Last Update : 2015/01/27
1 Questions related to parameter setting
Q1.1 How can we precisely simulate motion of low-energy neutrons? How can we use nuclear data library in PHITS?
A1.1 In general, nuclear reaction models such as Intra-Nuclear Cascade
(INC) or Quantum molecular dynamics (QMD) cannot simulate reaction processes
attributed to induced neutrons below 20 MeV because of complex resonance
structures. Therefore, nuclear data libraries are very useful for the simulation.
To utilize the data library, emin(2) and dmax(2) in the [parameters] section
have to be set appropriately, e.g. emin(2)=1.0e-10 and dmax(2)=20.0.
Q1.2 How can we simulate motion of photons, electrons and positrons?
A1.2 As the default setting of PHITS , photons, electrons and positrons are immediately cutoff when they are created. Thus, you have to set emin(12-14) and dmax(12-14) in the [Parameters] section. The typical minimum and maximum values of these parameters are 1.0e-3 and 1.0e2 for emin(12-14) and dmax(12-14), respectively, although dmax(14) can be extended up to 1.0e5. However, if you set emin(12) and emin(13) to 1.0e-3, computational time becomes very long. Thus, the recommended emin(12) and emin(13) in most cases are 1.0e-1. Please see recommendation.zip
in more detail. Note that dmax should be set to greater than (i.e. should not be equal to) the incident energy.
Q1.3 Does the default setting of nuclear reaction models give the most
A1.3 In general, the default models give the best results in most cases
from version 2.52. It should be noted that you have to use nuclear data
library to simulate neutrons below 20 MeV (see A1.1).
Q1.4 What kind of simulation does event-generator mode suit for?
A1.4 Event generator mode suits simulations by which the event-by-event
information is necessary to be obtained, e.g. neutron detector response
calculations and design of semi-conductor devices. It is also useful for
the simulation that must determine energy and type of charged particles
produced by low-energy neutron interactions. In concrete, event generator
mode generally suits does the simulations using [T-Deposit], [T-LET], [T-SED],
[T-Yield] and/or [T-Product] tallies. On the other hand, it is not suit
for the simulations only using [T-Track] and/or [T-Cross] tallies, such
as shielding calculation. See Manual
"4.2.19 Event Generator Mode" section in more detail.
Q1.5 When should I change the mode for the statistical uncertainty (the
setting of istdev)?
A1.5 We generally recommend the history variance mode (istdev=abs(2)),
where the statistical uncertainty depends on the total history number (maxcas*maxbch),
except for the case of shared-memory parallel computing, where only the
batch the batch variance mode (istdev=abs(2)) can be selected. However,
the computational time occasionally becomes extremely long in the history
variance mode, especially in the case of tallies using a lot of memories,
e.g. xyz mesh tally with very fine structure. When you perform the PHITS
calculation with such conditions, please change to the batch variance mode
and set maxbch to be more than 10.
Q1.6 Is it possible to use nuclear data libraries other than JENDL-4.0?
A1.6 Yes. PHITS can use nuclear data libraries that are written in the
ACE format, i.e. MCNP format. The followings are the instruction how to
use a new nuclear data library in PHITS.
Q1.7 How can I obtain neutron fluxes emitted from photonuclear reactions
with a good statistical uncertainty?
- Open "xsdir" contained in the package of the new nuclear data
library with a text editor, and copy all addresses of nuclear data (e.g.
1001.80c 0.999167 xdata/endf71x/H/1001.710nc 0 1 4 17969 0 0 2.5301E-08)
- Open "xsdir.jnd" included in the "data" folder of PHITS
with a text editor, and paste the copied addresses at the end of the file.
- Creating a new folder with appropriate name written in the address file
in the XS folder of PHITS, and copy data files of the new nuclear data
library to the created folder.
- Explicitly specify the library ID in the [material] section of your PHITS
input file (e.g. 1H.80c or 1001.80c for the above example). If you do not
specify the library ID, PHITS automatically find the data library of the
nucleus earlier written in " xsdir.jnd". Thus, JENDL-4.0 is selected
when the data for the nucleus is available.
A1.7 You can bias the photonuclear cross section using the "pnimul"
parameter. For example, the probability to cause photo-nuclear reaction
becomes double when you set pnimul=2.0, and the weights of secondary particles
emitted from the photonuclear reaction are 0.5. If you set very high value
for pnimul, e.g. above 100.0, the photon fluxes might be changed. Thus,
please check whether the photon fluxes does not change very much when you
use this parameter.
Q1.8 I cannot restart PHITS simulation due to error related to the inconsistency
of tally. Why?
A1.8 It is due to the loss of significant digit in the PHITS input file.
In that case, you have to set "ireschk = 1", then PHITS skips
the consistency check.
2 Questions related to error occurred in compiling or executing PHITS
Q2.1 I cannot compile PHITS.
