the most important contributor to ambient dose equivalent and effective dose. At aviation
altitudes, neutrons, protons, electrons/positrons, photons and muons are the most significant components. At
higher altitudes, nuclear ions heavier than protons start to contribute. Figures showing representative
normalized energy distributions of fluence rates of all the important particles at low and high cut-offs and
altitudes at solar minimum and maximum are shown in Annex A.
The Earth is also exposed to bursts of energetic protons and heavier particles from magnetic disturbances
near the surface of the sun and from ejection of large amounts of matter (coronal mass ejections — CMEs)
with, in some cases, acceleration by the CMEs and associated solar wind shock waves. The particles of these
solar particle events, or solar proton events (both abbreviated to SPE), are much lower in energy than GCR,
generally below 100 MeV and only rarely above 10 GeV. SPEs are of short duration, a few hours to a few
days, and highly variable in intensity. Only a small fraction of SPEs, on average one per year, produce large
numbers of high-energy particles which cause significant dose rates at high altitudes and low geomagnetic
cut-offs and can be observed by neutron monitors on the ground. Such events are called ground level
enhancements (GLEs). For aircraft crew, the cumulative dose from GCR is far greater than the dose from
SPEs. Intense SPEs can affect GCR dose rates by disturbing the Earth's magnetic field in such a way as to
change the galactic particle intensity reaching the atmosphere.
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ISO/DIS 20785-3
X Altitude (km)
Y Ambient dose equivalent rate (μSv/h)
Conditions: 1 GV cut-off and solar minimum (deceleration potential, of 465 MV) [9]
Figure 1 — Calculated ambient dose equivalent rates as a function of standard barometric altitude for
high latitudes at solar minimum for various atmospheric cosmic radiation component particles
The field comprises mainly neutrons, protons, electrons/positrons, photons and muons. There is not a
significant contribution to dose equivalent from energetic primary heavy charged particles (HZE) or fragments.
The electrons/positrons and muons are directly ionizing radiation, and together with indirectly ionizing photons
and secondary electrons, interact with matter via the electromagnetic force. Neutrons (and a small contribution
from pions), interact via the strong interaction producing directly ionizing secondary particles. Protons are both
directly ionizing via the electromagnetic force and indirectly via neutron-like strong interactions.
The directly ionizing component and the secondary electrons from indirectly ionizing photons, comprise the
non-neutron component. The neutrons plus the neutron-like interactions of protons comprise the neutron
component. Alternatively for dosimetric purposes, the field can be divided into low LET (<10 keV/μm) and high
LET (>10 keV/μm) components. This definition is based on the dependence of quality factor on LET. Quality
factor is unity below 10 keV/μm. This separation between low and high LET particles can be applied to TEPCs,
and to other materials and detectors, but the low LET/high LET threshold may vary between 5 keV/μm and
10 keV/μm. The low LET component comprises the directly ionizing electrons/positrons and muons;
secondary electrons from photon interactions, most of the energy deposition by directly ionizing interactions of
protons; and part of the energy deposition by secondary particles from strong interactions of protons and
neutrons. The high LET component is from relatively short range secondary particles from strong interactions
of protons and neutrons. The relative contributions to the total ambient dose equivalent of low LET and non-
neutron co
...
