7.3. [ T-Point ] section

It is impractical to calculate particle fluence at a specific point or line using the [t-track] tally. To address this, the point estimator tally [t-point] was introduced to estimate these quantities within a short computational time. However, to use this tally the following conditions must be satisfied in the PHITS simulation using [t-point]:

1. Only neutrons and photons with energies below their dmax can be transported. [1]

2. Only the fluence of neutrons and photons can be calculated by [t-point].

3. Neither event generator mode nor EGS5 should be used, e-mode=0, negs=0. [2]

4. The material should be uniform within a certain proximity to the point detector to avoid singularity.

5. Reflection or white boundary surface should not be used.

Please see the read-me file or the sample input file in /phits/utility/tpoint/ for more details.

Table 7.3.1 point

value	explanation
number of data	Option for point detectors. A subsection is required below this option.

Table 7.3.2 ring

value	explanation
number of data	Option for ring detectors. A subsection is required below this option.

Table 7.3.3 part

value	explanation
particle name (optional)	Tally particle. neutron photon are set when part is not specified.

Table 7.3.4 e-type

value	explanation
1, 2, 3, 4, 5	Energy mesh. See Section 6.6.1 for mesh subsection format.

Table 7.3.5 t-type

value	explanation
1, 2, 3, 4, 5 (optional)	Time mesh. See Section 6.6.1 for mesh subsection format.

Table 7.3.6 unit

value	explanation
1, 2, 3	1: [1/cm^2/source] 2: [1/cm^2/MeV/source] 3: [1/cm^2/Lethargy/source]
11, 12, 13	11: [1/cm^2/nsec/source] 12: [1/cm^2/nsec/MeV/source] 13: [1/cm^2/Lethargy/nsec/source]

Table 7.3.7 axis

value	explanation
eng, t	x axis value of output data.

Table 7.3.8 samepage

value	explanation
(optional, D=part)	The type of data to be displayed on the same page of the image output file. Parameters that can be defined in axis can be specified. point and ring can also be specified.

Table 7.3.9 file

value	explanation
file name	Define output file names. This is required by each setting of axis.

Table 7.3.10 resfile

value	explanation
(optional, D=file)	Define a file name of the past tally in the restart calculation. Even if several axis parameters were defined, specify only one resfile.

Table 7.3.11 factor

value	explanation
(optional, D=1.0)	Normalization factor.

Table 7.3.12 title

value	explanation
(optional)	Title.

Table 7.3.13 angel

value	explanation
(optional)	ANGEL parameters.

Table 7.3.14 sangel

value	explanation
(optional)	Special format for ANGEL parameters.

Lethargy in unit=3 or unit=13 is the natural logarithmic unit of energy defined by \(\ln(E_{\rm ref}/E)\) using a reference energy \(E_{\rm ref}\) and the particle energy \(E\). Setting these units enables obtaining results in units of Lethargy, which are given as Lethargy widths, \(\ln(E_{\rm high}/E_{\rm low})\), for each energy bin in the energy mesh subsection. Here \(E_{\rm high}\) and \(E_{\rm low}\) are the maximum and minimum values of the energy bins, respectively.

In [t-point], the number of points or rings, instead of the mesh as in other tallies, must be defined. For example, point=3 should be specified to define 3 point detectors. The maximum number of points or rings per [t-point] is 20. To set more detectors, another [t-point] tally must be defined. Point and ring detectors cannot be combined in one [t-point] tally. The information on a point or ring must be defined in successive lines following the definition of the point or ring parameter. The point detector definition is described as follows.

Listing 7.3.1 Example of point detector definition in [t-point].

  [ T-point ]
  point =    1     # number of point detectors
  non     x        y       z        r0
    1     10.0     0.0     50.0     1.0

Here x, y, and z indicate the coordinates of the point detector and r0 is the radius of the fictitious sphere. For more information on the fictitious sphere, see the read-me file in /phits/utility/tpoint/. These parameters are given in units of cm.

The ring detector is defined as follows.

Listing 7.3.2 Example of ring detector definition in [t-point].

