Leo Szilard (; Hungarian: Szilárd Leó [ˈsilaːrd
ˈlɛoː]; born Leó Spitz; February 11, 1898
– May 30, 1964) was a Hungarian-German-American
physicist and inventor. He conceived the nuclear
chain reaction in 1933, patented the idea
of a nuclear reactor with Enrico Fermi in
1934, and in late 1939 wrote the letter for
Albert Einstein's signature that resulted
in the Manhattan Project that built the atomic
bomb.
Szilard initially attended Palatine Joseph
Technical University in Budapest, but his
engineering studies were interrupted by service
in the Austro-Hungarian Army during World
War I. He left Hungary for Germany in 1919,
enrolling at Technische Hochschule (Institute
of Technology) in Berlin-Charlottenburg, but
became bored with engineering and transferred
to Friedrich Wilhelm University, where he
studied physics. He wrote his doctoral thesis
on Maxwell's demon, a long-standing puzzle
in the philosophy of thermal and statistical
physics. Szilard was the first to recognize
the connection between thermodynamics and
information theory.
In addition to the nuclear reactor, Szilard
submitted patent applications for a linear
accelerator in 1928, and a cyclotron in 1929.
He also conceived the idea of an electron
microscope. Between 1926 and 1930, he worked
with Einstein on the development of the Einstein
refrigerator. After Adolf Hitler became chancellor
of Germany in 1933, Szilard urged his family
and friends to flee Europe while they still
could. He moved to England, where he helped
found the Academic Assistance Council, an
organization dedicated to helping refugee
scholars find new jobs. While in England he
discovered a means of isotope separation known
as the Szilard–Chalmers effect.
Foreseeing another war in Europe, Szilard
moved to the United States in 1938, where
he worked with Enrico Fermi and Walter Zinn
on means of creating a nuclear chain reaction.
He was present when this was achieved on December
2, 1942. He worked for the Manhattan Project's
Metallurgical Laboratory on aspects of nuclear
reactor design. He drafted the Szilard petition
advocating a demonstration of the atomic bomb,
but the Interim Committee chose to use them
against cities without warning.
After the war, Szilard switched to biology.
He invented the chemostat, discovered feedback
inhibition, and was involved in the first
cloning of a human cell. He publicly sounded
the alarm against the possible development
of salted thermonuclear bombs, a new kind
of nuclear weapon that might annihilate mankind.
Diagnosed with bladder cancer in 1960, he
underwent a cobalt-60 treatment that he had
designed. He helped found the Salk Institute
for Biological Studies, where he became a
resident fellow. Szilard founded Council for
a Livable World in 1962 to deliver "the sweet
voice of reason" about nuclear weapons to
Congress, the White House, and the American
public. He died in his sleep of a heart attack
in 1964. According to György Marx he was
one of The Martians.
== Early life ==
Born as Leó Spitz in Budapest, Kingdom of
Hungary, on February 11, 1898. His middle-class
Jewish parents, Louis Spitz, a civil engineer,
and Tekla Vidor, raised Leó on the Városligeti
Fasor in Pest. He had two younger siblings,
a brother, Béla, born in 1900, and a sister,
Rózsi (Rose), born in 1901. On October 4,
1900, the family changed its surname from
the German "Spitz" to the Hungarian "Szilárd",
a name that means "solid" in Hungarian. Despite
having a religious background, Szilard became
an agnostic. From 1908 to 1916 he attended
Reáliskola high school in his home town.
Showing an early interest in physics and a
proficiency in mathematics, in 1916 he won
the Eötvös Prize, a national prize for mathematics.
With World War I raging in Europe, Szilard
received notice on January 22, 1916, that
he had been drafted into the 5th Fortress
Regiment, but he was able to continue his
studies. He enrolled as an engineering student
at the Palatine Joseph Technical University,
which he entered in September 1916. The following
year he joined the Austro-Hungarian Army's
4th Mountain Artillery Regiment, but immediately
was sent to Budapest as an officer candidate.