NORME ISO
INTERNATIONALE 20785-3
Première édition
2015-11-15
Dosimétrie pour les expositions au
rayonnement cosmique à bord d’un
avion civil —
Partie 3:
Mesurages à bord d’avions
Dosimetry for exposures to cosmic radiation in civilian aircraft —
Part 3: Measurements at aviation altitudes
Numéro de référence
ISO 20785-3:2015(F)
©
ISO 2015
---------------------- Page: 1 ----------------------
ISO 20785-3:2015(F)
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2015, Publié en Suisse
Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite ni utilisée
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Tel. +41 22 749 01 11
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copyright@iso.org
www.iso.org
ii © ISO 2015 – Tous droits réservés
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ISO 20785-3:2015(F)
Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 1
3.1 Grandeurs et unités . 1
3.2 Champ de rayonnement atmosphérique . 4
4 Considérations générales . 6
4.1 Description générale du champ de rayonnement cosmique dans l’atmosphère . 6
4.2 Considérations générales relatives au mesurage . 8
4.2.1 Généralités . 8
4.2.2 Choix des instruments appropriés . 8
4.2.3 Caractérisation des réponses des instruments . 8
4.2.4 Mesurages à bord d’un avion . 9
4.2.5 Application de facteurs de correction appropriés . 9
4.3 Exigences de sécurité et exigences réglementaires pour les mesurages en vol . 9
5 Mesurages aux altitudes de vol .10
5.1 Paramètres déterminant le débit de dose .10
5.1.1 Altitude barométrique .10
5.1.2 Coordonnées géographiques .10
5.1.3 Activité solaire .10
5.2 Grandeurs d’influence éventuelles .10
5.2.1 Généralités .10
5.2.2 Pression de l’air dans la cabine .10
5.2.3 Température de l’air dans la cabine .11
5.2.4 Humidité de l’air dans la cabine .11
5.3 Considérations particulières pour les instruments actifs .11
5.3.1 Alimentation .11
5.3.2 Vibrations et chocs .11
5.3.3 Perturbations électromagnétiques provenant de l’avion .11
5.4 Considérations particulières pour les mesures passives .11
5.4.1 Contrôle de sécurité aux rayons X.11
5.4.2 Soustraction du bruit de fond .12
6 Incertitudes.12
Annexe A (informative) Distributions en énergie représentatives de la fluence de particules
pour le champ de rayonnement cosmique à des altitudes de vol d’avion dans les
conditions de période d’activité solaire minimale et maximale et pour la rigidité de
coupure verticale minimale et maximale .13
Bibliographie .17
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ISO 20785-3:2015(F)
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes
nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est
en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.
L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier de prendre note des différents
critères d’approbation requis pour les différents types de documents ISO. Le présent document a été
rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www.
iso.org/directives).
L’attention est appelée sur le fait que certains des éléments du présent document peuvent faire l’objet de
droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de
brevets reçues par l’ISO (voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer
un engagement.
Pour une explication de la signification des termes et expressions spécifiques de l’ISO liés à
l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion de l’ISO aux principes
de l’OMC concernant les obstacles techniques au commerce (OTC), voir le lien suivant: Avant-propos —
Informations supplémentaires.
Le comité chargé de l’élaboration du présent document est l’ISO/TC 85, Énergie nucléaire, technologies
nucléaires, et radioprotection, sous-comité SC 2, Radioprotection.
L’ISO 20785 comprend les parties suivantes, présentées sous le titre général Dosimétrie pour les
expositions au rayonnement cosmique à bord d’un avion civil:
— Partie 1: Fondement théorique des mesurages
— Partie 2: Caractérisation de la réponse des instruments
— Partie 3: Mesurages à bord d’avions
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ISO 20785-3:2015(F)
Introduction
Le personnel navigant est exposé à des niveaux élevés de rayonnement cosmique d’origine galactique et
solaire, ainsi qu’au rayonnement secondaire produit dans l’atmosphère, dans la structure de l’avion et
son contenu. Suivant les recommandations de la Commission internationale de protection radiologique
[1] [2]
dans la Publication 60 , confirmées par la Publication 103 , l’Union européenne (UE) a établi la
[3]
révision d’une Directive relative aux normes de sécurité de base , classant parmi les expositions
professionnelles le cas de l’exposition aux sources naturelles de rayonnement ionisant, y compris
le rayonnement cosmique. Cette Directive requiert de prendre en compte l’exposition du personnel
navigant susceptible de recevoir plus de 1 mSv par an. Elle identifie ensuite les quatre mesures de
protection suivantes: (i) évaluation de l’exposition du personnel concerné; (ii) prise en compte de
l’exposition évaluée lors de l’organisation des programmes de travail, en vue de réduire les doses du
personnel navigant fortement exposé; (iii) information aux travailleurs concernés sur les risques
pour la santé que leur travail implique; et (iv) application des mêmes règles de protection spécifiques
en cas de grossesse pour le personnel navigant féminin, eu égard à «l’enfant à naître», que pour tout
autre travailleur exposé de sexe féminin. La Directive du Conseil de l’UE doit être intégrée aux lois
et réglementations des États membres de l’UE ainsi que dans les normes et les modes opératoires de
sécurité de l’aviation, des autorités communes de l’aviation (Joint Aviation Authorities) et de l’Agence
européenne pour la sécurité aérienne (European Air Safety Agency). D’autres pays tels que le Canada et
le Japon ont émis des règles ou des recommandations à l’attention de leurs compagnies aériennes pour
gérer la question de l’exposition du personnel navigant.
