Experimental and simulation studies of a neutron production target for boron neutron capture therapy at the Tandar accelerator

A.A. BURLON; A.J. KREINER; A.A. VALDA; D.M. MINSKY

Iguazú, Misiones. Presentación mural

Congreso; VI Latin American Symposium on Nuclear Physics and Applications; 2005

Dpto. de Física FCEN, UBA - Dpto. de Física UNLP – Lab. TANDAR, CNEA

In this work we studied an optimized neutron production target including a beam shaping assembly to be used for thermal and epithermal Accelerator-Based Boron Neutron Capture Therapy (AB-BNCT). The neutrons were produced through the  7Li(p,n)7Be reaction which has a pronounced resonance of 582 barns at 2.25 MeV. To maximize the neutron production and at the same time keep the maximum energy of the neutron spectrum at an acceptable low value it is convenient to use a proton beam of an energy slightly higher than 2.25 MeV. Since the Tandar accelerator was not designed to deliver such low energies implied in BNCT, we worked with a 6.5 MeV proton beam (3.25 MV terminal voltage). This beam was degraded to an average energy of 2.4 MeV by passing it through a 78 micrometers thick Ta foil and subsequently made to bombard a thick LiF target. The resulting neutrons were moderated by using an assembly consisting of slabs of Al,  polytetrafluoroethylene (PTFE) (commercially known as Teflon) of 15 cm x15 cm and a total length of 34 cm including slabs of LiF as a thermal neutron shield. The target and moderator were surrounded by a reflection mantle composed mainly of lead and some graphite with the aim of collecting the largest possible number of fast neutrons produced. At the output port of the assembly we installed a simplified water-filled acrilic head phantom. The neutron flux in and around the phantom was determined by the foil activation method using different materials sensitive to different energy portions of the neutron spectrum (Au, W, In, Co, Cu). Finally the experimental results were compared to the values obtained by simulation with the Monte Carlo method (MCNP).