Metrological characterization of intense ([formula omitted], n) neutron sources by coupling of non-destructive measurements

Abstract

Metrological non-destructive characterization of intense (α, n) neutron sources (emission rate between 107 and 3×108 s−1 into 4π sr solid angle) is a challenge for nuclear applications. In this article, we will present the design, development and in situ validation of two measurement cells especially dedicated to this characterization. The main goal consists in determining the absolute neutron emission rate of this type of neutron sources with relative uncertainties less than 5% (k=1). Another purpose is related to the qualitative and quantitative analysis of fission products present in irradiated neutron sources. Because of experimental constraints, acquisitions were carried out underwater which required a full remote control of the measurement cells. Neutron emission rate is assessed using three different non-destructive techniques: (i) global neutron counting, (ii) neutron activation using gold dosimeters and (iii) gamma-ray spectrometry. We will successively present the design step and associated constraints, main characteristics of measurement cells and associated laboratory characterization as well as experimental results obtained during the final in situ measurement campaign. The latter shows an excellent agreement regarding the neutron emission rate values provided by the three different non-destructive techniques and a relative combined standard uncertainty less than 5% (k=1) for the investigated neutron sources.