4.10. Decay chain scheme / change in inventory output file¶
The output of decay chain information to the *.dcs file is controlled by five parameters. IWRTCHN toggles the writing of this extra output file at all (0=off, 1=on). By default in [T-Dchain], IWRTCHN=1. The CHRLVTH parameter, essentially, has four modes as outlined in its entry for Card 4 which control when each decay chain is deemed relevant enough to be written to the output file. By default, CHRLVTH=-1.0, meaning an inventory change in the nuclide of interest of 1.0 atom/cm\(^3\) is required for a chain to be printed.
IWRCHDT toggles the output of the contribution to each nuclide’s change in inventory by the individual links of its chains (for both beam production and decay/neutron reaction [1] components) and adds three rows of numbers beneath the nuclides in each decay chain. In short, each value represents the number of atoms (per cm\(^3\)) of each nuclide in each column converted to the end-nuclide in that decay chain in that time step. The first row denotes change in inventory initiated by high-energy reactions ([T-Yield]’s *.dyld output) producing the end-nuclide directly (final column of the first chain for each end-nuclide) or after subsequent decays within the time step. The second row denotes change in inventory from decay and/or neutron reactions with the specific responsible reaction denoted by the text inside of the arrows connecting the nuclides in each chain (detailed at the end of this section). The sum of dN_Beam and dN_Decay/nx in each column is then listed in the third row as dN_Total, and then the sum of all items in the dN_Total row equal the value in the dN [atm/cc] column for that decay chain. Thus, this feature gives an itemized breakdown of exactly what reactions and decays contribute to the change in inventory of every nuclide in every time step. This is much more easily explained through an example which is provided below.
S 39 --(B-)-> Cl 39 --(B-)-> Ar 39
dN_Beam: 1.87215E+05 5.20911E+07 7.29774E+09
dN_Decay/nx: 8.61687E+03 6.81577E+08 -2.28468E+04
dN_Total: 1.95831E+05 7.33669E+08 7.29771E+09
In this case, the numbers show how the inventory of \(^{39}\)Ar changes in that time step from this specific decay chain. For the \(^{39}\)S and \(^{39}\)Cl columns, the numbers show how many atoms of each of those nuclides were converted to \(^{39}\)Ar during that time step by either beam interactions (and subsequent decays) in that time step (first row) or by decays/neutron reactions (exclusively \(\beta^-\) decay here) of existing inventory of those nuclides from previous time steps (second row). The \(^{39}\)Ar column itself shows the change in inventory of \(^{39}\)Ar due to direct production through beam interactions and production and destruction through decay/neutron reactions.
By default, this option is disabled (IWRCHDT=0) as it can make the output more verbose and difficult to read quickly; however, it is an extremely powerful utility in determining what reactions and decays are resulting in the buildup of each nuclide.
The IWRCHNUC input parameter allows users to limit what end-nuclides are written to this file. Since it by default contains this decay scheme information for all nuclides, it can become quite verbose. If only concerned about production of a few specific nuclides, this option allows for only those nuclides to be tracked in the *.dcs file.
Lastly, IWRCHSS toggles the printing of the IDIVS substeps in time in each irradiation step. By default, only the final substep in each irradiation step is printed (IWRCHSS=0), but setting IWRCHSS=1 will cause all time steps to have output printed. A longer explanation for how these time steps are calculated can be found in Section 4.8.
One special note to be made here is about the times at which output is printed for this file. Unlike the other output files where only the times specified in the “output time” section (ITOUT values) are printed, this file contains output at every calculation step which is a convolution of both the output times and irradiation times (and their IDIVS substeps). So, provided IWRCHSS=1, one can see the changes in each nuclide’s inventory at every single time step in the calculation attributed to each decay chain meeting the relevancy requirements set by CHRLVTH (and further broken down by each link in each chain if IWRCHDT=1).
Another note on this output file is that sometimes the chains list some very peculiar decays (i.e. \(^3\)H produced from 3 subsequent neutron decays of \(^6\)H). The first chain constructed by DCHAIN for each nuclide, regardless of how strange it may be, will include the decay and direct beam interaction production terms of the final nuclide in that time step, making it relevant to be outputted. All subsequent chains resulting in the same end-nuclide will only contribute changes in its inventory due to the production/decay/reactions of other nuclides in each chain. Using IWRCHDT=1, one can easily see which nuclides in the “strange” decay chains actually contribute to the end-nuclide’s inventory. In the example stated earlier, one would see that the change in \(^3\)H inventory was solely through beam interactions (directly yielding \(^3\)H) and its decay; the heavier isotopes of H listed in the chain contribute nothing and should be ignored.
Finally, Table 4.10.1 shows what decay/reaction modes that the symbols within the arrows of the printed decay chains (--(XX)-->) relate to. Most of them are fairly self evident, such as B- equating to \(\beta^-\) decay, but due to the 2-character limitation enforced some are not as clear. For any reaction or decay not explicitly stated, one can normally determine the reaction at hand by just assessing the parent’s and daughter’s differences in Z and A. The first two columns of the table, showing the ID numbers of these modes used internally by the DCHAIN code and it’s decay library database, can be ignored.
DCHAIN \(\#\) |
Decay library \(\#\) |
Decay mode |
DCHAIN symbol |
|---|---|---|---|
1 |
1.00 |
\(\beta^-\) |
|
2 |
3.00 |
IT |
|
3 |
n/a |
\((n,x)\) |
|
4 |
2.00 |
\(\beta^+/\)EC |
|
5 |
4.00 |
\(\alpha\) |
|
6 |
5.00 |
\(n\) |
|
7 |
6.00 |
s.f. |
|
8 |
– |
other |
|
20 |
1.10 |
\(\beta^-\beta^-\) |
|
21 |
1.50 |
\(\beta^-n\) |
|
22 |
1.55 |
\(\beta^-2n\) |
|
23 |
1.56 |
\(\beta^-3n\) |
|
24 |
1.40 |
\(\beta^-\alpha\) |
|
30 |
7.00 |
\(p\) |
|
33 |
7.70 |
\(2p\) |
|
41 |
2.70 |
\(\beta^+p\) |
|
42 |
2.77 |
\(\beta^+2p\) |
|
44 |
2.40 |
\(\beta^+\alpha\) |
|
47 |
2.60 |
\(\beta^+\)s.f. |
|
66 |
5.50 |
\(2n\) |
|