SIST EN ISO 20785-2:2020

SLOVENSKI STANDARD
01-oktober-2020
Nadomešča:
SIST EN ISO 20785-2:2017
Dozimetrija za merjenje izpostavljenosti kozmičnemu sevanju v civilnem letalskem
prometu - 2. del: Karakterizacija odziva instrumenta (ISO 20785-2:2020)
Dosimetry for exposures to cosmic radiation in civilian aircraft - Part 2: Characterization
of instrument response (ISO 20785-2:2020)
Dosimetrie zu Expositionen durch kosmische Strahlung in Flugzeugen der zivilen
Luftfahrt - Teil 2: Charakterisierung des Antwortverhaltens von Messinstrumenten (ISO
20785-2:2020)
Dosimétrie pour l'exposition au rayonnement cosmique à bord d'un avion civil - Partie 2:
Caractérisation de la réponse des instruments (ISO 20785-2:2020)
Ta slovenski standard je istoveten z: EN ISO 20785-2:2020
ICS:
17.240 Merjenje sevanja Radiation measurements
49.020 Letala in vesoljska vozila na Aircraft and space vehicles in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 20785-2
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2020
EUROPÄISCHE NORM
ICS 13.280; 49.020 Supersedes EN ISO 20785-2:2017
English Version
Dosimetry for exposures to cosmic radiation in civilian
aircraft - Part 2: Characterization of instrument response
(ISO 20785-2:2020)
Dosimétrie pour l'exposition au rayonnement Dosimetrie für die Belastung durch kosmische
cosmique à bord d'un avion civil - Partie 2: Strahlung in Zivilluftfahrzeugen - Teil 2:
Caractérisation de la réponse des instruments (ISO Charakterisierung des Ansprechvermögens von
20785-2:2020) Messinstrumenten (ISO 20785-2:2020)
This European Standard was approved by CEN on 30 June 2020.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20785-2:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 20785-2:2020) has been prepared by Technical Committee ISO/TC 85 "Nuclear
energy, nuclear technologies, and radiological protection" in collaboration with Technical Committee
CEN/TC 430 “Nuclear energy, nuclear technologies, and radiological protection” the secretariat of
which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2021, and conflicting national standards
shall be withdrawn at the latest by February 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 20785-2:2017.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 20785-2:2020 has been approved by CEN as EN ISO 20785-2:2020 without any
modification.
INTERNATIONAL ISO
STANDARD 20785-2
Second edition
2020-07
Dosimetry for exposures to cosmic
radiation in civilian aircraft —
Part 2:
Characterization of instrument
response
Dosimétrie pour l'exposition au rayonnement cosmique à bord d'un
avion civil —
Partie 2: Caractérisation de la réponse des instruments
Reference number
ISO 20785-2:2020(E)
©
ISO 2020
ISO 20785-2:2020(E)
© 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.
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Phone: +41 22 749 01 11
Email: copyright@iso.org
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Published in Switzerland
ii © ISO 2020 – All rights reserved

ISO 20785-2:2020(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 Terms related to quantities and units . 5
3.3 Atmospheric radiation field . 7
4 General considerations . 8
4.1 The cosmic radiation field in the atmosphere . 8
4.2 General considerations for the dosimetry of the cosmic radiation field in aircraft
and requirements for the characterization of instrument response . 9
4.3 General considerations for measurements at aviation altitudes .10
5 Calibration fields and procedures .12
5.1 General considerations .12
5.2 Characterization of an instrument .14
5.2.1 Determination of the dosimetric characteristics of an instrument .14
5.2.2 Reference radiation fields .16
5.2.3 Scattered radiation . .16
5.2.4 Effect of other types of radiation .16
5.2.5 Requirements for characterization in non-reference conditions .17
5.2.6 Use of numerical simulations .17
5.3 Instrument-related software .17
5.3.1 Software development procedures .17
5.3.2 Software testing .18
5.3.3 Data analysis using spreadsheets .18
6 Uncertainties .18
7 Remarks on performance tests .18
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 .19
Annex B (informative) Radiation fields recommended for use in calibrations .25
Annex C (informative) Comparison measurements .29
Annex D (informative) Charged-particle irradiation facilities .31
Bibliography .32
ISO 20785-2:2020(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 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
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 second edition cancels and replaces the first edition (ISO 20785-2:2011), which has been technically
revised. The main changes compared to the previous edition are as follows:
— revision of the definitions of the terms;
— 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.
iv © ISO 2020 – All rights reserved

