NCR: technical aspects and application to lithium mapping in mouse embryos

LR115 (type II), 7 mu m thick, Kodak-Pathe detector films were bombarded wi th Am-241 alpha-particles emitted at increasing distances (2.9 to 4.1 cm) f rom the detectors. We wished to determine the best etching conditions so th at the density of tracks was independent of non-controlled experimental flu ctuations. The detectors were etched for two-hour periods in 2.5 M sodium h ydroxide at 25 degrees C for a total of 40 h. After each etching period the number of alpha-tracks (partially or totally penetrating the detector) was counted for each field of view. The sample was then returned to the soluti on for the next etching period. In the nuclear reaction Li-6(n,alpha)H-3, t he initial energy of the alpha-particles is 2.05 MeV, an energy value close to that of the alpha-particles of 241Am having travelled 2.9 cm in air. Ta king into account that the range of the alpha-particles emitted by the nucl ear reaction occurs partly in the matter of the Li-containing samples under study, it was found that the optimal duration of etching was 38 h. These e xperimental conditions were used for the neutron capture radiography (NCR) mapping of lithium in embryos of Li-treated mice (at a blood Li concentrati on similar to that used in human therapy), via the nuclear reaction Li-6(n, alpha)H-3. Copyright (C) 2000 by Marcel Dekker, Inc.