The specification, design, and initial measurements of a thallium-doped sodium-iodide well-type scintillator for the principle use in detecting 40K concentrations in open-source potassium chloride aqueous solutions is discussed. The hazards, safety concerns and radwaste generation associated with using open-source radioactive isotopes present significant difficulties and costs to radioanalytical laboratory research. A solution to this is the use of non-hazardous alternatives - which mimic notable fission products (137Cs) - that can be utilised as reliable and safe substitutes. In this paper a scintillator detector designed to detect the active isotope present in potassium chloride, yet remaining portable for in situ measurements at nuclear sites, is described with preliminary results highlighting its effective use.