5.2.5. Stopping power models¶
Value |
Explanation |
(D=3) [1]
|
Options for \(dE/dx\) of charged particle and nucleus. Note that this option is not applicable for electrons and positrons.
|
=0
|
SPAR [2] for nucleus, NMTC for the rest of particle species.
|
=1
|
ATIMA [3] for nucleus and proton, NMTC for the rest of particle species.
|
=2
|
SPAR for nucleus, proton, pion, and muon, NMTC for the rest of particle species.
|
=3
|
ATIMA for all charged particles.
|
Value |
Explanation |
(D=500)
|
Maximum database size of ATIMA.
|
Value |
Explanation |
(D=0.0)
|
Cut-off energy of ATIMA database [MeV/n].
|
Value |
Explanation |
(D=-1)
|
Setting for the ionization potential of water in ATIMA. This setting is applicable for H \(_2\) O only.
|
< 0
|
Use of the default 75 eV.
|
> 0
|
User-defined value [eV].
|
Value |
Explanation |
(D=0)
|
Option for the charge number of source particles in ATIMA calculations.
|
=0
|
Effective charge. The charge number is equal to the \(Z\) number at high energies, and gradually decreases with decreasing energies.
|
=1
|
Fixed charge. The charge number is equal to the \(Z\) number as a constant, unless it is specified by the izst parameter in the [source] section.
|
Value |
Explanation |
(D=1)
|
Options for the method of considering \(\delta\) -ray energy in calculating \(dE/dx\) for charged particle and nuclei.
|
=0
|
Conventional method (subtract the energy of sampled \(\delta\) -ray from the unrestricted stopping power).
|
=1
|
Restricted LET. The cut-off energy of the delta rays is set in the [Delta Ray] section.
|
From version 2.85, the algorithm for calculating stopping power with ATIMA in PHITS was improved and speeded up. In the old algorithm, calculation of range and stopping power was always performed every time when a new charged particle was produced or a transporting particle entered a new material. The new algorithm creates a database for each combination of transporting particle and material when a new particle-material combination appears, and look up the range and stopping power in the database the next time, instead of calling the high computational-cost routine ATIMA. As such, PHITS simulation using ATIMA is compatible with SPAR in terms of calculation time but with higher accuracy.
Starting from ver. 2.97, the setting of ndedx=3 can be used for nuclei with the atomic number of \(93\le Z\le97\) (from Np to Bk) [4] . Ionization potentials and density correction parameters needed in calculating nuclear stopping powers for those nuclei are adopted from the literature [5] , and SPAR is used in the calculation of electronic stopping power.
The setting of ifixchg = 1 is not appropriate in most circumstances. The charge state of ions changes along their traveling paths in a material owing to attachment and disattachment of electrons. Thus, this setting only suits calculations of energy losses in a thin foil or gas.