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Nyhedsartikel16 April 2021

JRC specific target preparation for neutron-induced reaction measurements

Pictures five boron test targets prepared at JRC-Geel
Picture of five boron test targets prepared at JRC-Geel.
© EU, 2020

as support in fundamental and applied physics for international research and industry.

The JRC-Geel is one of the very few sites world-wide that has unique facilities and know-how in the preparation of thin film deposits (called targets) for nuclear data measurements at the JRC’s and international accelerator sites. The main users of these nuclear data are European Union member state organisations and international partners of the EURATOM program, in particular the OECD-NEA (Organisation for Economic Co-operation and Development, Nuclear Energy Agency) and the IAEA (International Atomic Energy Agency) but also research organisations and authorities in the field of non-energy nuclear applications. JRC targets are also a prerequisite for the open access to JRC Research Infrastructures (EUFRAT).

Targets have specific properties depending on the investigated reaction and the quantities being measured. Their characteristics influence the results of the experiments and their quality has a strong impact on the total uncertainty of neutron-induced reaction data, which are important for studies in fundamental physics, astrophysics, reactor safety, waste transmutation, nuclear medicine, material science, industry and nuclear safeguards. Depending on the experiment, the targets can be discs, foils, powder pellets or thin films made of either stable or radioactive materials.

Thin films of a thickness in the nanometres scale are prepared on a substrate by physical vapour deposition and the so-called "molecular plating". The latter is a cathode deposition of the material onto an aluminium substrate in isopropanol at a constant voltage. The total activity of the radioactive layers is determined by low-geometry alpha particle counting. The mass of the stable deposits is determined by accurate weighing. Recently, the preparation of thin boron layers has been a particular challenge due to the specific properties of this element. Thin 10B targets are of great importance in the field of nuclear data measurements as they are used to calibrate the neutron flux.

The JRC-Geel target preparation laboratory responded to the lack of supply of these type of targets by introducing novel equipment in the field of thin layer deposition and was successful in the preparation of high quality 10B targets by means of electron beam evaporation combined with in situ plasma cleaning. These targets were used at CERN for neutron induced fission cross-section measurement of 230Th targets, also prepared at JRC-Geel. Furthermore, the JRC is in the Board of Directors of the International Nuclear Targets Development Society (INTDS).

233U disc with a diameter of 30 mm and thickness of 0.64 mm prepared by punching and mounted in a measurement holder with 50 µm Al foil
Figure 1. 233U disc with a diameter of 30 mm and thickness of 0.64 mm prepared by punching and mounted in a measurement holder with 50 µm Al foil
© EU, 2020
Image of a multi-layer 235U based fluence monitor.
Figure 2. Multi-layer 235U based fluence monitor.
© EU, 2020

The JRC published two articles with the latest achievements in its core target preparation activities and in the production and characterisation of boron targets, found on the EPJ Web of Conferences website.

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16 April 2021