Les grandeurs de protection concernées, dans un cadre réglementaire et législatif, sont la dose
équivalente (au fœtus) et la dose efficace. L’exposition de l’organisme au rayonnement cosmique est
globalement uniforme et l’abdomen maternel ne fournit aucune protection particulière au fœtus.
Ainsi, la dose équivalente au fœtus peut être considérée comme égale à la dose efficace reçue par la
mère. Les doses liées à l’exposition à bord des avions sont généralement prévisibles, et des événements
comparables à des expositions non prévues à d’autres postes de travail sous rayonnement ne peuvent
pas habituellement se produire (à l’exception rare des éruptions solaires extrêmement intenses
produisant des particules solaires très énergétiques). Le recours à des dosimètres individuels pour
un usage de routine n’est pas considéré comme nécessaire. L’approche préférentielle pour l’évaluation
des doses reçues par le personnel navigant, si nécessaire, consiste à calculer directement le débit de
dose efficace, en fonction des coordonnées géographiques, de l’altitude et de la phase du cycle solaire,
et à combiner ces valeurs avec les informations concernant le vol et le tableau de service du personnel,
afin d’obtenir des estimations des doses efficaces pour les individus. Cette approche est recommandée
[4]
par une directive de la Commission européenne, la CIPR, dans la Publication 75 et l’ICRU, dans le
[5]
Rapport 84 .
Le rôle des calculs dans ce mode opératoire est unique par rapport aux méthodes d’évaluation
habituellement utilisées en radioprotection et il est largement admis qu’il convient de valider les doses
calculées par mesurage. La dose efficace n’est pas directement mesurable. La grandeur opérationnelle
utilisée est l’équivalent de dose ambiant, H*(10). En effet, tel que cela est mentionné notamment dans
le Rapport 84 de l’ICRU, l’équivalent de dose ambiant est considéré comme un estimateur conservateur
de la dose efficace si l’on considère que l’irradiation est isotrope, ou isotrope de l’hémisphère supérieur.
Afin de valider les doses évaluées en termes de dose efficace, il est possible de calculer les débits
d’équivalent de dose ambiant ou les doses pendant le vol, en termes d’équivalent de dose ambiant, ainsi
que les valeurs de cette grandeur déterminées par des mesurages traçables à des étalons nationaux. La
validation des calculs de l’équivalent de dose ambiant par une méthode de calcul particulière peut être
considérée comme la validation du calcul de la dose efficace par le même code de calcul, mais cette étape
du processus d’évaluation peut nécessiter d’être confirmée. La variante consiste à établir, a priori, que
l’équivalent de dose ambiant constitue un bon estimateur de la dose efficace et de la dose équivalente
destinée au fœtus pour les champs de rayonnements considérés, de la même façon que l’utilisation de
l’équivalent de dose individuel est justifiée pour l’estimation de la dose efficace des travailleurs sous
rayonnement. Le débit d’équivalent de dose ambiant en fonction des coordonnées géographiques, de
l’altitude et de la phase du cycle solaire, est ensuite calculé et combiné aux informations concernant le
vol et le tableau de service du personnel.
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ISO 20785-3:2015(F)
Le champ de rayonnement auquel est soumis un avion aux altitudes de vol est complexe, avec la présence
de nombreux types de rayonnements ionisants dont les énergies peuvent atteindre plusieurs milliers
de GeV. Il est difficile de déterminer l’équivalent de dose ambiant pour un champ de rayonnement si
complexe. Dans de nombreux cas, les méthodes employées pour déterminer l’équivalent de dose
ambiant à bord d’un avion sont semblables à celles utilisées auprès d’accélérateurs haute énergie
dans les laboratoires de recherche. Des méthodes dosimétriques et des méthodes d’étalonnage des
dispositifs dosimétriques peuvent par conséquent être recommandées, ainsi que les techniques
permettant de conserver la traçabilité des mesurages dosimétriques à des étalons nationaux. Les
mesurages dosimétriques effectués pour évaluer l’équivalent de dose ambiant doivent être réalisés à
l’aide de méthodes précises et fiables qui assurent la qualité des relevés fournis aux travailleurs et aux
autorités de réglementation. La présente partie de l’ISO 20785 décrit les modes opératoires permettant
de caractériser la réponse des instruments pour la détermination de l’équivalent de dose ambiant à
bord d’un avion.
