[en] In testing the applicability of the threshold system polyvinyl alcohol/methyl orange/chloral hydrate/sodium tetraborate to the quantitative detection of single particles, the chemical detector was irradiated with ⁴He, ¹²C, ¹⁸O, ²²He ions of different LET. Detectors with 4 different borax concentrations (chloral hydrate concentration kept constant) have been irradiated. The dose causing the colour change increased linearly with the borax concentration. For equal borax concentrations this dose increases with increasing LET due to the decreasing G value of the HCl. The fluence ranges measurable with the various detector compositions are given. ⁴He and ¹⁸O ion ranges have been determined. The measured depth dose curves have been corrected because the dose is LET-dependent. The experimentally determined ranges are in good agreement with values calculated for the detector material