ISO 20785-2:2011

INTERNATIONAL ISO
STANDARD 20785-2
First edition
2011-06-01
Dosimetry for exposures to cosmic
radiation in civilian aircraft —
Part 2:
Characterization of instrument response
Dosimétrie de l'exposition au rayonnement cosmique dans l'aviation
civile —
Partie 2: Caractérisation de la réponse des instruments

Reference number
©
ISO 2011
©  ISO 2011
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ii © ISO 2011 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .2
3.1 General terms .2
3.2 Terms related to quantities and units .7
3.3 Terms related to the atmospheric radiation field.11
4 General considerations.12
4.1 The cosmic radiation field in the atmosphere.12
4.2 General considerations for the dosimetry of the cosmic radiation field in aircraft and
requirements for the characterization of instrument response .14
4.3 General considerations for measurements at aviation altitudes .15
5 Calibration fields and procedures .16
5.1 General considerations.16
5.2 Characterization of an instrument .18
5.3 Instrument-related software .21
6 Uncertainties.22
7 Remarks on performance tests.22
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 .23
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

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 20785-2 was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 2, Radiological protection.
ISO 20785 consists of the following parts, under the general title Dosimetry for exposures to cosmic radiation
in civilian aircraft:
⎯ Part 1: Conceptual basis for measurements
⎯ Part 2: Characterization of instrument response
A Part 3 dealing with measurements at aviation altitudes is in preparation.

iv © ISO 2011 – All rights reserved

Introduction
Aircraft crews are exposed to elevated levels of cosmic radiation of galactic and solar origin and secondary
radiation produced in the atmosphere, the aircraft structure and its contents. Following recommendations of
[1] [2]
the International Commission on Radiological Protection in Publication 60 , confirmed by Publication 103 ,
[3]
the European Union (EU) introduced a revised Basic Safety Standards Directive which included exposure to
natural sources of ionizing radiation, including cosmic radiation, as occupational exposure. The Directive
requires account to be taken of the exposure of aircraft crew liable to receive more than 1 mSv per year. It
then identifies the following four protection measures: (i) to assess the exposure of the crew concerned; (ii) to
take into account the assessed exposure when organizing working schedules with a view to reducing the
doses of highly exposed crew; (iii) to inform the workers concerned of the health risks their work involves; and
(iv) to apply the same special protection during pregnancy to female crew in respect of the “child to be born”
as to other female workers. The EU Council Directive has already been incorporated into laws and regulations
of EU member states and is being included in the aviation safety standards and procedures of the Joint
Aviation Authorities and the European Air Safety Agency. Other countries, such as Canada and Japan, have
issued advisories to their airline industries to manage aircraft crew exposure.
For regulatory and legislative purposes, the radiation protection quantities of interest are equivalent dose (to
the foetus) and effective dose. The cosmic radiation exposure of the body is essentially uniform, and the
maternal abdomen provides no effective shielding to the foetus. As a result, the magnitude of equivalent dose
to the foetus can be put equal to that of the effective dose received by the mother. Doses on board aircraft are
generally predictable, and events comparable to unplanned exposure in other radiological workplaces cannot
normally occur (with the rare exceptions of extremely intense and energetic solar particle events). Personal
dosemeters for routine use are not considered necessary. The preferred approach for the assessment of
doses of aircraft crew, where necessary, is to calculate directly 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
[4]
the European Commission 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
[5]
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. 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 radiation workers.
The radiation field in aircraft at altitude is complex, with many types of ionizing radiation present, with energies
ranging up to many GeV. The determination of ambient dose equivalent for such a complex radiation field is
difficult. In many cases, the methods used for the determination of ambient dose equivalent in aircraft are
similar to those used at high-energy accelerators in research laboratories. 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 need to be performed using accurate and reliable
methods that ensure the quality of readings provided to workers and regulatory authorities. The purpose of
this part of ISO 20785 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 part of ISO 20785 is intended for the use of primary and secondary calibration laboratories for ionizing
radiation, by radiation protection personnel employed by governmental agencies, and by industrial
corporations concerned with the determination of ambient dose equivalent for aircraft crew.

vi © ISO 2011 – All rights reserved

INTERNATIONAL STANDARD ISO 20785-2:2011(E)

