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The Human Plutonium Injection Experiments
William Moss and Roger Eckhardt
T
he human plutonium injection experiments carried out during
and after the Manhattan Project have received tremendous noto-
riety in the past year or so owing to the Pulitzer-prize winning
journalism of Eileen Welsome in the Albuquerque Tribune in 1993.
The purpose of those experiments was to develop a diagnostic tool that
could determine the uptake of plutonium in the body from the amount
excreted in the urine and feces. This tool was essential for the protec-
tion of workers who would produce and fashion plutonium metal for
use in the early atomic bombs. The idea was to remove a worker from
the job if and when it was determined that the he had received an inter-
nal dose that was close to or over the limit considered safe.
Although some of the results of the studies were declassified and re-
ported in the scientific literature in the early fifties (and further reports
appeared in the seventies), the names of the subjects were not dis-
closed. Investigative reporting by Welsome uncovered the identities of
five of the eighteen subjects and gave details about the circumstances
and lives of three of them. The secret nature of the studies and the
fact that the subjects may not have been informed about what was
being done to them has generated outrage and distrust in the general
pubic regarding the practices of the national laboratories. Why were
such experiments done? Who allowed them to happen? The Secre-
tary of Energy, Hazel O’Leary, equally disturbed, pledged an era of
openness in the Department, promising to make available to the public
all information that could be located that was pertinent to those and
Louis Hempelmann
similar radiation experi-
ments with humans.
This article is intended to tell
the Los Alamos story of these
experiments and their aftermath.
The article is based on memos
and other documents that were
collected by one of the authors
(Moss) and were released to the
public as a result of Secretary
O’Leary’s openness initiative.
Los Alamos was not directly in-
volved in choosing the subjects
for the experiments nor in carry-
ing out the clinical studies. Nev-
ertheless, the motivation for the
experiments arose at Los Alamos
and scientists at Los Alamos were
involved in planning the experi-
mental protocols, preparing the ma-
terial to be injected in the subjects,
and analyzing the results. They
were involved both at the time the
experiments took place and years
later when it became clear that re-
analysis was appropriate.
Our intent in reviewing this story is to
give enough scientific and quantitative
details to bring out two areas that are
usually not adequately addressed in the
press and other popular reports. The
first area is the purpose of the studies.
What was to be learned, and how well
did the experiments succeed in accom-
plishing the stated goals? The second
area is the significance of the results for
the protection of plutonium workers.
How have those results aided our cur-
rent understanding of the uptake, distri-
bution, and retention of plutonium, and
how have the results helped us to mini-
mize the risks of internal exposure from
plutonium? We will, in fact, show a
new analysis of the data from the 1940s
that, coupled with a recent human plu-
tonium injection study using plutonium-
237, strengthens our understanding of
the manner in which plutonium, once it
has reached the bloodstream, distributes
itself in the body.
But first, we examine motivations and
try to reconstruct why things were done
as they were. For that we need
to go back to the atmosphere of World
War
II and the enormous pressures attendant
on using unknown and uncharacterized
materials to build the first atomic
weapons.
The Manhattan Project and
Its Need for Plutonium
In planning the development of the
atomic bomb, scientists considered
using two fissionable materials capable
of sustaining a chain reaction—urani-
um-235 and plutonium-239. Each pre-
sented a different set of production and
health-related problems.
Uranium-235 was present in natural
uranium in small amounts (0.7 per
cent). Scientists faced the daunting
task of separating kilogram amounts of
uranium-235 from the much more plen-
tiful uranium-238 isotope by taking ad-
vantage of the slight difference in the
mass of the two isotopes. For example,
in the gaseous-diffusion method,
gaseous compounds of the two
isotopes diffuse through porous
barriers or membranes at rates
that differ by about 6 parts per
thousand. Similarly, the elec-
tromagnetic method passes a
beam of ionized uranium
through a magnetic field, and
the two isotopes follow circu-
lar paths that very gradually
diverge.
In 1942, it was problematic
whether enough uranium-
235 could be separated by
such painstaking techniques
to achieve the goal of hav-
ing an atomic bomb by
January 1945. It was
deemed necessary to pur-
sue plutonium-239 as an-
other possible weapon ma-
terial. Because plutonium
is chemically different from uranium, it
was thought that it could be produced
in reactors through neutron absorption
and then separated easily from its ura-
nium parent and fission products by
chemical means.
Scientists had created tiny amounts of
plutonium with the cyclotron at the
University of California Radiation Lab-
oratory in 1941 and demonstrated its
favorable nuclear properties (see “The
Making of Plutonium-239”). The phys-
ical properties and the chemistry of plu-
tonium were determined using only mi-
crogram (micro = 10
-6
) quantities.
Such small amounts and the fact that
plutonium emits alpha radiation, which
doesn’t penetrate the skin, meant the
risk of handling plutonium, compared
to gamma-emitting radionuclides, was
not a major concern. In fact, the alpha
activity of these small quantities was
the only means to track and account for
the material.
The discovery of plutonium led the Of-
fice of Scientific Research and Devel-
opment to inaugurate work on plutoni-
um for a weapon design. The work
The Human Plutonium Injection Experiments
178
Los Alamos Science Number 23 1995