Unformatted text preview: Chapter 2 GERMAN NUCLEAR PROGRAM
© M. Ragheb
11/20/2008 2.1 INTRODUCTION
In December of 1938, the German radiochemist Otto Hahn, born in Frankfurt am
Main, Germany in 1879, and Fritz Strassmann, an inorganic chemist born in Boppard,
Germany in 1902, were the first to discover the nuclear fission process and the splitting
of the nucleus of uranium. They were both awarded the Nobel Prize in Chemistry for it
in 1944. Fig. 1: Otto Hahn, discoverer of nuclear fission.
The views of historians and authors about the German Nuclear Program during
World War II differ substantially.
Some German scientists claimed that they did not want to hand the Nazi regime a
horrible weapon, based on moral considerations. Another view was that accidental fires
with powdered uranium used in the first subcritical assemblies that they built discouraged
them. Inaccurate calculations about the lattice parameters in a heavy water moderated
thermal subcritical assembly misled them. The inability to secure sufficient heavy water
from Norway due to bombings raids and sabotage, or to manufacture it in Germany,
blocked their progress. Some of them used the nuclear research as a pretext to protect
themselves and their coworkers from being sent to the killing fields at the battle fronts.
Other did not want to make unachievable claims about projects they were not confident
could be carried out to a successful end, and be punished if they failed.
Nevertheless, the German nuclear program did in fact build a thermal heavy water
moderated natural uranium subcritical assembly that did not achieve criticality for lack of sufficient heavy water moderator and natural uranium fuel. This is in contrast to the
graphite moderated critical reactors built on a large industrial scale, and the fast
assemblies leading to the construction of nuclear weapons in the USA.
The brain drain of a large number of German scientists to the UK and the USA,
caused by the then prevalent religious fanaticism and racism, and unfair treatment, as
well as some German scientists’ overconfidence bordering on arrogance, thinking that
they knew better than their American and British counterparts, doomed them to failure.
The end result was that they never realized that criticality can be achieved in a
fast neutron assembly and limited their effort to a thermal neutron heavy water moderated
subcritical experiment that never achieved criticality up to the end of the war. 2.2 THE BRITISH MAUD COMMITTEE
Lise Meitner, a theoretical physicist, born in Vienna, Austria in 1878, who had
worked and corresponded with Otto Hahn, learned from him about the fission process
after leaving Germany to England. She communicated the news to Niels Bohr in
Denmark and with her nephew Otto Robert Frisch, a theoretical physicist born in Vienna,
Austria in 1904, developed a theoretical description and the naming of the process of
In the UK Rudolph Peierls, a theoretical physicist and Otto Frisch wrote a
“Memorandum on the Properties of a Radioactive Super Bomb” using nuclear fission.
Frisch at the University of Birmingham under Mark Oliphant, had worked on the process
of gaseous diffusion, and Peierls on the calculation of critical masses.
Mark Oliphant submitted the memorandum to the British Government which
formed the Military Applications of Uranium Disintegration (MAUD) committee to study
the military applications of nuclear fission.
A team of German scientists, led by the theoretical physicist Werner Heisenberg,
born in Wurzburg, Germany in 1901, collected and stockpiled uranium and heavy water
and built subcritical assemblies but did not achieve a self sustained chain reaction.
Heisenberg had pioneered the field Quantum Mechanics for which he won the
Nobel Prize in Physics in 1932. He met with Niels Bohr in a failed attempt to reassure
him that the efforts of his team were not directed toward the development of a weapon.
Carl Friedrichs von Weizäcker came the closest to conceptualizing a weapon by
discussing the production of Neptunium239, but not the more potent Np237, in a heavy
water subcritical assembly which never achieved criticality until the end of the war.
Harteck and Groth built a laboratory experiment for using an ultracentrifuge for
separating U235 from uranium that also did not reach an industrial stage. Fig. 2: Carl Friedrichs von Weizäcker.