Dosimetry for exposures to cosmic radiation in civilian
aircraft —
Part 2:
Characterization of instrument response
1 Scope
This part of ISO 20785 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 referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO/IEC Guide 98-1, Uncertainty of measurement — Part 1: Introduction to the expression of uncertainty in
measurement
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO 4037-1, X and gamma reference radiation for calibrating dosemeters and doserate meters and for
determining their response as a function of photon energy — Part 1: Radiation characteristics and production
methods
ISO 6980-1, Nuclear energy — Reference beta-particle radiation — Part 1: Methods of production
ISO 8529-1:2001, Reference neutron radiations — Part 1: Characteristics and methods of production
ISO 12789-1, Reference radiation fields — Simulated workplace neutron fields — Part 1: Characteristics and
methods of production
ISO 12789-2, Reference radiation fields — Simulated workplace neutron fields — Part 2: Calibration
fundamentals related to the basic quantities
ISO 20785-1, Dosimetry for exposures to cosmic radiation in civilian aircraft — Part 1: Conceptual basis for
measurements
ISO 29661, Reference radiation fields for radiation protection — Definitions and fundamental concepts
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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 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 It is important not to confuse calibration with adjustment of a measuring system, often mistakenly called
“self-calibration”, or with verification of calibration.
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 The calibration coefficient is equivalent to the calibration factor multiplied by the instrument constant.
NOTE 2 The reciprocal of the calibration coefficient, N , is the response.
coeff
NOTE 3 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 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 calibration coefficient with
Φ K
respect to absorbed dose, N .
D
3.1.4
calibration conditions
conditions, within the range of standard test conditions, actually prevailing during the calibration
3.1.5
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 The calibration factor is dimensionless.
NOTE 2 The corrected indication is the indication of the instrument corrected for the effect of influence quantities,
where applicable.
NOTE 3 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.
2 © ISO 2011 – All rights reserved

3.1.6
measured quantity value
measured value of a quantity
measured value
M
quantity value representing a measurement result
NOTE 1 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 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 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 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”.
3.1.7
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 The term “conventional true quantity value” is sometimes used for this concept, but its use is discouraged.
NOTE 2 Sometimes, a conventional quantity value is an estimate of a true quantity value.
NOTE 3 A conventional quantity value is generally accepted as being associated with a suitably small measurement
uncertainty, which might be zero.
NOTE 4 In ISO 20785, 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.
3.1.8
correction factor
k
factor applied to the indication to correct for deviation of measurement conditions from reference conditions
NOTE If the correction of the effect of the deviation of an influence quantity requires a factor, the influence quantity is
of type F.
3.1.9
correction summand
G
S
summand applied to the indication to correct for the zero indication or the deviation of the measurement
conditions from the reference conditions
NOTE If the correction of the effect of the deviation of an influence quantity requires a summand, the influence
quantity is of type S.
3.1.10
indication
G
quantity value provided by a measuring instrument or a measuring system
NOTE 1 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 An indication and a corresponding value of the quantity being measured are not necessarily values of
quantities of the same kind.
3.1.11
influence quantity
quantity that, in a direct measurement, does not affect the quantity that is actually measured, but affects the
relation between the indication and the measurement result
NOTE 1 An indirect measurement involves a combination of direct measurements, each of which may be affected by
influence quantities.
NOTE 2 In ISO/IEC Guide 98-3:2008, the concept “influence quantity” is defined as 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.
NOTE 3 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.
3.1.12
instrument constant
c
i
quantity value by which the indication 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 calculate the value of the
corr
measurand
NOTE 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 calibration factor and the
i
calibration coefficient 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.
3.1.13
measurand
quantity intended to be measured
3.1.14
point of test
point in the radiation field at which the conventional quantity value is known
NOTE The reference point of a detector assembly is placed at the point of test for calibration purposes or for the
determination of the response.
3.1.15
primary measurement standard
primary standard
measurement standard established using a primary reference measurement procedure or created as an
artifact, chosen by convention
NOTE A primary standard has the highest metrological quality in a given field.
4 © ISO 2011 – All rights reserved

