杏吧原创

NOBODY knows how it got in. In fact, for a long time, nobody even realised
that the problem had four legs. One moment, protons were hurtling round the 6.5
kilometre circumference of the Main Ring accelerator. Next moment, the particle
stream had faltered and died.

Physicists at Fermilab, the world-famous particle physics centre just
west of Chicago, downed tools to search for the cause of the crash. As it turns
out, they didn鈥檛 have far to look. The vital clue came from a thin pencil of
light that runs inside the subterranean tunnel housing the Main Ring. The beam
is an essential safety feature: accelerating protons give off powerful
synchrotron radiation, which is not conducive to good health. Anyone entering
the tunnel would interrupt the beam and trip the accelerator.

But, as the physicists discovered to their cost, it鈥檚 not just humans who can
break a light beam. Crawling about above the ring was a cat. As its tail dangled
down, it periodically cut the light beam and turned off the ring. It took four
hours to corner the cat. When the physicists finally caught it, they had to send
it away to have it checked for radiation exposure, says Bob Mau, head of
accelerator operations. 鈥淭here were 30 trillion protons a second flying round
that ring.鈥�

Nobody can remember the cat鈥檚 fate, although it definitely used up at least
one of its nine lives that day. What the incident does show, however, is just
what a nuisance animals can be to Fermilab. And the problems are not usually
caused by domestic animals. Last year, for instance, a raccoon squeezed,
Houdini-like, through a hole in a steel box just 125 millimetres by 50
millimetres. 鈥淯nfortunately, the box contained a 13 800 volt cable,鈥� says Mau.
鈥淭he raccoon short-circuited the high voltage and fried itself.鈥�

Powerless protons

Naturally, this was a tragedy for the raccoon and its loved ones鈥攁nd it
didn鈥檛 exactly do wonders for the Tevatron, the trillion electronvolt
accelerator that runs alongside the Main Ring. The high-voltage cable carried
power to the superconducting magnets that direct particles into experiments such
as the 5000-tonne CDF detector, which found the top quark.

It took six hours for engineers to restore the supply. But that was not the
end of the trouble. The reckless raccoon had also cut off power to the cryogenic
systems that feed supercold liquid helium to the Tevatron鈥檚 superconducting
magnets. 鈥淚t was days before we could replace all the helium that had boiled off
and get the magnets working again,鈥� says Mau.

The metal box, centrally heated by the high-voltage cable, must have been an
attractive place to shelter out of the wind. Indeed, warmth is one of the main
reasons why wild animals are attracted to Fermilab. The lab sits on 27 square
kilometres of prairie, where the temperature in winter can easily drop to
鈥�20 掳C.

Once, when the weather was particularly bad, Mau even saw a sodden raccoon
trying to find a dry place under the insulation on top of a large transformer.
The death-defying animal was caught and sent packing. This was fortunate because
the transformer, which converts 345 000 volts to 13 800 volts, was at Fermilab鈥檚
main electrical substation. 鈥淚f he鈥檇 shorted that out, it would have been the
ultimate wildlife disaster,鈥� says Mau. 鈥淲e鈥檇 have lost power to the experiments
for a week. Simply replacing the boiled-off helium around the 4-mile Tevatron
ring would have cost $80 000.鈥�

Headless snake

There is some dispute over what is the number one problem animal at Fermilab,
but Mau considers mice and snakes to be good candidates. 鈥淭hey get into
accelerator service buildings around the ring and build their nests in
electrical and electronic equipment,鈥� he says. 鈥淚t鈥檚 no fun for the guy who has
to clean out the blackened remains. I鈥檝e seen a snake with its head blown clear
辞蹿蹿.鈥�

Mike Becker, who is in charge of roads and grounds at Fermilab, reckons the
biggest problems are Canada geese and sex-starved male deer: 鈥淭he geese tend to
spend winter at Fermilab rather than going south because the ponds are warmed by
excess heat from the accelerators,鈥� he says. 鈥淟ast year, a goose turned itself
into a charred cinder by flying between the terminals of a transformer.鈥�

The sex-starved stags are members of a 1000-strong herd of white-tailed deer
which roam freely across the Fermilab site. The problems begin in the rutting
season between October and December, says Becker. When a stag has the doe of his
dreams in his sights, he pays no attention to minor distractions such as
speeding cars. 鈥淢ost of the collisions with deer occur at night,鈥� says Becker.
鈥淟ast year, there were 26 accidents.鈥�

The deer and geese illustrate another reason why Fermilab is irresistible to
wildlife. With a third woodland and the rest open grassland, the site is a
semi-wild island amid a sea of urban development.

Among the wilder residents are muskrats, groundhogs and beavers. 鈥淏eavers are
not a big problem,鈥� says Becker. 鈥淗owever, they have been known to put up a dam
and threaten a building or some equipment with the rising waters.鈥� Like beavers,
muskrats undertake serious engineering projects. One such venture involved
digging a hole between two large ponds. The first pond was used for cooling the
Main Ring. All its water poured into the other pond. 鈥淚t took us a whole day to
repair the damage and refill it,鈥� says Mau. 鈥淒uring the whole of that time we
had to have the accelerator 辞蹿蹿.鈥�

Part of Becker鈥檚 job is to trap any troublesome animals and relocate them to
a wild site far away from Fermilab. He says the struggle against the invaders is
a never-ending one and it is getting worse. 鈥淏efore Fermilab was built, the land
was used for farming,鈥� says Becker. 鈥淪ince then, wild animals have moved
back鈥攂ut without their natural predators.鈥�

Fermilab is also home to a herd of American buffalo. About 40 are kept in a
fenced-off corner of the site. An integral part of Becker鈥檚 job is maintaining
the herd. 鈥淲e鈥檙e doing our bit to preserve a bit of the Old West,鈥� says
Becker.

Buffalo stories abound among people who live around the site, and have
spawned some bizarre conspiracy theories. 鈥淪ome local people have got it into
their heads that buffalo are especially sensitive to radiation,鈥� Mau says. 鈥淭he
other day an attendant at a gas station near Fermilab asked me whether it was
true we take buffalo down into the tunnels to warn us of high radiation
濒别惫别濒蝉.鈥�

And if the idea of using buffaloes as overgrown canaries isn鈥檛 strange
enough, there鈥檚 also a theory that Fermilab is home to a 4-metre high mutant
buffalo. Mau dismisses this as nonsense. But then he works for FermiLab, so he
would wouldn鈥檛 he?