Les exigences relatives à la détermination et à l’enregistrement de l’exposition au rayonnement
cosmique du personnel navigant font partie intégrante de la législation nationale des États membres
de l’UE et des autres pays. Il est souhaitable d’harmoniser les méthodes permettant de déterminer
l’équivalent de dose ambiant et d’étalonner les instruments utilisés afin de garantir la compatibilité des
mesurages effectués avec de tels instruments.
La présente partie de l’ISO 20785 est destinée à être utilisée par les laboratoires d’étalonnages
primaire et secondaire dans le domaine des rayonnements ionisants, par le personnel des services de
radioprotection employé par les organismes publics et par les entreprises industrielles, intéressées par
la détermination de l’équivalent de dose ambiant du personnel navigant.
vi © ISO 2015 – Tous droits réservés
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NORME INTERNATIONALE ISO 20785-3:2015(F)
Dosimétrie pour les expositions au rayonnement cosmique
à bord d’un avion civil —
Partie 3:
Mesurages à bord d’avions
1 Domaine d’application
La présente partie de l’ISO 20785 donne les principes de base permettant de mesurer l’équivalent de dose
ambiant aux altitudes de vol pour l’évaluation de l’exposition au rayonnement cosmique à bord d’un avion.
2 Références normatives
Les documents suivants, en totalité ou en partie, sont référencés de manière normative dans le présent
document et sont indispensables pour son application. Pour les références datées, seule l’édition citée
s’applique. Pour les références non datées, la dernière édition du document de référence s’applique (y
compris les éventuels amendements).
ISO/IEC Guide 98-1, Incertitude de mesure — Partie 1: Introduction à l’expression de l’incertitude de mesure
ISO/IEC Guide 98-3, Incertitude de mesure — Partie 3: Guide pour l’expression de l’incertitude de
mesure (GUM:1995)
ISO 20785-1, Dosimétrie pour l’exposition au rayonnement cosmique à bord d’un avion civil — Partie 1:
Fondement théorique des mesurages
ISO 20785-2, Dosimétrie de l’exposition au rayonnement cosmique dans l’aviation civile — Partie 2:
Caractérisation de la réponse des instruments
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions suivants s’appliquent.
3.1 Grandeurs et unités
3.1.1
fluence de particules
fluence
Φ
à un point donné dans l’espace, nombre dN de particules incidentes sur un petit domaine sphérique
divisé par la section da de ce domaine
dN
Φ=
da
-2 -2
Note 1 à l’article: L’unité de la fluence est le m , le cm constitue une unité d’usage courant.
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ISO 20785-3:2015(F)
Note 2 à l’article: La distribution en énergie de la fluence de particules, Φ , est le quotient de dΦ sur dE, où
E
dΦ est la fluence des particules d’énergie comprise entre E et E+dE. Il existe une définition analogue pour la
distribution directionnelle, Φ , de la fluence de particules. La représentation complète de la fluence de particules
Ω
différentielle double peut s’écrire (avec les arguments) Φ (E,Ω), où les indices caractérisent les variables
E,Ω
(grandeurs) de différenciation et où les symboles entre parenthèses décrivent les valeurs des variables. Les
valeurs entre parenthèses sont requises pour des valeurs de fonction spéciales, par exemple la distribution en
énergie de la fluence de particules à l’énergie, E = E , s’écrit sous la forme Φ (E ). En l’absence d’indication de
0 E 0
toute valeur spéciale, les parenthèses ne sont pas nécessaires.
3.1.2
débit de fluence de particules
débit de fluence
Φ
2
dΦ d N
Φ ==
dt ddat⋅
où dΦ est l’incrément de la fluence de particules au cours d’un intervalle de temps infinitésimal
avec la durée dt
-2 −1 -2 −1
Note 1 à l’article: L’unité du débit de fluence est le m s , le cm s constitue une unité d’usage courant.
3.1.3
transfert linéique d’énergie non limité
transfert linéique d’énergie
TLE
L
∞
pour une particule chargée ionisante, énergie moyenne dE impartie localement à une matière le long
∞
d’un petit trajet à travers la matière, moins la somme des énergies cinétiques de tous les électrons
libérés, divisée par la longueur dl
dE
∞
L =
∞
dl
−1 −1
Note 1 à l’article: L’unité du transfert linéique d’énergie est le J m , le keV μm constitue une unité d’usage courant.
