5.3.19.8. Energy distribution of RI source

e-type = 28, 29 : The alpha-, beta- (including Auger electrons), and gamma-rays of radioisotope (RI) decay are generated by simply specifying the activity (in Bq) and names of the RIs. All kinds of radiation from decay, i.e. alpha-, beta-, gamma-rays, and fission neutrons, are generated when proj = all is set. The DECDC nuclear decay database [1] is used to obtain the energy spectra. This database is equivalent to ICRP Publication 107 and contains decay databases for almost all radionuclides, including metastables, with half-lives of more than one minute. To use this function, the directory containing the DECDC data file RIsource.dat must be specified by setting file(24) in the [parameters] section. When e-type = 28, spectra are expressed by changing the probabilities of generating particle energy spectra obtained from DECDC. When e-type = 29, spectra are expressed by changing the weights of the source particles while maintaining constant probabilities for all source energy.

Table 5.3.219 ni

value

explanation

Number of RIs. RI names and activities must be given in the next line using (RI(i),A(i),i=1,ni). RI(i) can be defined as 137Cs or Cs-137 ( Section 4.7 ). A(i) is specified in units of Bq.
Table 5.3.220 dtime

value

explanation

(D=-10.0)

Option for time evolution [s].

dtime > 0

The energy spectrum is determined from the specified RIs including daughter nuclides after the elapsed time, and the activity of each RI decreases accordingly.

dtime = 0

The energy spectrum is determined from the specified RIs without time evolution.

dtime < 0

The energy spectrum is determined including daughter nuclides after half-life times |dtime| have passed, while the specified activities of the original RIs are kept unchanged.
Table 5.3.221 actlow

value

explanation

(D=1.0e-10)

Lower limit of the activity [Bq]. If the activity after time evolution is smaller than this value, the corresponding RI is not included in the source.
Table 5.3.222 norm

value

explanation

(D=0)

Option for normalization of tally results.

0

Tally results are normalized in units of [/s]. The source intensity is determined by the specified activity.

1

Tally results are normalized in units of [/source]. This is equivalent to the general PHITS normalization.
Table 5.3.223 iaugers

value

explanation

(D=0)

Option for the production of Auger and internal-conversion electrons. Effective only for proj = electron.

0

All electrons are generated.

1

Only beta rays are generated.

2

Only Auger and internal-conversion electrons are generated.
Table 5.3.224 iannih

value

explanation

(D=1)

Option for the production of annihilation photons. Effective only for proj = photon.

0

Consider annihilation photons.

1

Ignore annihilation photons.
Table 5.3.225 icharctx

value

explanation

(D=0)

Option for the production of characteristic X-rays. Effective only for proj = photon.

0

All photons are generated.

1

Only gamma rays are generated.

2

Only characteristic X-rays are generated.

To use this function with multi-sources, set <source> = 1.0 and totfact as follows.

  • when all sources are defined by e-type = 28, 29, set totfact as the number of <source>

  • when the multi-sources include sources defined by e-type != 28, 29, set each <source> as the absolute intensity of each RI and set totfact as the sum of all values of <source>

If totfact is given as a negative value, the same particle is generated in each multi-source section with weights adjusted according to the ratio of the activities.

The following is an example using e-type = 28, 29.

[ Source ]
  totfact = 2.0
  <source> = 1.0
    s-type =   1
    proj =  photon
    dir =   all
    r0 =   0.
    z0 =   0.
    z1 =   0.
    e-type =   28
      ni =   1
        Cs-137  100.
      dtime =  -10.0
      actlow =   1.0
  <source> = 1.0
    s-type =   1
    proj =  photon
    dir =   all
    r0 =   0.
    z0 =   0.
    z1 =   0.
    e-type =   28
      ni =   1
        Cs-134  100.
      dtime =  -10.0
      actlow =   1.0

In this case, Cs-137 and Cs-134 after reaching radioactive equilibrium at 100 Bq are both defined as photon sources. Furthermore, setting actlow = 1 ensures that activity smaller than 1 Bq is ignored.

For example, to consider both gamma- and beta-rays by decay of Cs-137, make a multi-sources having two <source> sections with proj = photon and proj = electron. Because both the production rates of the gamma- and beta-rays are the same, their ratios can be specified as 1.0 by setting <source> = 1.0. In this case, totfact should be 2.0, which is the sum of the <source> sections.