The bombing of Hiroshima. Questions that have remained unanswered

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

On the morning of August 6, 1945, an American Enola Gay bomber, a specialized version of the B-29 Superfortress, flew over Hiroshima and dropped an atomic bomb on the city. It is customary to say that at this moment “the whole world has changed forever,” but this knowledge did not become generally known instantly. This article describes how scientists in Hiroshima studied the "new world", what they learned about it - and what remains unknown to this day.

The military administration of the city, as noted on the website of the Hiroshima Peace Memorial Museum, considered this plane an ordinary American reconnaissance officer who carried out mapping of the area and general reconnaissance. For this reason, no one tried to shoot him down or somehow prevent him from flying over the city, to the point above the military hospital, where Paul Tibbets and Robert Lewis dropped the Kid.

"Mushroom" atomic bomb explosion over Hiroshima

US Army / Courtesy of the Hiroshima Peace Memorial Museum

The ensuing explosion, which immediately claimed the lives of about a third of the city: about 20 thousand soldiers of the imperial army and 60 thousand civilians, as well as the address of US President Harry Truman, marked the entry of mankind into the "nuclear age." Among other things, these events also gave rise to one of the longest and most fruitful scientific and medical programs related to the study and elimination of the consequences of this disaster.

The fight against the consequences of the bombing, the nature of which remained a mystery to the townspeople, began in the very first hours after the explosion. Military and civilian volunteers began to clear the rubble, extinguish fires and assess the state of the city's infrastructure, guided by the same principles that the Japanese authorities and ordinary Japanese applied when fighting the consequences of bombing in other cities of the empire.

US aircraft have continuously bombed all major cities in Japan with napalm bombs since March 1945, acting as part of the intimidation concept developed by Curtis LeMay, the inspiration for Generals Jack Ripper and Badge Turgidson from Doctor Strenglaw. For this reason, the destruction of Hiroshima, despite the strange circumstances of the death of the city (not a massive raid, to which the Japanese were already accustomed to this moment, but a lone bomber), did not initially become a herald of a new era for the Japanese public - so, just a war.

August 7, 1945, Hiroshima. The still smoking ground 500 meters from the blast hypocenter

Mitsugi Kishida / Courtesy of Teppei Kishida

The Japanese press limited themselves to short reports that "two B-29 bombers flew over the city", without mentioning the scale of the destruction and the number of casualties. In addition, over the next week, the media, obeying the instructions of the Japanese military government, hid from the public the true nature of the bombing of Hiroshima and Nagasaki, hoping for the continuation of the war. Without knowing this, the inhabitants of the city: ordinary engineers, nurses and the military themselves, immediately began to eliminate the consequences of the atomic explosion.

In particular, rescuers partially restored the power supply of the railway and other important infrastructure facilities in the first two days after the start of work and connected a third of the surviving houses to the power grid about two weeks after the bombing. By the end of November, the lights in the city were fully restored.

The engineers, themselves injured by the explosion and in need of medical assistance, restored the city's water supply system to work in the first hours after the bomb fell. Its complete repair, according to the recollections of Yoshihide Ishida, one of the employees of the Hiroshima city water supply bureau, took the next two years: all this time, plumbers systematically found and manually repaired damage to the city's pipeline network, 90 percent of whose buildings were destroyed by a nuclear explosion.

260 meters from the hypocenter. Ruins of Hiroshima and one of the few buildings that survived the bombing. Now known as the "Atomic Dome": it was not restored, it is part of the memorial complex

US Army / Courtesy of the Hiroshima Peace Memorial Museum

Even before the beginning of winter, all the rubble was cleared and most of the victims of the atomic bombing were buried, 80 percent of whom, according to historians and eyewitnesses, died from burns and physical injuries immediately after the bomb exploded or in the first hours after the disaster. The situation was compounded by the fact that the doctors did not know that they were dealing with the aftermath of the atomic bomb, and not the usual Allied air raids.

Lost traces of "black rains"

The concealment of the true nature of the bombing of Hiroshima and Nagasaki prior to the surrender of Japan, which accepted the terms of the Allies the following week, on August 14, 1945, was due to two factors. On the one hand, the military leaders intended to continue the war at any cost and did not want to undermine the morale of the population - in fact, that was exactly what Truman's speech and the very use of atomic weapons were aimed at.

