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Radiation Lab RadCalc
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Limits of this dataset

Limits of this dataset

Every calculator here reads from one table of 147 nuclides covering 65 elements. What that table holds decides what the answers can mean, and several of the questions people arrive with cannot be answered from it at all. This page is a list of those, counted from the data rather than asserted, so that it stays true as the data grows.

Decay chains, beyond one step

The table holds nuclides, not chains. Where a nuclide's decay product happens also to be in the table, this site can compare the two and does — that comparison is what nuclides whose daughter sets the shield is built from, and it covers 7 of the 147. It is a one-step comparison and it stops there. Nothing here follows a chain down to its stable end, and no calculator on this site builds up a mixture and lets it evolve.

For 4 of them the next nuclide is not in the table at all: Ra-226 (decays to a nuclide not carried here), U-235 (decays to Th-231), U-238 (decays to Th-234), Ra-223 (decays to a nuclide not carried here). Those pages give the constant recorded for the nuclide itself and decline to draw a conclusion from it, because for an aged source of any of them the progeny supply most of the field and this table cannot say how much.

Branching ratios

The table records which decay mode a nuclide takes, not how the decays divide between modes when there is more than one. Nothing on this site therefore states what fraction of decays goes down a particular branch, and the daughter identities used in the comparison above follow from the decay mode and the atomic and mass numbers — arithmetic — rather than from a branching table. Where a nuclide has a mode not recorded here, its products are simply absent.

Photon lines below the cutoff

Air kerma rate constants are summed over recorded photon lines above 20 keV. The cutoff is a convention and it has consequences at both ends of the table. 46 nuclides have no photon line recorded at all, and a further 5 have lines that are all below the cutoff, so their constant is zero by that convention rather than by physics. A page that says no line is recorded is making a statement about this table, not about the nuclide.

Emissions the table does not describe

112 of the 147 carry no beta spectrum and 114 carry no alpha lines, so the corresponding sections are absent from those pages. Beyond that, some emissions are outside the scope of every calculator here: neutrons from spontaneous fission or from (α,n) reactions in the surrounding material, internal conversion and Auger electrons, and characteristic X-rays following electron capture where they are not in the recorded line list. For the heavy actinides in particular, a shield designed from the photon and alpha figures on this site is not a complete shield.

Pages not offered for indexing

10 nuclide pages are marked noindex and left out of the sitemap. All of them have half-lives under a second, which is short enough that the question a shielding calculator answers — how thick, of what — has no practical form. The pages remain and remain linked, because a decay chain can arrive at them; they are simply not offered to search engines as answers.

What the numbers themselves carry

Half-lives, photon energies and emission probabilities, beta maximum and mean energies, and alpha energies come from the IAEA Nuclear Data Section's Livechart interface, which serves ENSDF. Attenuation coefficients come from the NIST tables. Both are harvested once and committed, so results do not change between visits and the version is fixed. The derived quantities each carry their own approximation — beta ranges are a Katz–Penfold fit good to about ±10%, bremsstrahlung yield is a thick-target rule of thumb linear in atomic number and energy, and buildup is a fitted factor rather than a transport calculation. None of them is a substitute for a measurement, and this site is not a substitute for a dosimetry service.

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