For teaching purpose, I have used for many years an example of FLUKA corresponding to a neutron beam line for the production of cobalt 60.
The example was based from the 13th Fluka Course that took place at NEA Issy-les-Moulineaux, Paris, France (The official FLUKA site: Course intro).
Here is the source code of this example. ex4.inp (3.0 KB)
The following figure shows the distribution of activity one week after the irradiation. We can clearly see the peak of activity at the target’s position with an activity of a few 10¹¹ Bq/cm3 in fair agreement with the theoretical value of 10¹² Bq/cm3 (the neutron capture cross-section of 25 meV neutron on cobalt 59 is of 40 barns).
After a break of a few years, I used again this example. Surprisingly, the activity in the target is far much lower than expected (~10⁶ Bq/cm³), of the same order of magnitude of what is obtained in the air while the activity induced in the shielding at the beam impact is more or less similar to what was obtained a few years go (~10⁸ Bq/cm³).
I do not see any cross section issue, considering that (e.g., with the latest FLUKA release 4-4.1, requiring by the way the neutron libraries for the - now default - pointwise treatment), I get the following plot:
Note that (possibly independently of your weird result, of which I miss the exact origin):
AUXSCORE should be removed, since it’s not meant for the here intended filtering;
When producing a 2D color plot, the averaging interval along the third dimension is not innocent: Flair takes by default your USRBIN y-range (which is 20 times more extended than your actual target height), while I limited it as indicated;
You are getting the activity after one year (third cooling time as requested in DCYSCORE) and not one week (first cooling time);
ACTOMASS gives Bq/g, ACTIVITY gives Bq/cm^3;
The LOW-MAT cards have no point, in view of the default pointwise treatment;
The atomic weight of the MATERIAL card has been deprecated (FLUKA already takes the proper value, which was often unintentionally overwritten by the user; the latter can still do it, if for good reasons, by inserting the desired value with the negative sign).
