The Human Plutonium Injection Experiments

The Human Plutonium Injection Experiments

Number 23  1995  Los Alamos Science  

193

be tested was removed from the work-

place for forty-eight hours and asked to

“wear freshly laundered clothing . . .

and to bathe and wash their hands fre-

quently.”  After this period, the worker

was admitted to the hospital, asked to

shower, placed in a special room (the

“health pass ward”), and checked for

contamination.  He was instructed to

wash his hands and wear white cotton

gloves each time he urinated, and the

flask and funnel were placed so they

didn’t have to be touched.

A trial run with plutonium workers

vividly demonstrated the need for such

care: the average counts per minute

when the samples were collected by the

workers at home was 20, whereas the

average for samples collected using the

above procedure was only 2.2 counts

per minute!  Thus, external contami-

nates picked up at work made the plu-

tonium excretion rate appear ten times

larger than it actually was.

Other problems solved by people at the

Met Lab and at Los Alamos were the

maintenance of a laboratory free from

alpha contamination (including the

reagents used in the analysis), the de-

velopment of a method capable of han-

dling large volumes of urine (1-liter

rather than 100-milliliter samples), and

the development at Chicago of alpha-

counting instruments capable of detect-

ing less than 1 alpha count per minute.

By February 1945, which coincided

with delivery of multi-gram amounts of

plutonium from Hanford, the urinalysis

procedure appeared capable of detecting

0.02 nanogram of plutonium-239 alpha

activity in a 24-hour urine sample.  If

the human urinary excretion rate was

equal to the animal rate of 0.01 per cent

per day, the method could detect a

body burden of less than 1 microgram

with 95 per cent confidence.

The method was tested on thirty-six

workers at Los Alamos.  Fourteen of

these people had evidence of previous

inhalations of plutonium dust because

of at least one high nose-swipe count.

These fourteen people had an average

of 1.2 counts per minute in their 24-

hour urine samples.  The urine samples

of the other twenty-two people, who

had never shown a high nose-swipe

count, averaged 0.2 counts per minute.

The five most highly exposed people

had urine samples with an average of

2.2 counts per minute.  Such correla-

tions were strong evidence that devel-

opment of a sensitive analytical proce-

dure had succeeded at Los Alamos.

TTA extraction. The method devel-

oped at Berkeley for analyzing urine

samples used extraction with thio-

phenyltrifluoracetone (TTA).  After the

sample was ashed, a lanthanum-fluoride

precipitation was performed, followed

by the TTA extraction step.  This

method resulted in a negligible sample

mass and low background counts.

One of the main sources of alpha conta-

mination in the Berkeley and Los

Alamos methods was the lanthanum-

fluoride reagent.  The Los Alamos pro-

cedure ended with the lanthanum-fluo-

ride precipitation step, which

introduced alpha contaminants and lim-

ited the sensitivity of the technique be-

cause of a count-per-minute back-

ground.  In the Berkeley procedure, the

lanthanum-fluoride-precipitation step

preceded the extraction step, and the

alpha contaminants were left behind,

which yielded a background of only 0.2

counts per minute.

Each of the three techniques had its ad-

vantages and disadvantages, as well as

its proponents and detractors, but the

Los Alamos, Chicago, and Berkeley

sites were each able to acquire highly

satisfactory data using their particular

method. 

 

s

The Los Alamos Urine Analysis Method

The method developed in 1945 at Los Alamos for the plutonium analysis of

urine started by evaporating a 24-hour urine specimen almost to dryness.  (It

was recommended that people being tested keep their intake of liquids to a

minimum—one cup of liquid per meal and little or no liquids in between—to

expedite this step.)  The residue was then wet-ashed (by repeated additions

of concentrated acids and hydrogen peroxide) until a white solid almost com-

pletely free of organic matter remained.  The solid was dissolved in hy-

drochloric acid and precipitated as hydroxide.  After redissolving the precipi-

tate in hydrochloric acid and adjusting the pH, ferric iron was added as a

carrier, and the dissolved plutonium was complexed with cupferron (an or-

ganic compound that forms a soluble complex with iron).  Choroform was

then used to extract the cupferron complex, separating it from other dis-

solved materials in the aqueous solution.  (One of the most critical steps in

the process was using a separatory flask to draw off exactly the chloroform

layer.)  After the chloroform was evaporated, the cupferron residue was di-

gested with nitric and perchloric acids.  Finally, the plutonium was carried

out of this solution as part of a lanthanum fluoride precipitate, leaving the

iron behind.  The final precipitate was transferred to a platinum foil, dried,

and counted in an alpha-particle detector for thirty minutes.  The main rea-

son for these various steps was to concentrate the plutonium while minimiz-

ing material that would deposit on the foil and absorb part of the alpha radia-

tion.  Control urine samples spiked with plutonium analyzed concurrently with

regular samples demonstrated an average chemical recovery of 88 per cent

(

6

11 per cent one standard deviation) and a reagent-contaminate back-

ground of 1 count per minute.

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