A stochastic cascade model for Auger-electron emitting radionuclides

Abstract

To benchmark a Monte Carlo model of the Auger cascade that has been developed at the Australian National University (ANU) against the literature data. The model is applicable to any Auger-electron emitting radionuclide with nuclear structure data in the format of the Evaluated Nuclear Structure Data File (ENSDF). Schönfeld's algorithms and the BrIcc code were incorporated to obtain initial vacancy distributions due to electron capture (EC) and internal conversion (IC), respectively. Atomic transition probabilities were adopted from the Evaluated Atomic Data Library (EADL) for elements with atomic number, Z = 1-100. Atomic transition energies were evaluated using a relativistic Dirac-Fock method. An energy-restriction protocol was implemented to eliminate energetically forbidden transitions from the simulations. Calculated initial vacancy distributions and average energy spectra of I,I, and I were compared with the literature data. In addition, simulated kinetic energy spectra and frequency distributions of the number of emitted electrons and photons of the three iodine radionuclides are presented. Some examples of radiation spectra of individual decays are also given. Good agreement with the published data was achieved except for the outer-shell Auger and Coster-Kronig transitions. Nevertheless, the model needs to be compared with experimental data in a future study.

Strand breakage by decay of DNA-bound 124I provides a basis for combined PET imaging and Auger endoradiotherapy

“…Most of the extra yield in 125 I can be attributed to low energy OOX transitions. Our calculations (Lee et al 2016) show that these transitions are energetically forbidden even in a single ionized atom. While the shape of the emitted Auger and conversion electron spectrum is very similar for 124 I and 125 I, the average absorbed electron energy is different, due to the difference in the number of electrons per decay.…”

“…The complete list of the emitted radiations (c-rays, conversion electrons, Auger electrons and X-rays) are given in the Supplementary Information and in Lee et al (2016). The energy spectra of the Auger and conversion electrons are shown in Figure S5 and S6 for 124 I and 125 I decay, respectively.…”

Quantitative electron spectroscopy of 125I over an extended energy range

“…Consistent with this, the line shape is not very exp. Table 2: The intensity ratio of the various CE and Auger components compared with those given in the literature and as calculated based on BrIcc [27] and BrIccEmis [28] using mixing ratio δ = 0.015 and penetration parameter λ = −1.2, the evaluated nuclear parameters based on these and literature measurements.…”

“…The spectrum consists then of 5 peaks. This approach is adopted in BrIccEmis [28] and remains manageable when one calculates several steps down in the relaxation cascade, when more vacancies are present.…”

“…The total number of Auger electrons emitted per decay according to BrIccEmis is 20 electrons using the condensed phase approximation and 11.9 electrons using the isolated atom approximation (plus 0.93 CE per decay) [28]. Half of these electrons are expected to move into the Au film.…”