Methods and data

Sources

Nuclear decay data — half-lives, decay modes, photon energies and emission probabilities, beta maximum and mean energies with branch intensities, and alpha energies and intensities — are retrieved from the IAEA Nuclear Data Section's Livechart interface, which serves the evaluated nuclear structure data file (ENSDF). Photon mass attenuation coefficients and mass energy-absorption coefficients are taken from the NIST X-Ray Mass Attenuation Coefficients tables, covering 1 keV to 20 MeV, and are interpolated logarithmically in both energy and coefficient.

• IAEA Nuclear Data Section — Livechart API (ENSDF)
• NIST X-Ray Mass Attenuation Coefficients

Both datasets are harvested once and committed to the source repository rather than fetched at runtime. Results therefore do not change between visits, the site does not depend on an external service being up, and the data version is fixed and auditable.

Gamma constants

The air kerma rate constant is computed as Γ = Σ E_i·y_i·(µ_en/ρ)_air(E_i) / 4π, summed over photon lines above the low-energy cutoff δ. The default δ is 20 keV, the conventional value used by published compilations. Because the sum is performed at calculation time rather than baked into the data, δ is adjustable in the shielding calculator.

Air kerma and µSv/h targets

Every gamma dose rate in these calculators and on the nuclide sheets is an air kerma rate, worked out in gray per hour. Targets and action levels are usually written in sieverts — the 20 µSv/h the nuclide sheets work to, or a survey reading in µSv/h. Wherever a page sets an air kerma rate against such a figure, and wherever the gamma calculator shows its result in µSv/h or mSv/h, 1 µGy of air kerma is counted as 1 µSv. The values are unchanged: no energy-dependent conversion is applied in these calculators or on the sheets. The Field Pro workbench, a separate tool, does apply spectrum-averaged H*(10) coefficients to its Cs-137 and Co-60 reference fields.

That is a convention, not an identity. Area survey meters are calibrated in ambient dose equivalent, H*(10), and its ratio to air kerma depends on photon energy. ICRP Publication 74 tabulates the ratio for photons in its Table A.21; some of its values:

From 30 keV upwards the ratio is above one: largest, about 1.7, between 50 and 100 keV, and between 1.15 and 1.21 across the energies of Cs-137 and Co-60. For those photons an H*(10) reading of the same field is higher than the figures here, by 10 to 74 per cent, so a thickness that brings the air kerma rate to 20 µGy/h leaves somewhat more than 20 µSv/h of H*(10). Below 30 keV the ratio falls quickly and passes under one — 0.61 at 20 keV, the cutoff used here — so for the softest lines the air kerma figure is the higher of the two.

Two consequences follow. A sheet's statement that a gigabecquerel at a metre is already under 20 µSv/h can fail in H*(10) for a nuclide close to that line. And taken the other way, a survey reading in µSv/h entered into the gamma calculator is read as air kerma, so an activity worked back from it comes out high by the same ratio.

The unit converter keeps the two quantities apart and offers no such conversion. On the nuclide sheets and in the gamma calculator the one-to-one reading is flagged where it is used, with a link to this section.

Validation

The engine is covered by automated tests that run on every change. Specific activities for Co-60, Cs-137, Pu-239, U-238, Am-241, Sr-90 and H-3 agree with published values within 1%, and the NIST attenuation coefficients are checked at five points, four within 0.5% and an interpolated value for lead at 662 keV within 1.5%. Computed gamma constants are not compared with published constants, which describe a different quantity and often do not state the cutoff they apply: tests hold the constants of Cs-137, I-131, Cs-134, Co-60 and Ir-192 within 2% of fixed reference values set when the engine was written, so that a large unintended change shows, and the validation report checks the unit chain, the table interpolation and a sample of emission lines instead. Field rules of thumb are also checked for order of magnitude — one curie of Co-60 at one metre computes to 1.29 R/h against the remembered 1.32, and Cs-137 to 0.325 against 0.33 — but a remembered number is not a citable source, and those two checks are labelled as what they are rather than as validation.

Analytic identities are tested rather than asserted — one half-life leaves exactly half, one half-value layer transmits exactly 0.5, doubling the distance quarters the dose rate, and quadrupling the count time improves the detection limit by exactly two.

