Re: Residual radioactivity - metastable vs ground states

Dear George

Provided that you score with RESNUCLE activity (i.e., have RESNUCLE
associated with an irradiation profile and cooling time) FLUKA gives
results for all states, both ground and isomers (unless you switch it
explicitly off with RADDECAY/What(2)).

In your case of 196Au, for example, check the *_resnuclei_xx_sum.lis"
file:

The information on the ground state can be found in the wide table at the
beginning of the file. It is followed by a list for isomeric states, e.g.

  **** Isomers (Bq/cmc) ****
      A Z mth
...
      196 79 1 3.21E+07 +/- 99.0 %
      196 79 2 2.44E+06 +/- 99.0 %
...

where the third column indicates the isomer index.

However, please note that FLUKA cannot predict the correct branching for
the production of different states. Instead it equally distributes the
cross section over the different states.

Best regards
Stefan

Dear FLUKA experts,

According to the manual and some comments on the discussion board, when
predicting residual radioactivity using RESNUCLE card all the residuals
are scored in ground state and FLUKA does not distinguish between ground
states and isomeric states. However, when I try to predict residual
radioactivity in a 5-cm radius 10-cm long gold cylinder exposed to 1 GeV
electrons (same is true at lower energies), I get 2 different Au-196
isomers, which decay with half-lives that correspond to Au-196m (8.1
sec) and Au-196m2 (9.7 hours). Even though the second isomer should be
decaying to the first one 100% of the time (and establish equilibrium)
and both of these isomers should be decaying to the ground state of
Au-196 (half-life=6.2 days), the first isomer disappears several minutes
after the end of the irradiation (as if it wasn't generated by decay of
the second isomer) and the ground state is never scored. Could you
please explain what is going on, or tell me where this subject might be
discussed?
I saw the same when I ran this example with copper target: residual
radionuclides decay with half-lives that correspond to metastable states
and I never see ground states (of Co-60 for example).
Does this mean that if I calculate dose rates from the activated target
only the prompt radiation from those isomers will be contributing and
radiation coming from the decay of the ground states will be ignored?

Thank you very much for your time
 - George
Received on Mon May 10 2010 - 13:44:58 CEST