Reactor neutrino oscillations
1 February 2003
The Japanese-American experiment KamLAND has for the first time
discovered oscillations in electron antineutrinos produced by an
atomic reactor. The experimental facility, located in a mine in
Japan, contains about 1000 tonnes of liquid scintillator and
almost 2000 photomultipliers, to register scintillation glow from
electrons forming in neutrino-proton collisions. The experiment
registers neutrino flux from 69 atomic reactors in Japan and
South Korea, the neutrino signal observed being dominated by
several powerful reactors about 180 km away from the detector.
The anticipated signal was calculated to an accuracy of about 1%
based on the reactor characteristics. It was found that the
number of electron antineutrinos reaching the detector is 40%
less than what one would expect if no oscillations were present.
This suggests that 40% of electron antineutrinos transform
(oscillate) into other antineutrino types on route from a reactor
to the detector. The finding came as no surprise. Recent solar
neutrino experiments at the Sudbury neutrino observatory (see
Physics-Uspekhi 45 666 (2002)) in fact proved the existence of
neutrino oscillations. What the KamLAND experiment has now
achieved is another, independent proof. The KamLAND results are
in perfect agreement with the Sudbury data. Besides, they provide
a more accurate value for the mixing angle, a key parameter
involved in the theoretic description of the oscillation process.
Phys. Rev. Lett. 86 783 (2001)
The velocity of gravitational interactions
1 February 2003
According to the general theory of relativity, gravitational
interactions travel at the velocity of light. S.Kopeikin
(University of Missouri-Columbia) and E Fomalont (National Radio
Astronomy Observatory) in the USA have tested this prediction by
measuring the deflection that radio emission from a remote quasar
undergoes when passing the planet Jupiter. Using the VLBA radio
telescope in the USA and a 100-meter radio telescope in Germany,
they observed Jupiter passing almost exactly between the Earth
and the quasar J0842+1835 on September 8, 2002. The deflection
angle depends on the velocity at which the gravitational field
propagates from the planet. From the value of the deflection
angle the velocity of gravitational interaction was found to be
within 25% of the speed of light. Some scientific publications
have questioned the finding, however. Future observations of
gravitational waves are expected to provide more accurate
Brownian motion within a solid
1 February 2003
Using an analytical electron microscope, U Dahmen of the Lawrence
Berkeley National Laboratory and his colleagues have discovered
the Brownian motion of microscopic (nanometer-sized) liquid
droplets of lead within a solid crystal of aluminium. The motion
started when the crystal was heated to 423C, a temperature at
which aluminium, whose melting point is 660C, is still solid.
Statistical analysis of the patterns of the lead droplets'
trajectories showed that that was indeed Brownian motion.
Deviations from the random Brownian behaviour were observed only
for smallest droplets, which interacted with one another and
moved collectively. The motion of droplets within the crystal may
occur due to diffusion, but the microscopic mechanism of this
type of diffusion is not yet understood. The authors believe that
this Brownian motion is related to their observation of the late
1990s that microscopic lead droplets within solid aluminium are
restricted to a set of discrete sizes. Source: firstname.lastname@example.org
1 February 2003
T.Leisner and his colleagues in Germany have for the first time
observed a phenomenon Lord Rayleigh predicted as long ago as
1882. A theoretical analysis of the stability of charged droplets
of liquid led Rayleigh to conclude that for droplets below a
critical size (the Rayleigh limit) the electrical repulsion
should exceed the surface tension, making the droplet unstable.
Rayleigh conjectured that a droplet would assume an elongate
shape and eject two charge-carrying jets from either of its ends.
Although the stability of charged properties has been studied in
many experiments, the picture of exactly how stability is lost
has been unknown until now. The German team studied the droplets
of ethylene glycol using high-speed microphotographic apparatus.
The droplet size and charge-to-mass ratio were determined from
the way laser light was reflected by the droplets. In one of the
experiments, the initial radius of a spherical droplet, 58 mkm,
was reduced to the Rayleigh limit, 24 mkm, due to the evaporation
of neutral molecules. As predicted by Rayleigh, a droplet did
indeed assume an ellipsoidal shape and did eject two microscopic
jets along its major axis. These jets, consisting of about 100
still smaller droplets, carried 33% of the total electric charge
and only 0.3% of the total mass of the droplet. Source:
Nature 421 128 (2003)
Hot gas at a large distance from a black hole
1 February 2003
A team of Dutch astronomers led by S Migliari has discovered two
clouds of hot gas moving very fast (at one-fourth the speed of
light) in opposite directions from a black hole. This black hole
joins a massive star to form a binary star system SS433 in our
Galaxy. The observations were made using the space-based Chandra
X-ray Observatory, the key factor leading to the discovery being
the presence of X-ray-emitting iron atoms in the clouds. The
velocities of the clouds were measured by their Doppler redshift.
Earlier Chandra and Hubble observations showed that gas in the
vicinity of the black hole cools down as it moves away from it as
a result of expansion. The discovery of gas clouds with a
temperature of about 50 million degrees 0.25 light-years away
from the binary system came therefore as a surprise. The most
likely reason for the gas being reheated is the collisions of
blobs of gas that are ejected with great speed from the black
hole's vicinity. Such ejections occur every few minutes according
to optical observations made over a long period of time.
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.
Permanent editor is Yu.N. Eroshenko.
It is compiled from a multitude of Internet sources.