EN ISO 20785-1:2017

SLOVENSKI STANDARD
01-december-2017
'R]LPHWULMD]DPHUMHQMHL]SRVWDYOMHQRVWLNR]PLþQHPXVHYDQMXYFLYLOQHPOHWDOVNHP
SURPHWXGHO.RQFHSWXDOQDRVQRYD]DPHULWYH,62
Dosimetry for exposures to cosmic radiation in civilian aircraft - Part 1: Conceptual basis
for measurements (ISO 20785-1:2012)
Dosimétrie pour l'exposition au rayonnement cosmique à bord d'un avion civil - Partie 1:
Fondement théorique des mesurages (ISO 20785-1:2012)
Ta slovenski standard je istoveten z: EN ISO 20785-1:2017
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 20785-1
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2017
EUROPÄISCHE NORM
ICS 13.280; 49.020
English Version
Dosimetry for exposures to cosmic radiation in civilian
aircraft - Part 1: Conceptual basis for measurements (ISO
20785-1:2012)
Dosimétrie pour l'exposition au rayonnement
cosmique à bord d'un avion civil - Partie 1: Fondement
théorique des mesurages (ISO 20785-1:2012)
This European Standard was approved by CEN on 13 September 2017.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, 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: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20785-1:2017 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 20785-1:2012 has been prepared by Technical Committee ISO/TC 85 “Nuclear energy,
nuclear technologies, and radiological protection” of the International Organization for Standardization
(ISO) and has been taken over as EN ISO 20785-1:2017 by 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 April 2018, and conflicting national standards shall be
withdrawn at the latest by April 2018.
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.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 20785-1:2012 has been approved by CEN as EN ISO 20785-1:2017 without any
modification.
INTERNATIONAL ISO
STANDARD 20785-1
Second edition
2012-12-15
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 20785-1:2012(E)
©
ISO 2012
ISO 20785-1:2012(E)
© ISO 2012
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any
means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the
address below or ISO’s member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2012 – All rights reserved

ISO 20785-1:2012(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
2.1 General . 1
2.2 Quantities and units . 2
2.3 Atmospheric radiation field . 8
3 General considerations .10
3.1 General description of the cosmic radiation field in the atmosphere .10
3.2 General calibration considerations for the dosimetry of cosmic radiation fields
in aircraft .11
3.3 Conversion coefficients .13
4 Dosimetric devices .13
4.1 Introduction .13
4.2 Active devices .14
4.3 Passive devices .17
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
[80]
minimum and maximum vertical cut-off rigidity .20
Bibliography .24
ISO 20785-1:2012(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International
Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies
casting a vote.
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.
ISO 20785-1 was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 2, Radiological protection.
This second edition cancels and replaces the first edition (ISO 20785-1:2006), which has been
technically revised.
ISO 20785 consists of the following parts, under the general title Dosimetry for exposures to cosmic
radiation in civilian aircraft:
— Part 1: Conceptual basis for measurements
— Part 2: Characterization of instrument response
Measurements at aviation altitudes is to form the subject of a future Part 3.
iv © ISO 2012 – All rights reserved

ISO 20785-1:2012(E)
Introduction
Aircraft crews are exposed to elevated levels of cosmic radiation of galactic and solar origin and
secondary radiation produced in the atmosphere, the aircraft structure and its contents. Following
[1]
recommendations of the International Commission on Radiological Protection in Publication 60,
[2]
confirmed by Publication 103, the European Union (EU) introduced a revised Basic Safety Standards
[3]
Directive which included exposure to natural sources of ionizing radiation, including cosmic radiation,
as occupational exposure. The Directive requires account to be taken of the exposure of aircraft crews
liable to receive more than 1 mSv per year. It then identifies the following four protection measures:
(i) to assess the exposure of the crew concerned; (ii) to take into account the assessed exposure when
organizing working schedules with a view to reducing the doses of highly exposed crews; (iii) to inform
the workers concerned of the health risks their work involves; and (iv) to apply the same special protection
during pregnancy to female 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 dosemeters 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 fold these values with flight and staff roster information to obtain estimates of
effective doses for individuals. This approach is supported by guidance from the European Commission
[4]
and the ICRP in Publication 75.
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 by measurements traceable to national standards. The validation of calculations of ambient
dose equivalent for a particular calculation method may be taken as a validation of the calculation of
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 radiation workers. Ambient dose equivalent rate as a function of
geographic location, altitude and solar cycle phase is then calculated and folded with flight and staff
roster information.
The radiation field in aircraft at altitude is complex, with many types of ionizing radiation present, with
energies ranging up to many GeV. The determination of ambient dose equivalent for such a complex
radiation field is difficult. In many cases, the methods used for the determination of ambient dose
equivalent in aircraft are similar to those used at high-energy accelerators in research laboratories.
Therefore, it is possible to recommend dosimetric methods and methods for the calibration of dosimetric
devices, as well as the techniques for maintaining the traceability of dosimetric measurements to
national standards. Dosimetric measurements made to evaluate ambient dose equivalent must be
performed using accurate and reliable methods that ensure the quality of readings provided to workers
and regulatory authorities. This part of ISO 20785 gives a conceptual basis for the characterization of
the response of instruments for the determination of ambient dose equivalent in aircraft.
ISO 20785-1:2012(E)
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 part of ISO 20785 is intended for the use of primary and secondary calibration laboratories for
ionizing radiation, by radiation protection personnel employed by governmental agencies, and by
industrial corporations concerned with the determination of ambient dose equivalent for aircraft crews.
vi © ISO 2012 – All rights reserved

