Prompt fission γ -ray (PFG) spectra have been measured in a recent experiment with the novel directional fast-neutron source LICORNE at the ALTO facility of the IPN Orsay. These first results from the facility involve the comparative measurement of prompt γ emission in fast-neutron-induced fission of 235 U and 238 U. Characteristics such as γ multiplicity and total and average radiation energy are determined in terms of ratios between the two systems. Additionally, the average photon energies were determined and compared with recent data on thermal-neutron-induced fission of 235 U. PFG spectra are shown to be similar within the precision of the present measurement, suggesting that the extra incident energy does not significantly impact the energy released by prompt γ rays. The origins of some small differences, depending on either the incident energy or the target mass, are discussed. This study demonstrates the potential of the present approach, combining an innovative neutron source and new-generation detectors, for fundamental and applied research on fission in the near future.
Theoretical relations are developed for the effect of coincidence (simultaneous arrival of two or more particles in the sensing zone) on the observed particle count in a Coulter counter, a device for counting particles in liquid suspensions. Two limiting cases are treated: (a) two or more particles are seen as a particle whose volume is the total particle volume present, (b) two or more particles are seen as the largest particle present. The theory was tested experimentally with a ``monodisperse'' polystyrene latex. It is shown that absolute particle volumes may be obtained from the ratio of solids content to number of counts under certain conditions. Case (b) coincidence predominates. The apparent breadth of the particle-size distribution curves in the ``monodisperse'' latex was greater than expected.
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