[fluka-discuss]: Neutron output - big difference in results

From: babintsev <babintsev_at_ihep.ru>
Date: Tue, 15 Jan 2019 15:35:28 +0300

Dear experts,

I need to get total number of neutrons from the body (lead)
to compare  FLUKA results with those published in articles.

For this I use 2 cards : USRBDX  and  USRYIELD

I observed that output of N total is very different
and depends on the size of taget !
I have got the following results for the "small" geometry:

Lead, R= 5 cm, L = 9 cm,  beam - P , E= 3.5 GeV
-----------------------------------------------

*)  USRBDX: N Fl from Pb into Air :  Area:            1     cmq,

Tot. resp. (Part/cmq/pr)   27.26922      +/-  0.5661705 %
( -->      (Part/pr)       27.26922      +/- 0.5661705     % )

*)  USRYIELD:  Fl from Pb into Air : linOmega LogE (0-5)

Tot. response (integrated over x1)   3.654836   +/- 0.7171366  %
( --> Tot. response without normaliz.    3.654836   +/-
0.7171366  % )

Ntot= 3.654836 * 5 = 18.27418

*)  USRYIELD:  Fl from Pb into Air :  LogE LinOmega (0-4pi)

Tot. response (integrated over x1)   1.819517  +/- 0.7171366  %
( --> Tot. response without normaliz.    1.819517  +/- 0.7171366  % )

Ntot= 1.819517 *4*3.14156 = 22.864487

------------------------------------------------------

Then I use bigger volume :
accoring to the article: N.SOBOLEVSKY :

"Monte Carlo Calculation of Neutron Yield from Extended
Iron and Lead Targets Irradiated by 1 and 3.65 GeV/u Ion Beams"

where for Ep = 3.5 GeV Ntotal = 65 - 77 neutrons
----------------
So, I use :

Lead, R= 10 cm, L = 60 cm,  beam - P , E= 3.5 GeV --
-----------------------------------------------

Results:

*)  USRBDX: N Fl from Pb into Air :  area = 1

Tot. resp. (Part/cmq/pr)   125.0001      +/-  0.2880751     %
( -->      (Part/pr)       125.0001      +/- 0.2880751     % )

*)  USRYIELD:  N Fl from Pb into Air : linOmega LogE (0-5)
------------------
Tot. response (integrated over x1)   16.10910      +/-
0.2112415     %
( --> Tot. response without normaliz.    16.10910 +/-  0.2112415

Ntot = 16.10910 * 5 =  80.545

*) USRYIELD:  N Fl from Pb into Air :  LogE LinOmega (0-4pi)

Tot. response (integrated over x1)   8.019730      +/-
0.2112417     %
( --> Tot. response without normaliz.    8.019730 +/-  0.2112417

Ntot =  8.019730 *4*3.14156 = 100.777

---------------------------------------

Questions:

-  are there large leakage from "small" target  even for this
small energy ?
-  the presented results are very different from the published ones.
How to get "right" number of the output neutrons from a body
with FLUKA ?

Summary: measured N :  70 +- 7

simulated :  a) 125
b) 80
c) 100

thank you