Plutonium-238 is a powerful alpha emitter which makes it different from other types of Plutonium isotopes. There’s 20 classified radioisotopes of plutonium. Plutonium-238 makes up 1–2 percent of plutonium producing reactors. The half-life is about 88 years. What distinguishes Plutonium-238 is that it doesn’t realease the problematic types of radiation that plague most applications of other isotopes.
Why is it hard to make Plutonium-238?
The problem is that the production methodologies for Pu-238 are ridiculous and have a ridiculous number of volatile critical dependencies in both the creation and harvesting process.
“This has been the method of choice at the Department of Energy’s Savannah River Site (SRS) production reactors. However, there are several shortcomings with this method of production. First, the production efficiency is quite limited, i.e., to approximately 13% efficiency. This is seen from the fact that the Pu-238 produced in the target after only 2.12 day’s half-life decay, itself becomes a target for production of higher isotopes of plutonium, thus reducing the Pu-238 purity by producing Pu-239 and Pu-240. Second, this process produce a hazardous Pu-236 by-product. As noted on the decay chain, above, there is a η→2η or γ→η reaction that results in the production of Uranium-236 (U-236) and Pu-236. These reactions increase with exposure to fast neutron flux. Pu-236 decays to U-232, which has a hazardous gamma-ray energy emitting daughter product. Even a few parts per million U-232 increase the radiation exposure hazard to personnel dramatically. Lastly, Np-237 must be chemically purified before target fabrication. This is seen from the fact that Np-237 decays to Protactinium-233 (Pa-233), which in turn has a strong gamma-ray emission with its beta decay to U-233 (half-life 27 days). Therefore, the Np-237 was stored in solution at SRS and chemically processed immediately before fabricating targets. Solution storage of Np-237 may not be practical at an alternate production site.”
How does it affect interstellar flight?
The extent to which this should worry our interstellar concerns is huge. The voyager 1 went several billion kilometers away from the Sun. You know it’s crazy, it’s so far away that it takes 15–20 hours for the signal to reach us.