Resolving Power with Tritium Autoradiographs

Abstract

A practical direct test was made of the autoradiographic image of a tritium labeled structure of known configuration. Two methods were used. In the first, a straight edge of Araldite epoxy resin, made radioactive by combination with tritiated succinic acid, presented itself to the emulsion. The second method was less direct in its approach. A face was cut on a block of the radioactive Araldite and the angle of cutting was then altered by 0.5 mu so that subsequent sections were in the form of wedges, tapering in thickness. Discrepancy between the results by the two methods is possibly accounted for by inadequate allowance for grain size. This would mean an overestimate of the band- width by the first method and an underestimate in the second. If this is so, it may be concluded that a disk source will produce an image in which 50% of the grains, when pin-pointed, lie in a band of width somewhere between the two estimates, 0.24 to 0.34 mu that is, 50% of the grain centers lie within 0.12 to 0.17 V of the disk. By making use of the fact that the distribution is similar in form to a Gaussian probability curve, itmore » may be shown that the frequency distribution descends to half its peak value at 0.21 to 0.30 mu from the source. (P.C.H.)« less