Abstract: A tumorous patient is injected with a compound including an element that accumulates in tumors and that has an isotope which emits an alpha particle in a neutron capture reaction. The patient is positioned in front of a radiation beam that has been filtered to remove most neutrons having energies above 30 KeV and most thermal neutrons, leaving predominantly epithermal neutrons which are moderated to a thermal level by outer layers of tissue and are captured by the incorporated isotope.A radiation beam having neutrons with a wide distribution of energies is filtered with aluminum, sulfur and argon filters, whose cross sections complement each other in providing a beam with energies predominantly in the epithermal range. The filter mass attenuates the gamma radiation. Beams with lower ratios of undesirable gamma radiation to epithermal beam intensity can be attained with filter combinations which include liquid argon. A poor geometry filter of bismuth or lead can also improve the gamma to neutron ratio.

Abstract: A tumorous patient is injected with a compound including an element that accumulates in tumors and that has an isotope which emits an alpha particle in a neutron capture reaction. The patient is positioned in front of a radiation beam that has been filtered to remove most neutrons having energies above 30 KeV and most thermal neutrons, leaving predominantly epithermal neutrons which are moderated to a thermal level by outer layers of tissue and are captured by the incorporated isotope.A radiation beam having neutrons with a wide distribution of energies is filtered with aluminum and sulfur filters, whose cross sections complement each other in providing a beam with energies predominantly in the epithermal range. The filter mass attenuates the gamma radiation. Beams with lower ratios of undesirable gamma radiation to epithermal beam intensity can be attained with filter combinations which include liquid argon. A poor geometry filter of bismuth or lead can also improve the gamma to neutron ratio.