The MAUD committee recommendations were communicated to the USA
President Franklin D. Roosevelt in 1941. Although World War II had not yet started, the
discovery of nuclear fission ultimately led to the formation of the Manhattan District
Project, the USA government's secret project to build the bomb. 2.3 ALSOS TEAM MISSIONS
In the last days before the end of World War II, undercover Allied special agents
engaged in a frantic race across Europe, sometimes against each other, to capture the best
and brightest of Germany's scientific community. With the German army in retreat,
American, British, and Russian forces set their sights on the architects of the so called
advanced Vengeance Weapons. These included high technology jet and rocket airplanes,
rockets, laboratory experiments, stockpiles of uranium in different forms and a subcritical
heavy water moderated assembly. Fig. 3: Leipzig subcritical assembly showing a neutron source at the center with
heavy water as a neutron moderator and natural uranium powder as a fuel.
The reasoning behind the mission was that whoever captured the scientists, the
archives and the technology, was expected to gain a major scientific and technological
advantage in the looming Cold War. Another goal of the mission was to deny this
perceived advantage to the Russians and French. This assessment proved correct for the
USA in the enticement of Werner von Braun and most of his team in the establishment of
its space and Intercontinental Ballistic Missile Program (ICBM).
The USA military launched the Alsos mission to search Germany not just for its
scientists like von Braun and Heisenberg and their teams, but also their experiments,
equipment and laboratories and any stockpiled strategic materials such as gold, silver,
copper and uranium. One such experiment was a subcritical assembly of natural uranium
powder and heavy water designated as the Leipzig experiment.
The mission consisted of undercover special agents and led by Lieutenant Colonel
Boris T. Pash, and as scientific leader Sam Goudsmit. It was code named Alsos, the
Greek word for “grove,” as in “tree grove” in honor of General Leslie R. Groves, the head of the Manhattan Project. The mission followed immediately in the wake of, and
sometimes ahead of the allied armies invading Europe.
When the German scientists first discovered fission, the USA and UK worried
that Germany could develop a nuclear device, and this was the main incentive for the
initiation of the MAUD committee in the UK and the Manhattan project in the USA.
Those paranoid fears, based on overzealous and faulty intelligence were totally dispelled
just weeks before the end of the war. The special agents of the American Alsos team
discovered a German subcritical assembly under construction in a cave beneath a castle at
Haigerloch, Germany, but no functional reactor. Intentionally, or unintentionally
uninformed about the residual radiation hazard, they promptly dismantled by hand the
assembly which consisted of wire suspended natural uranium cubes in a heavy water
moderator contained in a steel vessel. Fig. 4: The Alsos team dismantling by hand the heavy water subcritical assembly at
Haigerloch, Germany. Fig. 5: Diagram of heavy water subcritical assembly. Fig. 6: Lid with wire suspended natural uranium cubes pulled out from the heavy
water moderator vessel of the Haigerloch subcritical assembly. It was realized that he German nuclear scientists in 1945 were no farther along in
their nuclear program than the Americans had been back three years earlier in 1942.
With interrogation and enticements of the scientists, a few days later, buried in a nearby
field, the agents uncovered a cache of about two metric tonnes of natural uranium. The
mission also tracked down and secured amounts of uranium in different chemical forms
in France, Belgium, and Germany. This uranium was shipped to the Manhattan Project
for use in the American nuclear weapon effort.
A first mission code named Alsos I headed to Italy in December 1943, but gained
little information of interest, due in part to the slow progress of the Allies forces advance
A second mission designated as Alsos II followed the Allies forces advance from
France to Germany in 1944 and 1945. It consisted of seven military officers and 22
Interrogation of the French and German scientists combined with the investigation
of laboratories confirmed that the German program was never close to producing an
atomic device, let alone even achieving a self sustained critical chain reaction. 2.4 HEISENBERG’S BACKGROUND
Werner Heisenberg (1901–1976) is considered to have led the German nuclear
program during World War II. He is known for his formulation of the uncertainty
principle in quantum mechanics and its physical interpretation in 1927. He had the
insight that quantum mechanical variables do not commute. Fig. 7: Werner Heisenberg, (1901-1976).
