The haefely-gfk fast-neutron generator

Abstract

The radiation source of the Haefely generator is a compact, sealed neutron tube, invented by K. A. Schmidt at the German Institute for Applied Nuclear Physics of the Gesellschaft fur Kernforschung (Nuclear Research Center) in Karlsruhe. Under the terms of an exclusive worldwide agreement, Haefely is licensed to manufacture and market the Karlsruhe Intense Neutron (KARIN) generator tube. The tube has axial symmetry with a concentric 250-kV accelerating structure. A mixed beam of deuterium and tritium ions impinges radially on a cone-shaped target electrode where 14MeV neutrons of the D-T fusion reaction are generated. Integral with the tube is a tritium reservoir. The only external connections required are the power supplies and the cooling water. The KARIN generator tube is enclosed in a shielded source head to suppress all emitted neutrons not directed at the patient. The protective shield consists of layers of steel, moderating material mixed with boron, and lead. The rotating gantry that positions the source head provides isocentric source motion for multi-port treatment or arc therapy. Dose level from the source is 20 rad/min at a source-to-skin distance of 85 em, or 15 rad/min at a source-to-skin distance of 100 cm. Laboratory models of the neutron tube have provided data on tube life and performance characteristics. The prototype of a clinical fast-neutron generator for cancer therapy was installed at the Deutsches Krebsforschungszentrum (German Cancer Research Center) in Heidelberg and became operational in August 1976. Initial tests with this clinical unit will include dosimetry and neutron-field mapping, followed shortly by clinical research on fast-neutron cancer therapy. Based upon the present experience, the mean lifetime of the tube is approximately 700 hr if operated at nominal neutron yield. The Haefely fast-neutron gererator will be marketed worldwide when the prototype at the German Cancer Research Center is fully operational and has proven the claimed performance.