.. _[t-let]:

[ T-LET ] section
==================================================

This tally can be used to obtain information on track length and dose as a function of the LET, :math:`dE/dx`, of a given material.
This tally counts the energy losses of charged particles and nuclei; accordingly, the Event Generator mode, **e-mode>=1**, must be used to transport low-energy neutrons.
Note that this tally does not consider the contributions of electrons or positrons below their cutoff energies, **emin**, in the result.

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

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

   * - value
     - explanation
   * - **reg, r-z, xyz**
     - Mesh type.
       A mesh type subsection is required below this option.

.. include:: ./commontally/part.rst
.. include:: ./commontally/material.rst
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.. list-table:: **letmat**
   :header-rows: 0

   * - value
     - explanation
   * - (optional)
     - Material id for LET, :math:`dE/dx`.
       If not defined, a real material is assumed.
       If a material not used in the geometry is selected, its material density must be defined in **[material]**.
       To calculate LET in water, define water with 1 g/cm^3 in **[material]**.
       When **letmat<0** is set, PHITS automatically calculates :math:`dE/dx` for water with 1 g/cm^3 for electrons and positrons.
       Please see ``ParticleTherapy`` in the recommendation setting for more details.

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.. list-table:: **l-type**
   :header-rows: 0

   * - value
     - explanation
   * - **1, 2, 3, 4, 5**
     - LET mesh.
       See :numref:`sec-mesh-type` for mesh subsection format.
       Note that the LET spectrum may have unnatural peaks when a very fine mesh, for example 20 meshes per order of magnitude, is set.

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

   * - value
     - explanation
   * - **1, 2, 3, 4, 5, 6**
     - 1: Track [cm/(keV/um)/source]
       2: Dose [MeV/(keV/um)/source]
       3: Track [cm/ln(keV/um)/source]
       4: Dose [MeV/ln(keV/um)/source]
       5: Track [cm/source]
       6: Dose [MeV/source]
   * - **7, 8, 9, 10, 11, 12**
     - 7: Track [1/cm^2/(keV/um)/source]
       8: Dose [MeV/cm^3/(keV/um)/source]
       9: Track [1/cm^2/ln(keV/um)/source]
       10: Dose [MeV/cm^3/ln(keV/um)/source]
       11: Track [1/cm^2/source]
       12: Dose [MeV/cm^3/source]
   * - **13, 14**
     - 13: :math:`L*f(L)` [dimensionless], where :math:`\int f(L)dL=1`.
       14: :math:`L*d(L)` [keV/um], where :math:`\int d(L)dL=1`.

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

   * - value
     - explanation
   * - **let, reg, x, y, z, r**
     - x axis value of output data.
   * - **xy, yz, xz, rz**
     - 2-dimensional.

.. include:: ./commontally/samepage.rst
.. include:: ./commontally/file.rst
.. include:: ./commontally/resfile.rst
.. include:: ./commontally/factor.rst
.. include:: ./commontally/title.rst
.. include:: ./commontally/angel.rst
.. include:: ./commontally/sangel.rst
.. include:: ./commontally/2d-type.rst
.. include:: ./commontally/gshow.rst
.. include:: ./commontally/rshow.rst
.. include:: ./commontally/x-txt.rst
.. include:: ./commontally/y-txt.rst
.. include:: ./commontally/z-txt.rst

From version 3.02, new options, **unit=13** and **unit=14**, were implemented.
Using them, the frequency and dose probability densities of LET :math:`L`, :math:`f(L)` and :math:`d(L)`, respectively, can be easily calculated.
The results obtained from **unit=13** and **unit=14** are proportional to those obtained from **unit=2** and **unit=4**, respectively, but their absolute values are different because the integral of the probability densities are normalized to 1 for the new options.
In place of **sum over**, the frequency mean is output when **unit=13**, and the dose mean is output when **unit=14**, though their statistical errors are not calculated, always shown as 0.000.
Note that **unit=13** and **unit=14** can be set only when **axis=let**.

.. include:: ./commontally/resol.rst
.. include:: ./commontally/width.rst
.. include:: ./commontally/volume.rst
.. include:: ./commontally/iechrl.rst
.. include:: ./commontally/volmat.rst
.. include:: ./commontally/epsout.rst
.. include:: ./commontally/maxangel.rst
.. include:: ./commontally/ctmin.rst
.. include:: ./commontally/ctmax.rst
.. include:: ./commontally/chmin.rst
.. include:: ./commontally/chmax.rst
.. include:: ./commontally/trcl.rst
.. include:: ./commontally/gslat.rst
.. include:: ./commontally/stdcut.rst