A 20 years of age, and well before the introduction of electron spin, Heisenberg
made the proposal to allow half-integral quantum numbers in the context of the Zeeman
effect. He was awarded the 1932 Nobel Prize “For the creation of quantum mechanics,
the application of which has led, among other things, to the discovery of the allotropic
forms of hydrogen.” He provided the quantum-mechanical explanation of the occurrence of para and
ortho helium and provided an explanation for ferromagnetism. His most important work
is the foundation of quantum field theory with Pauli. He became one of the founders of
theoretical nuclear physics with a description of the interactions between protons and
neutrons in a nucleus.
He went out of his way and used his influence to help his own students and
collaborators, both in peacetime and during the war, sometimes at risk to himself. Some
of them avoided death at the European and Asian fronts by being enlisted by Heisenberg
in his nuclear research program. At one point he had to face treason accusations by his
political opponents as a “White Jew.” He was investigated and cleared of the charges.
From a totally opposite perspective, he was also accused of reaching a Faustian pact with
the devil for his refraining from emigration like many other German scientists, and for
participating in the German nuclear program.
He tried his best during the war in preventing the German forces from destroying
physics laboratories such as at the University of Leiden and of Bohr’s institute in
Copenhagen, Denmark. He implied that he steered the German nuclear program toward
nuclear energy and scientific applications and away from weaponization. 2.5 THE URANIUM CLUB, URANVEREIN
In September 1939, Heisenberg was recruited to the German nuclear research
team known as “Uranverein” or “Uranium Club” by an order from the German military.
This team was assembled by Kurt Diebner, a competitor to Heisenberg on behalf of the
Heereswaffenamt (HWA) or Army Ordnance Office.
The formation of the Uranium Club followed suggestions by the physical chemist
and explosives expert Paul Harteck (1902–1985) and others that Germany should
investigate the possible relevance of nuclear energy to the war effort. Harteck built a
single stage ultra centrifuge experiment for the enrichment of uranium of scientific but no
industrial relevance. Fig. 8: Paul Harteck built an experimental centrifuge.
Kurt Diebner (1905–1964) was an experimental physicist who played a central
role in the German nuclear project. During the war he was the principal scientific
administrator of the project, simultaneously holding the positions of military adviser to
the HWA on nuclear physics, director of the Nuclear Research Council or
Kernforschungsrat, and managing director of the Kaiser Wilhelm Institute for Physics.
He ran his own subcritical experiments, in direct competition with Heisenberg. Diebner
was a Nazi party member, and was held in contempt by Heisenberg, maybe because he
was an experimentalist with ideas on experimental designs that were more successful
Heisenberg obeyed the order and generated a report on “The possibility of
technical energy production from Uranium fission,” which laid the theoretical
foundations for the subsequent research in Germany on that topic. The report correctly
foresaw that a nuclear reactor could be built in two qualitatively different ways, each
posing its own difficulties. In the first approach one could use either use enriched
uranium and an easily obtained moderator such as ordinary water, or one could adopt
natural uranium in association with heavy water or extremely pure graphite as a
moderator. He emphasized nuclear power production and not weapons production.
The use of graphite as a moderator was not pursued due to a miscalculation in
estimating its absorption cross section to neutrons, and the German team had only two
options left. Various isotopic separation projects such as centrifuge enrichment, as well
as a number of methods to produce heavy water, were pursued, principally by Paul
Harteck. 2.6 INTERNMENT AT FARM HALL, INTELLIGENT
The German nuclear research project was interrupted by heavy Allied bombing
and sabotage of Germany’s supply of heavy water from Norway. A subcritical
moderated assembly never achieved criticality all the way to the last days of the war.
Ten of the German nuclear physicists, including Heisenberg were taken prisoners
by the Allies between May and December 1945. To sanitize their detention, they were
designated as “interns” and kept during the last six months at a country estate, Farm Hall,
near Cambridge in England. Fig. 9: Unworkable diagram of a gun barrel design for a plutonium device of
alleged German origin. The design is unachievable since plutonium requires an
implosion process to attain supercriticality. Possibly drawn by some unknown
individual after the war. Source: Nova.
