MCNP Geometry Model

Tamarack reconstructs the MCNP geometry model directly from input decks, preserving all cell, surface, and Boolean definitions. It provides interactive 3D insight into the geometry without modifying the deck.

Surface Definitions

Surfaces in MCNP define the boundaries of cells using geometric primitives: planes, spheres, cylinders, cones, tori, and quadrics. Tamarack parses all standard surface types and recognizes advanced quadrics as defined in MCNP6.

Surface Mapping Diagram


c Example Surface Cards
1 px 0
2 py 5
3 cz 10
4 so 3.0

Each surface is assigned a unique ID and optionally a boundary type (e.g., vacuum, reflective). Tamarack preserves this metadata for visualization and validation.

Cell Definitions

Cells define volumes using Boolean combinations of surfaces. They include material assignments, density, and importance. Tamarack parses all cell cards, evaluates the surface combination logic, and constructs closed 3D regions.

Cell Structure Diagram


c Example Cell Definitions
1 1 -7.85 -1 2 -3 imp:n=1
2 0 1:-2:3 imp:n=0

Tamarack highlights invalid or empty cells and provides tools to inspect surface sense errors.

Boolean Geometry Logic

MCNP uses Boolean operators to define regions:

Intersection: All surfaces must be satisfied (AND).
Union: At least one surface satisfied (OR).
Complement: Negates a surface (NOT).

Boolean Logic Visualization

Tamarack evaluates Boolean logic exactly as MCNP does, ensuring visualization accuracy. No approximations are performed.

3D Visualization & Inspection

Tamarack renders all surfaces and cells in an interactive 3D viewport. Features include:

Toggle visibility of individual cells or materials
Highlight overlaps and voids
Inspect surface sense and cell inclusion
Navigate with standard 3D controls (rotate, zoom, pan)

3D Geometry View

CAD Import & Export

Tamarack allows importing CAD solids to serve as MCNP geometry templates. Imported models are converted to MCNP-compatible surfaces and cells.

Supported formats: STEP, IGES, Parasolid
3D Export: STL, OBJ
Validation: overlap detection, void checking, material assignments

Validation & Limitations

Tamarack provides built-in validation tools for:

Overlapping cells
Void regions
Incorrect surface sense
Empty or unassigned cells

Some complex MCNP features, such as lattice or universes with advanced transformations, may have visualization limitations. These do not affect MCNP execution.

Summary

Tamarack preserves MCNP’s text-based geometry while providing interactive 3D visualization, CAD integration, and validation tools. This improves workflow efficiency, reduces errors, and increases confidence in complex MCNP models.