Ernest Rutherford, in a series of experiments carried out in 1917 and published in 1919 in four papers titled "Collisions of Alpha Particles With Light Atoms", bombards nitrogen gas with alpha particles from natural radioactive sources and detects the release of high-speed hydrogen nuclei — what would later be called protons. It is the first time nuclear disintegration deliberately induced by humans is observed, in contrast to the spontaneous radioactivity studied until then. Rutherford did not identify the complete reaction mechanism nor confirm that nitrogen was transmuting into oxygen: that would be demonstrated by his former collaborator Patrick Blackett in 1925, using Wilson's cloud chamber to photograph the particle tracks. The 1919 result convinced Rutherford that artificially accelerated particles — not only those from natural radioactive sources — were needed to systematically explore nuclear structure, which would push his Cambridge group to develop an accelerator.