Resumen

VEGA-CARRILLO, Héctor René  y  TORRES-MUHECH, Celia. Low energy neutrons from a ²³⁹PuBe isotopic neutron source inserted in moderating media. Rev. mex. fis. [online]. 2002, vol.48, n.5, pp.405-412. ISSN 0035-001X.

Several neutron applications share a common problem: the neutron source design. In this work MCNP computer code has been used to design a moderated ²³⁹PuBe neutron source to produce low energy neutrons. The design involves the source located at the center of a spherical moderator. Moderator media studied were light water, heavy water and a heterogeneous combination of light water and heavy water. Similar moderating features were found between the 24.5 cm-radius container filled with heavy water (23.0-cm-thick) and that made with light water (3.5-cm-thick) plus heavy water (19.5-cm-thick). A ²³⁹PuBe neutron source inserted in this moderator produces, at 27 cm, a neutron fluence of 1.8 x 10^-4 n-cm^-2 per source neutron, with an average neutron energy of 0.34 MeV, where 47.8 % have an energy ≤ 0.4 eV. A further study of this moderator was carried out using a reflector medium made of graphite. Thus, 15-cm-thickness reflector improves the neutron field producing a neutron fluence of 1.1 x 10^-3 n-cm^-2 per source neutron, whose average neutron energy is 0.098 MeV, where 75.8 % have an energy ≤ 0.4 eV.

Palabras llave : Isotopic neutron source; moderation; Monte Carlo method.

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