How to avoid compression: a model study of latex sphere grid sections

The parameters which might play a role in the compression of plastic-embedded objects are studied. The compression is measured on spherical polystyrene latex particles, used as markers in the grid sectioning technique. By changing independently the hardness of the latex particles through a controlled electron irradiation and the hardness of the embedding medium, it is shown that compression is a local event depending only on the mechanical properties of the sectioned object and not on the properties of its surrounding materials. It is demonstrated on one hand that the intrinsic resin compression diminishes as resin hardness increases, and on the other hand that the latex compression can be completely eliminated after a preliminary irradiation by electrons (the electron-induced vulcanization is equivalent to a hardening). It is thus concluded that compression could be greatly reduced or eliminated if objects were sufficiently hardened during their preparation. Several preparation procedures for biological specimens are suggested. For comparison latex has also been irradiated 31/2 days near a 25 000-Ci 60Co gamma source and near the core of an 8-MW nuclear reactor. Neither of these irradiations was sufficient to produce a hardening equivalent to that of the electron irraidation.