Tickling the Dragon’s Tail1
It is a little known fact that the scientist who was a key figure in assembling the first
“atomic” bomb ever to be exploded was a native Winnipegger, Louis Slotin. When Louis
completed his Ph.D. in Chemistry in 1936, he tried, unsuccessfully, to get a position with
the National Research Council in Canada. Instead, Slotin moved to Chicago and ended up
working in the famous Met Lab where the first sustained nuclear reaction was carried out.
From there he was drafted into the crucial bomb-construction phase of the Manhattan
Project and, amazingly, he was the lead assembler of the first atomic bomb.
The Manhattan Project
America’s “Manhattan Project” to develop the
“atomic” bomb began as a result of the famous
letter of Albert Einstein to President Roosevelt
in 1939. The proposal was met with much skep-
ticism on the part of the US government at first,
but took on urgency after the bombing of Pearl
Harbor in December of 1941. Nobel Laureate,
Arthur Compton, directed the part of the pro-
ject that began in Chicago a few weeks later. The
top secret Chicago research project was code
named the “Metallurgical Laboratory,” or, as it
became known, the “Met Lab.” It took less than
a year for the team in Chicago to produce a self-
sustaining nuclear reaction—the world’s first.
Louis Slotin, a gifted chemist working as a phys-
icist on the cyclotron at the University of Chi-
cago, was immediately drafted into the project
despite being a Canadian. His name is included
on the famous list of fifty scientists who devel-
oped the world’s first nuclear reactor.
The competence of Slotin stood out in the
project and he was subsequently invited to join
the project in Oak Ridge Tennessee, where he
worked with Eugene Wigner on the problem of
plutonium production. Louis distinguished
1 This document is based, in large part, on an extract from Klassen 2009.
2 e-mail: dr.s.klassengmail.com
himself as competent and hard-working on each
project, ensuring his ultimate recruitment into
the heart of the A-bomb program.
The crucial bomb-construction phase of the
Manhattan Project was carried out in a top se-
cret facility near Los Alamos, New Mexico.
Louis arrived at Los Alamos in December of
1944 where he threw himself into his work with
the usual energy. Soon he had developed an un-
rivalled reputation at assembling the compo-
nents of the as-yet-unexploded prototype
bombs in order to achieve near criticality. Criti-
cality is that point in an intensifying set of nu-
clear reactions at which it becomes self-sustain-
ing and could, if not allowed to expand due to
the heating, result in an atomic explosion. Even
if the point of explosion is not reached, the crit-
icality threshold, when crossed, results in the re-
lease of massive amounts of radiation. When the
plan for creating near criticality was first de-
vised, it was described by one of the participants
as “tickling the tail of a sleeping dragon” (Frisch,
1979, p. 159). Thereafter, the criticality experi-
ments were known as “tickling the dragon’s
2 S. Klassen
On account of his expertise, Slotin was
trusted with the task of assembling the first
atomic bomb, code-named “Trinity,” and hand-
ing it over to army personnel for transportation
to the detonation site on July 16, 1945. One of
his most prized possessions was a scribbled re-
ceipt for the bomb. At this time, Louis had not
yet received his American citizenship and was
not allowed to travel to the launching site of the
Hiroshima and Nagasaki bombs.
So, how was it that Louis Slotin became a
central figure in the development of the atomic
bomb in Los Alamos?
Why did Louis Slotin Move to Los Alamos?
Louis Slotin was born in Winnipeg on Decem-
ber 1, 1912 to devout Russian-Jewish parents.
The family was fairly well to do and Louis’ fa-
ther, who ran a local livestock agency, pur-
chased a fine river property as their residence.
The property stands today, although no longer
owned by the family, but, essentially, the same
as it was then. After high school, the young
Louis enrolled at the University of Manitoba.
