Physics News Update
The American Institute of Physics Bulletin of Physics News
Number 325, June 11, 1997 by Phillip F. Schewe and Ben Stein
PROTON PAIRS EJECTED FROM NUCLEI help to reveal the nature of the strong
interaction. The force that holds atoms together, the electromagnetic interaction
between electrons and the nucleus, is much better understood than the force
that holds together the nucleus itself, namely the strong interaction among
the constituent protons and neutrons. Physicists can't directly reach inside
the nucleus with a force meter, but they can dislodge some of the nuclear
masonry and examine the fragments as would an archeologist looking at shards
of pottery from a sunken vessel. At the National Institute for Subatomic
Physics (NIKHEF in Dutch) in Amsterdam, a beam of electrons strikes oxygen
nuclei, knocking out pairs of protons. For just the right collision energy,
the protons (which are detected in coincidence with the scattered electron)
emerge primarily in a special state (an S state), one in which their relative
angular momentum is zero. Such protons would have been very close (less
than 10-15 m apart) to each other in the nucleus just before
being struck by the electron. The NIKHEF experiment, the first to compile
cleanly such ejected S-state proton pairs, can thus probe very short range
correlations between two particles inside the nucleus. (C.J.G. Onderwater
et al., , Physical
Review Letters, 30 June 1997 contact Willem Hesselink, whah@nikhef.nl.)
NUCLEAR WASTE FOREVER. You can't make omelettes without breaking eggs,
and the same is true of nuclear power. Cranking out decades of reactor-based
electricity has meant breaking a lot of nuclei---the leftover consists
of 30,000 tons of spent fuel rods in the US. Preparing for (or preventing)
nuclear war has spawned its own trove of nuclear-unstable matter: 400,000
cubic meters of high-level radioactive waste; the biggest repositories
are at Hanford (WA) and Savannah River (SC). The June issue of Physics
Today looks at the problem of nuclear waste from a variety of angles:
for example, turning the waste products into a more manageable form such
as glass; studying the feasibility of permanent storage sites such as the
proposed vault at Yucca Mountain (NV); and comparing the disposition of
waste worldwide. The current stock of spent reactor fuel is concentrated
largely in only a few countries. The biggest inventories are in the US
(18.3%), UK (16.6%), Canada (15.4%), France (14.9%), and the former USSR
(9.9%).
TRIGGERED STAR FORMATION, a process whereby particles cast off by an
energetic massive star help to compress nearby gas into globs that ignite
into stardom of their own, has been directly imaged in sharp detail for
the first time. A Hubble Space Telescope picture shows a mother star (in
the nearby Cone Nebula) and a brood of six offspring stars at distances
of less than a tenth of a light year away. The faint youngsters, which
can't be glimpsed at visible wavelengths because of a swaddling blanket
of dust, can be seen by Hubble's near infrared (NICMOS) camera. The picture
was released at the meeting of the American Astronomical Society this week
in North Carolina. (Hubble press release, 9 June; figures on the web at
Space Telescope
Science Institute)
VENUS' TAIL REACHES ALL THE WAY TO EARTH. Recently the Venus shadow,
cast by the Sun, passed across the SOHO satellite (in Earth orbit), allowing
SOHO to detect the plume of ions kicked out of Venus' upper atmosphere
by the solar wind. (Geophysical Research
Letters, Vol 24, p. 1163; New
Scientist, 31 May.)
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