Experimental validation of the Gaseous Proton Recoil Telescope for quasi-absolute neutron flux measurements

Abstract

The accuracy of neutronics simulations of actual or future reactor cores is nowadays driven by the precision of the nuclear data used as input. Among the most important neutron-induced fission cross sections to understand well are the actinides. It is, indeed, of primary importance to know accurately these cross sections around 1 MeV for the safety of Generation IV reactors. High accuracy measurements of neutron flux are essential for accurate cross section measurements; measurements of this flux with respect to the ¹H(n,n)p cross section can be made with the proton recoil technique. For an accurate measurement below 1 MeV, the Gaseous Proton Recoil Telescope (GPRT) is developed and characterized, with the aim to provide quasi-absolute neutron flux measurements with an accuracy better than 2%. This detector is composed of a double ionization chamber with a Micromegas segmented detection plane. The pressure of the gas can be adjusted to protons stopping range — and therefore to neutrons energy. An accurate neutron flux measurement requires that the GPRT has an intrinsic efficiency of 100%, and thus an important effort has been made to verify this. An alpha source and proton micro-beam have been used and the intrinsic efficiency is confirmed to be 100%. Additionally the dead-time of the detector has been investigated on a test bench, and is found to be 7.3 ms.