Testing of a gel equivalent to liver to perform neutron characterizations

Several characterizations are needed in the frame of the project of irradiation of sections II-III of the human liver left lobe. For trials including neutron irradiation, samples remain with a certain level of activity that avoids their promptly disposal. To not use biological materials, that degrades and add the requirement of proper conservation up to their safe disposal, gel phantoms with non-residual activation were developed and their behavior under neutron irradiation was studied and compared to the one already obtained in previous studies using a pig liver. Considering that response to neutrons depends mainly on the hydrogen content of the human tissue, materials chosen to construct phantoms equivalent to sections II-III of the liver left lobe were demineralized water and 2% agarose (C12H14O2(OH)4). The solution, still in its liquid phase, was poured into specially designed polyethylene bags in order to reproduce the portion of liver to be treated. To cover the variability range of sizes and weights in humans, three phantoms were prepared: 180, 240 and 300 g. Implantable rhodium based self-powered detectors were used to obtain neutron flux profiles in the developed phantoms, both external and internal. Implantation of SPND was done along the central longitudinal axis of the samples, where lowest flux is expected. Irradiations were carried out under the same conditions that are previewed for the liver, i.e. inside the same acrylic container and covered with demineralized water to simulate preservation solution. Phantoms construction was quite simple and its durability very good. Handling in order to insert instrumentation was easy. Obtained internal neutron profile resulted very similar to the obtained for the pig liver, which showed that it is possible to use the phantoms to perform neutron characterizations.