He rejoined his regiment in May 1918 but in
September, before being sent to the front,
he fell ill with Spanish Influenza and was
returned home for hospitalization. Later he
was informed that his regiment had been nearly
annihilated in battle, so the illness probably
saved his life. He was discharged honorably
in November 1918, after the Armistice.In January
1919, Szilard resumed his engineering studies,
but Hungary was in a chaotic political situation
with the rise of the Hungarian Soviet Republic
under Béla Kun. Szilard and his brother Béla
founded their own political group, the Hungarian
Association of Socialist Students, with a
platform based on a scheme of Szilard's for
taxation reform. He was convinced that socialism
was the answer to Hungary's post-war problems,
but not that of Kun's Hungarian Socialist
Party, which had close ties to the Soviet
Union. When Kun's government tottered, the
brothers officially changed their religion
from "Israelite" to "Calvinist", but when
they attempted to re-enroll in what was now
the Budapest University of Technology, they
were prevented from doing so by nationalist
students because they were Jews.Convinced
that there was no future for him in Hungary,
Szilard left for Berlin via Austria on December
25, 1919, and enrolled at the Technische Hochschule
(Institute of Technology) in Berlin-Charlottenburg.
He was soon joined by his brother Béla. Szilard
became bored with engineering, and his attention
turned to physics. This was not taught at
the Technische Hochschule, so he transferred
to Friedrich Wilhelm University, where he
attended lectures given by Albert Einstein,
Max Planck, Walter Nernst, James Franck and
Max von Laue. He also met fellow Hungarian
students Eugene Wigner, John von Neumann and
Dennis Gabor. His doctoral dissertation on
thermodynamics Über die thermodynamischen
Schwankungserscheinungen (On The Manifestation
of Thermodynamic Fluctuations), praised by
Einstein, won top honors in 1922. It involved
a long-standing puzzle in the philosophy of
thermal and statistical physics known as Maxwell's
demon, a thought experiment originated by
the physicist James Clerk Maxwell. The problem
was thought to be insoluble, but in tackling
it Szilard recognized the connection between
thermodynamics and information theory.Szilard
was appointed as assistant to von Laue at
the Institute for Theoretical Physics in 1924.
In 1927 he finished his habilitation and became
a Privatdozent (private lecturer) in physics.
For his habilitation lecture, he produced
a second paper on Maxwell's Demon, Über die
Entropieverminderung in einem thermodynamischen
System bei Eingriffen intelligenter Wesen
(On the reduction of entropy in a thermodynamic
system by the intervention of intelligent
beings), that had actually been written soon
after the first. This introduced the thought
experiment now called the Szilard engine and
became important in the history of attempts
to understand Maxwell's demon. The paper is
also the first equation of negative entropy
and information. As such, it established Szilard
as one of the founders of information theory,
but he did not publish it until 1929, and
did not pursue it further. Claude E. Shannon,
who took it up in the 1950s, acknowledged
Szilard's paper as his starting point.Throughout
his time in Berlin, Szilard worked on numerous
technical inventions. In 1928 he submitted
a patent application for the linear accelerator,
not knowing of Gustav Ising's prior 1924 journal
article and Rolf Widerøe's operational device,
and in 1929 applied for one for the cyclotron.
He also conceived the electron microscope.
Between 1926 and 1930, he worked with Einstein
to develop the Einstein refrigerator, notable
because it had no moving parts. He did not
build all of these devices, or publish these
ideas in scientific journals, and so credit
for them often went to others. As a result,
Szilard never received the Nobel Prize, but
Ernest Lawrence was awarded it for the cyclotron
in 1939 and Ernst Ruska for the electron microscope
in 1986.
== Developing the idea of the nuclear chain
reaction ==
Szilard received German citizenship in 1930,
but was already uneasy about the political
situation in Europe. When Adolf Hitler became
chancellor of Germany on January 30, 1933,
Szilard urged his family and friends to flee
Europe while they still could. He moved to
England, and transferred his savings of £1,595
(£103,900 today) from his bank in Zurich
to one in London. He lived in hotels where
lodging and meals cost about £5/5 a week.
