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

[Dalini]

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.

Cheers,
Dalini

[horvathd (Dávid Horváth)]

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:

Ignoring input

Dear Michaela, there are some issues with the material definitions in your input: The Americium 241 was not correctly defined, the atomic number was missing. In the element configuration you don’t need to specify the atomic weight (Am) unless you want to override the default. (See: https://flukafiles.web.cern.ch/flukafiles/manual/MATERIAL.html) Similarly, it is not necessary to fill the material number, FLUKA will automatically assign one. A low energy neutron cross section data set has to be…

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:

The following floating-point exceptions are signalling

Dear Li, the IEEE_UNDERFLOW_FLAG and IEEE_DENORMAL messages are normal, and can be ignored. The meaning of the message is explained on Wikipedia: In a normal floating-point value, there are no leading zeros in the significand; rather, leading zeros are removed by adjusting the exponent (for example, the number 0.0123 would be written as 1.23 × 10−2). Denormal numbers are numbers where this representation would result in an exponent that is below the smallest representable exponent (the expon…

Cheers,
David

[Dalini]

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