ISO 20785-1:2020
(Main)Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 1: Conceptual basis for measurements
Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 1: Conceptual basis for measurements
This document specifies the conceptual basis for the determination of ambient dose equivalent for the evaluation of exposure to cosmic radiation in civilian aircraft and for the calibration of instruments used for that purpose.
Dosimétrie pour l'exposition au rayonnement cosmique à bord d'un avion civil — Partie 1: Fondement théorique des mesurages
Le présent document spécifie les principes de base permettant de déterminer l'équivalent de dose ambiant pour l'évaluation de l'exposition au rayonnement cosmique à bord d'un avion civil, ainsi que pour l'étalonnage des instruments utilisés à cette fin.
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INTERNATIONAL ISO
STANDARD 20785-1
Third edition
2020-07
Dosimetry for exposures to cosmic
radiation in civilian aircraft —
Part 1:
Conceptual basis for measurements
Dosimétrie pour l'exposition au rayonnement cosmique à bord d'un
avion civil —
Partie 1: Fondement théorique des mesurages
Reference number
ISO 20785-1:2020(E)
©
ISO 2020
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ISO 20785-1:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii © ISO 2020 – All rights reserved
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ISO 20785-1:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms . 1
3.2 Quantities and units . 2
3.3 Atmospheric radiation field . 4
4 General considerations . 6
4.1 The cosmic radiation field in the atmosphere . 6
4.2 General calibration considerations for the dosimetry of cosmic radiation fields in
aircraft . 7
4.2.1 Approach . 7
4.2.2 Considerations concerning the measurement . 7
4.2.3 Considerations concerning the radiation field . 8
4.2.4 Considerations concerning calibration . 8
4.2.5 Simulated aircraft fields . 9
4.3 Conversion coefficients . 9
5 Dosimetric devices .10
5.1 Introduction .10
5.2 Active devices .10
5.2.1 Devices to determine all field components .10
5.2.2 Devices for low LET/non-neutron .11
5.2.3 Devices for high-LET/neutron component .12
5.3 Passive devices .13
5.3.1 General considerations .13
5.3.2 Etched track detectors .14
5.3.3 Fission foil detectors .14
5.3.4 Superheated emulsion neutron detectors (bubble) detectors .14
5.3.5 Thermoluminescent detectors.15
5.3.6 Photoluminescent detectors .15
Annex A (informative) Representative particle fluence rate 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 .16
Bibliography .22
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ISO 20785-1:2020(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 voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,
and radiological protection, Subcommittee SC 2, Radiation protection.
This third edition cancels and replaces the second edition (ISO 20785-1:2012), which has been
technically revised. The main changes are as follows:
— revision of the terms and definitions;
— updated references.
A list of all the parts in the ISO 20785 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 20785-1:2020(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
recommendations of the International Commission on Radiological Protection (ICRP) in Publication
[1] [2]
60 , confirmed by Publication 103 , the European Union (EU) introduced a revised Basic Safety
[3] [4]
Standards Directive and International Atomic Energy Agency (IAEA) issued a revised Basic Safety
Standards. Those standards included exposure to natural sources of ionizing radiation, including cosmic
radiation, as occupational exposure. The EU Directive requires account to be taken of the exposure of
aircraft crews liable to receive more than 1 mSv per year. It then identifies the following four protection
measures:
a) to assess the exposure of the crew concerned;
b) to take into account the assessed exposure when organizing working schedules with a view to
reducing the doses of highly exposed crews;
c) to inform the workers concerned of the health risks their work involves; and
d) to apply the same special protection during pregnancy to female crews 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 the
equivalent dose (to the foetus) and the 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 set 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 dosimeters for routine use are not
considered necessary. The preferred approach for the assessment of doses of aircraft crews, where
necessary, is to calculate directly the effective dose per unit time, as a function of geographic location,
altitude and solar cycle phase, and to combine these values with flight and staff roster information to
obtain estimates of effective doses for individuals. This approach is supported by guidance from the
[5] [6]
European Commission and the ICRP in Publications 75 and 132 .
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. The 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 from measurements. Traceability should be provided for a reasonable number of particle
types and energies of the atmospheric radiation field, corrections included for differences between the
calibration fields and the total atmospheric radiation field, and related uncertainties properly taken
into account. The validation of calculations of ambient dose equivalent for a particular calculation
method may be taken as a validation of the calculation of the 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 ground-based
radiation workers.
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
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ISO 20785-1:2020(E)
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 should be
performed using accurate and reliable methods that ensure the quality of readings provided to workers
and regulatory authorities. This document gives a conceptual basis 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
crews 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 document 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 crews.