For those less fortunate, he helped found
the Academic Assistance Council, an organization
dedicated to helping refugee scholars find
new jobs, and persuaded the Royal Society
to provide accommodation for it at Burlington
House. He enlisted the help of academics such
as Harald Bohr, G. H. Hardy, Archibald Hill
and Frederick G. Donnan. By the outbreak of
World War II in 1939, it had helped to find
places for over 2,500 refugee scholars.On
September 12, 1933, Szilard read an article
in The Times summarizing a speech given by
Lord Rutherford in which Rutherford rejected
the feasibility of using atomic energy for
practical purposes. The speech remarked specifically
on the recent 1932 work of his students, John
Cockcroft and Ernest Walton, in "splitting"
lithium into alpha particles, by bombardment
with protons from a particle accelerator they
had constructed. Rutherford went on to say:
We might in these processes obtain very much
more energy than the proton supplied, but
on the average we could not expect to obtain
energy in this way. It was a very poor and
inefficient way of producing energy, and anyone
who looked for a source of power in the transformation
of the atoms was talking moonshine. But the
subject was scientifically interesting because
it gave insight into the atoms.
Szilard was so annoyed at Rutherford's dismissal
that he conceived of the idea of nuclear chain
reaction (analogous to a chemical chain reaction),
using recently discovered neutrons. The idea
did not use the mechanism of nuclear fission,
which was not yet discovered, but Szilard
realized that if neutrons could initiate any
sort of energy-producing nuclear reaction,
such as the one that had occurred in lithium,
and could be produced themselves by the same
reaction, energy might be obtained with little
input, since the reaction would be self-sustaining.
The following year he filed for a patent on
the concept of the neutron-induced nuclear
chain reaction. Richard Rhodes described Szilard's
moment of inspiration:
In London, where Southampton Row passes Russell
Square, across from the British Museum in
Bloomsbury, Leo Szilard waited irritably one
gray Depression morning for the stoplight
to change. A trace of rain had fallen during
the night; Tuesday, September 12, 1933, dawned
cool, humid and dull. Drizzling rain would
begin again in early afternoon. When Szilard
told the story later he never mentioned his
destination that morning. He may have had
none; he often walked to think. In any case
another destination intervened. The stoplight
changed to green. Szilard stepped off the
curb. As he crossed the street time cracked
open before him and he saw a way to the future,
death into the world and all our woes, the
shape of things to come.
In early 1934, Szilard began working at St
Bartholomew's Hospital in London. Working
with a young physicist on the hospital staff,
Thomas A. Chalmers, he began studying radioactive
isotopes for medical purposes. It was known
that bombarding elements with neutrons could
produce either heavier isotopes of an element,
or a heavier element, a phenomenon known as
the Fermi Effect after its discoverer, the
Italian physicist Enrico Fermi. When they
bombarded ethyl iodide with neutrons produced
by a radon–beryllium source, they found
that the heavier radioactive isotopes of iodine
separated from the compound. Thus, they had
discovered a means of isotope separation.
This method became known as the Szilard–Chalmers
effect, and was widely used in the preparation
of medical isotopes. He also attempted unsuccessfully
to create a nuclear chain reaction using beryllium
by bombarding it with X-rays. In 1936, Szilard
assigned his chain-reaction patent to the
British Admiralty to ensure its secrecy.
== Manhattan Project ==
=== 
Columbia University ===
Szilard visited Béla and Rose and her husband
Roland (Lorand) Detre, in Switzerland in September
1937. After a rainstorm, he and his siblings
spent an afternoon in an unsuccessful attempt
to build a prototype collapsible umbrella.
One reason for the visit was that he had decided
to emigrate to the United States, as he believed
that another war in Europe was inevitable
and imminent. He reached New York on the liner
RMS Franconia on January 2, 1938. Over the
next few months he moved from place to place,
conducting research with Maurice Goldhaber
at the University of Illinois at Urbana–Champaign,
and then the University of Chicago, University
of Michigan and the University of Rochester,
where he undertook experiments with indium
but again failed to initiate a chain reaction.
In November 1938, Szilard moved to New York
City, taking a room at the King's Crown Hotel
near Columbia University. He encountered John
R. Dunning, who invited him to speak about
his research at an afternoon seminar in January
1939. That month, Niels Bohr brought news
to New York of the discovery of nuclear fission
in Germany by Otto Hahn and Fritz Strassmann,
and its theoretical explanation by Lise Meitner,
and Otto Frisch. When Szilard found out about
it on a visit to Wigner at Princeton University,
he immediately realized that uranium might
be the element capable of sustaining a chain
reaction.Unable to convince Fermi that this
was the case, Szilard set out on his own.
