Virtually everything astronomers known about objects
outside the solar system is based on the detection of
photons-quanta of electromagnetic radiation. Yet there
is another form of radiation that permeates the universe：
(5) neutrinos. With (as its name implies) no electric charge，
and negligible mass， the neutrino interacts with other
particles so rarely that a neutrino can cross the entire
universe， even traversing substantial ag美国GREgations of
matter， without being absorbed or even deflected. Neu-
(10) trinos can thus escape from regions of space where light
and other kinds of electromagnetic radiation are blocked
by matter. Furthermore， neutrinos carry with them
information about the site and circumstances of their
production： therefore， the detection of cosmic neutrinos
(15) could provide new information about a wide variety of
cosmic phenomena and about the history of the uni-
verse.
But how can scientists detect a particle that interacts
so infrequently with other matter? Twenty-five years
(20) passed between Pauli's hypothesis that the neutrino
existed and its actual detection： since then virtually all
research with neutrinos has been with neutrinos created
artificially in large particle accelerators and studied
under neutrino microscopes. But a neutrino telescope，
(25) capable of detecting cosmic neutrinos， is difficult to co-
nstruct. No apparatus can detect neutrinos unless it is
extremely massive， because 美国GREat mass is synonymous
with huge numbers of nucleons (neutrons and protons)，
and the more massive the detector， the 美国GREater the pro-
(30) bability of one of its nucleon's reacting with a neutrino.
In addition， the apparatus must be sufficiently shielded
from the interfering effects of other particles.
Fortunately， a group of astrophysicists has proposed
a means of detecting cosmic neutrinos by harnessing the
(35) mass of the ocean. Named DUMAND， for Deep Under-
water Muon and Neutrino Detector， the project calls for
placing an array of light sensors at a depth of five kilo-
meters under the ocean surface. The detecting medium is
the seawater itself： when a neutrino interacts with a
(40) particle in an atom of seawater， the result is a cascade of
electrically charged particles and a flash of light that can
be detected by the sensors. The five kilometers of sea-
water above the sensors will shield them from the interf-
ering effects of other high-energy particles raining down
(45) through the atmosphere.
The strongest motivation for the DUMAND project
is that it will exploit an important source of information英语作文
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