Nuclear Physics A 686 (2001) 187–203 www.elsevier.nl/locate/npe New evidence of an intense scission neutron source in the 252 Cf spontaneous fission N.V. Kornilov a , A.B. Kagalenko a , S.V. Poupko a , P.A. Androsenko a , F.-J. Hambsch b,∗ a RF Institute for Physics and Power Engineering (IPPE), Obninsk, Russia b EC-JRC-Institute for Reference Materials and Measurements (IRMM), Geel, Belgium Received 9 August 2000; revised 19 October 2000; accepted 25 October 2000 Abstract The neutron energy-angular distributions relative to the fragment direction of 252 Cf (SF) were analysed. The results of three independent experiments being in reasonable agreement allows the conclusion that a (30 ± 5)% neutron surplus exists at ∼ 90 ◦ relative to the direction of the moving fragments, which can not be accounted for with the assumption that all neutrons are emitted from fully accelerated fragments. This experimental fact required the incorporation of neutron emission from an additional source of neutrons. Angular and energy distributions of these additional neutrons were evaluated using data from an experiment performed at IRMM several years ago and were compared with the results in literature.  2001 Elsevier Science B.V. All rights reserved. PACS: 24.75.+I; 23.20.En; 21.10.Gv Keywords: RADIOACTIVITY 252 Cf(sf); Neutron energy-angular distributions; Deduced scission neutron yield; Scission neutron spectra 1. Introduction The investigations of the fission neutron angular-energy distribution relative to the fragment direction depending on mass split and fragment kinetic energy gives unique information about the neutron emission mechanism and the fission process. However, these experiments are very complicated and time consuming which may explain some contradictions between individual experimental results and rather different conclusions made by the authors. The fission neutrons may be emitted from three different sources. Our classification is very close to the one discussed in Ref. [1] but has some particular details. * Corresponding author. E-mail address: hambsch@irmm.jrc.be (F.-J. Hambsch). 0375-9474/01/$ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII:S0375-9474(00)00561-3