5.4. [ Material ] section¶
Materials, which are used to define 3-dimensional geometry, are defined in this section. The defined materials are refered to some sections such as [cell] section.
The [material] section is defined by material number, elements (or nuclides), and their composition ratios. Following a material number, element symbols and their ratios should be alternately written to define a compound or mixture.
The format is:
[ Material ] MAT[n] element ratio element ratio ... ...
Two formats to specify material numbers can be used as follows: MAT[n] and Mn, where n can be specified up to a material number of 99,999 unless it is over-defined. Note that a blank space cannot be set between MAT and [ in the format MAT[n].
The following comment marks can be used: #, %, !, $.
Although version 2.88 or before, c followed by a blank space can also be used as a comment mark, but after version 2.89 it is not permitted in the default setting.
To use c followed by a blank space as a comment mark in this section, set icommat = 1 in the [parameters] section.
5.4.1. Element (nuclide) definition¶
The element in the above format can be specified using element symbols. To define nuclide (isotope), add its mass number to the symbol as follows: 208Pb, Pb-208, or 82208. For instance, hydrogen is defined as 1H, H-1, or 1001. The natural abundance of isotopes can be defined using only an element symbol or a no-mass style as, e.g., Pb, 82000. Note that the natural isotope ratio format cannot be used for an isotope not included in the nuclear data library JENDL-4.0.
To use nuclear data libraries other than JENDL-4.0, copy all addresses of the new library and then paste it at the end of the address file file(7) (D=xsdir). When setting the new library of low-energy neutrons (below 20MeV) other than JENDL-4.0, specify the library id in each material number by NLIB parameter, which is shown in Table 5.4.3 . The library id consists of the library number (double-digit) and data class (character a-z). For example, 50c for the low-energy neutron data library of JENDL-4.0. The libraries of photons, electrons, and protons can be also specified by PLIB, ELIB, HLIB, respectively. The library id can be specified by nuclide instead of by material number following the element definition and a period as, e.g., 208Pb.50c, Pb-208.50c, or 82208.50c. In PHITS, only one type of the library should be used for each incident particle, and the id should be specified by the NLIB, PLIB, ELIB, HLIB parameters. Only for neutrons, the second library can be used; in this case, after specifying the library id by NLIB, define the nuclide by the expression of 208Pb.50c. Note that only neutron data library can be specified by the extension after each substance. For example, when you use proton data libraries of JENDL-4.0/HE for \(\mathrm{^6Li}\) and \(\mathrm{^7Li}\) , please specify them with HLIB as shown below:
6Li 0.001
7Li 0.999
hlib=51h
If the library id is not specified by the user, PHITS searches the address file file(7) (D = xsdir) from the top line for the library number id corresponding to the nuclide and uses the corresponding data library. Information on the data library used in a PHITS calculation is written in the summary output file file(6) (D=phits.out) when kmout=1 is set in the [parameters] section.
When specifying a metastable nuclide, use a five-digit integer format consisting of the atomic number followed by the mass number. In this case, add 50 to the mass number. For example, to specify Am-244m, use 95294. If a corresponding nuclear data library for the nuclide exists, it will be referenced.
5.4.2. Composition ratio definition¶
The composition ratios of the defined elements are given in ratio in the above format. Two ways are available for the ratio definition: if ratio takes a positive value, it means atomic ratio; for negative value, it does mass ratio. For instance, water ( \(\mathrm{H_2O}\) ) can be defined as follows:
MAT[1] H 2 O 1
or
MAT[1] H -2/18 O -16/18
In the latter case, the mass ratios of hydrogen and oxygen are given as about 2/18 and 16/18, respectively, because the molecular mass of the water is about 18.
The material densities used in transport calculations are usually given in the [cell] section. However, when the material density is defined as 0 in the [cell] section, or when the letmat parameter is used in the [t-deposit], [t-deposit2], [t-let], or [t-sed] sections, the material density must be defined here instead of the composition ratio. In this case, a positive value means the particle density [ \(10^{24}\,\mathrm{atoms/cm^3}\) ], and a negative value means the mass density [ \(\mathrm{g/cm^3}\) ].
5.4.3. Material parameters¶
For regions in which nuclear data are used, the material parameters for each material can be set using the format keyword=value. The parameters can be set anywhere in the material subsection. The full set of material parameters is listed in Table 5.4.3 .
