Direct calculation of the cross-sections for thick samples in this
experiment is hardly feasible, especially for the non-homogenous
‘‘foam + liquid” samples. The unique structure of the foams and
the polyenergetic property of the thermal neutron beam complicate
the total cross-section calculation and hence only experimental
data were considered in this work.
From the neutron spectra, transmission data were obtained for
pure bulk Al, 10 PPI 6101 Al foam, ‘‘foam + water” samples, and
‘‘foam + boric acid solution (1%, 2%, 3% w/v boric acid in water)”
samples. The attenuation effects for the four types of samples are
shown in Fig. 8 as transmission versus thickness. As seen from
Fig. 8 the ‘‘foam + boric acid solution” samples show the highest
attenuation, while ‘‘foam + water” samples have higher attenuation
than bulk samples, but foams-only samples show the lowest
attenuation. The effect of water can be seen as the result of its high
hydrogen content. It is also noticed that as the concentration of boric
acid solution increases, the attenuation increases. For the foam
samples filled with 2% and 3% (w/v) boric acid in water, the 1.5 in.
thickness samples totally stopped the beam, which is due to the