5.3.2. Common parameters

Common parameters for each source type are shown below. The order of the parameters in the source section is free. If a parameter has a default value (D = ***), it can be omitted. The energies of \(d, t, \alpha\), and nuclei are specified in \(\mathrm{MeV/nucleon}\). Please see sections Section 5.3.19, Section 5.3.20, and Section 5.3.21 for the definitions of energy, angular, and time distributions, respectively, for source description.

Table 5.3.5 proj

value	explanation
	Projectile. Specify particle by symbol or kf-code. See Section 4.7.

Table 5.3.6 sx

value	explanation
(D=0)	x-component of spin.

Table 5.3.7 sy

value	explanation
(D=0)	y-component of spin.

Table 5.3.8 sz

value	explanation
(D=0)	z-component of spin.

If its spin is not defined or zero, a neutron enters a magnetic field without spin. In this case, the initial spin of the neutron is determined at the entrance of the magnetic field by the direction of the magnetic field and the polarization factor. If the spin is defined in this section, the neutron enters the magnetic field with the defined spin direction irrespective of the direction of the magnetic field and polarization.

Table 5.3.9 reg

value

explanation

(D=all)

The source region can be restricted to the overlap(s) between the regions defined by s-type and those specified by this parameter. The format is reg = {1 - 5 } 10 34. The lattice and universe frame can be used as reg = (6 < 10[1 0 0] < u=3) . See the section of tally region specification for more details on the syntax. Note that this parameter cannot be written in the line right above <source> = if multi-source sub-sections are defined; otherwise it will cause a syntax error.

Table 5.3.10 ntmax

value	explanation
(D=1000)	Maximum number of re-sampling the source location from the region specified by s-type when reg is specified.

Table 5.3.11 trcl

value	explanation
(D=none)	Transform number, or definition of transform.

To transform coordinates, the trcl parameter, which specifies the transform number or the definition of the transformation itself, can be used.

Table 5.3.12 wgt

value	explanation
(D=1.0)	Weight of source particles.

Table 5.3.13 factor

value	explanation
(D=1.0)	Scaling factor fot tally results; all tally results are multiplied by the value of factor . When factor and totfact are both defined, \(\mathrm{totfact}\times\mathrm{factor}\) is the actual scaling factor. However, when multi-source is defined, use totfact only; do not use this parameter for scaling.

The relation between wgt and factor is reciprocal.

Table 5.3.14 izst

value

explanation

(D=charge of particle species specified by proj=)

Charge state of source particle. This value influences the particle motions under the electro-magnetic fields defined in [electro magnetic field] (and [magnetic field]) sections. In addition, ATIMA with the fixed charge mode (ifixchg=1) calculates the stopping power based on this charge state. The charge number defined with izst does not change while the particle travels. Note that this parameter is only valid for source particles, i.e., secondary particles produced from nuclear reactions carry the charges of their atomic numbers.

Table 5.3.15 cnt(i)

value	explanation
(D=0)	Initial value of counter i (i=1-3) of source particle. You can distinguish the contributions from each multi-source definition by assigning different values to their initial counter values.

Table 5.3.16 ispfs

value

explanation

(D=0)

Neutron sources from spontaneous fission. Note that the RI source function (e-type=28,29) can also reproduce spontaneous fission neutrons after version 3.31, so the use of RI source function is recommended to represent mixed fields with fission neutrons and \(\gamma\) -rays. If ispfs=1 or 2 is specified in the [source] section and the following 18 nuclei are chosen as proj, neutrons can be defined using spontaneous fission as a source. These nuclei are assumed to be spontaneous fission nuclei:U-238, Pu-238, Pu-240, Pu-242, Cm-242, Cm-244, Cf-252, Th-232, U-232, U-233, U-234, U-235, U-236, Np-237, Pu-239, Pu-241, Am-241, Bk-249. When ispfs=1 , the tally results are normalized per spontaneous fission event, and neutrons are generated using random sampling so as to reproduce the average neutron multiplicity. Therefore, correlations among neutrons emitted from the same fission can be evaluated. In contrast, when ispfs=2 , the results are normalized per neutron produced by spontaneous fission, and exactly one neutron is emitted in each history. In the case of ispfs = 1,2, e0 and e-type, dir, and a-type are neglected. Unlike the case of RI source (e-type=28,29), particle type specified by proj is not used, namely, neutrons are generated as source particles.

When ispfs = 1, 2 is specified, the multiplicity and energy spectrum of neutrons are taken from the reference [1].

The PHITS development team is grateful to Dr. Liem Peng Hong of NAIS, Co., Inc. for his support in developing this function to generate neutron sources.

[1]

10. 13. Verbeke, C. Hagmann, and D. Wright, Simulation of Neutron and Gamma Ray Emission from Fission and Photofission, UCRL-AR-228518 (2014).

Table 5.3.17 ibatch

value	explanation
(D=all)	Effective batch numbers of each multi-source when itall=4 . Each batch number should be separated by blank. You can specify successive batch numbers from n1 to n2 in the format of {n1 - n2} (n1 should be smaller than n2).