Target preparation for neutron-induced reaction measurements

Abstract

Neutron-induced reaction measurements, e.g. cross-sections and particle emission yields, require samples, called "targets", with specific properties depending on the reaction being studied and the quantities being measured. The target characteristics influence the results of these measurements and can have a strong impact on the total uncertainty of neutron-induced reaction data, which are important for industry and in research. This paper gives an overview of the main techniques applied in the target preparation laboratory at JRC-Geel for production and characterization of targets for neutron-induced reaction data measurements. The use of different targets is demonstrated with a few examples of total and reaction cross-section as well as nuclear fission experiments. In addition, on-going investigations and technical developments are presented.EPJ Web of Conferences 229, 04003 (2020) https://doi.org/10.1051/epjconf/202022904003 INTDS2018

The fission experimental programme at the CERN n_TOF facility: status and perspectives

“…The distance between the source material and the substrate determines the yield of the process and the homogeneity of the thin film. During the deposition process the film thickness can be monitored with a quartz crystal microbalance [169][170][171]. Prior to the vapour deposition, the substrate can be cleaned in situ with plasma generated e.g.…”

“…The molecular plating technique consists in the cathodic deposition of the source material onto an electrically conductive substrate in an organic solution like isopropanol [169,175,176] or isobutanol [177]. This technique is performed in a molecular plating cell designed according to the required dimensions of the substrate and the deposit.…”

“…In general the substrate needs to be as thin as possible, mechanically stable during and after the deposition process, during the transport, during the experiment and may not contain material that takes part in a nuclear reaction resulting in products that disturb the experiment. Typical substrates are made of aluminium [169], occasionally with a 50 nm titanium layer [177], with a thickness in the µm range glued onto a frame. While molecular plating requires a conductive substrate, evaporative deposition can be performed on plastic foils like mylar and polyimide foils [170].…”

“…In general, the areal density of the nuclide under investigation is determined along with the presence of contaminants and impurities which can influence the measurement and the homogeneity of the target, as far as possible. For stable deposits the areal density is calculated from the mass of the deposit which is determined by accurate difference weighing applying the substitution method and corrected for the isotopic abundance and impurities as provided by the supplier, and from the area of the deposit given by the inner diameter of the mask used during the deposition [169]. The hydrogen content of tristearin targets, for example, can be measured by combustion analysis [167].…”

“…For actinide layers the areal density of a specific radionuclide is calculated from the mass derived from the total activity measured by α-particle counting in a low-efficiency counting geometry and corrected for isotopic abundance determined by mass spectrometry and from the area derived from the inner diameter of the mask in front of the substrate during the deposition process [169]. The homogeneity is measured by scanning the target with a diaphragm with an αparticle counter [174] or by autoradiographic imaging [181].…”