[asa] Changing rate of radioactive decay (New Scientist)

Is someone here with expertise on nuclear physics able to comment on
The New
Scientist article on changing rate of radioactive decay:

http://physicsweb.org/articles/news/10/7/13/1

A cool solution to waste disposal

31 July 2006

A group of physicists in Germany claims to have discovered a way of
speeding
up radioactive decay that could render nuclear waste harmless on
timescales
of just a few tens of years. Their proposed technique - which involves
slashing the half-life of an alpha emitter by embedding it in a metal
and
cooling the metal to a few degrees kelvin - could therefore avoid the
need
to bury nuclear waste in deep repositories, a hugely expensive and
politically difficult process. But other researchers are sceptical and
believe that the technique contradicts well-established theory as
well as
experiment.

The leader of the German-based group, Claus Rolfs of Ruhr University in
Bochum, is an astrophysicist and made the discovery about alpha decay
after
replicating the fusion reactions that take place in the centre of stars.
Using the university's particle accelerator he fired protons and
deuterons
(nuclei containing a proton and a neutron) at various light nuclei. He
noticed that the rate of fusion reactions was significantly greater
when the
nuclei were encased in metals than when they were inserted into
insulators.
He also observed that the effect is enhanced at lower temperatures
(J. Phys.
G: Nucl. Part. Phys. 32 489).

Rolfs believed this effect could be explained in simple terms by
assuming
that the free electrons in a metal act like the electrons in a
plasma, as
described in a model by Dutch physicist Peter Debye. The lower the
temperature of the metal, the closer the free electrons get to the
radioactive nuclei. These electrons accelerate positively charged
particles
towards the nuclei, thereby increasing the probability of fusion
reactions.

But Rolfs realized that the reverse reaction might also occur and
that free
electrons could enhance the ejection of positively charged particles
from a
nucleus. This would reduce the half-lives of á-decay or â+-decay, and
increase half-lives for processes involving electrons (which are
repelled by
the free electrons within the metal), i.e. â--decay and electron
capture.

The group has investigated this hypothesis by embedding a number of
radioactive nuclei inside metals and then cooling the metal to a few
degrees
kelvin. As expected, they observed a longer half-life for the electron
capture of beryllium-7 and shorter half-lives for â+-decay in sodium-22
(Eur. Phys. J. A 28 251) and á-decay in polonium-210. They are now
investigating the á-decay of radium-226, a hazardous component of spent
nuclear fuel with a half-life of 1600 years. Rolfs calculates that this
half-life could be reduced to as little as a year and at the very
least to
100 years, and believes that the half-lives of all other hazardous alpha
emitters within nuclear waste could be shortened by similar amounts.

"This means that nuclear waste could probably be dealt with entirely
within
the lifetimes of the people that produce it," he says. "We would not
have to
put it underground and let our great-great-grandchildren pay the
price for
our high standard of living."

Rolfs admits that much engineering research needs to be done to
convert his
idea into practice, but he believes there are probably no insurmountable
technical barriers. Other physicists, however, think that the basic
idea may
be flawed. According to Nick Stone, a nuclear physicist recently retired
from Oxford University, physicists have already carried out
experiments in
which they cooled alpha emitters to 4 K and below, but found no
significant
changes in their half-lives.

Meanwhile, Hubert Flocard, director of the CSNSM nuclear-physics lab
near
Paris, believes that Rolfs' model contradicts standard solid-state
physics,
although he admits that he cannot explain the group's data himself.
Rolfs
concedes that he needs a more sophisticated theory, but stands by his
results. "Nature decides what is right," he says.
About the author

Edwin Cartlidge is News Editor of Physics World

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Received on Fri Oct 27 01:17:41 2006