Anonymous Kumquat submits:

"USA Developing "Quasi-Nuclear" Gamma-Ray Weaponry"

David Hambling, New Scientist, 16th August 2003

An exotic kind of nuclear explosive being developed by the
US Department of Defense could blur the critical
distinction between conventional and nuclear weapons. The
work has also raised fears that weapons based on this
technology could trigger the next arms race.

The explosive works by stimulating the release of energy
from the nuclei of certain elements but does not involve
nuclear fission or fusion. The energy, emitted as gamma
radiation, is thousands of times greater than that from
conventional chemical explosives. The technology has
already been included in the Department of Defense's
Militarily Critical Technologies List, which says: "Such
extraordinary energy density has the potential to
revolutionise all aspects of warfare."

Scientists have known for many years that the nuclei of
some elements, such as hafnium, can exist in a high-energy
state, or nuclear isomer, that slowly decays to a
low-energy state by emitting gamma rays. For example,
hafnium178m2, the excited, isomeric form of hafnium-178,
has a half-life of 31 years.

The possibility that this process could be explosive was
discovered when Carl Collins and colleagues at the
University of Texas at Dallas demonstrated that they could
artificially trigger the decay of the hafnium isomer by
bombarding it with low-energy Xrays (New Scientist, 3 July
1999, p42). The experiment released 60 times as much energy
as was put in, and in theory a much greater energy release
could be achieved.

Before hafnium can be used as an explosive, energy has to
be "pumped" into its nuclei. Just as the electrons in atoms
can be excited when the atom absorbs a photon, hafnium
nuclei can become excited by absorbing high-energy photons.
The nuclei later return to their lowest energy states by
emitting a gamma-ray photon. Nuclear isomers were
originally seen as a means of storing energy, but the
possibility that the decay could be accelerated fired the
interest of the Department of Defense, which is also
investigating several other candidate materials such as
thorium and niobium.

For the moment, the production method involves bombarding
tantalum with protons, causing it to decay into
hafnium-178m2. This requires a nuclear reactor or a
particle accelerator, and only tiny amounts can be made.
Currently, the Air Force Research Laboratory at Kirtland,
New Mexico, which is studying the phenomenon, gets its
hafnium-178m2 from SRS Technologies, a research and
development company in Huntsville, Alabama, which refines
the hafnium from nuclear material left over from other
experiments. The company is under contract to produce
experimental sources of hafnium178m2, but only in amounts
less than one ten-thousandth of a gram.

But in future there may be cheaper ways to create the
hafnium isomer -- by bombarding ordinary hafnium with
high-energy photons, for example. Hill Roberts, chief
scientist at SRS, believes that technology to produce gram
quantities will exist within five years. The price is
likely to be high- similar to enriched uranium, which costs
thousands of dollars per kilogram- but unlike uranium it
can be used in any quantity, as it does not require a
critical mass to maintain the nuclear reaction.

The hafnium explosive could be extremely powerful. One gram
of fully charged hafnium isomer could store more energy
than 50 kilograms of TNT. Miniature missiles could be made
with warheads that are far more powerful than existing
conventional weapons, giving massively enhanced firepower
to the armed forces using them.

The effect of a nuclear-isomer explosion would be to
release high-energy gamma rays capable of killing any
living thing in the immediate area. It would cause little
fallout compared to a fission explosion, but any
undetonated isomer would be dispersed as small radioactive
particles, making it a somewhat "dirty" bomb. This material
could cause long-term health problems for anybody who
breathed it in.

There would also be political fallout. In the 1950s, the US
backed away from developing nuclear mini-weapons such as
the "Davy Crockett" nuclear bazooka that delivered an
explosive punch of 18 tonnes of TNT. These weapons blurred
the divide between the explosive power of nuclear and
conventional weapons, and the government feared that
military commanders would be more likely to use nuclear
weapons that had a similar effect on the battlefield to
conventional weapons. By ensuring that the explosive power
of a nuclear weapon was always far greater, it hoped that
they could only be used in exceptional circumstance when a
dramatic escalation of force was deemed necessary.

Then in 1994, the US confirmed this policy with the
Spratt-Furse law, which prevents US military from
developing mini-nukes of less than five kilotons. But the
development of a new weapon that spans the gap between the
explosive power of nuclear and conventional weapons would
remove this restraint, giving commanders a way of
increasing the amount of force they can use in a series of
small steps.

Nuclear-isomer weapons could be a major advantage to armies
possessing them, leading to the possibility of an arms
race.

Andre Gesponer, director of the Independent Scientific
Research Institute in Geneva, believes that a nation
without such weapons would not be able to fight one that
possesses them. As a result, he says, "many countries which
will not have access to these weapons will produce nuclear
weapons as a deterrent", leading to a new cycle of
proliferation.

The Department of Defense notes that there are serious
technical issues to be overcome and that useful
applications may be decades away. But its Militarily
Critical Technologies List also says: "We should remember
that less than six years intervened between the first
scientific publication characterising the phenomenon of
fission and the first use of a nuclear weapon in 1945."