Going back to the alpha particle radiation, I had cited sources that state unequivocally, that a single sheet of paper does not block all alpha particle radiation, but that a half-inch to an inch of paper can be required even on earth to block mid-level range MeV radiation. The dispute was that a single sheet of paper was enough to block all alpha particle radiation, but this is not true, though it will block low-level (range +- 5 MeV) alpha. However, this thread is not about low-level MeV alpha radiation that exists on earth, alone. The topic deals with cislunar and cissolar, and extra (outside coming in) galatic cosmic radiation, which includes high-level alpha radiation.
"...
Alpha particles have a net spin of zero. Due to the mechanism of their production in standard alpha radioactive decay, alpha particles generally have a kinetic energy of about 5 MeV, and a velocity in the vicinity of 4% of the speed of light. (See discussion below for the limits of these figures in alpha decay.) They are a highly ionizing form of particle radiation, and (when resulting from radioactive alpha decay) usually have low penetration depth (stopped by a few centimeters of air, or by the skin).
However, so-called long range alpha particles from ternary fission are three times as energetic, and penetrate three times as far. The helium nuclei that form 10–12% of cosmic rays are also usually of much higher energy than those produced by nuclear decay processes, and thus may be highly penetrating and able to traverse the human body and also many meters of dense solid shielding, depending on their energy. To a lesser extent, this is also true of very high-energy helium nuclei produced by particle accelerators. ..." -
Alpha particle - Wikipedia
So, what I said was true, as well as what JonC said was true. We were speaking about differing area and differing value (MeV) alpha radiation.
JonC, graciously, shared in open forum, and in closed message, that circa range 5 MeV alpha radiation can be blocked by a simple sheet of paper, and this is true. However, this was where my confusion (as I did not immediately recognize what JonC (and thank you again, as your challenge helped me further research and understand what we were both referring to) was referring to, as I thought he was referring to radiation in space, not earth (earth is primarily protected from high value (MeV) alpha radiation, etc because of the multiple (now at least 3) Van Allen belts, electromagnetic fields, etc) was coming from,
as I was speaking about radiation in space, not on earth. I was speaking about high MeV radiation, not low level common everyday radiation experienced on earth, which the article above also shows the difference in.
Even in cosmic radiation, there is higher MeV alpha, even as there is in Ternary Fission,
"... Such alpha particles are termed "long range alphas" since at their typical energy of 16 MeV, they are at far higher energy than is ever produced by alpha decay. ..."
Yet, even 16 MeV is not a maximum.
This again ties right back to the suit composition and thickness (as also seen here -
https://ntrs.nasa.gov/api/citations/20040087145/downloads/20040087145.pdf consider the SPE (Solar Particle Events) **), as well a the skin exposure (in space, entirely exposed except for the suit, but anything penetrating the suit hits the exposed skin at the same area). The thickness (depth) of the suit and its material makeup (already provided) is not enough to prevent space radiation penetrating to damaging/deadly levels (even if NASA claims otherwise, it is contrary to recorded data, even their own, which is why their recent so called probe is unmanned, and supposedly has recorded even a third Van Allen belt, which is supposed to appear from time to time, if not simply there all the time, just unrecorded on occasions), neither to prevent bremsstrahlung (secondary radiation (deceleration radiation)) from piercing, of which is prevalent upon lunar surface, being entirely exposed to solar rays, cosmic rays, earth shine, CMB, etc.
Also, while a thickness of 1 inch of 'air' can 'stop' alpha radiation, in high atmosphere (where 'air' is especially 'thin') and especially space, and Van Allen belts range and beyond, where there is no 'air' or 'atmosphere', these measurements become irrelevant, since in a 'vacuum', the resistance and forces which alpha and other particles encounter is reduced to almost nothing, in which distance of travel (from origin, in the vector they move out away from) of said particles can potentially be infinite (though not in practicality, as even in 'space' and 'vacuum' there are plenty of things to collide, interact with though at far greater distances than on earth in atmosphere). This was already demonstrated by physics stack exchange -
Can a single piece of paper really block all non-electromagnetic ionizing radiation?
** "... The assumption that the February 23, 1956 solar particle event can be represented by the proxy of 10X the September 29, 1989 event leads to a difficult shield design problem. It is clear that designs based on the August 4, 1972 event series will be inadequate to protect the astronaut from this proxy event. Not only are the allowable limits greatly exceeded but also there is a real possibility of mortality in deep space exploration unless a very massive shelter shield is provided. Even then it is likely that the NCRP limits may be exceeded but without serious immediate medical consequence. ..."
A helpful study in radiation and Coulomb interactions, in NIEL, with various types of materials can be seen here -
https://radhome.gsfc.nasa.gov/radhome/papers/nsrec04_pa2_jun.pdf
When people speak about the so called ISS, that is well below the Van Allen belts, and still within the earth's upper atmosphere and electromagnetic fields, magnetosphere, etc. It would not record very high level radiations, though it can still be affected by burst of high level radiation from Solar SPE's.
NASA claims that a 3 year Mars mission, with current 'shielding', would only accrue a circa 1-2 Sv dose of radiation which is ridiculous. Even NASA says,
"... Mars has no global magnetic field to deflect energetic particles, and its atmosphere is much thinner than Earth’s, so they'll get only minimal protection even on the surface of Mars. ...
... The second source of energetic particles is harder to shield. These particles come from galactic cosmic rays, often known as
GCRs. They’re particles accelerated to near the speed of light that shoot into our solar system from other stars in the Milky Way or even other galaxies. Like solar particles,
galactic cosmic rays are mostly protons. However, some of them are heavier elements,
ranging from helium up to the heaviest elements. These more energetic particles can knock apart atoms in the material they strike, such as in the astronaut, the metal walls of a spacecraft, habitat, or vehicle, causing sub-atomic particles to shower into the structure.
This secondary radiation, as it is known, can reach a dangerous level." -
https://www.nasa.gov/feature/goddar...otect-astronauts-from-space-radiation-on-mars
How much less the lunar surface with 0 atmosphere, 0 magnetic shielding (except for earth protection).
The most telling statement of all:
"... “Ultimately, the solution to radiation will have to be a combination of things,” said Pellish. “Some of the solutions are technology we have already, like hydrogen-rich materials, but some of it will necessarily be cutting edge concepts that we haven’t even thought of yet.” ..." - ibid.
Wait. They don't have a final solution yet, and are still in experimental stages? I thought that they were supposed to have all that figured out way back when for the Van Allen and lunar surface, which is more exposed and dangerous than Mars (atmosphere or terrestrial plane) would be.
, and no less fitting for your own posts. 
