Accelerator-based neutron sources for BNCT

Abstract

Purpose In this paper we compare the main AB-BNCT facilities worldwide in terms of neutron-producing nuclear reactions, existing technologies and machines, and induced radioactivity both at the target and at the beam shaping assembly (BSA) level, by the resulting neutron beam. We also provide information on several aspects of the Buenos Aires project. Methods A comparison is made of the different active AB-BNCT projects and facilities worldwide using the information available in the literature. The radioactivity induced by both the direct beams (protons or deuterons) at the targets (7 Li, 9 Be and 13C) and the neutron beams at the BSAs is discussed. The main technical features of the Argentina project are presented. Results There are a number of different facilities for Accelerator-Based BNCT (AB-BNCT) worldwide, some already working and even treating patients and some under development and construction. They range from high-energy 30 MeV cyclotrons (using the 9 Be(p,n) reaction), medium-energy RFQ-DTL accelerators (at 8 and 10 MeV using likewise the 9 Be(p,n) reaction), low-energy electrostatic, both Tandem and single-ended, and RFQ machines (working on 7 Li(p,n) at about 2.5 MeV), to a very low-energy single-ended electrostatic quadrupole accelerator, ESQ (working on 9 Be(d,n) or 13C(d,n) at 1.45 MeV). This last accelerator, its ancillary systems and the associated facility is being developed and constructed at the National Atomic Energy Commission of Argentina. An important aspect about these facilities, relevant for their long term sustainability, is the production of radioactivity, which should be kept at a minimum according to the ALARA criterium, both at the neutron production target, by the primary beam, and at the Beam Shaping Assembly (BSA), by the induced neutrons. In a 30 day period with an operation schedule of 8 h a day the 7 Li(p,n) at 2.3 MeV option produces 2.1 TBq of 7 Be (30 mA), the Be(p,n) option at 8 MeV only produces prompt radiation while at 30 MeV (1 mA) other reaction channels are open which produce 0.39 TBq of 7 Be and 4.2 GBq of 3 H. The 13C(d,t) reaction produces 0.78 GBq of 3 H. Conclusions The use of exothermal deuteron-induced Be(d,n) and 13C(d,n) reactions allows us to use the smallest energy machine, at 1.45 MeV, for AB-BNCT. It is shown that among the systems proposed the 13C(d,n) solution is the one with the lowest overall activation (target+BSA). Coupled to an AlF3 BSA (which undergoes no long term activation), a 30 mA deuteron beam on a 13C target can deliver a good quality BNCT treatment for a deep seated brain tumor in one hour.