# Why is space radiation mainly positively charged? Where are all the electrons?

I've heard that space radiation is mainly, overwhelmingly positively charged. Wikipedia (Cosmic ray - Composition) says

...about 99% are the bare nuclei of well-known atoms (stripped of their electron shells), and about 1% are solitary electrons (that is, one type of beta particle).

What happened to all the electrons?

(I believe solar wind, from our own sun, is overall neutrally charged).

• Electrons are so light they scatter at large angles and lose energy readily, so they don't survive the atmosphere. You might think of them as cloud charges. Aug 11, 2021 at 13:41

When the particles that make up cosmic rays get boosted up to the speeds at which we see them, they're ionized. The electrons and nuclei are separated from the start.

Both types of particle are going to be releasing energy every time they accelerate (synchrotron radiation) and when they interact with photons (inverse Compton scattering). When it comes to inverse Compton scattering, the electrons scatter much more than the alpha particles - there's a $$\frac{1}{m}$$ factor in both the energy exchange and the angle involved.

What this results in is basically the electrons going in all directions, gradually losing energy. Meanwhile, the alpha particles continue on with less deflection and with most of their energy intact. The electron is the ping-pong ball to the alpha particle's bowling ball. (4 bowling balls, really, but you get the idea.)

We still get electrons from space, but more of them are coming in slow, which puts them out of the "cosmic ray" category.

• I mean, "slow" for an electron. They're still going a bajillion kilometers an hour, but they're not carrying cosmic ray levels of energy any more. Aug 11, 2021 at 17:29
• Good explanation, Colin. So the source (e.g. neutron star remnant of supernova) becomes negatively charged and the positive charges fly off to distant stars & galaxies? Aug 12, 2021 at 15:25
• @tim-cooper No, the neutron star will stay basically neutral. The electrons still leave, they just don't leave as quickly. It's more like high-speed diffusion. Aug 12, 2021 at 23:48

Look up 'target normal sheath acceleration'. The electrons get blown off, then get sucked back, but not before they've pulled a bunch of positive nuclei out of the material, which are too heavy to get pulled back and just fly off into space. So you get positive radiation in that case too. Maybe something similar going on with whatever process produces radiation in space.

https://cds.cern.ch/record/2203637

• So the source (e.g. neutron star remnant of supernova) becomes negatively charged and the positive charges fly off to distant stars & galaxies? Aug 12, 2021 at 15:24
• I'm not completely sure. But it is possible for these big objects to become charged. The earth has some overall negative charge. Venus has a large positive charge. I'm not sure if there's a common process in all cases. There are just various situations which can do things like this..
– Matt
Aug 12, 2021 at 16:13