The Field Guide to Particle Physics
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cc by-sa-4.0The definitive resource for all data in particle physics is the Particle Data Group:
https://pdg.lbl.gov.
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A few References and Resources for you.Isotopes of Helium:
https://en.wikipedia.org/wiki/Isotopes_of_heliumHelium Fact Sheet from NIST:
https://webbook.nist.gov/cgi/inchi/InChI%3D1S/HeCDC Fact sheet on Uranium-238:
https://www.cdc.gov/nceh/radiation/emergencies/isotopes/uranium.htmBerkeley National Lab Essay on Earth's Heat
https://newscenter.lbl.gov/2011/07/17/kamland-geoneutrinos/Space Weather Prediction Center and the Solar Wind
https://www.swpc.noaa.gov/phenomena/solar-windA couple of articles on the Dynamo Effect
https://news.mit.edu/2010/explained-dynamo-0325https://en.wikipedia.org/wiki/Dynamo_theoryhttps://courses.seas.harvard.edu/climate/eli/Courses/EPS281r/Sources/Earth-dynamo/1-Wikipedia-Dynamo-theory.pdfThe Alpha Particle
Part 5 : The Solar WindIntroductionIn the past few weeks, we’ve learned that helium - that useful, noble gas, is created deep underground by the radioactive decay of heavy elements like Uranium and Thorium. Those decays generate quite a bit of heat - about half the heat inside the Earth is credited to these decays.
As we’ve seen, that heat has tectonic consequences! The churning of molten rock not only drives volcanic eruptions, but also is responsible for all the moving and shaking of the continents on earth. Most of this movement is slow and imperceptible to us, but when we can sense major movement. It’s usually as a violent earthquake.
The collective impact of all those humble alpha particles literally shapes the world around us.
We say humble in part because, alpha radiation is mostly harmless. Human skin is pretty good at stopping alpha particles emitted from a decaying nucleus. You wouldn’t want to ingest any uranium, that’s for sure, but having a tiny bit in room with you isn’t necessarily a problem. This is NOT true for all radioactive materials, some of which can be extremely hazardous.
This is because alpha particles come out with a characteristic velocity that - frankly - isn’t very high. Remember, alpha particles are just little fragments of a nucleus that just kind of escaped. Other forms of nuclear radiation include beta and gamma rays, which are essentially electrons and photons. These decays are driven directly by the subnuclear forces and because they have less electric charge and far less mass, can penetrate much deeper into living tissue.
And that’s what makes them hazardous. They can mess with your insides.
Nuclear decays are NOT the only radiation we are exposed to. They is plenty raining down on us from the sky. You see, the enormous nuclear furnace known as the sun does more than light up our skies. It is constantly streaming a LOT other particles, like electrons, protons, alpha particles, a bunch of other ionized stuff. Not the kind of stuff you want to be directly exposed regularly.
As we’ll see, the collective effects of the humble alpha particle inside the Earth protects us from a lot this “solar wind” of electrically charged particles.
GeomagnteismThe Earth, like some of the other planets in our solar system, generates it’s own magnetic field. It’s a weak magnetic field - it takes the WHOLE EARTH to move your tiny compass needle just a little bit - but it’s still big in size. It reaches out into space, well past our own atmosphere.
As we discussed in part two of this series, magnetic fields are created by the motion of electric charges. Big magnetic fields require a bunch of electric charges working together, moving coherently. For the electromagnets used in MRI machines, many many electrons - otherwise known as the electrical current - are pushed through many, many loops of wire.
To generate the Earth’s magnetic field, something even bigger must be happening. Our best working type of model - one that best fits the data - is known as a magnetic dynamo. I’ll sketch the idea for you here.
For a plant like Earth to generate a magnetic field via the dynamo model, we need three things:
1. A conducting liquid inside the planet.
2. A large amount of coherent motion
3. And heat. Lots of heat.
As to the conducting liquid:The outer core of the Earth is believed to be made of iron. Liquid iron. Heavy things - like iron - sink, remember? So there’s a lot of it deep within the earth. The earth is so big and so hot inside that that there’s a whole inner layer of that metal in liquid form, churning.
As to the large collective motion:The earth itself is spinning - which we see as day and night. The rotational motion of the Earth itself stirs up that liquid iron coherently - like the loops of wire in an electromagnet. For the experts out there, it’s the Coriolis Force - as sort of three-dimensional version of the centripetal acceleration you feel in the car when taking a turn too sharply. It’s the same effective force that drives hurricanes to spin counter clockwise in the northern hemisphere, and clockwise in the Southern Hemisphere.
And finally, As to the heat:Well. We discussed that in part four. About half of the Earth’s radiant heat comes from the radioactive decay of uranium and thorium. In other words, from the production of helium.
All that collective motion of a hot, conducting fluid is what builds the coherent magnetic field - the dipole field - that surrounds the Earth. And it’s a good thing that we have one. We’re probably alive today because of it.
The Solar WindBack to that issue of the solar wind. The atmosphere of the sun is hot. REALLY hot. Millions of degrees hot. Way hotter than the inside of the Earth. When matter is that hot, atoms can’t exist in their familiar state. The nuclei and electrons separate into a PLASMA.
The tongues of light emitted by a bonfire - or a bolt of lightning from the sky - are both examples of a plasma. They’re hot, and because the electrons and nuclei are separated into a sort of electrically active gas, they cause a lot of electromagnetic disturbance. For us that mostly means they generate a lot of light.
Given that, it might not surprise you to learn that the atmosphere of the sun is a plasma.
But there is more to a plasma than just light. Each tiny particle - each electron or charge nucleus - carries with it an electromagnetic field. When they are bound together, the positive charges in the nucleus neutralize the negative charges of the electrons. That tight binding keeps the surrounding electromagnetic field pretty tame.
When things get hot enough to separate the atoms in something as BIG as a planet or the solar atmosphere, all those tiny electromagnetic fields merge to form large, collective magnetic fields.
Kind of like a SUPERCHARGED version of the magnetic dynamo we just discussed.
Some of the charged particles in the upper atmosphere of the sun - the corona - escape into space. It’s a constant stream. The further they get from the sun, the less of its gravitational pull they experience, and so the faster they travel. But it’s not just the intense heat of the sun that drives them away. The collective magnetic field of all those churning, charged particles in the solar further accelerates those particles away from the the sun and… unfortunately… towards us.
The Magnetosphere and the IonosphereThe magnetic field that surrounds the Earth is our shield from this solar wind. That shield extends way out into space, its a bit over five times as big as the Earth. At that distance, much of that incoming solar plasma get deflected back out into space. What isn’t is caught up by the magnetic field and driven to the poles, where they eventually get focused into a donut shaped belt around the Earth.
Occasionally, when that so-called space weather is REALLY bad, it literally lights up our skies as the Aurora.
By keeping those charged particles away from the surface, the Earth’s magnetic field protects us from direct exposure to that radiation. But the protection afforded by the dynamo magnetic field goes far beyond that.
Neither Venus nor Mars generates its own magnetic field. Exposed to the solar wind, their atmospheres are literally being blown away by the impact of those charged particles. Venus still has a lot of its atmosphere left to give, but poor little mars has all but lost its protective atmosphere.
That protective magnetic field - driven in part by the same radioactive, alpha decays that create helium - protects both us and our atmosphere.