His younger brother recalls Louis studying with
Figure 1 Louis Slotin (on the left), with open shirt and wearing shorts, leans against the Trinity bomb
Tickling the Dragon’s Tail 3
extreme intensity. The hard work paid off as
Louis received the University Gold Medal in
both Chemistry and Physics upon graduating
with a Bachelor’s degree. Louis continued his
studies at the University of Manitoba, and in
1933 obtained his Master of Science degree in
chemistry. That same year Louis moved to Lon-
don, England to continue his studies under Pro-
fessor A. J. Allmand at King’s College London.
In July of 1936, Louis successfully defended his
doctorate in chemistry, winning the prize for
The following year, Louis tried to get a posi-
tion with Canada’s National Research Council,
but was turned down. Getting a position should
have been automatic; however, Slotin was a Jew
and anti-Semitism was on the rise at that time.
We will never know if this was a factor in his in-
Long before then, the Physics Department at
the University of Chicago had gained world
prominence, with the likes of Millikan, Michel-
son, and Compton having worked there. It is not
surprising, then, that Louis headed to Chicago
as a research associate, in order to work on the
cyclotron. The work was difficult and Louis re-
ceived no pay whatsoever for two years. During
that time his father regularly sent him money for
food and rent.
Had Louis not persevered under these ad-
verse conditions, he would not have been in
Chicago when the Manhattan Project began. As
it was, he was invited by Compton to join the
team that was charged with the task of produc-
ing a self-sustaining nuclear reaction at the Uni-
versity of Chicago. Had he not joined the initial
phase of the project in Chicago, he would never
have moved to Los Alamos and the following
true story would never have taken place.
The Dragon’s Revenge
It was a typically sunny spring morning in 1946
as Louis Slotin hurried towards the institution-
ally-drab laboratory building. Lou chuckled
wryly to himself. Life had turned out rather dif-
ferently for him, having grown up in Winnipeg,
graduating from the University of Manitoba as
a chemist, and now known as a physicist work-
ing in Los Alamos on the A–bomb! A sobering
thought crossed his mind, like it did frequently.
Was he right in his belief that the restoration of
world peace had depended on Manhattan pro-
ject research? But his thoughts were interrupted
as he strode up to the top–secret Pajarito lab
housing the bomb criticality tests. He recalled
crossing paths with Nobel Laureate Enrico
Fermi here a while back. What Professor Fermi
said to him then kept coming back to his mind
like a recording—“You won't last a year if you
keep doing that experiment.” “That Experi-
ment” was testing the assembly of the pluto-
nium bomb core with its beryllium shell. The
procedure had been dubbed, ominously, as
“tickling the dragon's tail”.
The day passed quickly for Lou as it will for
someone obsessed with his work. It was now
past 3:00 in the afternoon and Lou was ready to
demonstrate the testing of the bomb core to Al-
Figure 2 Dr. Louis Slotin, c. 1936
4 S. Klassen
vin Graves, who was to take his place on the pro-
ject. Six observers were looking on from a dis-
tance. Grabbing the hemispherical beryllium
shell by the thumb–hole on the top, Lou care-
fully lowered the top half onto the bottom half
covering the plutonium core, holding them
apart with a screwdriver. Lou had mastered the
technique of making the shell come as close to
the core as possible without becoming super
critical and emitting a lethal dose of radiation. It
was necessary to test the bomb cores in this way
to insure that they functioned correctly. As he
rotated the screwdriver slightly this way and
that, the shell moved up and down. From across
the room the familiar crunching sound of the
Geiger counters swelled and ebbed. Then it hap-
pened. No one knows what broke Lou's concen-
tration, but something did. The screwdriver
slipped and clattered to the floor and a blue flash
filled the room as the top shell touched the bot-
tom, releasing an unimaginable torrent of neu-
trons and gamma-rays. Time seemed to come to
a screeching halt. Almost instinctively, Lou, us-
ing his hands, grabbed the lethal assembly and
flipped the bomb–shell off the table and onto
the floor with what seemed a deafening crash.
“Well, that does it—I'm dead!” Lou heard him-
self say. “Tell me this is a nightmare,” he
thought. But it wasn’t.
