Technical Paper Abstract

Compact, Linac-based Source of Epithermal Neutrons for BNCT

D.A. Swenson,

A new rf-focused linac structure, designed specifically to increase the acceleration efficiency and reduce the cost of linac
structures in the few-MeV range, may win the role as the optimum accelerator-based epithermal neutron source for the Boron
Neutron Capture Therapy (BNCT) application. This new linac structure resembles a drift tube linac (DTL) with radio
frequency quadrupole (RFQ) focusing incorporated into each "drift tube", hence the name, Rf-Focused Drift tube (or RFD)
Linac. It promises superior acceleration properties, focusing properties and CW capabilities.

We have a proposal under consideration for the development of an epithermal neutron source, based on the 2.5 MeV RFD linac
system with an average current of 10 mA, having the following components: an ion source, a short low-energy beam transport
system, a short RFQ linac section, an RFD linac section, an rf power system, a high-energy beam transport system, a neutron
production target, and a neutron beam moderator system. We propose to develop a solid lithium target for this application in the
form of a thin lithium layer on the inner surface of a truncated aluminum cone cooled by the heavy water moderator, where the
proton beam is expanded to a diameter of 3 cm and scanned along a circular path, striking the lithium later at the cone's
half-angle of 30 degrees. We propose to develop a moderator assembly to transmit a large fraction of the source neutrons
from the target to the patient treatment port, while shifting the neutron energies to an appropriate epithermal energy
spectrum and minimizing the gamma-ray dose.