mcnp

Source Specifications in MCNPSource Specifications in MCNP

Presented by:Seyed Amir Hossein Feghhi

I t t O t t Fl DiInput to Output Flow Diagram:

S C dSource Commands :Th f ibl t

SDEF Fixed (general source)

There are four possible source types:

KCODENeeds KSRC,SDEF card or

Reactor,

SRCTP file from SSWcard

SSW / SSR MCNP generated surface source

User subroutine

source

write your ownif SDEF SSR d KCODEif SDEF,SSR and KCODE are

all missing

G l C dGeneral Cards : These general cards can be sed ith an of These general cards can be used with any of

the above sources:

SI (source information), SP (source probability),( p y), SB (source bias), DS (dependent source)

MODE card implied the type of source i lparticle.

MODE dMODE card :

MCNP b i l diff t dMCNP can be run in several different modes:

N — neutron transport only (default) N P — neutron and neutron-induced photon transport P — photon transport only P photon transport only E — electron transport only P E — photon and electron transport N P E — neutron, neutron-induced photon and electron transport

S S ifi tiSource Specifications : A particle source has: A particle source has:

Intensity, Energy,

Di i Direction, Shape, Temporal characteristics, A position somewhere within the phase space of the problem

We are concerned here with fixed sources, or primary sources; not secondary sources such as those generated by fission, neutron capture, or electron recoilor electron recoil.

The source strength in represented in MCNP by the starting weight, WGT, which is usually assigned to unity to represent a normalized source.Th f f f i l f i l ib i The frequency of occurrence of a particle of a particular attribute is determined by the source’s probability density function (pdf).

S S ifi tiSource Specifications : The starting age TME in needed if a time dependent The starting age, TME, in needed if a time dependent

problem is to be solved

Time dependence is provided by keeping track of the chronological age (distance of travel/velocity) of each

ti lparticle. If the source is not mono energetic, it has to be sampled

from a given, or designated energy spectrum, f(x). If the g , g gy p , ( )spectrum source is biased according to an importance function,g(x), the source energies are selected from the distribution f(x)g(x)distribution f(x)g(x).

G l S C d (SDEF)General Source Card (SDEF) : The SDEF command with its many variables is one of The SDEF command with its many variables is one of

the more complex MCNP commands and is capable of producing an incredible variety of sources

The SDEF command has many variables or parameters that are used to define all the characteristics of all

i th blsources in the problem

The source and type of radiation particles for an e sou ce a d type o ad at o pa t c es o aMCNP problem is defined by the SDEF command

Only one SDEF card is allowed in an input file Only one SDEF card is allowed in an input file

SDEF ri bl d th ir d f ltSDEF variables and their defaults :

SDEF ri blSDEF variables:

SDEF ri blSDEF variables: Values of variables can be specified at three levels: Values of variables can be specified at three levels:

(1) explicitly (e.g., ERG=1.25), (2) with a distribution number (e.g., ERG=d5), (3) as a function of another variable (e.g., ERG=Fpos).

Specify variables at levels 2 and 3 requires the use of four other source cards: SI (source information), SP (source probability), SB (source bias),( ), DS (dependent source)

I p rt t P i tImportant Point

When developing a new source definition, always check andrecheck that source particles are truly being generated where

hi k h h ld b l h dyou think they should be. HINT: Always use the VOID cardand the PRINT 110 statement somewhere in data block ofh i fil Th PRINT 110 h i l ithe input file. The PRINT 110 causes the starting locations.

directions, and energies of the first 50 particles to be printedt th t t fil E i thi t t t bl t ito the output file. Examine this output table to convinceyourself that particles are being generated as you expect.

Sp ti l Di trib ti (Sh p )Spatial Distribution (Shape):

I l SUR f f d CELL f l

Volume Sources :SUR 0 (d f lt l )

In general, use SUR for a surface source and CELL for a volume source.

SUR=0 (default value). Cartesian (These are specified with X, Y, and Z.)

P i X Y d Z ll Point: X, Y and Z are all constant.Line: one variable, the others are constant,Rectangular Plane: Fix one variable and vary the otherRectangular Plane: Fix one variable and vary the other

two.Rectangular Polyhedron: vary the three variables.

Sp ti l Di trib ti (Sh p )Spatial Distribution (Shape):S h i l (Th ifi d b POS ( t f h ) Spherical (These are specified by POS (center of sphere)

and RAD (radius), do not specify XYZ and AXS.) Point: RAD=0, or not specified at all., p Spherical shell: specify two radii for RAD on an SIn card.

Cylindrical (These are specified with POS (point on axis), AXS (direction cosines of axis), RAD (radius of

li d ) d EXT (di t f POS)cylinder), and EXT (distance form POS). Disk :set EXT=0, which provides a source with circular symmetry on a

plane.

