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Programs in Physics & Physical Chemistry



Manuscript Title: MICELLE, the micelle size effect on the LS counting efficiency
Authors: A. Grau Carles
Program title: MICELLE
Catalogue identifier: ACPU_v3_0 Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 176(2007)305
Programming language: FORTRAN 77.
Computer: any IBM PC compatible with 80386 or higher Intel processors.
Operating system: MS-DOS and higher systems.
RAM: 235 kword
Word size: 16 bits
Keywords: Radioactivity, liquid-scintillation counting, electron-capture decay.
PACS: 07.57.Kp, 29.30.Dn..
Classification: 2.3.
Does the new version supersede the previous version?: Yes
Nature of problem: Both β and electron-capture are decay processes characterized by a large variability in energy. In the first case, one single β-particle is emitted per decay following the Fermi distribution. In the second, several electrons (Auger and/or Coster-Kronig) of very different energies can be ejected simultaneously. The detailed simulation of these two electron release processes has practical interest in two situations: (1) to standardize radionuclides with a liquid-scintillation counter, (2) to compute the absorbed dose in the surroundings of a radiolabeled molecule.
Solution method: Although the application of simplified deterministic models is sufficiently accurate for pure β-ray emitters, the large stochastic variability of both electron-capture and internal conversion processes restricts the accuracy of the deterministic models KLM, KLMN and KL₁L₂L₃M to nuclides of low atomic numbers. To extend the applicability of the method to larger nuclei, both M_i- and N_j-subshells must be included into the model. However, the addition of these outer atom subshells to the deterministic model involves a huge number of atomic rearrangement pathways, requiring from simplifications which are frequently limited to certain nuclides. A more feasible method considers using random numbers to simulate step by step the rearrangement of the atom.
Reasons for new version: This version extends the computation of the liquid-scintillation counting efficiency to electron-capture radionuclides of 30≤ Z≤ 54. The simplified deterministic models of previous versions are replaced by a complete stochastic model, which considers all possible subshells involved in the atomic rearrangement of the atom. The program can simulate samples in the gel phase, including the effects of the micelles on the counting efficiency. These effects have been found to be useful for building nanodosimeters based on gel scintillators.
Restrictions: The program is restricted to radionuclides of atomic numbers within the interval 30≤ Z≤ 54. This version ignores the photoionization quench correction, which can be obviated for Z≥30. On the other hand, the simulation of the mechanisms of multiple ionization require from more elaborated models for Z>54. Experiments with gases are only available for nuclides with atomic numbers larger than that of ¹³¹I, for which the emission of Auger electrons, and consequently the ionization of xenon (Z = 54), stops for transitions other than N₄O₂O₂.
Running time: The test runs each take approximately 3 minutes to complete.