3.1.16
quantity value
number and reference together expressing the magnitude of a quantity
NOTE 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.
3.1.17
reference conditions
conditions of use prescribed for testing the performance of a detector assembly or for comparing the results of
measurements
NOTE 1 The reference conditions represent the values of the set of influence quantities for which the calibration result
is valid without any correction.
NOTE 2 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).
3.1.18
reference direction
direction, in the coordinate system of the detector assembly, with respect to which the angle of the direction of
radiation incidence is measured in reference fields
NOTE At the angle of incidence of 0°, the reference direction of the detector assembly is parallel to the direction of
radiation incidence. At the angle of 180°, the reference direction of the detector assembly is anti-parallel to the direction of
radiation incidence.
3.1.19
reference orientation
orientation of the detector assembly for which the direction of the incident radiation coincides with the
reference direction of the detector assembly
3.1.20
reference point
point in the instrument that is placed at the point of test for calibration and test purposes
NOTE The distance of measurement is given by the distance between the radiation source and the reference point of
the detector assembly.
3.1.21
response
R
quotient of the indication, G, or the corrected indication, G , and the conventional quantity value to be
corr
measured
NOTE 1 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 that for the corrected indication, G ) has been used. Furthermore, it is necessary, in order to
corr
avoid confusion, to state the quantity to be measured, for example the response with respect to fluence, R , the response
Φ
with respect to kerma, R or the response with respect to absorbed dose, R .
K D
NOTE 2 The reciprocal of the response under the specified conditions is equal to the calibration coefficient, N .
coeff
NOTE 3 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 The response usually varies with the energy and direction distribution of the incident radiation. It is therefore
JJG
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
JJG
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.
3.1.22
secondary measurement standard
secondary standard
measurement standard established through calibration with respect to a primary measurement standard for a
quantity of the same kind
NOTE 1 Calibration can be carried out directly between a primary measurement standard and a secondary
measurement standard or it can involve an intermediate measuring system calibrated by the primary measurement
standard followed by assignment of a measurement result to the secondary measurement standard.
NOTE 2 A secondary standard can be variously represented, e.g. as a measuring device or a radionuclide source unit.
NOTE 3 The secondary standard can be used for calibrating a detector assembly and/or for determining its response.
The calibration of the secondary standard needs to be valid for the irradiation conditions used, e.g. energy, dose and/or
dose rate, and environmental conditions. The stability and reproducibility of the secondary standard has to be verified
periodically.
NOTE 4 The quantity value of the secondary standard is equated to the best estimate of the quantity, i.e. the
conventional quantity value.
3.1.23
standard test conditions
conditions represented by the range of values for the influence quantities under which a calibration or
determination of the response is carried out
NOTE Ideally, calibrations are carried out under reference conditions. As this is not always possible (e.g. for ambient
air pressure) or convenient (e.g. for ambient temperature), a (small) interval around the reference values can be
acceptable. If a calibration factor or response determined under standard conditions deviates significantly from the value
that would be obtained under reference conditions, a correction will normally be applied.
3.1.24
true quantity value
true value of a quantity
true value
quantity value consistent with the definition of a quantity
NOTE 1 In the error approach to describing a measurement, a true quantity value is considered unique and, in practice,
unknowable. The uncertainty approach is to recognize that, owing to the inherently incomplete amount of detail in the
definition of a quantity, there is not a single true quantity value but rather a set of true quantity values consistent with the
definition. However, this set of values is, in principle and in practice, unknowable. Other approaches dispense altogether
with the concept of a true quantity value and rely on the concept of metrological compatibility of measurement results for
assessing their validity.
NOTE 2 In the special case of a fundamental constant, the quantity is considered to have a single true quantity value.
NOTE 3 When the definitional uncertainty associated with the measurand is considered to be negligible compared to
the other components of the measurement uncertainty, the measurand can be considered to have an “essentially unique”
true quantity value. This is the approach taken by ISO/IEC Guide 98-3 and associated documents, in which the word “true”
is considered to be redundant.
6 © ISO 2011 – All rights reserved

3.2 Terms related to quantities and units
[71]
Most of the definitions in this subclause have been adapted from ISO 80000-10:2009 and ICRU
[6] [7]
Reports 36 and 51 .
3.2.1
particle fluence
fluence
Φ
at a given point in space, the mean number, dN, of particles incident on a small spherical domain, divided by
the cross-sectional area, da, of that domain:
dN
Φ =
da
–2 –2
NOTE 1 The base unit of particle fluence is m ; a frequently used unit is cm .
NOTE 2 The energy distribution of the particle fluence, Φ , is the quotient dΦ by dE, where dΦ is the fluence of
E
particles of energy between E and E + dE. There is an analogous definition for the directional distribution, Φ , of the
Ω
particle fluence.
3.2.2
particle fluence rate
fluence rate