3.1.4
équivalent de dose
H
au point concerné dans le tissu
HD= Q
où D est la dose absorbée et Q est le facteur de qualité moyen à ce point
Note 1 à l’article: Q est déterminé par le transfert linéique d’énergie non limité, L (souvent désigné par L ou
∞
LET), de particules chargées traversant un élément de faible volume (domaines) au niveau de ce point (la valeur
de L est donnée pour les particules chargées dans l’eau, pas dans le tissu; la différence, cependant, est faible).
∞
L’équivalent de dose à un point dans le tissu est alors donné par l’équation suivante:
∞
HQ= ()LD dL
L
∫
L−0
où D = dD/dL est la distribution en fonction de L de la dose absorbée au point concerné.
L
Note 2 à l’article: La relation de Q et L est donnée dans la Référence [2].
−1
Note 3 à l’article: L’unité de l’équivalent de dose est le J kg , également appelé sievert (Sv).
2 © ISO 2015 – Tous droits réservés
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ISO 20785-3:2015(F)
3.1.5
équivalent de dose ambiant
H*(10)
équivalent de dose en un point dans un champ de rayonnement, qui serait produit par le champ expansé
et unidirectionnel correspondant, dans la sphère ICRU, à une profondeur de 10 mm sur le rayon faisant
face à la direction du champ unidirectionnel
−1
Note 1 à l’article: L’unité de l’équivalent de dose ambiant est le J kg , également appelé sievert (Sv).
3.1.6
coefficient de conversion fluence de particules-équivalent de dose ambiant
h(10)*
Φ
quotient de l’équivalent de dose ambiant, H*(10), et de la fluence de particules, Φ
H *(10)
h 10 * =
()
Φ
Φ
2
Note 1 à l’article: L’unité du coefficient de conversion fluence de particules-équivalent de dose ambiant est le J m
−1 2 2
kg et son équivalent est le Sv m , le pSv cm constitue une unité d’usage courant.
3.1.7
facteur de correction
K
facteur appliqué à une indication en vue de corriger l’écart existant entre les conditions de mesurage et
les conditions de référence
3.1.8
profondeur atmosphérique
X
v
masse d’une colonne atmosphérique par surface unitaire au-dessus d’un point donné dans l’atmosphère
-2 -2
Note 1 à l’article: L’unité de la profondeur atmosphérique est le kg m , le g cm constitue une unité d’usage courant.
3.1.9
altitude barométrique étalon
pression d’altitude
altitude déterminée par un altimètre barométrique étalonné par référence à l’atmosphère type
internationale (ISA) (ISO, 1975) lorsque les données de l’altimètre sont établies à 1 013,25 hPa
Note 1 à l’article: Le niveau de vol est parfois donné sous la forme FL 350, où le numéro représente les multiples
de 100 pieds d’altitude-pression, sur la base de l’atmosphère ISA et d’un paramétrage de données à 1 013,25 hPa.
Cependant, dans certains pays, les niveaux de vol sont exprimés en mètres, auquel cas il convient que les
conversions appropriées soient réalisées avant d’appliquer les données communiquées dans la présente partie
de l’ISO 20785.
3.1.10
rigidité magnétique
P
quantité de mouvement par charge (d’une particule dans un champ magnétique) donnée par:
p
P=
Ze
où p est la quantité de mouvement de la particule, Z est le nombre de charges sur la particule et e est la
charge du proton
–1
Note 1 à l’article: L’unité de la rigidité magnétique est le tesla-mètre (T m) (= V m s). Une unité d’usage courant
est le V (ou GV) dans un système d’unités où les valeurs de la vitesse de la lumière, c, et la charge sur le proton, e,
sont toutes deux de 1, et la rigidité magnétique est donnée par pc/Ze.
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ISO 20785-3:2015(F)
Note 2 à l’article: La rigidité magnétique caractérise des trajectoires de particules chargées dans des champs
magnétiques. Toutes les particules en présence de la même rigidité magnétique ont des trajectoires identiques
dans un champ magnétique sous vide, indépendantes de la masse, de la vitesse ou de la charge des particules.
