<P> The following year, Ramsay liberated another inert gas from a mineral called cleveite; this proved to be helium, previously known only in the solar spectrum . In his book The Gases of the Atmosphere (1896), Ramsay showed that the positions of helium and argon in the periodic table of elements indicated that at least three more noble gases might exist . In 1898 Ramsay and the British chemist Morris W. Travers isolated these elements--called neon, krypton, and xenon--from air brought to a liquid state at low temperature and high pressure . Sir William Ramsay worked with Frederick Soddy to demonstrate, in 1903, that alpha particles (helium nuclei) were continually produced during the radioactive decay of a sample of radium . Ramsay was awarded the 1904 Nobel Prize for Chemistry in recognition of "services in the discovery of the inert gaseous elements in air, and his determination of their place in the periodic system ." </P> <P> In 1897, J.J. Thomson discovered the electron using the cathode ray tube . In 1898, Wilhelm Wien demonstrated that canal rays (streams of positive ions) can be deflected by magnetic fields, and that the amount of deflection is proportional to the mass - to - charge ratio . This discovery would lead to the analytical technique known as mass spectrometry in 1912 . </P> <P> Marie Skłodowska - Curie was a Polish - born French physicist and chemist who is famous for her pioneering research on radioactivity . She and her husband are considered to have laid the cornerstone of the nuclear age with their research on radioactivity . Marie was fascinated with the work of Henri Becquerel, a French physicist who discovered in 1896 that uranium casts off rays similar to the X-rays discovered by Wilhelm Röntgen . Marie Curie began studying uranium in late 1897 and theorized, according to a 1904 article she wrote for Century magazine, "that the emission of rays by the compounds of uranium is a property of the metal itself--that it is an atomic property of the element uranium independent of its chemical or physical state ." Curie took Becquerel's work a few steps further, conducting her own experiments on uranium rays . She discovered that the rays remained constant, no matter the condition or form of the uranium . The rays, she theorized, came from the element's atomic structure . This revolutionary idea created the field of atomic physics and the Curies coined the word radioactivity to describe the phenomena . </P> <P> Pierre and Marie further explored radioactivity by working to separate the substances in uranium ores and then using the electrometer to make radiation measurements to' trace' the minute amount of unknown radioactive element among the fractions that resulted . Working with the mineral pitchblende, the pair discovered a new radioactive element in 1898 . They named the element polonium, after Marie's native country of Poland . On December 21, 1898, the Curies detected the presence of another radioactive material in the pitchblende . They presented this finding to the French Academy of Sciences on December 26, proposing that the new element be called radium . The Curies then went to work isolating polonium and radium from naturally occurring compounds to prove that they were new elements . In 1902, the Curies announced that they had produced a decigram of pure radium, demonstrating its existence as a unique chemical element . While it took three years for them to isolate radium, they were never able to isolate polonium . Along with the discovery of two new elements and finding techniques for isolating radioactive isotopes, Curie oversaw the world's first studies into the treatment of neoplasms, using radioactive isotopes . With Henri Becquerel and her husband, Pierre Curie, she was awarded the 1903 Nobel Prize for Physics . She was the sole winner of the 1911 Nobel Prize for Chemistry . She was the first woman to win a Nobel Prize, and she is the only woman to win the award in two different fields . </P>

Who are the scientists credited with introducing the phenomena known as radioactivity