Accelerator source of epithermal neutrons for the hospital-based boron neutron capture therapy was proposed [1] and presented on previous NCT Symposium [2]. Results of realization of this project are presented here.

Kinematically collimated neutrons are produced via near-threshold ⁷Li(p,n)⁷Be reaction at proton energies of 1.9 MeV. Dc accelerator current of tens of milliamperes allows to provide therapeutically useful beams with treatment times of tens of minutes. The basic components of the facility are: a hydrogen negative ion source, an electrostatic tandem accelerator with vacuum insulation, a sectioned rectifier, and a thin lithium neutron generating target on the surface of molybdenum disk cooled by liquid metal heat carrier.

At test desk available, dc H- ion beam of 9.5 mA was obtained with negative ion source having Penning geometry electrodes. Development of tandem surface plasma source of H- ions was continued to obtain dc 40 mA H- ion beam with small emittance, high gas efficiency and low attendant electron current.

Computer simulation of transport of a dense beam is carried out taking account of space charge and emittance of the beam. Focusing optic system was to be optimized for transporting 10 mA hydrogen ion beam.

An analysis of application of different charge-exchange targets has been made. A gas target was chosen for use. Charge-exchange target, cryogen pump-out system, system for transporting target gas, liquid and gas nitrogen under the high voltage electrode potential were manufactured.

A set of experiments on study of high voltage durability of vacuum gap with large square electrodes were finished on available 0.6 MeV tandem-accelerator. The results allowed to determine high voltage and energetic parameters of 2.5 MeV accelerator.

2.5 MeV vacuum insulation tandem accelerator is under construction now in a 3-layered protected bunker. Mechanic and mounting works at sectionized rectifier were finished, it was started-up and operating voltage was obtained. Vacuum tank for accelerator was manufactured.

Various neutron production targets have been worked in draft. The first specimen of neutron production target with liquid metal heat-carrier was made. Thermal mode of the target was investigated using powerful electron beam.

Spatial-energy distribution of source neutrons and attendant g , and spatial distribution of the absorbed doze and optimization of physical shield are under calculating.

A conception of accelerator based neutron source for neutron-capture therapy at hospital appropriate for commercial use is presented and discussed. Design features of facility components are discussed. The possibility of stabilization of proton energy is considered. At proton energy of 2.5 MeV the neutron beam production for NCT use after moderation is also considered.

1. B. Bayanov et al, Nucl. Instr. and Meth. in Phys. Res. A 413 (1998) 397.

Neutron capture therapy; neutron source; tandem-accelerator

Sergey Taskaev, Dr., Budker Institute of Nuclear Physics, 11 Lavrentiev ave., 6300090 Novosibirsk, Russia, Tel: 7 3832 394121, Fax: 7 3832 342163, e-mail: taskaev@inp.nsk.su