INTERNATIONAL STANDARD ISO 20785-1:2012(E)
Dosimetry for exposures to cosmic radiation in civilian
aircraft —
Part 1:
Conceptual basis for measurements
1 Scope
This part of ISO 20785 gives 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 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1 General
2.1.1
calibration
operation that, under specified conditions, establishes a relation between the conventional quantity, H ,
and the indication, G
Note 1 to entry: A calibration may be expressed by a statement, calibration function, calibration diagram,
calibration curve, or calibration table. In some cases, it may 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.
2.1.2
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
ISO 20785-1:2012(E)
2.1.3
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.
2.1.4
reference conditions
conditions of use prescribed for testing the performance of a detector assembly or for comparison of
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 may 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 may influence
the calibration result and the response.
2.1.5
response
R
quotient of the indication, G, or the corrected indication, G , and the conventional quantity value
corr
to be 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 quantity
corr
to be measured, for example: the response with respect to fluence, R , the response with respect to kerma, R , the
Φ K
response with respect to absorbed dose, R .
D
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 may 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.
2.2 Quantities and units
2.2.1
particle fluence
fluence
Φ
number, dN, at a given point of 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 .
2 © ISO 2012 – All rights reserved

ISO 20785-1:2012(E)
Note 2 to entry: The energy distribution of the particle fluence, Φ , is the quotient, dΦ, by dE, where dΦ is the
E
fluence of particles of energy between E and E+dE. There is an analogous definition for the direction distribution,
Φ , of the particle fluence. The complete representation of the double differential particle fluence can be written
Ω
(with arguments) Φ (E,Ω), where the subscripts characterize the variables (quantities) for differentiation and
E,Ω
where the symbols in the brackets describe the values of the variables. The values in the brackets are needed for
special function values, e.g. the energy distribution of the particle fluence at energy E = E is written as Φ (E ). If
0 E 0
no special values are indicated, the brackets may be omitted.
2.2.2
particle fluence rate
fluence rate

Φ
rate of the particle fluence 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 .
2.2.3
energy imparted
ε
for ionizing radiation in the matter within a given three-dimensional domain,
εε=
∑ i
where
ε is the energy deposited in a single interaction, i, and given by ε = ε – ε + Q, where
i i in out
ε is the energy of the incident ionizing particle, excluding rest energy,
in
ε is the sum of the energies of all ionizing particles leaving the interaction, excluding rest
out
energy, and
Q is the change in the rest energies of the nucleus and of all particles involved in the interaction
Note 1 to entry: Energy imparted is a stochastic quantity.
Note 2 to entry: The unit of the energy imparted is J.
2.2.4
mean energy imparted
ε
mean energy imparted to the matter in a given domain, expressed as
ε =−RR + Q
in out ∑
ISO 20785-1:2012(E)
where
R is the radiant energy of all those charged and uncharged ionizing particles that enter the
in
domain,
R is the radiant energy of all those charged and uncharged ionizing particles that leave the
out
domain, and
∑Q is the sum of all changes of the rest energy of nuclei and elementary particles that occur in
that domain
Note 1 to entry: This quantity has the meaning of expected value of the energy imparted.
Note 2 to entry: The unit of the mean energy imparted is J.
2.2.5
specific energy imparted
specific energy
z
for any ionizing radiation,
ε
z =
m
where
ε is the energy imparted to the irradiated matter,
m is the mass of the irradiated matter
Note 1 to entry: Specific energy imparted is a stochastic quantity.
Note 2 to entry: In the limit of a small domain, the mean specific energy imparted is equal to the absorbed dose.
Note 3 to entry: The specific energy imparted can be the result of one or more (energy-deposition) events.
–1
Note 4 to entry: The unit of specific energy is J⋅kg , with the special name gray (Gy).
2.2.6
absorbed dose
D
for any ionizing radiation,
dε
D=
dm
where
is the mean energy imparted by ionizing radiation to an element of irradiated matter of mass
dε
dm, where
ε = Dmd
∫
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).
4 © ISO 2012 – All rights reserved