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INTERNATIONAL STANDARD ISO 20785-1:2020(E)
Dosimetry for exposures to cosmic radiation in civilian
aircraft —
Part 1:
Conceptual basis for measurements
1 Scope
This document specifies the conceptual basis for the determination of ambient dose equivalent for the
evaluation of exposure to cosmic radiation in civilian aircraft and for the calibration of instruments
used for that purpose.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 General terms
3.1.1
calibration
operation that, under specified conditions, establishes a relation between the conventional quantity,
H , and the indication, G
0
Note 1 to entry: A calibration can be expressed by a statement, calibration function, calibration diagram,
calibration curve, or calibration table. In some cases, it can consist of an additive or multiplicative correction of
the indication with associated measurement uncertainty.
Note 2 to entry: Calibration should not be confused with adjustment of a measuring system, often mistakenly
called "self-calibration", or with verification of calibration.
Note 3 to entry: Often, the first step alone in the above definition is perceived as being calibration.
3.1.2
response
response characteristic
R
quotient of the indication, G, or the corrected indication, G , and the conventional quantity value to be
corr
measured
Note 1 to entry: To avoid confusion, it is necessary to specify which of the quotients, given in the definition of
the response (to G or to G ) is applied. Furthermore, it is necessary, in order to avoid confusion, to state the
corr
quantity to be measured, for example: the response with respect to fluence, R , the response with respect to
Φ
kerma, R , the response with respect to absorbed dose, R .
K D
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ISO 20785-1:2020(E)
Note 2 to entry: The reciprocal of the response under the specified conditions is equal to the calibration
coefficient N
coeff.
Note 3 to entry: The value of the response can vary with the magnitude of the quantity to be measured. In such
cases the detector assembly's response is said to be non-constant.
Note 4 to entry: The response usually varies with the energy and direction distribution of the incident
radiation. It is, therefore, useful to consider the response as a function, R(E,Ω), of the radiation energy, E, and
of the direction, Ω of the incident monodirectional radiation. R(E) describes the "energy dependence" and R(Ω)
the "angle dependence" of response; for the latter, Ω may be expressed by the angle, α, between the reference
direction of the detector assembly and the direction of an external monodirectional field.
3.2 Quantities and units
3.2.1
particle fluence
fluence
Φ
number, dN, at a given point in space, 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 .
Note 2 to entry: The energy distribution of the particle fluence, Φ , is the quotient, dΦ, by dE, where dΦ is
E
the 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
Ω
can be written (with arguments) Φ (E,Ω), where the subscripts characterize the variables (quantities) for
E,Ω
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 energy
E = E is written as Φ (E ). If no special values are indicated, the brackets may be omitted.
0 E 0
3.2.2
particle fluence rate
fluence rate
Φ
rate of the particle fluence (3.2.1) expressed as
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 .
3.2.3
absorbed dose
D
for any ionizing radiation,
dε
D=
dm
where dε is the mean energy imparted by ionizing radiation to an element of irradiated matter of mass
dm
Note 1 to entry: In the limit of a small domain, the mean specific energy is equal to the absorbed dose.
−1
Note 2 to entry: The unit of absorbed dose is J kg , with the special name gray (Gy).
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ISO 20785-1:2020(E)
3.2.4
kerma
K
for indirectly ionizing (uncharged) particles, the mean sum of the initial kinetic energies dE of all the
tr
charged ionizing particles liberated by uncharged ionizing particles in an element of matter, divided by
the mass dm of that element:
dE
tr
K=
dm
Note 1 to entry: Quantity dE includes the kinetic energy of the charged particles emitted in the decay of excited
tr
atoms or molecules or nuclei.
−1
Note 2 to entry: The unit of kerma is J kg , with the special name gray (Gy).
3.2.5
dose equivalent
H
at the point of interest in tissue,
HD= Q
where
D is the absorbed dose;
Q is the quality factor at that point, and
∞
HQ= ()LD dL
L
∫
L=0
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 the above formula, where D = dD/dL is the distribution in terms of L of the absorbed dose at the
L
point of interest.
[2]
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).
3.2.6
lineal energy
y
quotient of the energy, ε , imparted to the matter in a given volume by a single energy deposition event,
s
by the mean chord length, l , in that volume:
ε
s
y=
l
−1 −1
Note 1 to entry: The unit of lineal energy is J m , a frequently used unit is keV μm .
3.2.7
dose-mean lineal energy
y
D
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ISO 20785-1:2020(E)
expectation
∞
yy= dy()dy
D
∫
0
where d(y)is the dose probability density of y.
Note 1 to entry: The dose probability density of y is given by d( y), where d( y)dz is the fraction of absorbed dose
delivered in single events with lineal energy in the interval from y to y+dy.
Note 2 to entry: Both the dose-mean lineal energy and distribution d( y) are independent of the absorbed dose or
dose rate.
3.2.8
ambient dose equivalent
H*(10)
dose equivalent (3.2.5) 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).
