Although plastic waste receives a lot of bad publicity, for some applications there are advantages to using synthetic polymers over the use of other materials. Recycling is often readily practicable if the component materials are known, and so the balance of benefits and end-use costs needs to be carefully evaluated.
A recent study using the Larmor instrument tested the feasibility of using a 3D-printed boron carbide composite as neutron absorbing components for instruments and as parts for sample holders. The researchers, as they are based in Sweden, are obliged to use environmentally favourable alternatives to metals like cadmium.
Composites have been demonstrated as effective in several applications and simple calculations provide reasonable estimates of the absorption. However, it is important to verify their accuracy and, in particular, to determine any scattering of neutrons, even if it is low, that can arise when the material is used in proximity to detectors.
Previous reports of materials that have been used for shielding have sometimes suggested that they did not attenuate as expected. These measurements were often limited to the use of neutron beams with unknown energy or wavelength and, due to limits in fabrication, only relatively thick samples could be used.
Use of additive manufacturing has allowed thin layers with different thicknesses to be prepared and tested at ISIS. Measurements of both transmission and scattering of the Addbor N25 composite (25% wt boron carbide in nylon) were made on Larmor at wavelengths between 0.9 and 12.5 Å (about 0.5 to 100 meV).
Thicknesses between 0.07 mm and 0.6 mm were measured and showed the expected variation in transmission, with a slightly better absorption than calculated from tabulated cross-sections. The clear wavelength dependence of the observed incoherent scattering is of interest not just for performance of absorbing composites but, more generally, can be important in many SANS experiments.
These promising results paved the way for the company involved in this research to produce focussing collimators and other components made of a safer, and environmentally friendly alternative to cadmium.
The company is also working with materials that absorb X-rays and γ-rays, and combining these with their neutron shielding material, as there is now a strong interest in development of shielding for other types of radiation such as medical X-rays, to reduce the use of lead.
Although the main activity of the company involved in this work involves polymer composites, they are using their additive manufacturing skills elsewhere, and are now exploiting an invention [2] of tough, high transparency, low background scattering glassy metal as windows for neutron beams or to make sample environment components.
Their results show how measurements that began purely to verify the technical performance of a commercial product can provide important insights into general aspects of scattering studies.
Further information
The study was initiated by the company Additive Composite Uppsala AB (www.additivecomposite.com) by Adam Engberg and Olle Eriksson in a collaboration with Uppsala University, Adrian Rennie.
[1] A. R. Rennie, A. Engberg, O. Eriksson, R. M. Dalgliesh 'Understanding neutron absorption and scattering in a polymer composite material' Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 984, (2020), 164613. https://doi.org/10.1016/j.nima.2020.164613
[2] M. Sahlberg, A. R. Rennie, J. J. Marattukalam, C. A. Ericsson, V. M. Pacheco 'A beam path component for use in neutron scattering equipment and method of producing such' Provisional Patent Applications 2020. US No. 63/124174 and Sweden 2041446-9.
