Radiation measuring instruments by purpose
Start here when you know the instrument and need the standard. Two classes of instrument measure ionising radiation for two different purposes. They are similar in appearance, are frequently supplied by the same manufacturers, and are not interchangeable. The class determines which standard applies and what the acceptance requirements are.
Working the other way — you know the standard and want its scope, characteristics and test procedures — start from Standards instead.
Classification by purpose
Protection instruments are used to prevent a dose limit from being exceeded. The measurand relates to a person or a location: the dose equivalent, or its rate, present there.
Quality control instruments are used to verify that equipment produces the radiation output it is specified to produce. The measurand relates to the equipment: the output actually delivered. The principal application is diagnostic and therapeutic medical equipment; the same classification covers industrial irradiators, sterilisation plant and analytical X-ray systems.
That difference in measurand determines the remaining differences: measuring range, required accuracy, physical form, and the governing standard.
| Protection | Quality control | |
|---|---|---|
| Purpose | Verify a location or person is within dose limits | Verify equipment output against specification |
| Subject | A person or an area | A machine |
| Typical quantity | Dose equivalent (rate) — H*(10), H′(0,07), Hp(10) | Air kerma, absorbed dose to water, dose area product |
| Measuring range | Very wide — many decades, background to accident levels | Narrow — around one known operating point |
| Accuracy expected | Broad tolerance bands, sized for range and energy coverage | Tight — a few percent, because the machine is calibrated against it |
| Energy range | Wide and often unknown in advance | Narrow and known — the beam quality is a controlled condition |
| Environment | Field: temperature, humidity, handling, drops | Controlled room, repeatable geometry |
| Alarms | Required; the alarm is the safety function | Not applicable |
Basis for the difference in tolerance
A protection instrument reading 30 % low would fail a medical physics acceptance test; a diagnostic dosimeter with that error would be withdrawn from service. A survey meter with the same error can be fully compliant with its own standard.
The difference follows from how the value is used. A protection instrument must remain within its band across five or six decades of dose rate, over an energy range that is not known in advance, at incidence angles that are not controlled, under field environmental conditions. Requiring a few percent across that domain would make the instrument either technically impracticable or prohibitively expensive, and it would not change the decisions being taken, which are of the order "background", "elevated", "evacuate". The width of the tolerance band is a deliberate exchange of precision for range, robustness and energy coverage.
A quality control instrument operates under the opposite constraints: one known beam quality, a fixed geometry, a narrow range, and a controlled ambient temperature. In exchange it is held to a few percent, because a treatment machine or an imaging system is adjusted to agree with it. An error in that value propagates directly into patient dose.
Practical consequence: the two classes are not interchangeable. A survey meter cannot verify a radiotherapy output: its accuracy is insufficient and it measures a different quantity. A diagnostic dosimeter cannot be used to survey an area: it saturates, it provides no alarm function, and its energy response is characterised only over the beam qualities it was designed for.
Protection instruments
Grouped by application. The quantity column is decisive: an instrument calibrated for one operational quantity does not measure another correctly regardless of how it is used.
| Instrument | Form and detector | Quantity | Used for | IEC standard |
|---|---|---|---|---|
| Survey meters / dose rate meters | Hand-held, battery powered, ruggedised. Geiger–Müller tube, scintillator or ionisation chamber. | H*(10), H′(0,07) | Area surveys, boundary monitoring, and assessment of whether an area may be entered. | IEC 60846-1 |
| Area monitors | Fixed installation with local display and remote output. Continuous operation, mains powered with battery backup. | H*(10) | Continuous monitoring of a room or boundary, normally with alarm outputs to a control room. | IEC 60846-1 |
| High-range emergency instruments | Survey-meter form, with detectors and electronics selected to remain linear well above normal working levels. | H*(10), H′(0,07) | Accident and emergency response, at dose rates above the saturation point of routine instruments. | IEC 60846-2 |
| Electronic personal dosimeters | Worn on the body. Small, low power, logging, usually with dose and dose rate alarms. | Hp(10), Hp(0,07) | Recording the dose received by an individual, as distinct from the dose rate at a location. | IEC 61526 |
| Contamination monitors | Large-area thin-window detectors — pancake GM, gas flow proportional, thin plastic scintillator. | Surface activity (Bq/cm²) | Detection of removable contamination on surfaces, hands, clothing and equipment. | IEC 60325 |
| Neutron survey meters | Moderated thermal-neutron detector, typically a proportional counter inside a moderating sphere or cylinder. | Neutron ambient dose equivalent | Workplaces with a neutron field — accelerators, reactors, sealed neutron sources and transport packages. | IEC 61005 |
| Environmental monitoring equipment | Transportable, vehicle-mounted or permanently installed photon measuring equipment, usually reporting continuously. | Photon radiation, environmental levels | Site boundary and environmental networks, where levels are far below workplace values and the measurement runs unattended. | IEC 61017 |
| Installed dose rate meters and warning assemblies | Fixed detector, processing unit and warning devices, wired into the facility. | X and gamma dose rate, 50 keV to 7 MeV | Permanent installations in facilities, where the assembly must warn as well as measure. | IEC 60532 |
| Passive dosimetry systems | Integrating passive detectors read out later — thermoluminescence, optically stimulated luminescence and film. | Individual, workplace and environmental monitoring of photon and beta radiation | Legal dose of record over a wear period, read by a dosimetry service rather than by the wearer. | IEC 62387 |
Each row names the standard written for that instrument class; the standard column links to it. Only the first two rows have an evaluation tool on this site so far (IEC 60846-1:2009). The rest are close relatives — the evaluation logic rhymes, but the quantities and the acceptance rules do not transfer between them.
