Fluka stopped in Lowset: undefined atomic density for the low en. xsec mat

Dear all,

I am trying to run a simple script to determine the neutron spectrum at different theta-positions of a spherical detector. However, when I try to run the script, Fluka terminates the process and Flair spits the notification “Finished with errors”. I inspected my output files and see the following note in each of the generated log files IEEE_UNDERFLOW_FLAG IEEE_DENORMAL

I’ve attached my flair and inp files for reference. There are 5 instances of the input file as I’ve spawned the job.

epithermalstudies.flair (6.2 KB) epithermalstudies_test_05.inp (6.4 KB) epithermalstudies_test_04.inp (6.4 KB) epithermalstudies_test_03.inp (6.4 KB) epithermalstudies_test_02.inp (6.4 KB) epithermalstudies_test_01.inp (6.4 KB)

Thanks in advance.


Dear Danili,

the real error message is at the and of the .out file:

Fluka stopped in Lowset: undefined atomic density for the low en. xsec mat. corresponding to the Fluka comp. mat. n. 27

The issue in your input is that you assigned a low energy neutron cross section to the compound H2O with a LOW-MAT card, which is incorrect. Only elements need to have a cross section assigned. More on this see point 4 of this post:

There is an incomplete PHYSICS card in your input as well. In Flair it seems the CHARMDEC option is selected, but in the input file the card is empty.

The IEEE_* warnings are normal. For a more detailed explanation see:


Dear David, thanks for your response. It was very helpful for clarifying numerous issues.