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Nuclear fusion is the
mechanism which powers the Sun.
Photo: SOHO (ESA & NASA) |
The strongest of nature’s four forces is the “strong nuclear
force”. It makes the Sun shine, providing energy to almost all
life on earth. It controls how atomic nuclei interact, creating all
atoms via two processes: fission and fusion. Nuclear fission has been
harnessed by mankind to generate power on earth for many decades now.
But nuclear fusion (where two light nuclei come together to create
a larger nucleus) is much more powerful. It is this mechanism which
powers the Sun.
Controlling nuclear fusion on earth has proven to be very difficult.
The problem is that atomic nuclei have a very strong positive electric
charge that makes them hard to bring together, since like charges
repel. To overcome the electric repulsion, the nuclei must be heated
to very high temperatures, as they are in stars. These “thermonuclear”
fusion devices are very crude, allowing us to make big bombs and
little else. But there are other ways to coax the nuclei together.
In conventional experiments a beam of nuclei is fired into a target
nucleus, sometimes resulting in fusion.
Michael Kuchiev and Victor Flambaum, along with Boris Altshuler
of Princeton University have uncovered a new enhancement mechanism
that will allow nuclei to come together. Continuing work they started
with Vladimir Zelevinsky of Michigan State University, USA, they
found that when the target nucleus is surrounded by heavy nuclei,
a chain of preliminary collisions transforms the projectile-target
experiment into one with colliding beams.
Firstly, a projectile nucleus hits the lighter target nucleus,
sending it hurtling away. The projectile nucleus continues along
its original path, while the target flies ahead at high speed. The
target then bounces off very heavy nuclei in the environment back
towards the projectile nucleus, so they are once again on a collision
course. Finally they collide inelastically, this time giving rise
to a nuclear reaction. This game of atomic ping-pong results in
a drastic exponential increase in the probability of overcoming
the electric repulsion, and hence sharply increases the likelihood
of nuclear reaction.
This seemingly simple idea has many applications in non-equilibrium
fusion, such as in understanding how fusion occurs in the explosions
of supernovae. It should also help nuclear technology on earth,
in fields such as laser-induced fusion, which may one day become
an economical means of generating power.
Julian Berengut
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