Neutron-capture therapy with ultra-cold neutrons

The status of neutron-capture therapy of malignant tumors and its problems – damage to healthy tissue as a result of neutron transport to the irradiation location and presence in the therapeutic beam of a background consisting of γ rays and fast neutrons – are presented. To solve these problems, the authors have proposed using ultracold neutrons with energy less than 10^–7 eV, whose unique capability is to undergo total reflection from the surface of a condensed substance at any angle of incidence. Numerous works have demonstrated that such neutrons can be transported along neutron guides. The cross section for inelastic scattering of neutrons by hydrogen-containing substances – water, ethyl alcohol, and biological tissue – has been measured in an IR-8 beam of ultracold and very cold neutrons. At temperature 200–300 K, the experimental data are in very good agreement with calculations, but as temperature decreases further a discrepancy appears, which could be due to the inaccuracy of the model spectra of the oscillations hydrogen-containing substances used in the calculations. The use of ultracold neutrons opens up new possibilities of neutron-capture therapy for treating malignant tumors localized in body cavities or organs.