IEC TS 62396-5:2008

Process management for avionics - Atmospheric radiation effects - Part 5: Guidelines for assessing thermal neutron fluxes and effects in avionics systems

IEC TS 62396-5:2008 (E) provides a more precise definition of the threat that thermal neutrons pose to avionics as a second mechanism for inducing single event upset (SEU) in microelectronics. Addresses more in detail the following: detailed evaluation of the existing literature on measurements of the thermal flux inside of airliners; an enhanced compilation of the thermal neutron SEU cross section in currently available SRAM devices (more than 20 different devices).

General Information

• Status: Replaced
• Publication Date: 18-Aug-2008
• ICS: 03.100.50 - Production. Production management
• ICS: 31.020 - Electronic components in general
• ICS: 49.060 - Aerospace electric equipment and systems
• Technical Committee: TC 107 - Process management for avionics
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 22-Aug-2014

Relations

• Replaces: IEC PAS 62396-5:2007 - Process management for avionics - Atmospheric radiation effects - Part 5: Guidelines for assessing thermal neutron fluxes and effects in avionics systems
• Effective Date: 05-Sep-2023
• Replaced By: IEC 62396-5:2014 - Process management for avionics - Atmospheric radiation effects - Part 5: Assessment of thermal neutron fluxes and single event effects in avionics systems
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC/TS 62396-5
Edition 1.0 2008-08
TECHNICAL
SPECIFICATION
Process management for avionics – Atmospheric radiation effects –
Part 5: Guidelines for assessing thermal neutron fluxes and effects in avionics
systems
IEC/TS 62396-5:2008(E)
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IEC/TS 62396-5
Edition 1.0 2008-08
TECHNICAL
SPECIFICATION
Process management for avionics – Atmospheric radiation effects –
Part 5: Guidelines for assessing thermal neutron fluxes and effects in avionics
systems
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
R
ICS 03.100.50; 31.020; 49.060 ISBN 2-8318-9959-1
– 2 – TS 62396-5 © IEC:2008(E)
CONTENTS
FOREWORD.3
1 Scope.5
2 Normative references .5
3 Terms and definitions .5
4 Overview of thermal neutron single event rate calculation .5
5 Thermal neutron flux inside an airliner.6
5.1 Definition of thermal neutron .6
5.2 Overview .7
5.3 Background on aircraft measurements.7
5.4 Calculational approach .8
5.5 Processing of in-flight neutron flux data.9
6 Thermal neutron SEU cross sections .12
6.1 Overview of the issue .12
6.2 Mechanism involved .13
6.3 Thermal neutron SEU cross sections and Ratio-2.14
7 Recommendation for devices in avionics at present time .16

Bibliography.17

Figure 1 – Atmospheric neutron spectra measured in four aircraft.9

Table 1 – Tabulation of the various atmospheric neutron measurements used .9
Table 2 – Comparison of thermal and high energy neutron fluxes and their ratios .11
Table 3 – Calculated neutron fluxes in the Boeing 747 structure .12
Table 4 – SRAM SEU cross sections induced by thermal and high energy neutrons.15

TS 62396-5 © IEC:2008(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PROCESS MANAGEMENT FOR AVIONICS –
ATMOSPHERIC RADIATION EFFECTS –

Part 5: Guidelines for assessing thermal neutron
fluxes and effects in avionics systems

FOREWORD
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The main task of IEC technical committees is to prepare International Standards. In
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• the required support cannot be obtained for the publication of an International Standard,
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• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC/TS 62396-5, which is a technical specification, has been prepared by IEC technical
committee 107: Process management for avionics.

– 4 – TS 62396-5 © IEC:2008(E)
This standard cancels and replaces IEC/PAS 62396-5 published in 2007. This first edition
constitutes a technical revision.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
107/82/DTS 107/89/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 62396 series, under the general title Process management for
avionics – Atmospheric radiation effects, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended
A bilingual edition of this document may be issued at a later date.

TS 62396-5 © IEC:2008(E) – 5 –
PROCESS MANAGEMENT FOR AVIONICS –
ATMOSPHERIC RADIATION EFFECTS –

Part 5: Guidelines for assessing thermal neutron
fluxes and effects in avionics systems

1 Scope
The purpose of this technical specification is to provide a more precise definition of the threat
that thermal neutrons pose to avionics as a second mechanism for inducing single event
upset (SEU) in microelectronics. There are two main points that will be addressed in this
technical specification:
a) a detailed evaluation of the existing literature on measurements of the thermal flux inside
of airliners and
b) an enhanced compilation of the thermal neutron SEU cross section in currently available
SRAM devices (more than 20 different devices).
The net result of the reviews of these two different sets of data will be two ratios that we
consider to be very important for leading to the ultimate objective of how large a threat is the
SEU rate from thermal neutrons compared to the SEU threat from the high energy neutrons
(E >10 MeV). The threat from the high energy neutrons has been dealt with extensively in the
1)
literature and has been addressed by two standards (IEC/TS 62396-1 in avionics and [1] in
microelectronics on the ground).
2 Normative references
The following referenced documents are indispensable for the application of this document,
only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
IEC/TS 62396-1, Process management for avionics – Atmospheric radiation effects – Part 1:
Accommodation of atmospheric radiation effects via single event effects within avionics
electronic equipment
3 Terms and definitions
For the purpose of this document, the terms and definitions of IEC/TS 62396-1 apply.
4 Overview of thermal neutron single event rate calculation
The two ratios that this technical specification considers to be so important are:
a) the ratio of the thermal neutron flux inside an airliner relative to the flux of high energy
(> 10 MeV) neutrons inside the airliner and
b) the ratio of the SEU cross section due to thermal neutrons relative to that due to high
energy neutrons.
These ratios are considered to be important because with them, once we know what the SEU
rates are from the high energy neutrons for an avionics box, a topic which has been dealt with
___________
1)
Numbers in square brackets refer to the bibliography.

– 6 – TS 62396-5 © IEC:2008(E)
extensively, such as in [1], then the additional SEU rate due to thermal neutrons can be
obtained with these ratios. Thus, given the SEU rate from high energy neutrons, multiplying
this by the two ratios gives the SEU rate from the thermal neutrons. The total SEU rate will be
the combination of the SEU rates from both the high energy and thermal neutrons.
The process for calculating the SEU rate from the thermal neutrons is shown in the following
set of equations, (1) to (5).
SEU Rate
2 2
= Φ (neutron flux = 6 000 n/cm h) × σ(Hi E, SEU X-Sctn. cm /dev) (1)
Hi
(Hi E, Upset/dev·h)
SEU Rate
Φ (neutron flux)
σ(therm SEU X-Sctn.)
therm
=×SEU Rate (Hi E) ×  (2)
(thermal neutron,
Φ (neutron flux) σ(Hi E SEU X-Sctn.)
Hi
Upset/dev·h)
Ratio-1
Φ (neutron flux)
thermal
= (3)
Φ (neutron flux)
Hi
Ratio-2
σ (therm SEU Cross Section)
= (4)
σ(Hi E SEU Cross Section)
SEU Ra
...