A calculation of the efficiency of Makrofol fission track detectors for fission fragments from thin and thick fission foils

The efficiency of Makrofol foils for detecting fission fragments emerging from thin and thick fission foils (2 π geometry) is calculated. The formulas for the efficiency are deduced on the experimentally confirmed assumption that the track etching rate is at least 200 times greater than the bulk etching rate and they are based on the mean range of fission products in the plastic and in the fission foil. The loss of visibility for very flat tracks with small penetration angle is taken into account by calculating an effective thickness of the etched bulk layer from a minimum visible length and diameter of these tracks. Values of the efficiency for a thin UF4 foil and a thick uranium foil are given. (author)