Cosmic Rays Hit 50-Year High – Yahoo!

By | September 30, 2009 cosmic rays have just hit a Space Age high, new data from a NASA spacecraft indicates.

“In 2009, cosmic ray intensities have increased 19 percent beyond anything we’ve seen in the past 50 years,” said Richard Mewaldt of Caltech. “The increase is significant, and it could mean we need to re-think how much radiation shielding astronauts take with them on deep-space missions.”

The surge, which poses no threat to Earth, was detected by NASA’s ACE (Advanced Composition Explorer) spacecraft. The cause of the surge is solar minimum, a deep lull in the sun’s activity that began around 2007 and continues today. Researchers have long known that cosmic rays go up when solar activity goes down, because strong solar activity inflates and bolsters a protective bubble around our entire solar system.

Right now solar activity — marked by sunspots, solar flares and space storms — is as weak as it has been in modern times, setting the stage for what Mewaldt calls “a perfect storm of cosmic rays.”

… Galactic cosmic rays come from outside the solar system. They are subatomic particles — mainly protons but also some heavy nuclei — accelerated to almost light speed by distant supernova explosions. Cosmic rays cause “air showers” of secondary particles when they hit Earth’s atmosphere, where they can pose a threat to orbiting satellites — a single cosmic ray can disable a satellite if it hits an unlucky integrated circuit. Though some have suggested that cosmic rays might be behind the Earth’s current warming climate, research has shown no firm link between these invading rays and global warming. Cosmic rays also pose a health hazard to astronauts. Several reports have outlined the risks from cosmic radiation that might exist for future missions to Mars or stints on the moon.

The sun’s magnetic field — the heliosphere, which surrounds the entire solar system —is our first line of defense against these highly-charged, energetic particles. But the current state of solar activity means the solar system isn’t as protected right now.

via Cosmic Rays Hit 50-Year High – Yahoo! News.

From NASA:

Galactic cosmic rays (GCRs) come from outside the solar system but generally from within our Milky Way galaxy. GCRs are atomic nuclei from which all of the surrounding electrons have been stripped away during their high-speed passage through the galaxy. They have probably been accelerated within the last few million years, and have traveled many times across the galaxy, trapped by the galactic magnetic field. GCRs have been accelerated to nearly the speed of light, probably by supernova remnants. As they travel through the very thin gas of interstellar space, some of the GCRs interact and emit gamma rays, which is how we know that they pass through the Milky Way and other galaxies.

The elemental makeup of GCRs has been studied in detail , and is very similar to the composition of the Earth and solar system. but studies of the composition of the isotopes in GCRs may indicate the that the seed population for GCRs is neither the interstellar gas nor the shards of giant stars that went supernova. This is an area of current study.

I was thinking, Yahoo! more energy! Lets tap it and use it … but this changed my mind:

Cosmic rays in outer space are abundant and diverse. There’s a whole periodic table worth of nuclei (mostly H, He, C, and Fe), electrons and positrons, neutrons, and high-energy photons (x rays, gamma rays) … ejected by solar winds, distant supernovae, and all sorts of ill-understood processes.

At the Earth’s surface things are completely different. The atmosphere is dense enough to stop basically everything that comes in (except neutrinos!) and only some of the secondaries, the by-products of the collisions that stopped the original particles, manage to percolate down. These secondary particles are typically lightweight (certainly nothing heavier than a proton) and most of them are pretty rare … a few protons and a few tens of electrons, say, per square meter per second.

The one secondary that doesn’t have to percolate is the muon. Muons produced very high in the atmosphere are able to penetrate all the way to the surface (and a ways underground as well!) without losing all of their energy. This is because they’re very heavy (lots of inertia) and they don’t interact strongly with nuclei (which is what stops cosmic-ray protons and neutrons so quickly). So muons are the most important component of cosmic rays at the surface.

When building and testing new particle detectors, we do see cosmic ray muons on a regular basis. They’re a quick and dirty way to make sure a detector is working properly: if it gets triggered too often, or too infrequently, with respect to the cosmic ray flux, then you want to know why. The number to remember is ~70 muons per square meter per second, or one per square centimeter per minute.

As for the energy flux? First of all, it’ll be fantastically small amounts of energy, when you think about it on the scales we’re used to. The mean muon energy is ~4 giga-electron-volts (GeV), so that gives you an energy flux of 280 GeV/second. But one electron volt is ~10^-19 joules. That’s fantastically small. This does’t imply that we can’t detect them; in fact, it’s not too hard to detect them at all, as you know if you’ve seen a simple cloud-chamber setup. Fortunately, even a tiny amount of energy – a few electron volts – is enough to ionize an atoms, and free ions and electrons are what we detect. But you’re not going to see your detector heating up.

You also mentioned one-foot-thick concrete walls and roof. Now, that will attentuate the muons somewhat … if you want an order-of-magnitude answer we can ignore it. It’ll be a factor of 2, not 10. This is calculable, though; check out Chapter 23 of “The Passage of Particles through Matter” in the Review of Particle Physics (click here). –

Leave a Reply