Card 3: Calculation options
---------------------------

.. _`param:idivs`:

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

.. list-table:: **IDIVS** :phits-same:`PHITS: same name`
   :header-rows: 0

   * - Value
     - Description
   * - (D=50)
     - Number of time subdivisions of each irradiation time step.

.. _`param:ichain`:

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

.. list-table:: **ICHAIN** :phits-same:`PHITS: same name`
   :header-rows: 0

   * - Value
     - Description
   * - (D=100 [#]_)
     - Maximum number of linear chains considered per nuclide.

.. _`param:ilchain`:

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

.. list-table:: **ILCHAIN** :phits-same:`PHITS: same name`
   :header-rows: 0

   * - Value
     - Description
   * - (D=\ ``ICHAIN``, D\ :sub:`P`\ =100)
     - Maximum length of each linear decay chain.

.. _`param:itdecs`:

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.. list-table:: **ITDECS** :phits-same:`PHITS: same name`
   :header-rows: 0

   * - Value
     - Description
   * - (D=0, D\ :sub:`P`\ =1; requires ``JMODE``\ =0,2)
     - Option for considering depletion/burnup of target nuclides by the continuous primary beam irradiation [#]_.
   * - = 0
     - Target nuclides are not depleted from beam interactions.
   * - = 1
     - Beam-induced target nuclide burnup is taken into account.

.. _`param:itdecn`:

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

.. list-table:: **ITDECN** :phits-same:`PHITS: same name`
   :header-rows: 0

   * - Value
     - Description
   * - (D=0, D\ :sub:`P`\ =1; requires ``JMODE``\ =1,2)
     - Option for considering depletion/burnup of target nuclides by transmutations from neutrons below 20 MeV [#]_.
   * - = 0
     - Target nuclides are not depleted from neutron reactions.
   * - = 1
     - Neutron-induced target nuclide burnup is taken into account.

.. _`param:isomtr`:

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

.. list-table:: **ISOMTR** :phits-same:`PHITS: same name`
   :header-rows: 0

   * - Value
     - Description
   * - (D=0, D\ :sub:`P`\ =2,0 [#]_)
     - Option for treatment of isomers in the nuclide yield file.
   * - = 0
     - Isomers are considered distinct nuclides from their ground state.
   * - = 1
     - Isomers are treated as if they were the ground state.
   * - = 2
     - All isomers and the ground state are treated as being produced with equal probability.

.. _`param:ixsrall`:

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

.. list-table:: **IXSRALL** :phits-same:`PHITS: same name`
   :header-rows: 0

   * - Value
     - Description
   * - (D=0, D\ :sub:`P`\ =1)
     - Option for accelerating calculation time by reading and storing all neutron reaction cross section data into memory at once rather than reading and then discarding each cross section once per region.
   * - = 0
     - :math:`\sigma` data is read once per region (slower for multiple regions but consumes less memory; “old” methodology).
   * - = 1
     - :math:`\sigma` data is read once and saved for calculations in all regions (faster for multiple regions but consumes more memory).

.. _`param:ifisyd`:

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

.. list-table:: **IFISYD** :phits-same:`PHITS: same name`
   :header-rows: 0

   * - Value
     - Description
   * - (D=1, D\ :sub:`P`\ =0,2 [#]_)
     - Option for :math:`<`\ 20 MeV neutron-induced fission yields.
   * - = 0
     - No effect (these fissions not considered).
   * - = 1
     - Fission yields from induced fission reactions are taken into account. (requires ``JMODE``\ =1,2)
   * - = 2
     - Fission yields from induced and spontaneous fission reactions are taken into account. If ``JMODE``\ = -1 or 0, only spontaneous fission yields are taken into account.

Note: It is strongly recommended to increase ``ICHAIN`` from its default value of 100 to 500\ :math:`\sim`\ 1000 instead (demonstrated in Sec. :ref:`4.7 <fission-settings>`) if your problem contains fissioning nuclides as fission greatly increases the number of possible decay and reaction pathways/chains producing each nuclide.

.. [#]
   [T-Dchain] increases default ``ICHAIN`` to 500 if ``IFISYD``\ \ \ :math:`>`\ \ 0 and any A\ \ :math:`>`\ \ 220 target nuclides are found.

.. [#]
   This option toggles burnup calculations using the negative yields present in the \*.dyld file generated by PHITS to deplete target nuclides and using Pearlstein systematics :cite:`Pearlstein1987` with the ``ebeam`` and ``amp`` parameters (assuming a proton beam) to reduce the beam flux as the target is depleted.

.. [#]
   When a neutron reaction occurs, one nuclide is transmuted into another. This option allows for the user to either ignore or consider destruction/removal of target nuclides in these reactions.

.. [#]
   If the PHITS parameter ``igamma`` is set to 3, as recommended, the PHITS default for ``ISOMTR`` is 0. Note ``igamma``\ \ \ ``=2`` is the parameter’s default value in PHITS if not specified, setting ``ISOMTR``\ \ \ ``= 2`` by default.

.. [#]
   [T-Dchain] sets ``IFISYD`` to 0 by default; if any target nuclides have A\ \ :math:`>`\ \ 220, it is set to 2 instead.