Before revision: KCl is useful as a beta radiation source for calibration of radiation monitoring equipment , because natural potassium contains 0.0118%DIF < of the isotope 40K.
After revision: Because natural potassium contains a tiny amount of the isotope potassium-40, potassium chloride is used as a beta radiation source to calibrate radiation monitoring equipment , because natural potassium contains 0.0118%DIF < of the isotope 40K.