ABSTRACT
A neutron irradiation facility consisting of six 241Am-Be neutron sources of 30â¯Ci total activity and 6.6 × 107 n/s total neutron yield is designed. The sources are embedded in a cubic paraffin wax, which plays a dual role as both moderator and reflector. The sample passage and irradiation channel are represented by a cylindrical path of 5â¯cm diameter passing through the facility core. The proposed design yields a high degree of space symmetry and thermal neutron homogeneity within 98% of flux distribution throughout the irradiated spherical sample of 5â¯cm diameter. The obtained thermal neutron flux is 8.0 × 104 n/cm2.s over the sample volume, with thermal-to-fast and thermal-to-epithermal ratios of 1.20 and 3.35, respectively. The design is optimized for maximizing the thermal neutron flux at sample position using the MCNP-5 code. The irradiation facility is supposed to be employed principally for neutron activation analysis.
ABSTRACT
In this work structural, magnetic and electrical properties of R(0.7)Ca(0.3)Mn(0.95)Fe(0.05)O(3) (R = Pr and Nd) perovskite manganites are presented. Structural characterization of these compounds shows that both have orthorhombic (Pbnm) phase. The Mössbauer spectra show clear evidence of the local structural distortion of the Mn(Fe)O(6) octahedron on the basis of non-zero nuclear quadrupole interactions for high-spin Fe(3+) ions. It was found that the local structural distortion decreases significantly on replacing Pr(3+) by Nd(3+). This replacement dependence of the Jahn-Teller coupling strength estimated from the Mössbauer results was found to be consistent with the electrical and magnetic properties.
