[fluka-discuss]: Minimum distance to the nearest boundary: information about the DDNEAR variable.

From: Francisco Ogallar Ruiz <fogallar_at_correo.ugr.es>
Date: Mon, 04 Nov 2019 17:07:14 +0100

Dear FLUKA experts,

I am writing to ask several questions that are, in reality, the
continuation of an older discussion already started here in 2017 by
Chris Theis. In particular, I will refer to the information provided by
Lechner in his answer, which is available in the following link:
http://www.fluka.org/web_archive/earchive/new-fluka-discuss/10512.html .

Using the usrrnc.f routine, we are getting information concerning the
radionuclides created under some conditions in order to later use it for
further solid-state diffusion calculations. In this context, given the
position of a certain radionuclide, we would like to know, if possible,
the minimum distance to the nearest boundary in our FLUKA geometry.
Thanks to the discussion previously mentioned, we know that an
approximation to this distance (smaller than the real one) is available
sometimes (depending on the type of body it may not be calculated at
all). This variable is called DDNEAR and seems to be accessible in the
common CMMDNR. For our applications, we are still interested in using it
whenever it is available, but after some tests, there are some questions
that we would like to address with your help:

1. If we export DDNEAR during a call to usrrnc.f, are we really getting
the DDNEAR corresponding to our nuclide? Or are we accessing the DDNEAR
corresponding to the particle simulated just before the creation of the
radionuclide? If the second is correct, can we be positive that the
point with respect to which DDNEAR is calculated coincides with the
position of the radionuclide? Since DDNEAR is a purely geometrical
variable, this condition is enough for our purposes.

2. We have observed negative values of DDNEAR quite often (remember that
we always obtain it during a call to usrrnc.f). We would like to know if
this is a ”normal” outcome of its calculation since, even without real
physical meaning, for sure is a smaller value than the real minimum.

3. We have also noted that, for consecutive calls to usrrnc.f that
provides information about several radionuclides created in exactly the
same position, sometimes we obtain different DDNEAR for each of them.
But if the isotopes are in the same position, it should be the same.
After some tests, we have seen that the first one provided seems to be
the correct one. We suspect that this may be related to the first
question: maybe we are not accessing the DDNEAR corresponding to our
isotope, but something else. Could you shed some light on this?

Thank you very much in advance. Any help is highly appreciated.

Best regards,

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Received on Mon Nov 04 2019 - 18:17:12 CET

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