A Variation of the F-Test for Determining Statistical Relevance ofParticular Parameters in EXAFS Fits

A general problem when fitting EXAFS data is determining whether particular parameters are statistically significant. The F-test is an excellent way of determining relevancy in EXAFS because it only relies on the ratio of the fit residual of two possible models, and therefore the data errors approximately cancel. Although this test is widely used in crystallography (there, it is often called a 'Hamilton test') and has been properly applied to EXAFS data in the past, it is very rarely applied in EXAFS analysis. We have implemented a variation of the F-test adapted for EXAFS data analysis in the RSXAP analysis package, and demonstrate its applicability with a few examples, including determining whether a particular scattering shell is warranted, and differentiating between two possible species or two possible structures in a given shell

Tritium production from ternary fission

The tritium gas emission in the thermal neutron induced ternary fission of 249Cf has been determined for the first time in a measurement at the intense neutron beam PF1B of the Institut Laue-Langevin in Grenoble (France). A 249Cf sample was mounted in the centre of a vacuum chamber, at a short distance of a ΔE-E telescope which permitted the identification of the ternary particles. The binary fission fragments were detected in a separate run, using only the E detector. From these measurements, the energy distributions and the emission probabilities of the ternary 3H particles emitted in the thermal neutron induced ternary fission of 249Cf could be determined. Based on this result and on measurements published by us recently, we could enlarge the database related to 3H emission probabilities (denoted t/B) and their energy distributions in particular for the Cm and Cf isotopes. The impact of the excitation energy of the fissioning nucleus on the ternary particle emission probability is discussed, comparing for a given compound nucleus, the t/B data obtained from thermal neutron induced fission (excitation energy of the fissioning nucleus = the neutron binding energy) and from spontaneous fission (excitation energy = zero). In addition, semi-empirical relations between t/B data and characteristics of the binary fission process are proposed