Grid Tally Data

Mesh Tally Data

Tally mesh data is written to mdata files by MCNPX and to meshtal files by MCNP5. These files are imported with the Read Mdata and Read MCNP5 Mesh Tally items in the File menu.

Meshtal and mdata files must be in ASCII format. MCNP5 writes ASCII meshtal files directly. The gridconv program (supplied with the MCNPX distribution) must be used to convert from the binary mdata files as written by MCNPX to ASCII format (recent versions of MCNPX have an input option to write ASCII mdata files directly).

The Mesh Tally Source property page shows the full path name of the data file, the comment line from the file, and the number of histories used in the calculation.

When reading mesh tally lines in an MCNPX input file, the tally number, particle, and most data items on the RMESH/CMESH lines are remembered and included when writing an MCNPX file. Any arguments to DOSE are ignored, as are MFACT, ERGSH, MSHMF, and any arguments. MCNP5 mesh tally input items that are similarly read and written include the tally number, particle, transformation (TR), output format (OUT), and tally multiplier (FACTOR).

Moritz colors the tally mesh cells according to the selected tally type. This Figure shows a 2D plot of grid tally data; this Figure shows a 3D plot. (These 2 simple examples are from one of the MCNPX test problems.)

Mesh Matching. After a data file is read, Moritz either uses an existing mesh or creates meshes from the specifications in the file. An existing mesh would most usually be from the MCNP input file used to create mesh tally. The mesh matching algorithm compares all mesh lines in sequence, ignoring the distinction between coarse and fine mesh lines. A transformation may be applied to the tally mesh in the MCNPX/MCNP5 input file. The transformation information is lacking in both the mdata and meshtal files. If an existing mesh is the same as an mdata mesh and it carries a transformation, it is used for the grid tally data if it has the same tally number. If the numbers are not the same, Moritz asks the user whether or not to use the existing mesh.

When displaying both the geometry and grid tally data, the MCNPX/MCNP input file should be read before the data file.

Internally, Moritz handles cylindrical tally meshes as aligned with the Z axis; a transformation is applied to the mesh to accommodate other axis directions. This treatment follows the MCNPX mesh tally specification where a transformation must be supplied for non Z aligned meshes. The MCNP5 input allows specification of both the mesh axis vector and a transformation. If a cylindrical mesh from an MCNP5 input file is not aligned with the Z axis and also carries an explicit transformation, the matching algorithm ignores the axis orientations and origins and only considers the mesh values. When writing MCNP5 FMESH specifications, cylindrical meshes are always oriented along the Z axis and the appropriate transformation is supplied even if the original mesh as read from an MCNP5 input carried a different axis vector.

Data Selection and Scaling. After a data file is read, the data is displayed. If an input file with matching meshes had been read previously and one or more of those meshes are visible, the data is displayed for those visible meshes. Otherwise, if only a single visible mesh is permitted, the first data set for the last mesh read is displayed. If multiple meshes are permitted, the first data set in all meshes are displayed; in this case, the initial color coding may not be correct. Various settings on the Mesh property sheet can affect these actions. The Only 1 Mesh Visible at a Time checkbox on the Mesh Style property page controls multiple mesh visibility.

The data can be shown in 2D, 3D, or both. The Mesh Tally property page shows the types of data available for the selected mesh. For MCNPX mesh tallies, this data may include flux, population, dose, etc. MCNP5 data consists of flux and, optionally, flux multiplied by mesh cell volume. MCNP5 permits multiple energy bins for a mesh; a pull down menu permits selection of which energy bin to display. More than one mesh may be selected for display. If so, the same data type must be selected for each visible MCNPX tally mesh. Moritz does not check if consistent energy bins are chosen for visible MCNP5 tally meshes or if the flux or flux times volume choices are the same. The property page also has a choice for display of the data or its relative error. The data/error choice must be the same for all visible meshes.

The Data Limits fields show the minimum and maximum of the data values for the chosen data set or all visible data sets. When Logarithmic Scaling is in effect, the minimum value does not include data <= 0. The color coding of the data is determined by the values in the Plot Limitsfield. These values are initially set from the Data Limits, but do not change as different meshes or data sets are chosen. The Copy button copies the Data Limits to the Plot Limits. The Copybutton is useful to set the color scaling when changing meshes in the one mesh at a time mode.

The user can choose to apply the color coding the data values or the logarithm of the values. When Logarithmic Scaling is used, cells with a data value < 0 can be either colored black or not shown. Nonpositive data is not shown in This Figure , resulting in the notch at the top, the blank lower left corner resulting from a void, and in a few mesh cells colored grey in the shield at the center of the mesh. The same mesh is shown in 3D in This Figure . This Figure shows cells with nonpositive data in the cylindrical void surrounding the model.

Data Visibility. The Mesh Tally property page controls the visibility of the mesh data and its mesh. For a data set to be visible, both the data and its mesh must be marked visible in the Show Data and Show Mesh boxes. Separate visibility choices exist for 2D and 3D. Unchecking a checkbox in the Show Mesh box is sufficient to hide both the mesh and data. When only one mesh is visible at a time, checking a Show Mesh checkbox hides any other visible mesh. Whether the mesh is shown together with the data is controlled by the Show Mesh with Data checkboxes on the Mesh Tally Style property page.

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