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A potentially big step forward.

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One of fusion energy’s biggest selling points is that it is supposed to be different from traditional nuclear power. 

Unlike today’s fission reactors, which rely on uranium fuel and produce materials that can be linked to nuclear weapons programs, fusion machines are often portrayed as a cleaner and safer alternative. 

However, as governments and companies pour billions of dollars into making fusion commercially viable, some researchers are asking a burning question: How will anyone ensure that future fusion plants are being used exactly as advertised?

This is important because “fusion power systems can in principle be used to make significant amounts of fissile material,” researchers note.

A new study suggests antineutrinos, tiny particles produced in nuclear reactions, could act as independent witnesses to what is happening inside a fusion reactor. If this idea works as expected, future inspectors may be able to spot attempts to produce weapons-related materials without opening up the reactor or interrupting its operation.

When clean energy creates an unexpected security question

Most fusion designs under development rely on a reaction between two forms of hydrogen called deuterium and tritium. When these atomic nuclei merge, they release enormous amounts of energy. 

They also release fast-moving neutrons, which are essential for extracting that energy and converting it into electricity. Those neutrons, however, do not care how they are used.

If uranium-238 were placed near the fusion reaction, some of the neutrons could be absorbed by the uranium. Through a sequence of nuclear transformations, the uranium could eventually become plutonium-239, one of the materials that can be used in nuclear weapons.

This possibility does not mean that fusion reactors are secret weapons factories. Producing plutonium in this way would require deliberate action. Yet regulators generally prefer to design safeguards before a technology becomes widespread rather than after. 

“Demonstrating methods to assure the timely detection of such a misuse scenario would be extremely valuable as part of the efforts to guarantee the peaceful use of fusion energy systems,” the study authors said.

The challenge has been finding a monitoring method that can reliably reveal what is happening inside a reactor without becoming intrusive or technically impractical.

Listening for particles that cannot be silenced

The study authors investigated whether antineutrinos could provide that monitoring capability.

Antineutrinos are among the most elusive particles known to science. 

Trillions pass through the human body every second without leaving a trace. Since they interact so weakly with matter, they cannot realistically be blocked by walls, shielding, or other barriers.

That property turns them into a unique source of information. If plutonium production were taking place inside a fusion reactor, the nuclear reactions involved would generate a characteristic antineutrino signal. In principle, that signal could reveal activity that operators might otherwise try to conceal.

The researchers used computer simulations to test whether such a signal would be detectable in practice. They modeled the antineutrinos expected from plutonium-producing reactions and compared them with other sources of background noise, including signals generated during normal reactor operation and particles arriving from space.

Their results indicate that the difference should be measurable. According to the study, a relatively compact detector could detect the production of only a few kilograms of plutonium over about 30 days. 

In one benchmark scenario examined by the researchers, the production of 8 kilograms of plutonium in a month generated a strong and easily detectable antineutrino signal. This is a small enough amount to provide an early warning that something unusual is happening.

“Our results confirm that even a modestly-sized antineutrino detector should be able to detect the presence of fertile material during operation in a reliable and timely manner,” the study authors added.

Equally important, the detector would not need to sit inside the reactor complex. This is because antineutrinos travel through matter almost unhindered; the monitoring system could operate from outside the facility, making it less disruptive for reactor operators.

Building the rulebook before the reactors arrive

No commercial deuterium-tritium fusion power plants exist today, which means there is currently no facility where the approach can be tested under full operating conditions. The researchers therefore relied on simulations rather than real-world measurements.

That limitation also highlights why the study matters now. Fusion developers are still working to prove that their reactors can generate electricity economically. 

If they succeed, governments and international agencies will eventually need a framework for monitoring the technology. Creating such safeguards after hundreds of reactors are already operating would be far more difficult.

The new work does not solve every question surrounding fusion security, but it does offer a practical way to verify that future reactors are doing only what they are supposed to do. 

The study is published in the journal Physical Review Applied.

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America’s Government Accountability Office (GAO) watchdog has warned that the US may struggle to sustain a long-term conflict with China should hostilities break out. The issue is not about technical capability (the US military is arguably the world’s most powerful), but rather a matter of logistics.

For combat operations thousands of miles from home, as would be the case in the Indo-Pacific, the GAO argues that the US may struggle to refuel and resupply assets, notably its considerable aircraft fleet.

The issue mainly centers around aging refueling aircraft and issues with spare parts. If tensions over Taiwan were to go hot, these could both conspire to make American efforts in the region trickier than expected.

“The percentage of aerial refuelling tankers that are available and mission capable has remained persistently below the standards that the [US] Air Force established for the fleet,” the report said.

To give you some idea of the problem, imagine an F-35 running a sortie from Hawaii to Taiwan, say. These aircraft have a combat radius of around 700 miles (1,127 km), and the distance between these two islands is about 5,000 miles.

An army marches on its stomach

The fighter wouldn’t be able to make it on its own and would need several midair refueling operations to safely get there and back. After the mission, it may also need repairs, which require a sufficient stock of spare parts lying around.

If enough tankers aren’t available, the fighters couldn’t arrive in meaningful numbers. A bit of a quandary.

Of course, travel distances for fighters can be dramatically reduced by deploying carrier groups closer to Taiwan, but that puts them at risk of being attacked by long-range missiles (including hypersonics), submarines, or Chinese aircraft.

The main weakness, the report argues, is the US reliance on aging aircraft like Boeing KC-135 Stratotankers. Many of the current airframes entered service in the 1950s and 1960s, and are still going strong.