On the other hand, the Japanese government initially did not believe in the words of the US President that "America conquered the power from which the Sun draws its energy and directed it to those who kindled the fire of war in the Far East." According to Tetsuji Imanaka, an associate professor at Kyoto University, a native of Hiroshima and one of the leaders of Japan's anti-nuclear movement, four groups of scientists were sent to Hiroshima at once to verify this statement.

October 12, 1945. View of the area of Hiroshima, located in the hypocenter of the explosion

US Army / Courtesy of the Hiroshima Peace Memorial Museum

Two of them, who arrived in the city on August 8 and 10, were very qualified in this matter, since their participants, Yoshio Nishina - a student of Nils Bohr, - Bunsaku Arakatsu and Sakae Shimizu, were "Japanese Kurchatovs": direct participants in the secret Japanese nuclear programs aimed at solving the same problem as the "Manhattan Project".

The Japanese government's disbelief in Truman's statements was partly due to the fact that the leaders of its nuclear projects, carried out under the auspices of the Imperial Army and the Japanese Navy, prepared a report back in 1942, where they suggested that the United States would not have time or could not develop an atomic bomb in a war. …

The very first measurements that they carried out on the territory of the destroyed Hiroshima immediately showed that they were mistaken in their past estimates. The United States did indeed create the atomic bomb, and it is traces of it that have survived in the soil of Hiroshima, in the light-up film on the shelves of its photographic stores, on the walls of surviving houses, and in the form of sulfur deposits on telegraph poles.

In addition, Shimizu and his team managed to collect unique information about the level of background radiation at different heights in different regions of the city and dozens of samples of contaminated soils. They were obtained in those parts of Hiroshima and its outskirts, where the so-called "black rain" fell.

Drawing of one of the residents of Hiroshima. “Black rain poured down over the Sentei Garden, which was overcrowded with wounded. The city on the other side was engulfed in flames"

Jitsuto Chakihara / Courtesy of the Hiroshima Peace Memorial Museum

So first, the inhabitants of the city, and then the scientists began to call a special form of atmospheric precipitation, which consisted of a mixture of water, ash and other traces of an explosion. They spilled on the outskirts of the city about 20-40 minutes after the bombing - due to a sharp drop in pressure and rarefaction of air caused by the explosion of the bomb. Now they have become in many ways one of the symbols of Hiroshima, along with photographs of the destroyed city and photographs of its dead residents.

The study of soil samples saturated with "black rains" could play an invaluable role in studying the consequences of the nuclear bombings of Hiroshima and Nagasaki and their elimination, if this were not prevented by subsequent events related to both politics and nature.

Estimates of the area covered by black rains. Dark zones (black / gray correspond to rainfall) - estimates from 1954; the dotted lines also delineate rains of varying strengths already in 1989 estimates.

Sakaguchi, A et al. / Science of The Total Environment, 2010

In September 1945, military specialists from the United States arrived in the destroyed cities, who were interested in the effect of the use of atomic weapons, including the nature of the destruction, the level of radiation and other consequences of the explosion. The Americans studied in detail what their Japanese colleagues managed to collect, after which they confiscated all the reports and soil samples and took them to the United States, where, according to Susan Lindy, a professor at the University of Pennsylvania, they disappeared without a trace and have not been found until now.

The fact is that the American military was going to use atomic weapons further - as a tactical tool suitable for solving any combat missions. For this, it was critical that atomic bombs were perceived by the public as an extremely powerful, yet relatively clean type of weapon. For this reason, until 1954 and the scandal surrounding the thermonuclear bomb tests in Bikini Atoll, the US military and government officials consistently denied that "black rains" and other forms of radioactive contamination of the area would have any negative impact on human health.

By the will of time and wind

Many modern researchers of Hiroshima's legacy attribute the lack of serious research on "black rains" to the fact that since 1946 the activities of all scientific groups and the Japanese-American Atomic Bomb Victims Commission (ABCC) have been directly controlled by the American Atomic Energy Commission (AEC). Its representatives were not interested in looking for negative aspects of their main product, and many of its researchers until 1954 believed that low doses of radiation had no negative consequences.

For example, as Charles Perrow, a professor at Yale University, writes, in the first days after both atomic bombs were dropped, government experts and representatives of official Washington began to assure the public that radioactive contamination was either absent or insignificant.

