© 2020 Atomic Energy Society of Japan. All rights reserved. For a highly enriched uranium subcritical core driven by an inherent or an external Am-Be source in Kyoto University Critical Assembly (KUCA), a series of the source multiplication measurements, the Feynman-α and the Rossi-α neutron correlation analyses was carried out to demonstrate quantitatively that the use of the former inherent source had some advantages over that of the latter external source. Under a reactor drive by the external source, the subcriticality obtained by the neutron source multiplication method (NSM) significantly depended on neutron counter position and was consequently in very poor agreement with that calculated by the continuous-energy Monte Carlo code MVP (version 3) with the nuclear data library JENDL-4.0. In contrast to the above drive, the other drive by the inherent source spectacularly reduced the counter-position dependence and lead to a good agreement with the calculation by the MVP. The prompt-neutron decay constant determined from the Feynman-α analysis under the external source was also significantly dependent on the counter position. The Rossi-α analysis had a relatively slight counter-position dependence of the decay constant to the Feynman-α analysis but had a very low S/N ratio, which indicated an inferior applicability of the Rossi-α analysis to the reactor drive and enlarged a statistical uncertainty of the decay constant. On the other hand, the reactor drive by the inherent source considerably reduced the counter-position dependence of the Feynman-α analysis and spectacularly enhanced the S/N ratio of the Rossi-α analysis. An effective strength of the inherent source could be also determined from the S/N ratio. When the prompt-neutron decay constant obtained under this reactor drive was transformed into each subcriticality by the Simmons and King method, where a subcritical dependence of the generation time and the effective delayed-neutron fraction was neglected, the subcriticality transformed seemed to agree well with that calculated by the MVP. When the decay constant was transformed by the inhour method, where the subcritical dependence of these kinetic parameters was considered, a systematic disagreement between the transformed and the calculated subcriticality appeared.