Month: September 2022

On 3 October 2015, a Gulfstream V research jet belonging to the National Science Foundation recorded a massive spike in atmospheric radiation while flying over the South Atlantic between Antarctica and the tip of South America. For 11 minutes, its on-board radiation detector watched as levels doubled, as if the aircraft had flown through a cloud of radiation.

That was not the only incident. Since 2013, airborne detectors have recorded 57 similar radiation bursts, each lasting between ten minutes and an hour.

The observations have raised significant questions, not least about the risks to aircrew and the safe operation of airborne electronics. But most of all, scientists want to know what causes these radiation bursts.

Radiation Dose

Today we have an answer thanks to the work of Kent Tobiska at Space Environment Technologies in California, and colleagues, who have studied the incidents and think they know the radiation source.

Their work raises important questions about the safety of frequent fliers such as aircrew and how to protect them from events that “are analogous to planes flying through radiation clouds,” say Tobiska and co.

Space scientists have long known that Earth is bombarded from space by a steady flux of high energy radiation from beyond the Solar System, called Galactic Cosmic Rays, and by more sporadic bursts from the Sun called Solar Energetic Particles. This radiation generally takes the form of high energy electrons, protons and alpha particles.

The Earth is protected from these particles by the Sun’s magnetic field, which slows down much of the incoming galactic radiation, and by its own magnetic field high above the atmosphere, which channels charged particles towards the poles.

However, high energy particles still get through to the upper atmosphere at about 100km where they collide with oxygen and nitrogen atoms creating lower energy electrons and photons that cascade in chain reactions into the lower atmosphere. These cascades reach a maximum intensity at altitudes of about 20 km but are steadily absorbed at lower altitudes by the thicker atmosphere.

Commercial aircraft operate at altitudes up to about 10 km and so experience a higher dose of this radiation than on the ground. The concern is that this kind of radiation can ionize atoms and rip apart DNA, potentially causing health problems such as cancer. It can also interfere with electronic instruments.

So any new source of ionizing radiation is a significant concern.

Although radiation is a well known issue at high altitudes for decades, there has been no attempt to monitor it continuously on a global scale. So in 2012, various US agencies began developing a real-time, global monitoring system to measure the levels. The system was called the Automated Radiation Measurements for Aerospace Safety (ARMAS) program and Tobiska’s company, Space Environment Technologies, has played a key role in it.

Since then, the program has taken hundreds of thousands of radiation measurements during 599 flights all over the globe.

It soon became clear that the background level of radiation isn’t constant at all. Instead, various monitoring aircraft experienced sudden rapid increases in radiation which would die away relatively quickly.

Tobiska and co focus their analysis on 57 events of this kind.

They first compared the radiation bursts to background readings elsewhere on the planet to rule out the possibility that a solar storm or an increase in galactic cosmic rays were to blame. They found no increase in activity elsewhere.

Clearly this radiation was being generated closer to home and only over small areas. Judging by the aircraft’s speed, these radiation patches cover areas no greater than 1000km in diameter.

Catching the Culprit

The obvious culprit was Earth’s Van Allen radiation belts, the part of the magnetosphere that traps high energy charged particles creating a high-altitude ocean of plasma. Like any other ocean, this plasma is buffeted by environmental conditions — the space weather in the form of changes to the sun’s magnetic field and by solar storms.

This generates turbulence and sets up powerful plasma waves. It is these plasma waves, called electromagnetic ion cyclotron waves, that Tobiska and co think are the source of the radiation bursts.

That’s because charged particles can surf on electromagnetic ion cyclotron waves, becoming vastly accelerated. Any particles that escape do so as powerful bursts of high energy radiation. Indeed, plasma wave accelerators are an emerging technology for next generation particle colliders.

But the bursts only head downwards, towards the Earth’s surface, where the Earth’s magnetic field is beginning to point back towards the surface. And this only happens at high latitudes.
As it turns out, one of the features of the observed radiation spikes is that they only occur at high latitudes.

The team also found that the radiation spikes tended to coincide with periods of turbulent space weather, which promote conditions in which electromagnetic ion cyclotron waves can form. It’s also possible to see evidence of these waves from the ground.

“Evidence points to the [radiation] beam being produced at higher altitudes by incident relativistic electrons coming from the Van Allen radiation belts and that have been generated by electromagnetic ion cyclotron wave,” say Tobiska and co.

The consequences are significant. Over many years, scientists have calculated the background rates of high-altitude radiation and worked out safe limits on the time aircrew should spend in these conditions. This allows them to operate safely.

But this new source of radiation threatens to upend these calculations, particularly for those flying more northerly routes.