Φ
ddΦ N

Φ==
ddta⋅dt
where dΦ is the mean increment in the particle fluence, dΝ /da, during an infinitesimal time interval of duration
dt
–2 –1 –2 –1
NOTE The base unit of the particle fluence rate is m ⋅s ; a frequently used unit is cm ⋅s .
3.2.3
energy imparted
ε
for ionizing radiation in the matter in a given three-dimensional domain,
ε = ∑ε
i
where the energy deposit, ε, is the energy deposited in a single interaction, i, and is given by
i
ε = ε − ε + Q, where ε is the energy of the incident ionizing particle, excluding rest energy, ε is the
i in out in out
sum of the energies of all ionizing particles leaving the interaction, excluding rest energy, and Q is the change
in the rest energies of the nucleus and of all particles involved in the interaction
NOTE 1 Energy imparted is a stochastic quantity.
NOTE 2 The unit of energy imparted is J.
3.2.4
mean energy imparted
ε
for the matter in a given domain,
ε = R − R + ΣQ
in out
where R is the radiant energy of all those charged and uncharged ionizing particles that enter the domain,
in
R is the radiant energy of all those charged and uncharged ionizing particles that leave the domain and ΣQ
out
is the sum of all changes in the rest energies of nuclei and elementary particles that occur in that domain
NOTE 1 This quantity has the meaning of the expected value of the energy imparted.
NOTE 2 The unit of mean energy imparted is J.
3.2.5
specific energy imparted
specific energy
z
for any ionizing radiation,
ε
z =
m
where ε is the energy imparted to the irradiated matter and m is the mass of that matter.
NOTE 1 Specific energy imparted is a stochastic quantity.
NOTE 2 In the limit of a small domain, the mean specific energy imparted is equal to the absorbed dose.
NOTE 3 The specific energy imparted can be the result of one or more (energy-deposition) events.
–1
NOTE 4 The unit of specific energy is J⋅kg , with the special name gray (Gy).
3.2.6
absorbed dose
D
for any ionizing radiation,
dε
D =
dm
where dε is the mean energy imparted by the ionizing radiation to an element of irradiated matter of mass dm
NOTE 1 ε = D dm , where dm is the element of mass of the irradiated matter.
∫
NOTE 2 In the limit of a small domain, the mean specific energy imparted is equal to the absorbed dose.
–1
NOTE 3 The unit of absorbed dose is J⋅kg , with the special name gray (Gy).
3.2.7
kerma
K
for indirectly ionizing (uncharged) particles, the sum of the initial kinetic energies, dE , of all the charged
tr
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 The quantity dE includes the kinetic energy of the charged particles emitted in the decay of excited atoms or
tr
molecules or nuclei.
–1
NOTE 2 The unit of kerma is J⋅kg , with the special name gray (Gy).
8 © ISO 2011 – All rights reserved

