Focalizing slow neutron beams at and below micron scales and discussion on BNCT (II)

摘要

We studied the propagation of slow neutrons and their waveguiding properties in certain suitable thin films where Ti and Si play a key role, having in mind their possible use in Boron Neutron Capture Therapy (BNCT) of small tumors. In PBSi2017 we presented a general overview and some specific proposals for improved focalization of slow neutrons (at and a bit below one micron, with propagation up to about 1 m. with relatively small attenuation), by omitting a good number of quantitative aspects. The present work, based upon our presentation in PBSi2018, extends our previous proposals in PBSi2017 and provides more quantitative descriptions of part of them. Neutron wavelengths versus characteristic dimensions of the waveguides in our proposals typically require quantum-mechanical analysis: specifically, the description of the confined neutrons by means of propagation modes. The confined propagation of incoming waves along waveguides, the evolution of the resulting propagation modes and related issues are investigated. Those features give rise to computational challenges, depending on the smallness of (neutron wavelengths/characteristic dimensions). Approximate analytical formula is provided for the corresponding quantum-mechanical probability. Numerical estimates and the results of some simulations are presented. Consequences of the latter for BNCT will be discussed briefly.