FLUKA simulations updated

The results of the simulations performed by the FLUKA team are available on EOS at this address: /eos/experiment/ntof/simul/phase4_NEAR/data_scoring_shielding_ext/. In this analysis, the results for 120 million proton primaries, stored in the first subdirectory 00___ are used.

A full description of these simulations is given in the "Report on FLUKA simulations for the NEAR Station", by J.A. Pavon Rodriguez and F. Garcia Infantes, presented at the NEAR Station Working Group meeting of May 2021.

The geometry adopted in the simulation is shown in the figure below. The position of the marble wall is at x = 250 cm with respect to the origin of the frame of reference. The center of the collimator hole, at its exit, is set at (x [cm], y [cm], z [cm]) = (250, 0, 15).

NEAR station geometry adopted in the new simulation

Here below, the distribution of all neutrons scored on the marble wall is shown on the left panel. On the right panel, only those neutrons emitted within a 10 degrees with respect to the x-axis direction are selected.

Neutron distribution at the marble wall (all)

Neutron distribution at the marble wall (θx < 10 deg)

The neutron flux, integrated over the full energy range, in n/cm2/ppulse, depends on the surface adopted for scoring the neutrons. The following figure shows this dependence. The scoring surface (circle) is set at position (250 cm, 0 cm, 15 cm), corresponding to the center of the collimator hole at the exit side. The energy integrated neutron flux value of the M81 configuration (simulations performed by Massimo Barbagallo) is shown for comparison. In all instances shown here, a standard ppulse of 7x10¹² protons is adopted.

Energy integrated neutron flux vs the radius of a scoring circle.

A table with the numerical data is available here >>.

Flux

The energy-dependent neutron flux, for a set of circular-surface score, with different R-values is shown in the plots below

R [cm]	ratio to M81 flux
1.0	1.91
Neutron flux	Isoletargic plot

R [cm]	ratio to M81 flux
3.0	1.70
Neutron flux	Isoletargic plot

R [cm]	ratio to M81 flux
5.0	1.02
Neutron flux	Isoletargic plot

R [cm]	ratio to M81 flux
10.0	0.28
Neutron flux	Isoletargic plot

-- AlbertoMengoni - 2022-01-09