Radiation comes in several varieties, of which the
most important is light. Light is not matter, and
so Is not radioactive. Also common are electrons
(beta particles) and helium nuclei (alpha
particles), and Plain vanilla protons. None of
these are radioactive,but they can easily have
enough energy to become so.
Space suits are
white because it reflects visible light, making it
(1) cool, in the bright, hot,sunlight (which
is mostly in the visible frequencies),and
a white space-suit makes the astronaut easy to see
because it reflects so much.
For the most part, I believe that cosmic radiation
should not be radioactive.Cosmic radiation can be
either photons(light particles) or cosmic rays,
which are atomic nuclei.
Most cosmic rays are
protons (hydrogen nuclei) or alpha particles
(helium nuclei) but there are also a small amount
of heavier particle cosmic rays. A small fraction
of the heavier particles could theoretically be
unstable or radioactive but chances are that any
radioactive particle would collide with something
or otherwise decay into other particles before
anyone would notice.
Since there is no air
in space to carry heat away from objects, things
can heat up very quickly if the Sun is shining on
them. Now it turns out that the Sun shines mainly
with visible radiation (which is why we can see
it)and things that are at 300 K (27 degrees C)
radiate in the infrared (not visible). The beauty
of some white paints is that they radiate much
better in the infrared then they absorb in visible
light. So when the Sun shines on something that
is white, it absorbs a small fraction of the
incoming radiation and then re-radiates it all
away if the object isat a temperature around 300
K, which is the perfect temperature for someone
who is used to being on Earth.
think of why the visors on space suit helmets are
coated with thin layers of gold or other metal
rather than being clear?