module for calculations involving radioactive decay?

[frederik aa de jonge]

does anybody know of a package/module which will facilitate/simplify
calculations with radioactive samples?
as a minimum spec:
- user definable list of radionuclides + names + halflives (expressable in
time units like sec min etc as appropriate)
- choice of units (Bq or Ci, with appropriate modifiers kGM etc
- initial activity at given time (sample calibration)
- activity calculation at other times, taking into account timezones
- operators: add, subtract to simulate adding or removing activity
(needs an "history" mechanism, so that activity at time T is always
correctly calculated)

any help kindly appreciated
Frederik