Tandem-ESQ for Accelerator-Based BNCT

A.J. KREINER; J.W. KWAN; A.A. BURLON; H. DI PAOLO; E. HENESTROZA; D.M. MINSKY; A.A. VALDA; M.E. DEBRAY; H.R.SOMACAL

Takamatsu, Japón. Exposición oral (A.Kreiner)

Congreso; 12th International Congress on Neutron Capture Therapy; 2006

International Society for Neutron Capture Therapy y Japanese Society of Neutron Capture Therapy

Boron Neutron Capture Therapy (BNCT) is considered by a significant international community as a promising option for the treatment of certain types of cancer [1]. The progress of BNCT will require neutron sources suitable for installation in a hospital environment. Low-energy particle accelerators are most appropriate for this purpose and can be constructed for modest cost. We report here on a project to develop a Tandem-ElectroStatic-Quadrupole (ESQ) accelerator for accelerator-based BNCT. The project goal is a machine capable of delivering 30 mA, 2.3 MeV protons to be used in conjunction with a neutron production target based on the 7Li(p,n)7Be reaction slightly beyond its resonance at 2.25 MeV. In order to make a decision as to the most appropriate accelerator for BNCT, different options have been evaluated, comprising d-d or d-t neutron generators, RFQs and electrostatic machines of various types. The technologically simplest and cheapest solution points to an electrostatic machine. Existing electrostatic accelerators, produce only a few mA of proton beam current limited by the column design. High beam current density, as implied by a size limited 30 mA proton beam, needs strong focusing in the transverse plane. In this regard ESQs are much stronger than the aperture lens used in conventional Tandem accelerators. An ESQ column can be designed using a lower field stress than a Pierce column in multi-MeV beam energy applications [2]. Strong transverse fields will also suppress secondary electrons sideways through the electrodes hence preventing induced X-rays and electrical breakdown. In the present work a compact combination of an ESQ column with a Tandem in a folded geometry is discussed. This option would allow the ion source to be operated at ground potential and would require a voltage of 1.15 MV to reach the desired 2.3 MeV proton energy. On the other hand such a machine requires an H- ion source and the transport of a high intensity beam through a gas stripper. Furthermore, if a lower voltage solution is needed (at the expense of higher current), extensive simulations and safety considerations have shown that up to 1 MeV the d-d reaction (on a TiD2 target) is best and that at 1.1 MeV the 9Be(d,n) reaction takes over. At somewhat higher energies still, the 13C(d,n) comes into play. In this energy regime the accelerator could be a single-ended ESQ column operating with a multicusp positive ion source.[1] Topics in Neutron Capture Therapy, Eds. J.A.Coderre et al., Appl. Rad. and Isot. 61, 5 (2004).[2] J.W.Kwan et al., Application of Accel. in Research and Industry, AIP Press, N.Y. (1997) 1313.