Energy Dependence of the U235 Fission Cross-section THE measurements of the fission cross-section of U2”j as function of neutron energy, reported in the first issue of this Journal (page 3) have been extended up to 0.4 eV, and a fission resonance at about 0.26 eV has been found. In this paper the whole curve qiss/OB versus energy is given. Due to appreciable isotropic scattering background, small glancing angles, and relatively poor resolution, the measured points of the resonance peak are not very
0.8 0.008
0.01
0.04 0~06.0-08.0~10 Neutron energy (eV)
0 20
030
0.40
FIG. 1
well defined. The spread of the measured points is higher than statistical errors could account for. The curve drawn is therefore an approximate one. This particular curve would give the position of the resonance peak at about 0.28 eV. We are indebted to the Joint Establishment for Nuclear Energy Research for the opportunity to make these measurements at the Kjeller Pile. We are particularly grateful to Dr. GUNNAR RANDERS for the constant support and encouragement during the work and for presenting the curve at the International Conference of Nuclear Engineering in Ann Arbor on 24 June 1954. We are also indebted to Dr. J. J. WENT and Dr. I. KISTEMAKER from the Netherlands for providing the u”35 for the measurements. DRAGOSLAV POPOVI~* JENER,