Value |
Explanation |
(D=0)
|
Density effect correction to electron stopping power.
|
=0
|
Appropriate for materials in the condensed (solid or liquid) state used.
|
=1
|
Appropriate for material in the gaseous state.
|
Value |
Explanation |
sub step number for electron transport.
|
|
=n
|
Make sub step number n for electron transport: ignored when n is smaller than the built-in default value.
|
Value |
Explanation |
Default neutron library number id.
|
|
=id
|
Change default neutron library number id.
|
Value |
Explanation |
Default photon library number id.
|
|
=id
|
Change default photon library number id.
|
Value |
Explanation |
Default electron library number id.
|
|
=id
|
Change default electron library number id.
|
Value |
Explanation |
Default proton library number id.
|
|
=id
|
Change default proton library number id.
|
Value |
Explanation |
(D=0)
|
Conductor settings.
|
<0
|
Non-conductor.
|
=0
|
Non-conductor if there exists at least 1 non-conductor; otherwise, conductor.
|
>0
|
Conductor if there exists at least 1 conductor.
|
5.4.4. Direct specification of stopping power¶
In general, PHITS automatically calculates the stopping power of each material using models such as ATIMA and SPAR specified by ndedx parameter in [parameters] section. If you need to use certain databases of the stopping power such as those given in ICRU90, you can use them by specifying the filename of the database as follows:
dedxfile = filename
This database file should be contained in the folder specified by file(29) whose default setting is file(1)/data/dedx. In the default folder, the databases of stopping powers of protons and \(\alpha\) particles in several materials calculated by PSTAR and ASTAR [1] , respectively, are contained. Note that this function is effective only for particles whose stopping power is set to be calculated by ATIMA. The energy and angular straggling can be considered according to nedisp and nspred parameters, respectively, in the same as the model calculation.
5.4.4.1. Format of stopping-power database¶
In the stopping-power database, $ and # can be used as the comment remark. All letters are case-insensitive in the same as the PHITS input file. Only two parameters can be specified in the database, which are unit and kf for defining the unit of particle energy and particle type, respectively. unit should be defined before specifying kf parameter.
unit = 1: MeV (Total kinetic energy, default)
= 2: MeV/u (Kinetic energy per atomic mass unit)
= 3: MeV/n (Kinetic energy per nucleon)
kf indicates the kf code of the radiation. After specifying kf, the database of the stopping power should be given as
Energy StoppingPower
in the ascending order of the energy. The unit of the stopping power should be \(\mathrm{MeV\,g^{-1}\,cm^{2}}\) . The stopping power of radiation having an energy outside the defined region or having kf code that is not defined in the file is calculated by ATIMA. You can define stopping power databases for more than 1 radiation type in one file, but you cannot use more than 1 stopping power database file for a material.
5.4.5. \(S(\alpha,\beta)\) settings¶
In the transport of low-energy neutrons, the library of the thermal scattering law data \(S(\alpha,\beta)\) may be required. This library plays an important role in describing the transport of thermal neutrons. This library can be set as follows:
MTn materialID
where n is the material number and materialID is the ID number, such as lwtr.20t, written in xsdir. For example, the library for water at room temperature (at 296K) can be set as follows:
M1 H 2.0
O 1.0
MT1 lwtr.20t
See /XS/tsl/tsl-table for detailed information for these data.
5.4.6. Chemical form specification for track structure calculation¶
Chemical form of the material is important for track-structure calculation. Specification of chemical form is not necessary for proton/carbon ion track-structure calculation by KURBUC and electron track structure calculation because the cross section is calculated by scaling the cross section of liquid water. However, track-structure simulation of protons and ions by ITSART (Ion Track Structure calculation model for Arbitrary Radiation and Targets) can consider the elemental composition of the materials. Moreover, the molecular structure of following substances is considered if specified in [material] section.
\(\mathrm{H_2O, CO_2, NH_2, NH_3, SF_6, TeF_6, CH_4, CH_3, }\) \(\mathrm{C_2H_2, C_2H_4, C_2H_6, C_6H_6,(CH_3)_2NH}\)
The chemical form of a compound is specified as follows.
M1 H 2.0 O 1.0
chem = H2O
Mixture of compounds and pure materials is written in this way using molar ratios.
M1 H 1.62 O 0.01 N 1.6 C 0.4 Ar 0.1
chem = H2O 0.01 N2 0.8 CH4 0.4 Ar 0.1
The molar ratio inside Chem is automatically normalized therefore the magnitude is not important.
5.4.7. Examples¶
Some examples using the materials parameter are shown below.
Material example (1)
[ Material ]
MAT[ 1 ]
1H 1.0000000E-04
208Pb 1.7238000E-02
204Pb 4.6801000E-04
206Pb 7.9430000E-03
207Pb 7.2838000E-03
MAT[ 2 ]
1H 1.0000000E-09
14N 4.6801000E-05
16O 7.9430000E-06
By default, the order is element, then ratio; these can be specified in reverse by putting den and nuc as,
Material example (2)
[ Material ]
den nuc
MAT[ 1 ]
1.0000000E-04 1H
1.7238000E-02 208Pb
4.6801000E-04 204Pb
7.9430000E-03 206Pb
7.2838000E-03 207Pb
MAT[ 2 ]
1.0000000E-09 1H
4.6801000E-05 14N
7.9430000E-06 16O
Material example (3)
[ Material ]
m1 80196.49c 5.9595d-5
80198.49c 3.9611d-3
80199.49c 6.7025d-3
80200.49c 9.1776d-3
80201.49c 5.2364d-3
80202.49c 1.1863d-2
80204.49c 2.2795d-3
$ ...Be...
