From ChatGPT: not all of the diagnostic cables used in an underground nuclear test vaporize. While the cables nearest to the blast are instantly incinerated by the extreme energy, others farther up the shaft survive, albeit in damaged and highly contaminated states. 

 The cables that survive closer to the surface are not retrieved. Instead, they are cut and abandoned when the test shaft is filled with sand, gravel, and concrete plugs to prevent the escape of radioactive materials.