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BNCT is an experimental binary cancer radiotherapy modality involving the administration of a boronated pharmaceutical that preferentially accumulates in malignant tissue, followed by exposure of the treatment volume to a thermal neutron field. This procedure causes the selective destruction of the boron-containing cells by the energetic products of the 10B (n, alpha) Li interaction. BNCT research in the United States and Europe has been focused on the use of an epithermal (0.5 eV to 10 keV) neutron beam as the most effective method for generating the necessary thermal neutron field in deep-seated treatment volumes. Epithermal-neutron beams can be generated by small nuclear reactors1'and by accelerator-based neutron sources6" 8. So far, however, only reactors have actually been used to produce therapeutically-useful epithermal-neutron beams for BNCT. Some low-intensity prototypes of accelerator-based sources, generally featuring the use of proton or deuteron beams and beryllium or lithium targets have been constructed. Scaling of these devices to output levels suitable for clinical application will in many cases require additional developments in the relevant accelerator technology, as well as the resolution of some rather difficult issues associated with target cooling. This report describes an alternate approach to the realization of a clinically-useful accelerator-based source of epithermal neutrons for BNCT that reconciles the often-conflicting objectives of target cooling, neutron beam intensity, and neutron beam spectral purity via a two-stage photoneutron production process driven by an electron linear accelerator rather than by a …