As part of the ISIS@MACH access programme, users from Italian companies Mardel and Bariblock have used the wide range of neutron energies available on the VESUVIO beamline to characterise the neutron cross section of barite-enriched concrete.
Concrete used in radiation protection can be enhanced by the addition of barite, BaSO4, to increase the absorbance of ϒ-rays for a layer of the same thickness. This means that thinner shielding is needed, making it more suitable for smaller-scale applications such as those in hospitals.
To determine the optimum concentration of barite within the concrete, it is important to understand the neutron-attenuation properties, as measured by the neutron cross section. This is impacted by the concentration of different elements present, especially the amount of hydrogen.
Although the shielding behaviour of these materials is well known for neutrons at high energies (above 1 MeV), there is little knowledge of the behaviour at lower neutron energies.
In this study, published in EPJ Plus, the researchers measured the cross section of the materials under bombardment from neutrons between 1 meV and 1 keV.
They found that, unlike at high neutron energies, the total cross section is dominated by the scattering off the hydrogen atoms within the concrete, rather than by the neutron capture by barium. Combined with the fact that increased barite concentration leads to lower hydrogen concentrations, this means that the barite-enriched concrete is less effective at shielding from low energy neutrons than regular concrete.
The group also expanded their work to look at the effect of water and found that measuring the sample under vacuum leads to up to a 10% change in neutron cross section, showing how important it is for the temperature and humidity of the environment to be controlled.
Both of these findings illustrate that care should be taken when considering which recipe of concrete to use for shielding, depending on the energy of the neutrons present. The knowledge gained from this study is able to inform additional guidelines for radioprotection workers when determining the optimal concentration of barite in concrete used for shielding in mixed gamma/neutron radiation environments.
The experiment's Principal Investigator, Dr Martellucci from Mardel srl, stressed the importance of characterising shielding materials with detailed measurements, and commented that; “neutrons are expected to continue to be a unique tool in the study of radioprotection in medical, research and industrial shielding."
The full paper can be found online at DOI: 10.1140/epjp/s13360-021-01243-z