ISO 20785-1:2012(E)
2.2.7
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).
2.2.8
unrestricted linear energy transfer
linear energy transfer
LET
L
Δ
for an ionizing charged particle, the mean energy, dE , imparted locally to matter along a small path
Δ
through the matter minus the sum of the kinetic energies of all the electrons released with kinetic
energies in excess of Δ, divided by the length, dl:
dE
Δ
L =
Δ
dl
Note 1 to entry: This quantity is not completely defined unless Δ is specified, i.e. the maximum kinetic energy of
secondary electrons whose energy is considered to be “locally deposited”. Δ may be expressed in eV.
Note 2 to entry: Linear energy transfer is often abbreviated LET, but to which should be appended the subscript
Δ or its numerical value.
−1 −1
Note 3 to entry: The unit of the linear energy transfer is J m , a frequently used unit is keV μm .
Note 4 to entry: If no energy cut-off is imposed, the unrestricted linear energy transfer L is equal to the linear
∞
electronic stopping power S and may be denoted simply as L.
el
2.2.9
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.
ISO 20785-1:2012(E)
[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).
2.2.10
single-event dose-mean specific energy
dose-mean specific energy per event
z
D
expectation
∞
zz= dz()dz
D 1
∫
where d (z)is the dose probability density of z
Note 1 to entry: The dose probability density of z is given by d (z), where d (z) dz is the fraction of the absorbed
1 1
dose delivered in single events with specific energies in the interval from z to z+dz.
2.2.11
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 .
2.2.12
dose-mean lineal energy
y
D
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.
2.2.13
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).
6 © ISO 2012 – All rights reserved

ISO 20785-1:2012(E)
2.2.14
particle-fluence-to-ambient-dose-equivalent conversion coefficient
h∗
Φ
quotient of the particle ambient dose equivalent, H*(10), and the particle fluence, Φ:
H∗()10
h∗=
Φ
Φ
2 −1
Note 1 to entry: The unit of the particle-fluence-to-ambient-dose-equivalent conversion coefficient is J m kg
2 2
with the special name Sv m , a frequently used unit is pSv cm .
2.2.15
atmosphere depth
X
v
mass of a unit-area column of air above a point in the atmosphere
−2 −2
Note 1 to entry: The unit of atmosphere depth is kg m ; a frequently used unit is g cm .
2.2.16
standard barometric altitude
pressure altitude
altitude determined by a barometric altimeter calibrated with reference to the International Standard
Atmosphere (ISA) (ISO 2533, Standard Atmosphere) when the altimeter’s datum is set to 1 013,25 hPa
Note 1 to entry: The flight level is sometimes given as FL 350, where the number represents multiples of 100 ft of
pressure altitude, based on the ISA and a datum setting of 1 013,25 hPa. However, in some countries flight levels
are expressed in meters, in which case appropriate conversions should be made before applying the data given in
this International Standard.
2.2.17
magnetic rigidity
P
momentum per charge (of a particle in a magnetic field), given by
p
P=
Ze
where
p is the particle momentum,
Z is the number of charges on the particle, and
e is the charge on the proton
–1
Note 1 to entry: The base unit of magnetic rigidity is the tesla metre (T⋅m) ( = V⋅m ⋅s). A frequently used unit is
V (or GV) in a system of units where the values of the speed of light, c, and the charge on the proton, e, are both 1,
and the magnetic rigidity is given by pc/Ze.
Note 2 to entry: Magnetic rigidity characterizes charged-particle trajectories in magnetic fields. All particles having
the same magnetic rigidity have identical trajectories in a magnetic field, independent of particle mass or charge.
ISO 20785-1:2012(E)
2.2.18
geomagnetic cut-off rigidity
cut-off rigidity
r
c
minimum magnetic rigidity an incident particle can have and still penetrate the geomagnetic field to
reach a given location above the Earth
Note 1 to entry: Geomagnetic cut-off rigidity depends on angle of incidence. Often, vertical incidence to the Earth’s
surface is assumed, in which case the vertical geomagnetic cut-off rigidity is the minimum magnetic rigidity a
vertically incident particle can have and still reach a given location above the Earth.
2.2.19
vertical geomagnetic cut-off rigidity
vertical cut-off
cut-off
minimum magnetic rigidity a vertically incident particle can have and still reach a given location
above the Earth
2.3 Atmospheric radiation field
2.3.1
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
2.3.2
primary cosmic radiation
primary cosmic rays
cosmic radiation incident from space at the Earth’s orbit
2.3.3
secondary cosmic radiation
secondary cosmic rays
cosmogenic particles
particles which are created directly or in a cascade of reactions by primary cosmic rays 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.
2.3.4
galactic cosmic radiation
galactic cosmic rays
GCR
cosmic radiation originating outside the solar system
2.3.5
solar particles
solar cosmic radiation
solar cosmic rays
cosmic radiation originating from the sun
8 © ISO 2012 – All rights reserved

