The Curies noticed that uranium ore (pitchblende) emitted more intense radioactivity than pure uranium, hinting at unknown elements. By repeatedly separating the ore chemically, they discovered polonium in mid-1898 and radium later that year. Marie Curie, an uncommon female scientist of her era, led improvements of laboratory techniques and precise radiation measurements. Radium’s spontaneous glow and heat release proved that atoms can break apart, establishing the concept of atomic disintegration. Because radiation can destroy cancer cells, her findings laid the groundwork for radiotherapy. Thus, her work is significant both for nuclear physics and for medical treatment.

Because polonium (Z = 84) and radium (Z = 88) occur only in trace amounts within pitchblende, their isolation required reiterated precipitation, recrystallization, and eventually early forms of chromatography. Curie combined a self-built electrometer with enormous sample masses, optimizing each separation step by monitoring increases in specific activity. Although radium salts are chemically analogous to Ba²⁺, continuous radioactivity measurements enabled reliable tracking. Roughly 100 mg of pure radium salt were finally obtained from ~8 t of ore, and its spectral lines and atomic weight were determined. These results empirically supported Rutherford’s emerging view that atoms are not immutable and stimulated studies of α, β, and γ radiation as well as complete decay series. As a high-energy radiation source, radium sparked innovations in cancer therapy, luminous paints, and calibration standards, revolutionizing early-20th-century physical chemistry and medicine.

Curie developed a wet-chemical protocol that used specific activity as a quantitative indicator, enriching RaCl₂ via fractional crystallization exploiting Ba/Ra distribution coefficients. Ionization chamber–quartz electrometer measurements of ~10⁻¹¹ A currents exceeded contemporary detection limits by an order of magnitude and foreshadowed modern radioactivity standardization. The isolated RaCl₂ exhibited characteristic blue-green emission lines in flame and photographic spectroscopy, yielding an atomic weight of 225 ± 1. Her dataset aligned with the Rutherford-Soddy decay series framework and hinted that α-decay energy release correlates with mass deficit. Radium needles for contact irradiation (Curie therapy) became a standard oncological technique in the early 20th century, catalyzing systematic dosimetry. These accomplishments influenced nuclear-chemical methodology, radiation biology, safety regulations (e.g., post-Radium Girls), and ultimately underpinned today’s isotope industry and medical physics.