Preparation and characterization of ¹⁰B targets at JRC-Geel

European Commission, Joint Research Centre, Directorate G, Retieseweg 111, Geel B- 2440, Belgium

^* Corresponding author: david.vanleeuw@ec.europa.eu

Published online: 28 February 2020

Abstract

Measurements of neutron-induced cross sections to generate nuclear data are a core activity of the JRC-Directorate G Standards for Nuclear Safety, Security and Safeguards unit in Geel. Thin ¹⁰B layers are of great importance in this activity as they are used to measure the absolute neutron flux in the beam using the standard ¹⁰B(n,α)⁷Li reaction cross-section as a reference. After a period of reduced activity and in line with a renewed interest for nuclear data, the demand for high quality ¹⁰B targets increased. In this paper we describe the design and features of a new e-beam evaporator specifically customized for the preparation of boron targets as replacement of the old dysfunctional equipment. Several ¹⁰B targets of varying thicknesses were prepared and characterized as part of the factory acceptance tests and implementation in the JRC-Geel target preparation laboratory. Differential substitution weighing was applied for mass determination and in order to calibrate the thickness monitor. Comparative time-of-flight measurements relative to ¹⁰B and ²³⁵U standard targets were conducted at the GELINA neutron time-of-flight facility at the JRC-Geel site as second methodology for the determination of ¹⁰B areal density. The morphology of the layers was assessed by means of Scanning Electron Microscopy (SEM). The determination of impurities was realized by means of Energy Dispersive X-ray (EDX). Finally, two boron targets were prepared in the frame of the measurement of the neutron induced fission cross-section of ²³⁰Th at the n_TOF neutron time-of-flight facility at CERN.