MCNP Tally f8 unreliable since neutron transport is nonanalog

  • Thread starter dando
  • Start date
In summary, the equation for the detector HPGE is V-51 and the equation for the cover is CACBON COMPOSIT WINDOW.
  • #1
dando
1
0
Homework Statement: mcnp5
Relevant Equations: mcnp5

please help me to fix the error for mcnp5

Code:
C Source  V-51
C COMPTON SUPPRESSION SIMULATION BY MCNP6                                                            
c CELL CARD                                                                     
c ***********DETECTOR HPGE***************************                           
c ---------- INNER ELECTRODE ------------------------------------------         
    1     1  -5.323 (1 -3 -15) (-1:2:14) 
c ---------- HPGE -----------------------------------------------------
    2     1  -5.323 (9 -4 -16) (-9:3:15)
c ---------- OUTER ELECTRODE ------------------------------------------         
    3     1  -5.323 (1 -5 -17) (-1:4:16)
c ---------- UNDER ELECTRODE -----------------------------------------          
    4     1  -5.323 (1 -9 15 -16)
c ---------- KAPTON --------------------------------------------------- 
    5     2  -1.42  (5 -300 -17)
c ---------- MYLAR ---------------------------------------------------
    6     7  -1.4   (300 -6 -17)
c ---------- CRYOSTAT HODER -------------------------------------------       
    7     3  -2.7   (301 -6 17 -18):(-6 18 -19 11):(-10 11 -18 303):&
(-11 305 303 -302):(306 -303 305 -304)
c ---------- TEFLON --------------------------------------------        
    8    11  -2.25 (-10 -303 304 14):(-307 304 -14)
c ---------- Cu --------------------------------------------        
    9    12  -8.94 (-2 307 -308)
c ---------- VACUUM IN HPGE ------------------------------------------       
    10     0  (-7 12 -20)#1#2#3#4#5#6#7#8#9
c ---------- ALLUMIUM HPGE COVER -----------------------------------            
    11     3  -2.7   (13 -7 -21) (-12:7:20)
c ---------- CACBON COMPOSIT WINDOW -----------------------------               
    12     4  -0.145 (7 -8 -21)
c                                                                               
c ****** PHAN BGO PLUG-IN VA LOP NHOM BAO BOC******                                
c ---------- AIR ------------------------------------------------------
    13     6 -0.001204 (-22 24 28 -33) (22:-23:-27:32):(-24 30 -31 25)
c ---------- ALLUMIUM COVER -------------------------------------------         
    14     3    -2.7 ((-13 24 29 -34) (22:-24:-28:33)):((-24 26 29 -34)&
            (24:-30:31:-25))
c ****** PHAN BGO ANNULAR VA LOP NHOM BAO BOC****                               
c ---------- SURROUDING BGO -------------------------------------------         
    15     5   -7.13 (-47 61 60 -62 -63):(-61 58 -63 64 -65):(-22 23 27 -32)
c ---------- ALLUMIUM COVER -------------------------------------------         
    16     3    -2.7 (-46 45 40 -43 ):(-45 38 42 -43 ):(-38 39 34 -44 ):&
(-35 47 41 -52):(-47 51 -52 -54):(-51 53 -54 -56):&
(-53 50 55 -56):(-50 38 43 -56):(50 -59 67 -55):(50 -59 43 -66):&
(-35 46 40 -41):(-71 72 -73 56 (74:71:-72) (75:71:-72) &
(76:71:-72) (77:71:-72) (78:71:-72) (79:71:-72) &
(80:71:-72) (81:71:-72))
c ---------- AIR ---------------------------------------------------------------
    17     6 -0.001204 (-47 41 -60 46):(60 -61 46 -43):(43 -61 -64 59):&
(64 59 -58 -65):(66 50 -59 -67):(65 59 -63 -55):&
(63 -62 -53 -55):(62 -47 -51 -53)
c                                                                               
c ************* PB SHIELDING ***************************                        
c ---------- PB ----------------------------------------------------------------
    18     8   -11.3 (82 35 -83 -84):(-86 88 89 -91 -85):(-89 93 95 -91):&
(96 97 -90 -94)
c ---------- PB (first - STEEL ) -----------------------------------------------
    19    8   -11.3 (86 87 -35 -84):(87 -88 -86 71):(-89 71 88 -93):&
(-71 92 -93 94):(94 -95 93 -90):(-84 85 -86 -90):(-85 91 -90 95)
c ---------- CHAMBER ----------------------------------------------------------
c ---------- SAMPLE V-51--------------------------------------------------------
    20     14 -6 (124 -125 -126)       $ Mật độ của V51 = -6.0
c ---------- POLYETHYLENE - BORATED----------------------------------------------
    21     13 -1    (108 -111 113 -115 118 -121) (-109:110:-113:114:-119:120)&
#(108 -109 -123)
c ---------- PB ------------------------------------V--------------------------
    22     8   -11.3 (107 -112 113 -116 117 -122) (-108:111:-113:115:-118:121)&
#(107 -108 -123)
c ---------- Window POLYETHYLENE - BORATED--------------------------------------
    23     13 -1    (309 -310 311 -312 313 -107)
c ---------- AIR ---------------------------------------------------------------
    24     6 -0.001204 -99 (8:21:-13) (13:34:-26:-29)#15#16#17#18#19#20#21#22#23
c ---------- NON-WORKING SPACE REGION --------------------------                
    25     0         99 

