I was just trying to find out how frequent the high energy particles of the GCR are.
And as usual, the answer is, "It depends..." You're not the first to ask this. In fact, every damn time I'm on television or giving an interview or something, the host -- who honestly never has any ulterior motives -- wants a simple answer. "So how much radiation is there in the Van Allen belts?" Well, it depends... But they want a number. Their job is to commit the interviewee to some particulat thing, because wishy-washy answers lack punch. It's also their job to interpret and simplify things for their readers, to cut through the tech-speke. They aren't even usually interested in correctish sound-bites such as, "Well, it depends on your exact path, how fast you're going, and the construction of your space vehicle."
I picked this one at random.
https://space.stackexchange.com/questions/9331/how-do-the-effects-of-different-cosmic-rays-compareIt has the shape I'm familiar with, which is humpy at the low-energy side and sharply falling off on the high-energy side. The first thing to notice is that they've broken out the data by particle species. The letters up in the data field are the chemical symbols of the elements whose nucleii are plotted in that particular point shape. You've got hydrogen, helium, carbon, and iron. Someone else's graph might have different species. These are just the nucleii of those elements; no electrons. That's why the graph labels mention "nucleon". They want you to remember that the data is categorized and plotted on the same scales.
The x-axis is energy in millions of electron-volts (MeV). The scale is exponential, in case that's not obvious. This happens all the time in astrophysics (well, physics in general). You're often not interested in the changes in a phenomenon that amount to only marginal increases or decreases. You're interested in order-of-magnitude changes. It's how the Richter scale works in principle for earthquakes.
The y-axis is flux, which is what we term frequency when we're talking about particle flow. That axis label looks like modem line noise, so I'll walk you through it. It's all exponentiated to -1, which is shorthand for putting it all in a denominator. So read all the elements of the label as "per this" or "per that." The implied numerator is "number of particles." The first element is "per square meter," which normalizes the area of the conceptual window through which the particles are flying.
Next is "per sr" or "per steradian." That's a measurement of solid angles. I'm going to assume you know or can figure out what a solid angle is. GCR is istotropic, meaning it comes from all directions. It doesn't matter which direction your window is facing; it will get the same flow. SPEs, in contrast, are directional. If you were drawing this graph for one of those, you wouldn't say "per [solid angle]" because the measurement would be different depending on which particular part of the sky you were facing. In that case you'd specify the direction of measurement.
Then "per s" for "per second," since flux is, after all, a rate. Then the "MeV/nucleon" to remind is that this is a categorized reading. The scale of the y-axis graph is also exponential, but in the negative direction. 10
-1 particles per second makes sense if you think about it as one particle every 100 seconds. It's not like they're measuring fractional particles.
The highest reading on the graph is for hydrogen, at 2 particles per second, per solid angle, per square meter occurring at about 10
2.1 MeV -- about 126 MeV. I've seen other graphs where the flux peak is closer to 30 MeV, but I don't remember what circumstances applied to it. But the 2 particles per second figure is only for that one energy level. If you want to know the flux for all energies, you need to integrate -- that is, use calculus. If you're just out in space bare naked, you're exposed to all the energies. So you'd need to integrate from the lowest energy to the highest, essentially adding up all the fluxes at each of the energies as you go. More typically we want to estimate an exposure, which means you apply the effects of shielding, if any, and integrate only over those energies that are significant notwithstanding the shield. That gives you the flux behind the shield, which is what some astronaut's dosimeter would be seeing. Then you would integrate that over exposure time to get a new value called fluence. If flux varies over time for any reason, the integral can get interesting. Fluence is most directly connected to cumulative exposure, such as what a dosimeter would give you at the end of the day.
The dosimeter method just skips to the end. It won't necessarily differentiate between kinds of radiation (although many do), or keep a detailed breakdown of whether it was a little bit over a long time, or a lot in a short time. A health physicist's first question will be what the total absorbed dose is. Imagine filling up a pitcher at the sink, where you vary the water flow by idly twisting the knob as it fills. Sure, a physicist can get all over that and integrate the varying flow rate over time and predict with math how much water ended up in the pitcher. But the quick and dirty method is just to measure the amount of water that got in there. This is essentially what Tim's dosimeter data does. It doesn't account for different sources of radiation. It doesn't account for varying effects of shielding. It doesn't account for natural fluctuations in the dose rate. It just gives you total accumulated dose. Of course in practice the Apollo crews read off their dosimeter readings at periodic intervals, so we at least have some time-varied data.
