‘1903 – Awarded the Nobel-Prize for Physics jointly with Marie and Pierre Curie’
The phenomenon of fluorescence – displayed under short wavelength radiation
Stimulated by WILHELM CONRAD ROENTGEN’s discovery of X-rays in 1895, Becquerel chanced upon the phenomenon that is now known as radioactivity in 1896. The Frenchman believed that Röntgen’s X-rays were responsible for the fluorescence displayed by some substances after being placed in sunlight. Although he was wrong to assume that fluorescence had anything to do with X-rays, he tested large numbers of fluorescent minerals.
He found that uranium, the heaviest element, caused an impression on a covered photographic plate, even after being kept in the dark for several days, and concluded that a phenomenon independent of sunlight induced luminescence.
Investigation isolated the uranium as the source of ‘radioactivity’, a name given to the occurrence by Mme. Curie.
The SI unit of radioactivity, the becquerel is named in his honour.
‘Pitchblende, the ore from which uranium is extracted, is much more radioactive than pure uranium. The ore must therefore contain unknown radioactive elements’
Following the discovery of radioactivity by HENRI BECQUEREL (1852-1908) in 1896, Marie Curie conclusively proved that radioactivity is an intrinsic property of the element in question and is not a condition caused by outside factors.
She correctly concluded that pitchblende contained other, more radioactive elements than uranium.
The Curies isolated two new radioactive elements, polonium and radium, from pitchblende. The discovery of new elements by their radioactivity was proof that radioactivity was a property of atoms.
Even today, Marie Curie’s notebooks of her studies remain too radioactive to handle.
Fermi established his reputation with his concept of radioactive beta decay, the theory that a proton could be created from a neutron via the shedding of an electron (a beta particle) and an antineutrino.
The Joliot-Curies had announced their discovery that radioactive isotopes could be generated artificially by showering certain elements with alpha particles in 1934. Fermi realised that the newly discovered neutrons would be even better suited to this purpose as their lack of charge would allow them to slip into elements’ nuclei without resistance.
Fission chain reaction
Fermi established the concept of ‘slow-neutrons’ by placing a piece of solid paraffin in front of the target element during bombardment. Working his way through the elements he created a number of new radioactive isotopes.
He was awarded the 1938 Nobel Prize for physics and later the significance of his work when applied to uranium was realised. Using his neutron-bombarding technique in a series of experiments with 235uranium, Fermi and NIELS BOHR confirmed that a nuclear chain reaction could almost certainly be created as the basis of an atomic bomb.
By Dec 2 1942 his team had created an ‘atomic pile’ of graphite blocks, drilled with uranium, which went on to produce a self-sustaining chain reaction for nearly half an hour.