DISCOVERY OF THE RADIOACTIVITY
After a few weeks of Roentgen's discovery, Antoine Henri Becquerel began to experiment
with known fluorescent or phosphorescent substances. He began his experiment
with a uranium compound, which is highly fluorescent after exposure to sunlight.
He noted that photographic plates were darkened by the uranium salt even if
they had not been first exposed to sunlight. He observed that radiation that
darkened the plate was from the substance itself, and this phenomenon was
called the radioactivity of that particular substance. The rays were emitted
continuously and spontaneously from the entire uranium compound even if they were
not exposed to sunlight. Becquerel demonstrated that the radiation emitted by
uranium shared certain characteristics with X-rays but, unlike X-rays, could be
deflected by a magnetic field and therefore must consist of charged particles.
For his discovery of radioactivity, Becquerel was awarded the 1903 Nobel Prize
for Physics.
DISCOVERY OF RADIUM
Although
the phenomenon of radioactivity was discovered by Henri Becquerel, the term
radioactivity was coined by Marie. Marie Curie and Pierre Curie discovered
radium in December 1898 and before that, they discovered polonium in July 1898. The
Curies were awarded the 1903 Nobel Prize in Physics for their work on
radioactivity. Pierre died 3 years later in a tragic accident while crossing a
street in a rainstorm. In his honour, the 1910 Radiology Congress chose the
‘curie’ as the basic unit of radioactivity: the quantity of radon in
equilibrium with 1 g of radium (current definition: 1 Ci = 3.7 × 1010
dps).
A
year later, Marie was awarded the Nobel Prize in Chemistry for her discoveries
of radium and polonium, thus, becoming the first person to receive two Nobel
Prizes. For the remainder of her life she tirelessly investigated and promoted
the use of radium as a treatment for cancer. Marie Curie died on 4 July 1934,
overtaken by pernicious anaemia; no doubt caused by years of overwork and radiation
exposure.