How Good is the Plutonium Found Orbiting Saturn?

Benji, the computer entity, was guiding the exploration of Saturn’s moons by Capt. Marcos and his team of spatons (space robots) with his space ship ‘Napolean.’
    Napoleon was roving about ‘Find 68’ mapping the region for radio activity carefully. It was not long before Capt. Marco sent message to Benji that the radio active (RA) source pinpointed to what looked like a bundle of Chinese noodles floating the outermost orbit of Saturn’s moons. Their bundle appeared to be 1kilometer wide and about 5 kilometers long. It consisted of long strands of wire bundled together. It was in the same orbit as ‘Rhea’ a known moon of Saturn. A little calculation showed that the bundle of rods was trailing Rhea by 60 degrees in its orbit. It seemed to have been caught in the L5 Lagrange point of Rhea and was its trojan. It was 527,000 km from Saturn and its orbit time was almost exactly 100 Earth hours. The unusual mass seemed to have come from outer space and caught in orbit by Saturn’s gravity and Rhea’s pull without any impact.
    As the ship went nearer, Capt. Marco saw that the wiry rods, and said, “Each wire-like rod is cylindrical with a shiny silvery surface.” The ship went closer. He observed, “It looks like a kind of pure metal, but the radio activity is very high. Each strand is about 1 meter in diameter and 50-100 m long. There are hundreds of them tangled together.”
    “Send a Spaton down to the rod and take a sample of the material for analysis”, Benji ordered.
    Capt. Marco sent down a Spaton who touched the rod with its newly developed ‘claws’ and held firmly on to the surface. He took a shaving of the material and returned to the ship. Capt. Marco put the sample in the analyzer and sent the data down to Earth for Benji. Benji forwarded the data from the material to a specialized lab which identified it as Plutonium. Further analysis and research showed it to be Plutonium 244. The lab sent the analysis report with a short note to Benji. ‘On Earth Plutonium is not found in nature. It is a byproduct in the atomic reactor. It gets made from Uranium 238. When an atom of U-238 is exposed to neutron radiation, its nucleus captures a neutron, changing it to U-239. The U-239 rapidly undergoes beta decay to produce Neptunium-239, which rapidly undergoes second beta decay, producing Plutonium-239. A part of it gets converted to Plutonium 240 in the process, but not to Plutonium 244. Plutonium 239 is a very valuable material. Just 15 kg is enough to make a nuclear bomb. The total quantity of Plutonium 239 in the whole world, stockpiled by nuclear countries was only about 1000 tons!’
    Kalpa was the first to speak out. “It is pure Plutonium 244. It’s only 2% spent, indicating that it might have come there about 3 million years ago. The 244 isotope is not made on Earth. It has a half life of 83 million years, much longer than the 24,000 years of Plutonium 239. The longer the half life, the better it is for making nuclear weapons. The contaminant of Plutonium 239 on Earth is Plutonium 240 which has a half life of only 6,500 years. There is no contamination of Plutonium 240 in our Plutonium 244. But we must understand why the mass has not exploded by itself. The critical mass for spontaneous explosion of an unreflecting sphere of pure Plutonium 239 is only 16 kg. Since the density of our Plutonium 244 is the same as Plutonium 239, i.e. 19.8 g/ml, the critical mass must be about the same, as it is inversely proportional to the square of the density. Here we have thousands of kilos of Plutonium 244 existing without having exploded.”
    “What is critical mass?” Alby asked.
    “It is the mass beyond which the fission reaction becomes a self sustaining chain reaction, leading to explosion” explained Kalpa.
    “But when you talk about kilogram, it’s the weight on Earth. As there is zero gravity on the satellite, the weight of 16 kilograms is not achieved and hence there is no explosion” remarked Alby.
    “This time you have spoken like a genius. The critical mass depends on density which is measured in grams per ml. The weight in grams in the orbit is a negligible fraction of that on Earth as there is no gravity. The density therefore is near to zero, and critical mass of Plutonium may be more than tens of thousand times that of Earth, and since the critical mass is not reached in this place, there is no explosion.” Benji concluded.
    “But there is gravity on the moon where we want to store it. So we have to make it into pieces sized less than its critical mass for moon’s gravity and keep the pieces apart” added Kalpa.
    They gloated over the find. Kalpa continued to voice her thoughts. “It is impossible to make so much quantity of Plutonium 244 on Earth, and of such pure quality. It has remained in space because there was no gravity and no oxygen to oxidize it. All the other isotopes have vanished due to their short half lives. Only Plutonium 244 survived with its half life of 83 million years. Generally in a period of 20 half lives, the trace of the substance vanishes. That is the reason why Plutonium 240 was not found.”
    “So we have found Plutonium 244. I concede that it’s a huge find. Now what should we do with it?” asked Benji.
    “I think we should mine it there and bring it in pieces to the moon base.”  Kalpa said.
    “I’ll improve on that. Let’s send in a factory ship and cut it into standard sized bars which are at least one tenth of their critical mass on the moon and pack them separately and then move them to the moon base.” Benji concurred with her, and looked at Albert. 
    “But the entire mass is more than a million tons. We’ll just guard it there in its place and take what we need,” suggested Albert.
    Just what did they do with the Plutonium? Read the book to find out. ---Dilip Dahanukar