Number 518 , December 22, 2000 by Phil Schewe, James
Riordon, and Ben Stein
Dual-proton Decay May be in the Cards
When it comes to some aspects of the strong force that binds nucleons
together in atoms, nature has long worn a poker face. But in recent
experiments focusing on nuclear decay processes in neon, nature may
at last be showing her hand, and it looks like she's showing a pair.
Researchers at
the Oak Ridge National Laboratory (ORNL) believe that they have detected
the emission of paired protons from an excited state of neon-18, an
isotope which they formed by firing fluorine atoms at a hydrogen-rich
target. Although theorists in decades past predicted such decays, no
prior experiment had managed to detect the phenomenon. If confirmed,
the process could provide new insights into the strong force that both
holds nuclei together and shackles the emitted protons into a single
helium-2 nucleus. It's possible that nature is bluffing once again,
and that the protons are leaving the neon nuclei separately but simultaneously
through an effect known as democratic emission (see
Physics News Graphics). The researchers (Alfredo Galindo-Uribarri,
Oak Ridge National Laboratory, uribarri@mail.phy.ornl.gov,
865-574-6124), however, are hopeful that they can validate the elusive
paired-proton decay with a new detector due to come online at ORNL within
a year. (J. Gómez
del Campo et al, Physical Review Letters, 1 January 2001.)
A Hidden Ocean on Ganymede
The largest moon in the solar system, Ganymede joins two of Jupiter's
other satellites, Callisto and Europa, in (most likely) possessing a
subsurface ocean. In case of Europa, the liquid ocean might lie beneath
an Arctic-like icepack with a thickness perhaps only a few km or less.
For Ganymede the several-km-deep ocean is thought to reside at a depth
of 170 km or so.
At last week's meeting of the American Geophysical Union (AGU) in San
Francisco several researchers associated with the Galileo spacecraft
summarized the evidence---visual, infrared, and magnetic—for the ocean.
James Head of Brown University displayed sharp photographs (resolution
as good s 28 m) of the much furrowed surface of Ganymede. The furrows
and the many lanes of smooth, bright material running between darker
areas (a banding pattern not unlike that found on Europa) suggests not
volcanism but the kind of deformations that could be caused by brittle,
cold, upper ice layers being fractured by contact with warmer, more
ductile, lower ice in contact with liquid water. (The water would be
kept liquid by the warmth of radioactivity and also by the heat generated
from the gravitational flexing of the whole moon during its travels
near Jupiter.)
Infrared data, reported by Thomas McCord of the University of Hawaii,
indicates the presence of the salt minerals (in this case, MgSO4)
needed for making any worldwide water stratum into an electrically conducting
circuit. As Ganymede sweeps through Jupiter's potent magnetic field
a current could be induced in the saltwater ocean which would modulate
Ganymede's own permanent magnetic field. Margaret Kivelson of UCLA reported
magnetometer measurements which could best be interpreted as exactly
the kind of magnetic moderation one would expect if a deep salt ocean
were present (see website).
A Green Ocean in Brazil
Using a sophisticated version of weather radar imaging, scientists
have now been able to track the movement of rainstorms and even to measure
the amount of rainfall released, and from which altitudes. At the AGU
meeting members of the Tropical Rainfall Measuring Mission (TRIM) reported
the most precise rain maps ever achieved for the region within 38 degrees
latitude north and south of the equator, a zone crucial to worldwide
weather because of its vast ocean currents, rain forests, and the huge
amount of solar radiation falling there.
Daniel Rosenfeld
of the Hebrew University of Jerusalem said that when air over the Amazon
rainforest was clean, storms there unexpectedly rivaled those over the
ocean in the amount of rainfall. In other words, Brazil was acting more
like a "green ocean" than like a continental land mass. Rosenfeld explained
that although some particulate matter is useful for seeding raindrops,
when too many fine particles are present (from wood fires, say) then
water droplets are actually inhibited from forming into drops large
enough to precipitate. Brazil then, at least during a period of very
clear air, could approximate the conditions over the ocean (TRIM
website ).
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