The airframes have been upgraded repeatedly, but old aircraft require more maintenance and suffer more breakdowns. And that leads to the second main issue: a lack of spare parts.

The US military increasingly struggles to obtain parts for older systems. Some suppliers no longer exist, and some components must be specially manufactured. Any break in supply means that assets, like aircraft, can sit grounded while waiting for parts.

Not how much you make, it’s how much you keep

So, even if you have 400 tankers on paper, perhaps only 250 are actually flyable on a given day. Other issues cited include a shortage of skilled personnel and delays in replacement hardware for older tech, like the planned Boeing KC-46 Pegasus.

But the KC-46 program has experienced years of technical problems and delays. The Air Force expected newer tankers to reduce pressure on older aircraft.

When factoring in the fact that China reportedly possesses long-range missiles specifically designed to target US bases and support aircraft, any direct conflict could prove very expensive for the US.

China’s military planners, the South China Morning Post (SCMP) reports, understand that destroying tankers may be more effective than trying to shoot down stealth fighters.

So, would such a conflict mean China could win? Not necessarily, since China has its own issues (like a lack of combat experience), but a “home advantage” would certainly tip the odds in its favor unless the US can cure its growing logistical bottlenecks.

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Apollo astronauts trying to rest on the way to the Moon kept noticing the same thing in the dark. With the cabin lights down and their eyes adjusted, they saw brief flashes and streaks of light, dots and lines that no one else could see and that were not there in any ordinary sense. The cause, worked out over the missions that followed, was cosmic rays from deep space passing through the visual system. The broad cause is now well supported, even if the exact biophysics of how a passing particle turns into a flash of light is still not fully pinned down.

The flashes are an example of a phosphene, a sensation of light produced by something other than light entering the eye.

In this case, the something was radiation.

What the astronauts saw

The reports began on Apollo 11. After a period of dark adaptation, with eyes open or closed, crew members saw flashes they described as pinpoints, thin streaks, or small clouds of light. They were almost always colourless. They came at a rate of roughly one-half to two a minute, often enough to be a distraction when someone was trying to sleep.

This was not confined to one crew or one flight. Flashes were reported across the Apollo missions, and later by astronauts on Skylab, on Mir, and on the International Space Station. The phenomenon even had a kind of forecast. As early as 1952, the biophysicist Cornelius Tobias had suggested that people exposed to cosmic radiation in space might see exactly this sort of thing, and the team that investigated the Apollo reports traced them back to that idea.

How they tied it to cosmic rays

Suspecting a cause and demonstrating it are different tasks. To test whether the flashes really were caused by particles passing through the head, the Apollo 16 and 17 crews carried a device called the Apollo Light Flash Moving Emulsion Detector, worn on the head during the coast to and from the Moon. It used stacked photographic emulsion to record the tracks of charged particles, so that the path of a particle could be matched against the moment an astronaut reported a flash.

The numbers were small but telling. The detector was worn for about an hour on each of the last two Apollo missions. On Apollo 17, seventeen flashes were reported during the session, and two of them were matched to heavy cosmic-ray nuclei passing through an eye. Combined with the geometry of the eye and statistical modelling, that was enough for the investigators to attribute the flashes to cosmic rays. Ground experiments pointed the same way: when volunteers had their dark-adapted eyes exposed to beams of heavy ions, they saw comparable flashes.

What is still uncertain

The confirmed part is that cosmic rays cause the flashes. The unconfirmed part is the step in between, the biophysics of how a single fast particle produces a perceived point of light. Several mechanisms have been proposed, and more than one may contribute.

The leading idea is that the particle ionises tissue directly in the retina, stimulating the light-sensing cells or the neurons behind them as it passes through. This fits the ground experiments, where heavy ions produced flashes at intensities too low for any light to have been generated. A second idea is Cherenkov radiation: a particle moving through the clear jelly of the eye faster than light moves through that medium emits a faint glow, real photons generated inside the eye itself. The trouble is that Cherenkov light should look bluish and diffuse, and most astronauts described sharp white dots and streaks, which do not match. A third possibility is that some flashes come from particles striking the optic nerve or the visual centres of the brain, bypassing the eye altogether.

Decades on, reviews of the phenomenon still describe the specific mechanism as undefined, and note that the effects on the different parts of the visual system have not been fully separated.

The cause is well established; the wiring is not.

Why it still matters

On Earth’s surface, we are mostly shielded from this by the atmosphere and the magnetic field. In low Earth orbit the shielding is reduced but not gone, which is why astronauts on stations such as Mir and the ISS have also reported the effect. The Apollo crews saw the flashes more strongly still because they left that protection behind, travelling beyond the magnetosphere. The flashes were, in effect, the radiation environment of deep space made briefly visible inside a human head.

That is why they are treated as more than a curiosity. They are a perceptible sign that high-energy particles are passing through the body, the brain included, and the same radiation is a serious concern for long missions beyond Earth. On the International Space Station, experiments have used the visual system as a way to study how cosmic radiation affects the central nervous system. For a crew bound for Mars, who would spend months outside the magnetosphere, the dose to the brain over that time is one of the open problems of the trip.

What to watch

The people who travel back to lunar distance under Artemis and later missions will almost certainly see the flashes again. They will also carry better instruments and a sharper reason to use them. Pinning down how the flashes are produced would be a small result. Understanding what months of that radiation does to the brain behind the eye is the one that matters.

The post Apollo astronauts trying to sleep on the way to the Moon kept seeing flashes and streaks in the dark, and the cause turned out to be cosmic rays from deep space passing straight through their eyes. appeared first on Space Daily.

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One of the most violent events the Solar System has ever witnessed.

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