3.2.9
standard barometric altitude
pressure altitude
altitude determined by a barometric altimeter calibrated (3.1.1) with reference to the International
[7]
Standard Atmosphere (ISA) (ISO 2533 , Standard Atmosphere) when the altimeter's datum is set to
1 013,25 hPa
Note 1 to entry: ISO/IEC Directives Part 2 Clause 9 requires ISO documents to use SI units and to conform with
[8]
ISO 80000 so the default should be metres. However, in aviation, the flight level is mostly given as FLxxx, where
xxx is a three-digit number representing multiples of 100 feet of pressure altitude, based on the ISA and a datum
setting of 1013,25 hPa; for instance FL350 corresponds to 35 000 ft or, using 1 foot = 0,304 8 m, 10 668 m.
3.2.10
vertical geomagnetic cut-off rigidity
vertical cut-off
cut-off
rc
minimum magnetic rigidity a vertically incident particle can have and still reach a given location above
the Earth
3.3 Atmospheric radiation field
3.3.1
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
3.3.2
primary cosmic rays
cosmic radiation (3.3.1) incident from space at the Earth’s orbit
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ISO 20785-1:2020(E)
3.3.3
secondary cosmic radiation
secondary cosmic rays
cosmogenic particles
particles which are created directly or in a cascade of reactions by primary cosmic rays (3.3.2)
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.
3.3.4
galactic cosmic radiation
galactic cosmic rays
GCR
cosmic radiation (3.3.1) originating outside the solar system
3.3.5
solar particles
solar cosmic radiation
solar cosmic rays
cosmic radiation (3.3.1) originating from the Sun
3.3.6
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.
3.3.7
ground level enhancement
GLE
sudden increase of cosmic radiation (3.3.1) 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. GLEs are numbered; the first
number being given to that occurring in February 1942.
3.3.8
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.
3.3.9
solar maximum
time period of maximum solar activity during a solar cycle (3.3.8), usually defined in terms of relative
sunspot number
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ISO 20785-1:2020(E)
3.3.10
solar minimum
time period of minimum solar activity during a solar cycle (3.3.8), usually defined in terms of relative
sunspot number
3.3.11
cosmic radiation neutron monitor
large detector used to measure the time-dependent relative fluence rate of high-energy cosmic radiation
(3.3.1), in particular the secondary neutrons generated in the atmosphere (protons, other hadrons and
muons can 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.
4 General considerations
4.1 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
[9][10] 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 GCRs penetrate the magnetic field of the solar
system, the peak of their energy distribution is at a few hundred MeV to 1 GeV per nucleon, depending
−2,7 15
on 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 eV. The fluence rate of GCR entering the solar system is
fairly constant in 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 on the fluence basis for low geomagnetic cut-off and
low solar activity is approximately 90 % protons, 9 % He ions, 1 % heavier nuclei; at a vertical cut-off
[11][12]
of 15 GV, the 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
...
NORME ISO
INTERNATIONALE 20785-1
Troisième édition
2020-07
Dosimétrie pour l'exposition au
rayonnement cosmique à bord d'un
avion civil —
Partie 1:
Fondement théorique des mesurages
Dosimetry for exposures to cosmic radiation in civilian aircraft —
Part 1: Conceptual basis for measurements
Numéro de référence
ISO 20785-1:2020(F)
©
ISO 2020
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ISO 20785-1:2020(F)
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Publié en Suisse
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ISO 20785-1:2020(F)
Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 1
3.1 Termes généraux . 1
3.2 Grandeurs et unités . 2
3.3 Champ de rayonnement atmosphérique . 5
4 Considérations générales . 6
4.1 Champ de rayonnement cosmique dans l’atmosphère . 6
4.2 Considérations générales d’étalonnage pour la dosimétrie du rayonnement
cosmique à bord d’un avion . 8
4.2.1 Approche . 8
4.2.2 Facteurs à considérer pour le mesurage . 8
4.2.3 Facteurs à considérer pour le champ de rayonnement . 9
4.2.4 Aspects à considérer pour l’étalonnage .10
4.2.5 Champs de rayonnement simulés à bord d’un avion .10
4.3 Coefficients de conversion .11
5 Dispositifs dosimétriques .11
5.1 Introduction .11
5.2 Dispositifs actifs .11
5.2.1 Dispositifs permettant de déterminer l’ensemble des composantes de champ .11
5.2.2 Dispositifs applicables à la composante à faible TLE/non neutronique .13
5.2.3 Dispositifs applicables à la composante à fort TLE/neutronique .14
5.3 Dispositifs passifs .15
5.3.1 Considérations générales .15
5.3.2 Détecteurs à traces .16
5.3.3 Détecteurs à fission à feuille .16
5.3.4 Détecteurs de neutrons à émulsion métastable (détecteurs à bulles) .16
5.3.5 Détecteurs thermoluminescents .17
5.3.6 Détecteurs photoluminescents .17
Annexe A (informative) Distributions en énergie représentatives des débits de 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 coupure de rigidité verticale minimale et maximale .18
Bibliographie .24
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ISO 20785-1:2020(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 attirée 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 nature volontaire des normes, 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’Organisation mondiale du commerce (OMC) concernant les obstacles
techniques au commerce (OTC), voir le lien suivant: www .iso .org/ iso/ fr/ avant -propos.
