The Nazis were far from completing a working reactor for their atomic bomb program, despite claims by the project's leader that it was almost ready, a new study finds.

The German physicist Werner Heisenberg wrote in 1947 that the reactor for the "Nazi bomb" project ‪— which culminated in Germany's B8 nuclear reactor ‪— was almost finished at the end of World War II.

Heisenberg, who led the reactor's development, claimed the reactor was "just insufficient" to create a self-sustaining fission reaction and that it lacked only a "relatively small amount of uranium" to work.

If it had worked, the B8 reactor would have confirmed that a fission chain reaction was possible, marking a key step toward the German development of an atomic bomb. It could have also spurred the development of specialized fission reactors used to create weapons-grade plutonium from uranium. Instead, the atomic bomb was developed first by the United States and was used to force the surrender of Japan in August 1945. (Germany had already surrendered in May 1945.)

The new study, published Sept. 29 in the journal PNAS Nexus, used historical documents and forensic investigations of two of the project's surviving uranium cubes to refute Heisenberg's claim. The new research indicates that the German B8 reactor had less than half the amount of "heavy water" and about half the amount of uranium it would have needed for a continuous chain reaction.

"My results argue that Heisenberg was off by roughly a factor of two," said first author Patrick Park, a doctoral student at Princeton University who co-wrote the study while at Columbia University.

Park said Heisenberg's mistake was understandable: His calculations were only approximate, and the project was relocated to a rock cellar in the town of Haigerloch, Germany, after Berlin was bombed.

"People were dying or starving and so these reactor calculations were not his first priority," while many details of neutron physics were unknown at that time, Park told Live Science in an email. "Given these circumstances, I think he did the best he could."

Heavy water

To answer the question of how far the reactor for the Nazi bomb project got, the scientists began by tracing archival records of hundreds of uranium cubes that had been used by German scientists. The B8 reactor consisted of five concentric circles of uranium cubes suspended on chains within the heavy water tank. The German scientists planned to place a radium-beryllium neutron source into the reactor's core to kick-start the chain reaction with a flood of neutrons that would split the uranium nuclei and release more neutrons, furthering the chain reaction.

Heavy water is a form of water that contains the neutron-heavy hydrogen isotope deuterium. Like the mainly-graphite blocks and rods used in many reactors, it can be used to "moderate" or slow down fast neutrons created in a fission reaction so they trigger fission — and more neutrons — in nearby uranium atoms. The Germans also used small amounts of graphite in their reactor, but as a coating to reflect neutrons back into the chamber.

By combining the records of the cubes, heavy water and graphite used by the German scientists with measurements of the two surviving cubes, the study authors created a mathematical model of the reactor that agreed closely with historical measurements. This enabled them to establish that the heavy water reactor was far from achieving a stable reaction. The findings also helped them examine the suggestion that the Germans should have instead built a graphite-based reactor like the nuclear pile developed at the University of Chicago to build the American bomb.

But the study authors determined that a graphite-moderated reactor was unfeasible in wartime Germany because the local supply of coal available to create graphite contained high levels of neutron-absorbing boron, making it useless.

Instead, the heavy water used in the B8 reactor was produced at a single factory in Norway, which was occupied by Germany from April 1940 until May 1945. However, the reactor contained only about 370 gallons (1,400 liters) of heavy water, instead of the more than 780 gallons (roughly 3,000 liters) it would have needed, the researchers determined.

Heavy water makes up a tiny fraction of a percent of ordinary water, and extracting it by electrolysis in the Norwegian factory took extraordinary effort. The factory was producing as much heavy water as it could, but the B8 reactor would have needed more than twice the amount it produced during the entire war, the researchers wrote.

Another finding is that the B8 reactor had about half the amount of uranium it would have needed to sustain a fission chain reaction. The reactor contained a total of 664 cubes, each weighing about 5.11 pounds (2.32 kilograms), for a total of 3,390 pounds (1,540 kilograms) of uranium. Similar cubes were distributed among other experimental groups, giving a total inventory in wartime Germany of about 1,100 cubes of uranium.

But the researchers determined that the B8 reactor would have needed at least 1,200 cubes to work. Germany, therefore, was not about to develop a reactor for an atomic bomb in 1945. Contrary to Heisenberg's claims, the heavy-water reactor was not nearly ready, and a working graphite reactor was impossible.

"We conclude Germany could not have built heavy water nor graphite reactors during World War II," the researchers wrote.