“The net effect on aircraft crew and frequent flyers for these routes will be an increase in the monthly and annual exposures, which may have career-limiting health consequences,” say Tobiska and co.

That conclusion is likely to send shockwaves through the aviation industry. The significance of this extra exposure has yet to be calculated but this work must be given the highest priority. At the very, this should be designed to give clarity to the many men and women who will be concerned about the effect of this radiation on their health.

Ref: Increased Radiation Events Discovered At Commercial Aviation Altitudes : https://ift.tt/4uFsGDn

If you remember little else from high school geometry, you probably remember the Pythagorean Theorem: The square of the hypotenuse of a right triangle is equal to the sum of the squares of the other two sides. Or, to put it in a formula:

The formula comes in handy in construction, land surveying and navigation, among other down-to-earth pursuits such as deciding what size monitor or television to purchase. The theorem also led to mathematical breakthroughs, such as calculus.

But who was Pythagoras, the person behind the famous and useful theorem?

Of Math and Mystics

Beyond the fact that he was born on the Greek isle of Samos around 569 B.C. and died around 475 B.C., not much is known about him. Pythagoras left no writings, but he did found a sect (or, what some would deem a cult): the Divine Brotherhood of Pythagoras. Its followers are often referred to as simply the Pythagoreans, a secret society dedicated to a combination of scientific and mystical precepts.

They were an eccentric bunch, and the legends surrounding Pythagoras and his followers are delightful. It’s said that Pythagoras refused to eat beans, and would not allow his followers to do so, because he thought beans had souls. The Pythagoreans were also said to be highly suspicious of sex, and according to Jordan Ellenberg in his book How Not to Be Wrong: The Power of Mathematical Thinking, they may have believed Earth had a twin planet on the other side of the sun.

Some of Pythagoras’ followers, it has been said, believed that he was a god. Yet they are also said to have tossed him into the sea and left him to die because the Pythagorean theorem was too, as we might say today, disruptive.

While that last myth is as unlikely as the others — and the poor sod thrown overboard is usually identified as Hippasus of Metapontum, another Pythagorean, rather than Pythagoras himself — it is certainly fitting, considering the impact of the theorem. It was dangerous, at least to the Pythagorean worldview. In working out that specific properties of a triangle, Pythagoras had stumbled upon the existence of irrational numbers. And that was a big problem.

‘All Is Number’

The basic tenet of Pythagoreanism was that numbers are the essence of everything, as declared in their motto: “All Is Number.” They had some good reasons for looking at things this way. They were the ones who worked out that musical intervals corresponded to the lengths of the strings on a stringed instrument, and they had derived the golden mean, or golden ratio, from examining patterns in nature, such as nautilus shells and the petals of flowers. 

As David Foster Wallace explains in Everything and More: A Compact History of Infinity, the Pythagoreans’ “attempts to articulate the connections between mathematical reality and the physical world were part of the larger project of pre-Socratic philosophy, which was basically to give a rational, nonmythopoeic account of what was real and where it came from.” They wanted to figure out how things worked — absent gods with thunderbolts — and everywhere they looked, they found numbers.

Prior to the discovery of the Pythagorean Theorem, the Greeks thought all numbers could be expressed as either a whole number or a fraction — a ratio of two whole numbers. But the Pythagorean theorem blew a big hole in that notion. Hiding in plain sight in the theorem was something very disturbing. If, for example, you look at a right triangle with two sides of 1 inch (or foot, or some such), the hypotenuse is a number the square of which is 2.

So what’s the square root of 2? Something the Pythagoreans couldn’t deal with: an irrational number; that is, a number that can’t be written as a fraction (or ratio). To us, this just means that the math is a bit more challenging (OK, maybe a lot more challenging). To the Pythagoreans, it was a challenge to their entire worldview, which was built on the supremacy, even divinity, of numbers that did not do such weird things.

Of course, now we have all kinds of weird numbers: imaginary numbers, transcendental numbers, the truly disruptive zero, plus quantum mechanics. And we muddle along more or less fine — even managing to make airplanes fly and invent computers.

Older Version of the Theorem

Writings by other members of the society were often attributed to Pythagoras himself, rather than the actual writer, presumably out of respect (or maybe as a form of self-defense). So it’s really not fair to pin all the oddity or all the credit on Pythagoras.

Much of what we attribute to Pythagoras could well be the work of another or multiple Pythagoreans. But real or composite, Pythagoras was not the first to figure out the famous ratio. Clay tablets found in what is now central Iraq show that Babylonian mathematicians were aware of the basics of the famous theorem at least 1,000 years before it freaked out the Pythagoreans. We don’t know how the Babylonians responded, but we can hope they resisted pushing anybody off a boat.