Le présent document a été élaboré par le comité technique ISO/TC 85, Énergie nucléaire, technologies
nucléaires, et radioprotection, sous-comité SC 2, Radioprotection.
Cette troisième édition annule et remplace la deuxième édition (ISO 207851:2012), qui a fait l’objet
d’une révision technique. Les principales modifications sont les suivantes:
— révision des termes et définitions;
— mise à jour des références.
Une liste de toutes les parties de la série ISO 20785 se trouve sur le site web de l’ISO.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes
se trouve à l’adresse www .iso .org/ fr/ members .html.
iv © ISO 2020 – Tous droits réservés
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ISO 20785-1:2020(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
[1] [2]
radiologique (CIPR) dans la Publication 60 , confirmées par la Publication 103 , l’Union
[3]
européenne (UE) a établi la révision d’une Directive relative aux normes de sécurité de base et
[4]
l’Agence internationale de l’énergie atomique (IAEA) a publié une version révisée des normes de
sécurité de base. Ces normes classaient parmi les expositions professionnelles le cas de l’exposition
aux sources naturelles de rayonnements ionisants, y compris le rayonnement cosmique. Cette Directive
de l’UE exige 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:
a) évaluer l’exposition du personnel concerné;
b) prendre en compte l’exposition évaluée lors de l’organisation des programmes de travail, en vue de
réduire les doses du personnel navigant le plus fortement exposé;
c) informer les travailleurs concernés sur les risques pour la santé que leur travail implique; et
d) appliquer les 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 a déjà été 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 préférée pour l’évaluation des doses
reçues par le personnel navigant, si nécessaire, consiste à calculer directement la dose efficace par
unité de temps, 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
[5] [6]
par la directive de la Commission européenne et la CIPR dans les Publications 75 et 132 .
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). 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 à partir de
mesurages. Il convient que la traçabilité soit assurée pour un nombre raisonnable de types de particules
et d’énergies du champ de rayonnement atmosphérique, que des corrections soient effectuées pour
tenir compte des différences entre les champs d’étalonnage et le champ de rayonnement atmosphérique
total, et que les incertitudes associées soient correctement prises en compte. 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
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ISO 20785-1:2020(F)
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 au sol.
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 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. Il convient de réaliser
les mesurages dosimétriques destinés à évaluer l’équivalent de dose ambiant à l’aide de méthodes
précises et fiables qui assurent la qualité des relevés fournis aux travailleurs et aux autorités en charge
de la réglementation. Le présent document décrit les bases conceptuelles 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
d’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.
Le présent document est destiné à être utilisé par les laboratoires d’étalonnages primaires et secondaires
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 2020 – Tous droits réservés
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NORME INTERNATIONALE ISO 20785-1:2020(F)
Dosimétrie pour l'exposition au rayonnement cosmique à
bord d'un avion civil —
Partie 1:
Fondement théorique des mesurages
1 Domaine d’application
Le présent document spécifie les principes de base permettant de déterminer l’équivalent de dose
ambiant pour l’évaluation de l’exposition au rayonnement cosmique à bord d’un avion civil, ainsi que
pour l’étalonnage des instruments utilisés à cette fin.
2 Références normatives
Le présent document ne contient aucune référence normative.
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions suivants s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp;
— IEC Electropedia: disponible à l’adresse http:// www .electropedia .org/ .
3.1 Termes généraux
3.1.1
étalonnage
opération qui, dans des conditions spécifiées, établit une relation entre la grandeur conventionnelle, H ,
0
et l’indication, G
Note 1 à l'article: Un étalonnage peut être exprimé sous la forme d’un énoncé, d’une fonction d’étalonnage, d’un
diagramme d’étalonnage, d’une courbe d’étalonnage ou d’une table d’étalonnage. Dans certains cas, il peut
consister en une correction additive ou multiplicative de l’indication avec une incertitude de mesure associée.
Note 2 à l'article: Il convient de ne pas confondre l’étalonnage avec l’ajustement d’un système de mesure, souvent
appelé improprement «auto-étalonnage», ni avec la vérification de l’étalonnage.
Note 3 à l'article: Souvent, la première étape seule dans la définition ci-dessus est perçue comme étant
l’étalonnage.
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ISO 20785-1:2020(F)
3.1.2
réponse
caractéristique de la réponse
R
quotient de l’indication, G, ou de l’indication corrigée, G , et de la valeur conventionnelle d’une
corr
grandeur à mesurer
Note 1 à l'article: Pour éviter toute confusion, il est nécessaire de spécifier lequel des quotients indiqués dans
la définition de la réponse (celui associé à G ou G ) a été utilisé. De plus, il est nécessaire, pour éviter toute
corr
confusion, d’indiquer la grandeur à mesurer, par exemple la réponse en ce qui concerne la fluence, R , la réponse
Φ
en ce qui concerne le kerma, R , ou la réponse en ce qui concerne la dose absorbée, R .