ISO 20785-2:2020(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
[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] [4]
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 crew
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 crew;
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 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 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 crew, 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
[5] [6]
effective doses for individuals. This approach is supported by the ICRP in Publications 75 and 132
and in guidance from the European Commission.
The role of calculations in this procedure is unique in routine radiation protection, and it is widely
[7]
accepted that the calculated doses should be validated by measurement . Effective dose is not directly
measurable. The operational quantity of interest is the 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 and taking instrument responses and
related uncertainties properly 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 effective dose by
the same computer code, but this step in the process might 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 instrument response to particles and energies of the
atmospheric radiation field that are not covered by reference fields are carefully taken into account in
the evaluation of measurement results. While, 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
ISO 20785-2:2020(E)
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. The purpose of this document is to specify
procedures for the determination of the responses of instruments in different reference radiation
fields, as a basis for proper characterization of instruments used for the determination of ambient dose
equivalent in aircraft at altitude.
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 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 crew.
vi © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 20785-2:2020(E)
Dosimetry for exposures to cosmic radiation in civilian
aircraft —
Part 2:
Characterization of instrument response
1 Scope
This document specifies methods and procedures for characterizing the responses of devices used
for the determination of ambient dose equivalent for the evaluation of exposure to cosmic radiation in
civilian aircraft. The methods and procedures are intended to be understood as minimum requirements.
2 Normative references
The following five documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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, 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
me a s ur ement (GUM: 1995)
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
angle of radiation incidence
α
angle between the direction of radiation incidence and the reference direction of the instrument
3.1.2
calibration
operation that, under specified conditions, establishes a relation between the conventional quantity,
H , and the indication, G
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: It is important not to confuse calibration with adjustment of a measuring system, often
mistakenly called “self-calibration”, or with verification of calibration.
ISO 20785-2:2020(E)
3.1.3
calibration coefficient
N
coeff
quotient of the conventional quantity value to be measured and the corrected indication of the
instrument
Note 1 to entry: The calibration coefficient is equivalent to the calibration factor multiplied by the instrument
constant.
Note 2 to entry: The reciprocal of the calibration coefficient, N , is the response.
coeff
Note 3 to entry: For the calibration of some instruments, e.g. ionization chambers, the instrument constant and
the calibration factor are not identified separately but are applied together as the calibration coefficient.
Note 4 to entry: It is necessary, in order to avoid confusion, to state the quantity to be measured, for example:
the calibration coefficient with respect to fluence, N , the calibration coefficient with respect to kerma, N , the
Φ K
calibration coefficient with respect to absorbed dose, N .
D
3.1.4
calibration factor
N
fact
factor by which the product of the corrected indication and the associated instrument constant of the
instrument is multiplied to obtain the conventional quantity value to be measured under reference
conditions
Note 1 to entry: The calibration factor is dimensionless.
Note 2 to entry: The corrected indication is the indication of the instrument corrected for the effect of influence
quantities, where applicable.
Note 3 to entry: The value of the calibration factor can vary with the magnitude of the quantity to be measured.
In such cases, a detector assembly is said to have a non-constant response.
3.1.5
measured quantity value
measured value of a quantity
measured value
M
quantity value representing a measurement result
Note 1 to entry: For a measurement involving replicate indications, each indication can be used to provide a
corresponding measured quantity value. This set of measured quantity values can be used to calculate a
resulting measured quantity value, such as an average or a median value, usually with a decreased associated
measurement uncertainty.
Note 2 to entry: When the range of the true quantity values believed to represent the measurand is small
compared with the measurement uncertainty, a measured quantity value can be considered to be an estimate
of an essentially unique true quantity value and is often an average or a median of individual measured quantity
values obtained through replicate measurements.
Note 3 to entry: In the case where the range of the true quantity values believed to represent the measurand is
not small compared with the measurement uncertainty, a measured value is often an estimate of an average or a
median of the set of true quantity values.
Note 4 to entry: In ISO/IEC Guide 98-3:2008, the terms “result of measurement” and “estimate of the value of the
measurand” or just “estimate of the measurand” are used for “measured quantity value”.
2 © ISO 2020 – All rights reserved