  [ T-point ]
  ring =    1     # number of ring detectors
  non   axis    ar       rr       r0
    1    z      50.0     10.0     1.0

Here axis indicates the direction of the ring axis specified as x, y, or z. ar is the distance from the origin to the center of the ring, rr is the ring radius, and r0 is the radius of the fictitious sphere. The order of these parameters can be changed by changing the order of notation, for example x y z r0 can be changed to z y x r0. Aside from these factors, the parameters defined in [t-point] are the same as those in [t-track], including the multiplier option. Thus, the radiation dose at a specific point can be estimated using [t-point]. However, material, 2-dimensional plot options, and transforms cannot be specified in [t-point].

Table 7.3.15 epsout

value	explanation
0 (default), 1, 2	When epsout=1, results are plotted into eps files. The eps file is named by replacing the extension with .eps. When epsout=2, error bars are also displayed in the eps file, except for the 2-dimensional type, axis=xy, yz, xz, rz.

Table 7.3.16 maxangel

value	explanation
Number of part (default)	Specify the number of part shown in the eps file. This parameter limits the number of particles shown in a tally eps file, while it does not limit them in a numerical data file.

Table 7.3.17 ctmin(i)

value	explanation
(optional, D=-9999)	Minimum value for the i-th counter.

Table 7.3.18 ctmax(i)

value	explanation
(optional, D=9999)	Maximum value for the i-th counter.

Table 7.3.19 chmin(i)

value	explanation
(optional, D=-9999)	Minimum value for the i-th history-counter. This parameter cannot be specified in the batch variance mode, istdev=1.

Table 7.3.20 chmax(i)

value	explanation
(optional, D=9999)	Maximum value for the i-th history-counter. This parameter cannot be specified in the batch variance mode, istdev=1.

Table 7.3.21 stdcut

value	explanation
(optional, D=-1)	Threshold value of STD cut off.

When specifying stdcut, PHITS automatically stop the calculation depending on values of STD, standard deviation. This function is available when stdcut is positive and itall=0,1 is set in [parameters] section. When all relative values of STD of the tally result are larger than 0 and smaller than stdcut at the last of one batch, the calculation is stopped. If stdcut in two or more tally sections is set, all the results of the tally sections have to satisfy the conditions in order for the function to work.

Table 7.3.22 multiplier

value	explanation
Number of material	Multiplier for each material.
(optional)	A multiplier subsection is required below this option. See the multiplier subsection for detailed usage.

Table 7.3.23 iextstat

value

explanation

0 (default), 1, 2

Option for extended statistical indicators. 0: Output the transition of the mean and statistical error as a function of the total history number and batch number. 1: In addition to the contents of iextstat=0, output variance of the variance, VOV, and figure of merit, FOM, as a function of the total history number and batch number, and output a statistical check sheet. 2: In addition to the contents of iextstat=1, the probability density distribution, PDF, of the tally results is output. In this case, run a test calculation to check the range of tally results, then set the output range and run the main calculation.

To output the extended statistical indicators, set itall=3 in [parameters], set the anatally subsection in the tally section, and specify iextstat. The anatally subsection should be defined between the lines of anatally start and anatally end written in the tally section. If you output a PDF with iextstat=2 and you know the range of possible tally results, specify the PDF output range with prodenmn, prodenmx, and nbproden, and run PHITS in the main calculation. If you do not know the range, please run PHITS in a test calculation mode without specifying these three parameters and check the range before proceeding to the main calculation. Note that iextstat, prodenmn, prodenmx, and nbproden should be specified outside the anatally subsection. See Section 6.10 for more details.

Table 7.3.24 prodenmn

value	explanation
(optional, D=1e-2)	Lower limit of the PDF output range.

Table 7.3.25 prodenmx

value	explanation
(optional, D=1e+2)	Upper limit of the PDF output range.

Table 7.3.26 nbproden

value	explanation
(optional, D=100)	Number of divisions in the PDF output, logarithmic scale.

[1]

From version 3.36, charged-particle and photo-nuclear data libraries can be used.

[2]

When EGS mode is used, the photon fluence cannot be evaluated correctly; however, it is possible to evaluate the neutron fluence in combination with the photonuclear reaction library. If EGS mode is not used, electron and positron transport cannot be considered. Therefore, when evaluating neutron production from an electron accelerator, please use EGS mode together with the photonuclear reaction library.