Number 553, August 23, 2001
by Phil Schewe, James Riordon, and Ben Stein
Superheavy Hydrogen
Superheavy hydrogen, a nucleus with one proton and four neutrons, has
been made by Russian, French, and Japanese physicists at the accelerator
at the Joint Institute for Nuclear Physics (JINR) near Moscow.
An exotic beam of helium-6 nuclei struck a hydrogen target, resulting
in the occasional production of a hydrogen-5 nucleus plus a helium-2
nucleus. These unstable particles quickly fly apart. The debris--two
protons from the 2He breakup and a triton and two neutrons
from the 5H breakup--tell the story.
If the two-nucleon version of hydrogen is called deuterium and the
three-nucleon hydrogen is called triton, what would one call a five-nucleon
(intensely neutron rich) hydrogen--pentium? (Korsheninnikov
et al., Physical Review Letters, 27 August 2001.)
A Superconducting Single-Photon Detector
A superconducting single-photon detector has been built by a Russian-US
collaboration (Roman Sobolewski, University of Rochester, 716-275-1551,
sobolewski@ece.rochester.edu), offering immediate applications in testing
computer chips and more speculative applications for Mars-Earth communications.
The researchers fabricated extremely thin strips of niobium nitride,
a metallic compound that becomes superconducting in liquid helium near
absolute zero. Then, they made a detector based on these strips, each
only a micron wide and several atoms thick.
The detector enabled the researchers to observe single visible and
infrared photons. That's because the superconducting strips lack the
electrical noise that ordinarily obscures a single-photon signal.
The detector can record the small amount of infrared light that is
released when a transistor switches on or off. A California company
is using the detector for this purpose. Since the detector can detect
bursts as short as picoseconds, they can determine whether or not high-speed
transistors are switching on at the right time.
In more speculative applications, this detector could be employed as
an efficient detector of optical signals for wireless communications
between Mars and Earth. (Gol'tsman
et al., Applied Physics Letters, 6 August 2001; also
see Rochester
press release.)
An Electromechanical Transistor
An electromechanical transistor (EMT) developed at the University of
Munich shuttles a single electron from one electrode to another at 100
MHz rates. There was a time when solid state devices, in which only
electrons are moving, were preferable to mechanical devices with lots
of moving parts. But this attitude is changing as new advances come
about in the field of nanomechanical systems (NEMS).
Artur Erbe (artur.erbe@physik.uni-meunchen.de, 49-89-2180-3349) and
his colleagues have succeeded in placing a metal island atop a swinging
silicon pendulum oscillating at radio frequencies between two other
electrodes. One can think of the pendulum as the clapper of a bell resonating
at a frequency of 100 MHZ, or the whole device as a transistor in which
a single electron is being shoveled from a "source" electrode
to a "drain" electrode.
The Munich setup may afford a new way of establishing a high-precision
current standard since although somewhat slower than some other single
electron transistors (SET) it allows the single electron only one way
(riding on the moving island) of getting from one electrode to the other,
in comparison to other metallic SETs in which the electron can tunnel
in a variety of paths, a habit which actually lowers the effective control
one has over the electron. With the mechanical approach to transferring
single electrons, the high sensitivity to environmental conditions may
allow the SET to serve as an ultra-sensitive position, gas, or force
sensor. (Erbe
et al., Physical Review Letters, 27 August 2001.)
Crystalline Ion Beams
Crystalline ion beams have been created by scientists at the Ludwig-Maximilians
University (LMU) in Munich. Even as beams of positively charged ions
zip around an accelerator at high longitudinal speeds, they can be "cooled"
in the transverse direction through the mediation of electrons or laser
light. This allows the beam to become denser.
The LMU scientists went about their business in the following way:
first they cooled the ions, using two laser beams, and then accelerated
the ion-crystal with the same lasers. The Mg ion crystal moves through
the PALLAS storage ring at 2800 m/sec (equivalent to a beam energy of
1 eV) around a track with a diameter of about 12 cm. The crystal can
survive for up to about 3000 circuits. (Schatz et al., Nature,
16 August 2001.)
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