Ref: http://www.aip.org/enews/physnews/2004/672.html
Physics News Update - Number 672, February 2, 2004
by Phil Schewe, James Riordon, and Ben Stein

Element 115 Has Been Discovered

Element 115 has been discovered at the Joint Institute for Nuclear
Research (JINR) in Dubna, Russia. JINR physicists and their longtime
collaborators from Lawrence Livermore National Lab in the US produced 4
atoms of the new superheavy element by striking a target of
americium-243 atoms with a beam of calcium-48 ions. The beam energy
used, 248 MeV, was chosen to produce just the right energy conditions
for making the amalgamated nucleus but not causing it to break up, at
least not right away.

The long lifetime observed for element 115 suggests that physicists
might be getting closer to the "island of stability," the presumed
region on the chart of possible nuclear isotopes for which certain
combinations of protons and neutrons (collectively known as nucleons,
the regular constituents of all nuclei) are much more stable than some
of the other heavy nuclei made artificially at accelerators.

In general, nature doesn't produce elements heavier than uranium
(element 92) and scientists must resort to colliding smaller nuclei to
build up heavyweight elements. In previous experiments conducted by the
same team at Dubna, evidence has been recorded for elements 114 and
116.

One sequential decay event corresponding to element 118 was also seen.
(Claims for a separate discovery of element 118 by a group at the
Lawrence Berkeley National Lab in the US were later withdrawn.)

In the new experiment, using the same approach, a beam of calcium-48
atoms (atomic number, or Z, equal to 20) was plowed into a target of
americium-243 atoms (Z=95). By bringing together element 95 with
element 20, four atoms of element 115 were created.

The nuclei of these precious atoms apparently lived for 90 msec. They
expired in the following way: by decaying first to element 113 by the
emission of an alpha particle (a nuclear morsel consisting of two
protons and two neutrons); thence to element 111 by alpha emission
again; and then by three more alpha decay steps to element 105
("Dubnium") which, after the delay of a whole day (almost an eternity
in nuclear physics) from the time of the original interaction, finally
fissioned.

Besides being a very difficult physics experiment to carry out, this
work represents a great feat of nuclear chemistry, since it entailed
sifting 4 atoms out of trillions of candidates. In other words, the
gas-filled separator, employing chemistry, proved to be just as
important as the accelerator.

In the past decade or so even-Z superheavy nuclei---112, 114, 116,
118---were sought at Dubna chiefly because of the facility's intense
beams of Ca-48 and the ready availability of even-Z actinide targets.

By the way, this experiment also marks the discovery of a second
element, 113, which had not been seen before either. (Oganessian et
al., Physical Review C, February 2004; contact Yuri Oganessian at JINR,
, 011-7-09621-62151; Ken Moody at Livermore,
925-423-4585, , or Mark Stoyer, , cell
phone 301-661-1169; background article by Oganessian in Scientific
American, Jan 2000.)

Carbon Nanotube Gel

Carbon nanotube gel, the first example of a liquid crystalline material
consisting of single-walled nanotubes, has been made by physicists at
the University of Pennsylvania. Basically the gel is a mass of
half-micron long nanotubes, aligned like little logs along a single
direction, in a polymer matrix. The gel exhibits hallmark properties of
a nematic liquid crystal (in which rod shaped molecules are aligned)
including optical anisotropy (birefringence) and topological defects.

The gel's anisotropic characteristics and its sensitivity to changes in
solvent quality might make it a candidate for novel applications. It
could be useful, for example, as an osmotic or an electrical actuator
in which changes in electrical field or salt concentration produce
volume and shape changes.

The gel was made by coating the nanotubes with surfactant chemicals and
mixing in polymers which form a cross-linking network among the tubes.
Next the volume was compressed. The resultant densities of isolated
single-wall nanotubes are higher than can be produced in simple aqueous
suspensions. (Islam et al., Physical Review Letters, upcoming article;
contact Arjun.G. Yodh, , 215-898-6354, Mohammad
Islam, , or Tom Lubensky,
.)