Research Papers in Physics and Astronomy


Date of this Version

January 1965


Published in Physical Review 137:1B (January 11, 1965), pp. B198-B203. Copyright ©1965 The American Physical Society. Used by permission. Online at URL:


The width of the tracks of ions in emulsion has been calculated from the assumption that a developable image is formed when the energy dosage deposited by delta rays exceeds a threshold value, here found to be 6000 ergs/cm2 in G-5 emulsion. The theory agrees with measurements of track width obtained by projecting track images to a magnification of 3000× and tracing around their outline, while truncating isolated delta rays at their bases. Agreement is to within a grain diameter to a range of about 4 cm. From the theory we infer that there is no Z intelligence contained in the last 10 μ of track length, and that very poor resolution in Z (above 15) is obtained in thin-down region (last 150 μ). The calculation has been extended to infer the width of the track of a Dirac monopole as a function of its range. The length of track required for discrimination between ions and monopoles depends on the monopole mass. Thus monopoles of mass 5 amu, unit pole strength (137e / 2), and energy 1500 MeV will have a range of 1000 μ and can be confused in width with ions of charge 20. On the other hand 3-amu unit-strength monopoles of 100-MeV energy will have a range of 100 μ and can be clearly distinguished from any ion. If 1 cm of track is available, any monopole (to mass 50 amu) can be clearly distinguished from all ions by the fact that its track width does not diminish with increasing range, and achieves a value of about 4 μ, in G- 5 emulsion.

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