Dr. Louis Slotin had been exposed to 21 Sie-
verts of radiation in an instant as the bomb be-
came supercritical when the top half came com-
pletely in contact with the bottom. His quick re-
action may have saved the lives of everyone else
in the room that day, May 21, 1946. However,
Dr. Slotin died an excruciating death from ex-
treme radiation exposure on May 30. Slotin's
close friend, Dr. Philip Morrison, sat with him
night and day as his organs shut down one by one
and gangrene set in. Everyone considered Dr.
Slotin a hero. The local newspaper in Los Alamos
published a tribute written by associate editor
Thomas P. Ashlock, which began,
May God receive you, great–souled scientist!
While you were with us, even strangers knew
The breadth and lofty stature of your mind
‘Twas only in the crucible of death
We saw at last your noble heart revealed.
What a tragedy! If the science of radiation pro-
tection had been sufficiently developed by 1946,
then this story would likely never have taken
Background and Commentary
After Japan surrendered in August of 1945,
Loius was finally able to tell his family about his
wartime occupation. Louis’ father learned, to his
shock, of his son’s role in working on the atom
bomb. The son’s response to his father was that
“we had to get it before the Germans” (Zeilig,
1995, p. 24). Louis’ family recalled that despite
his seeming zeal for the project, Louis was nev-
ertheless somewhat troubled by what he was do-
ing. Slotin’s close friend, Philip Morrison, re-
membered that the two of them frequently
spoke about war and peace. After the war, Slotin
was assigned to Navy nuclear tests, “much to
[his] disgust” (Zeilig, 1995, p. 24). Louis would
much rather have returned to Chicago to re-
sume his peacetime research. Moreover, the
post-war experiments in which Slotin was in-
volved were not without their perils. While
Louis was away from the laboratory on August
21, 1945, his friend, Harry Dalglian, had a hor-
rendous criticality experiment accident, expos-
ing himself to a lethal dose of radiation. Slotin
spent many hours at the bedside of his dying
friend. After Harry’s death, the criticality tests
were moved to the Palajito laboratory from the
Omega Site laboratory where they had been
working before (Loaiza & Gehman, 2006). En-
rico Fermi, who was also in Los Alamos at the
time, warned Slotin that he would be dead in a
year if he kept on doing the criticality experi-
ment. Although there was some work being
done on designing a remote control for the test,
“such devices had not been fully developed to
Tickling the Dragon’s Tail 5
the point where they were considered reliable to
perform the task of critical assembly studies”
(Hayes, 1956, p. 8), and so, the manual tests con-
tinued. By this time, Slotin had taken over the
leadership of the critical assembly group from
Otto Frisch (Frisch, 1969).
Slotin began to make plans to return to Chi-
cago. Having received his American citizenship,
he was scheduled to travel to the Marshall Is-
lands to attend the Operation Crossroads test at
Bikini Atoll on July 1. After that, he planned to
move back to Chicago. By May 21, 1946, Alvin
Graves had already been assigned to take Louis’
place on the project. On that day, Slotin was to
orient Graves in the experimental procedures so
that he could leave. Five other scientists were
working on other projects in the laboratory at
the time, and a security guard was stationed
there, as always. Graves asked Slotin to demon-
strate a critical assembly. At first, Slotin didn’t
think he had the materials on hand, then re-
membered that they had a number of bomb
cores there and announced that he could put to-
gether a demonstration “in about two minutes”
(Froman & Schreiber, 1946, p. 1). Some light-
hearted banter ensued, with Darol Froman, also
a Canadian, remarking that if Slotin “were going
to do it in two minutes [he] was going to leave,
but would stick around if he took a half-hour for
it” (Froman & Schreiber, 1946, p. 2). Froman
notes that this was not meant seriously, as eve-
ryone in the room had complete confidence in
Louis’ ability and judgment. At the time the crit-
icality experiments were being done manually
by placing the core of the bomb into a pair of
hemispherical beryllium shells hollowed out in
the center where the core fit, exactly. The pluto-
nium core had a nickel covering which pre-
vented both contamination and the escaping of
the alpha radiation. The cores were strangely
warm but, by themselves, harmless to the touch.
