[ Counter ] section
==================================================

In PHITS, each particle maintains an individual value called a *Counter* in addition to other information such as energy and position.
The counter value can be updated whenever specific events occur, such as entering or exiting a certain region ( **in**, **out** ), scattering or nuclear reactions within that region ( **coll** ), or reflection at a boundary ( **ref** ).
This allows users to investigate in detail the history and origin of how tallied particles reached their locations. Therefore, the counter serves as an *event logger* in PHITS simulations.
To enable restrictions based on counters, the **ctmin** or **ctmax** parameters must be set in each tally section or the [Parameters] section.
This allows you to either selectively tally only particles with specific counter values (gate function) or terminate the actual tracking of particles that satisfy certain conditions (cutoff function).

Three counters can be used in tally sections.
The counter basically counts when

1. a particle enters a specified region, **in** [#]_
2. a particle goes out of a specified region, **out**
3. a particle undergoes scattering or a nuclear reaction in a specified region, **coll**
4. a particle reflects back on a certain boundary of the region, **ref**
5. a yield value is tallied in **[t-yield]** or **[t-dchain]** with **ndata=2,3**, **ndata**

You can set one progress value of the counter from **-9999** to **9999**, or zero set, **10000**.
Counter values are attached to particles.
Secondary particles produced in collisions inherit the counter value of their parent.
The capacity of the counter is from **-9999** to **9999**.
The counter changes only within this range.
You can set the counter for each particle by using **part=** definition, and you can exclude some particles from counter actions by **\*part=** definition.

.. code-block:: text
  :caption: **[ Counter ]** section example (1)

      [ Counter ]
         counter = 1
            part = neutron proton
          reg     in     out    coll    ref
            1      1   10000       0      0
           11      1   10000       0      0
         counter = 2
           *part = proton deuteron triton 3he alpha nucleus
          reg                        in     out    coll
           ( { 2 - 5 } 8 9 )          -1       0       1
         counter = 3
            part = 208Pb
          reg                        coll
           ( 11 12 15 )                 5
           ( 6<10[1 0 0]<u=3 )        100
          ....            ........
          ....            ........

If you want to change the order of region number, **reg**, **in**, **out**, **coll**, and **ref**, set it as **reg coll in out ref**.
You can use the skip operator **non**.
At least one must be defined among **in**, **out**, **coll**, and **ref**.
If nothing is defined, it is assumed to be no counter.
A numeric value gives one progress value of the counter.
**10000** means zero set.
The initial counter value of a source particle is zero.

You can use the format **( { 2 - 5 } 8 9 )**, and you can use the lattice and universe style **( 6 < 10[1 0 0] < u=3 )**.
However, a value must be enclosed by **(   )** if it is not a single numeric value.
When you make the **[Cell]** section using a universe, specify the cell number defined in the universe instead of the cell number of the frame where the universe is inserted.

In the definition of **part=**, you can specify up to 20 particles.
For nuclei, you can use expressions like **208Pb** and **Pb**.
In the latter case, **Pb** denotes all isotopes of **Pb**.

From version 2.90, more detailed classifications for **coll** are available.
The opportunities shown in :numref:`tbl-counter` can be used as keywords so that the counter counts.
**nucl**, **atom**, and **dcay**, which are particular interactions, belong to **coll**.
Furthermore, **nucl** and **atom** are classified into three and ten kinds, respectively.
When you want to analyze the PHITS simulation in detail, set these keywords.
Note that if you set **coll** and **nucl** at the same time, counting is duplicated when a nuclear reaction event occurs.

When **fiss** is specified, the counter is called when fission channels of the nuclear data library and the statistical decay model, GEM, are chosen.

.. list-table:: Categories of reaction events belonging to **coll**
  :name: tbl-counter
  :widths: 18 18 64
  :header-rows: 1

  * - Interaction
    - Event
    - Explanation
  * - **nucl**
    -
    - A particle undergoes nuclear interactions in a specified region.
  * - 
    - **elst**
    - A particle undergoes elastic scattering in a specified region.
  * - 
    - **iels**
    - A particle undergoes inelastic scattering in a specified region.
  * - 
    - **fiss**
    - A particle undergoes fission in a specified region.
  * - **atom**
    -
    - A particle undergoes atomic interactions and generates a secondary particle in a specified region.
  * - 
    - **delt**
    - A particle generates delta-rays in a specified region.
  * - 
    - **knoe**
    - An electron or positron generates knock-on electrons in a specified region.
  * - 
    - **fluo**
    - A particle generates atomic fluorescence X-rays in a specified region.
  * - 
    - **auge**
    - A particle generates Auger electrons in a specified region.
  * - 
    - **brem**
    - A particle undergoes bremsstrahlung in a specified region.
  * - 
    - **phel**
    - A particle undergoes the photoelectric effect in a specified region.
  * - 
    - **cmpt**
    - A particle undergoes Compton scattering in a specified region.
  * - 
    - **pprd**
    - A particle generates an electron-positron pair in a specified region.
  * - 
    - **anih**
    - A particle is annihilated in a specified region.
  * - 
    - **rayl**
    - A particle undergoes Rayleigh scattering in a specified region.
  * - **dcay**
    -
    - A particle decays in a specified region.

When **in** or **out** is specified, the counter value changes after particle information has been tallied in **[t-cross]**.
Therefore, if the counter value before the change is not specified, the information at the moment of crossing the boundary plane will not be tallied.
On the other hand, when **coll** or reaction events belonging to **coll** are specified, the counter value changes before particle information has been tallied in **[t-yield]**, **[t-product]**, **[t-interact]**, and **[t-point]**.
Therefore, to tally the information at the moment the reaction event occurs, specify the counter value after the change.

Specifying **ndata** in **[counter]** changes the counter value when a yield value in **[t-yield]** or **[t-dchain]** using **ndata=3** is replaced with cross section data in a directory specified by **file(27)**, with default **file(1)/XS/yield/**.
This setting can avoid double-counting of tally yield.
When you set the **ndata** option in **[t-yield]** or **[t-dchain]**, a value based on cross section data is tallied instead of a result of nuclear reaction models.
However, for example, if a secondary particle produced by a nuclear reaction model has an energy greater than **emin**, it will be counted twice, with the contribution of replacement at the time of the reaction event and the contribution at the time of energy cutoff after its transport.
To avoid this double-counting, setting a value of **ndata** to **+1** in **[counter]** and specifying **ctmax(i)=0**, **i=1,2,3**, in the tally section are useful, because the contribution of secondary particles is ignored.

.. [#] The counter also counts when a source particle is generated within the region specified by **in**. This specification was not written in the manual, but has been included since the counter function was implemented. If you have performed a calculation that generates sources within the region specified by **in**, please confirm it.