Edition 2.0 · 2015 📄 Reference only

IEC 60846-2:2015 explained

Part 2 of the IEC 60846 series: portable and transportable instruments for the dose rates encountered in an emergency, above the ranges Part 1 covers.

Designation

IEC 60846-2:2015

Title

Radiation protection instrumentation — Ambient and/or directional dose equivalent (rate) meters and/or monitors for beta, X and gamma radiation — Part 2: High range beta and photon dose and dose rate portable instruments for emergency radiation protection purposes

Instruments

High-range portable instruments for emergency response

Committee

IEC TC 45 / SC 45B, WG 8

On this site

Described here for reference. An evaluation tool for it is planned, not built.

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Scope and purpose

Part 2 applies to portable or transportable ambient and directional dose equivalent (rate) meters and monitors for the measurement of external beta, X and gamma radiation at energies up to 10 MeV, intended for use during emergency situations. It specifies the design requirements and performance characteristics for instruments used to determine dose equivalent and dose equivalent rate under those conditions, with the emergency exposure situations as characterised in ICRU Report 47 as its reference.

The second edition was published in 2015 and brought Part 2 into line with the revisions introduced by IEC 60846-1:2009.

Relationship to Part 1

The two parts share a series number, a set of operational quantities and much of their test methodology. They differ in the range of the field.

Part 1 covers portable workplace and environmental instruments across their normal ranges. Part 2 covers the decades above, where the measurement exists to support decisions in an accident or a radiological emergency: whether an area may be entered, for how long, and what dose a responder has accumulated.

An instrument is not automatically covered by both. An instrument declared to Part 1 has not been demonstrated to behave correctly at the dose rates Part 2 addresses, and the failure mode at high dose rate is not a graceful loss of accuracy.

Characteristics that dominate at high dose rates

Overload behaviour

Overload is the behaviour of the instrument when the field exceeds its measuring range. The requirement is not that the instrument continue to measure — it cannot — but that it must not indicate a low value. A counting instrument driven far past its range can saturate and then indicate a falling reading as the true dose rate rises, because the detector’s dead time consumes an increasing fraction of each interval. An instrument that indicates a safe value in a lethal field has failed in the specific way this requirement exists to prevent.

The requirement is therefore that an unambiguous off-scale or overload indication is displayed and maintained for as long as the condition persists. See the overload test for how this is evaluated.

Recovery after exposure

An emergency instrument is used continuously, not in a single reading. After exposure to a field above its range it must return to correct indication, and the standard is concerned with how long that takes and whether the instrument’s response is altered afterwards. An instrument that reads correctly again only after several minutes is of limited use while moving through a field gradient.

Response time

The response time — the interval to reach 90 % of the final indication after a step change in the field — determines whether the indication reflects the field the operator is currently standing in. Where dose rate varies by orders of magnitude over metres, a slow instrument indicates the field that was, not the field that is.

Measured quantities

The same operational quantities as Part 1: ambient dose equivalent H*(10) for strongly penetrating radiation and directional dose equivalent H′(0,07) for the weakly penetrating component, the latter being the relevant quantity for beta radiation and skin dose. Both are defined in the ICRU sphere and are properties of the field rather than of a person.

The energy range extends to 10 MeV, higher than most workplace instruments require. Photon energy response at the upper end is therefore a genuine test point rather than an extrapolation, and beta response matters because emergency fields from fresh fission products carry a substantial beta component.

Related standards

Coverage on this site

No evaluation tool for IEC 60846-2 exists here yet. Of the standards described on this site it is the closest to the implemented one: the quantities are the same, the characteristics largely correspond, and the arithmetic is unchanged. What differs is the range, the acceptance limits, and the weight given to overload and recovery. Those are declared values in the standard definition layer rather than new computation, which makes this the most tractable of the planned additions.