K D
Note 2 à l'article: La réciproque de la réponse dans les conditions spécifiées est égale au coefficient
d’étalonnage N
coeff.
Note 3 à l'article: La valeur de la réponse peut varier selon l’expression quantitative de la grandeur à mesurer.
Dans de tels cas, la réponse de l’ensemble de détecteur est dite non constante.
Note 4 à l'article: La réponse varie habituellement avec la distribution en énergie et la distribution directionnelle
du rayonnement incident. Par conséquent, il est utile de considérer la réponse sous forme d’une fonction, R(E,Ω),
de l’énergie de rayonnement, E, et de la direction, Ω du rayonnement monodirectionnel incident. R(E) décrit la
«dépendance énergétique» et R(Ω) décrit la «dépendance angulaire» de la réponse. Pour cette dernière, Ω peut
être exprimée par l’angle, α, entre la direction de référence de l’ensemble de détecteur et la direction d’un champ
monodirectionnel externe.
3.2 Grandeurs et unités
3.2.1
fluence de particules
fluence
Φ
en un point donné de l’espace, quotient du nombre, dN, de particules incidentes sur un petit domaine
sphérique, par l’aire de la section, da, de ce domaine
dN
Φ=
da
−2 −2
Note 1 à l'article: L’unité de base de la fluence de particules est le m ; le cm constitue une unité d’usage courant.
Note 2 à l'article: La distribution en énergie de la fluence de particules, Φ , est le quotient, dΦ par dE, où dΦ est
E
la fluence des particules dont l’énergie est 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 toute
0 E 0
valeur spéciale, les parenthèses ne sont pas nécessaires.
3.2.2
débit de fluence de particules
débit de fluence
Φ
taux de fluence de particules (3.2.1) exprimé par:
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 de base du débit de fluence est le m s ; le cm s constitue une unité d’usage courant.
2 © ISO 2020 – Tous droits réservés
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ISO 20785-1:2020(F)
3.2.3
dose absorbée
D
pour tout rayonnement ionisant,
dε
D=
dm
où dε est l’énergie moyenne transmise par le rayonnement ionisant à un élément de matière irradiée
de masse dm
Note 1 à l'article: Dans la limite d’un petit domaine, l’énergie spécifique moyenne est égale à la dose absorbée.
−1
Note 2 à l'article: L’unité de la dose absorbée est le joule par kilogramme (J kg ) et son équivalent est le gray (Gy).
3.2.4
kerma
K
pour des particules indirectement ionisantes (non chargées), la somme moyenne des énergies cinétiques
initiales, dE , de toutes les particules ionisantes chargées libérées par les particules ionisantes non
tr
chargées dans un élément de matière, divisée par la masse, dm, de cet élément:
dE
tr
K=
dm
Note 1 à l'article: La grandeur dE comprend l’énergie cinétique des particules chargées émises au cours de la
tr
décroissance des atomes, molécules ou noyaux excités.
−1
Note 2 à l'article: L’unité du kerma est le joule par kilogramme (J kg ) et son équivalent est le gray (Gy).
3.2.5
équivalent de dose
H
au point considéré dans le tissu,
HD= Q
où
D est la dose absorbée;
Q est le facteur de qualité en ce point; et
∞
HQ= ()LD dL
L
∫
L=0
Note 1 à l'article: Q est déterminé par le transfert linéique d’énergie non limité, L (souvent désigné L ou LET),
∞
des particules chargées passant par un petit élément de volume (domaine) en ce point (la valeur de L est donnée
∞
pour des particules chargées dans l’eau et non dans le tissu; la différence est cependant faible). L’équivalent
de dose en un point dans le tissu est alors donné par la formule ci-dessus où D = dD/dL est la distribution en
L
fonction de L de la dose absorbée au point considéré.
[2]
Note 2 à l'article: La relation entre Q et L est donnée dans la Publication 103 de l’ICRP (ICRP, 2007) .
−1
Note 3 à l'article: L’unité de l’équivalent de dose est le joule par kilogramme (J kg ), et son équivalent est le
sievert (Sv).
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ISO 20785-1:2020(F)
3.2.6
énergie linéale
y
quotient de l’énergie, ε , transmise à la matière dans un volume donné par un seul événement de
s
transmission d’énergie, par la longueur de corde moyenne, l , dans ce volume:
ε
s
y=
l
−1
Note 1 à l'article: L’unité de base de l’énergie linéale est le joule par mètre (J m ); le kiloélectron-volt
−1
par micromètre (keV μm ) constitue une unité d’usage courant.
