minum 6101 alloy. All the samples were cut to slabs shapes which
could be stacked on top of each other to obtain various thicknesses
for convenient comparisons of experimental results. The intensities
of transmitted photons without samples (I0) and with samples (I)
were measured to evaluate the linear attenuation coefficient.
Transmitted intensities were determined from the photopeak in
a narrow energy range symmetrical arrangement with respect to
the peak centroid. Appropriate counting time (fixed preset time
was set as 90s on the Genie 2000) for each measurement was chosen
such that 105106 counts were recorded under each photo
peak to keep statistical uncertainty below 0.3%. The linear attenuation
coefficients of pure aluminum plates were calculated and
compared to theoretical data as a verification of the accuracy of
the experimental measurements. The first run was conducted
using bulk and foam samples with different thicknesses. The second
run was repeated with water added into the container to fill
the foam samples. Another run was performed by filling water
with 2% (w/v) boric acid into the foam samples. The experiments
were conducted at constant temperature to avoid any shift of peak.
In the neutron attenuation/absorption experiments, the sample
arrangements were changed taking into account of the horizontal
neutron beam being used instead of vertical c-rays. Fig. 2 shows
the set up of the samples where a plastic container with bottom
grooves is used to house the samples. A plastic sheet separator in-