http://www.physorg.com/news10392.html
Two super heavy elements
discovered
Physics : January 31, 2006
A Swiss research
group has participated in the discovery of new chemical elements. The elements
have the numbers 113 and 115 and were discovered by a
combination of physical and chemical techniques in the Russian nuclear research
centre in Dubna. With its radiochemical expertise the Paul Scherrer Institute
was central to the experiment's success.
Chemistry is currently pushing
the boundaries of the scientific unknown. Until 1940 Uranium was the heaviest
known element. This naturally occurring metal has the periodic number 92, as it
has 92 positively charged protons in its nucleus. Since then over twenty
elements with higher atomic numbers have been discovered.
The birth of
element 115
Heavy elements decay by emitting charged helium atoms - alpha
particles. Such decay chains were used by American, Russian and Swiss scientists
to physically prove the existence of elements 115 and its decay product after
emission of the first alpha particle - element 113. In order to synthesize the
atoms of element 115 a rotating target disc of americium was bombarded with a
calcium beam. In a fusion reaction between target and beam particles element 115
was born. However their formation was not sufficient to prove the element's
existence as its atoms only lived a mere tenth of a second and were difficult to
detect. The radiochemical experiment proved much more successful as it yielded
five times as many atoms.
Radiochemical proof
As expected, the
element 115 decayed by emitting an alpha particle to become element 113 and then
in further emissions of four alpha particles, to dubnium, element 105. It was
here that the elegant experimental approach from the PSI came into play. Behind
the rotating americium disc (target) a copper plate was placed which collected
all element 115 atoms emitted from the target. The copper plate was chemically
processed by means of liquid chromatography techniques and 15 atoms of dubnium
(which have a half-life of 32 hours) were observed. The decay pattern of these
atoms supported the evidence of the physics experiment. Thus the discovery of
element 115 and its progeny, element 113, was proven. All elements below atomic
number 113 are already known.
"Switzerland can celebrate a scientific
first, even when the experiment was performed abroad", commented Heinz Gäggeler,
leader of the Swiss research group, Head of the Department of Particles and
Matter at the PSI and Chemistry Professor at the University of Berne. It is the
first time Switzerland has been at the forefront of the race to expand the
periodic table.
Source: Paul Scherrer
Institut