Figures & data
Table 1 The lattice parameters of BeF2 and LiF crystals
Figure 1 Fragment of the BeF2 quartz structure (left) and its unit cell (right). There are three beryllium atoms and six fluorine atoms in one unit cell of BeF2
Figure 2 The fcc structure of LiF (left) and its unit cell (right)
Figure 3 Lithium (left) and fluorine (right) phonon distribution in LiF. 3*3*2 supercell is implemented and 5*5*5 k-mesh point is selected to confine the Brillion zone. Acoustic mode mainly contributed by fluorine and optic mode contributed by lithium
Figure 4 Phonon spectrum of BeF2. 3*3*2 supercell is implemented and 5*5*5 k-mesh point is selected. The line for fluorine mainly contributes to acoustic mode and the curve for beryllium mainly contributes to optic mode
Table 2 The slow-down property comparison
Table 3 The coherent scattering cross section of free atom and compounds
Figure 5 Cross section of thermal neutron scattering of BeF2 (left) and LiF (right). Both BeF2 and LiF have the same trend. The inelastic scattering cross sections increase with temperature; on the contrary, elastic scattering cross sections decrease when temperature increase
Table 4 Effect of different TSL data of BeF2 and LiF crystals on k eff
Figure 6 Influences of thermal neutron scattering data to spectrum. The elastic scattering cross section makes spectrum getting hardened, and BeF2 has stronger influence on spectrum than LiF
