SIST EN ISO 20785-1:2020

SLOVENSKI STANDARD
01-oktober-2020
Nadomešča:
SIST EN ISO 20785-1:2017
Dozimetrija za merjenje izpostavljenosti kozmičnemu sevanju v civilnem letalskem
prometu - 1. del: Konceptualna osnova za meritve (ISO 20785-1:2020)
Dosimetry for exposures to cosmic radiation in civilian aircraft - Part 1: Conceptual basis
for measurements (ISO 20785-1:2020)
Dosimetrie zu Expositionen durch kosmische Strahlung in Flugzeugen der zivilen
Luftfahrt - Teil 1: Konzeptionelle Grundlage für Messungen (ISO 20785-1:2020)
Dosimétrie pour l'exposition au rayonnement cosmique à bord d'un avion civil - Partie 1:
Fondement théorique des mesurages (ISO 20785-1:2020)
Ta slovenski standard je istoveten z: EN ISO 20785-1:2020
ICS:
13.280 Varstvo pred sevanjem Radiation protection
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 20785-1
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2020
EUROPÄISCHE NORM
ICS 13.280; 49.020 Supersedes EN ISO 20785-1:2017
English Version
Dosimetry for exposures to cosmic radiation in civilian
aircraft - Part 1: Conceptual basis for measurements (ISO
20785-1:2020)
Dosimétrie pour l'exposition au rayonnement Dosimetrie für die Belastung durch kosmische
cosmique à bord d'un avion civil - Partie 1: Fondement Strahlung in Zivilluftfahrzeugen - Teil 1:
théorique des mesurages (ISO 20785-1:2020) Konzeptionelle Grundlage für Messungen (ISO 20785-
1:2020)
This European Standard was approved by CEN on 1 July 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 20785-1:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 20785-1:2020) 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 20785-1:2017.
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 20785-1:2020 has been approved by CEN as EN ISO 20785-1:2020 without any
modification.
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
ISO 20785-1:2020(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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

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
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.
iv © ISO 2020 – All rights reserved

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
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.
vi © ISO 2020 – All rights reserved

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
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
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
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).
2 © ISO 2020 – All rights reserved

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
ISO 20785-1:2020(E)
expectation
∞
yy= dy()dy
D
∫
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
4 © ISO 2020 – All rights reserved

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
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 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 significant
components. At higher altitudes, nuclear ions heavier than protons start to contribute. Figures showing
representative normalized energy distributions of fluence rates of all the important particles at low
and high cut-offs and altitudes at solar minimum and maximum are shown in Annex A.
The Earth is also exposed to bursts of energetic protons and heavier particles from magnetic
disturbances near the surface of the Sun and from ejection of large amounts of matter (coronal mass
ejections – CMEs) with, in some cases, acceleration by the CMEs and associated solar wind shock waves.
The particles of these solar particle events, or solar proton events (both abbreviated to SPEs), are much
lower in energy than GCR: generally below 100 MeV and only rarely above 10 GeV. SPEs are of short
duration, a few hours to a few days, and highly variable in intensity. Only a small fraction of SPEs, on
average one per year, produce large numbers of high-energy particles, which cause significant dose
rates at high altitudes and low geomagnetic cut-offs and can be observed by neutron monitors on the
ground. Such events are called ground level enhancements (GLEs). For aircraft crews, the cumulative
dose from GCR is far greater than the dose from SPEs. Intense SPEs can affect GCR dose rates by
disturbing the Earth's magnetic field in such a way as to change the galactic particle intensity reaching
the atmosphere.
6 © ISO 2020 – All rights reserved