He obtained permission from the head of the
Physics Department at Columbia, George B.
Pegram, to use a laboratory for three months.
To fund his experiment, he borrowed $2,000
from a fellow inventor, Benjamin Liebowitz.
He wired Frederick Lindemann at Oxford and
asked him to send a beryllium cylinder. He
convinced Walter Zinn to become his collaborator,
and hired Semyon Krewer to investigate processes
for manufacturing pure uranium and graphite.Szilard
and Zinn conducted a simple experiment on
the seventh floor of Pupin Hall at Columbia,
using a radium–beryllium source to bombard
uranium with neutrons. Initially nothing registered
on the oscilloscope, but then Zinn realized
that it was not plugged in. On doing so, they
discovered significant neutron multiplication
in natural uranium, proving that a chain reaction
might be possible. Szilard later described
the event: "We turned the switch and saw the
flashes. We watched them for a little while
and then we switched everything off and went
home." He understood the implications and
consequences of this discovery, though. "That
night, there was very little doubt in my mind
that the world was headed for grief".While
they had demonstrated that the fission of
uranium produced more neutrons than it consumed,
this was still not a chain reaction. Szilard
persuaded Fermi and Herbert L. Anderson to
try a larger experiment using 500 pounds (230
kg) of uranium. To maximize the chance of
fission, they needed a neutron moderator to
slow the neutrons down. Hydrogen was a known
moderator, so they used water. The results
were disappointing. It became apparent that
hydrogen slowed neutrons down, but also absorbed
them, leaving fewer for the chain reaction.
Szilard then suggested Fermi use carbon, in
the form of graphite. He felt he would need
about 50 tonnes (49 long tons; 55 short tons)
of graphite and 5 tonnes (4.9 long tons; 5.5
short tons) of uranium. As a back-up plan,
Szilard also considered where he might find
a few tons of heavy water; deuterium would
not absorb neutrons like ordinary hydrogen,
but would have the similar value as a moderator.
Such quantities of materiel would require
a lot of money.Szilard drafted a confidential
letter to the President, Franklin D. Roosevelt,
explaining the possibility of nuclear weapons,
warning of the German nuclear weapon project,
and encouraging the development of a program
that could result in their creation. With
the help of Wigner and Edward Teller, he approached
his old friend and collaborator Einstein in
August 1939, and convinced him to sign the
letter, lending his fame to the proposal.
The Einstein–Szilárd letter resulted in
the establishment of research into nuclear
fission by the U.S. government, and ultimately
to the creation of the Manhattan Project.
Roosevelt gave the letter to his aide, Brigadier
General Edwin M. "Pa" Watson with the instruction:
"Pa, this requires action!"An Advisory Committee
on Uranium was formed under Lyman J. Briggs,
a scientist and the director of the National
Bureau of Standards. Its first meeting on
October 21, 1939, was attended by Szilard,
Teller, and Wigner, who persuaded the Army
and Navy to provide $6,000 for Szilard to
purchase supplies for experiments—in particular,
more graphite. A 1940 Army intelligence report
on Fermi and Szilard, prepared when the United
States had not yet entered World War II, expressed
reservations about both. While it contained
some errors of fact about Szilard, it correctly
noted his dire prediction that Germany would
win the war.Fermi and Szilard met with representatives
of National Carbon Company, who manufactured
graphite, and Szilard made another important
discovery. He asked about impurities in graphite,
and learned that it usually contained boron,
a neutron absorber. He then had special boron-free
graphite produced. Had he not done so, they
might have concluded, as the German nuclear
researchers did, that graphite was unsuitable
for use as a neutron moderator. Like the German
researchers, Fermi and Szilard still believed
that enormous quantities of uranium would
be required for an atomic bomb, and therefore
concentrated on producing a controlled chain
reaction. Fermi determined that a fissioning
uranium atom produced 1.73 neutrons on average.
It was enough, but a careful design was called
for to minimize losses. Szilard worked up
various designs for a nuclear reactor. "If
the uranium project could have been run on
ideas alone," Wigner later remarked, "no one
but Leo Szilard would have been needed."
