- Bernstein, Jeremy.
Plutonium.
Washington: Joseph Henry Press, 2007.
ISBN 0-309-10296-0.
-
When the Manhattan Project undertook to produce a
nuclear bomb using plutonium-239, the world's inventory of
the isotope was on the order of a microgram, all produced
by bombarding uranium with neutrons produced in cyclotrons.
It wasn't until August of 1943 that enough had been produced
to be visible under a microscope. When, in that month, the
go-ahead was given to build the massive production reactors
and separation plants at the Hanford site on the
Columbia River, virtually nothing was known of the physical
properties, chemistry, and metallurgy of the substance
they were undertaking to produce. In fact, it was only
in 1944 that it was realised that the elements starting with
thorium formed a second group of “rare earth”
elements: the periodic table before World War II had
uranium in the column below tungsten and predicted that
the chemistry of element 94 would resemble that of osmium.
When the large-scale industrial production of plutonium
was undertaken, neither the difficulty of separating the
element from the natural uranium matrix in which it was
produced nor the contamination with Pu-240 which would
necessitate an implosion design for the plutonium bomb
were known. Notwithstanding, by the end of 1947 a total
of 500 kilograms of the stuff had been produced, and today
there are almost 2000 metric tons of it, counting both
military inventories and that produced in civil power
reactors, which crank out about 70 more metric tons a year.
These are among the fascinating details gleaned and presented
in this history and portrait of the most notorious of
artificial elements by physicist and writer Jeremy Bernstein.
He avoids getting embroiled in the building of the bomb,
which has been well-told by others, and concentrates on
how scientists around the world stumbled onto nuclear fission
and transuranic elements, puzzled out what they were seeing,
and figured out the bizarre properties of what they had
made. Bizarre is not too strong a word for the chemistry
and metallurgy of plutonium, which remains an active area of
research today with much still unknown. When you get that far down
on the periodic table, both quantum mechanics and special
relativity get into the act (as they start to do
even with gold),
and you end up with six allotropic phases of the metal (in
two of which volume decreases with increasing temperature), a melting
point of just 640° C and an anomalous atomic radius which
indicates its 5f electrons are neither localised nor itinerant, but
somewhere in between.
As the story unfolds, we meet some fascinating characters,
including
Fritz Houtermans,
whose biography is such that, as the author notes
(p. 86), “if one put it in a novel, no one
would find it plausible.” We also meet stalwarts of the
elite 26-member UPPU Club: wartime workers at Los Alamos whose
exposure to plutonium was sufficient that it continues to be
detectable in their urine. (An epidemiological study of these people
which continues to this day has found no elevated rates of mortality,
which is not to say that plutonium is not a hideously hazardous
substance.)
The text is thoroughly documented in the end notes, and
there is an excellent index; the entire book is just 194
pages. I have two quibbles. On p. 110, the author states
of the
Little Boy
gun-assembly uranium bomb dropped on
Hiroshima, “This is the only weapon of this design
that was ever detonated.” Well, I suppose you could
argue that it was the only such weapon of that precise design
detonated, but the
implication is that it was the first and last gun-type
bomb to be detonated, and this is not the case. The U.S.
W9 and
W33 weapons,
among others, were gun-assembly uranium bombs, which between
them were tested three times at the
Nevada Test Site.
The price for plutonium-239 quoted on p. 155, US$5.24
per milligram, seems to imply that the plutonium for
a critical mass of about 6 kg costs about 31 million
dollars. But this is because the price quoted is
for 99–99.99% isotopically pure Pu-239, which has been
electromagnetically separated from the isotopic mix you get
from the production reactor. Weapons-grade plutonium can have
up to 7% Pu-240 contamination, which doesn't require the
fantastically expensive isotope separation phase, just
chemical extraction of plutonium from reactor fuel. In
fact, you can build a bomb from so-called
“reactor-grade” plutonium—the U.S.
tested
one in 1962.
November 2007 