Using a sophisticated way of extracting information, the British did not use
torture, dogs, water boarding, nor sexual humiliation or coercion à la Abu Ghraib,
Bagram and Guantanamo Bay styles against them. In a smart interrogation fashion, they
treated them with the utmost respect and called them interns instead of prisoners. They nicely housed and generously dined and wined them. However, their conversations were
cleverly and secretly monitored and recorded and were made public in 1992. At Farm
Hall, the internees produced a carefully drafted statement in their own defense whose
main point was that: “It was the view of the researchers that the resources for the
production of a bomb were not available in the context of the technical possibilities
prevailing in Germany.” They seem to be hedging their bets so as not to be considered as
traitors who sabotaged the effort by the defeated Germans and not as war criminals by the
From the Farm Hall transcripts, Heisenberg and his German colleagues believed
that their knowledge about nuclear technology and its possible military uses was superior
to that of the Allied scientists. Their belief was shattered by the BBC News at 9 pm on
August 6, 1945, announcing the nuclear bombing of Hiroshima.
Heisenberg suggested on various occasions in an ambiguous manner that he had
actually actively withheld the bomb from the German leaders. This line was defended
more vigorously by von Weizsäcker.
Heisenberg’s published writings on the German nuclear project emphasized that
its goal had been the “Technical utilization of atomic energy.” He stated that “The
project could not have succeeded under German war conditions. To obtain the necessary
support, the experts would have been obliged to promise early results, knowing that these
promises could not be kept. Faced with this situation, the experts did not attempt to
advocate with the supreme command a great industrial effort for the production of atomic
At Farm Hall Heisenberg said: “We wouldn’t have had the moral courage to
recommend to the government in the Spring of 1942 that they should employ 120,000
men just to build that thing up.” He also said: “Well, how have they actually done it? I
find it is a disgrace if we, the professors who have worked on it, cannot at least work out
how they did it.” 2.7 GOUDSCHMIT ROLE
Sam Goudschmit (1902-1978), was an emigrant scientist from Brookhaven
National Laboratory (BNL) in the USA who was assigned as scientific head to the Alsos
project which was a scientific intelligence mission that followed the Allied troops in the
wake of their invasion of Europe. Its initial goal was to ‘”Learn as soon as we could
what the Germans might be able to do if they exerted every possible effort to produce an
After it had become clear that nothing of substance was to be feared, its goal
evolved into keeping whatever scientists and scientific equipment that would be of any
military value out of the hands of the Russian and French. Reporting directly to General
Leslie Groves in the USA, its military commander in Europe was Boris Pash, and its
scientific head was Sam Goudschmit.
A plea was made by Goudschmit to Heisenberg in 1943 for help in saving his
Jewish parents from deportation and almost certain death in a concentration camp. Short
of approaching Himmler this time or any German authority in Germany or Holland,
Heisenberg merely sent a letter of support to Goudschmit’s colleague, Coster. As pointed out by Goudschmit himself, it is doubtful that any action by Heisenberg would have been
effective in his parents’ sad tragedy.
The internment of Heisenberg and other German nuclear physicists at Farm Hall
in 1945 was part of the Alsos work. A purpose of Farm Hall was to prepare the German
scientists for reintegration into the zones of Germany that, after the war, were occupied
by the UK and by the USA.
Goudschmit wrote three popular articles and a book about the Alsos mission,
which served as a point of reference for all later assessments of the German wartime
His conclusions were that the German nuclear project had not achieved even the
basics of understanding nuclear weapons, and that it had failed because of the totalitarian
climate in Germany, complacency, the interference of politicians in the affairs of science,
particularly of “utterly incompetent” key men in administrative positions, the
deterioration of interest in pure science and its lack of prestige, the anti Semitism doctrine
of the Nazis that led to the exile and migration of notable scientists, the lack of vision of
the German scientists, and, finally, because of the role of hero worship.
