Reproducibility of Track Length Measurements in Nuclear Emulsions

Despite significant advances in the technique of measuring particle ranges in nuclear emulsions[^1], the literature contains certain critical remarks which, while not denying the success achieved in determining various points of range–energy curves, cast doubt on the reproducibility of these measurements because of the influence of various subjective and objective factors: the observer’s errors, the development time of the plate, the chemical composition of the emulsion, the relative humidity of the air during exposure and observation of the developed plate, the type of emulsion, etc.

Since only a few fragmentary studies[^1–^4] had been devoted to this question, the author of the paper under review[^5] undertook a systematic quantitative investigation of the influence of the above-mentioned factors on the measurement of ranges in nuclear emulsions.

The author studied tracks of α-particles and tritons from the reaction Li⁶(n, α)H³ with a total length of about 43 μ, tracks of α-particles of ThC′ (~47 μ) and ThA (~32 μ). The results of measurements of track lengths were treated statistically. As the statistical criterion for the significance of the difference between two mean ranges \(\bar{x}\) and \(\bar{y}\), the expression \(|\bar{x}-\bar{y}| > 2\sigma\) was used, where \(\sigma\) is the standard deviation of the range. The quantities \(\bar{x}\) and \(\bar{y}\) were determined from samples containing 100–500 tracks. This method made it possible to detect a relative fluctuation of the measurement results equal to 0.25–0.5%.

As a result of studying the factors listed above, the author establishes that, when working with plates of one type under hygrometric conditions close to normal and with the usual development procedure observed, the reproducibility of the results of track-length measurements reaches 0.5%. The subjective errors of an experienced observer do not reduce the indicated reproducibility. The relative humidity of the air at the moment of observing developed plates does not affect the result. These data indicate the complete reliability of the photographic method, provided certain precautions are observed that ensure the standard nature of the process.

A. Kh.

Cited Literature

1. P. Cüer, J. P. Lonchamp, Comptes Rendus 232, 1824 (1951).
2. Albred, Philips, Rosen, Tallmag, Rev. Sci. Instr. 21, 225 (1950).
3. J. Rotblat, Nature 165, 387 (1950).
4. J. Rotblat, Nature 167, 550 (1951).
5. M. Braun, J. phys. et rad. 13, 347 (1952).