Double Layer Collimator for BNCT Neutron Source Based on 30 MeV Cyclotron

<span>A research of design of double layer collimator using </span>⁹<span>Be(p,n) neutron source has been conducted. The research objective is to design a double layer collimator to obtain neutron sources that are compliant with the IAEA standards. The approach to the design of double layer collimator used the MCNPX code. From the research, it was found that the optimum dimensions of a beryllium target are 0.01 mm in length and 9.5 cm in radius. Collimator consists of a D</span>₂<span>O and Al moderator, Pb and Ni as a reflector, and Cd and Fe as a thermal and fast neutron filter. The gamma filter used Bi and Pb. The quality neutron beams emitted from the double layer collimator is specified by five parameters: epithermal neutron flux 1 ×10</span>⁹<span> n/cm</span>²<span>s; fast neutron dose per epithermal neutron flux 5 ×10</span>¹³<span> Gy cm</span>²<span>s; gamma dose per epithermal neutron flux 1×10</span>¹³<span> Gy cm</span>²<span>s; ratio of the thermal neutron flux of epithermal neutron flux 0; and the ratio of epithermal neutron current to total epithermal neutron 0.54.</span>

New type of versatile neutron diffractometer with a double-crystal monochromator system

Properties of a special double-crystal (DC) monochromator employing bent-perfect crystals of Si in (1, −1) and (n, −m) settings are presented. The first monochromator was the bent Si(111) crystal (4 mm thickness) and the second one was in the form of a sandwich consisting of two bent Si(111) and Si(220) slabs (2 and 1.3 mm thickness, respectively). It has been found that by a simple exchange of diffraction conditions on the second monochromator one can use either Si(111) + Si(111) bent crystals in (1, −1) setting providing good luminosity and worse diffractometer resolution or Si(111) + Si(220) bent crystals in quasi-dispersive (n, −m) setting providing very good diffractometer resolution and correspondingly weaker luminosity. It has been found that besides an excellent focusing and reflectivity properties of the dispersive double-bent-crystal setting the obtained monochromatic neutron current is sufficiently high for diffraction experiments even at the medium-power research reactor.