Occupational radiation dose estimation for NORM-handling environments
Dose Rate: enter source activity and distance to calculate the gamma dose rate and annual exposure estimate.
Activity: enter a target dose rate and distance to find the source activity that would produce it.
Shielding: enter activity, distance, and a target dose rate to calculate the required shield thickness for a chosen material.
Distance: enter activity and a target dose rate to find the minimum safe working distance.
Enable secular equilibrium for isotopes with active decay chains (Ra-226, Ra-228, Rn-222, etc.) to include progeny gamma contributions. Results are point-source estimates for planning purposes only.
Type any value into any field; all other units in the same group update instantly. Each block is independent: activity, dose equivalent, absorbed dose, air/water concentration, and mass/surface concentration convert separately. Clear a field or type 0 to reset a group.
Dose rate: multiply by 1000 to convert µSv/hr → mSv/hr, etc. 1 Sv = 100 rem (photon Q=1).
1 pCi/L = 37 Bq/m³. Radon reference level (WHO): 100 Bq/m³. ICRP action level: 300 Bq/m³.
| Material / Setting | Isotope | Typical Range (Bq/g) | Notes |
|---|---|---|---|
| Background soil (global) | Ra-226 | 0.01 – 0.05 | Global crustal average ~0.025 Bq/g |
| Background soil (global) | Th-232 | 0.02 – 0.05 | Global crustal average ~0.030 Bq/g |
| Background soil (global) | K-40 | 0.1 – 0.6 | Depends heavily on soil type |
| Oil & gas scale (TENORM) | Ra-226 | 0.1 – 1000+ | Highly variable; pipe scale can be extreme |
| Oil & gas scale (TENORM) | Ra-228 | 0.1 – 100 | Ra-228/Ra-226 ratio varies by reservoir |
| Water treatment sludge | Ra-226 | 0.1 – 10 | Groundwater processing |
| Mineral sands (ilmenite, zircon) | Th-232 | 1 – 100 | Depends on ore grade and mineral fraction |
| Phosphate fertiliser | U-238 | 0.1 – 1.5 | Ra-226 often in secular equilibrium |
| Coal ash / fly ash | Ra-226 / Th-232 | 0.05 – 0.5 | Enriched ~5–10× vs raw coal |
| Uranium ore (mill feed) | U-238 | 0.3 – 30+ | 0.03% = ~3.7 Bq/g U-238 |
Activity (Bq / Ci): The becquerel (Bq) is the SI unit of radioactivity: one nuclear disintegration per second. The curie (Ci) is the legacy unit; 1 Ci = 3.7 × 10¹⁰ Bq. In NORM characterisation, source terms are typically expressed in Bq/g (specific activity), Bq/kg (bulk concentration), or total Bq for discrete sources. Reporting in Bq is required under most modern regulatory frameworks; Ci remains common in US oil and gas TENORM.
Dose equivalent (Sv / rem): The sievert (Sv) accounts for radiation weighting factors. For gamma radiation the quality factor Q = 1, so 1 Sv = 1 Gy numerically for gamma dose. Occupational limits are expressed in mSv/yr (ICRP: 20 mSv/yr averaged over 5 years; US NRC/OSHA: 50 mSv/yr). The rem is the legacy unit; 1 Sv = 100 rem.
Air / water concentration (Bq/m³ / pCi/L): Used for radon and dissolved radionuclide assessments. The WHO radon reference level is 100 Bq/m³; ICRP action level is 300 Bq/m³. 1 pCi/L = 37 Bq/m³. Groundwater radiological assessments often report in Bq/L or pCi/L depending on jurisdiction.
Mass / surface concentration: Bq/g and Bq/kg are used for solid material characterisation (soils, scale, sludge). Surface contamination is reported in Bq/cm² or dpm/100 cm². The dpm (disintegrations per minute) is a counting unit: 1 Bq = 60 dpm. Clearance levels for NORM waste under IAEA guidelines are typically expressed in Bq/g.
