PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 729 April 27, 2005
by Phillip F. Schewe, Ben Stein
                                                                
PYROFUSION: A ROOM-TEMPERATURE, PALM-SIZED NUCLEAR FUSION DEVICE has been
reported by a UCLA collaboration, potentially leading to new kinds of
fusion devices and other novel applications such as microthrusters for MEMS
spaceships.  The key component of the UCLA device is a pyroelectric
crystal, a class of materials that includes lithium niobate, an inexpensive
solid that is used to filter signals in cell phones.  When heated a
pyroelectric crystal polarizes charge, segregating a significant amount of
electric charge near a surface, leading to a very large electric field
there.  In turn, this effect can accelerate electrons to relatively high
(keV) energies (see Update 564,
http://www.aip.org/pnu/2001/split/564-2.html).  The UCLA researchers (Seth
Putterman, 310-825-2269) take this idea and add a few other elements to it.
 In a vacuum chamber containing deuterium gas, they place a lithium
tantalate (LiTaO3) pyroelectric crystal so that one of its faces touches a
copper disc which itself is surmounted by a tungsten probe.  They cool and
then heat the crystal, which creates an electric potential energy  of about
120 kilovolts at its surface.  The electric field at the end of the
tungsten probe tip is so high (25 V/nm) that it strips electrons from
nearby deuterium atoms. Repelled by the negatively charged tip, and crystal
field, the resulting deuterium ions then accelerate towards a solid target
of erbium deuteride (ErD2), slamming into it so hard that some of the
deuterium ions fuse with deuterium in the target.  Each deuterium-deuterium
fusion reaction creates a helium-3 nucleus and a 2.45 MeV neutron, the
latter being collected as evidence for nuclear fusion.  In a typical
heating cycle, the researchers measure a peak of about 900 neutrons per
second, about 400 times the "background" of naturally occurring
neutrons.   During a heating cycle, which could last from 5 minutes to 8
hours depending on how fast they heat the crystal, the researchers estimate
that they create approximately 10^-8 joules of fusion energy.  (To provide
some perspective, it takes about 1,000 joules to heat an 8-oz (237 ml) cup
of coffee one degree Celsius.)  By using a larger tungsten tip, cooling the
crystal to cryogenic temperatures, and constructing a target containing
tritium, the researchers believe they can scale up the observed neutron
production 1000 times, to more than 10^6 neutrons per second.  (Naranjo,
Gimzewski, Putterman, Nature, 28 April 2005).  The experimental setup is
strikingly simple: "We can build a tiny self-contained handheld object
which when plunged into ice water creates fusion," Putterman says. 
(http://rodan.physics.ucla.edu/pyrofusion )

NICKEL-78, THE MOST NEUTRON-RICH OF THE DOUBLY-MAGIC NUCLEI, has had its
lifetime measured for the first time, which will help us better understand
how heavy elements are made.  Indeed, where do gold atoms come from? 
Physicists believe gold and other heavy elements (beyond iron) were built
from lighter atoms inside star explosions billions of years ago.  In the
"r-process" (r standing for rapid) unfolding inside the
explosion, a succession of nuclei bulk up on the many available neutrons. 
This evolutionary buildup is nicely captured in a movie simulation showing
all the species in the chart of the nuclides being made one after the other
(http://www.jinaweb.org/html/movies.html).  In some models the buildup can
slow down at certain strategic bottlenecks.   Nickel-78 is one such
roadblock.  This is because Ni-78 is a "doubly magic" nucleus. 
It has both closed neutron and proton shells; it is "noble" in a
nuclear sense in the way that a noble gas atom is noble in the chemical
sense owing to its completely filled electron shell.   Knowing more about
this crucial nuclide is made difficult by the fact that it is, in our
modern era, very rare, and hard to make artificially.  Nevertheless,
scientists at the National Superconducting Cyclotron (NCSL) at Michigan
State University have now culled 11 specimens of Ni-78 from among billions
of high-energy collision events recorded.  In effect, the NCSL is a factory
for reproducing supernova conditions here on Earth.  Hendrik Schatz
(schatz{at}ncsl.msu.edu, 517-333-6397), speaking at last week's American
Physical Society meeting in Tampa, reported that from the available Ni-78
decays recorded, a lifetime of 110 milliseconds could be deduced.  This is
some 4 times shorter than previous theoretical estimates, meaning that the
bottleneck nucleus lived shorter than was thought, which in turn means that
the obstacle to making heavier elements was that much less.  So far the
exact conditions and site for the r-process are still unknown. With the new
measurement model conditions have to be readjusted to produce the observed
amounts of precious metals in the universe. This will provide a better idea
of what to look for  when searching for the
site of the r-process.   (See also Hosmer et al., Physical Review Letters,
25 March 2005)

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