The calculations you actually repeat, with the data behind them shown.
Seven tools for routine radiation protection work. Every constant is computed from open primary data — IAEA evaluated nuclear data and NIST attenuation coefficients — rather than copied from a handbook table, so you can see which assumptions produced the number.
Free and open. No sign-in, no account, nothing you type leaves your browser.
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Unit converter
How many becquerels is 5 µCi? How many Bq/cm² is 6000 dpm/100 cm²?
Activity, dose, dose equivalent, exposure and surface contamination — converted within each quantity, never across.
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Decay and half-life
How much is left after 18 months? When does this source drop below the limit?
Activity after elapsed time, the time to reach a target, half-life from two measurements, and decay chains.
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Gamma dose rate and shielding
What is the dose rate at 2 m from 37 GBq of Ir-192, and how much lead brings it under 20 µSv/h?
Point-source dose rate from the emission spectrum, with attenuation and buildup, and the shield thickness solved backwards.
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Mass and activity
How many grams of Pu-239 is 1 GBq? What is the specific activity of Sr-90?
Grams to becquerels and back for 147 nuclides, from half-life and mass number.
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Detection limits (MDA / MDC)
What can this counter actually detect in a 10-minute count? How slowly must I scan?
Critical level, detection limit and minimum detectable activity for fixed counting, plus scan MDC with observer efficiency.
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Beta dose rate and shielding
How thick must acrylic be to stop Y-90 beta, and how much bremsstrahlung does lead make instead?
Infinite-medium dose rate, Katz–Penfold range, transmission through absorbers, and bremsstrahlung yield by atomic number.
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ALARA and job planning
How long can two workers stay? How far back must the barrier go?
Inverse square, stay time against a dose budget, collective dose across tasks, and half- and tenth-value layers.
Why the constants are computed, not copied
A gamma dose rate constant taken from a table is a single number whose assumptions are invisible. You cannot see which photon lines were included, which low-energy cutoff was applied, or which evaluation of the decay data it came from — and those choices change the answer. For Am-241, moving the cutoff from 20 keV to 10 keV raises the constant roughly eightfold.
So this site computes the constants instead. Photon energies and emission probabilities come from the IAEA Livechart interface to the evaluated nuclear structure data; mass attenuation and mass energy-absorption coefficients come from the NIST tables. Summing over the spectrum gives the constant directly, and the cutoff becomes a control you can move rather than a hidden assumption. The computed values agree with published constants to within about 2% for the well-characterised nuclides, and that comparison is part of the test suite.
What is covered
147 nuclides, of which 96 emit photons and 45 emit only beta or alpha radiation — the pure beta and alpha emitters that dominate waste characterisation and decommissioning work, including H-3, C-14, Ni-63, Sr-90, Tc-99, I-129, Zr-93, Se-79 and the transuranics. Eight shielding materials with attenuation data from 1 keV to 20 MeV.
What is deliberately absent
Skin dose from surface contamination is not calculated, because doing it properly needs a point kernel over the source geometry and the answer is very sensitive to inputs a simple form cannot capture. Buildup factor coefficients are not shipped, because the standard tabulation is the body of a paid consensus standard; the buildup form is implemented and takes coefficients you supply. Where a calculation would be misleading without information the tool does not have, it says so rather than returning a number.
None of this replaces an accredited calibration, a shielding design, a dose assessment or a survey. It is for orientation, for cross-checking something you have already calculated, and for seeing how an answer moves when an assumption does.