Simulating Radioactive Species

The GoldSim RT Module provides some specialized features to assist in simulation of radioactive species The chemical (or non-chemical, such as bacterial or viral) constituents that are stored and transported through an environmental system in a contaminant transport model. In GoldSim, the Species element defines all of the contaminant species being simulated (and their properties).. For practical reasons, you may often wish to enter and present inventories, concentrations, quantities and flux rates for radioactive species in terms of activity. As used here, the activity of a radioactive species represents the number of disintegrations per unit time (and should not be confused with the thermodynamic activity of a species).

To facilitate this, GoldSim allows you to specify that a species is radioactive. If the Radioactive checkbox is checked, GoldSim displays the specific activity A property of radioactive species, it defines the number of disintegrations per unit mass per unit time. It is typically defined in terms of Becquerels (Bq) or Curies (Ci) per gram (g). Bq and Ci both have dimensions of disintegrations per unit time.. (The Radioactive checkbox is cleared and grayed out in the CT Module).

The specific activity has units of activity per unit mass and is computed as:

(Avogadro's Number)(Decay Rate) / (Atomic Weight)

Activity (disintegrations per unit time) is measured in units of Becquerels (Bq) or Curies (Ci), so specific activity has units of Bq or Ci per unit mass. A drop-down list allows you to specify which of these units you wish to use.

In addition to displaying the specific activity here, the Species element always produces a vector A one-dimensional array. output consisting of the specific activities of each of the species. Note that, by definition, the specific activity of a non-radioactive species is zero.

Note: Some radioactive species decay into multiple daughter products (e.g., 95% of the disintegrations may produce species A, and 5% may produce species B). In this case, you should use the Stoichiometry to specify this "splitting". In this example, the Stoichiometry would be 0.95 for the first daughter, and 0.05 for the second daughter.