Optimization of Scintillating simulation

Physics, Transport and Magnetic Fields
1

I am implementing a simulation for the generation of scintillation photons in an optical fiber with 1 mm diameter and 1 m long. The scintillating (optical) will be produced by the excitation of an external source. In a first attempt, I am using electrons of 2.28 MeV impinging at a 45º angle laterally.

The fiber is made of polystyrene and is placed in air. The materials have the following optical properties (OPT-PROP):

AIR: n=1, no attenuation

POLYSTR: n=1.59, Attenutaion length = 400 cm (0.0025 cm^-1)

Since the scintillation emission range is between 400 and 600 nm, with a maximum at 450 nm, I placed a card with WV-LIMIT with these parameters for each material. I also introduced a card for quantum efficiency (SENSITIV) of 33% (0.33).

Regarding scintillation production (OPT-PROD/SCINT-WV), I am considering only emission in polystyrene with the following parameters:

Single emission: 450 nm (2.8 eV)

Decay time: 2.8 ns

fraction = 2.8E-6 MeV x 12 000 photons/MeV = 0.033.

The Cerenkov radiation is switched off for the moment.

About scoring, I am only considering now three USERBIN (in bin format) to obtain the spatial distribution of the fluence of electrons, photons, and optical photons in the fiber and around it. I am using PRECISIO defaults and have not implemented any bias or cuts.

Even with only 1000 primaries, the simulation takes a long time and hangs in 1st cycle. With 10 primaries I was able to complete the simulation, but when processing the five cycles I get the message:

At line 239 of file usbsuw.f

Fortran runtime error: Index ‘81000000’ of dimension 1 of array ‘gmstor’ outside of expected range (60000000:1)

When I tried a larger volume of scintillating material (I tried with a 4 cm x 4 cm x 4 cm polystyrene box), it could not even complete the first cycle after 48 hours. I believe I am producing too many scintillating photons and I would like some help on how I can optimize the simulation… (inp file: electronfibre.inp (2.0 KB) )

Thanks in advance,
Jorge Miguel Sampaio

2

Dear Jorge,

I can answer the issue with the post processing program usbsuw. It has a limitation on how many bins it can process in one file. This limit was set to 60 million in FLUKA 2011-3.0

In FLUKA 4-0.0 this limitation has been removed.

Cheers,
David

PS.: FLUKA 4 currently has a bug preventing the use of optical photons.

3

Dear Jorge,

your input file runs at a reasonable speed (1.5 min / 10’000 primaries), so the issue should be with the system you are using.

Could you tell your the operating system, memory size, etc. of your PC?

Cheers,
David

4

Dear Dávid,

Thanks for the prompt answer. Indeed the binning was a problem and now I managed to produce plots. Now I am running the same example with 1000 primaries (5 cycles) using the FLUKA-Docker (version 2020.0.3) on my mac osX (2,8 GHz Dual-Core Intel Core i7, 16 GB 1600 MHz DDR3). The speed is about 1 second/primary, which is considerably slower than yours.

I will move the simulation to the FARM of my institute that has several processors with 4 cores (Intel® Xeon® CPU L5420@ 2.50GHz) to see if it improves.

My goal is to use an external LED source to produce the scintillation. In this case, I don’t know if it is possible to use optical photons as primaries, or should I use “normal” photons to ensure that the energy is deposited and the scintillation is produced?

Cheers,
Jorge

5

Dear Jorge,

FLUKA 2020.0.3 is not supported on this forum.

We only provide support for FLUKA 4-0.0 distributed at https://fluka.cern

Cheers,
David