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Universal Decay Calculator - HELP

(last updated 19 Jun 2024)



This calculator performs radioactive decay and air kerma calculations for any nuclides or nuclide mixes.

Initial activities of up to 16 nuclide series can be defined in the Nuclide Input table. For a time given in the Output Parameters table, the resulting activities of the nuclides given, plus those of any decay products growing in are calculated.
The calculator moreover assesses the radiation hazard from the nuclides by calculating the air kerma (kinetic energy released per unit mass: the kinetic energy of charged particles liberated by photon and neutron interactions per unit mass), whereby the nuclides are treated as a point source.
The database contains a total of 1252 nuclides.

The calculator performs a complete decay analysis 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 Kair,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 results are presented in numerical form in the Results table for the end time specified, and optionally, in an Output Chart showing the total series activities for each series specified, or individual nuclide activities, vs. time. The output chart type can be chosen as a line chart, a stacked area chart, or an animated bar chart.
If charts are enabled, computing time may increase. Please be aware that in line charts, a nuclide may hide one or more others.
The contents of the numerical result field can be marked and copied to the clipboard for further use.

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 that only alpha and beta decays are listed: in addition, each decay emits gamma radiation.

See special instructions for offline use of this calculator.

For decay calculations of uranium, the Uranium Decay Calculator offers more options, such as a variety of uranium compounds found in the uranium mining and nuclear fuel industry, and the inclusion of decay energy results.

For comparison of the activities of the various wastes produced during nuclear fuel production and use, see the Nuclear Fuel Chain Waste Activity Calculator.


Nuclide Input

Enter initial activities for each nuclide in up to 16 nuclide series, or select one of the pre-defined nuclide mixes from the sample data pick list: *) strictly speaking, the term "natural thorium" is nonsense; here it is used for Th-232 in secular equilibrium with Th-228.
Activity Unit
the selected unit is used for all activity entries in this table

Series Name
Enter nuclide name using the notation  Th-232 , for example.
Enter here the first member (for which an activity is to be specified) of a decay series, or a nuclide which is not a member of a series.
The name is checked with the database immediately on entry. If the nuclide is not found, the available nuclides resp. elements are listed.
Upon entry of a valid nuclide name, all decay products are listed in the "Nuclide Name" pick list; minor nuclides are listed at the end.

Nuclide Name
Select nuclide within the series, for which an activity value is to be entered or viewed.

Initial Activity
enter number for initial activity of the nuclide selected in the "Nuclide Name" pick list.
(uses Activity Unit selected at top of table)

check, in case only the pure nuclide shown in "Series Name" is present initially. The activities of all decay products are set to zero.

check, in case the decay products of the nuclide shown in "Series Name" initially are present in secular equilibrium. The activites of all decay products are initialized to the equilibrium state.

check, in case individual entries are to be made for the initial activities of each nuclide in the series.
If only single nuclides of the series differ from the "Pure" or "Equil." state, select the appropriate button first, and then select "Indiv." and change the activity of the desired nuclide(s).

Note: it is possible, though not advisable, to explicitly specify a nuclide as a series which also is a member of the decay series of another nuclide entered. In this case, all calculations are performed independently, leading to multiple listing of the nuclide and any decay products in the result.


Output Parameters

Enter numbers for Start, End, and List time and select appropriate time unit.
The numerical results displayed in the Results field are for the specified List Time, while the charts cover the whole time period between Start and End time.
Note: For List Time = 0, the numerical result shows all initial activities.
Note: In case of a linear time axis, the Start time 0 is used, independent of the entry made.

Chart Type
Select option.

Chart Data
Select option.
If "air kerma" is chosen, select air kerma unit and enter air kerma point source distance [m]

Chart Detail
Select options.
If "skip minor nuclides" is selected, then the chart legend shows only those nuclides that are visible in the chart. The number of minor nuclides can further be reduced by reducing the "Decades on log. Y axis" value, if "log. Y axis" is chosen for line charts.

Chart Axes
Select option.


[ICRP 2008] ICRP Publication 107: Nuclear Decay Data for Dosimetric Calculations , by A. Endo and K.F. Eckerman, 2008

[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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