Dear all,
I am simulating reactions that produce the Ta-181 at excited states.
According to ENSDF (Evaluated August 2005), for Ta-181 the ground state, first and second excited states of Ta-181 are:
Energy (keV) Jpi T1/2
0.0 7/2+ stable
6.237 9/2- 6.05 microseconds
136.262 9/2+ 39.5 picoseconds
The expected (and experimentally observed) decay of the 136.3 keV state is 100% to the ground state.
So, the only observed gamma ray has 136.3 keV.
But in simulations with Geant4, there is also a branch to the metastable 6.2 keV, which is forbidden by selection rules (9/2+ → 9/2-).
My simulated spectrum has two gamma rays: besides the expected 136.2 keV, Geant4 generates the forbidden 130.0 keV gamma ray.
I do not understand very well all the information of the Photon Evaporation files, but for Tantalum 181 I see the following lines in the beginning of the file
… data/PhotonEveporation5.5/z73.a181:
0 - 0 -1 3.5 0
1 - 6.237 6.05e-06 -4.5 1
0 6.237 100 2 0 70.5 0 0 0 0 0.06528 0.1154 0.2236 0.1733 0.2377 0.1847
2 - 136.262 3.95e-11 4.5 2
1 130.025 100 2 0 1.75 0 0 0 0 0 0 0 0 0 0
0 136.262 100 304 0.396 1.75 0.793 0.1114 0.03031 0.01789 0.02501 0.007486 0.00456 5.414e-05 4.24e-05 0.01025
It seems to me that there are two branches for the second excited state, one with 130.025 keV and another one with 136.262 keV.
I hope someone can fix this problem. And maybe it occurs also for the deexcitation of other nuclei.
Regards.
Mauricio Moralles