AUTOH ADIOGR A1»IIY 



then lowering the temperature gradually to 

 about 4°C. The cold phase of development is 

 for about 30 minutes. The developer used 

 in this case was Amidol. The cold developer 

 is poured off and the surface of the slides 

 dried with filter paper. Warm slides to 22° 

 to 24°C in a thermostatically controlled 

 tank. The temperature of the warm stage 

 must be chosen by trials. The slides are then 

 placed in a stop bath of 0.2% acetic acid 

 solution for about 30 to 40 minutes at 4°C. 

 Fixation is at 4°C in a 40 % sodium thiosul- 

 phate solution until the emulsion is clear. 

 The emulsion is thoroughly washed at the 

 low temperature and the emulsion allowed 

 to dry slowly. The preparation is then 

 capped with a thin coverslip. 



One of the reasons for Guidotti's success 

 with P^- autoradiography is the varied tem- 

 perature development allowing all layers of 

 the emulsion to be penetrated by the devel- 

 oper; another is the thinness of the section, 

 which is considerably less than most routine 

 preparations. This allows the site of origin 

 of the beta tracks to be more accurately 

 located. 



Fig. 12. Autoradiogram of rat ovary and adja- 

 cent tissue illustrating even diffuse distribution of 



Cs"'. 



Cs^^'^, a beta and gamma emitter, with a 

 half -life of 30 years, is an example of a water- 

 soluble isotope that presents difficulties re- 

 garding methods for autoradiographic regis- 

 tration. 



The usual fixing fluids leach Cs''^ from 

 tissues as will any contact with water; there- 

 fore, a mixture of 80% acetone and 20% 

 benzene was used as a fixative (10). This 

 combination was decided upon after ex- 

 perimentation in which the leaching loss was 

 determined by radiochemical analysis. There 

 was a minimum cesium loss when this fixa- 

 tive was used. Tissues were then processed 

 through "Cellosolve" and benzene and 

 blocked in paraffin. 



Since the sections could not be floated on 

 water for transfer to the emulsion, sections 

 were attached to the No-Screen x-ray emul- 

 sion by warming the slide until the emulsion 

 became tacky, then the sections were at- 

 tached by finger pressure. The slides were 

 then exposed, the paraffin dissolved by im- 

 mersion in xylene. The slides were run down 

 to water from "Cellosolve" and the autora- 

 diograms stained and the slides capped. 



Figure 12 is an illustration of Cs'^^ deposi- 

 tion in a rat ovary. It will be noted that there 

 is a homogeneous distribution in the ovary 

 and the surrounding tissue. There is no evi- 

 dence of leaching into the emulsion area not 

 covered by the tissue. Figure 13 is the adja- 

 cent section for histological comparison. 

 Greater definition could have been obtained 

 by using an NTB emulsion. 



Limited Autoradiographic Techniques 

 for Plant Tissue 



An interesting experiment performed by 

 Hungate et at. (11) involved exposure of 

 plants to fallout from the experimental burn- 

 ing of an irradiated fuel element. 



The fission products resulting from the 

 burning of the fuel element were carried by 

 the air to plants located downwind from the 

 burning site. Later the plant leaves were 

 exposed to double-coated Type KK indus- 



8 



