Electrostatic charges may be generated at the specimen block/knife These charges are most likely interface during cleavage of a section. distributed over the block face and on the back surface of the knife. Charges on the block face probably remain after section cleavage and appear on the upper surface of the section as it floats on the water surface. of charge dissipation are important to the sectioning process. of charge dissipation is, at least in part, dependent on climatic conditions (e.g., humidity) in the vicinity of the knife edge.
Excessive charge build up may cause sections to be dragged over the knife edge and possibly contributes to the formation of chatter and compression in the section. Charge neutralization at the specimen block/knife interface minimizes these problems and greatly improves the probability of obtaining good sections (Fraser, 1976;Haskins and Nesbitt, 1975).
Charge neutralization can be accomplished by placing radioactive substances in the vicinity of the knife edge. Typically, this takes the form of a polonium strip mounted so as to project ionizing radiations onto the knife edge and block face. For convenience, these strips are often mounted on flexible shafts so that they can be positioned properly (e.g., Haskins and Nesbitt, 1975). Electrostatic guns (e.g., Fraser, 1976) also have been used for charge neutralization. effective, they are both bulky and inconvenient. Therefore, alternative configurations for a neutralizing device were examined.
It was found that effective charge dissipation could be achieved by radiating only the block face. The water in the boat effectively neutralized charge build up on the inner (wet) face of the diamond knife. This could be demonstrated by noting that salt added to the boat fluid to increase its conductivity had little or no effect on sectioning. Charges on the back (dry) face of the knife, though undoubtedly present, also had little or no effect on the sectioning presumably because the sections were shielded from these charges by the intervening layer of water. Thus, to improve sectioning, it was only necessary to neutralize charge build up on the block face.
The minimum charge neutralizing device that still seemed effective w a s a modification of the polonium strip method mentioned above. It consisted of a very small polonium strip glued to the back (dry) face of the knife (Fig. 1).
Both the amount of charge formed during sectioning and the rate The rate
Though the above methods are
The strip was mounted so that it irradiated the block face 0 1986 ALAN R. LISS, INC.