Re: Isomers

From: Alfredo Ferrari <>
Date: Sun, 18 Sep 2011 18:00:11 +0200

Hi Chris

it is possible to include correct branchings for isomer production, but
only for low energy neutrons (that is for neutron interactions below 20
MeV). This will likely show up in the next release and is quite a
substantial work (involving also one of your RP colleagues).

For all other reactions (neutrons above 20 MeV, and all other particles),
the prediction of correct ground state/isomer ratios would imply
spin-parity dependent calculations (so called Hauser-feshbach approach) in
the evaporation part, which to my knowledge have never been implemented in
any Monte Carlo because too slow and complex. Some non Monte Carlo codes
are able to perform such calculations, for protons and neutrons only and
only below 150 MeV, however their success in predicting these ratios
has been spotty. There is no short/medium plan term to implement something
along these lines in FLUKA (and likely there will never be for the above
reasons). Something simpler, albeit less accurate, will be implemented in
some specific cases where enough informations about the deexcitation paths
are known.

In your case (Ag-110m), it would be important to know the reactions which
produce that isotope in your problems, an information that you can easily
derive from FLUKA user routines. Again, production related to low
energy neutrons (and to low energy neutron induced fission to some extent)
can be cured.

                     Best regards

| Alfredo Ferrari || Tel.: + |
| CERN-EN/STI || Fax.: + |
| 1211 Geneva 23 || e-mail: |
| Switzerland || |

On Fri, 16 Sep 2011, Chris Theis wrote:

> Dear colleagues,
> we are currently looking into the assessment of the radiological risk of
> various materials and in connection with this we're studying the various
> isotopes produced. In this context the production of isomers becomes
> important and to my knowledge FLUKA uses a fixed branching ratio of
> 50:50 between ground state and isomeric states. For some cases this
> approximation may have negligible impact but for others it might result
> in gross under- or overestimation. For Ag-110m we found that the
> production is for example overestimated by a factor of ~11 due to this
> equal branching ratio. Depending on the respective material composition
> such factors could of course have a notable impact on the classification
> and the associated radiological risk.
> Some time ago it was discussed to include physically correct branching
> ratios for the production of ground and isomeric states and I wanted to
> ask what is the current plan and, if known, time frame regarding their
> implementation.
> Thanks a lot for your help
> Chris
> ----------------------------------------------------------------------------------------
> Chris Theis
> CERN/DGS-RP - European Organization for Nuclear Research
> 1211 Geneva 23, Switzerland
> e-mail:<>
> www:
> ----------------------------------------------------------------------------------------
Received on Sun Sep 18 2011 - 18:49:05 CEST

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