.. _[t-point]:

[ T-Point ] section
==================================================

It is impractical to calculate particle fluence at a specific point or line using the **[t-track]** tally.
To address this, the point estimator tally **[t-point]** was introduced to estimate these quantities within a short computational time.
However, to use this tally the following conditions must be satisfied in the PHITS simulation using **[t-point]**:

1. Only neutrons and photons with energies below their **dmax** can be transported. [#]_
2. Only the fluence of neutrons and photons can be calculated by **[t-point]**.
3. Neither event generator mode nor EGS5 should be used, **e-mode=0, negs=0**. [#]_
4. The material should be uniform within a certain proximity to the point detector to avoid singularity.
5. Reflection or white boundary surface should not be used.

Please see the read-me file or the sample input file in ``/phits/utility/tpoint/`` for more details.

.. rst-class:: no-caption-number

.. list-table:: **point**
   :header-rows: 0

   * - value
     - explanation
   * - number of data
     - Option for point detectors.
       A subsection is required below this option.

.. rst-class:: no-caption-number

.. list-table:: **ring**
   :header-rows: 0

   * - value
     - explanation
   * - number of data
     - Option for ring detectors.
       A subsection is required below this option.

.. rst-class:: no-caption-number

.. list-table:: **part**
   :header-rows: 0

   * - value
     - explanation
   * - particle name (optional)
     - Tally particle.
       **neutron photon** are set when **part** is not specified.

.. include:: ./commontally/e-type.rst
.. include:: ./commontally/t-type.rst
.. rst-class:: no-caption-number

.. list-table:: **unit**
   :header-rows: 0

   * - value
     - explanation
   * - 1, 2, 3
     - 1: [1/cm^2/source]
       2: [1/cm^2/MeV/source]
       3: [1/cm^2/Lethargy/source]
   * - 11, 12, 13
     - 11: [1/cm^2/nsec/source]
       12: [1/cm^2/nsec/MeV/source]
       13: [1/cm^2/Lethargy/nsec/source]

.. rst-class:: no-caption-number

.. list-table:: **axis**
   :header-rows: 0

   * - value
     - explanation
   * - **eng, t**
     - x axis value of output data.

.. rst-class:: no-caption-number

.. list-table:: **samepage**
   :header-rows: 0

   * - value
     - explanation
   * - (optional, **D=part**)
     - The type of data to be displayed on the same page of the image output file.
       Parameters that can be defined in **axis** can be specified.
       **point** and **ring** can also be specified.

.. include:: ./commontally/file.rst
.. include:: ./commontally/resfile.rst
.. include:: ./commontally/factor.rst
.. include:: ./commontally/title.rst
.. include:: ./commontally/angel.rst
.. include:: ./commontally/sangel.rst

Lethargy in **unit=3** or **unit=13** is the natural logarithmic unit of energy defined by :math:`\ln(E_{\rm ref}/E)` using a reference energy :math:`E_{\rm ref}` and the particle energy :math:`E`.
Setting these units enables obtaining results in units of Lethargy, which are given as Lethargy widths, :math:`\ln(E_{\rm high}/E_{\rm low})`, for each energy bin in the energy mesh subsection.
Here :math:`E_{\rm high}` and :math:`E_{\rm low}` are the maximum and minimum values of the energy bins, respectively.

In **[t-point]**, the number of points or rings, instead of the mesh as in other tallies, must be defined.
For example, **point=3** should be specified to define 3 point detectors.
The maximum number of points or rings per **[t-point]** is 20.
To set more detectors, another **[t-point]** tally must be defined.
Point and ring detectors cannot be combined in one **[t-point]** tally.
The information on a point or ring must be defined in successive lines following the definition of the **point** or **ring** parameter.
The point detector definition is described as follows.

.. code-block:: text
   :caption: Example of point detector definition in **[t-point]**.

     [ T-point ]
     point =    1     # number of point detectors
     non     x        y       z        r0
       1     10.0     0.0     50.0     1.0

Here **x**, **y**, and **z** indicate the coordinates of the point detector and **r0** is the radius of the fictitious sphere.
For more information on the fictitious sphere, see the read-me file in ``/phits/utility/tpoint/``.
These parameters are given in units of cm.

The ring detector is defined as follows.

.. code-block:: text
   :caption: Example of ring detector definition in **[t-point]**.

     [ T-point ]
     ring =    1     # number of ring detectors
     non   axis    ar       rr       r0
       1    z      50.0     10.0     1.0

Here **axis** indicates the direction of the ring axis specified as **x**, **y**, or **z**.
**ar** is the distance from the origin to the center of the ring, **rr** is the ring radius, and **r0** is the radius of the fictitious sphere.
The order of these parameters can be changed by changing the order of notation, for example **x y z r0** can be changed to **z y x r0**.
Aside from these factors, the parameters defined in **[t-point]** are the same as those in **[t-track]**, including the multiplier option.
Thus, the radiation dose at a specific point can be estimated using **[t-point]**.
However, material, 2-dimensional plot options, and transforms cannot be specified in **[t-point]**.

.. rst-class:: no-caption-number

.. list-table:: **epsout**
   :header-rows: 0

   * - value
     - explanation
   * - **0** (default), **1, 2**
     - When **epsout=1**, results are plotted into eps files.
       The eps file is named by replacing the extension with ``.eps``.
       When **epsout=2**, error bars are also displayed in the eps file, except for the 2-dimensional type, **axis=xy, yz, xz, rz**.

.. include:: ./commontally/maxangel.rst
.. include:: ./commontally/ctmin.rst
.. include:: ./commontally/ctmax.rst
.. include:: ./commontally/chmin.rst
.. include:: ./commontally/chmax.rst
.. include:: ./commontally/stdcut.rst
.. rst-class:: no-caption-number

.. list-table:: **multiplier**
   :header-rows: 0

   * - value
     - explanation
   * - Number of material
     - Multiplier for each material.
   * - (optional)
     - A multiplier subsection is required below this option.
       See the multiplier subsection for detailed usage.

.. include:: ./commontally/iextstat.rst
.. include:: ./commontally/prodenmn.rst
.. include:: ./commontally/prodenmx.rst
.. include:: ./commontally/nbproden.rst

.. [#] From version 3.36, charged-particle and photo-nuclear data libraries can be used.

.. [#] When EGS mode is used, the photon fluence cannot be evaluated correctly; however, it is possible to evaluate the neutron fluence in combination with the photonuclear reaction library. If EGS mode is not used, electron and positron transport cannot be considered. Therefore, when evaluating neutron production from an electron accelerator, please use EGS mode together with the photonuclear reaction library.