m3 4009.37c 1.2362E-1
mt3 be.01
$ ...h2o (25C)...
m4 1001.37c 6.6658d-2 8016.37c 3.3329d-2
mt4 lwtr.01
$ ...b4c (natural boron; 25%-density)...
m5 6012.37c 6.8118d-3
5011.37c 2.1825d-2
$ ...liquid-h2 (20K)...
m6 1001.49c 3.1371d-2 1011.49c 1.0457d-2
mt6 orthoh.00 parah.00
5.4.8. Predefined materials¶
Since Version 3.37, predefined materials can be selected from predefined_material.dat in the data folder. When a predefined material itself is expanded in the [material] section, its alias must be enclosed by @. The format is as follows:
[ Material ]
MAT[material-number] @material-name@
The @material-name@ part must be an alias name written in
predefined_material.dat.
Multiple alias names are defined for a single material. For example,
water is defined with aliases such as @WATER@, @H2O@
@WATER_LIQUID@, @LIQUID_WATER@,
@276_WATER_LIQUID_H2O@, and @WATER_WATERDB_H2O_ICRU-276@.
For the full list of predefined materials, see
predefined_material_index.csv in the data folder or
13.4 Predefined materials.
In the default setting, 641 materials included in the Flair [2] material list, plus three types of standard concrete used in Japan and the United States [3] [4] are defined.
The material name written in [] and name parameter of each material is also registered as an alias.
Since spaces are not allowed in alias names, spaces in these
parameters are replaced with _.
The predefined material database can also be edited by users.
Examples are shown below.
[ Material ]
MAT[1] @DRY_AIR@
m2 @iodine@
With this description, @DRY_AIR@ and @iodine@ are automatically
expanded to the material compositions (material parameters) registered
in the database.
Conceptually, the above sample is expanded to the following:
MAT[1] C -1.503641e-07 N -0.0009099761 O -0.0002792591 Ar -1.545449e-05 gas=1
dedxfile = air_icru90.txt
m2 I -4.93
However, the actual format shown in the input echo follows the normal PHITS [material] section format.
By default, the predefined material database file is
%PHITSPATH%/data/predefined_material.dat.
If you want to use another database file, write the following before
the first line that uses a predefined material:
set:%predefined_material.dat%[d:/test/predefined_material.dat]
When a predefined material is expanded in the [material] section, its alias name is also automatically registered as a character variable representing the corresponding material number. In subsequent sections, this material-number variable is written using %. For example,
[material]
m1 @WATER@
after this definition, the [cell] section can be written as
[cell]
100 %WATER% 0.0 -10
which is equivalent to
[cell]
100 1 0.0 -10
Therefore, when using this function, the [material] section must be
defined before the [cell] section and any other section that refers
to the material number.
Since the density of the predefined material is already included in the
database, the [cell] section can define the density as 0.0 to
use that database value as it is.
If an \(S(\alpha,\beta)\) data name is defined in
predefined_material.dat, the corresponding MT line is also added
automatically.
For example, if a material with sab = lwtr.20t in the database is
expanded, the corresponding MTn lwtr.20t is inserted automatically.
On the other hand, if the sab entry is empty, no MT line is
added.
If dedxfile is defined in predefined_material.dat, the corresponding
dedxfile line is also added automatically.
For example, when @DRY_AIR@ is expanded, it becomes
MAT[1] C -1.503641e-07 N -0.0009099761 O -0.0002792591 Ar -1.545449e-05 gas=1
dedxfile = air_icru90.txt
On the other hand, when a material such as @iodine@ is expanded and
no dedxfile is defined for it, no dedxfile line is added.
The available dedxfile names are those registered in the
data/dedxfile folder. See Direct specification of stopping power
for details.
The following points should be noted when using this function:
A predefined material alias is written in the form such as
@WATER@in the [material] section.To use an alias such as
%WATER%in the [cell] section or elsewhere, the corresponding mapping to a material number must be defined beforehand in the [material] section.If you want to use a database file other than the default one, specify it with
set:%predefined_material.dat%[...]before the first use of a predefined material.Alias names in predefined_material.dat are searched case-insensitively. However, when using the registered name as a character variable, keep the same capitalization. For example, if you define
@WATER@, use%WATER%; if you define@Water@, use%Water%.
An example using this function is shown below.
[ Material ]
mat[1] @polyethylene@
mat[2] @Fe@
mat[3] @WATER@
[ Cell ]
101 %Fe% 0.0 -10
102 %polyethylene% 0.0 -11 10
103 %WATER% 0.0 -12 11
...
[ Mat Name Color ]
mat name color
%polyethylene% Polyethylene yellow
%Fe% iron black
%WATER% water red