c SURFACE CARD                                                                  
c                                                                               
c ****************** HPGE DETECTOR ********************                         
    1        pz -1.8 $ 0 - 1.8
    2        pz 4.15 $ 5.95 -1.8
    3        pz 4.35 $ 4.2 $ 6 -1.8
    4        pz 5.54992 $ 7.34992 -1.8
    5        pz 5.55 $ 7.35 -1.8
  300        pz 5.56046  $ 7.36046  -1.8
  301        pz 5.4853076 $ 7.2853076  -1.8
    6        pz 5.561306 $ 7.361306  -1.8
    7        pz 7.813067 
    8        pz 7.873067 
    9        pz -1.7 $ -1.72 $ 0.08  -1.8
   10        pz -2.3 $ -0.5  -1.8
   11        pz -2.62 $ -0.82  -1.8
   12        pz -5.4886933 
   13        pz -5.6386933 
   14        cz 0.6 
   15        cz 0.8 $ 0.85 
   16        cz 3.42 $ 3.49992 
   17        cz 3.5 
   18        cz 3.6078 
   19        cz 3.6838 
   20        cz 4.6125 
   21        cz 4.7625 
   302       cz 1.245
   303       cz 0.925
   304       pz -4.12
   305       pz -4.44  
   306       cz -0.15
   307       pz -3.62
   308       cz 0.3 
c                                                                               
c ******** PLUG-IN BGO AND ALUMINIUM COVER ********                             
   22        pz -5.7186933 
   23        pz -10.7186933 
   24        pz -10.9086933 
   25        pz -18.3086933 
   26        pz -19.1086933 
   27        cz 1.47375 
   28        cz 1.38 
   29        cz 1.3 
   30        cz 1.6 
   31        cz 4.45 
   32        cz 4.57625 
   33        cz 4.67 
   34        cz 4.75 
c                                                                               
c ******* ANNULAR BGO AND ALUMINIUM COVER *******                               
   35        pz 11.6413067 
   38        pz -16.5086933 
   39        pz -16.9086933 
   40        cz 2.5 
   41        cz 2.58 
   42        cz 4.94 
   43        cz 5.02 
   44        cz 6 
   45        kz 12.7911696 1 -1 
   46        kz 12.9043067 1 -1 
   47        pz 10.9413067 
   50        pz -16.2086933 
   51        kz 16.9820426 1 -1 
   52        kz 17.4013067 1 -1 
   53        kz 101.8803822 0.007654266246 -1 
   54        kz 105.9724962 0.007654266246 -1 
   55        cz 8.625 
   56        cz 8.925 
   58        pz -8.0586933 
   59        pz -15.2086933 
   60        cz 2.66 
   61        kz 13.01744378 1 -1 
   62        kz 15.84587091 1 -1 
   63        kz 87.53824064 0.007654266246 -1 
   64        cz 5.1 
   65        cz 7.85 
   66        cz 6.325 
   67        cz 8.325 
   71        pz -5.2586933 
   72        pz -6.7586933 
   73        cz 10.425 
   74       c/z 9.7 0 0.25 
   75       c/z -9.7 0 0.25 
   76       c/z 0 9.7 0.25 
   77       c/z 0 -9.7 0.25 
   78       c/z 6.858935778 6.858935778 0.25 
   79       c/z -6.858935778 6.858935778 0.25 
   80       c/z 6.858935778 -6.858935778 0.25 
   81       c/z -6.858935778 -6.858935778 0.25 
c                                                                               
c **************** LEAD AND STEEL ****************                              
c                                                                               
   82        kz 41.6413067 0.006944444444 -1 
   83        pz 17.6413067 
   84        kz 86.6413067 0.11111111111 -1 
   85        kz 84.6903712 0.11111111111 -1 
   86        pz 10.6413067 
   87        cz 9.25 
   88        cz 10.1319078 
   89        pz -4.6586933 
   90        cz 30 
   91        cz 29.4180922 
   92        cz 18.8 
   93        cz 19.3819078 
   94        pz -15.8586933 
   95        pz -14.8586933 
   96        pz -20.8586933 
   97        cz 10.75 
c                                                                               
c *********** CHAMBER ***********  
  309        px -2.5
  310        px 2.5
  311        py -2.5
  312        py 2.5
  313        pz 18.7486223
  107        pz 19.3486223
  108        pz 24.3486223
  109        pz 26.8486223
  110        pz 41.8486223 
  111        pz 44.3486223
  112        pz 49.3486223
  113        px -56.490863
  114        px 104.009137
  115        px 106.509137
  116        px 111.509137
  117        py -15
  118        py -10
  119        py -7.5
  120        py 7.5
  121        py 10
  122        py 15
  123        cz 2
c *********** SAMPLE ***********  
  124        px -0.5003381
  125        px 0.5003381
  126        c/x 0 35.823067 0.5
c *********** Surface source *********** 
  130        px -1
c ********* UNIVERSE *********************************                          
   99        so 200 