=== Metallurgical Laboratory ===
The December 6, 1941, meeting of the National
Defense Research Committee resolved to proceed
with an all-out effort to produce atomic bombs,
a decision given urgency by the Japanese attack
on Pearl Harbor the following day that brought
the United States into World War II, and then
formal approval by Roosevelt in January 1942.
Arthur H. Compton from the University of Chicago
was appointed head of research and development.
Against Szilard's wishes, Compton concentrated
all the groups working on reactors and plutonium
at the Metallurgical Laboratory of the University
of Chicago. Compton laid out an ambitious
plan to achieve a chain reaction by January
1943, start manufacturing plutonium in nuclear
reactors by January 1944, and produce an atomic
bomb by January 1945.In January 1942, Szilard
joined the Metallurgical Laboratory in Chicago
as a research associate, and later the chief
physicist. Alvin Weinberg noted that Szilard
served as the project "gadfly", asking all
the embarrassing questions. Szilard provided
important insights. While uranium-238 did
not fission readily with slow, moderated neutrons,
it might still fission with the fast neutrons
produced by fission. This effect was small
but crucial. Szilard made suggestions that
improved the uranium canning process, and
worked with David Gurinsky and Ed Creutz on
a method for recovering uranium from its salts.A
vexing question at the time was how a production
reactor should be cooled. Taking a conservative
view that every possible neutron must be preserved,
the majority opinion initially favored cooling
with helium, which would absorb very few neutrons.
Szilard argued that if this was a concern,
then liquid bismuth would be a better choice.
He supervised experiments with it, but the
practical difficulties turned out to be too
great. In the end, Wigner's plan to use ordinary
water as a coolant won out. When the coolant
issue became too heated, Compton and the director
of the Manhattan Project, Brigadier General
Leslie R. Groves, Jr., moved to dismiss Szilard,
who was still a German citizen, but the Secretary
of War, Henry L. Stimson, refused to do so.
Szilard was therefore present on December
2, 1942, when the first man-made self-sustaining
nuclear chain reaction was achieved in the
first nuclear reactor under viewing stands
of Stagg Field, and shook Fermi's hand.Szilard
became a naturalized citizen of the United
States in March 1943. The Army offered Szilard
$25,000 for his inventions before November
1940, when he officially joined the project.
He refused. He was the co-holder, with Fermi,
of the patent on the nuclear reactor. In the
end he sold his patent to the government for
reimbursement of his expenses, some $15,416,
plus the standard $1 fee. He continued to
work with Fermi and Wigner on nuclear reactor
design, and is credited with coining the term
"breeder reactor".With an enduring passion
for the preservation of human life and political
freedom, Szilard hoped that the U.S. government
would not use nuclear weapons, but that the
mere threat of such weapons would force Germany
and Japan to surrender. He also worried about
the long-term implications of nuclear weapons,
predicting that their use by the United States
would start a nuclear arms race with Russia.
He drafted the Szilard petition advocating
demonstration of the atomic bomb. The Interim
Committee instead chose to use atomic bombs
against cities over the protests of Szilard
and other scientists. Afterwards, he lobbied
for amendments to the Atomic Energy Act of
1946 that placed nuclear energy under civilian
control.
== After the war ==
In 1946, Szilard secured a research professorship
at the University of Chicago that allowed
him to dabble in biology and the social sciences.
He teamed up with Aaron Novick, a chemist
who had worked at the Metallurgical Laboratory
during the war. The two men saw biology as
a field that had not been explored as much
as physics, and was ready for scientific breakthroughs.
