Page "Francium" Paragraph 2

Eka-caesium was discovered in 1939 by Marguerite Perey of the Curie Institute in Paris, France when she purified a sample of actinium-227 which had been reported to have a decay energy of 220 keV.

However, Perey noticed decay particles with an energy level below 80 keV.

Perey thought this decay activity might have been caused by a previously unidentified decay product, one which was separated during purification, but emerged again out of the pure actinium-227.

Various tests eliminated the possibility of the unknown element being thorium, radium, lead, bismuth, or thallium.

The new product exhibited chemical properties of an alkali metal ( such as coprecipitating with caesium salts ), which led Perey to believe that it was element 87, caused by the alpha decay of actinium-227.

Perey then attempted to determine the proportion of beta decay to alpha decay in actinium-227.

Her first test put the alpha branching at 0. 6 %, a figure which she later revised to 1 %.