Sp ti l Di trib ti (Sh p )Spatial Distribution (Shape):

Warning about Volume Sources:Never position any kind of volume distribution inp y

such a way that it lies on one of the definedsurfaces of the problem geometry.p g y

move to a position just a little way off of thesurface. It will not make any detectablesurface. It will not make any detectabledifference in the answers, and it will preventparticles from getting lost.particles from getting lost.

Sp ti l Di trib ti (Sh p )Spatial Distribution (Shape): Surface Sources: Surface Sources:

SUR ≠0, Sampled values of X Y and Z determine position (make sure that the point is on surface). IF X Y Z are not specified, the position is sampled from SUR

Plane (SUR d fi f l POS b i l(SUR defines a name of a plane, POS must be a point on plane.

The position of sampled uniformly on the circle of radius RAD centered around).)

Cylindrical (This must be specified with as a volume source, specify two

l dii f A S d)equal radii for RAD on an SIn card).

Sp ti l Di trib ti (Sh p )Spatial Distribution (Shape): Spherical Spherical(SUR is the name of a spherical surface. If AXS is not

specified, position is sampled uniformly on surface. p , p p yIf AXS is specified, EXT in used for the cosine of the angle between the direction AXS and the vector from the center of the sphere to the position pointfrom the center of the sphere to the position point (EXT can have a distribution).

SpheroidalSpheroidalSUR is the name of ellipse revolved around one of its

axis. A spheroid must have its axis parallel to one of the coordinate axis.

E r Sp trEnergy Spectrum: ERG= starting energy (default 14 MeV): Use an SP card to define a distribution from Built-In

Functions for Source Probability and Bias Specification

Dir ti l di trib tiDirectional distribution: The default is isotropic distribution. VEC defines a reference vector (which can be itself a

distribution); the default for a surface source is the normal to the source in a

direction defined by NRM. DIR defines the cosine of the polar angle; DIR defines the cosine of the polar angle; cosine distribution for a surface source is the default. The azimuthal angle is sampled uniformly The azimuthal angle is sampled uniformly. DIR=l gives a mono-directional source (beam) in the

,direction of VEC.,direction of VEC. DIR can be biased to a preferred direction,

T p r l di trib tiTemporal distribution:TME = time (in units of shakes, default=O).TME time (in units of shakes, default O).

SP with f=-1 defines a Gaussian distribution with timewith time.

Alternatively, DS can be used to define a discrete distribution.discrete distribution.

Bi iBiasing:It allows the production of more sourceIt allows the production of more source

particle, with suitably reduced weights, inthe more important regimes of eachthe more important regimes of eachvariables. Source biasing is the only

i d ti ll d ith F8 t llivariance reduction allowed with F8 tallieshaving energy bins.

Oth rOthers:See manual for :See manual for :Repeated source structure

S f it (SSW d)Surface source write (SSW card).Surface source read (SSR card)Criticality source (KCODE and KSRC cards).User supplied source (Subroutines SOURCEUser supplied source (Subroutines SOURCE

and SRCDX).

E plExamples :

Point Isotropic Sources

Isotropic Volumetric Sources

Line and Area Sources

Monodirectional and Collimated Sources

E plExamples (Point Isotropic Sources):

Two Point Isotropic Sources at Different Positions

SDEF ERG=E PAR=n POS=d5 $ energy particle type locationSDEF ERG=E PAR=n POS=d5 $ energy, particle type, locationSI5 L x1 y1 z1 x2 y2 z2 $ (x,y,z) coords of the two pt sources SP5 p1 p2 $ relative strengths of each source


Point Isotropic Source with Discrete Energy Photons

SDEF POS X0 Y0 Z0 PAR=n ERG=d1SDEF POS X0 Y0 Z0 PAR=n ERG=d1SI1 L E1 E2 E3 E4 $ the 4 discrete energies (MeV)SP1 f1 f2 f3 f4 $ frequency of each energy


Point isotropic with a Histogram of energies

SDEF POS X0 Y0 Z0 PAR ERG d1 $ iti ti l tSDEF POS X0 Y0 Z0 PAR=n ERG=d1 $ position, particle type, energySI1 H E1 E2 E3 E4 E5 $ histogram boundaries (MeV)SP1 D p1 p2 p3 p4 p5 $ probabilities for each bin


Point Isotropic Source with a Continuum of Energies

SDEF POS X0 Y0 Z0 PAR=n ERG=d1 $ position, particle type, energySP1 F a b $ Function No. and input parametersS $ p p


Two Point Sources with Different Energy Distributionssrc 1 (4-bins) & src 2 (4 discrete Ei)

