Uranium Decay Calculator - HELP

(last updated 18 Feb 2026)

Contents:

• Introduction · Material Input · Bibliography

Introduction

The calculator performs a complete decay analysis (i.e. including all branches) for the nuclides entered and all their decay products, according to [Bateman 1910]; minor nuclides are listed at the end.
Note: For the air kerma calculations, the air kerma coefficient K_air,δ for a hypothetical point source from [ICRP 2008] is used. It includes gamma rays, characteristic x rays, and inner bremsstrahlung, but does not necessarily cover all radiations from a real source.

The parameters used for the calculation can be set in the Material Input table. These parameters show reasonable initial values which can be modified as needed. There are no other hidden parameters used in the calculation. Any assumptions made for the calculations are described on this page.

The results for the List Time chosen are presented in numerical form in the Results table.

Half lives of radionuclides are shown in a color scheme changing from blue for long half lives to red for short ones.

The hazard from the point source air kerma rate is illustrated by the following icons:

• ☢   ≥ 100 nGy/h   (10 µrad/h)   - higher than typical background radiation
• ⚠   ≥ 10 µGy/h   (1 mrad/h)   - higher than average dose rate allowed for workers (20 mSv/a @ 2000 h/a)
• ⛨   ≥ 1 mGy/h   (100 mrad/h)   - annual allowed dose for workers (20 mSv) attained within 20 hours (and less)
• ☠   ≥ 1 Gy/h   (100 rad/h)   - radiation sickness after 1-2 hours, lethal after 3-4 hours (and less)

In addition, the results are optionally presented in an Output Chart showing the total series values for each series specified, or values for each individual nuclide, vs. time. The output chart type can be chosen as a line chart, a stacked area chart, or an animated bar chart.
Note: If the mouse pointer is hovering over the graph, the name of the nuclide under the pointer is shown above the graph (for stacked areas), or - along with data details - next to the pointer (for line charts).
Note: Please be aware that, in line charts, a nuclide curve may be hidden by others. Clicking on a nuclide name in the legend toggles the corresponding curve on/off.

The contents of the database for any nuclide can be checked with the "Query nuclide database" button (shows half-life, specific activity, possible parent nuclides, and decay products with branching ratios and decay type).
Note: Only alpha and beta decays are listed: in addition, each decay emits gamma radiation.

See special instructions for offline use of this calculator.

Other calculators of interest:

• Universal Decay Calculator for decay calculations of other nuclides, or for other nuclide mixes than covered by this calculator,
• External Radiation Dose Calculator (Virtual Geiger Counter) for dose calculations from shielded radiation sources,
• Nuclear Fuel Chain Waste Activity Calculator comparing activities and decay of the wastes arising from nuclear fuel production and power plant operation.
• Alpha-Neutron Reaction Calculator for determining the neutron radiation from spontaneous fission of uranium and from alpha-neutron reactions in some uranium compounds,

Material Input

Input

enter number (mandatory!) and select appropriate unit.

• If the checkbox "U in/as" is checked in combination with a mass unit, then the input means the uranium contents of the material selected, otherwise it means the mass of the material selected.
  
• If the unit "Bq U-238 in" is checked, the input mass is determined from the uranium-238 activity contained.
  
• If the unit "Bq U_nat in" is checked, the input mass is determined from the combined activities of the natural uranium isotopes U-238, U-234, and U-235.
  
• If the unit "Bq Ra-226 in" is checked, the input mass is determined from the radium-226 activity contained (this is in particular useful for mill tailings). It is assumed that Ra-226 is in secular equilibrium with its parent nuclide Th-230 and with all of its decay products.
  

Type

select appropriate type

Parameters: ore grade [% U] (used for types "ore" and "mill tailings")

Weight-percent of uranium contained in the ore removed from the ore body for processing in the mill. Other units used are % U₃O₈, among others (see also Unit Conversion). Ore grades being processed at present cover a wide range of 0.026% U (Rössing, Namibia) to 1.1% U (Key Lake, Canada). New uranium mining projects under develepment even have ore grades of up to 12.7% U (McArthur River Project, Canada).
Note: this parameter can also be used to assess the exposures to waste rock, by entering the appropriate uranium concentration.