This specifically refers to Heisenberg, who is portrayed as holding competent
research groups, such as those lead by Ardenne and Diebner, in contempt. At the same
time, Heisenberg’s own erroneous judgments and decisions, of which there were many
according to Goudschmit, were hardly openly questioned by the other German
researchers. Heisenberg is portrayed as a man of ideals, and as a fierce nationalist who
had put his support for any German cause ahead of his dislike of the Nazis.
Heisenberg seemed far more worried about accusations that he had not
understood bomb physics than about criticism of his general behavior during the Nazi
era. It appears that Heisenberg did not understand how his courageous behavior during
the Nazi era, which he contrasted with the treason of emigration, could possibly be the
subject of controversy. 2.8 HEISENBERG AND NIELS BOHR MEETING
Heisenberg met Niels Bohr in September 1941. The accounts about that meeting
have been contradictory. Bohr stated about the meeting that he remembers quite clearly
that Heisenberg was confident that Germany would win the war, and that Heisenberg had
made it clear to him that he was leading a German program to develop atomic weapons,
with whose details he claimed to be completely familiar. Niels Bohr communicated this
opinion to the UK and the USA, and this contributed to the decision to initiate the
von Weizsäcker responded about this statement with: ‘‘Bohr’s memory is deeply
mistaken.” He asserted that he, Heisenberg, and other German scientists had already
stopped their work on an atomic weapon in September 1941, and that Heisenberg had
tried to persuade Bohr that the USA and the UK should not build atomic weapons either,
an option Bohr allegedly refused to consider.
Bohr agreed with Heisenberg that no technical discussions took place, and that
Heisenberg refrained from pumping Bohr for information. 2.9 BAGGE AND DIEBNER ACCOUNT Erich Bagge (1912) was a theoretical physicist who had written his thesis with
Heisenberg, but who later became closely associated with Diebner, politically as well as
scientifically. He was a member of both the Nazi party and the Dozentenbund. During
his internment at Farm Hall, he kept a diary which was later turned into a book.
Bagge and Diebner state their views on the German nuclear project claiming that
the crucial error was the HWA’s requirement in December 1941 that something of
immediate military use should emerge from the nuclear research project within 9 months.
Following the physicists’ clarification that this would be impossible, the consequent
transfer of authority from the HWA to the Reichsforschungsrat (RFR) or National
Research Council, and the appointment of the technical physicist Abraham Esau as the
man in charge, sealed the fate of a possible German nuclear device, despite the fact that
almost simultaneously the RFR was placed under Goring’s supervision.
Esau was followed later by Speer as head of the RFR but had nothing to do with
these decisions since he became involved with the project only in the Spring of 1942.
There is no mention by Bagge and Diebner of Heisenberg’s encounter with Speer in June
1942, which according to Heisenberg had been the pivotal meeting leading to Speer’s,
and not the HWA’s, decision to assign a relatively low profile to the German nuclear
project. This corresponds to Heisenberg’s perception that he was the main figure in the
project and he possessed the power to influence the cardinal decision to step up the
project to industrial proportions.
Bagge and Diebner maintained that Goudsmit was incorrect in his statements that
the Germans had failed to recognize that a bomb could be made from plutonium, a point
that had earlier been made by Heisenberg in his correspondence with Goudsmit.
In their failed attempts to at least build a critical assembly, Bagge and Diebner
blamed the repeated Allied attacks on the Norske Hydro factory at Rjukan, the main
source of heavy water for the German project, for their failure. Rivalry and
disagreements about the subcritical assembly design between Heisenberg’s group and
Diebner’s also led to failure. 2.10 THE VIRUS HOUSE
In the book: Virus House, David Irving, a controversial British citizen author
wrote about the German nuclear project. He got himself employed as a factory worker in
Germany to perfect his mastery of the German language. This gave him access to the
German documents, literature and publications about the World War II seized by the
USA. He used that capability to translate the documents and was able to publish several
books about various aspects of the Third Reich, some of which became best sellers.
