SPECTRA-PKA is a command-line driven programme for calculating the expected primary knock-on atom (PKA) spectra for a given target nuclide under neutron or charged particle irradiation. NJOY-processed recoil matrices must be provided as the input nuclear data for each nuclide and reaction channel of interest. SPECTRA-PKA will read the nuclear data and collapse the data for each reaction channel in a file with a user-defined energy spectrum of incident particles. SPECTRA-PKA outputs the resulting PKA spectra for each reaction channel read-in, as well as summed PKA distributions for each different recoiling nuclide or element, including both the typically heavy residuals and the secondary-emitted light gas particles. Crucially, SPECTRA-PKA has the ability to process data, in a single run, for a complex material containing many different target species. The user must specify the atomic percentage for each target and the appropriate recoil cross section file, but then SPECTRA-PKA will automatically read-in and process each file and create global average (including as a function of isotope and element) PKA distributions. This feature, in particular, is a significant advancement over what was possible before (such as with SPECTER [1985] from ANL), where typically PKA distributions were only provided for single elements (and not separated by reaction channel) and based on only one nuclear data library (ENDF/B-V in the case of SPECTER). It allows, for example, the user to investigate the variation in PKA distributions as a function of time under irradiation, where a materials composition may change due to transmutation. More recent additions to the code include per-channel evaluations of damage rates (measured as the so-called NRT-dpa metric), the ability to import a user-defined energy grid for the output of distributions (e.g. to overload the logarithmically-distributed scale commonly used for nuclear physics applications with a more modelling-friendly linear scale), and the application of PKA distributions to "real" atomistic systems to define when and where PKAs will occur in a given lattice of atoms, which can be subsequently applied to modelling activities. The latter has been extended further with a prototyped interface to a code (SDTrimSP) that applies the binary collision approximation (BCA) to simulate the cascade of recoil events associated with a given PKA.
SPECTRA-PKA comes with a simple makefile, requiring GNU make and a compatible Fortran compiler. It has been tested with multiple operating systems and compiler permutations, including the standard GNU Fortran compiler.
SPECTRA-PKA is executed from the command-line. By default, the programme expects to find an input file called specter.input in the execution folder, but this behaviour can be over-ridden by specifying the name of an input file on the command-line. The input file provides the user with the option to over-ride the default values of the various code words (see below) that SPECTRA-PKA relies upon to control its execution. The input file should be a text file but is largely free from other formatting requirements. Code word values are specified in any order, one per line, via syntax of type:
<code word name> = <code word value>A complete list of code words (with explanation) can be found on the pdf readme. An alternative syntax allowing an easier description of a complex alloy (containing multiple target species) is also described.
In the subfolder containing the pdf manual distributed with SPECTRA-PKA there are example calculations to get the user started. The first, in "manual/test", contains the necessary input files to evaluate the PKA distributions of pure zirconium (Zr) in a typical PWR fission spectrum. To run the test navigate to the test folder and then, on the command line, type:
<location of SPECTRA-PKA>SPECTRA_PKA ZR.inHere <location of SPECTRA-PKA> is the folder containing the SPECTRA-PKA executable. The input file (ZR.in) is:
flux_filename="fluxes_specter.dat"
results_stub="ZR"
num_columns=6
columns= pka_filename pka_ratios parent_ele parent_num ngamma_parent_mass ngamma_daughter_mass
"<PKA data folder>Zr090s.asc" 0.51450000 Zr 90 89.904697659 90.905639587
"<PKA data folder>Zr091s.asc" 0.11220000 Zr 91 90.905639587 91.905034675
"<PKA data folder>Zr092s.asc" 0.17150000 Zr 92 91.905034675 92.906469947
"<PKA data folder>Zr094s.asc" 0.17380000 Zr 94 93.906310828 94.908038530
"<PKA data folder>Zr096s.asc" 0.02800000 Zr 96 95.908271433 96.910951206
flux_norm_type=2
pka_filetype=2
do_mtd_sums=.true.
do_ngamma_estimate=.t.
do_global_sums=.t.
do_exclude_light_from_total=.t.
number_pka_files=5
flux_rescale_value=3.25e14
max_global_recoils=400
energies_once_perfile=.t.Note that in the test folder <PKA data folder> in the above has been replaced by the appropriate directory path for the default hierarchy of the FISPACT-II system. The user should tailor this file as necessary to their own system configuration before running the test.