Passing tests are evidence to whoever can read them. Where a calculation can be worked by hand from a published definition, the working itself is published, so that the result can be checked without taking the test suite on trust. The validation reports set out that working in full, name the sources each expected value comes from, and state how much of the tool has actually been covered. 7 of the 8 calculators have one — Unit converter, Decay and half-life, Gamma dose rate and shielding, Beta dose rate and shielding, Mass and activity, Detection limits (MDA / MDC), ALARA and job planning. The X-ray tube spectrum has no worked report; its results rest on the automated tests and the check stated on its own page.

Known limitations

• Point-source geometry in air. No room scatter, skyshine, source self-absorption or capsule.
• Gamma dose rates are air kerma; against a µSv/h target, 1 µGy is counted as 1 µSv (above).
• Attenuation without buildup is a narrow-beam result and underestimates behind thick shields.
• Buildup coefficients are not supplied; the Berger form accepts values you provide.
• Skin dose from surface contamination is not calculated.
• Decay chains assume a simple unbranched series.
• Beta range uses the Katz–Penfold empirical fit. It gives a depth of penetration, not the path length, and no accuracy is claimed for it here — see the validation report.
• Bremsstrahlung yield uses a thick-target approximation and is an order-of-magnitude guide.

How to cite

If a figure from this site ends up in a report, a procedure or a paper, cite the source of the underlying data rather than only this site — the evaluated data are the IAEA's and NIST's work, and the value of a citation belongs with them. Cite this site in addition when it is the derivation, not the input, that you are relying on: the gamma constants, the spectrum-solved half-value layers and the per-line dose shares are computed here and appear in this form here.

This site

Min, J. RadCalc — nuclide reference sheets and spectrum-solved shielding for radiation protection. Radiation Lab. 10.5281/zenodo.22794265

The source and the data it carries are deposited with Zenodo, which mints the identifier above and keeps a copy independently of this site and of GitHub. Quote that identifier rather than a URL: it is the thing that is meant to still resolve when the address has moved.

It is a concept DOI, so it always resolves to the most recent deposit. If you need the exact state you worked from — because a number you quote must stay quotable — take the version DOI of that release from the record page instead. Both are listed there.

The committed datasets do not change between visits. They change when the upstream evaluations are re-harvested or when an error in them is corrected; each change is listed under Changes to the calculators and data and goes out in a release with its own version DOI.

The decay data

IAEA Nuclear Data Section, Livechart of Nuclides — evaluated nuclear structure and decay data (ENSDF), International Atomic Energy Agency, Vienna.

Used with acknowledgement under the IAEA website terms of use, which permit reproduction and dissemination of IAEA data provided the IAEA is credited as the source. The IAEA does not endorse this site, its methods or its results.

The attenuation coefficients

J. H. Hubbell and S. M. Seltzer, Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients from 1 keV to 20 MeV for Elements Z = 1 to 92 and 48 Additional Substances of Dosimetric Interest, NISTIR 5632, NIST Standard Reference Database 126, National Institute of Standards and Technology, Gaithersburg MD (data content last updated July 2004). doi:10.18434/T4D01F

NIST Standard Reference Database 126, © 1989, 1990, 1996 by the U.S. Secretary of Commerce on behalf of the United States of America, all rights reserved. Used here for computation with attribution. NIST does not endorse this site and makes no warranty as to the accuracy of any result derived from these data.

Note that these tables are a NIST Standard Reference Database rather than a public-domain work of the United States government. A transcription of them is present in the public source tree, because the code computes with them; that file is covered by the NIST terms above and not by the MIT licence this site is released under, and it is not offered as a dataset or as standard reference data. Anyone wanting the tables themselves should take them from NIST.

What is not carried

The formulas above describe what is computed. What the underlying table does not hold — decay chains past one step, branching ratios, photon lines below the cutoff, and the emissions no calculator here describes — is counted in limits of this dataset.

How the pages are written

The figures and tables on the calculator and nuclide pages, and the summary sentences at the top of each nuclide page, are computed from the data described above rather than written by hand, so a correction to the data carries through to every page that uses it. The prose around them, from the tool guides to the notes on each nuclide page, is written by the author, who sets the scope and direction of every page and takes responsibility for its content; AI models assist with drafting. A note that ends with a list of sources is prepared from those sources and checked against them in two automated review passes. In October 2026 the author, who works in the radiation field, reviewed all 40 notes that then carried a source list, reading each in full and verifying its facts against professional knowledge. Notes add context and change no computed value.

Corrections

If a value here disagrees with a source you trust, the disagreement is worth reporting — several figures in the test suite exist because a check found an error during development. Contact details are on the contact page. What has been corrected since the first release, and which figures it moved, is listed under Changes to the calculators and data.