Even though an Anglo Saxon, his books reflect the German perspective about
World War II. His first book describes the fire storm bombing of Dresden. Another
book: “The Virus House,” was the first full study of the German Uranium project. It is
based on thousands of documents, many of which were unearthed by Irving himself, as
well as on interviews and correspondence with the main actors.
The bombings, raids and sabotage of the Norske Hydro plant producing heavy
water for the German nuclear project are described in detail. Paul Harteck is placed in the center stage instead of Heisenberg. Irving is of the
opinion that the German nuclear scientists failure to “Fire Speer’s imagination with the
possibilities of nuclear fission” as their greatest shortcoming. Irving suggests that the
German scientists “Given the funds, the men, and the materials, could certainly have
produced an atomic bomb for Germany.” He blames the slow pace of the project on the
fact that the project was directed by scientists and not by the military, as in the USA: “In
short, the behavior of the German scientific leaders demonstrated that during war, science
cannot be safely left to scientists.” He blames its failure on the emphasis on theory with
direct reference to Heisenberg, whom he implies intentionally sabotaged the project by
slowing it down and directing it into unpromising directions. Fig. 10: Ultra centrifuge experimental setup by Harteck and Groth.
Heisenberg’s commented: “Irving’s book is a very good book in the sense that it
gives all the facts or practically all the facts. But it has one deficiency. When he tries to
determine motives he does not do very well because he cannot think himself into the
atmosphere of a totalitarian country making war.”
Irving follows Heisenberg’s version of the events, such as in his emphasis on
incorrect measurements by Bothe of the graphite nuclear properties. The measurements
were in impure graphite leading to a large absorption cross section for neutrons, which
precluded its use as a moderator instead of heavy water in the German program, whilst it
was used in the USA program. He describes the subsequent decision to continue with
heavy water as a moderator. He sides with Heisenberg’s claims against those of
Goudsmit, that he had fully understood the principles of the atomic bomb.
Irving discards the suggestion by many German scientists that they did not pursue
the bomb because they did not want it on moral principles. He wrote that: “There is no
indication that at any stage in the logical process of development the scientists’ scruples
would have become powerful enough to overcome their natural curiosity to see what
came next.” 2.11 HEISENBERG’S PERSPECTIVE
In his autobiography: “Der Teil und das Ganze” or “Physics and Beyond,”
Heisenberg relates conversations between himself and some of his friends on the
principal themes that occupied his mind. He states that he saw National Socialism as a
catastrophe right from the beginning, which could only lead to the destruction of
Germany. He relates a conversation in 1939 with Fermi, Goudsmit, and other colleagues
in the USA, in which he expressed no doubt whatsoever that Germany would lose the
Heisenberg maintains that the German physicists had fully understood applied
nuclear physics with regard to both reactors and bombs. Heisenberg denies the fact that
the German scientists basically told their military all they knew, even about fast neutrons.
This implies that a German nuclear device was never built because the German
politicians and military officials, based on information provided by their scientists,
decided that it would not be possible before the end of the war, and allocated their limited
resources to what they perceived as more promising concepts such as military airplanes
Heisenberg saw himself as the originator of the decision not to proceed in the
direction of building a weapon which he subsequently placed it in the hands of Speer. 2.12 HEISENBERG MISCALCULATION
In the book: “Heisenberg and the Nazi Atomic Bomb Project: A Study in German
Culture,” P. L. Rose advances a thesis about the German nuclear project that was
repeated a number of times. He suggests that in 1940 Heisenberg incorrectly estimated
or calculated the critical mass of a pure U235 device, obtaining an answer in the order of
tons or thousands of kilograms, instead of the correct value of 15-56 kg; depending on
whether the assembly was bare or had a reflector/tamper as shown in Table 2.
