IEC 63506:2026

• Abstract:

  IEC 63506:2026 specifies the calibration method of prompt fission neutron logging tools. This document applies to the calibration of prompt fission neutron logging tools for uranium exploration and mining.

• Status: Published
• Publication Date: 17-Jun-2026
• ICS: 17.240 - Radiation measurements
• ICS: 27.120.01 - Nuclear energy in general
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: TC 45 - Nuclear instrumentation
• Drafting Committee: PT 63506 - TC 45/PT 63506
• Current Stage: PPUB - Publication issued
• Start Date: 18-Jun-2026
• Completion Date: 03-Jul-2026

IEC 63506:2026 is an IEC International Standard for the calibration of prompt fission neutron logging tools. It specifies a calibration method for tools used in uranium exploration and mining, including how to prepare the instrument, use calibration pits, and evaluate sensitivity, indication error, nonlinearity, repeatability, and short-term stability.

What does IEC 63506:2026 specify?

IEC 63506:2026 specifies the calibration method for prompt fission neutron logging tools used in uranium exploration and mining. The document is organized into scope, normative references, terms and definitions, working principle, preparation, control of measuring instruments, and a bibliography.

• Clause 1 states the scope.
• Clause 2 lists the normative references needed to apply the document correctly.
• Clause 3 defines the main terms used in the calibration method.
• Clause 4 explains the operating principle of a PFN logging tool.
• Clause 5 covers preparation before calibration.
• Clause 6 sets the calibration conditions, calibration items, safety requirements, measurement methods, and calibration cycle.

What are the key requirements of IEC 63506:2026?

IEC 63506:2026 focuses on practical calibration control: the tool must be ready for use, the calibration site must be controlled, and the measured response must be checked against uranium pits. In practice, this gives laboratories and site teams a repeatable way to verify whether a PFN logging tool is suitable for uranium work.

Preparation and calibration setup

Clause 5 requires the PFN logging tool to be free of damage that could affect operation, identified by model, serial number, and manufacturer, and accompanied by complete accessories and information. The detector sensitive volume should be marked externally, and the tool should be warmed up for at least 10 min. That matters because stable operating conditions reduce drift before calibration starts.

Clause 6.1.1 requires calibration facilities based on saturated uranium calibration pits for neutron logging, including at least one blank pit and three uranium pits with reasonable uranium concentration settings. Table 1 gives the pit types and concentration ranges. This means calibration is not done against an arbitrary source - it is tied to reference pits with defined uranium content.

Clause 6.1.2 limits calibration conditions to ambient temperature of 0 °C to 35 °C, relative humidity below 80 %, and a site with no additional radioactive or electromagnetic source that could affect results. In practice, the environment must not distort the neutron counts.

What is checked during calibration

Clause 6.2 separates the calibration items by use case in Table 2. Uranium concentration sensitivity, indication error, nonlinearity, and repeatability apply to first calibration, subsequent calibration, and in-use inspection. Short-term stability applies only to first calibration. This helps users choose the right test set for acceptance, periodic checks, or routine inspection.

Clause 6.3 requires radiation protection to follow IEC 62598, with storage, transport, and use also subject to national and international radiation safety rules. That means calibration planning must include radiation safety controls, not only measurement steps.

Clause 6.4.1 determines uranium concentration sensitivity by using at least two uranium pits and one blank pit in the recommended 0.1 g/kg to 10 g/kg range, with correction for neutron flux decay by methods such as the epithermal neutron lifetime or E/T method. Clause 6.4.2 then uses a separate verification pit to calculate indication error. Clauses 6.4.3 to 6.4.5 cover nonlinearity, repeatability, and short-term stability from corrected neutron counting rates. In practice, these checks show whether the tool is linear, repeatable, and stable enough for field use.

Clause 6.5 recommends a 12-month calibration interval and requires recalibration after maintenance. That gives buyers and operators a clear maintenance trigger for keeping results comparable over time.

What terms does IEC 63506:2026 define?

• Prompt fission neutron (PFN) logging tool - a pulsed neutron logging instrument that uses an accelerator neutron generator to measure uranium mineralization around a borehole.
• Uranium concentration sensitivity - the change in indication divided by the change in uranium concentration.
• Saturated uranium calibration pits for neutron logging - reference uranium material that simulates the radiation field of a natural uranium deposit.
• D-T neutron generator - a device where deuterium and tritium react to produce fast neutrons.
• Indication error - the difference between the instrument indication and the actual value of the measurand.
• Measurement repeatability - measurement precision under repeatability conditions.
• Short-term stability - the ability of the instrument to keep performance unchanged during 8 h.

Who uses IEC 63506:2026?

IEC 63506:2026 is used by calibration laboratories, nuclear instrumentation engineers, uranium exploration and mining operators, quality managers, maintenance teams, and radiation safety personnel. They use it to set up calibration pits, verify tool performance before field deployment, check instruments after maintenance, and document calibration results for internal control or customer acceptance.

Which standards are used with IEC 63506:2026?

• IEC 60050-395 - provides nuclear instrumentation vocabulary used for terms and concepts in the document.
• IEC 62598 - provides constructional requirements and classification of radiometric gauges, and is referenced for radiation protection.
• ISO/IEC Guide 99:2007 - supplies the metrology vocabulary source used for the definition of repeatability.
• IEC 60050-311 - supplies the measurement vocabulary source used for the definition of short-term stability.

What does the IEC 63506:2026 document contain?

IEC 63506:2026 contains a working principle section that explains how D-T neutrons are moderated and how uranium is inferred from epithermal and thermal neutron response. It also includes a preparation checklist for tool condition and warm-up, plus calibration conditions for pits and environment.

The document provides Table 1 for pit specifications and Table 2 for which calibration items apply in each calibration case. It also gives formulas for sensitivity, background, indication error, nonlinearity, repeatability, and short-term stability, so users can calculate results in a consistent way.

IEC 63506 ®
Edition 1.0 2026-06
INTERNATIONAL
STANDARD
Calibration of the prompt fission neutron logging tools

ICS 27.120.01; 17.240 ISBN 978-2-8327-1284-9

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CONTENTS
FOREWORD . 2
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Working principle . 5
5 Preparation . 5
6 Control of measuring instruments . 6
6.1 Calibration conditions . 6
6.1.1 Calibration equipment. 6
6.1.2 Environment condition . 6
6.2 Calibration items . 6
6.3 Safety requirements . 6
6.4 Calibration method. 6
6.4.1 Uranium concentration sensitivity . 6
6.4.2 Indication error . 7
6.4.3 Nonlinearity . 8
6.4.4 Repeatability . 9
6.4.5 Short-term stability . 9
6.5 Calibration cycle . 9
Bibliography . 10

Table 1 – Main technical specifications of various pits . 6
Table 2 – Calibration items . 6

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Calibration of the prompt fission neutron logging tools
FOREWORD
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IEC 63506 has been prepared by IEC technical committee 45: Nuclear instrumentation. It is an
International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
45/1044/FDIS 45/1052/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
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1 Scope
This document specifies the calibration method of prompt fission neutron logging tools.
This document applies to the calibration of prompt fission neutron logging tools for uranium
exploration and mining.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050-395, International Electrotechnical Vocabulary (IEV) - Part 395: Nuclear
instrumentation - Physical phenomena, basic concepts, instruments, systems, equipment and
detectors
IEC 62598, Nuclear instrumentation - Constructional requirements and classification of
radiometric gauges
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-395 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online br
...