The test folder also has an example_results folder containing the .out and .indexes files that should be produced from a successful execution of the test. The plot_example folder provides example .plt files for GNUPLOT that will produce plots of the summed elemental and isotopic PKA distributions. Users familiar with GNUPLOT will note the use of the index option in each plot command. The index numbers currently used in the .plt files are appropriate for the example results (see example_results/ZR.indexes). Important: Using a different version of the PKA source libraries could result in a different ordering of the results, and so the user should compare the .plt files with the .indexes file from their execution of the test to check that the correct distributions are plotted. The images that should result from this test are shown on the pdf readme and the FISPACT-II wiki page.
A further example, which doesn't include a plot example (as described above), can be found in the folder "manual/usergrid_test". This "test" calculates the PKA distributions for a single Fe isotope (Fe56) irradiated in a typical fission irradiation spectrum. It exemplifies the use of a user-defined energy output grid for the PKA distributions and additionally provides examples of the format of the required user-grid input file.
A final example demonstrates the possibilities of the atomistic PKA capabilities newly developed in the code, including the ability to interface with BCA simulations. In the folder "manual/bca_test" is another Zr example. In this case the code is asked to stochastically define the PKA events that would take place in a hcp box of 500x500x500 unit cells during a 100 s irradiation under the PWR fission spectrum. Additionally, the BCA code SDTrimSP is run for each PKA above the 40 eV threshold for atomic displacement in Zr. Two example plot scripts are provided to plot the resulting final accumulation of PKA events and the corresponding cascade distributions. Figures in the manual demonstrate how the output produced from this simulation could be viewed.
To get started with SPECTRA-PKA, the minimum terminal inputs to download, compile and run the basic test case with Zr would be:
git clone https://github.com/fispact/SPECTRA-PKA.git
cd SPECTRA-PKA
make
cd manual
cd test
../../spectra-pka ZR.inIf this has worked the last line of the command output from the test case should be "END as expected". The above sequence of inputs should work on Unix, Mac and maybe even a properly configured unix-like environment on Windows, and should get a user started before moving on to more complex simulations, requiring more nuclear data files (see below).
SPECTRA-PKA uses NJOY-generated recoil cross section matrices. The output files required from NJOY are non-standard and are produced by a slightly modified version of the GROUPR module within NJOY. An evolving selection of databases produced using various international reaction cross section libraries (for various incident particle types) have been pre-calculated and are available to download as compressed tar archives from links on the FISPACT-II website at fispact.ukaea.uk/nuclear-data/downloads/ . These can be used immediately with SPECTRA-PKA, or can be used as a template to guide users who may want to create their own input data files (for example, for libraries not currently included on the download page).
- M.R. Gilbert, J. Marian, J.-Ch. Sublet, Energy spectra of primary knock-on atoms under neutron irradiation, J. Nucl. Mater 467 (2015) 121-134. doi:https://doi.org/10.1016/j.jnucmat.2015.09.023.
- M.R. Gilbert, J.-Ch. Sublet, PKA distributions: Contributions from transmutation products and from radioactive decay, Nucl. Mater. Energy 9 (2016) 576-580. doi:http://dx.doi.org/10.1016/j.nme.2016.02.006.
- M.R. Gilbert, J.-Ch. Sublet, Differential dpa calculations with SPECTRA-PKA, J. Nucl. Mater. 504 (2018) 101-108. doi:https://doi.org/10.1016/j.jnucmat.2018.03.032.
- M.R. Gilbert, Coupling Nuclear Predictions into Damage Simulations with SPECTRA-PKA. Nucl. Sci. Eng. (2024) doi:https://doi.org/10.1080/00295639.2024.2342506