SDEF PAR=2 POS=d1 ERG FPOS d2SDEF PAR=2 POS=d1 ERG FPOS d2SI1 L -10 0 0 10 0 0 $ coords of srcs on x-axisSP1 .4 .6 $ rel strengths of sourcesDS2 S 3 4 $ energy distributionsSI3 H .1 .3 .5 1. 2.5 $ E bin limits src 1SP3 D 0 .2 .4 .3 .2 $ bin prob for src 1SI4 L .3 .5 .9 1.25 $ discrete Ei for src 2SP4 .20 .10 .30 .40 $ rel freq for src 2

E plExamples (Isotropic Volumetric Sources):

Rectangular Parallelepiped Parallel to Axes :

SDEF X=d1 Y=d2 Z=d3 ERG=E PAR=n SI1 –X +X $ x-range limits for source volumeS $ gSP1 0 1 $ uniform probability over x-rangeSI2 –Y +Y $ y-range limits for source volumeSP2 0 1 $ niform probabilit o er rangeSP2 0 1 $ uniform probability over y-rangeSI3 –Z +Z $ z-range limits for source volumeSP3 0 1 $ uniform probability over z-range


Source in a Complex Cell: Enclosing Cube Rejection Method :

SDEF X=d1 Y=d2 Z=d3 ERG=E PAR=n CEL=8SI1 –X +X $ x-range limits for source volumeS $ gSP1 0 1 $ uniform probability over x-rangeSI2 –Y +Y $ y-range limits for source volumeSP2 0 1 $ niform probabilit o er rangeSP2 0 1 $ uniform probability over y-rangeSI3 –Z +Z $ z-range limits for source volumeSP3 0 1 $ uniform probability over z-range


Source in a Complex Cell: Enclosing Sphere Rejection Method :

SDEF POS=X0 Y0 Z0 RAD=d1 CEL=8SI1 R1 R2 $ radial sampling rangeSI1 R1 R2 $ radial sampling rangeSP1 -21 a $ weighting for radial sampling

E plExamples (Line and Area Sources):

Line Source:

SDEF POS=X0 Y0 Z0 X=d1 Y=Y0 Z=Z0 PAR=n ERG=ESI1 X +X $ Xmin to Xmax for line sourceSI1 -X +X $ Xmin to Xmax for line sourceSP1 -21 a $ sampling weighting (a=0 for uniform sampling)


Disk Source:

SDEF POS=X0 Y0 Z0 AXS=i j k EXT=0 RAD=d1 PAR=n ERG=ESI1 R1 R2 $ radial sampling range (for example 0 to Rmax)SI1 R1 R2 $ radial sampling range (for example 0 to Rmax)SP1 -21 a $ radial sampling weighting (a=1 for disk source)


Plane Source:

SDEF POS=X0 Y0 Z0 X=d1 Y=d2 Z=0 PAR=n ERG=ESI1 -X X $ sampling range Xmin to Xmax S $ p g gSP1 0 1 $ weighting for x sampling: here constantSI2 -Y Y $ sampling range Ymin to YmaxSP2 0 1 $ eighting for sampling: here constantSP2 0 1 $ weighting for y sampling: here constant


Line Source:

SDEF POS=X0 Y0 Z0 AXS=i j k EXT=d1 RAD=0 PAR=n ERG=ESI1 X +X $ axial sampling range: X to XSI1 -X +X $ axial sampling range: -X to XSP1 -21 a $ weighting for axial sampling (a=0 for uniform sampling)

E plExamples (Monodirectional and Collimated Sources):

Monodirectional Disk Source:

SDEF POS=X0 Y0 Z0 AXS=i j k EXT=0 RAD=d1 PAR=n ERG=EVEC=i j k DIR=1VEC=i j k DIR=1

SI1 R1 R2 $ radial sampling rangeSP1 -21 a $ radial sampling weighting (a=1 for disk source)

E plExamples (Monodirectional and Collimated Sources):

Point Source Collimated into a Cone of Directions:

SDEF POS=X0 Y0 Z0 ERG=E PAR=n VEC=i j k DIR=d1SI1 c1 c2 c3 $ histogram for cosine bin limitsSP1 p1 p2 p3 $ fraction. solid angle for each binWith this conical source, tally normalization is per source particle in 4л steradians.

Examples (M l i l V l i S )Examples (Multiple Volumetric Sources):

Two Cylindrical Volumetric Sourcesy2 volumetric sources uniformly distributed in cells 8 & 9:

SDEF ERG=E CEL d1 AXS=0 0 1 POS 0 0 0 RAD d2 EXT d5SI1 L 8 9 $ source cells: src 1 =cell 8, src 2 =cell 9SP1 0.8 0.2 $ 80% from src 1; 20% from src 2SI2 0 50 $ radius of cyl. containing cells 8 & 9SI2 0 50 $ radius of cyl. containing cells 8 & 9SI5 -30 30 $ axial range of cyl. containing src cells

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