ISO 20785-1:2020(E)
Key
X altitude (km)
Y ambient dose equivalent rate (μSv/h)
[13]
Conditions: 1 GV cut-off and solar minimum (deceleration potential, ϕ, of 465 MV)
Figure 1 — Calculated ambient dose equivalent rates as function of standard barometric
altitude for high latitudes at solar minimum for various atmospheric cosmic radiation
component particles
4.2 General calibration considerations for the dosimetry of cosmic radiation fields in
aircraft
4.2.1 Approach
The general approach necessary for measurement and calibration is given here. Details of calibration
[14]
fields and procedures are given in ISO 20785-2 .
4.2.2 Considerations concerning the measurement
[15]
Ambient dose equivalent cannot be measured directly by conventional dosimetric techniques . The
experimental determination of ambient dose equivalent for the complex radiation field considered
here (see Figure 1) is particularly difficult. An approximate approach is to use a tissue equivalent
proportional counter (TEPC) to measure dose equivalent to a small mass of tissue, by measuring the
absorbed dose distribution in lineal energy (which is an approximation for LET), with corrections
applied, and directly applying the LET-dependent quality factor. However, this measurement still does
not realize the quantity.
Dosimetry of the radiation field in aircraft requires specialized techniques of measurement and
calculation. The preferred approach would be to use devices that have an ambient dose equivalent
ISO 20785-1:2020(E)
response that is independent of the energy and the direction of the total field, or the field component
to be determined. It is generally necessary to apply corrections using data on the energy and direction
characteristics of the field and the energy and angle ambient dose equivalent response characteristics
of the device.
4.2.3 Considerations concerning the radiation field
The field comprises mainly photons, electrons, positrons, muons, protons and neutrons. There is not
a significant contribution to dose equivalent from energetic primary heavy charged particles (HZE)
or fragments. The electrons, positrons and muons are directly ionizing radiation, and, together with
indirectly ionizing photons and secondary electrons, interact with matter via the electromagnetic
force. Neutrons (and a small contribution from pions) interact via the strong interaction producing
directly ionizing secondary particles. Protons are both directly ionizing via the electromagnetic force
and indirectly via neutron-like strong interactions.
The directly ionizing component and the secondary electrons from indirectly ionizing photons comprise
the non-neutron component. The neutrons plus the neutron-like interactions of protons comprise
the neutron component. Alternatively, for dosimetric purposes, the field can be divided into low-LET
(<10 keV/μm) and high-LET (≥10 keV/μm) components. This definition is based on the dependence of
quality factor on LET. Quality factor is unity below 10 keV/μm. This separation between low and high
LET particles can be applied to TEPCs, and to other materials and detectors, but the low-LET/high-LET
threshold can vary between 5 keV/μm and 10 keV/μm. The low-LET component comprises the directly
ionizing electrons, positrons and muons; secondary electrons from photon interactions, most of the
energy deposition by directly ionizing interactions of protons; and part of the energy deposition by
secondary particles from strong interactions of protons and neutrons. The high-LET component is
from relatively short-range secondary particles from strong-interactions of protons and neutrons. The
relative contributions to the total ambient dose equivalent of low-LET and non-neutron component,
and high-LET and neutron and neutron-like component are not necessarily the same, but are generally
similar in magnitude.
The operational dose quantity relevant for these determinations, ambient dose equivalent, is reasonably
approximated, assuming suitable calibration and normalization, by the response of a tissue equivalent
proportional counter (TEPC), recombination ionization chamber or semiconductor spectrometer. The
low-LET or non-neutron energy deposition can be determined using an ionization chamber, silicon-
based detector, or scintillation detector; or a passive luminescence or ion storage detector. The high-LET
or neutron component can be measured using an extended range neutron survey meter or multi-sphere
spectrometer; or a passive etched track detector, bubble detector or fission foil with damage track
detector. The summed components, low LET plus high LET, or non-neutron plus neutron and neutron-
like, with suitable calibration and normalization, give total ambient dose equivalent. It is essential for
the measurement of the complex radiation fields that instruments used are characterized at national
standards laboratories in relevant radiation fields, corrections included for differences between the
calibration fields and the total atmospheric radiation field, and related uncertainties properly taken
into account.
Definitions of terms and details of normal procedures used in the calibration and use of measurement
[16] [17]
devices are given in various ISO and ICRU documents (for instance, ISO 4037-3 , ISO 8529-3 ,
[14] [15]
ISO 20785-2 and ICRU Report 66:2001 ). The determination of the uncertainties associated with
any set of measurement is an important part of dosimetry. Uncertainties associated with specific
methods of dosimetry are frequently not statistically independent. Even when they are independent,
the total uncertainty is frequently not simply the root mean square of the individual uncertainties but
[18]
depends upon the procedure for measurement and analysis. Details are given in ISO/IEC Guide 98-3 .
4.2.4 Considerations concerning calibration
In terms of ambient dose equivalent, the main contributions to the radiation field at aviation altitudes
are from neutrons from a few hundred keV up to a few GeV, protons from a few tens of MeV to a few
GeV, electrons, positrons and photons from a few MeV to a few GeV. The determination of the response
characteristics, both energy and angle dependence, of devices used for the determinations of ambient
dose equivalent for the cosmic radiation fields in aircraft should be carried out where possible in ISO
8 © ISO 2020 – All rights reserved

ISO 20785-1:2020(E)
reference radiations. However, ISO reference radiations do not fully cover the energy range of photons,
neutrons and electrons to account for the majority of the contributions to total ambient dose equivalent.
Thus, additional calibration fields are required, including, for some devices, proton radiation fields.
To determine the response characteristics to high-energy low-LET radiation field components for which
reference fields are not available, it can be demonstrated by measurement and calculation for particular
devices, for example the tissue equivalent proportional counter (TEPC), that the details of the energy
deposition distribution in the sensitive volume of the device are similar for these components to those
for the ISO high-energy photon reference field R–F. This addresses the particular problems associated
[19][20][21]
with the setting of the low-LET threshold of TEPCs and other devices . Quasi-monoenergetic
[22][23][24][25][26]
neutron fields are avai
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