Dallas began to feed numbers from the control rod mechanism gauges into his computerized TLD.
‘However,’ he said, ‘should the computer decide that the MF has dropped below one, it will withdraw control rods to provide more fission-causing neutrons and maintain the chain reaction — thereby exposing us to much greater contamination. What I’m trying to do now is have the computer provide us with an estimate of whether that is likely to occur or not.’
‘It might not happen at all. I think that’s what you’re saying.’
‘Yes. But changes to a multiplication factor can occur in just a few seconds. It’s what’s called the generation time. Moreover, the changes are very hard to predict. Heisenberg’s Uncertainty Principle says that you can never know everything about a quantum state. A great deal depends on how near the end of their useful life these uranium fuel rods are. And on how much electrical power we’ve used by our presence here in the main facility. Doors opening, electric cars, that kind of thing.’
Cavor sighed and sat down on his spare life-support pack. ‘Now I know why they say ignorance is bliss.’
‘I had hoped to count on your higher facilities.’
‘I wouldn’t put too great an estimate on those, if I were you,’ said Cavor. ‘If I was all that intelligent, I wouldn’t be here now.’
But Dallas was too absorbed in his calculations to pay this remark much heed.
‘According to these readings, a change to the MF occurred several weeks ago. That was probably around the time of the last scheduled delivery of blood from Earth. It would seem the reactor has been running fairly predictably since then. Now, let’s see what the radiation levels are like in the containment room itself.’
Dallas walked to the containment room door and peered through a twelve-inch-thick leaded glass window that was set in the steel door. A radiometer was mounted there for easy consultation.
‘What’s the verdict?’
‘It’s high, of course,’ said Dallas. ‘But nothing we weren’t expecting.’
Dallas keyed this reading into his computer, and when he was satisfied with the computations, he tapped the TLD that was attached to the computer on Cavor’s sleeve.
‘Remember the way miners used to take canaries down coal mines?’ he asked.
‘Right. If the canary stopped singing, it meant there was gas and you should get out.’
‘This operates on the same principle. The TLD contains crystals that are highly sensitive to radiation. As soon as we go through the door, the radiation will start to change the crystals. Those changes will tell the computer how much radiation our bodies are absorbing and, as a result, how much time we will have to work in there. Current readings in the room would indicate a dose rate of around thirty centigrays a minute. Taking into account our body weights, and assuming there’s no change in the MF, I calculate that we would receive a dose lethal to fifty percent of people exposed within sixteen and a half minutes. According to the computer, however, we could work for as long as twenty minutes with as little as a fifteen percent chance of a lethal dose, provided we could expect a minimum of two blood infusions.’
Dallas waited a moment to be sure that Cavor had understood, and then continued.
‘There are some early somatic effects of radiation we have to watch out for. In less than three to six hours of exposure we’ll start to experience nausea, perhaps even vomiting. I’ve never puked inside an EVA suit, but I don’t imagine it’s very pleasant, so we’ll want to be back on board Mariner by the time that happens. But feeling ill is also an indicator of our treatment window. We will need blood transfusions within twenty-four hours of being sick if we’re to stand an eighty-five percent chance of recovery.’
‘I feel sick already.’ Cavor swallowed.
‘You’re doing fine, Cav.’ Dallas clapped Cavor on the shoulder and then drew him to the leaded window of the containment room.
‘Time for a guided tour,’ he said. ‘On the right there, we have the steam generator. On the left, the primary coolant pump. Behind them is the reactor itself. It’s surrounded with a primary radiation shield, but don’t expect much protection from that. It’s designed to give you time to get the hell out of there, not to try for an endurance test. Behind the reactor is the wall dividing the containment room from the labyrinth. It’s made of three-foot-thick concrete blocks. Each block is just over two and half feet square and weighs around five hundred pounds. Of course, in microgravity it won’t feel like anything that heavy. The cement holding the block in place is smart in that it contains a length of heat-sensitive metal, part of a dedicated circuit that includes all four walls of the containment room. If the reactor encounters a loss-of-coolant accident and begins to overheat, the metal circuit is designed to detect that and create an alarm condition. The alarm condition will override all other operating considerations, scram the reactor, and initiate emergency core-cooling. That means the whole room will fill with extremely low-temperature helium gas, freezing everything in the reactor room, including us. However, it’s an imperfect system. A section of the metal circuit surrounding any concrete block can be bypassed, after which it can be easily melted. Melting it shatters the surrounding mortar, enabling us to push the block through and into the labyrinth.’
‘Mind telling me what’s in there? This stealth robot, for instance.’
‘Okay, the labyrinth is completely dark. A total blackout. And the robot could be anywhere in there. It’s light-activated. A series of photoelectric beam receivers throughout the labyrinth are designed to reflect any ambient light to another receiver on the robot. The robot converts that radiant energy into an electrical signal that is amplified for a detector processor which then arms the robot to hunt down the light source and kill intruders. Only seventy-five milliseconds of light appearing anywhere inside the labyrinth are required for all that to happen. Which means that we switch out the lights in here and shift the block using only the infrared flashlights.
‘The block I’ve selected is on the back wall of the room, nearest the floor. As soon as I’ve managed to bypass the circuit, we’ll each take one side of the block and start to melt the smart metal using the UHTs.’
‘I was nearly killed by one of those on Artemis Seven,’ said Cavor. ‘One of the other lunatics, screwing around.’
‘Is that how you lost your arm?’
‘No, that was a rock crusher. A UHT gun would have done a much neater job.’
‘Then you won’t need me to remind you to be careful where you point it. If a five-hundred-kilovolt beam of electrons, carelessly directed, were to penetrate the reactor, I hardly like to think what might happen.’
‘Don’t worry. I’ll be careful.’
‘See that you are, Cav, otherwise my atoms will see your atoms in the next universe.’
VII
With the blood component sent by the Descartes computer aboard, Ronica was glad to be kept busy preparing it for infusion to Rameses Gates. She had a pretty good idea of how he was feeling, although he didn’t complain. And being much larger than Ronica meant that donating two whole units still left him conscious, although very weak. His physiological response to such a large blood loss fell short of actual hemorrhagic shock, but there was no way Ronica could tell what the sudden decrease in hemoglobin and hemocrit might do to someone with P2. And in the knowledge that Gates was the only person who could fly them back to Earth, she worked as quickly as she dared. Blood was not something that could be rushed.