5.10. [ Mat Time Change ] section

By this section, you can change the material of certain cells to the other material as a function of time. This function is useful to describe a shutter of beam line, T0 chopper and the other devices for neutron optics. The unit of time is nsec.

The format is as follows.

[ Mat Time Change ]
  mat   time    change
  1     50.0    11
  2     100.0   12
  3     1000.0  0
  ...   ...     ...
  ...   ...     ...

In the above example, the material 1 is changed to material 11 at t=50.0 nsec, 2 to 12 at 100 nsec and 3 to void at 1000 nsec. If you want to replace the order of the initial material (mat), time (time) and the final material (change), set as mat change time. You can use the skip operator non. These three columns are always necessary to define the mat time change function. Note that the material is not switched at the exact moment the elapsed time equals the specified time value; it is switched only once the elapsed time strictly exceeds it.

If multiple definitions can apply to the same source material (mat), the definitions are referenced in the order they are written in the input file, and only the first definition whose condition (matching source material and elapsed time exceeding the specified time) is satisfied is applied. If the resulting new material number matches the source material (mat) of another definition written later in the input file, and that definition’s time condition is also satisfied, a chained multi-step change (for example, material A to B to C) occurs at the same instant. However, if the matching definition is written earlier in the input file, this chaining does not occur at the same instant and is instead carried over to the next transport step. To make the chaining behavior intuitive, it is recommended to write the definitions in ascending order of time.