3.2.8
unrestricted linear energy transfer
linear energy transfer
LET
L
∆
for an ionizing charged particle, the mean energy, dE , imparted locally to matter along a small path through
∆
the matter, minus the sum of the kinetic energies of all the electrons released with kinetic energies in excess
of ∆, divided by the length dl:
dE
∆
L =
∆
dl
NOTE 1 This quantity is not completely defined unless ∆, i.e. the maximum kinetic energy of secondary electrons
whose energy is considered to be “locally deposited”, is specified. ∆ may be expressed in eV.
NOTE 2 Linear energy transfer is often abbreviated to LET, but the subscript ∆ or its numerical value should be
appended to it.
–1 –1
NOTE 3 The base unit of linear energy transfer is J⋅m ; a frequently used unit is keV⋅µm .
NOTE 4 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
3.2.9
dose equivalent
H
at the point of interest in tissue,
H = D ⋅ Q
where D is the absorbed dose and Q is the quality factor at that point
NOTE 1 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:
∞
H = QL()D 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 The relationship between Q and L is given in ICRP Publication 103 .
–1
NOTE 3 The unit of dose equivalent is J⋅kg , with the special name sievert (Sv).
3.2.10
lineal energy
y
quotient of ε by l , where ε is the energy imparted to the matter in a given volume by a single energy
s s
deposition event and l is the mean chord length in that volume:
ε
s
y =
l
–1 –1
NOTE The base unit of lineal energy is J⋅m ; a frequently used unit is keV⋅µm .
3.2.11
dose-mean lineal energy
y
D
∞
expectation value given by yy= d()y dy , where d(y) is the dose probability density of y
D
∫
NOTE 1 The dose probability density of y is given by d(y), where d(y) dz is the fraction of the absorbed dose delivered in
single events with lineal energy in the interval from y to y+dy.
NOTE 2 Both y and the distribution d(y) are independent of the absorbed dose and the dose rate.
D
3.2.12
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 The unit of ambient dose equivalent is J⋅kg , with the special name sievert (Sv).
3.2.13
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 The base unit of the particle fluence to ambient dose equivalent conversion coefficient is J⋅m ⋅kg , with the
2 2
special name Sv⋅m ; a frequently used unit is pSv⋅cm .
3.2.14
magnetic rigidity
r
momentum per charge (of a particle in a magnetic field), given by:
r = p/Ze
where p is the particle momentum, Z the number of charges on the particle and e the charge on the proton
–1
NOTE 1 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 Magnetic rigidity characterizes charged-particle trajectories in magnetic fields. All particles having the same
magnetic rigidity will have identical trajectories in a magnetic field, independent of particle mass or charge.
3.2.15
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 Geomagnetic cut-off rigidity depends on the angle of incidence. Often, vertical incidence is assumed.
10 © ISO 2011 – All rights reserved

3.2.16
vertical geomagnetic cut-off rigidity
vertical cut-off
cut-off
minimum magnetic rigidity a vertically incident particle can have and still reach a given location above the
Earth
3.3 Terms related to the 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 radiation
primary cosmic rays
cosmic radiation incident from space
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 radiation interacting with
the atmosphere or other matter
NOTE 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 originating outside the solar system
3.3.5
solar cosmic radiation
solar cosmic rays
solar particles
cosmic radiation 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, or the sudden increase in
cosmic radiation observed when such particles arrive at the Earth
3.3.7
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 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 GLEs are rare, occurring on average about once per year.
3.3.8
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
3.3.9
solar cycle
period during which the solar activity varies, with successive maxima separated by an average interval of
about 11 years
NOTE 1 If the reversal of the sun's magnetic-field polarity in successive 11-year periods is taken into account, the
complete solar cycle can be considered to average some 22 years, the Hale cycle.
NOTE 2 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.
3.3.10
relative sunspot 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 The relative sunspot number is also known as the Wolf number.
3.3.11
solar maximum
period of maximum solar activity during a solar cycle, usually defined in terms of the relative sunspot number
3.3.12
solar minimum
period of minimum solar activity during a solar cycle, usually defined in terms of the relative sunspot number
3.3.13
cosmic ray neutron monitor
ground level neutron monitor
GLNM
large detector used to measure the time-dependent relative fluence rate of high-energy cosmic radiation, in
particular the secondary neutrons generated in the atmosphere
NOTE 1 Protons, other hadrons and muons might also be detected.
NOTE 2 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 aviation altitudes
[8][9] 20
to sea level . Galactic cosmic radiation (GCR) can have energies up to 10 eV, but lower-energy particles
are the most frequent. After the GCR penetrates the magnetic field of the solar system, the peak of its energy
distribution is at a few hundred MeV to 1 GeV per nucleon, depending on solar magnetic activity, and the
–2,7 15
spectrum follows a power function of the form E eV up to 10 eV; above that energy, the spectrum
–3
steepens to E . The fluence rate of GCR entering the solar system is fairly constant with time, and these
energetic ions approach the Earth isotropically.
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The magnetic fields of the Earth and sun alter the relative number of GCR protons and heavier ions reaching
the atmosphere. The GCR ion composition for low geomagnetic cut-off and low solar activity is approximately
90 % protons, 9 % He ions and 1 % heavier ions; at a vertical cut-off of 15 GV, the composition is
[10][11]
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 SPE), are much lower in energy than GCR,
generally below 10
...