Enter the isotope, a known activity at a reference date, and a target date to calculate the activity at that point in time. Future dates give forward decay; past dates give back-calculation.
Enable secular equilibrium progeny to list the expected activity of short-lived daughters at the target date (useful for Ra-226, Ra-228, Th-228, Rn-222).
The target activity field is optional; if filled, the tool calculates the date on which the source will reach that activity level. Useful for planning storage-to-decay timelines or scheduling re-assay.
Enter measured activity concentrations (Bq/g) for each NORM isotope present. The tool compares each value against IAEA GSR Part 3 (2014) clearance levels, the EU Basic Safety Standards Directive 2013/59/Euratom indicative thresholds, and ARPANSA RPS C-1 (2020) reference levels. Leave fields blank if an isotope has not been measured. Results indicate whether each isotope and the material as a whole may require regulatory attention.
Note: this tool provides a first-pass screening only. Regulatory requirements for NORM depend on the jurisdiction, industry, material form, and exposure pathway. Formal assessment must be conducted by or under the supervision of a qualified health physicist or Radiation Protection Adviser.
| Isotope | Decay series | Measured (Bq/g) | IAEA clearance (GSR Part 3 Table I) |
EU BSS (2013/59/Euratom) |
ARPANSA (RPS C-1) |
EPA (US) DW† (drinking water) |
Status |
|---|
IAEA GSR Part 3 (2014) Table I provides unconditional clearance levels — activity concentrations below these values are cleared from regulatory control in all circumstances. Values for natural radionuclides in secular equilibrium: U-238 series (incl. Ra-226, Pb-210) 1 Bq/g; Th-232 series (incl. Ra-228, Th-228) 1 Bq/g; K-40 10 Bq/g. The IAEA also recognises that for large quantities of NORM, conditional clearance may be applied with site-specific assessments.
EU BSS Directive 2013/59/Euratom Annex XVI requires Member States to regulate NORM industries where worker doses may exceed 1 mSv/yr above background. For building materials, an Activity Concentration Index is used. For industrial NORM, the 1 Bq/g threshold is a widely cited indicative value but specific regulatory requirements vary by Member State and industry.
ARPANSA RPS C-1 (2020) sets out the regulatory framework for naturally occurring radioactive material in Australia. The Schedule 2 threshold for regulation of NORM activities is based on source or practice. Uranium and thorium series nuclides in concentrations exceeding 1 Bq/g (or 10 Bq/g for K-40) may be subject to state/territory radiation protection legislation. Contact your state/territory regulator for specific obligations.
Ra-226 and Ra-228 deserve particular attention in NORM screening: they are highly radiotoxic due to bone-seeking behaviour, are significant contributors to occupational dose in oil & gas and mining, and may have lower clearance thresholds than the generic IAEA values in some national frameworks. Always verify current regulatory thresholds with your local radiation authority.
US TENORM (EPA / state regulation): The United States does not have a single federal NORM/TENORM regulatory framework. The US EPA regulates naturally occurring radioactive material under the Safe Drinking Water Act (radionuclide rule, 40 CFR 141) and the Clean Air Act, but TENORM (Technologically Enhanced NORM) from industrial processes is largely regulated by individual states under their own radiation protection programmes. TENORM regulations vary significantly — some states have adopted IAEA-consistent clearance levels (≈1 Bq/g), while others apply lower or higher thresholds. Key sectors subject to US state TENORM regulation include oil and gas (piping scale, produced water), uranium mining legacy sites, phosphate processing, and drinking water treatment residuals. Always consult the relevant state radiation control programme before disposing of or releasing TENORM materials.
† EPA (US) DW column: drinking water maximum contaminant levels (MCLs) from 40 CFR Part 141 (National Primary Drinking Water Regulations). These are drinking water standards and are not directly comparable to solid material Bq/g concentrations. Shown for informational reference only. Ra-226+Ra-228 MCL is combined 5 pCi/L; gross alpha MCL (excluding U and Rn) is 15 pCi/L; uranium MCL is 30 µg/L.