Decaying Isotopes

What killed forty men in the dark without scorching their clothes? Levmir stood beside the workbench in Vault 4B, holding the answer wrapped in sterile waxed parchment. The intercom horn in the corridor outside still vibrated from Kordov's station-wide inspection summons, and Levmir needed that answer before the patrol reached his hatch.

He laid the parchment flat on the soapstone counter beside his sample rack. Inside sat the fragment he had chipped from the primary radiator vent ninety meters above: a pale crumb of calcified marrow no larger than a dried lentil, cold and brittle. Normal bone turned chalky under vacuum. This shard had an oily, greenish crust where the vent's eighty-degree glycol vapor had cooked it against the pipe wall.

Levmir flicked the toggle on his bench centrifuge. The small electric motor hummed up to four thousand revolutions, vibrating the slate work surface. While the housing warmed, he pulled a brass optical refractometer from its padded cedar box. It was a brewer's instrument, designed to measure dissolved sugars in wort and detect sulfate impurities in re-condensed boiler run-off.

To test mineral inclusions, he needed a clear liquid matrix. Levmir uncorked a glass dropper bottle of eighty-five percent phosphoric acid, the standard solvent used to strip mineral scale from the copper kettle coils. With a pair of steel tweezers, he transferred the bone crumb into an agate mortar.

The pestle crushed the shard with a dry snap. Levmir ground the grain down into an even flour, then drew two drops of the acid into a pipette and let them fall into the mortar.

A sharp hiss followed. White froth rose from the stone cup, smelling of burnt hair and bitter lime. The acid ate through the calcium phosphate scaffold, turning the solid mineral into a syrupy suspension of dissolved salts. Levmir scooped the fluid with a platinum loop and smeared a thin film across the quartz face of the sample prism.

He clamped the glass cover plate down tight. No air bubbles showed in the liquid film.

Across the room, Mash Vat Seven ticked softly in its steel cradle. The pressure gauge read three point two bar, and the thermal jacket held at thirty-eight point two degrees Celsius. The three tons of Spirka-yeast mash inside were feeding steadily on the pulverized basalt slurry, completely ignorant of the bronze token resting deep inside their sump trap. The iron skin of the vat hummed with fermentation gases.

Levmir turned back to the microscope assembly on his desk. He swung the secondary mirror into place and lit the bench's cobalt arc lamp. The narrow beam of bluish light lanced through the collimating slit, struck the prism, and refracted through the acid-digested sample.

He pressed his right eye to the brass eyepiece.

A horizontal rainbow stretched across the reticle grid, marked in nanometer divisions from red to ultraviolet. In ordinary bone ash, the Fraunhofer lines formed a predictable fingerprint: sharp dark notches at six hundred and forty-three nanometers for calcium, a pair of faint absorption bands in the yellow spectrum for sodium, and a dull smudge near the edge for phosphorus.

Levmir adjusted the fine vernier screw on the prism mount. The spectrum slid across the hair-lines.

The calcium bands sat exactly where they belonged. But two millimeters to the left, inside the deep blue spectrum at four hundred and sixty point seven nanometers, a stark, thick black notch cut through the beam. Beside it, an even sharper absorption line stood out at four hundred and twenty-one point five nanometers.

His fingers stayed fixed on the vernier wheel.

Those were not standard slag contaminants. The miners who died in Year 12 were supposed to have suffocated during an accidental manifold blowout, according to the official founding history recited at every solstice ration ceremony. Hypoxia left empty red blood cells and undamaged mineral marrow.

These absorption lines belonged to strontium.

Not the harmless, stable isotope found in traces throughout raw asteroid rock, either. Natural strontium-88 existed in the Zhelezkova stone at less than twenty parts per million, far below the detection limit of a manual refractive bench. To produce an optical absorption notch this wide, the sample required a concentration above three thousand parts per million, concentrated directly into the living osteoblast matrix.

The founders had not suffocated in a sudden hull puncture. They had breathed hot vapor laced with refined strontium-90 straight from an unshielded reactor loop.

Levmir loosened his grip on the focusing screw. The cooperative's old founding anthem had a verse praising the first generation for having "bones of iron." The lyricists had missed the mark by thirty-two atomic mass units. Their bones had been turned into radioactive fuel poisons while their lungs were still drawing air. Someone on the founding council had opened the primary steam circuit into their living quarters, then packed their bodies into the radiator manifolds to hide the unburned cores.

The sound of hard metal struck the deck grating in the corridor outside.

It was not the rhythmic tap of a maintenance runner's soft boots. It was the heavy, rhythmic iron clatter of magnetic soles clamping to the steel deck plates, three paces apart. Two men, moving with the measured stride of security enforcers.

Levmir did not scramble. He capped the acid bottle and placed the ground pestle into the rinse sink. With a steady turn of his wrist, he opened the petcock on the neutralizing wash line and flooded the mortar with saturated sodium carbonate solution. The remaining bone pulp dissolved in an effervescence of harmless salt water and washed down the waste conduit.

He unlatched the quartz slide from the microscope mount, slipped it into a glass beaker of pure industrial alcohol, and scrubbed the surface clean with a swab of degreased wool.

"Brewer Levmir," a flat voice barked through the outer bulkhead speaker. "Open the outer pressure dog. Security inspection under Sector 4 containment mandate."

Levmir pulled a clean white apron from the wall hook and tied the cotton cords around his waist. He picked up his brass hydrometer and the slate tally board, walking toward the outer hatch with measured steps.

He reached the heavy dog-wheel and gripped the cold steel spokes. "Stand clear of the seal," Levmir called through the copper speaking tube. "The mash is under pressure."

He spun the wheel three turns to the left, letting the lock bolts drop into their housings with a dry, mechanical thud, and pulled the slab open.

Two security enforcers stood in the threshold, carbines slung barrel-down across their gray canvas riggings. The lead guard carried a handheld gamma counter that crackled with nothing more than the sluggish, ambient click of deep-strata basalt. He swept an inspection beam over the fermenter's copper fittings, the scrubbed worktable, and the simmering hull of Mash Vat Seven.

"Telemetry logged an eighty-kilowatt thermal sink on this circuit twenty minutes back," the guard said, his visor catching the blue glow of the cobalt lamp. "Central wants every heat tap verified."

Levmir thrust the slate board into the guard's gauntleted hand, tapping the chalked specific gravity with a blackened thumbnail. "Vat Seven took a fresh basalt charge at the start of the shift. If you throttle my cooling return to balance the grid, the Spirka culture overheats by four degrees, the mash curdles, and the drilling shifts go without caloric paste tomorrow."

The guard stared at the chalked columns, then at the steady pressure needle on the vat jacket. He grunted, dragged a yellow wax pencil across the doorframe to certify the inspection, and stepped back onto the corridor grating. "Keep your valves within tolerance, Brewer."

"Tolerances are the only thing keeping us breathing," Levmir said.

He shoved the hatch shut and spun the dog-wheel until the brass dogs seated home. In the warm quiet of Vault 4B, he hung the slate board back on its peg. The inspection was over, but the strontium absorption lines burned in his memory. Only one man on Zhelezkova had tended the primary reactor loops during Year 12 and survived the founding years with his lungs intact.

Levmir unhooked his grease-stained wool jacket from the locker. It was time to head down to Lower Hydroponics and find Ignat.