Suddenly Ymir was filling the window. It was dead ahead of them. The glowing Earth, a third of a million kilometers away, “set” below its black horizon as they sidled in behind it. Markus had placed them on a trajectory that would slowly cross that of Ymir, bringing them laterally across the ice ship’s aft end.
Dinah’s older relatives might have described Ymir as having a sugarloaf shape, meaning a cone with a blunted tip. If so, this sugarloaf had been splashed with boiling water and attacked with a screwdriver in several places, giving it a scarred, irregular form. But it clearly had a fat end and a narrow end. These were about half a kilometer apart. The fat end, which was beginning to swing across their field of view, was a couple of hundred meters wide. It had a big circular hole in it, which was the outlet of the ice nozzle. New Caird could have flown into that hole and followed it almost all the way up to the throat before running out of room. And perhaps they would do so later, if they could find no other way in. But for now they were just going to make a lazy swing across it. The edge of the hole was blurry because of the evanescent steam cloud leaking out of it. This looked not so much like rocket exhaust as like breath emerging from someone’s mouth on a cold day. It didn’t so much block their view as soften it. But the visual landscape of space was one of intense contrasts, and so it was impossible to see down into the nozzle bell, even when they were squarely in the middle of the cavernous hole. It was just a black disk—like staring into the muzzle of a rifle. Hair-thin needles of frost grew on the window as the steam condensed.
Jiro focused intensely on his tablet until they had drifted past the midway point, then seemed to draw back into himself. He switched his Eenspektor back on. It was making a lot more noise than it had a few minutes ago, but this gradually diminished as they traversed beyond the nozzle exit and across the wide base of the sugarloaf. With a tap on the thrusters Markus got them moving forward with respect to Ymir. Earth “rose” on her other side. New Caird moved up alongside the shard, headed for her forward end.
“What’s the verdict, Jiro?” Markus asked, when he was satisfied with how things were going.
“Based on the gamma spec,” Jiro said, “I would say that at least one of the fuel rods ruptured. Not at the beginning, when the rods were new, and not recently, when they were full of fission fragments and daughters, but somewhere in between. Could be worse, could be better.”
A memory came back to Dinah. “One of Sean’s last messages said he was thrusting at full power.”
Jiro shrugged. “This reactor contains sixteen hundred fuel rods, grouped in assemblies of forty, so the failure of a single rod wouldn’t measurably affect performance. Even the ruptured rod still makes power, remember. It’s just that it would be spewing fuel fleas, fragments, and daughters into the rocket exhaust. We would expect to see a mixture of alpha, beta, and gamma—which is just what the Eenspektor is reporting.”
Dinah was no nuclear physicist, but she’d had enough radiation facts drilled into her to get the gist. Gamma was high-energy light. It would pass through just about anything. So, bad news, good news: It was hard to shield against the stuff. But most of it passed right through your body without interacting—that is, without doing damage. It made scary noises on the Eenspektor.
Betas were free-flying electrons. They were easy to shield against. Good news, bad news: You could stop them with a little bit of water or plastic. But by the same token, if they came into contact with your body they were certain to break something inside of you.
Alphas were helium nuclei, four thousand times as massive as betas, moving at relativistic speed. They could not pass quietly through matter any more than cannonballs could, but they did a lot of damage to whatever they hit.
In order to detect anything other than gamma, Jiro had been forced to switch over to equipment mounted on the outside of New Caird, since alpha and beta couldn’t penetrate the hull. And by looking at the energies of the various particles striking that equipment he had been able to diagnose conditions inside the reactor.
Since she could no longer see Ymir out the front window, Dinah focused on the slivers of frost that had grown on the glass. These were rapidly sublimating into space, and would be gone in a few more minutes. She’d found them beautiful until Jiro had made them aware that they were probably contaminated.
“Any residual beta now?” she asked.
“We are well clear of the nozzle and the plume,” Jiro said, a little taken aback.
“I mean, did we pick up any contamination on that flyby?”