It was a field that Szilard had been working
on in 1933 before he had become subsumed in
the quest for a nuclear chain reaction. The
duo made considerable advances. They invented
the chemostat, a device for regulating the
growth rate of the microorganisms in a bioreactor,
and developed methods for measuring the growth
rate of bacteria. They discovered feedback
inhibition, an important factor in processes
such as growth and metabolism. Szilard gave
essential advice to Theodore Puck and Philip
I. Marcus for their first cloning of a human
cell in 1955.Before relation with his later
wife Gertrud Weiss, Leo Szilard's life partner
in the period 1927 – 1934 was kindergarten
teacher and opera singer Gerda Philipsborn,
who also worked as a volunteer in a Berlin
asylum organization for refugee children and
in 1932 moved to India to continue in this
work. Szilard married Gertrud (Trude) Weiss,
a physician, in a civil ceremony in New York
on October 13, 1951. They had known each other
since 1929, and had frequently corresponded
and visited each other ever since. Weiss took
up a teaching position at the University of
Colorado in April 1950, and Szilard began
staying with her in Denver for weeks at a
time when they had never been together for
more than a few days before. Single people
living together was frowned upon in the conservative
United States at the time, and after they
were discovered by one of her students, Szilard
began to worry that she might lose her job.
Their relationship remained a long-distance
one, and they kept news of their marriage
quiet. Many of his friends were shocked when
they found out, as it was widely believed
that Szilard was a born bachelor.
In 1949 Szilard wrote a short story titled
"My Trial as a War Criminal" in which he imagined
himself on trial for crimes against humanity
after the United States lost a war with the
Soviet Union. He publicly sounded the alarm
against the possible development of salted
thermonuclear bombs, explaining in radio talk
on February 26, 1950, that sufficiently big
thermonuclear bomb rigged with specific but
common materials, might annihilate mankind.
While Time magazine compared him to Chicken
Little, and the Atomic Energy Commission dismissed
the idea, scientists debated whether it was
feasible or not. The Bulletin of the Atomic
Scientists commissioned a study by James R.
Arnold that concluded that it was.Szilard
published a book of short stories, The Voice
of the Dolphins (1961), in which he dealt
with the moral and ethical issues raised by
the Cold War and his own role in the development
of atomic weapons. The title story described
an international biology research laboratory
in Central Europe. This became reality after
a meeting in 1962 with Victor F. Weisskopf,
James Watson and John Kendrew. When the European
Molecular Biology Laboratory was established,
the library was named The Szilard Library
and the library stamp features dolphins. Other
honors that he received included the Atoms
for Peace Award in 1959, and the Humanist
of the Year in 1960. A lunar crater on the
far side of the Moon was named after him in
1970. The Leo Szilard Lectureship Award, established
in 1974, is given in his honor by the American
Physical Society.In 1960, Szilard was diagnosed
with bladder cancer. He underwent cobalt therapy
at New York's Memorial Sloan-Kettering Hospital
using a cobalt 60 treatment regimen that he
designed himself. A second round of treatment
with an increased dose followed in 1962. The
doctors tried to tell him that the increased
radiation dose would kill him, but he said
it wouldn't, and that anyway he would die
without it. The higher dose did its job and
his cancer never returned. This treatment
became standard for many cancers and is still
used.Szilard spent his last years as a fellow
of the Salk Institute for Biological Studies
in La Jolla, California, which he had helped
to create. He was appointed a non-resident
fellow there in July 1963, and became a resident
fellow on April 1, 1964, after moving to La
Jolla in February. With Trude, he lived in
a bungalow on the property of the Hotel del
Charro. On May 30, 1964, he died there in
his sleep of a heart attack; when Trude awoke,
she was unable to revive him. His remains
were cremated.His papers are in the library
at the University of California in San Diego.
In February 2014, the library announced that
they received funding from the National Historical
Publications and Records Commission to digitize
its collection of his papers, extending from
1938 to 1998.
== Patents ==
GB 630726 —Improvements in or relating to
the transmutation of chemical elements—L.
Szilard, filed June 28, 1934
U.S. Patent 2,708,656—Neutronic reactor—E.
Fermi, L. Szilard, filed December 19, 1944,
issued May 17, 1955
U.S. Patent 1,781,541—Einstein Refrigerator—co-developed
with Albert Einstein filed in 1926, issued
November 11, 1930
== Recognition and remembrance ==
Atoms for Peace Award, 1959
Albert Einstein Award, 1960
American Humanist Association's Humanist of
the Year, 1960
Szilard (crater) on the back side of the Moon,
named in 1970
Leo Szilard Lectureship Award, since 1974
Asteroid 38442 Szilárd discovered in 1999
Leószilárdite, mineral, reported in 2016
== Notes
