How are astronauts protected from radiation (alpha, beta, gamma rays, uv rays) by their spacecraft? Is the spacecraft built in a special material?
This may sound strange, but part of the protection is a lack of shielding. The high-energy particles that make up a large portion of the radiation environment mostly just pass through the human body. They do, however, interact with traditional shielding materials (eg. lead) to produce secondary radiation that does affect humans. Because of this, light shielding is worse than no shielding: it's thick enough to turn high-energy, low-danger radiation into medium-energy, high-danger radiation, but not thick enough to absorb that radiation.
Hence the use of hydrogen-rich shielding (water, plastics): it's not as effective as traditional materials, but it doesn't produce secondary radiation.
In current spacecraft, the materials for e.g. the hull are chosen primarily because they are light and strong. Aluminium is common. A few mm of aluminium blocks most of the radiation you would encounter in low Earth orbit. In the ISS, 95% of the radiation is blocked.
This is enough for low Earth orbit: these orbits are inside the Van Allen Belts, so they are protected from the worst radiation. If we want to go beyond LEO for longer periods, more protection is needed. You could make the hull thicker, but this makes the launch more expensive. One way around this would be to use a small asteroid and build the spaceship inside it, but that leaves the problem of capturing an asteroid and bringing it to Earth. We've never done that.
Another way is a magnetic shield. This requires a lot of power. I seem to remember a figure of 500 kW for a reasonable shield for a small spacecraft (I can't find the reference at the moment though). The ISS (with its massive solar arrays) can produce about 200 kW.
Most space-based radiation, primarily charged particles, is very effectively blocked with hydrogen-rich materials. Scientists for the Lunar Reconnaissance Orbiter discovered that, pound for pound, polyethylene was a more effective radiation shield than aluminum.