The critical angle for fission fragment registration in Makrofol after a sufficiently long storage time in air

If Makrofol detectors for fission tracks are exposed to air for a sufficient length of time after irradiation and before etching, the ratio of the initial etching rate Vsub(T) in the direction of the tracks to the bulk etching rate Vsub(B) is strongly enhanced, with Vsub(T)/Vsub(B) > 500. As a result of this, a very low value of the critical angle for registration αsub(r) is expected, below which no track is revealed. After a storage time of a minimum of two days and for two different etching conditions, the values of these critical angles were determined as αsub(r) = 0.8 deg and αsub(r) = 0.5 deg, respectively. These values are compared to calculations based only on the mean range of fission fragments in the foil, the radius of the fully-etched track and a minimum length of a visible track. The calculated values are in good agreement with the results of the measurements. (author)