3.2.7
énergie linéale moyenne en dose
y
D
espérance
∞
yy= dy()dy
D
∫
0
où d(y) est la densité de probabilité en dose de y
Note 1 à l'article: La densité de probabilité en dose de y est donnée par d( y), où d( y)dz est la fraction de dose
absorbée délivrée lors d’événements uniques avec une énergie linéale dans l’intervalle de y à y+dy.
Note 2 à l'article: L’énergie linéale moyenne en dose et la distribution d( y) sont indépendantes de la dose absorbée
ou du débit de dose.
3.2.8
équivalent de dose ambiant
H*(10)
équivalent de dose (3.2.5) en un point d’un champ de rayonnement qui serait produit par le champ
correspondant expansé et aligné, 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 joule par kilogramme (J kg ), et son équivalent est
le sievert (Sv).
3.2.9
altitude barométrique étalon
pression d’altitude
altitude déterminée par un altimètre barométrique étalonné (3.1.1) par référence à l’atmosphère type
[7]
internationale (ISA) (ISO 2533 , Atmosphère type) lorsque les données de l’altimètre sont établies à
1 013,25 hPa
Note 1 à l'article: L’Article 9 de la Partie 2 des Directives ISO/IEC impose d’utiliser les unités SI dans les documents
[8]
ISO et de se conformer à l’ISO 80000 . Il convient donc que l’unité par défaut soit le mètre. Cependant, dans le
domaine de l’aviation, le niveau de vol est souvent donné sous la forme FLxxx, où xxx est un nombre à trois chiffres
qui représente les multiples de 100 fts d’altitude-pression, sur la base de l’atmosphère ISA et d’un paramétrage de
données à 1 013,25 hPa; par exemple, FL350 correspond à 35 000 ft ou, en utilisant 1 pied = 0,304 8 m, 10 668 m.
3.2.10
coupure de rigidité géomagnétique verticale
coupure verticale
coupure
rc
rigidité magnétique minimale qu’une particule à incidence verticale peut avoir tout en atteignant un
emplacement donné au-dessus de la surface de la Terre
4 © ISO 2020 – Tous droits réservés
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ISO 20785-1:2020(F)
3.3 Champ de rayonnement atmosphérique
3.3.1
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
3.3.2
rayons cosmiques primaires
rayons cosmiques (3.3.1) provenant de l’espace au niveau de l’orbite terrestre
3.3.3
rayonnement cosmique secondaire
rayons cosmiques secondaires
particules d’origine cosmique
particules créées, directement ou par des réactions en cascade, par les rayons cosmiques primaires
(3.3.2) 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.
3.3.4
rayonnement cosmique galactique
rayons cosmiques galactiques
GCR
rayons cosmiques (3.3.1) provenant de l’extérieur du système solaire
3.3.5
particules solaires
rayonnement cosmique solaire
rayons cosmiques solaires
rayons cosmiques (3.3.1) provenant du Soleil
3.3.6
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.
3.3.7
augmentation au niveau du sol
GLE
augmentation soudaine du rayonnement cosmique (3.3.1), observée au niveau du sol par au moins
deux moniteurs à 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 en moyenne environ une fois
par an. Les GLE sont numérotées, le premier numéro étant affecté à la GLE qui s’est produite en février 1942.
© ISO 2020 – Tous droits réservés 5
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ISO 20785-1:2020(F)
3.3.8
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 h
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 20785-1
ISO/TC 85/SC 2
Dosimetry for exposures to cosmic
Secretariat: AFNOR
radiation in civilian aircraft —
Voting begins on:
2020-04-03
Part 1:
Voting terminates on:
Conceptual basis for measurements
2020-05-30
Dosimétrie pour l'exposition au rayonnement cosmique à bord d'un
avion civil —
Partie 1: Fondement théorique des mesurages
ISO/CEN PARALLEL PROCESSING
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 SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 20785-1:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 20785-1:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 20785-1:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms . 1
3.2 Quantities and units . 2
3.3 Atmospheric radiation field . 4
4 General considerations . 6
4.1 The cosmic radiation field in the atmosphere . 6
4.2 General calibration considerations for the dosimetry of cosmic radiation fields in
aircraft . 7
4.2.1 Approach . 7
4.2.2 Considerations concerning the measurement . 7
4.2.3 Considerations concerning the radiation field . 8
4.2.4 Considerations concerning calibration . 8
4.2.5 Simulated aircraft fields . 9
4.3 Conversion coefficients . 9
5 Dosimetric devices .10
5.1 Introduction .10
5.2 Active devices .10
5.2.1 Devices to determine all field components .10
5.2.2 Devices for low LET/non-neutron .11
5.2.3 Devices for high-LET/neutron component .12
5.3 Passive devices .13
5.3.1 General considerations .13
5.3.2 Etched track detectors .14
5.3.3 Fission foil detectors .14
5.3.4 Superheated emulsion neutron detectors (bubble) detectors .14
5.3.5 Thermoluminescent detectors.15
5.3.6 Photoluminescent detectors .15
Annex A (informative) Representative particle fluence rate 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 .16
Bibliography .22
© ISO 2020 – All rights reserved iii
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ISO/FDIS 20785-1:2020(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
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This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,
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This third edition cancels and replaces the second edition (ISO 20785-1:2012), which has been
technically revised. The main changes are as follows:
— revision of the terms and definitions;
— updated references.