Table 1: Critical masses for bare and reflected U235 and Pu239. Bare
Infinite U Reflector/Tamper U235
5 His mistake was probably based on the misconception that a nuclear explosive
reaction would only occur by creating a supercritical condition in a moderated assembly
such as what he built with heavy water and natural uranium, instead of a fast assembly
consisting of separated metallic U235 or Pu239.
This may have precluded him from recommending a serious effort on the atomic
weapons problem. Rose suggests that this was the true reason why Germany failed to
achieve the bomb, and it was a situation that the Heisenberg version events tried to
conceal. Rose’s conclusion is that the explanation must be “Grounded in the peculiarities
of the German mentality,” in particular in the “German capacity for self-delusion, a trait
exemplified to an astonishing degree in Heisenberg himself.”
Rose confirms what Goudsmit had said that as far as nuclear weapons were
concerned, the German scientists never got beyond some very basic insights and had not
done any relevant experimentation. He concludes he Germans knew that natural uranium
was not suitable for a weapon, that one had to use either almost pure U235 or some higher
transuranic element such as neptunium or plutonium, and that fission by fast neutrons
should cause the explosion as opposed to the case of a moderated reactor.
However, they had not measured any of the relevant reaction cross-sections, had
not isolated neither U235 nor Pu239 and had not considered how subcritical lumps should
be brought together to initiate an explosion.
Rose exposes in detail an initial and erroneous Farm Hall argument made by
Heisenberg that led to an estimation of a critical mass of a uranium device of the order of
tons. At Farm Hall, Heisenberg arrived at a realistic value for the critical mass only in
his lecture on August 14, 1945. Rose projects Heisenberg’s initial Farm Hall calculation
back to 1940, to conclude that the Germans thought throughout the war that the critical
mass of a U235 bomb was of the order of tons. Heisenberg presented his earlier incorrect
Farm Hall calculation without much thought, whereas his later correct argument was
arrived at only after a week of intense thinking.
During the war, and certainly in 1942, the Germans did work with a perceived
critical mass of 10–100 kg in the 1942 HWA report: “Energiegewinnung aus Uran.”
Heisenberg’s made a famous remark about the volume of an atomic weapon being of the
size of a pineapple” in June 1942.
Rose suggests that the 10–100 kg must refer to plutonium. The 10–100 kg seems
a rough estimate, whose origin is unknown. Even if by chance the German scientists got
the value of the critical mass roughly right, they had not nearly arrived at the correct
reasoning leading to this value. On the USA side, this reasoning started with the work of
Frisch and Peierls in England in March and April 1940. Even Fermi’s estimates of the
critical mass were initially wrong by orders of magnitude.
Rose gives an interesting account of various ideas on “reactor bombs,” showing
that at a certain stage Heisenberg saw a nuclear device as an extreme type of a nuclear
reactor, with highly enriched uranium and large quantities of moderator that went
supercritical. This idea was subsequently pursued by some of Heisenberg’s associates.
Heisenberg did in fact study in detail the self-stabilization of ordinary nuclear reactors at
high temperature. Rose maintains that Heisenberg was basically incompetent in spite of
his established genius as a theoretical physicist. After all weapons design is in essence an
engineering problem and Heisenberg was neither an experimental physicist nor an
engineer. 2.13 CAUSES OF FAILURE AND SUCCESS
Heisenberg was an excellent theoretical physicist, but not a skillful project
manager, an experimentalist nor an engineer. He was the wrong choice for leading the
German nuclear program. He did not know how to correctly compute the critical mass of
a nuclear device, and was not able to generate its outline. Heisenberg’s lack of leadership has been suggested as the main cause behind the failure of the German nuclear program.
The significant lead time that Germany initially possessed, by the discovery of nuclear
fission on its soil, was promptly lost.
The “hero worship” alluded to by Goudsmit, worked against other members of the
Uranium Club correcting Heisenberg’s faulty calculations and ideas.
In addition, Heisenberg’s intensely competitive spirit and egocentrism led him to
control much of the uranium and heavy water that the Germans possessed for his own
experiments, even at times denying Paul Harteck and Diebner both of whose experiments
were generally superior to Heisenberg’s their fair share.
