Number 146, October 5, 1993 by Phillip F. Schewe and Ben Stein
BEAMS OF ULTRA-COLD, SPIN-POLARIZED HYDROGEN ATOMS can be focused with
a parabolic copper mirror coated with superfluid helium-4. Hydrogen atoms
like to form diatomic molecules but can be kept from doing so by spin-polarizing
the electrons in a magnetic field; the Pauli Exclusion principle takes
over and keeps the atoms apart. Such atoms are usually confined to a closed
vessel, but scientists at the University of Michigan (contact Alan Krisch,
313-936- 1027) have used the recently discovered technique of reflecting
hydrogen atoms from a helium- covered surface (the light H's bounce off
the He film) to achieve the first externally-extracted beam of spin-polarized
hydrogen atoms. The beam delivers 3.7 x 10**15 H's per second. The scientists
plan to collide the beam with protons circulating through a high-energy
accelerator. For this type of experiment atomic hydrogen (at a temperature
of 300 mK) is much preferable to molecular hydrogen, which has internal
energy states that complicate the collision process. The hydrogen beam
will probably be of use in other areas of physics as well. (V.G. Luppov
et al., 11 Oct. Physical Review Letters.)
THE CENTRAL TEMPERATURE OF THE SUN might be measured by comparing the
energies of neutrinos from the sun with those produced in labs here on
Earth. According to John Bahcall of the Institute for Advanced Study, the
process in which an electron is captured by a Beryllium- 7 ion, converting
it into a lithium-7 ion plus a neutrino, is affected by the extreme conditions
inside the sun, which endow particles with an appreciable kinetic energy.
In particular the peak in the neutrino energy spectrum should be shifted
and broadened by an amount related to the central temperature of the sun,
which Bahcall estimates to be 16.6 x 10**6 K. Recording the spectrum of
Be-7 solar neutrinos on Earth would entail the development of a neutrino
detector with better energy resolution than is now available. (11 Oct.
Phys. Rev. Lett.)
A B-MESON FACTORY WILL BE BUILT AT SLAC . After a long competition with
its rival at Cornell, the Stanford Linear Accelerator Center won the right
to build a facility dedicated to producing B mesons. The study of the decay
of B mesons, some theorists believe, will lead to a greater understanding
of CP violation, an effect (the combined non-conservation of charge conjugation
and parity in certain particle interactions) which may have been responsible
for the apparent disparity between matter and antimatter in the universe.
For the research to be practical, the B's must first be produced in large
numbers in electron-positron collisions. At SLAC this will occur in a modified
version of the existing accelerator. The four-year construction should
cost about $177 million. (The New York Times, 5 Oct. 1993.)
FERMILAB'S CRYOGENIC COOLING SYSTEM has been designated as a Mechanical
Engineering Landmark by the American Society of Mechanical Engineers. The
cryogenic system, the largest in the world, maintains Fermilab's Tevatron
collider at only a few degrees above absolute zero; keeping the machine's
magnet coils superconducting permits higher currents, higher magnetic fields,
and therefore higher-energy proton beams. The cooling system cycles 5000
liters of liquid helium an hour through the Tevatron magnet network. (Fermilab
news release, 27 Sept. 1993.)
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