A list of all the parts in the ISO 20785 series can be found on the ISO website.
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ISO/FDIS 20785-1:2020(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
recommendations of the International Commission on Radiological Protection (ICRP) in Publication
[1] [2]
60 , confirmed by Publication 103 , the European Union (EU) introduced a revised Basic Safety
[3] [4]
Standards Directive and International Atomic Energy Agency (IAEA) issued a revised Basic Safety
Standards. Those standards included exposure to natural sources of ionizing radiation, including cosmic
radiation, as occupational exposure. The EU Directive requires account to be taken of the exposure of
aircraft crews liable to receive more than 1 mSv per year. It then identifies the following four protection
measures:
a) to assess the exposure of the crew concerned;
b) to take into account the assessed exposure when organizing working schedules with a view to
reducing the doses of highly exposed crews;
c) to inform the workers concerned of the health risks their work involves; and
d) to apply the same special protection during pregnancy to female crews 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 the
equivalent dose (to the foetus) and the 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 dosimeters for routine use are not
considered necessary. The preferred approach for the assessment of doses of aircraft crews, where
necessary, is to calculate directly the effective dose per unit time, as a function of geographic location,
altitude and solar cycle phase, and to combine these values with flight and staff roster information to
obtain estimates of effective doses for individuals. This approach is supported by guidance from the
[5] [6]
European Commission and the ICRP in Publications 75 and 132 .
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. The 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 from measurements. Traceability should be provided for a reasonable number of particle
types and energies of the atmospheric radiation field, corrections included for differences between the
calibration fields and the total atmospheric radiation field, and related uncertainties properly taken
into account. The validation of calculations of ambient dose equivalent for a particular calculation
method may be taken as a validation of the calculation of the 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 ground-based
radiation workers.
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.
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ISO/FDIS 20785-1:2020(E)
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 should be
performed using accurate and reliable methods that ensure the quality of readings provided to workers
and regulatory authorities. This document gives a conceptual basis 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
crews 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 document 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 crews.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 20785-1:2020(E)
Dosimetry for exposures to cosmic radiation in civilian
aircraft —
Part 1:
Conceptual basis for measurements
1 Scope
This document specifies the conceptual basis for the determination of ambient dose equivalent for the
evaluation of exposure to cosmic radiation in civilian aircraft and for the calibration of instruments
used for that purpose.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 General terms
3.1.1
calibration
operation that, under specified conditions, establishes a relation between the conventional quantity,
H , and the indication, G
0
Note 1 to entry: A calibration can be expressed by a statement, calibration function, calibration diagram,
calibration curve, or calibration table. In some cases, it can consist of an additive or multiplicative correction of
the indication with associated measurement uncertainty.
Note 2 to entry: Calibration should not be confused with adjustment of a measuring system, often mistakenly
called "self-calibration", or with verification of calibration.
Note 3 to entry: Often, the first step alone in the above definition is perceived as being calibration.
3.1.2
response
response characteristic
R
quotient of the indication, G, or the corrected indication, G , and the conventional quantity value to be
corr
measured
Note 1 to entry: To avoid confusion, it is necessary to specify which of the quotients, given in the definition of
the response (to G or to G ) is applied. Furthermore, it is necessary, in order to avoid confusion, to state the
corr
quantity to be measured, for example: the response with respect to fluence, R , the response with respect to
Φ
kerma, R , the response with respect to absorbed dose, R .
K D
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Note 2 to entry: The reciprocal of the response under the specified conditions is equal to the calibration
coefficient N
coeff.
Note 3 to entry: The value of the response can vary with the magnitude of the quantity to be measured. In such
cases the detector assembly's response is said to be non-constant.
Note 4 to entry: The response usually varies with the energy and direction distribution of the incident
radiation. It is, therefore, useful to consider the response as a function, R(E,Ω), of the radiation energy, E, and
of the direction, Ω of the incident monodirectional radiation. R(E) describes the "energy dependence" and R(Ω)
the "angle dependence" of response; for the latter, Ω may be expressed by the angle, α, between the reference
direction of the detector assembly and the direction of an external monodirectional field.
3.2 Quantities and units
3.2.1
particle fluence
fluence
Φ
number, dN, at a given point in space, 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 .
Note 2 to entry: The energy distribution of the particle fluence, Φ , is the quotient, dΦ, by dE, where dΦ is
E
the 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
Ω
can be written (with arguments) Φ (E,Ω), where the subscripts characterize the variables (quantities) for
E,Ω
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 energy
E = E is written as Φ (E ). If no special values are indicated, the brackets may be omitted.