3.1.11
rigidité de coupure géomagnétique
rigidité de coupure
r
c
rigidité magnétique minimale potentielle pour une particule incidente, pénétrant effectivement le
champ géomagnétique pour atteindre un emplacement donné au-dessus de la surface de la Terre
Note 1 à l’article: La rigidité de coupure magnétique dépend de l’angle d’incidence. Souvent, l’incidence verticale
à la surface de la Terre est supposée, auquel cas, la rigidité de coupure géomagnétique verticale représente la
rigidité magnétique minimale potentielle pour une particule incidente verticale, atteignant effectivement un
emplacement donné au-dessus de la surface de la Terre.
3.1.12
rigidité de coupure géomagnétique verticale
coupure verticale
coupure
rigidité magnétique minimale potentielle pour une particule incidente verticale, atteignant
effectivement un emplacement donné au-dessus de la surface de la Terre
3.1.13
potentiel de décélération
ϕ
paramètre de modulation du rayonnement cosmique déduit à partir d’observations spatiales de la
variation d’abondance de différentes espèces en fonction de l’époque du cycle solaire
Note 1 à l’article: Le potentiel de décélération peut être déduit soit à partir de l’indice des taches solaires, soit à
partir des données des moniteurs à neutrons de Climax, en utilisant une simple équation linéaire qui dépend de
la phase du cycle solaire.
3.2 Champ de rayonnement atmosphérique
3.2.1
rayonnement cosmique
rayons cosmiques
particules cosmiques
rayonnement ionisant composé de particules de haute énergie, des atomes totalement ionisés du
rayonnement cosmique primaire, d’origine extraterrestre et de particules engendrées par interaction
avec l’atmosphère et toute autre matière
3.2.2
rayonnement cosmique primaire
rayons cosmiques primaires
rayons cosmiques provenant de l’espace au niveau de l’orbite terrestre
3.2.3
rayonnement cosmique secondaire
rayons cosmiques secondaires
particules d’origine cosmique
particules créées, directement ou par des réactions en cascade, par les rayons cosmiques primaires
interagissant avec l’atmosphère ou toute autre matière
Note 1 à l’article: Les neutrons, protons, photons, électrons, positrons, muons et, dans une moindre mesure, les
pions et les ions plus lourds que les protons constituent des particules importantes, eu égard à la radioprotection
et aux mesurages des rayonnements à bord d’un avion.
4 © ISO 2015 – Tous droits réservés
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ISO 20785-3:2015(F)
3.2.4
rayonnement cosmique galactique
rayons cosmiques galactiques
GCR
rayons cosmiques provenant de l’extérieur du système solaire
3.2.5
rayons cosmiques solaires
particules solaires
rayonnement cosmique solaire
rayons cosmiques provenant du Soleil
3.2.6
événement de particules solaires
SPE
débit de fluence important de particules solaires énergétiques, projetées dans l’espace par une
éruption solaire
Note 1 à l’article: Les événements de particules solaires sont directionnels.
3.2.7
augmentation au niveau du sol
GLE
augmentation soudaine du rayonnement cosmique, observée au niveau du sol par au moins deux
stations de surveillance des neutrons enregistrant simultanément une augmentation supérieure à 3 %
du taux de comptage moyenné sur 5 min associée aux particules solaires énergétiques
Note 1 à l’article: Une GLE est associée à un événement de particules solaires ayant un débit de fluence de
particules élevé ainsi qu’une énergie élevée (supérieure à 500 MeV).
Note 2 à l’article: Les GLE sont des événements relativement rares, se produisant environ une fois par an en moyenne.
3.2.8
modulation solaire
variation du champ de rayonnement cosmique galactique (à l’extérieur de la magnétosphère terrestre),
due à un changement de l’activité solaire et à la modification associée du champ magnétique de
l’héliosphère
3.2.9
cycle solaire
période durant laquelle l’activité solaire varie, avec des écarts maximaux successifs d’un intervalle
moyen de 11 ans environ
Note 1 à l’article: Si l’inversion de la polarité du champ magnétique solaire dans un hémisphère donné selon des
périodes successives de 11 ans est prise en compte, il peut être considéré que le cycle solaire complet s’effectue
en moyenne en quelque 22 années, soit le cycle de Hale.
Note 2 à l’article: Le cycle d’activité solaire, tel que mesuré par le nombre de taches solaires relatif, appelé nombre
de Wolf, dure à peu près 11 ans, mais ce nombre varie entre 7 ans et 17 ans environ. Un cycle approximatif
de 11 ans a été observé ou
...
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