ISO 20785-2:2020(E)
3.1.6
conventional quantity value
conventional value of a quantity
conventional value
H
quantity value attributed by agreement to a quantity for a given purpose
Note 1 to entry: The term “conventional true quantity value” is sometimes used for this concept, but its use is
discouraged.
Note 2 to entry: Sometimes, a conventional quantity value is an estimate of a true quantity value.
Note 3 to entry: A conventional quantity value is generally accepted as being associated with a suitably small
measurement uncertainty, which might be zero.
[8][9][10]
Note 4 to entry: In ISO 20785 series , the conventional quantity value is the best estimate of the value of
the quantity to be measured, determined by a primary or a secondary standard which is traceable to a primary
standard.
3.1.7
correction factor
k
factor applied to the indication (3.1.9) to correct for deviation of measurement conditions from reference
conditions
Note 1 to entry: If the correction of the effect of the deviation of an influence quantity requires a factor, the
influence quantity is of type F.
3.1.8
correction summand
G
S
summand applied to the indication (3.1.9) to correct for the zero indication or the deviation of the
measurement conditions from the reference conditions
Note 1 to entry: If the correction of the effect of the deviation of an influence quantity requires a summand, the
influence quantity is of type S.
3.1.9
indication
G
quantity value provided by a measuring instrument or a measuring system
Note 1 to entry: An indication can be presented in visual or acoustic form or can be transferred to another device.
An indication is often given by the position of a pointer on the display for analogue outputs, a displayed or printed
number for digital outputs, a code pattern for code outputs, or an assigned quantity value for material measures.
Note 2 to entry: An indication and a corresponding value of the quantity being measured are not necessarily
values of quantities of the same kind.
3.1.10
influence quantity
quantity that, in a direct measurement, does not affect the quantity that is actually measured, but
affects the relation between the indication (3.1.9) and the measurement result
Note 1 to entry: An indirect measurement involves a combination of direct measurements, each of which can be
affected by influence quantities.
Note 2 to entry: In ISO/IEC Guide 98-3:2008, the concept “influence quantity” is defined as
[11]
in ISO/IEC Guide 99:2007 , covering not only the quantities affecting the measuring system, as in the definition
above, but also those quantities that affect the quantities actually measured. Also, in ISO/IEC Guide 98-3, this
concept is not restricted to direct measurements.
ISO 20785-2:2020(E)
Note 3 to entry: The correction of the effect of the influence quantity can require a correction factor (for an
influence quantity of type F) and/or a correction summand (for an influence quantity of type S) to be applied to
the indication of the detector assembly, e.g. in the case of microphonic or electromagnetic disturbance.
EXAMPLE The indication given by an unsealed ionization chamber is influenced by the temperature
and pressure of the surrounding atmosphere. Although needed for determining the value of the dose, the
measurement of these two quantities is not the primary objective.
3.1.11
instrument constant
c
i
quantity value by which the indication (3.1.9) of the instrument, G (or, if corrections or normalization
were carried out, G ), is multiplied to give the value of the measurand or of a quantity to be used to
corr
calculate the value of the measurand
Note 1 to entry: If the instrument's indication is already expressed in the same units as the measurand, as is
the case with area dosemeters, for instance, the instrument constant, c , is dimensionless. In such cases, the
i
calibration factor and the calibration coefficient (3.1.3) can be the same. Otherwise, if the indication of the
instrument has to be converted to the same units as the measurand, the instrument constant has a dimension.
3.1.12
measurand
quantity intended to be measured
3.1.13
primary measurement standard
primary standard
measurement standard established using a primary reference measurement procedure or created as
an artefact, chosen by convention
Note 1 to entry: A primary standard has the highest metrological quality in a given field.
3.1.14
quantity value
number and reference together expressing the magnitude of a quantity
Note 1 to entry: A quantity value is either a product of a number and a measurement unit (the unit “one” is
generally not indicated for quantities of dimension “one”) or a number and a reference to a measurement
procedure.
3.1.15
reference conditions
conditions of use prescribed for testing the performance of a detector assembly or for comparing the
results of measurements
Note 1 to entry: The reference conditions represent the values of the set of influence quantities for which the
calibration result is valid without any correction.
Note 2 to entry: The value of the measurand can be chosen freely in agreement with the properties of the
detector assembly to be calibrated. The quantity to be measured is not an influence quantity but can influence
the calibration result and the response (see also Note 1 to entry).
3.1.16
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 (that for the indication, G or G ) is applied. Furthermore, it is necessary, in order to avoid confusion,
corr
to state the quantity to be measured, for example the response with respect to fluence, R , the response with
Φ
respect to kerma, R or the response with respect to absorbed dose, R .
K D
4 © ISO 2020 – All rights reserved

