Presentation on theme: "Lecture 3:Basic Concepts"— Presentation transcript:
1Lecture 3:Basic Concepts MCNP reinforcement of conceptsIntroduction to VisEdAdvanced source distributionsSurface and volume sourcesRepresenting particle beamsTally review
2VisEd Cheat Sheet Start VisEd. File->Open (Do not modify input) to choose and open the input fileClick “Color” in both windowsZoom in OR Zoom out to get them rightAs desired:Click “Cell” or “Surf” to see cell numbersClick “Origin” to make the window “sensitive” to subsequent clicks (in either window)Insert origin coordinates to move around
3VisEd example Inside a box (100x100x100) Torus of Rmajor=20, Rminor=5 on floorCylinder of radius 20, ht 40 on top of torusSphere of radius 10 centered in cylinder
4Source Definition: SDEF Card For a point source:PAR=1/2/3 particle type (1/2/3=n/p/e)ERG=xx Energy of particle (MeV)POS=x y z Position indicatorExample: 9.5 MeV neutron source at point (1., 4., 5.)SDEF PAR=1 ERG=9.5 POS=1 4 5
6X axis of a distribution: SI Syntax:Description: The SIn and SPn cards work together to define a pdf to select a variable from.option= blank or Hhistogram=Ldiscrete=A(x,y) pairs interpolated=Sother distribution #’sMCNP5 Manual Page: 3-61
7Y axis of a distribution: SP Syntax:Description: Specification of y axis of pdf for distribution n.option=blankcompletes SI=-ppredefined functionThe P values are the y-axis values OR the parameters for the desired function p—and the SI numbers are the lower and upper limits. (Table 3.4)MCNP5 Manual Page: 3-61
8Examples SI2 H 0 5 20 SP2 0 1 2 … SI3 L 1 2 SP3 1 2 SI4 A 0 5 20
9Input shortcuts Description: Saving keystrokes MCNP5 Manual Page: 3-4 Syntax:2 4R =>1.5 2I 3 =>0.01 2ILOG 10 =>1 1 2M 3M 4M =>1 3J => 1 d d d 5.4(where d is the default value for that entry)
10Energy bins: En Syntax: En Description: Upper bounds of energy bins (MeV) for tally nMCNP5 Manual Page: 3-90
11Source description variables Commands:POS=Position of a point of interestRAD=How to choose radial pointAXS=Direction vector of an axisEXT=How to choose point along a vectorX,Y,Z=How to choose (x,y,z) dimensionsVEC=Vector of interestDIR=Direction cosine vs. VEC vectorCombinations:X,Y,Z: Cartesian (cuboid) shapePOS, RAD: Spherical shapePOS, RAD, AXS, EXT: Cylindrical shapeVEC,DIR: Direction of particle
12Particle crossing tally: F1 Syntax:Description: Tally of current integrated over a surface. Prefixing with ‘*’ changes the units—particles to MeV. Like other tallies, the time dependence is inherited from the source—the code doesn’t care.MCNP5 Manual Page: 3-78
13Surface flux tally: F2 Syntax: Description: Tally of flux averaged over a surface. Prefixing with ‘*’ changes the units—particles/cm2 to MeV/cm2.MCNP5 Manual Page: 3-78
14Cell flux tally: F4 Syntax: Description: Tally of flux averaged over a cell. Prefixing with ‘*’ changes the units—particles/cm2 to MeV/cm2.MCNP5 Manual Page: 3-78
15Point Flux TallyA point flux tally is a special tally that collects the flux at a pointNow, of course, neither of the flux tallies that we have studied—collision estimates or track length estimates—could possibly be applied to a POINTThis is a very specially designed tally in EVERY source point created and EVERY scattered particle contributes its POTENTIAL for scattering to the point in question
16Point FluxA point flux tally is a special tally that collects the flux at a pointThe MCNP tally 5 is used to set this up, with syntax:Fx5:n x0 y0 z0 R0 x1 y1 z1 R1 …where:(x0,y0,z0) and (x1,y1,z1) are points where the flux is desiredR0 and R1 are the radii around the points where flux contributions will NOT be madeAn extra bonus that you get from a point flux tally is that the UNCOLLIDED flux (the contribution from particles that come straight from the source) are separately reported
17Point flux tally: F5 Syntax: Description: Tally of flux at a point or ring detector. Prefixing with ‘*’ changes the units—particles/cm2 to MeV/cm2.MCNP5 Manual Page: 3-78
18HW 2.4Use a hand calculation to calculate both the flux and the current on a 5 cm radius disk lying on the z=0 plane, centered on the origin. For the source use a point isotropic 2 MeV neutron source located at (0,0,10). Assume void material fills an enclosing sphere of radius 30 cm (centered on the origin).Check your calculation with an MCNP calculation (within 1% error)
19HW 2.5Repeat problem 2.4 with the source located at (0,0,20). Explain why the current/flux ratio is different for the two cases (and why it increases).Check your calculation with an MCNP calculation (within 1% error)
20HW 2.6Repeat the MCNP calculation of problem 2.4 with the enclosing sphere filled with water, only collecting the uncollided neutrons. Explain why the current/flux ratio is different for the two cases (and why it increases).
21HW 3.1Find the Legendre coefficients for a 2nd order expansion of e-x, -1<x<1Create a curve of the approximation vs. the actual curve
22HW 3.2If you have a parallelepiped volumetric isotropic source with a strength of 100 particles/cc/sec and W=20 cm (x dimension), L=10 cm (y dimension), H=50 cm (z dimension):Find the equivalent surface source if the analyst judges that L is insignificant.Find the equivalent line source if the analyst judges that W is also insignificant; andFind the equivalent point source if the analyst judges that H is insignificant as well.For each of these be sure the source size, placement and strength (in appropriate units) is specified.
23HW 3.3For each of the four sources in the previous problem (the original cuboid + the three bulleted approximations) create the source in MCNP—with the origin at the center of the original cuboid—and compute the fluxes at the point (250,0,0) using an F5 tally.
24HW 3.4Use the Appendix H data to give me the appropriate source description for an isotropic 1 microCurie Co-60 point source that is 10 years old. Use a hand calculation to find the flux at a distance of 100 cmCheck your calculation with an MCNP calculation (within 1% error) using an F5 tally
25HW 3.5Use an MCNP calculation of a beam impinging on the small water sample to estimate the total cross section of water for 0.1 MeV, 1 MeV, and 10 MeV photons. Compare your answers to the values in Appendix C of the text.