For 6101 aluminum foam materials, the figures show that they have the lowest
gamma-ray attenuation among all the samples. It can be explained as the foam samples
have the lowest density, which is the result from their porous structure. The 10 PPI and
20 PPI foam have close attenuation at all the three energies. The pore size of foam has
not shown obvious effect upon attenuation for gamma-rays.
• For “foam + water” sample, the attenuation has shown to be much better than the
foam. However, the effect from pore size of foam is not obviously seen either.
This improvement in attenuation might be contributed to the water filled into the
foam. These tendencies are consistent with the theory. In the energy range in this experiment,
the dominating interaction mechanism is Compton scattering. Therefore the total attenuation
is dependent on the total number of electrons as scattering targets in the sample material.
Because Compton scattering involves the least tightly bound electrons, the nucleus has only a
minor influence and the probability for interaction is nearly independent of atomic number
[58]. The interaction probability depends on the electron density, which is proportional to
Z/A and nearly constant for all materials [58]. Compared with only foams, the water content
in the “foam + water” samples contributes to total electron density of the sample thus
increases the total narrow-beam attenuation coefficient.
For “foam + boric acid solution” sample, the measurements were only performed at
the lower energy (0.662 MeV). It shows a bit better attenuation than “foam+water” samples.