A drawing of one of the residents of Hiroshima, was about 610 meters from the hypocenter of the explosion. “They say the explosion of an atomic bomb looked like a fireball, but that's not what I saw. The room seemed to be illuminated by a stroboscopic lamp, I looked out the window and saw a disc of fire flying at an altitude of about 100 meters with a tail of black smoke, which then disappeared behind the roof of a two-story house"

Torao Izuhara / Courtesy of the Hiroshima Peace Memorial Museum

In particular, in the newspaper "New York Times" in August 1945, an article was published with the heading "There is no radioactivity on the ruins of Hiroshima," hours".

Such statements, however, did not prevent the Japanese occupation administration from conducting a comprehensive study of the consequences of the bombing, including radiation sickness, and measuring the level of induced radiation and the amount of radionuclides in the soil. From mid-September 1945, this research was carried out in collaboration with Japanese scientists, which ultimately led to the creation of the famous Atomic Bomb Victims Commission (ABCC), which began in 1947 a long-term study of the aftermath of Hiroshima and Nagasaki.

Almost all the results of these studies remained classified and unknown to the Japanese public, including the city authorities of Hiroshima and Nagasaki, until September 1951, when the San Francisco Peace Treaty was signed, after which Japan formally regained its independence.

These studies undoubtedly helped to reveal some of the consequences of atomic explosions, but they were not complete for two reasons, independent of the politics and will of people - time and natural disasters.

The first factor has to do with two things - how the Kid exploded, and also when Japanese scientists and American military experts began to study the consequences of its release on Hiroshima.

The first atomic bomb exploded at an altitude of about 500 meters: the destructive force of the explosion was maximum, but even then the decay products, unreacted uranium and other remnants of the bomb, for the most part, flew into the upper atmosphere.

Drawing of one of the residents of Hiroshima.

OKAZAKI Hidehiko / Courtesy of the Hiroshima Peace Memorial Museum

Detailed calculations of such processes, as Stephen Egbert and George Kerr of SAIC Corporation, one of the key contractors of the US Department of Defense, write, were carried out only in the 1960s and 1970s, when sufficiently powerful computers appeared and data collected during the observation of explosions of much more powerful thermonuclear warheads in the upper atmosphere.

These models, as well as modern attempts to estimate the level of radioactivity in the soil in the suburbs of Hiroshima and the vicinity of the epicenter of the explosion, show that about half of the short-lived isotopes resulting from both the decay of uranium and the irradiation of the soil with a neutron flux should have decayed in the first day after the explosion. …

The first measurements of the general level of radioactivity were carried out by Japanese scientists much later, when this value had already dropped to background values in many places. According to Imanaki, in the most polluted corners of the city, located 1-2 kilometers from the hypocenter of the explosion, it was about 120 counter beats per minute, which is somewhere 4-5 times higher than the natural background for southern Japan.

For this reason, scientists neither in 1945 nor now can say for sure how many radioactive particles settled on the land of Hiroshima as a result of "black rains" and other forms of precipitation, and how long they could exist there, given that the city after the explosion burned.

620 meters from the hypocenter. One of the houses that did not collapse as a result of the explosion

Shigeo Hayashi / Courtesy of the Hiroshima Peace Memorial Museum

An additional "noise" in these data was introduced by a natural factor - typhoon Makurazaki and unusually heavy rains that fell in Hiroshima and Nagasaki in September-November 1945.

Showers began in mid-September 1945, when Japanese scientists and their American colleagues were just preparing to begin detailed measurements. Heavy rainfall, several times higher than monthly norms, washed away bridges in Hiroshima and flooded the hypocenter of the explosion and many parts of the city, recently cleared of the bodies of Japanese dead and building debris.

As Kerr and Egbert suggest, this led to the fact that a significant part of the traces of the atomic explosion was simply carried away to the sea and the atmosphere. This, in particular, is evidenced by the extremely uneven distribution of radionuclides in modern soil on the territory and in the suburbs of Hiroshima, as well as serious discrepancies between the results of theoretical calculations and the first real measurements in the concentration of potential traces of "black rains".

The legacy of the nuclear age

Physicists are trying to overcome such problems by using new mathematical models and methods for assessing the concentration of radionuclides in soil, which their colleagues from the middle of the last century did not have. These attempts to clarify the situation, on the other hand, often lead to the opposite - which is connected both with the secrecy of data on the exact mass of the "Baby", the fractions of uranium isotopes and other components of the bomb, and with the common legacy of the "nuclear age" in which we we live now.

