The Joliot-Curie couple’s demonstration that radioactive isotopes could be synthesized artificially, not merely found in nature, revolutionized nuclear physics. Using α particles emitted from polonium, they bombarded light elements and obtained new nuclei that emitted neutrons or positrons. Their decisive experiment involved aluminium-27, which produced phosphorus-30 whose beta-plus decay they measured. This proved that nuclear transmutation is a general process, not restricted to exotic heavy elements. Artificial radioisotopes are now applied as medical tracers, industrial thickness gauges, and tools for age dating. Understanding these reactions later underpinned reactor development and particle-physics research. Their discovery revealed both the enormous potential of science and the societal need to manage radiation risks, influences that persist today.

In 1934 the pair combined a Po-210 α source with metallic foils and cloud-chamber or Geiger counters to examine a wide set of (α,n) reactions in detail. The Al-27(α,n)P-30 product was shown to have a 2.5-minute half-life, decaying by β+ emission accompanied by a 511 keV annihilation line. Using the same methodology they produced artificial activities from B-10, Mg-24, and Si-28, proving that transmutation of light elements is a general phenomenon. The post-irradiation monitoring of residual activity and chemical separation used to identify the isotopes became the prototype of modern activation analysis. The idea of artificial radioactivity provided crucial experimental data for β-decay theory and stimulated early meson and weak-interaction studies. Synthesis of short-lived nuclides gave birth to tracer techniques that allowed visualization of metabolic pathways and eventually the development of PET scanners. After World War II, large-scale production via reactors and cyclotrons turned radioisotopes into indispensable infrastructure for medicine, industry, and agriculture. Today, RI centers and isotope policies include comprehensive discussions on waste management and radiation protection. All of these developments can trace their origin back to the 1935 Nobel-winning research.

Joliot and Curie irradiated Al, B, Mg, Si and other targets with 5.3 MeV Po-210 α particles, performing delayed counting at several cooling intervals to separate prompt events from delayed β+ activity. In Al they observed a T1/2≈2.5 min positron emitter, which retained its half-life after chemical isolation and was therefore assigned to 15P30. Concurrent neutron counting quantified the dominance of the (α,n) channel, and systematic analysis of Q-values and thresholds supported a compound-nucleus mechanism followed by sequential particle emission. The measured cross sections agreed with liquid-drop-model estimates, reinforcing systematics in light-nucleus reactions. Endpoint energies of the β+ spectra served to test parameters of Fermi’s theory and became benchmarks for selection-rule studies. Angular correlations of the positron annihilation line foreshadowed later parity-violation experiments. Establishing artificial radioactivity paved the way for reactor-based (n,γ) production, cyclotron (p,n) routes, and polarized RI synthesis, driving advances in targetry and hot-cell technologies. Remote production and distribution of short-lived radionuclides created multifaceted engineering challenges in medical accelerators, enrichment, and nuclear data compilation. These results remain heavily cited as a bridge between nuclear chemistry and weak-interaction physics, retaining both historical and technological significance. Regulatory frameworks for isotope management and the modern isotope economy likewise stem from this foundational work.