7.18. [ T-Volume ] section

When you set mesh=reg in tally sections, you have to give volumes of each cell to estimate results in the unit of (/volume). PHITS has a function of automatic calculation to obtain the volumes using [t-volume]. In this function, PHITS calculates the volumes by performing a Monte Carlo integration with setting the material of each cell to be void and a special source region.

[t-volume] is effective only when setting icntl=14 in the [parameters] section. Only one [t-volume] section can be set in one input file.

The format of parameters in [t-volume] is as follows.

Table 7.18.1 mesh

value

explanation

reg

Mesh type. Only reg can be set. A mesh type subsection is required below this option.
Table 7.18.2 file

value

explanation

file name

Define file names.
Table 7.18.3 resfile

value

explanation

(omitted, D=file)

Define a file name of the past tally in the restart calculation.
Table 7.18.4 r-out

value

explanation

(omitted, D=0.0)

Radius of the outer void [cm].
Table 7.18.5 title

value

explanation

(optional)

Title.
Table 7.18.6 method

value

explanation

(omitted, D=0)

Option for Monte Carlo integration. 0: By particle track lengths. 1: By source points.
Table 7.18.7 s-type

value

explanation

1, 2

Source type for volume calculation. 1: Sphere source. The coordinates of the sphere, x0, y0, z0, and its radius, r0, have to be defined. 2: Rectangular solid source. The coordinates x0, x1, y0, y1, z0, and z1 have to be defined.
Table 7.18.8 x0, y0, z0

value

explanation

Coordinates.
Table 7.18.9 x1, y1, z1

value

explanation

Coordinates.
Table 7.18.10 r0

value

explanation

Radius.
Table 7.18.11 stdcut

value

explanation

(optional, D=-1)

Threshold value of STD cut off.

When specifying stdcut, PHITS automatically stop the calculation depending on values of STD, standard deviation. This function is available when stdcut is positive and itall=0,1 is set in [parameters] section. When all relative values of STD of the tally result are larger than 0 and smaller than stdcut at the last of one batch, the calculation is stopped. If stdcut in two or more tally sections is set, all the results of the tally sections have to satisfy the conditions in order for the function to work.

The source type in the volume calculation is specified by s-type. In s-type=1, the source generates on a sphere of the center coordinates (x0,y0,z0) and the radius r0 with the inward direction. This is the same condition as dir=-all in s-type=9 of the [source] section. In s-type=2, the source uniformly generates on surfaces of a rectangular solid which are defined by 6 planes, x=x0, x1, y=y0, y1, z=z0, and z1. Its direction is inward. In either case, you have to set the source region to be large so as to cover all specified cells.

Attention: the boundaries in [t-volume] must be smaller than the boundaries of the geometry. There must not be any ‘outside’ cells, -1, inside these boundaries.

When executing PHITS using [t-volume], the information on the source used in the volume calculation is output in [source] of the summary file file(6), default phits.out. [source] written in the input file of PHITS is not output in the summary file.

An example of [t-volume] is as follows.

Listing 7.18.1 Example of [t-volume]
     1:   [ T - V o l u m e ]
     2:     mesh =  reg            # mesh type is region-wise
     3:      reg = 101  102  103  104  105
     4:     file = volume.out      # file name of output for [volume]
     5:   s-type =    1            # 1: Sphere source, 2: Rectangular source
     6:       x0 =  0.0            # (D=0.0) x of sphere center
     7:       y0 =  0.0            # (D=0.0) y of sphere center
     8:       z0 =  0.0            # (D=0.0) z of sphere center
     9:       r0 =  50.0           # radius of sphere

[t-volume] section should have the setting of mesh=reg. The cell numbers should be specified after reg=. By setting s-type and the related parameters such as x0, you can define the special source region for the volume calculation. Note that the source region should be set to cover all cells specified in reg=, otherwise the calculated volumes would be wrong. On the contrary, if you set an extremely large source region, the statistical uncertainties of the calculated results would be large. The obtained volumes are output in a file named by file=. The format of the output file is as follows.

Listing 7.18.2 Output format of [t-volume]
[ T - V o l u m e ] off
     mesh =  reg            # mesh type is region-wise
          ....   ....     ....   ....
          ....   ....     ....   ....

[ V o l u m e ]
  non      reg      vol      non
    1      101   5.0370E+02  0.2909
    2      102   2.4727E+03  0.1634
          ....   ....     ....   ....
          ....   ....     ....   ....

# Information for Restart Calculation
          ....   ....     ....   ....
          ....   ....     ....   ....

Because the volumes are output in the format of the [volume] section, the results can be used in the main calculation with icntl=0 by the infl command. Here, values of the last column in [volume] are statistical uncertainties, relative values. If the uncertainties are large, you can perform the restart calculation by adding istdev=-1 or -2 in the [parameters] section, because the output file of [t-volume] has information for the restart mode.