ISO 20785-1:2012(E)
2.3.6
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.
2.3.7
ground-level enhancement
GLE
sudden increase of cosmic radiation observed on the ground by at least two neutron monitor stations
recording simultaneously a greater than 1 % increase in the five-minute-averaged count rate associated
with solar energetic particles
Note 1 to entry: A GLE is associated with a solar-particle event having a high fluence rate of particles with high
energy (greater than 500 MeV).
Note 2 to entry: GLEs are relatively rare, occurring on average about once per year. GLEs are numbered; the first
number being given to that occurring in February 1942.
2.3.8
solar modulation
change of the GCR field (outside the Earth’s magnetosphere) caused by change of solar activity and
consequent change of the magnetic field of the heliosphere
2.3.9
solar cycle
period during which the solar activity varies with successive maxima separated by an average interval
of about 11 years
Note 1 to entry: If the reversal of the Sun’s magnetic field polarity in successive 11 year periods is taken into
account, the complete solar cycle may be considered to average some 22 years, the Hale cycle.
Note 2 to entry: The sunspot cycle as measured by the relative sunspot number, known as the Wolf number, has
an approximate length of 11 years, but this varies between about 7 and 17 years. An approximate 11 year cycle
has been found or suggested in geomagnetism, frequency of aurora, and other ionospheric characteristics. The u
index of geomagnetic intensity variation shows one of the strongest known correlations to solar activity.
2.3.10
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 the observatory (location and instrumentation)
2.3.11
solar maximum
time period of maximum solar activity during a solar cycle, usually defined in terms of relative
sunspot number
2.3.12
solar minimum
time period of minimum solar activity during a solar cycle, usually defined in terms of relative
sunspot number
ISO 20785-1:2012(E)
2.3.13
cosmic ray neutron monitor
ground level neutron monitor
cosmic radiation neutron monitor
GLNM
large detector used to measure the time-dependent relative fluence rate of high-energy cosmic radiation,
in particular the secondary neutrons generated in the atmosphere (protons, other hadrons and muons
may also be detected)
Note 1 to entry: Installed worldwide at different locations and altitudes on the ground (and occasionally placed
on ships or aircraft), cosmic radiation neutron monitors are used for various cosmic radiation studies and to
determine solar modulation.
3 General considerations
3.1 General description of the cosmic radiation field in the atmosphere
The primary galactic cosmic radiation (and energetic solar particles) interact with the atomic nuclei of
atmospheric constituents, producing a cascade of interactions and secondary reaction products that
contribute to cosmic radiation exposures that decrease in intensity with depth in the atmosphere from
[5][6] 20
aviation altitudes to sea level. Galactic cosmic radiation (GCR) can have energies up to 10 eV, but
lower energy particles are the most frequent. After the 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 for low geomagnetic cut-off and low solar activity is
approximately 90 % protons, 9 % He ions, 1 % heavier nuclei; at a vertical cut-off of 15 GV, the composition
[7][8]
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 events (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.
10 © ISO 2012 – All rights reserved

ISO 20785-1:2012(E)
Key
X altitude (km)
Y ambient dose equivalent rate (μSv/h)
[9]
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
3.2 General calibration considerations for the dosimetry of cosmic radiation fields in
aircraft
3.2.1 Approach
The general approach necessary for measurement and calibration is given here. Details of calibration
fields and procedures are given in ISO 20785-2.
3.2.2 Considerations concerning the measurement
[10]
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
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
ISO 20785-1:2012(E)
characteristics of the field and the energy and angle ambient dose equivalent response characteristics
of the device.
3.2.3 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 may vary between 5 keV/μm and 10 keV/μm. The low-LET component comprises the
directly ionizing electrons, positrons and muons; secondary electrons from photon interactions, most
of the energy deposition by directly ionizing interactions of protons; and part of the energy deposition
by secondary particles from strong interactions of protons and neutrons. The high-LET component is
from
...