Bioanalytical investigations on experimental BNCT with cold neutrons at the Juelich Research Reactor FRJ-2, status report

Until recently 'cold neutrons' with an average energy of 0.005 eV generated in Juelich were only used for 10Boron micro-analysis of blood and tissue samples of tumor bearing mice using quantitative neutron capture radiography (QNCR). Because of the high quality of the pure cold neutron beam with respect to low core γ-ray and fast neutron contamination, this neutron beam would constitute an excellent treatment modality for superficial tumors like malignant melanoma of the skin. If one considers that living tissue contains 70-80% water, the predominant interaction with neutrons is scattering by hydrogen atoms. The hydrogen scattering cross section for (0.005 eV) cold neutrons is 80 barn (1 barn = 10-24 cm2) and the H-capture cross section in only 1 barn, so that the neutrons will be scattered many times before absorption. This leads to thermalization of the cold neutrons by collision with the room-temperature H atoms in the skin. The depth-dose distribution of a cold neutron beam in living tissue in regard to the half-value layer might be essentially the same as for a (0.025 eV) thermal neutron beam