Quality control instruments
In this class the instrument serves as the reference: the machine is adjusted until it agrees with the meter, so the meter's own traceability determines the validity of the result.
| Instrument | Form and detector | Quantity | Used for | IEC standard |
|---|---|---|---|---|
| Diagnostic X-ray dosimeters | Solid-state or ionisation-chamber probe with a dedicated meter. Bench or table-top use. | Air kerma, air kerma rate, air kerma length product | Radiography, mammography, radioscopy and CT — verification of output, reproducibility and dose indices. | IEC 61674 |
| Dose area product meters | Flat transmission chamber permanently mounted at the tube collimator, within the beam. | Dose area product | Recording patient exposure per examination during routine clinical operation. | IEC 60580 |
| Radiotherapy dosimeters | Reference-class ionisation chamber and electrometer, used with a phantom and a defined measurement geometry. | Absorbed dose to water, air kerma | Establishing and verifying the dose delivered by a treatment machine. | IEC 60731 |
| Beam-quality and output test devices | Multi-parameter meters and test tools used with phantoms and test objects, often modality-specific. | Tube potential, half-value layer, exposure time, image performance parameters | Acceptance and constancy testing of imaging equipment in a medical imaging department. | IEC 61223 series |
IEC 61674 covers diagnostic dosimeters for radiography including mammography, radioscopy and computed tomography, for X-radiation generated at potentials up to 150 kV. IEC 60731 covers dosimeters with ionisation chambers used in radiotherapy, for absorbed dose to water or air kerma. IEC 60580 covers dose area product meters. The IEC 61223 series is different in kind — it does not specify the meter, it specifies the acceptance and constancy tests a medical imaging department performs on its equipment, part by part for each modality.
Performance characteristics by application
Both classes are evaluated for "energy response" and "linearity". The terms are identical and the requirements are not. The table below applies when comparing a specification sheet written for the other class.
| Characteristic | In protection | In quality control |
|---|---|---|
| Energy response | Must hold across a wide, largely unknown spectrum. Broad acceptance band. | Characterised at the specific beam qualities in use. Corrections are applied rather than tolerated. |
| Linearity | Across many decades of the measuring range. | Across the working range of the modality, which may be under one decade. |
| Angular response | Important — radiation arrives from wherever it arrives. | Largely irrelevant — the geometry is fixed by the test setup. |
| Statistical fluctuation | Dominant at low dose rates, where counting statistics limit what can be known. | Usually negligible — signal levels are high. |
| Response time | Critical. A slow instrument tells you about a hazard you already walked into. | Not a safety matter; integration windows are chosen deliberately. |
| Overload behaviour | Critical, and a genuine failure mode: an instrument that reads low in an intense field is worse than one that reads nothing. | Rarely tested — the field is known and bounded. |
| Alarm accuracy | Tested, because the alarm is the safety function. | Not applicable. |
| Environmental influence | Temperature, humidity, mechanical shock, electromagnetic fields — all field conditions. | Air density correction matters for open chambers; the rest is controlled away. |
Scope of this tool
RadiMeter implements the evaluation methods of IEC 60846-1:2009 — the protection side, and specifically the portable workplace and environmental instruments in the first three rows above. It applies to survey meters, dose rate meters and area monitors. It does not apply to the verification of a diagnostic or therapeutic beam: the quantity, the tolerances and the governing standard all differ, and the acceptance rules are not transferable.
The tool is built so that adding a standard means adding a definition rather than rewriting the program. Requests for additional instrument classes are collected through the contact page and determine the order in which they are added.