MODE N P E
phys:N
phys:P
phys:E
imp:N 1 23r 0          $ 1-24=1 ; 25=0
imp:P 1 23r 0          $ 1-24=1 ; 25=0
imp:E 0 1 0 11r 1 0 9r $ 2,15=1 ; 1,3-14,16-25=0
RAND GEN=2 HIST=1
c MATERIAL CARD                                                                 
m1    32072.     -1 nlib = 30y plib = 84p   $ Ge
m2    6000.66c      -0.691133&  $ KAPTON
      1002.66c      -0.026362&
      7014.66c      -0.073270& 
      8016.66c      -0.209235   
m3    13027.66c     -1          $ Al
m4    6000.66c      -1          $ CACBON COMPOSITE
m5    83209.66c     -0.67099    $ BGO
      32072.        -0.17490  
      8016.66c      -0.15411  nlib = 30y plib = 84p
m6    6000.66c      -0.000124&  $ KK
      7014.66c      -0.755268&
      8016.66c      -0.231781&
      18000.35c     -0.012827   $ NLIB=66c 
m7    6000.66c      -0.625016&  $ MYLAR
      1002.66c      -0.041959&
      8016.66c      -0.333025 
m8    82208.66c     -1          $ Pb
m10   6000.66c      -0.200000&  $ STEEL
      15031.66c     -0.050000&
      25055.66c     -0.540000 
m11   6000.66c      -0.240183&  $ Teflon
      9019.66c      -0.759818   
m12   29063.62c     -0.691500&  $ 29000     -1 Cu
      29065.62c     -0.3085   
m13   1001.66c      -0.125355&  $ Boron
      5010.66c      -0.100000&
      6000.66c      -0.774645    
m14   23000.62c     -1          $ V-51 
C DEFINE SOURCE 
SDEF erg=0.0000000253 par=1 sur=130 pos = -1 0 35.823067 dir=1 &
 vec = 1 0 0 rad=d1 WGT=10000000                 
si1 0 0.5                                                                     
sp1 -21 1                                             
c TALLY CARD
f18:p 2                     $ HPGe
f28:p 2                     $ HPGe-BGO PHL                          
e28 0 0.00001 0.001 109989i 11   $ bin 0.1 keV - (1keV - 11MeV)            
ft28 GEB 9.455E-4 2.837E-5 0                                                                                                     
nps 100000000
 

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  • #2
Welcome to PF. :smile:

dando said:
please help me to fix the error for mcnp5
Can you say more about your simulation and what you are trying to do? That will make it a lot easier for our MCNP helpers to give you a hand. Thanks.
 
