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 given in the [cell] section. Note that material densities must be defined in the [material] section instead of composition ratios when using letmat parameter in [t-deposit], [t-deposit2], [t-let], [t-sed] sections. In this case, if it takes a positive value, the particle density is [ \(10^{24}\,\mathrm{atoms/cm^3}\) ], and for negative value, it is given as a 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