0 E 0
3.2.2
particle fluence rate
fluence rate
Φ
rate of the particle fluence (3.2.1) expressed as
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 .
3.2.3
absorbed dose
D
for any ionizing radiation,
dε
D=
dm
where dε is the mean energy imparted by ionizing radiation to an element of irradiated matter of mass
dm
Note 1 to entry: In the limit of a small domain, the mean specific energy is equal to the absorbed dose.
−1
Note 2 to entry: The unit of absorbed dose is J kg , with the special name gray (Gy).
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3.2.4
kerma
K
for indirectly ionizing (uncharged) particles, the mean sum of the initial kinetic energies dE of all the
tr
charged ionizing particles liberated by uncharged ionizing particles in an element of matter, divided by
the mass dm of that element:
dE
tr
K=
dm
Note 1 to entry: Quantity dE includes the kinetic energy of the charged particles emitted in the decay of excited
tr
atoms or molecules or nuclei.
−1
Note 2 to entry: The unit of kerma is J kg , with the special name gray (Gy).
3.2.5
dose equivalent
H
at the point of interest in tissue,
HD= Q
where
D is the absorbed dose;
Q is the quality factor at that point, and
∞
HQ= ()LD dL
L
∫
L−0
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 the above formula, where D = dD/dL is the distribution in terms of L of the absorbed dose at the
L
point of interest.
[2]
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).
3.2.6
lineal energy
y
quotient of the energy, ε , imparted to the matter in a given volume by a single energy deposition event,
s
by the mean chord length, l , in that volume:
ε
s
y=
l
−1 −1
Note 1 to entry: The unit of lineal energy is J m , a frequently used unit is keV μm .
3.2.7
dose-mean lineal energy
y
D
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expectation
∞
yy= dy()dy
D
∫
0
where d(y)is the dose probability density of y.
Note 1 to entry: The dose probability density of y is given by d( y), where d( y)dz is the fraction of absorbed dose
delivered in single events with lineal energy in the interval from y to y+dy.
Note 2 to entry: Both the dose-mean lineal energy and distribution d( y) are independent of the absorbed dose or
dose rate.
3.2.8
ambient dose equivalent
H*(10)
dose equivalent (3.2.5) 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).
3.2.9
standard barometric altitude
pressure altitude
altitude determined by a barometric altimeter calibrated (3.1.1) with reference to the International
[7]
Standard Atmosphere (ISA) (ISO 2533 , Standard Atmosphere) when the altimeter's datum is set to
1 013,25 hPa
Note 1 to entry: ISO/IEC Directives Part 2 Clause 9 requires ISO documents to use SI units and to conform with
[8]
ISO 80000 so the default should be metres. However, in aviation, the flight level is mostly given as FLxxx, where
xxx is a three-digit number representing multiples of 100 feet of pressure altitude, based on the ISA and a datum
setting of 1013,25 hPa; for instance FL350 corresponds to 35 000 ft or, using 1 foot = 0,304 8 m, 10 668 m.
3.2.10
vertical geomagnetic cut-off rigidity
vertical cut-off
cut-off
rc
minimum magnetic rigidity a vertically incident particle can have and still reach a given location above
the Earth
3.3 Atmospheric radiation field
3.3.1
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
3.3.2
primary cosmic rays
cosmic radiation (3.3.1) incident from space at the Earth’s orbit
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3.3.3
secondary cosmic radiation
secondary cosmic rays
cosmogenic particles
particles which are created directly or in a cascade of reactions by primary cosmic rays (3.3.2)
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.
3.3.4
galactic cosmic radiation
galactic cosmic rays
GCR
cosmic radiation (3.3.1) originating outside the solar system
3.3.5
solar particles
solar cosmic radiation
solar cosmic rays
cosmic radiation (3.3.1) originating from the Sun
3.3.6
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.
3.3.7
ground level enhancement
GLE
sudden increase of cosmic radiation (3.3.1) 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. GLEs are numbered; the first
number being given to that occurring in February 1942.
3.3.8
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.
3.3.9
solar maximum
time period of maximum solar activity during a solar cycle (3.3.8), usually defined in terms of relative
sunspot number
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3.3.10
solar minimum
time period of minimum solar activity during a solar cycle (3.3.8), usually defined in terms of relative
sunspot number
3.3.11
cosmic radiation neutron monitor
large detector used to measure the time-dependent relative fluence rate of high-energy cosmic radiation
(3.3.1), in particular the secondary neutrons generated in the atmosphere (protons, other hadrons and
muons can 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.
4 General considerations
4.1 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
[9][10] 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 GCRs penetrate the magnetic field of the solar
system, the peak of their energy distribution is at a few hundred MeV to 1 GeV per nucleon, depending
−2,7 15
on 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 eV. The fluence rate of GCR entering the solar system is
fairly constant in
...
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