In comparison, one can surmise that the USA Manhattan Project successfully
reached its goal, albeit after the surrender of Germany, because of the following tentative
1. There was a strong initial drive by a dedicated group of scientists and physicists to get
the project started. Key figures such as Einstein lent their support with a letter to the
2. There was unconditional support from the USA and UK governments and adoption by
the leadership and by the USA president.
3. The top management of the project was assigned to the military and engineers, and not
just the envious and competing scientists, in the person of Brigadier General Leslie
Groves, from the USA Corps of Engineers who had earlier built the Pentagon structure.
These have the resources and technical experience to carry an armament project to its
4. Unlimited industrial resources such as from the DuPont Company and manpower were
made available to the project.
5. There was an unprecedented concentration of brilliant and dedicated scientists working
on the project under the leadership of Robert Oppenheimer.
In contrast, the German scientists did not trust and in some cases despised their
government officials, and vice versa. From the Farm Hall transcripts it is clear that some
of the German scientists, including Heisenberg, were afraid of ending up in a
concentration camp in case they would start a project and then fail in achieving its stated
Whether or not he was aware of the concept of a critical fast spectrum mass
during the war, Heisenberg correctly foresaw the massive industrial scale at which
isotope separation and heavy water production would have had to take place. In the early
years of the war, when Germany seemed to be on the winning side, such an industrial
effort might have been possible, but it was seen to be unnecessary to win the war. In later
years with the tide turning against Germany, the resources and man power were not
available, and the task became impossible to achieve.
Overconfidence, racism and religious fanaticism led to the emigration or
expulsion of both Jewish and non Jewish scientists such as Shrödinger, leaving Germany
with a reduced limited scientific base.
Heisenberg and von Weizsäcker saw an open road to an atomic bomb based on
the extraction of plutonium from a heavy water nuclear reactor burning natural uranium,
but they were unaware of the monumental technological difficulties of actually extracting
and separating this plutonium. It was mentioned that von Weizäcker was mistaken in considering neptunium239
rather than plutonium239 or neptunium237 as possible weapon materials. Even if they had
obtained it, they had no idea of the difficulties of bringing a plutonium bomb to explosion
by the implosion process.
Some historians contend that Heisenberg and his colleagues in wartime Germany
had only a shallow understanding of the physics and technology of nuclear weapons.
This agrees with the conclusion of Allied intelligence work during and after the war.
Heisenberg and some of his colleagues were in no position to claim that during the war
they had known how to build a nuclear device, let alone that they had refrained from
doing so for moral reasons, as some of them conveniently claimed after the war. 2.14 DISCUSSION
There has been an unsubstantiated rumor that during the last months of the war, a
small group of scientists working in secret under Diebner and with the support of the
physicist Walther Gerlach, who became head of the uranium project, tried to build and
tested a nuclear device. The allegation is that the German scientists run an unsuccessful
test using chemical high explosives configured in a hollow shell in an attempt at initiating
both nuclear fission and nuclear fusion reactions.
The greatest irony is that the German scientists, their politicians and their military
apparently never tried nor realized the practical and industrial possibility of building a
nuclear device, and concentrated their efforts on the pure scientific goal of achieving a
self sustained chain reaction. Heisenberg never took the possibility of building a nuclear
device seriously and hardly tried. He was aware of the possibility of achieving criticality
in a thermal moderated assembly, but not in a fast neutron spectrum assembly. He
expended a substantial effort to achieve criticality in a moderated subcritical assembly to
impress the Allies in future peace time, thereby hoping to secure Germany’s physics and
his own personal leading role in it. Through rivalry and misconception he hindered the
effort of other German scientists such as Diebner.
Another irony was that the atomic bomb developed by the USA and meant to be
used against Germany, could not be used against it any more after its surrender, and was
targeted instead against Japan. REFERENCES
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New York: Random House, 1988 ...
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- Nuclear weapon, Heisenberg, Werner Heisenberg