  • #3
This seems to be neutron activation analysis with a HPGe detector around which there is a BGO scintillator for Compton supression. There is a beam of thermal neutrons going into a target which, before I look at more closely, I assume to be the vanadium. This is a fun problem.

Things that jump out at me...
f18 is the HPGe, no energy bins are defined.
f28 is also the HPGe but it's labeled HPGe-BGO, energy bins are defined and they are broadened with an FT GEB card.
I'm a little confused as to how this is intended to work. You could get a spectrum from the BGO but that is of limited use.
That is a fearsome number of source particles, you must be throwing some serious computing power at it.

A big problem with MCNP is that it's ruthless in it's pursuit of tally answers to the extent that the standard versions of the program I know do not obey conservation laws. That is to say individual events ignore any physics that does not affect the aggregate tally.

There is a version called MCNP-CP (correlated particles) which is a patched version of MCNP4c3 by Dr Andrey Berlizov. There may be other versions, there may even be a feature in MCNP6 but I don't know this off hand, I note your input mentions MCNP6 and the options switch a lot of things on.

So I don't see exactly what is being attempted or how it's supposed to work with vanilla MCNP5. The Compton signal isn't a subtraction of course, it's a veto signal for the (incomplete) pulse from the HPGe which MCNP-CP also has extra tally code to make work.

I think we do need a little more information about what is being done and exactly what isn't working.
 
  • Informative
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Likes berkeman and dando
  • #4
I know a bit more now. The correlation problem is not fatal. Compton scattering events are simulated and since only a threshold energy is needed from the shield the suppressed spectrum should be mostly right.

Having a tally in anti-coincidence is more of a challenge and I don't have a solution for MCNP5. 6 and X have the PHL keyword on the FT card. The method builds an F8 tally from two F6 tallies and displays the result in grid form. The cunning plan is that the shield, in the OPs case BGO but in the official example a plastic scintillator, is given two energy bins - a zero and a not zero bin. The detector is given a full range of energy bins. When this is displayed in the output file with the two shield bins across, the whole column down under the zero bin is the anti-coincidence 'Compton suppressed' spectrum. The whole of the second column is the rejected spectrum.

I do not understand the syntax yet and there are other mandatory cards I have not looked up yet like FU (!), but this is example 6 in MCNP6 Advanced Tallies Tutorial.
 

Related to MCNP Tally f8 unreliable since neutron transport is nonanalog

What is MCNP and what does the F8 tally represent?

MCNP (Monte Carlo N-Particle) is a software package used for simulating nuclear processes, such as neutron, photon, electron, or coupled transport. The F8 tally in MCNP is used to calculate the energy deposition in a cell, which is often referred to as the "pulse-height tally." It is particularly useful in simulating the response of detectors to radiation.

Why is the F8 tally considered unreliable for neutron transport in nonanalog mode?

The F8 tally can be unreliable for neutron transport in nonanalog mode because nonanalog techniques, such as variance reduction methods, can distort the statistical nature of the neutron interactions. This distortion can lead to inaccurate representations of energy deposition, as the nonanalog methods may artificially alter the neutron flux and interaction rates, leading to incorrect pulse-height spectra.

What are some common variance reduction techniques that affect the F8 tally?

Common variance reduction techniques that can affect the F8 tally include weight windows, importance sampling, and Russian roulette. These techniques are designed to reduce computational time and improve the efficiency of the simulation, but they can also introduce biases that affect the accuracy of tallies that depend on the precise statistical nature of particle interactions, such as the F8 tally.

How can one improve the reliability of the F8 tally in neutron transport simulations?

To improve the reliability of the F8 tally in neutron transport simulations, it is recommended to use analog transport mode, where particles are simulated without any variance reduction techniques. This ensures that the statistical nature of neutron interactions is preserved. Additionally, increasing the number of simulated particles can help reduce statistical uncertainties and improve the accuracy of the tally.

Are there alternative methods to the F8 tally for calculating energy deposition in neutron transport simulations?

Yes, there are alternative methods to the F8 tally for calculating energy deposition in neutron transport simulations. One common alternative is using the F6 tally, which calculates the energy deposition per unit mass (dose) in a cell. The F6 tally is generally more reliable in nonanalog mode because it is less sensitive to the distortions introduced by variance reduction techniques. Another approach is to use detailed event-by-event tracking and scoring to directly calculate energy deposition, although this can be more computationally intensive.

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