Gloves were not necessarily used to handle
them. The shells, called tampers, were placed
one on top of the other to make a sphere, and
served as neutron reflectors so that the neutron
density in the core would reach the level to ini-
tiate a nuclear chain reaction. Of course, the up-
per shell was never allowed to touch the lower
one, as criticality would be achieved, instantly.
To prevent that from happening, spacers had
been machined to place between the two halves.
However, in order to approach criticality, Slotin
would have to remove the spacers and use a
screwdriver as a wedge and hand-manipulate
the spheres into a state of near-criticality. Slotin
soon had the demonstration ready to go, and
when it no longer interfered with other work go-
ing on in the room, he lowered the upper hemi-
sphere with his hands and kept the hemispheres
separate with a screwdriver blade, which also
served to gradually decrease the gap between the
spheres. The onset of criticality was detected by
the increased emission of gamma-radiation,
which was detected by Geiger counters. The ex-
periment began and what happened next was
recorded by Froman shortly thereafter. Froman
[i]t could not have been more than two or three
minutes after the start that I turned because of
some noise or sudden movement. I saw a blue
flash around the Be tamper and felt a heat wave
simultaneously. At the same instant, Slotin
flipped the outer top tamper shell off. … This
stopped the reaction.
… Slotin’s left hand, which was holding the
top hemisphere, was definitely in the glowing re-
gion. The total duration of the flash could not
have been more than a few tenths of a second.
Slotin reacted very quickly in flipping the tamper
piece off. …
A few seconds after the accident, only Slotin,
Graves, and myself [sic] were left in the room. …
The rest of us left immediately, going up the cor-
Slotin called for an ambulance and then pre-
pared a sketch showing our positions at the time
of the accident. (Froman & Schreiber, 1946, p. 3)
Raemer Schreiber, who was also present in the
room, described the accident this way, almost 50
What [Slotin] did was to lower one of the hemi-
spheres of beryllium over the core sitting in the
bottom half and hold it open with a screwdriver.
The idea was to lower it down to where there was
6 S. Klassen
just a small gap and, if it gets critical, then you
could stop it at that point. You could waggle the
screwdriver and make it multiply or quit. …
But the screwdriver slipped. The thing
dropped completely closed and that made it su-
per critical, prompt critical. It was stopped by the
expansion of the core and the beryllium but it was
enough to put out a lethal shot of radioactivity.
(quoted in Calloway, 1995, p. 2)
According to Schreiber’s recollection, Slotin
said at the instant after the accident: “Well, that
does it”, meaning that he probably knew in an
instant that he was a dead man (quoted in Cal-
loway, 1995, p. 2). Louis became very ill and died
an excruciating death nine days later, on May
30th. Slotin’s close friend, Philip Morrison, was
constantly at his beside during that time. Ironi-
cally, both Harry Dalglian and Louis Slotin’s ac-
cidents happened on Tuesday the 21st of the
month, using the same bomb core, and they
both died in the same hospital room. The fu-
neral for Louis Slotin was held on June 2nd out-
side the family home with almost 3,000 people
in attendance. Some time later, a memorial park
was established nearby on Luxton Avenue over-
looking the Red River. The inscription on the
bronze plaque reads:
This park is dedicated to the memory of Dr. Louis
Slotin who willingly and heroically laid down his
life to save seven fellow scientists during an ex-
periment May 21, 1946 at the Los Alamos atomic
research project in New Mexico, U.S.A.
As the laboratory was being swept with
deadly radiation, Dr. Slotin spontaneously leaped
forward covering the experiment with his body.
Dr. Slotin was taken to hospital where he died
nine days later. His seven co-workers survived.