ISO 20785-2:2020(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 the direction,

Ω , of the incident monodirectional radiation. R(E) describes the “energy dependence” and R(Ω) the “angle

dependence” of the 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 Terms related to quantities and units
[12]
Most of the definitions in this subclause have been adapted from ISO 80000-10:2019 and ICRU
[13] [14]
Reports 36 and 51 .
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 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 energy E = E is written as Φ (E ). If
0 E 0
no special values are indicated, the brackets may be omitted.
3.2.2
particle fluence rate
fluence rate

Φ
rate of the particle fluence (3.2.1) expressed as
dΦ d N

Φ ==
dt ddat⋅
where dΦ is the increment of the particle fluence during an infinitesimal time interval of duration dt
–2 –1 –2 –1
Note 1 to entry: The base unit of the fluence rate is m ⋅s ; a frequently used unit is cm ⋅s .
3.2.3
kerma
K
for indirectly ionizing (uncharged) particles, the 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
ISO 20785-2:2020(E)
Note 1 to entry: The quantity dE includes the kinetic energy of the charged particles emitted in the decay of
tr
excited atoms or molecules or nuclei.
–1
Note 2 to entry: The unit of kerma is J⋅kg , with the special name gray (Gy).
3.2.4
dose equivalent
H
at the point of interest in tissue,
H = DQ
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 by L or LET), of
∞
charged particles passing through a small volume element (domain) 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
[2]
Note 2 to entry: The relationship between Q and L is given in ICRP Publication 103 .
–1
Note 3 to entry: The unit of dose equivalent is J⋅kg , with the special name sievert (Sv).
3.2.5
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).
3.2.6
particle fluence to ambient dose equivalent conversion coefficient
*
h
Φ
quotient of the particle ambient dose equivalent (3.2.5), H*(10), and the particle fluence (3.2.1), Φ:
H*(10)
*
h =
Φ
Φ
2 –1
Note 1 to entry: The base 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 .
3.2.7
vertical cut-off
vertical geomagnetic cut-off rigidity
cut-off
minimum magnetic rigidity a vertically incident particle can have and still reach a given location above
the Earth
6 © ISO 2020 – All rights reserved

ISO 20785-2:2020(E)
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
secondary cosmic radiation
secondary cosmic rays
cosmogenic particles
particles which are created, directly or in a cascade of reactions, by primary cosmic radiation (3.3.1),
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.
3.3.3
galactic cosmic radiation
galactic cosmic rays
GCR
cosmic radiation (3.3.1) originating outside the solar system
3.3.4
solar particles
cosmic radiation (3.3.1) originating from the sun
3.3.5
solar particle event
SPE
large fluence rate of energetic solar particles ejected into space by a solar eruption
3.3.6
ground level enhancement
GLE
sudden increase in 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 energetic solar 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.
3.3.7
solar modulation
change in the GCR field (outside the Earth's magnetosphere) caused by change in solar activity and
consequent change in the magnetic field of the heliosphere
ISO 20785-2:2020(E)
3.3.8
relative sunspot number
Wolf number
measure of sunspot activity, computed from the expression k(10g + f ), where f is 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)
Note 1 to entry: The relative sunspot number is also known as the Wolf number.
3.3.9
solar maximum
time period of maximum solar activity during a solar cycle, usually defined in terms of the relative
sunspot number (3.3.8)
3.3.10
solar minimum
time period of minimum solar activity during a solar cycle, usually defined in terms of the relative
sunspot number (3.3.8)
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
[15][16] 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 on the fluence basis 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
[17][18]
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 component is the most important contributor to ambient dose equivalent and effective dose. At
aviation altitudes, neutrons, electrons, positrons, protons, photons and muons are the most measurable
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 statistically
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 usually far greater than the dose from SPEs. Intense SPEs can disturb
the Earth's magnetic field and often leads to a reduction of the GCR dose rates.
8 © ISO 2020 – All rights reserved

ISO 20785-2:2020(E)
Key
X altitude (km)
Y ambient dose equivalent rate (µSv/h)
[19]
Conditions: 1 GV cut-off and solar minimum (deceleration potential, ϕ, of 465 MV) .
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
4.2 General considerations for the dosimetry of the cosmic radiation field in aircraft
and requirements for the characterization of instrument response
Detailed consideration of the measurements to be made an
...