A2.1 The status of most variables used in PHITS was changed from "static"
to "dynamic". Consequently, PHITS 2.52 or later cannot be compiled
by old Fortran compilers such as f77 and g77. Therefore, Fortran compilers
recommended by PHITS office are Intel Fortran Compiler 11.1 (or later)
and gfortran 4.71 (or later). See Manual
"2.4 Compilation using makefile for Linux&Mac" section in
Q2.2 Segmentation fault occurred during the execution of PHITS.
A2.2 It might be due to the overflow of the memory used in PHITS. In that case, you have to increase the maximum size of memory acceptable to PHITS. The maximum size is defined as "mdas" parameter in "param.inc" in the "src" directory. Thus, you have to increase this number, and re-compile PHITS. You may also have to increase "latmax" parameter if you would like to use a huge lattice structure such as voxel phantom. See Manual
"2.9 Array sizes" or Advanced course (I)
p28-29 in more detail.
Q2.3 An error occurred when I try to use "infl:" in my PHITS input file.
A2.3 When "infl:" command is used in your PHITS input file (let
name input.dat), you have to type "file = input.dat" at the first
line of "input.dat" file. Or you have to make another input file
(let name phits.in) whose first line is "file = input.dat", and
use phits.in as the input file of the PHITS. For example
phits_c.exe < phits.in > output.dat
"2.7 Executable file" section in more detail
Q2.4 An error occurred when I try to execute PHITS on Linux or Unix console,
but I can execute it on Windows using the same input file.
A2.4 Many reasons are considered to cause the error, but the most probable one is the difference of "return code" used in Linux (or Unix) and Windows. If you prepare your input file in your Windows computer, and transfer to your Linux (or Unix) system using FTP software, you have to check the status of transfer mode; i.e. you have to select "ASCII mode" in your FTP software.
Q2.5 Can PHITS be executed on Cygwin?
A2.5 Yes, you can. You can find the Cygwin option in "makefile"
of PHITS .
3 Questions related to Tally
Q3.1 What is the difference between [t-heat] and [t-deposit] tallies?
A3.1 The two tallies give basically the same values of deposition energies as each other.
However, the [t-heat] tally can also give the deposition energy estimated by the Kerma approximation for neutrons and photons.
When you use this approximation, set e-mode=0 in [parameters] section and electron=0 in [t-heat] section for neutrons and photons, respectively.
The [t-deposit] tally is useful for calculating deposition energy weighted by user defined function, such as Q(L) relationship for calculating dose equivalent.
"6.4 [t-deposit]" section in more detail.
Q3.2 The track length or fluence of heavy ions calculated by [T-Track] or [T-Cross] is strange.
A3.2 It might be due to the miss-define of the energy mesh in the tally section. The energy of heavy ions should be defined in MeV in the tally section, although it should be written in MeV/nucleon in the [Parameter] section.
Q3.3 Results obtained by [T-LET] and/or [T-SED] tally are strange.
A3.3 You have to check the density of material selected by "letmat".
If you select the material that is not used in your geometry, you have
to define its absolute atomic densities (1H 6.893407e-2 16O 3.446704e-2)
in [Material] section. See ParticleTherapy.inp in recommendation.zip
Q3.4 How can we estimate the statistical uncertainty from the tally output?
A3.4 Version 2.52 or later, the standard deviations or standard errors
are correctly outputted in the tally results. See Manual
"4.2.2 Number of history and bank" section in detail.
Q3.5 Can I use "dump" function when I execute PHITS in parallel machine?
A3.5 From version 2.30, it works. Please ask phits office how to use the
Q3.6 Why do some events deposit energies greater than the incidentenergy
using [t-deposit] with "output=deposit" option.
A3.6 When exothermic nuclear reaction occurs, the total energy of secondary
particles becomes greater than the incident energy. Such events are also
observed when mesh = xyz or r-z and nedisp <> 0. This is due to the
algorithm for considering the energy straggling of charged particle in
PHITS. In that case, you have to set mesh = reg in [t-deposit], and define
cells that correspond to each xyz or r-z mesh in [cell] section.
4 Questions related to source generation
Q4.1 How can we normalize PHITS outputs when I use the isotropic source (s-type=9 or 10, dir = -all) ?
A4.1 If there is nothing inside the sphere of the isotropic source, the fluence inside the sphere is normalized to
) (/source), where r1
is the radius of the sphere. Thus, if you would like to convert the tally
output (/source) to the unit fluence, you have to multiply the result with
. It should be noted that the weight control method is employed in generating the isotropic source, and thus, the event-by-event information cannot be derived from the simulation using the isotropic source. If you would like to obtain event-by-event information for isotropic irradiation, you have to set "dir = iso" in the [source] section.
Q4.2 Source particle does not created in the cell where it should be.
A4.2 If you set the source generating surface (or point) exactly on the surface of a certain cell, PHITS sometimes miss-identify the cell where it should be. In this case, please move the source surface a little bit different from the cell surface.