Li7andF19Nuclear Magnetic Resonances in Neutron-Irradiated LiF

Abstract

PHYSICAL REVIEW LETTERS DECEMBER 15, 1958 excitons are in quasi-thermal equilibrium with the free carriers, i.e., if the most likely mode of breakup of the exciton is thermal dissociation. For a given n andwhere % is the binding energy of the exciton, N x> N v , N c are the effective densities of states of the exciton, valence, and conduction bands, respectively, near their respective extrema. Taking T=4°K and assuming that { } 8/2 « 1 and that E x & 10&T«4 x 10"" 3 ev, we obtain n x max « 10~i 2 np under these conditions.

Color centers in neutron-irradiated Y3Al5O12, CAF2 and LiF single crystals

“…High-quality single crystals of Y 3 Al 5 O 12 , CaF 2 approximately 315 K and fast and thermal neutron flux are respectively 1.48 Â 10 13 and 2.68 Â 10 13 n cm À2 s À1 . The thermal neutron flux is measured with uncovered and Cd-covered gold foil.…”

“…In the case of ionic crystals, the color centers induced by irradiation by lowly and highly ionizing radiation (electrons, g-rays, neutrons and swift heavy ions) has been well studied by means of several techniques [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. These defects may be F-centers (an electron trapped by an anion vacancy), or aggregate centers (F 2 , F 3 , F 4 ) or alkali colloids.…”

Li colloids formation study induced by reactor neutrons in LiF single crystals

“…Trautmann et al [9] assume that Li colloids are responsible for the swelling of LiF single crystal irradiated with ions. Li colloids and lithium atoms present in the form of platelets are also shown by several authors in LiF irradiated with neutrons [10][11][12][13][14][15][16][17][18]. Nevertheless, the annealing process of colour centers in irradiated-lithium fluoride is not well understood.…”

Effect of irradiation parameters on defect aggregation during thermal annealing of LiF irradiated with swift ions and electrons

“…In LiF irradiated with fast neutrons at nuclear reactors, much larger metallic colloids of several tens of nanometer were observed by means of NMR and ESR. [19][20][21] Later Beuneu et al [22][23][24] detected metallic Li colloids in crystals exposed to fast electrons at a dose above 1 GGy. The colloid formation strongly depends on the electron flux.…”

“…Also nucleation and growth processes of halogen clusters have to be considered because fluorine-molecule clusters were evidenced by means of NMR in neutron-irradiated LiF crystals. 19,20 The formation of such H-center sinks prevents the complete disappearance of F cen-ters and their complexes. 5,43 The recombination of H centers with electron color centers results in an overall decrease in the F-and F 2 -center concentration as well as a drop of the ratio .…”