Dr. Slotin and his family had resided at 125
Scotia Street, just a short walk north of this park.
Figure 3 Authentic original photograph, an official re-enactment of Louis Slotin “Tickling the Dragon’s
Tail”, taken from McLaughlin, T.
P., et. al., (2000). Report LA–16368, A Review of Criticality Accidents: 2000
. Los Alamos Laboratory.
Tickling the Dragon’s Tail 7
Descendents and family members of the late Dr.
Slotin still reside in Winnipeg.
There was a fairly general consensus that
Slotin was not culpable in the accident and that
his quick reaction, not to mention the shielding
effect of his body, had literally saved the lives of
the others in the room. What scientists of the
time did not know is that it was the self-limiting
nature of the nuclear chain reaction that had ter-
minated the burst of radiation and not Slotin’s
quick reaction. The US government issued a ci-
tation of bravery and the editor of the local
newspaper wrote a poem in Slotin’s honor.
However, a report issued at the time blamed
project management for being “negligent in fail-
ing to recognize the need for effective safety
controls, requirements to ensure reproducibil-
ity, and the development and implementation of
suitable procedures” (Malenfont, 1996, p. 2).
Many of the experiments done at that time pre-
sented serious dangers. Hacker (1987) writes
[t]he reasons were largely psychological. Proper
care precluded any danger at all; nothing could
happen unless an assembly exceeded the critical
amount. A long series of trouble-free tests could
foster a degree of overconfidence. “Those of us
who were old hands felt impervious to the invisi-
ble danger,” a member of the critical assemblies
group recalled. “I am afraid that familiarity in-
deed breeds contempt of danger.” (Hacker, 1987,
Although much work had been done on radia-
tion safety before the war, standards and proce-
dures were developed hazard by hazard and
project by project. As new situations and haz-
ards presented themselves, there were, literally,
no generally set standards, procedures, or even
an adequate realization of the degree of danger
presented (Malenfont, 1996, Hacker, 1987). In
retrospect, the experimental procedures of sci-
entists at the time may seem reckless now, but
considering the context of the time, it is not
clear whether scientists like Slotin should, in-
deed, have known better.
Calloway, L. (1995). Nuclear Naiveté. An Albuquer-
que Journal Special Reprint, July, 1995.
Frisch, O. R. (1969). The Dragon Experiment. Key-
note address at the Fast Burst Reactors Conference
held at the University of New Mexico, Albuquer-
que, January 28–30, 1969. In R. E. Malenfont.
(2005). Experiments with the Dragon Machine. Re-
port LA-14241-H, Los Alamos National Labora-
Frisch, O. R. (1979). What Little I Remember. Cam-
bridge, MA: Cambridge University Press.
Froman, D. K., & Schreiber, R. E. (1946, May 28).
Report on May 21 Accident at Pajarito Labora-
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ley, CA: University of California Press.
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How to Cite this Document
In APA format: Klassen, S. (2015). Tickling the Dragon’s Tail. Publisher: Author. Retrieved from
About the Author
Stephen Klassen is a Senior Scholar at The University of Winnipeg.
His Ph.D. (University of Manitoba) is in Science Education, and his
background is in experimental physics. Dr. Klassen’s research focuses
on the writing, analysis, and use of stories (from the history of science)
in science teaching and the analysis of physics textbooks for their por-
trayal of the history of science. His work, in part, is published in Sci-
ence & Education, Science Education, Interchange, and the Canadian
Journal of Science, Mathematics, and Technology Education. Since
1997, he has presented papers at the International Conference on His-
tory of Science in Science Education (ICHSSE) and has contributed
significantly to its organization, especially in co-chairing the Planning
Committees. As of 2001, he has been actively involved in the Interna-
tional History, Philosophy, and Science Teaching Group (IHPST) by having presented at each of its confer-
ences, having served as Program Chair in 2003, and joining its governing Council from 2010 to 2015 and the
Editorial Committee of Science & Education from 2011 through 2014.