Parameters: mill loss [%] (used for type "mill tailings")

Not all of the uranium contained in the ore is recovered in the milling process. The extraction losses are depending on the grade of the ore processed. Upon entry of an ore grade value, the calculator presents an estimated value for the Mill Extraction Losses. If you want to use another value for the losses, you can overwrite it.

Parameters: natural uranium (used for types U ... U₃O₈)

uranium obtained from natural sources. The U-238 and U-235 decay series are considered.

in equilibrium with progeny (used for natural uranium)

uranium of natural isotope composition, in secular equilibrium with its decay products (U-238 and U-235 series)

pure (used for natural uranium)

pure uranium of natural isotope composition, without decay products. (0.711 weight-% U-235; U-234 in equilibrium with U-238).

enriched to ... wt% U-235 (used for natural uranium)

pure uranium with U-235 contents enriched to level higher than natural. Values for use in pressurized water reactors (PWR) range between 3.6% and 4.1 wt-% (weight-percent), and for use in boiling water reactors (BWR) between 3.0% and 3.2%.

depleted to ... wt% U-235 (used for natural uranium)

Pure uranium with U-235 contents depleted to lower than natural level. Typical values range between 0.2% and 0.3%. This tails assay can be selected according to economic feasibilty. Since the concentration of U-234 in depleted uranium is depending on the product assay obtained in the enrichment process, an input is also required for this figure.

Parameters: recycled uranium (used for types U ... U₃O₈)

uranium obtained from recycling of spent fuel. The U-237, U-236, U-233, and U-232 decay series are considered in addition to the U-238 and U-235 series. Fission products and transuranics are not considered.
The composition of the uranium isotopes is determined according to the selection from the "burnup / initial enrichment" pick list, based on [Neghabian 1991]. The burnup unit GWd/tHM stands for Giga-Watt-days per metric tonne heavy metal. A 5 year storage time after reactor unload is assumed.

as is (used for recycled uranium)

uranium as is recycled from spent fuel

re-enriched to initial U-235 equivalent (used for recycled uranium)

recycled uranium re-enriched to initial U-235 equivalent; the actual U-235 concentration is higher to compensate for the presence of U-236.

depleted to 0.2 wt% U-235 (used for recycled uranium)

recycled uranium depleted to 0.2 wt% U-235

Output Parameters

Time

Enter numbers for Start, End and List time.
The numerical results displayed in the Results field are for the specified List Time, while the chart covers the whole time period from Start to End Time.
Note: In case of a linear time axis, the Start Time 0 is used, independent of the entry made.
Note: The List Time can also be set by clicking in the output chart.

Chart Type

Select option.

Chart Data

Select option.
"pt src air kerma" stands for point source air kerma at 1 m distance

Chart Detail

Select options.
If "skip minor nuclides" is selected, then the chart legend shows only those nuclides that are actually visible in the chart.

Chart Axes

Select option.
Note: The number of decades on the log. Y axis is automatically reduced, if there are no curves in the lower decades.

Bibliography

[Neghabian 1991] Verwendung von wiederaufgearbeitetem Uran und von abgereichertem Uran, von A.R. Neghabian, H.J. Becker, A. Baran, H.-W. Binzel, Der Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit (Hg.), Schriftenreihe Reaktorsicherheit und Strahlenschutz, BMU-1992-332, November 1991, 186 S.

[Bateman 1910] Harry Bateman: Solution of a system of differential equations occurring in the theory of radioactive transformations , in: Proceedings of the Cambridge Philosophical Society, Mathematical and physical sciences. Cambridge [etc.] Cambridge Philosophical Society. v. 15 (1908-10): Pages 423-427

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