On the impact of the fissile coating on the fission chamber signal

Abstract

In this paper, we address the question of how the signal of a uranium fission chamber is sensitive to the thickness of its fissile coating. We first review the electrodeposition technique in order to status on the maximum surface density reasonably achievable. Then, we assess the effect of the neutron flux perturbation on the possible loss of detection efficiency. The most important part of this work is the assessment how the energy spectrum of a fission chamber is affected by the so-called self-absorption of the fission products in the fissile coating. We present a Monte Carlo code we developed in order to achieve that goal. That numerical tool allowed us to reveal the linear relation between the sensitivity loss and the coating thickness, with a slope of 8%/(mg/cm2). Numerical results are discussed with respect to experimental data and a need of new experiments is expressed. Finally, we showed the frequent assumption of the straight trajectory of fission products is not valid for a small fraction of those particles which have a kinetic energy less than 20keV/amu.