Mark Walker, a historian at Union College in Schenectady, New York, who wasn't involved in the study, said the findings explain Germany's decision to develop a heavy-water reactor, since a graphite reactor was not feasible and they didn't know at the time how much heavy water would be needed.

Walker is the author of "Hitler's Atomic Bomb: History, Legend, and the Twin Legacies of Auschwitz and Hiroshima" (Cambridge University Press, 2024) and a noted expert on Germany's wartime nuclear efforts. He agreed that Germany could not have made a graphite reactor during World War II.

"This paper argues that if the Germans had done something they did not do, then this would have failed," he told Live Science in an email. "While this is counterfactual history, it is an interesting engineering analysis."

Archaeologists in southern Russia have unearthed the 2,000-year-old grave of an elite warrior who was buried with his weapons, horse — and a human sacrifice. The grave and sacrifices were found with other lavish goods, including two gold coins featuring Alexander the Great.

A team found the elite grave in Russia's Kuban region east of the Crimean Peninsula, in a necropolis of more than 150 ancient graves arranged around it. This central placement indicates the man had been a member of the social elite, according to the study, which was published in September in the journal Russian Archaeology.

The evidence of a human sacrifice comes from another burial assemblage beside the warrior's grave. This neighboring burial had the remains of three horses, two cattle, a pig, a dog and a fragment of a human pelvis that seems to have come from a sacrificed person, the researchers wrote.

The two gold coins — one found on the warrior's skeleton and one found nearby — indicate that the burial took place in the early first century B.C., while the location and style of the burial indicated the warrior had been a noble of the Indigenous Maeotian people. At that time, the Maeotians were allied with the neighboring Mithridatic Empire, a Hellenistic-Persian kingdom and the enemy of the expanding Roman Republic.

The researchers think the two gold coins were prestige items, rather than ordinary currency for commerce. "It is likely not money in the conventional sense, but rather a means of storing wealth, akin to a … cryptocurrency," study first author Mikhail Abramzon of the Institute of Archaeology at Russia's Academy of Sciences, told Live Science in an email.

Ancient gold

The two gold coins are key to the discovery. One was found in a ritual shaft near the burial in the center of the necropolis; the researchers think it was placed there as an offering to the gods.

The second was found beneath the jaw of the skeleton of the ancient warrior, which indicates it had been placed in the dead man's mouth before the burial and is an example of "Charon's obol" — the traditional ancient Greek payment for the mythical ferryman of the dead.

Both coins are gold "staters" in the Greek style adopted by Alexander the Great (who lived from 356 to 323 B.C.) and show portraits of Alexander.

Experts have determined that these coins were minted during the much later reign of Mithridates Eupator (lived 135 to 63 B.C.), also known as Mithridates the Great, who claimed descent from both Alexander and the Persian nobility and who initiated the three Mithridatic Wars with Rome. The Alexander portraits on the coins are designed to also look like Mithridates Eupator, the researchers wrote in the study.

According to the Greek geographer Strabo, writing in the first century A.D., the Maeotians were an Indigenous people integrated into the nearby Bosporan kingdom, a Greek and Scythian state founded on the north side of the Black Sea in the fifth century B.C. The Greek historian Appian, in the second century A.D., wrote that the Bosporan kingdom became part of the expanding Mithridatic Empire in the second century B.C. — and so the Maeotians were Mithridatic allies at the time of the burial in the first century B.C.

Grave goods

The warrior was buried with weapons — two iron spearheads and an iron arrowhead were found in his grave — as well as his riding gear and his horse, which had been sacrificed. The grave also held luxury items, including a rare glass "alabastron" — a small vessel for oil or perfumes, which had probably been imported from Cyprus or the Levant region of the eastern Mediterranean, the researchers wrote.

A two-handled clay cup, called a "kantharos" in ancient Greek, was also found in the grave. Its surface was engraved with a pentagram, a symbol of the sun, which the researchers think was considered spiritual protection against magical threats.

The researchers think the sacrifices in the nearby burial assemblages could have had different purposes. The cattle may have been offerings in the style of an ancient "hecatomb" — a mass slaughter of animals that would supposedly please a god. The horses were for riding in the afterlife, the pig was for eating in the afterlife, and the dog may have been intended to guide the dead warrior's spirit. The role of the human sacrificed with the animals is unknown, but it may have been to act as a servant for the warrior.

The researchers wrote that the coins and grave goods illustrate both the beliefs of the Maeotian people at this time, and the extent to which they had been influenced by the ancient Greek traditions of the neighboring Bosporon kingdom.