The latter is due to the fact that after the tragedies in Hiroshima and Nagasaki, mankind has detonated in the upper and lower layers of the atmosphere, as well as under water, over two thousand nuclear weapons, significantly superior to the first atomic bombs in destructive power. They were terminated in 1963 after the signing of the Treaty Banning Nuclear Testing in Three Areas, but during this time a huge amount of radionuclides got into the atmosphere.

Nuclear explosions in the twentieth century. Filled circles - atmospheric tests, empty - underground / underwater

Radical geography / CC BY-SA 4.0

These radioactive substances gradually settled on the Earth's surface, and the atomic explosions themselves made irreversible changes in the balance of carbon isotopes in the atmosphere, which is why many geologists quite seriously suggest calling the current geological era the "nuclear age."

According to the most rough estimates, the total mass of these radionuclides exceeds the volume of Chernobyl emissions by about a hundred or even a thousand times. The accident at the Chernobyl nuclear power plant, in turn, generated about 400 times more radionuclides than the explosion of "Malysh". This makes it very difficult to assess the consequences of the use of atomic weapons and the level of soil pollution in the vicinity of Hiroshima.

Considerations like these made the study of black rains an even higher priority for scientists, as their supposedly uneven nature could reveal some of the secrets of the disaster 75 years ago. Now physicists are trying to obtain such information by measuring the proportions of various isotopes of elements that have arisen in the course of a nuclear explosion and are not normally found in nature, as well as by methods that are usually used in paleontology.

In particular, the gamma radiation generated by the explosion of a bomb and the subsequent decays of radionuclides, in a special way, changes how grains of quartz and some other minerals glow when they are irradiated with ultraviolet light. Kerr and Egbert carried out the first measurements of this kind: they, on the one hand, coincided with the results of studies of the exposure level of "hibakushi", surviving residents of Hiroshima, and on the other hand, they differed from theoretical forecasts by 25 percent or more in some regions of the city and its suburbs.

These discrepancies, as scientists note, could be caused by both "black rains" and the fact that the typhoon and autumn rains could extremely unevenly redistribute isotopes in the soil of Hiroshima. In any case, this does not allow an unambiguous assessment of the contribution of these radioactive fallouts to the change in the thermoluminescent properties of the soil.

Japanese physicists came to similar results when they tried to find traces of "black rains" in 2010. They measured the concentration of uranium-236 atoms, as well as cesium-137 and plutonium-239 and 240, in the soil of Hiroshima and its surroundings, and compared the data with analyzes of samples collected in Ishikawa Prefecture, located 500 kilometers to the northeast.

Points in the vicinity of Hiroshima where scientists took soil samples for comparison with soil in Ishikawa Prefecture

Sakaguchi, A et al. / Science of The Total Environment, 2010

Uranium-236 does not occur in nature and occurs in large quantities inside nuclear reactors and in atomic explosions, as a result of the absorption of neutrons by uranium-235 atoms. It has a fairly long half-life, 23 million years, so that uranium-236, which got into the soil and atmosphere as a result of atomic explosions, should have survived to this day. The results of the comparison showed that the traces of the "Malysh" explosion were "trampled" by traces of radionuclides that got into the soil due to late nuclear tests in other parts of the world: uranium-236 and other isotopes were indeed present in the upper and lower layers of the Hiroshima soil, however, the reconstruction of the rain "is impossible due to the fact that the real number of its atoms was about 100 times less than predicted by theoretical calculations. Additional problems, once again, were introduced by the fact that scientists do not know the exact mass of uranium-235 in that very bomb.

These studies, as well as other similar works that Japanese physicists and their foreign colleagues carried out back in the 1970s and 1980s, suggest that "black rain", in contrast to radiation sickness and the long-term consequences of radiation, will remain a mystery for a very long time. for scholars studying the heritage of Hiroshima.

The situation can change radically only if a new methodology appears for studying modern or archived soil samples, which makes it possible to unambiguously separate the "black rain" and other traces of the atomic bomb from the consequences of other nuclear tests. Without this, it is impossible to fully describe the effect of the explosion of the "Kid" on the surroundings of the destroyed city, its inhabitants, plants and animals.

For the same reason, the search for archival data related to the missing first measurements by Japanese researchers should become an even higher priority and important task for historians and natural scientists interested in ensuring that humanity fully absorbed the lessons of Hiroshima and Nagasaki.