PenNuc: Monte Carlo simulation of the decay of radionuclides

Abstract

The Fortran subroutine package PenNuc that performs Monte Carlo simulation of the decay of radioactive nuclides is described. The adopted nuclear decay characteristics (possible disintegration modes and branching ratios, energies and half-lives of nuclear energy levels, types and energies of emitted particles) are from the nucleide evaluated database ( http://www.nucleide.org/DDEP_WG/DDEPdata.htm) in the specific format PenNuc. The initial energies of electrons and positrons emitted in beta disintegrations are sampled from their continuous spectra by means of the RITA (rational inverse transform with aliasing) algorithm, which is described in the Appendix. Electronic relaxation of the residual ion after electron capture and internal conversion is simulated by using the data and sampling methods of the penelope code system. At each call the subroutines deliver a list of state variables of the particles (photons, electrons, positrons and alphas) emitted in a random decay path of the considered radionuclide down to a metastable level or to the ground state of the daughter nucleus. The distribution package includes a main program that simulates the emission spectrum of a radionuclide and, optionally, produces a list of particles emitted in a prescribed number of decays. Program summaryProgram Title: PenNucProgram Files doi:http://dx.doi.org/10.17632/dy28h8xmkv.1Licensing provisions: CC by NC 3.0Programming language: Fortran 90/95Nature of problem:PenNuc simulates the emission of energetic particles in random decay pathways of radionuclides. The initial state of a particle is described by the following variables: type of particle (photon, electron, positron, or alpha), energy, direction, and emission time relative to the start of the decay. For each decay the program provides a list of initial states of the particles emitted with energies higher than the adopted cutoff ECNUC, which is set to 200 eV in the original source file.Solution method: The nuclear disintegration mode and the subsequent de-excitation of the daughter nucleus are simulated by using decay information from the nucleide evaluated databases. De-excitation of ions produced in electron capture and internal conversion is simulated by using atomic transition data and sampling methods from the Monte Carlo code system penelope [1]. The energy of beta particles is sampled using the RITA (rational inverse transform with aliasing) algorithm, which optimizes both simulation speed and accuracy.Additional comments: Although PenNuc can describe several radionuclides simultaneously, the selection of the active nuclide (appropriate to the characteristics of the radioactive source) must be done in the main program. The subroutines provide the complete set of particles emitted with energies higher than the cutoff ECNUC in each nuclear decay, including x rays and Auger electrons.[1] F. Salvat, penelope-2014: A code System for Monte Carlo Simulation of Electron and Photon Transport, OECD/NEA Data Bank, Issy-les-Moulineaux, France, 2015. Available from http://www.nea.fr/lists/penelope.html.