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In this work we calculated the self-shielding factor, $G$, as a function of the neutron energy, which is important to consider in precise neutron activation experiments.
Twelve samples of pure metallic materials were simulated using the Geant4 Monte Carlo toolkit[1,2] and the MCNP[3] code.
The self-shielding factor is defined as the ratio between the neutron flux inside the sample volume and the flux in the surface of the sample,
$$ G = \left( \int_{E_1}^{E_2}dE\Phi_V \right) \div \left( \int_{E_1}^{E_2}dE\Phi_S \right). $$ We have simulated the behaviour of the self-shielding factor for neutron energies from 10$^{-5}$ eV to 20 MeV. Results obtained by running 10$^{6}$ neutron events in MCNP6 using the ENDF-B/VII.1, JEFF 3.2 and TENDL2014 neutron cross section libraries, shows that the self-shielding factor is relevant to include in neutron activation analysis experiments for thermal neutron energies and for sample thickness greater than 10$^{-4}$ m, as seen in the recent calculation of the neutron flux at the RECH-1 nuclear reactor[4].
- S. Agostinelli, et al., Geant4: A simulation toolkit, Nucl. Instrum. Meth. A, 506 3 (2003) 250-303.
- J. Allison, et al., Geant4 developments and applications, Nuclear Science, IEEE Transactions on, 53 1 (2006) 270-278.
- T. Goorley, et al., Initial MCNP6 Release Overview, Nuclear Technology 180 (2012) 298-315.
- F. Molina, et al., Energy distribution of the neutron flux measurements at the Chilean Reactor RECH-1 using multi-foil neutron activation and the Expectation Maximization unfolding algorithm, Appl. Radiat. Isot. 129 (2017) 28-34.
