question about spallation neutron spectrum

From: <sszdzl1_at_mail.ustc.edu.cn>
Date: Tue, 11 Oct 2011 08:35:58 +0800 (CST)

Dear Fluka users,
    I am a student in University of Science and Technolegy of China. I got a lead Cylindrical target which is 50 cm high and 10 cm
in radius whichis hitted by a protron beam of 1 GeV energy in the bottom. I try to get the spallation neutron spectrum use USRTEACK,
but find the spectrum below 20 MeV can not match. I show my result and my input file in the last of this letter.
    I think since what I want is the spallation neutron spectrum, the affect of the neutron transport should be eliminate, but I
don't know how to do that. Can anyone tell me how to do? Or where did I make mistakes?It will be of great help to me. Thank you very
much!
                                                                           yours Sincerely
here are me result and my input file

Energy(MeV) Literature value my result
19.64--4.99 0.1985 0.07968
4.99--3.03 0.157 0.08019
3.03--1.84 0.178 0.1707
1.84--1.11 0.165 0.2033
1.11--0.675 0.122 0.1796
0.675--0.410 0.08 0.1245
0.410--0.248 0.05 0.07698
0.248--0.151 0.0545 0.04278
0.151--5.62E-7 0 0.04223

* ..+....1....+....2....+....3....+....4....+....5....+....6....+....7...
TITLE
FLUKA Course Exercise
*
* use names everywhere and free format for geometry
DEFAULTS NEW-DEFA
*
* beam definitions
BEAM -1.0 0.0 0.0 -10.0 -10.0 1.0PROTON
BEAMPOS 0.0 0.0 25.0 0.0 0.0 NEGATIVE
GEOBEGIN COMBNAME
     0 0 Cylindrical Target
*
* Bodies
* ------
*
* General definitions:
* blackhole to include geometry
SPH BLK 0.0 0.0 0.0 10000.0
RCC VOI 0.0 0.0 -320.0 0.0 0.0 640.0 320.0
*
* Lead target:
RCC TARG1 0.0 0.0 -25.0 0.0 0.0 50.0 10.0
END
*
* Regions
* -------
*
* Blackhole
BLKHOLE 5 +BLK -VOI
* Void
VOID 5 +VOI -TARG1
* Target
TARGET 5 +TARG1
END
GEOEND
ASSIGNMA BLCKHOLE BLKHOLE
ASSIGNMA VACUUM VOID
ASSIGNMA LEAD TARGET
USRTRACK -1. NEUTRON -21. TARGET 15708.0 70.02
USRTRACK 0.02 1.0E-7 &
*
RANDOMIZ 1.
START 10000.01000000000 0.0 10000000.
STOP
Received on Tue Oct 11 2011 - 09:13:31 CEST

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